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Dissertations / Theses on the topic 'Planetary Modeling'
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1
Chan, Tsz-pan Henry, and 陳子斌. "Morpho-kinematic modeling of planetary nebulae." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42182293.
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Chan, Tsz-pan Henry. "Morpho-kinematic modeling of planetary nebulae." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42182293.
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Sondkar, Prashant B. "Dynamic Modeling of Double-Helical Planetary Gear Sets." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338481548.
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Eisen, Howard J. (Howard Jay). "Scale and computer modeling of wheeled vehicles for planetary exploration." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/43001.
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Wagner, Richard A. "Sand modeling of crustal extension." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/59038.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.
Vita.
Bibliography: leaf 53.
by Richard A. Wagner, Jr.
M.S.
6
Hoffman, Nick(Nicholas D. ). "Modeling methylmercury in Maine's tribal meres." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/122866.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018Cataloged from PDF version of thesis.
Includes bibliographical references (pages 59-76).
Methylmercury (MeHg) concentrations in the fish of twenty Maine lakes were projected for the year 2035 under three different policy scenarios. A mechanistic model of Hg fate and transport was calibrated for Maine's environment using four parameters: volumetric outflow rate, settling velocity, burial velocity, and Hg(II) biotic solids partitioning coefficient. The model was evaluated through comparison with measured results from the year 1993. The model results showed that the strictest global Hg regulations will lead to the greatest decreases in MeHg concentration. No piscivore will be safe for frequent consumption, even under the strictest regulations in the cleanest lakes. The Wabanaki traditional-subsistence diet will continue to entail unsafe MeHg exposures.
by Nick Hoffman.
S.B.
S.B. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences
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Alsaadan, Sami Ibrahim. "Modeling velocity dispersion In Gypsy site, Oklahoma." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62484.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 73-76).
Discrepancies in interval velocities estimated from vertical well measurements made with different source central frequencies at Gypsy site could be primarily explained in terms of intrinsic attenuation. Four intervals were chosen for this study based on varying rock properties. The first interval is predominantly shale, second interval is mostly sandstone, and the third interval is made up of shale and sandstone. The fourth interval is the second and third intervals combined. The data used are acquired from three seismic sources; Full Wave Sonic (FWS), Bender log, and Vertical Seismic Profile (VSP) with estimated central frequencies 10kHz, 1kHz, and 100Hz, respectively. The modeling was done using the Discrete Wavenumber (DWN) method and the Logarithmic Dispersion Relation (LDR) to calculate a constant Quality Factor (Q) that best explains the observed velocity dispersion for each of the intervals of interest. The elastic scattering component of the dispersion is negligible. Intrinsic quality factors of 54,35,28, and 30 best explain the field data for first, second, third, and fourth intervals, respectively. The identification and subsequent modeling of velocity dispersion and its components provide key information for integrated reservoir characterization and better enable the prediction of the seismic response at different frequencies.
by Sami Ibrahim Alsaadan.
S.M.
8
Minsley, Burke J. "Modeling and inversion of self-potential data." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40863.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 235-251).
This dissertation presents data processing techniques relevant to the acquisition, modeling, and inversion of self-potential data. The primary goal is to facilitate the interpretation of self-potentials in terms of the underlying mechanisms that generate the measured signal. The central component of this work describes a methodology for inverting self-potential data to recover the three-dimensional distribution of causative sources in the earth. This approach is general in that it is not specific to a particular forcing mechanism, and is therefore applicable to a wide variety of problems. Self-potential source inversion is formulated as a linear problem by seeking the distribution of source amplitudes within a discretized model that satisfies the measured data. One complicating factor is that the potentials are a function of the earth resistivity structure and the unknown sources. The influence of imperfect resistivity information in the inverse problem is derived, and illustrated through several synthetic examples. Source inversion is an ill-posed and non-unique problem, which is addressed by incorporating model regularization into the inverse problem. A non-traditional regularization method, termed "minimum support," is utilized to recover a spatially compact source model rather than one that satisfies more commonly used smoothness constraints. Spatial compactness is often an appropriate form of prior information for the inverse source problem. Minimum support regularization makes the inverse problem non-linear, and therefore requires an iterative solution technique similar to iteratively re-weighted least squares (IRLS) methods.
(cont.) Synthetic and field data examples are studied to illustrate the efficacy of this method and the influence of noise, with applications to hydrogeologic and electrochemical self-potential source mechanisms. Finally, a novel technique for pre-processing self-potential data collected with arbitrarily complicated survey geometries is presented. This approach overcomes the inability of traditional processing methods to produce a unique map of the potential field when multiple lines of data form interconnected loops. The data are processed simultaneously to minimize mis-ties on a survey-wide basis using either an 12 or 11 measure of misfit, and simplifies to traditional methods in the absence of survey complexity. The 11 measure requires IRLS solution methods, but is more reliable in the presence of data outliers.
by Burke J. Minsley.
Ph.D.
9
Quinn, Katherine J. (Katherine Jane) 1971. "Atmospheric delay modeling for satellite laser altimetry." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8061.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.Includes bibliographical references.
NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) is a laser altimetry mission with the primary purpose of measuring the mass balance of the ice sheets of Greenland and Antarctica. It will provide 5 years of topography measurements of the ice, as well as land and ocean topography. In order to accurate topography measurements the laser altimeter ranges must be corrected for certain biases. Atmospheric delay is one such bias. As the laser pulse travels through the atmosphere it will be refracted, introducing a delay into the travel time. This delay must be estimated to correct the ranges and the delay estimations need to be validated. Of particular concern are errors in the delay estimates that have the same characteristics as the expected mass balance variations. The main focus of this dissertation is to formulate algorithms for calculating the ICE-Sat atmospheric delay and estimate the expected delay values and errors. Our atmospheric delay algorithm uses numerical weather model data to estimate delay values. We have validated these algorithms using Automatic Weather Stations (AWS) in the polar regions and GPS data over the globe. The GPS data validation was also augmented by in-situ meteorology measurements at some the stations. The GPS validation process additionally allowed us to investigate the estimation of precipitable water vapor using GPS data. The validation studies have shown that our atmospheric delay algorithm errors are well within the ICESat error budget of 20 mm. The overall global delay errors are estimated to be approximately 5.4 mm and the polar delay errors are 12.2 mm. There are no discernible biases in the error and the seasonal variations in error magnitudes are well characterized.
by Katherine J. Quinn.
Ph.D.
10
DesAutels, Christopher Gerald 1975. "Upper-ocean influences on hurricane intensification modeling." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53046.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000.Includes bibliographical references (leaves 32-33).
Hurricane intensification modeling has been a difficult problem for the atmospheric science community. Complex models have been built to simulate the process, but with only a certain amount of success. A model developed by Dr. Kerry Emanuel is much simpler compared to previous studies. The Emanuel model approaches hurricane intensification as an ocean-controlled process where the upper-ocean heat content limits intensification. It is shown that this ocean-based model can produce very accurate results when the true structure of the ocean can be determined. The Ocean Topography Experiment (TOPEX) provides an opportunity for the model to be tested through the use of satellite altimetry. Measurements of the mixed layer depth and upper-ocean heat content are incorporated into the model for Hurricanes Bret, Gert, Opal, Mitch and Dolly. This technique is shown to be quite reliable for many storms, especially in the Gulf of Mexico. Limitations are examined where this method breaks down and improvements are suggested for its development into a forecasting tool.
by Christopher Gerald DesAutels.
