To see the other types of publications on this topic, follow the link: Crest vertical curves.
Journal articles on the topic 'Crest vertical curves'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Crest vertical curves.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Sun, Jian Cheng, and Chen Feng Chen. "Length Requirements for New Single-Arc Unsymmetrical Crest Vertical Curve for Highways." Advanced Materials Research 1065-1069 (December 2014): 755–59. http://dx.doi.org/10.4028/www.scientific.net/amr.1065-1069.755.
Full textAbstract:
Existing highway vertical curves may be grouped into two categories: symmetrical vertical curves and unsymmetrical vertical curves. In the past vertical curves design, parabolic arc was used as the vertical curve. This paper presents the new single-arc unsymmetrical vertical curve which is include only one cubic parabola. This curve has the gradual change of the rates of change in grade so that it can provide more comfort to the driver. This paper mainly presents the method by which to find the minimum length for a new single-arc unsymmetrical crest vertical curve based on the minimum sight distance . The discussion will be divided into two situations: the sight distance is longer than the curve length and the sight distance is not longer than the curve length.
2
Hasan, Moudud, Tarek Sayed, and Yasser Hassan. "Influence of vertical alignment on horizontal curve perception: effect of spirals and position of vertical curve." Canadian Journal of Civil Engineering 32, no. 1 (February 1, 2005): 204–12. http://dx.doi.org/10.1139/l04-090.
Full textAbstract:
Several studies have shown that the perception of horizontal curves can be influenced by an overlapping vertical alignment. A previous two-phase study investigated the hypothesis that a horizontal curve appears flatter when overlapping with a vertical sag curve and sharper when overlapping with a vertical crest curve. The study concluded that the hypothesis was valid. The study also developed several statistical models to estimate the perceived radius of horizontal curves in a combined alignment. This study extends the earlier work by investigating the effect of additional geometric parameters on the perception. The parameters examined include the presence of spiral curves, the length of the spirals, and the position of the vertical curve midpoint relative to the horizontal curve. It was found that (1) driver misperception of the horizontal curvature increases as the radius of the horizontal curve increases, (2) the presence of a spiral curve affects driver perception of the horizontal curvature in the case of crest combination only, (3) the length of the spiral curve has no effect on the perception whether on crest or sag combinations, and (4) while the effect of the position of the vertical curve midpoint relative to the horizontal curve is not statistically significant, it seems that the perception problem appears to diminish as the positive offsets increases.Key words: highway geometric design, visual perception, combined alignment.
3
Taignidis, Ioannis, and George Kanellaidis. "Required Stopping Sight Distance on Crest Vertical Curves." Journal of Transportation Engineering 127, no. 4 (August 2001): 275–82. http://dx.doi.org/10.1061/(asce)0733-947x(2001)127:4(275).
Full text
4
Ko, Myunghoon, Dominique Lord, and Josias Zietsman. "Environmentally Conscious Highway Design for Crest Vertical Curves." Transportation Research Record: Journal of the Transportation Research Board 2270, no. 1 (January 2012): 96–106. http://dx.doi.org/10.3141/2270-12.
Full text
5
Easa, Said M. "Improved speed-profile model for two-lane rural highways." Canadian Journal of Civil Engineering 30, no. 6 (December 1, 2003): 1055–65. http://dx.doi.org/10.1139/l03-021.
Full textAbstract:
The speed-profile model has been suggested as a valuable tool for evaluating geometric design consistency for two-lane rural highways with isolated and combined horizontal and vertical alignments. The model determines the operating speeds on the speed-change (SC) segment, which is the distance between speed-limiting curves. The speed-limiting curves are the horizontal curves and the limited sight-distance crest vertical curves on horizontal tangents, where the sight distance required by the design guides is not satisfied. The model assumes that deceleration begins where required, which implies that the next curve is visible when deceleration starts. This paper presents an extension to the speed-profile model to incorporate the effect of sight obstruction on operating speeds and deceleration rates. The SC segment may