S.M.
11
Guérendel, Philippe. "Ultrasonic modeling--application to deep-water multiples imaging." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52920.
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Baumgardner, Sarah E. "Modeling the sorting of sediments on delta tops." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/114361.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009.Cataloged from PDF version of thesis. Page 40 blank.
Includes bibliographical references (pages 36-37).
Sediment sorting in fluvial rivers produces great variation in the grain-size of deposit over the length of a river. Knowledge of the pattern of sediment deposition may help to shed light on the processes that sort by grain size. A simple geometric model was developed to predict the location of the transition between coarse and fine sediment in a bimodal sediment distribution and tested against flume-created deposits with a variety of flow and depositional conditions. The models agreed well with the overall form of plane-bed clinoform deposits but not with rippled-bed clinoform deposits, thus a new model for predicting transitions in rippled-bed deposits is needed.
by Sarah E. Baumgardner.
S.B.
13
Hilbert, Bryan (Bryan Nathaniel) 1977. "Stellar occultation lightcurve modeling for elliptical occulting bodies." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/54444.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.Includes bibliographical references (leaf 41).
We present a new method of calculating model lightcurves for stellar occultations by the Jovian planets. We model the occulting planet as a three-dimensional body of non-zero ellipticity, and define two ellipses of intersection with the body which dictate the appearance of the lightcurve. These include the visible-limb plane ellipse, which is the observed figure of the body as seen in the sky, and the line-of-sight ellipse, which contains the line of sight to the occulted star, and is the plane in which the starlight is refracted. The observed stellar flux during the occultation is primarily dictated by the ellipticity and subsequent radius of curvature of the instantaneous ellipse in the line-of-sight plane. This new method is applied to several test cases, as well as to the Jovian occultation of HIP9369 on 10 October 1999. Lightcurves generated by this model are compared to identical situations using the method published in Hubbard et al. (1997), showing that the Hubbard model works well for low-latitude occultations, but fails at higher latitudes. In the case of the high-latitude Jovian occultation, the best-fit lightcurve, produced from this new method, yielded a half-light equatorial radius of 71,343±1.2 km with a scale height of 19.25±0.5km, and an isothermal temperature of 139K. The same data, fit using a lightcurve generated by the method described in Hubbard et al. (1997), resulted in a half-light equatorial radius of 71,819km with a scale height of 17.9km with errors comparable to the previous fit, resulting in an isothermal temperature of 129K. Lightcurves are numerically generated for an ellipsoidal planet and, for comparison, an approximation to the ellipsoidal case consisting of a sphere with radius equal to the radius of curvature of the ellipsoid at the half-light point. We find that in the case of an occultation where the line-of-sight ellipticity does not vary, that the radius of curvature approximation matches the ellipsoidal planet lightcurve to within 0.007%. For an oblique occultation however, the line-of-sight ellipticity varies, and the approximation, using only a single radius of curvature sphere, is only good to about 1%. As a result, we find that using a model such as that presented in Baum and Code (1953) to fit the lightcurve of an ellipsoidal planet can return values for half-light radius (after accounting for the distance between the center of curvature and the center of the body) which may match the local distance to the center of the ellipsoid to a fraction of a percent, while returning values of scale height which may be in error by several percent. Test cases are also then put through numerical inversions, to obtain temperature versus pressure profiles. Test cases with spherical planets return temperature profiles that match those used to create the lightcurves, while test cases with ellipsoidal planets return temperature profiles which can differ from the input temperatures by tens of degrees, assuming a constant local gravity over the course of the occultation.
by Bryan Hilbert.
S.M.
14
Hayashi, Koichi 1967. "Variable grid finite-difference modeling including surface topography." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9367.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, September 1999."August 6, 1999."
Includes bibliographical references (leaves 188-190).
We have developed a two-dimensional viscoelastic finite-difference modeling method for highly complex surface topography and subsurface structures. Realistic modeling of seismic wave propagation in the near surface region is complicated by many factors, such as strong heterogeneity, topographic relief and large attenuation. In order to account for these complications, we use a velocity-stress staggered grid and employ an 0(2,4) accurate viscoelastic finite-difference scheme. The implementation includes an irregular free surface condition for topographic relief and a variable grid technique in the shallow parts of the model. Several methods of free surface condition are bench marked, and an accurate and simple condition is proposed. In the proposed free surface condition, stresses are calculated so that the shear and normal stresses perpendicular to the boundary are zero. The calculation of particle velocities does not involve any specific calculations, and the particle velocities are set to zero above the free surface. A stable variable grid method is introduced, where we use a three times finer grid in the near surface or low velocity region compared to the rest of the model. In order to reduce instability, we apply averaging or weighting to the replacement of the coarse grid components within the fine grid. The method allows us to avoid any limitation of the shape of the grid size boundary. Numerical tests indicate that approximately ten grid-points per shortest wavelength with the variable grid method results in accurate calculations. The method requires a stair-shaped discretization of a free surface. We investigated the stair-shaped structures, and found that the cause of the dispersion from irregular free surface is mainly a numerical error due to the large grid sizes rather than the Rayleigh waves scattering due to the stair-shaped boundary. The finite-difference modeling is applied to the investigation of near surface wave propagation. Several numerical simulations are performed to show the characters of wave propagation in the near surface region. The simulations show that the low velocity thin layers just below the surface and anelastic attenuation have significant effect on surface seismic record. The 2-D modeling of near surface structure beneath a 2-D refraction survey line is carried out. The comparison of the observed data with theoretical waveforms is performed. The characters in the observed data can be explained by a subsurface model constructed by P-wave traveltime tomography.
by Koichi Hayashi.
S.M.
15
Lockner, David Avery. "Modeling of brittle failure and comparisons to laboratory experiments." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/54338.
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Hooper, Heather J. (Heather Julie) 1975. "Analysis and modeling of induced seismicity in petroleum reservoirs." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/54445.
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Thesis (S.M. in Geosystems)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.Includes bibliographical references (p. 53).
Since 1998, a producing oil field in Oman has been experiencing microearthquake activity. The aim of this project is to compare numerical models of wave propagation using simple source representations to a small subset of these microearthquakes, with three goals in mind: 1) to understand whether the microearthquakes are generated by movement along a known fault system in the field, or by some other mechanism; 2) if the source is fault related, to better understand what kind of movement is occurring on the fault; and 3) to see if this simple modeling method provides useful results, and forms a basis for future work. Synthetic waveforms are generated using a one-dimensional, discrete wavenumber numerical model (Bouchon, 1980) with two simple source representations: an explosive point source and a vertical force. Comparison of the synthetic waveforms to the microearthquake data indicates that the vertical force results in a better match than the explosive point source. In addition, a simple model consisting of the superposition of four vertical forces (representing vertical fault rupture), results in waveforms that are very similar to the recorded events. These results suggest that the source of the microearthquakes is motion along a near-vertical normal fault system that has been mapped in the field. These results are also consistent with work by Sze and Toksoz (2001) in which relocation of the same events imaged a near-vertical normal fault in the field. Further work using fault rupture source modeling may provide additional insight into the amount of fault motion that is occurring in relation to these events.
by Heather J. Hooper.
S.M.in Geosystems
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Jerolmack, Douglas J. "Modeling the dynamics and depositional patterns of sandy rivers." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37277.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006.Includes bibliographical references.
This thesis seeks to advance our understanding of the dynamic nature, spatial organization and depositional record of topography in sand-bedded rivers. I examine patterns and processes over a wide range of scales, on Earth and Mars. At the smallest scale, ripples and dunes (bedforms) arise spontaneously under most natural flow conditions, acting as the primary agents of sediment transport and flow resistance in sandy rivers. I use physical modeling in a laboratory flume to explore the feedbacks among bedform geometry, fluid flow and sediment transport. Field observations of dunes in the North Loup River, Nebraska, show that bed roughness displays a statistical steady state and robust scaling. Motivated by these data, I develop a nonlinear stochastic surface evolution model for the topography of sandy rivers which captures the essence of bedform evolution in space and time. I then use a simplified kinematic model for bedform evolution to simulate the production of stratigraphy from migrating dunes, allowing a more accurate reconstruction of river flow conditions from preserved bedform remnants in rocks. At the channel scale I examine the conditions that lead to avulsion, the rapid abandonment of a river channel in favor of a new course at lower elevation.
(cont.) Simple scaling arguments and data from 30 natural systems reveal that anastomosing (multi-branch) rivers and distributary deltas are morphologies that arise when avulsion is the dominant mechanism of channel adjustment. I apply these arguments to the Niobrara River, Nebraska, which has experienced rapid in-channel deposition due to base level rise. I show that the planform pattern of the Niobrara is dominated by base-level-driven avulsions, and is decoupled from the smaller-scale sediment transport. At the largest considered scale are depositional fans, which are constructed by avulsing rivers. The evolution of a fan profile may be modeled at long time- and space-averaged scales as a diffusive process. I use such a model to invert topographic and volumetric data from a fluvial fan on Mars, producing an estimate of the time required to build the fan out of channel and overbank deposits.
by Douglas J. Jerolmack.
Ph.D.
18
Rigel, Adam C. "Modeling sea surface height in the Gulf of Mexico." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/114359.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008.Cataloged from PDF version of thesis. "May 9, 2008."
Includes bibliographical references (pages 25-26).
A model was created to form synthetic plots of sea surface height (SSH) from monthly SSH statistics in the Gulf of Mexico generated from satellite laser altimetry data. SSH is a signal of the upper ocean mixed layer heat content and is an input for hurricane intensity models. A significant ocean feature in the Gulf of Mexico is the Loop Current (LC) which sheds warm eddies into the Gulf of Mexico at irregular intervals, which adds to the variability in monthly SSH readings beyond seasonal change. Satellite laser altimetry data was used from October 14th 1992 to May 23rd 2007. The SSH data included an area of the Gulf of Mexico (16°N-30°N latitude, 80°W-100°W longitude) with a resolution of 1/3° by 1/3° on a Mercator grid. Monthly SSH averages, variances, and covariances were created from a total of 763 samples, which allowed for approximately 65 samples per month. Once monthly SSH averages, variances, and covariances were made, synthetic plots were made by using a Karhunen-Loève transform, the Singular Variable Decomposition of the SSH monthly covariance, and random vector composed of random numbers in a Gaussian distribution. Differences in synthetic SSH plots compared to individual SSH observations could vary greatly; the average of all synthetic SSH plot nodes differed by no more than plus or minus 10 cm. The difference between observed and synthetic SSH variance was no more than 400 cm². The large differences occurred in the in the eddy shedding region of the LC. To assess the effectiveness of the model, the synthetic SSH model will need to be used in a hurricane intensity model.
by Adam C. Rigel.
S.B.
19
Sullivan, Zachary S. "Karst Landscape Influence on the Planetary Boundary Layer Atmosphere." TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1638.
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Karst landscapes cover approximately 20% of the ice-free land area worldwide. The soluble nature of the bedrock within a karst landscape allows for the formation of caverns, joints, fissures, sinkholes, and underground streams, which affect the hydrological behavior of the region. Currently, the Noah Land-Surface Model (Noah- LSM), coupled with the Weather Research and Forecasting (WRF) model, does not provide a representation of the physical behavior of a karst terrain. Previous research has attempted to model karst behavior through soil moisture and land cover/land use changes to determine the influence this unique landscape may have on atmospheric phenomenon. This highlights the need to study the potential influence that karst landscapes may have on model simulations. For this study, several factors were taken into account while studying karst and meteorology: the verification of a current operational forecasting model against observational data over five years (2007 to 2011), the formation of a karstlike soil type for use within an operational forecasting model, and model behavior once this karst-like soil type was added to the operational forecasting model.
The verification of a currently operational forecasting model, the North American Mesoscale (NAM), indicated that, overall, the karst regions may exhibit an influence on local winds (greater error) and precipitation (frequency and forecasting). When developing a realistic karst-like soil proxy for use in the Noah-LSM, hydraulic conductivity values show a variation ranging from around 10-7 and 10-5 m s-1 for the karst bedrock within Tennessee and Kentucky. Sandy loam and clay soils were used, along with bedrock parameters, to determine an average soil parameter type for the epikarst bedrock located within this region. The model study demonstrated that the addition of karst highlighted the potential influence on precipitation distribution and energy fluxes, through RMSD and R2 values taken at a 95% confidence interval.
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Kárason, Hrafnkell 1970. "Constraints on mantle convection from seismic tomography and flow modeling." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8059.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.Includes bibliographical references (p. 205-224).
In this thesis I combine high resolution seismic tomography and realistic flow modeling to constrain mantle convection. The bulk of the data used in the tomographic imaging are millions of P, pP and pwP travel time residuals, read from high frequency seismic records. The distribution of earthquakes and stations results in uneven data coverage and to improve the model I use core phases (PKP, Pdiff) for the deep mantle and surface reflected phases (PP) for the shallow mantle. Since narrow rays are not adequate for low frequency measurements, I construct broad 3-D sensitivity kernels to relate some of the added data to earth's structure. Furthermore, the parameterization of the tomographic model is adapted to data density and the model shows, among other details, the varying style of subduction in the shallow mantle and complex flow patterns around the transition zone between the upper and lower mantle. I develop a novel and efficient method of modeling buoyancy driven mantle flow in spherical geometry. Here, the linear Stokes equation is solved using a Green's function approach and 3-D surfaces, representing the boundaries of dense material, such as subducting slabs, are tracked through time.
by Hrafnkell Kárason.
(cont.) I describe the basis of the approach, represent tests, and investigate the thickening and slowing of subducting slabs for different viscosity contrasts between the upper and lower mantle. I compare seismic tomography, flow modeling and reconstructed plate motions associated with the collision of India to mainland Asia, in particular, the south and south-west motion of the Sunda block. This way I can evaluate subduction scenarios and make quantitative comparison between tomography and plate reconstructions. I conclude that a viscosity increase of -200 in the lower mantle, resulting in -10 times higher viscosity than previously estimated, best fits the observations. Juxtaposing the tomography, the flow models and inversion tests using the flow models as input, indicates that the results are robust.
Ph.D.
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Shi, Weiqun 1965. "Advanced modeling and inversion techniques for three-dimensional geoelectrical surveys." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9878.
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Li, Lin. "Computer modeling of a vertical array in a stratified ocean." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/54393.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.GRSN 698569
Includes bibliographical references (leaves 76-78).
by Lin Li.
M.S.
23
Busfar, Hussam A. (Hussam Abdullah). "Determining the focal mechanisms of earthquakes by full waveform modeling." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53105.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009.Includes bibliographical references (leaves 76-78).
Determining the focal mechanism of an earthquake helps us to better characterize reservoirs, define faults, and understand the stress and strain regime. The objective of this thesis is to find the focal mechanism and depth of earthquakes. This objective is met using a full waveform modeling method in which we generate synthetic seismograms using a discrete wavenumber code to match the observed seismograms. We first calculate Green's functions given an initial estimate of the earthquake's hypocenter, the locations of the seismic recording stations, and the velocity model of the region for a series of depths with intervals of 1 km. Then, we calculate the moment tensor for 6840 different combinations of strikes, dips, and rakes for each of those depths. These are convolved with Green's function and with an assumed smooth ramp source time function to produce the different synthetic seismograms corresponding to the different strikes, dips, rakes, and depths.
We use a grid search in order to find the synthetic seismogram, with the combination of depth, strike, dip, and rake, that best fits the observed seismogram. These parameters will be the focal mechanism solution of an earthquake. The whole procedure is repeated for a reduced number of recording stations in order to determine a minimum number of recording stations that is needed for a reliable source mechanism and depth solution. We tested the method using two earthquakes in Southern California. Their locations, depths, and source mechanisms were determined using data from a multitude of stations. Southern California Seismic Network's real-time solution of earthquake 9718013 puts the earthquake at a depth of 15.22 km. The moment tensor inversion method determines the depth of the earthquake to be 8 km with a strike, dip, and rake of 318, 33, -180, respectively. The same network determines the depth of earthquake 14408052 to be 7.3 km.
The moment tensor solution determines the strike, dip, rake, and depth of earthquake 14408052 to be 162, 82, -167, and 5 km, respectively. In this study, we wanted to test our method using seismograms from a relatively few stations. We used five stations for each earthquake, then 3 stations for earthquake 9718013, and two stations for earthquake 14408052. When using five recording stations, the strike, dip, rake, and depth of earthquake 9718013 are 300, 60, -170, and 15 km, respectively. When using three recording stations for the same earthquake, the strike, dip, rake, and depth are 300, 60, -180, and 14 km, respectively. For earthquake 14408052, the strike, dip, rake, and depth are 160, 80, -170, and 7 km, respectively, when using five recording stations. The strike, dip, rake, and depth for this same earthquake are 160, 80, -160, and 8 km, respectively, when using only two stations.
The results show that the ten best solutions for each earthquake are very similar, and identical in many cases, indicating that the method is robust and the solution is unique. This assures us that the full waveform modeling method is a fast and reliable way to find the focal mechanisms and depths of earthquakes using seismograms from a few stations when the velocity structure is known.
by Hussam A. Busfar.
S.M.
24
Sena, Giuseppe A. (Giuseppe Antonio). "Very large scale finite differences in modeling of seismic waves." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/58055.
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Siu, Ho Chit. "A discrete forward-modeling method for characterizing occultation lightcurves of tenuous planetary atmospheres." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98677.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 108-110).
We present a discrete numerical approach for forward-modeling lightcurves from stellar occultations by planetary atmospheres. Our discrete approach provides a way to arbitrarily set atmospheric properties at any radius from the occulting body, giving it flexibility for applying models of vertical variation in atmospheric conditions. The method is used to examine trends in lightcurve characteristics resulting from changes in the atmosphere of the occulting body. We find that for Pluto-like atmospheres, temperature and pressure variations affect the characteristics of the lightcurve much more than the gas composition. We also find that the half-light radius is more sensitive to atmospheric changes than either the minimum normalized flux or the slope at half-light. Temperature is found to be the most easily-constrained atmospheric parameter, as the gradients for changes in lightcurve characteristics are much more aligned with the temperature axis of the atmospheric parameter space than any other axis. Trends in lightcurve characteristics were examined in and around the parameter space occupied by the atmospheric conditions predicted for Pluto based on the 2011 and 2013 occultation events. Our error analysis method produced uncertainty values consistent with the reported uncertainties for half-light radius. This kind of lightcurve characterization is potentially useful for constraining the level of precision required in measuring given lightcurve characteristics in order to provide certain uncertainty bounds on the atmospheric conditions of the occulting body.
by Ho Chit Siu.
S.M.
26
Zhang, Huai-Min Ph D. Massachusetts Institute of Technology. "Application of an inverse model in the community modeling effort results." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/58152.
Full text
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Nisancioglu, Kerim Hestnes 1975. "Modeling the impact of atmospheric moisture transport on global ice volume." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16703.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004.Includes bibliographical references (leaves 137-154).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Following Milankovitch's original hypothesis most model studies of changes in global ice volume on orbital time scales have focused on the impact of ablation on ice sheet mass balance. In most cases, poleward moisture flux is fixed and accumulation of snow only depends on local temperature. In this study, a simple coupled atmosphere-ice process model is introduced. An improved representation of the atmospheric hydrological cycle is included, and accumulation is related to the meridional flux of moisture by large scale baroclinic eddies. The ice sheets in the Northern Hemisphere respond to both precession and obliquity frequencies when the model is forced with seasonal insolation. Obliquity variations are introduced by the impact of earth's tilt on the meridional temperature gradient and the poleward flux of moisture, whereas precession governs surface melting by regulating summer temperatures. The response of the ice sheet to obliquity and precession is comparable, and significantly smaller than what is observed in the oxygen isotope record of the late Pliocene and early Pleistocene (2.7 - 0.8 Ma BP). This suggests that in order to successfully reproduce the strong 41 Ka periodicity observed in the record, other mechanisms must be involved such as nonlinear self-sustained, or stochastic processes, or alternatively the obliquity dominated signal originates from Antarctica. In Antarctica the seasonal cycle is damped due to the large thermal mass of the southern ocean, and surface melt is insignificant. Both of these factors reduce the influence of precession in regulating ice volume. Instead, the mass balance is dominated by accumulation and calving, thereby enhancing the role of obliquity in controlling ice volume.
by Kerim Hestnes Nisancioglu.
Ph.D.
28
Wing, Allison A. "Physical mechanisms controlling self-aggregation of convection in idealized numerical modeling simulations." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90606.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 141-146).
The ubiquity of cloud clusters and their role in modulating radiative cooling and the moisture distribution underlines the importance of understanding how and why tropical convection organizes. In this work, the fundamental mechanism underlying the self-aggregation of convection is explored using a cloud resolving model. The objective is to identify and quantify the interactions between the environment and the convection that allow the convection to spontaneously organize into a single cluster. Specifically, the System for Atmospheric Modeling is used to perform 3-d cloud system resolving simulations of radiative-convective equilibrium in a non-rotating framework, with interactive radiation and surface fluxes and fixed sea surface temperature. Self-aggregation only occurs at sea surface temperatures above a certain threshold. As the system evolves to an aggregated state, there are large changes to domain averaged quantities important to climate, such as radiative fluxes and moisture. Notably, self-aggregation begins as a dry patch that expands, eventually forcing all the convection into a single clump. Thus, when examining the initiation of self-aggregation, we focus on processes that can amplify this initial dry patch. Sensitivity tests suggest that wind-dependent surface fluxes and interactive longwave radiative fluxes are important for permitting self-aggregation. A novel method is introduced to quantify the magnitudes of the various feedbacks that control self-aggregation within the framework of the budget for the spatial variance of column - integrated frozen moist static energy. The absorption of shortwave radiation by atmospheric water vapor is found to be a key positive feedback in the evolution of aggregation. In addition, there is a positive wind speed - surface flux feedback whose role is to counteract a negative air-sea enthalpy disequilibrium - surface flux feedback. The longwave radiation - water vapor feedback transitions from positive to negative in the early and intermediate stages of aggregation. The long-wave radiation - cloud feedback is the dominant positive feedback that maintains the aggregated state once it develops. Importantly, the mechanisms that maintain the aggregated state are distinct from those that instigate the evolution of self-aggregation. These results and those of a companion study suggest that the temperature dependence of self-aggregation enters through the longwave feedback term.
by Allison A. Wing.
Ph. D.
29
Pearce, Frederick D. (Frederick Douglas) 1978. "Seismic scattering attributes to estimate reservoir fracture density : a numerical modeling study." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/30127.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003.Includes bibliographical references (leaves 26-27).
We use a 3-D finite difference numerical model to generate synthetic seismograms from a simple fractured reservoir containing evenly-spaced, discrete, vertical fracture zones. The fracture zones are represented using a single column of anisotropic grid points. In our experiments, we vary the spacing of the fracture zones from 10-meters to 100-meters, corresponding to fracture density values from 0.1- to 0.01-fractures/meter, respectively. The vertical component of velocity is analyzed using integrated amplitude and spectral attributes that focus on time windows around the base reservoir reflection and the scattered wave coda after the base reservoir reflection. Results from a common shot gather show that when the fracture zones are spaced greater than about a quarter wavelength of a P-wave in the reservoir we see 1) significant loss of amplitude and coherence in the base reservoir reflection and 2) a large increase in bulk scattered energy. Wavenumber spectra for integrated amplitude versus offset from the time window containing the base reservoir reflection show spectral peaks corresponding to the fracture density. Frequency versus wavenumber plots for receivers normal to the fractures separate backscattered events that correspond to spectral peaks with positive wavenumbers and relatively narrow frequency ranges. In general, backscattered events show an increase in peak frequency as fracture density is increased.
by Frederick D. Pearce.
S.M.
30
Almuhaidib, Abdulaziz M. "Numerical modeling, suppression, and imaging of elastic wave scattering by near-surface heterogeneities." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90680.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
In arid environments, near-surface complexity and surface topography present major challenges to land seismic data acquisition and processing. These challenges can severely affect data quality and introduce uncertainty into reservoir imaging and characterization. The primary objectives of this thesis are to model and study the contribution of near-surface heterogeneities on seismic wavefield scattering for better understanding of land seismic data, develop an effective approach to filter out the scattered noise from the seismic records to enhance the signal-to-noise ratio, and to accurately image and locate the near-surface heterogeneities. The first part of this thesis is concerned with simulating the effects of seismic wave scattering from buried, shallow, subsurface heterogeneities through finite difference numerical forward modeling. The near-surface scattered wavefield is modeled by separating the incident (i.e., in the absence of scatterers) from the total wavefield by means of a perturbation method. Wave propagation is simulated for several earth models with different near-surface characteristics to isolate and quantify the influence of scattering on the quality of the seismic signal. We show that the scattered field is equivalent to the radiation field of an equivalent elastic source excited at the scatterer locations. Moreover, the scattered waves consist mostly of body waves scattered to surface waves and are, generally, as large as, or larger than, the reflections. These scattered waves often obscure weak primary reflections and can severely degrade the image quality. The results indicate that the scattered energy depends strongly on the properties of the shallow scatterers and increases with increasing impedance contrast, increasing sizes of the scatterers, decreasing depth of the scatterers, and increasing the attenuation factor of the background medium. Also, sources deployed at depth generate weak surface waves, whereas deep receivers record weak scattered surface waves. The analysis and quantified results help in the understanding of the scattering mechanisms and, therefore, can lead to developing new acquisition and processing techniques to reduce the scattered surface waves and enhance the quality of the seismic image. The second part of this thesis develops an approach based on spatially varying local-slope estimation, aiming at alleviating the effects of scattered surface waves and enhancing the quality of the seismic signal. Understanding the mechanism and behavior of the simulated scattered surface waves in the first part of this thesis form the basis for designing the filtering scheme. The algorithm is based on predicting the spatially varying slope of the noise, using steerable filters, and separating the signal and noise components by applying a directional non-linear filter oriented toward the noise direction to predict the noise and then subtract it from the data. The slope estimation step using steerable filters is very efficient, as it requires only a linear combination of a set of basis filters at fixed orientation to synthesize an image filtered at an arbitrary orientation. We apply our filtering approach to simulated data as well as to seismic data recorded in the field to suppress the scattered surface waves from reflected body-waves, and demonstrate its superiority over conventional f - k techniques in signal preservation and noise suppression. The third part of this thesis presents an approach for prestack elastic reverse time migration (RTM) to locate and image near-surface heterogeneities using the near-surface scattered waves (e.g., body to P, S, and surface waves). The approach back-projects the scattered waves until they are in phase with the incident waves at the scatterer locations. The P wave components (divergence of the wavefield) are derived from the spatial derivatives of the measured wavefields. Imaging the near-surface heterogeneities is important for planning seismic surveys or explaining nearsurface related anomalies in the data. The scattered body-to-surface waves travel horizontally along the free surface, and, therefore, they provide optimal illumination of the near-surface compared to scattered body-to-body waves. Additionally, the elastic RTM scheme preserves the relative amplitude because all wave propagation losses, including mode conversions, are properly taken into account. We demonstrate, using synthetic data, that elastic RTM of near-surface scattered waves constructs an accurate and reliable depth image of near-surface scatterers.
by Abdulaziz M. Almuhaidib.
Ph. D.
31
Pike-Thackray, Colin Michael. "An uncertainty-focused approach to modeling the atmospheric chemistry of persistent organic pollutants." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107106.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 103-109).
In this thesis, I study polycyclic aromatic hydrocarbons (PAHs) and perfluorocarboxylic acids (PFCAs). PAHs are by-products of burning and therefore have important anthropogenic sources in the combustion of fuels, biomass, etc. PFCAs and their atmospheric precursors are used in making firefighting foams, non-stick coatings, and other surfactant applications. I quantitatively examine the relative importance of uncertainty in emissions and physicochemical properties (including reaction rate constants) to Northern Hemisphere (NH) and Arctic PAH concentrations. NH average concentrations are more sensitive to uncertainty in the atmospheric lifetime than to emissions rate. The largest uncertainty reductions would come from precise experimental determination of PHE, PYR and BaP rate constants for the reaction with OH. I calculate long-chain PFCA formation theoretical maximum yields for the degradation of precursor species at a representative sample of atmospheric conditions from a three dimensional chemical transport model, finding that atmospheric conditions farther from pollution sources have both higher capacities to form long chain PFCAs and higher uncertainties in those capacities. I present results from newly developed simulations of atmospheric PFCA formation and fate using the chemical transport model GEOS-Chem, simulating the degradation of fluorotelomer precursors, as well as deposition and transport of the precursors, intermediates and end-products of the PFCA formation chemistry. I compare the model results to remote deposition measurements and find that it reproduces Arctic deposition of PFOA effectively. Given the most recent precursor emission inventory, the atmospheric indirect source of PFOA and PFNA is 10-45 t/yr globally and 0.2-0.7 t/yr to the Arctic.
by Colin Michael Pike-Thackray.
Ph. D.
32
Dawson, Mathew Walter 1977. "The effects of viscous stressed and mantle velocities on subduction : finite difference modeling." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/53084.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.Includes bibliographical references (leaf 107).
This thesis presents a two-dimensional finite-difference model of subduction, which is used to explore the characteristics of subduction that are most closely related to deformation in the overriding plate. The model focuses on how the angle, a, at which the slab subducts and the rate, Vr , at which the subduction boundary "retreats" are affected by the negative buoyancy of the subducting lithospheric slab and the viscous forces that arise where the mantle and subducting slab are in motion relative to one another ...
by Matthew Walter Dawson.
S.M.
33
Zhan, Xin Ph D. Massachusetts Institute of Technology. "Transport and seismoelectric properties of porous permeable rock : numerical modeling and laboratory measurements." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57794.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
The objective of this thesis is to better understand the transport and seismoelectric (SE) properties of porous permeable rock. Accurate information of rock transport properties, together with pore geometry, can aid us to better quantify the frequency dependence of its SE coupling coefficient. With the development of micro-CT (pCT) scanners, microstructure of the sedimentary rock can now be obtained in three dimensions at micron level resolution. Pore scale modeling on the rock 3-D pCT images provides us the ability to obtain different rock properties all at once and without much ambiguity. In this thesis, we build numerical tools to compute a range of transport properties and pore geometry parameters (e.g., porosity, electrical conductivity, hydraulic permeability, pore surface area) on the microstructures from basic physical laws. A staggered-grid finite difference (FD) scheme is used to solve the Laplace equation for electrical conductivity and the Stokes equation for hydraulic conductivity. The Laplace solver can handle different levels of conductivity contrast so that different saturations (gas, oil and brine) can be modeled. A three-phase conductivity model developed on the binary representation of the microstructure, which is based on the geometric average of free electrolyte conductance and surface conductance in the EDL, is illustrated. Two different edge detection methods are applied to recognize surface voxel in a binary image. One is a gradient based, first order differential method and the second one is a connectivity-number-based edge detection (CNED) method. Computations are done for a family of synthetic sand packs - Finney pack with low, medium to high porosities - to provide a benchmark of numerical tools and to compare with analytic solutions. Then, the numerical methods are used to calculate properties of Berea Sandstone 500 (BS500) with 23.6% porosity, whose 3-D microtomograms with 2.8 micron resolution are available. Using the numerical methods, rock porosity, pore surface area, (cont.) electrical conductivity and permeability are calculated.
These are compared with the laboratory measurements made on the same rock. The numerical and laboratory values compare very well. Impact of various aspects of numerical modeling on the accuracy of results are evaluated. It is demonstrated that increasing the sample used in the computation improves the match between the numerical values and laboratory measurements. Reducing the spatial resolution (i.e. increasing grid size), most affects the accuracy of electrical conductivity and hydraulic permeability. Seismoelectric measurements are carried out at 10 kHz - 120 kHz range for the BS500 sample. Both single sine pulse and five-cycle sine burst are adopted as acoustic source wavelets. Streaming potential is collected on freshly cut BS500 cylinder core samples saturated with different brine conductivities under the same experimental condition as the AC measurements. With the transport and geometrical parameters previously obtained from ptCT image and laboratory measurements, the frequency dependent coupling coefficient of BS500 is theoretically calculated using available rock properties. Comparison between the theoretical prediction and the experimental data is found to be promising. This experiment extends our ability to conduct quantitative seismoelectric measurements at frequency ranges applied for field and laboratory acoustic borehole logging.
by Xin Zhan.
Ph.D.
34
Briggs, Victoria Alice 1974. "Numerical modeling of borehole acoustics : parallel implementation of a loggin-while-drilling (LWD) model." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/58061.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000.Includes bibliographical references (p. 41-42).
A finite difference code is used to investigate acoustic waves in a borehole environment. The wave response to a logging-while-drilling (LWD) geometry is modeled in a fast formation. Helical waves circling the tool are shown to asymptote to the Stoneley wave velocity, giving confirmation of the fluid velocity in the borehole. Parameter studies for simpler borehole geometries show that the Stoneley wave, in soft formations where no shear arrival is present, can be used to invert for the shear velocity of the rock. A Beowulf parallel computer is used to implement the finite difference code showing the efficiency of cluster computing in a discretized space.
by Victoria Alice Briggs.
S.M.
35
Chen, Changsheng. "Variability of currents in Great South Channel and over Georges Bank : observation and modeling." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/51500.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992.Title as it appears in the M.I.T. Graduate List, June 1992: Variability of currents in Great South Channel and Georges Bank, observation and modeling.
Includes bibliographical references (leaves 260-270).
by Changsheng Chen.
Ph.D.
36
Zhu, Xiang 1970. "3-D numerical modeling of the P and SV wave reflections from fractured reservoirs." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/58162.
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Kosiarek, Molly (Molly R. ). "Modeling Pluto's light curve in the near infrared : implications for observation post new horizons." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104599.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 81-91).
The effects of volatile transport on Pluto's surface on ground-based observations of Pluto's light curve were studied. Due to Pluto's eccentricity of 0.249, obliquity of 123 degrees, and atmosphere, the transfer of volatiles may cause global surface change over the course of Pluto's orbit. Magellan visible and near infrared data were gathered one month before the New Horizons flyby in order to compare ground-based observing with spacecraft data. Furthermore, a model was created in order to predict how volatile transport will affect ground-based observations in the future. The near-infrared data show large scale surface composition as a function of longitude and confirm New Horizons' compositional results. The model determines that the composition of the underlying layer on Pluto's north pole can be determined by monitoring the J - Ks ratio, if the nitrogen ice currently located on the north pole is sublimated due to volatile transport. Therefore, ground based observing can monitor volatile transport and global surface changes can be monitored after the New Horizon's flyby.
by Molly Kosiarek.
S.M.
38
Stracke, Barbara [Verfasser], and Heike [Akademischer Betreuer] Rauer. "Modeling of terrestrial extrasolar planetary atmospheres in view of habitability / Barbara Stracke. Betreuer: Heike Rauer." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/102891296X/34.
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Mackie, Randall Lee. "Three-dimensional magnetotelluric modeling and inversion with applications to the California Basin and Range Province." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13753.
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40
Kostek, Sergio. "Modeling of elastic wave propagation in a fluid-filled borehole excited by a piezoelectric transducer." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13834.
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41
Zavala-Pérez, Miguel Angel. "Uncertainties in estimates of the oxidative capacity of the urban atmosphere : a modeling and measurement approach." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42274.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.Includes bibliographical references (p. 203-212).
Mobile emissions represent a significant fraction of the total anthropogenic emissions burden in megacities and have a deleterious effect on air quality at local and regional scales. Due to the significant sources of uncertainties involved during the estimation of mobile emissions, an adequate treatment of emission uncertainties is critical during the design of air quality control strategies using AQMs. This thesis focuses on quantifying the effects of parametric uncertainties of input emission fields on model uncertainties of ozone predictions. We obtained direct measurements of mobile emission sources in the Mexico City Metropolitan Area (MCMA) using a novel measurement technique and quantified the magnitude and variability of key pollutant species. This analysis allowed a direct evaluation of the emissions inventory used in AQMs for the MCMA. Measured selected VOCs and NOy showed a strong dependence on traffic mode and indicated a larger than expected burden of emitted NOx and aldehydes. Our measurements of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate that the emissions of these toxic pollutants are similar or higher than for some US cities. We derived approximate historical trends of the VOC/NOx emission ratio and quantified the impact of changes of mobile emission sources on the photochemical levels using the Brute Force Method and Direct Decoupled Method sensitivity techniques with the CAMx model. The model reasonably reproduces concentrations of ozone and VOCs and accurately those of CO and NOx but over predicts OH by about 25% and severely under-predicts HO2 by a factor of 2 to 3 suggesting that the radical formation pathways in current state of the art AQMs should be revised.
(cont.) The model successfully reproduces the corresponding relative changes in historical observations of ozone peak and diurnal average concentrations and suggests a current moderate VOC-sensitive regime. The analysis of the model's sensitivity coefficients to individual perturbations of VOC group species as described by the SAPRC99 chemical mechanism showed that the model is particularly sensitive to aromatics, higher alkenes, and formaldehyde emissions. We found, however, that NOx, olefins and aromatic species can potentially contribute significantly to uncertainties in ozone predictions.
by Miguel Angel Zavala-Perez.
Ph.D.
42
Rogers, Anna Louise. "Poroelastic modeling of groundwater and hydrocarbon reservoirs : investigating the effects of fluid extraction on fault stability." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113792.
Full textAbstract:
Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 91-93).
The possibility of human-triggered earthquakes is critical to understand for hazard mitigation. This project was developed to better understand the stability of faults in areas with high amounts of fluid extraction, and was applied to both a groundwater and hydrocarbon basin. The theory of poroelasticity was used to calculate the stress changes resulting from fluid flow. Then, the resulting fault stability was evaluated with the the Coulomb Failure Function ([Delta]CFF). A COMSOL and MATLAB workflow was used to derive the results. Two applications were completed. The primary research focused on the extraction from a groundwater aquifer in Lorca, Spain, in relation to the M, 5.1, 2011 earthquake. A smaller project was completed for the production of an oil well in Wheeler Ridge, California, in relation to the Mw 7.7, 1952 earthquake. In Lorca, it was found that extraction from a local aquifer promoted failure on an antithetic fault to the major Alhama de Murcia Fault. Specifically, while the left-lateral portion of the slip was stabilized, the reverse component of the slip was promoted (depth -5 km). Published InSAR and focal mechanism results support a rupture plane aligned with the antithetic fault. The final stress change was ~0.03 MPa which is small but not negligible compared to the expected total stress drop (~2 MPa). In California, the production from Well 85-29 was of interest. It was found that oil extraction promoted failure on the White Wolf Fault. There was a region adjacent to but below the reservoir that tended toward destabilization after the production. However, there was a notably small stress change (~0.5 kPA). This project lends to some important conclusions, and demonstrates that the poroelastic deformation of an aquifer or reservoir can result in distinct zones of stabilization and destabilization on pre-existing faults.
by Anna Louise Rogers.
S.M. in Geophysics
43
Haartsen, Matthijs W. (Matthijs Willem). "Coupled electromagnetic and acoustic wavefield modeling in poro-elastic media and its application in geophysical exploration." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11069.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.Includes bibliographical references (leaves 389-300).
by Matthijs W. Haartsen.
Ph.D.
44
Jensen, Christopher D. (Christopher David) 1974. "Terrestrial sources and sinks of atmospheric methyl bromide : three-dimensional modeling of tropospheric abundance and sensitivities." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/54436.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999.Includes bibliographical references (p. 87-92).
Current estimates of methyl bromide surface fluxes are inconsistent with the observed tropospheric mole fractions (9 to 10 ppt, globally averaged) and the calculated atmospheric lifetime (1.7 ± 0.2 years), with mid-range estimates of sinks exceeding sources by at least 50 Gg y-I. Given the uncertainties in process-specific surface flux estimates, we consider several distributions of terrestrial sources and sinks that satisfy the constraints on atmospheric abundance, Mole fractions corresponding to each distribution are simulated with a three-dimensional chemical transport model based on analyzed observed winds, coupled to a simple model of the ocean mixed layer. All of the resulting scenarios overestimate the observed zonal gradient, with interhemispheric ratios ranging from 1.39 to 1.60. In the absence of unknown sources, model results imply a biomass burning source near the upper limit of the range of present estimates (50 Gg y-1). Sensitivities to surface fluxes are also calculated to determine the extent to which uncertain terms in the methyl bromide budget can be better quantified using long-term measurements. Results show that a global network capable of accurately monitoring the monthly, zonal mean distribution of CH3Br would be able to distinguish between biomass burning fluxes and other known terrestrial sources and sinks. Modeled sensitivities to biomass burning emissions also highlight the importance of including tropical locations in any long-term monitoring network. However, technological sources and soil sinks have similar zonal patterns, and long-term, "background" mole fractions are relatively insensitive to zonal flux distributions. It is only when we examine the high frequency variability of the concentration that the effect of longitudinal gradients in the flux field becomes apparent.
by Christopher D. Jensen.
S.M.
45
Zhang, Yang Ph D. Massachusetts Institute of Technology Dept of Earth Atmospheric and Planetary Sciences. "Modeling of the effects of wave-induced fluid motion on seismic velocity and attenuation in porous rocks." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62322.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 169-181).
In this thesis, we use the X-ray CT images of Berea sandstones to carry out the numerical study of the effects of wave-induced fluid motion on seismic velocity and attenuation in porous rocks. In numerical modeling, it is possible to control the factors and inputs that are hard to accomplish in laboratory measurements and isolate those of interest that have significant impact on the seismic responses; this can help in understanding the fundamental physics of seismic waves propagating in saturated porous rocks. The ultimate goal of computational rock physics is to supplement the traditional laboratory measurements, that are time consuming and costly, with cheaper numerical experiments that allow the parameter space to be explored more thoroughly. For this purpose, in this thesis we develop a computational method for time domain simulation of wave propagation in poroelastic medium. The medium is composed of an elastic matrix saturated with a Newtonian fluid. The method operates on a digitized representation of the medium where a distinct material phase and properties are specified at each volume cell. The dynamic response to an acoustic excitation is modeled mathematically with a coupled system of equations: elastic wave equation in the solid matrix and linearized Navier-Stokes equation in the fluid. Implementation of the solution is simplified by introducing a common numerical form for both solid and fluid cells and using a rotated-staggered-grid finite-difference scheme which allows stable solutions without explicitly handling the fluid-solid boundary conditions. A stability analysis is incorporated and can be used to select gridding and time step size as a function of material properties. The numerical results are shown to agree with the analytical solution for an idealized porous medium of periodically alternating solid and fluid layers. When applying the linear solver to compute the effective elastic properties of 3D digitized porous rocks, we find discrepancies between the numerical results and the laboratory measurements. The reason for such a problem is the loss of small features, such as cracks and micro-pores, in the digitized matrix of rocks during the imaging process of aggregation. A hybrid approach, combining the numerical computation 3 and the effective media theories, is developed to deduce the lost cracks from a limited number of laboratory measurements. This approach can recover the lost cracks and is capable of predicting the effective elastic properties of the rock matrix. Compared to the traditional inversion schemes based only on the effective media theories, this hybrid scheme has the advantage of utilizing the complex micro-structures of 3D digitized porous rocks that are resolved in the imaging process, and it helps limit the inversion space for crack distribution. In the study of the dynamic and low-frequency responses of saturated porous rocks, we employ the stress-strain calculation in numerical modeling so as to compute the velocities and attenuations of rock samples, the sizes of which are much smaller than the seismic wavelength of interest. For these cases, transmission measurement cannot be used. Realizing the significant contribution of small cracks to the total attenuation, we extend the hybrid approach by incorporating the modified squirt-flow model where a fluid with frequency-dependent bulk modulus is introduced. Therefore, attenuation due to viscous fluid in stiff pores, that are resolved in the imaging process, can be computed numerically. Attenuation due to viscous fluid in compliant pores can be determined by the modified squirt-flow model since we know the crack distribution. In the inversion for crack distribution, besides using the velocities of P- and S-waves measured in laboratory for the dry and water-saturated cases, measured attenuation data of P-waves are also used so as to further constrain the inversion, and to improve the uniqueness of the inversion results. By using such an extended hybrid approach, we are able to predict both the velocities of saturated porous rocks and the attenuations. From numerical study with the linear solver, we can conclude that the linear solver is able to accurately couple elastic solid and viscous fluid and handle high material contrast and the complex micro-structures of 3D digitized porous rocks. The stress-strain calculation is capable of computing the velocities and attenuations of saturated porous rocks the sizes of which are much smaller than the wavelength of interest. The hybrid approach is a practical way to study the seismic properties of saturated porous rocks until high enough resolution digitized data and enough computational resources are available. From the computations, we observe that the small features, such as cracks lost in the imaging process, are critical for accurately predicting velocities and attenuations of saturated porous rocks. Generally, attenuation is more sensitive to the viscosity of the saturating fluid than velocity is, and attenuation due to viscous fluid in compliant pores is greater than that due to viscous fluid in stiff pores.
by Yang Zhang.
Ph.D.
46
Ling, Christopher S. K. "A test for a see-saw oscillation between the Amazon and Congo basins using regional climate modeling." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/114128.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2006.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 49-50).
The Amazon and Congo basins represent two of the three largest regions of rainfall found on the globe. Eltahir et al. (2004) have proposed the existence of a "see-saw" oscillation between these two basins, where a reduction of rainfall in one region is marked by an increase in the other. This inverse relationship has been observed both directly by Eltahir et al., using satellite data of regional rainfall (Simpson et al. 1988), and indirectly through changes in river flow measurements (Amarasekera et al. 1977) during the last century. However, little work has been done to study this see-saw effect through the use of climate models. Using a regional climate model (RegCM), the appearance of the oscillation was tested by converting rainforest area in one basin into two different land types, simulating drought-like climate conditions to induce additional rainfall in the other basin. In total, one control run and four land-modified runs were simulated for this experiment. The effects of these conditions were modeled over a one-year period (1980). It was found that in some cases, reduction of rainfall in one basin resulted in increased rainfall in small areas of the other; however, over the entirety of both basins, evidence of the see-saw hypothesis was not simulated. Several factors may have contributed to this result, including the limitations associated with using a regional model, as well as the initial conditions set for the five climate simulations.
by Christopher S. K. Ling.
S.B.
47
Lehmann, M. (Marius). "Waves in planetary rings:hydrodynamic modeling of resonantly forced density waves and viscous overstability in Saturn’s rings." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221168.
Full textAbstract:
Abstract
The present thesis investigates the dynamics of wave structures in dense planetary rings by employing hydrodynamic models, along with local N-body simulations of the particulate ring flow. The focus is on the large-scale satellite induced spiral density waves as well as on the free short-scale waves generated by the viscous overstability in Saturn's A and B rings.
An analytic weakly nonlinear model is derived by using perturbation theory based on multi-scale methods to compute the damping behavior of nonlinear spiral density waves in a planetary ring subject to viscous overstability. In order to study the complex spatio-temporal evolution of these wave structures, numerical schemes are developed to integrate the hydrodynamical equations in time on large radial domains, taking into account collective self-gravity forces of the ring material, as well as the forcing by an external satellite. The required numerical stability and accuracy is achieved by applying Flux-Vector-Splitting methods aligned with advanced shock-capturing techniques. The free short-scale overstable waves are also investigated with local N-body simulations of the sheared ring flow. In particular, the influence of collective self-gravity between the ring particles as well as the periodic forcing due to a nearby Lindblad resonance on the overstable wave pattern is considered.
The linear stability criterion for spiral density waves in Saturn’s rings is found to be identical to the condition for the onset of spontaneous viscous overstability in the limit of long wavelengths and agrees with the stability criterion for density waves derived by Borderies et al. within the streamline formalism. The derived nonlinear damping behavior of density waves can be very different from what has previously been thought. The role of collective self-gravity on the nonlinear evolution of short-scale overstable waves is determined, reconciling the partly contradicting results of previous studies. It is shown that collective self-gravity plays an important role in setting the length-scale on which the nonlinear overstable waves saturate in a planetary ring. A co-existence of spiral density waves and short-scale overstable waves is modeled in terms of one-dimensional large-scale hydrodynamical integrations.
Due to the restriction to one space dimension, certain terms in the hydrodynamical equations that arise from the spiral shape of a density wave need to be approximated based on the weakly nonlinear model. These integrations reveal that density waves and spontaneous viscous overstability undergo complex interactions. In particular it is found that, depending on the relative magnitude of the two wave structures, the presence of short-scale overstable waves can lead to a damping of an overstable density wave and vice versa, density waves can suppress overstability. The effect of a density wave on the viscous overstability is also studied in terms of a simplified axisymmetric model of a ring perturbed by a nearby Lindblad resonance. A linear hydrodynamic stability analysis and local N-body simulations of this model system conform the corresponding results of the large-scale hydrodynamical integrations.
48
Hamilton, Brandi B. "Modeling Exoplanet Interiors from Host Star Elemental Abundances." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou157382737367536.
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49
Kaufman, Peter Stanley. "Extensional tectonic history of the Rhodope metamorphic core complex, Greece, and geophysical modeling of the Halloran Hills, California." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11788.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.Two maps in pocket following text.
Includes bibliographical references.
by Peter Stanley Kaufman.
Ph.D.
50
Liu, Yuexin. "Modeling the emissions of nitrous oxide (N₂O) and methane (CH₄) from the terrestrial biosphere to the atmosphere." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/59869.
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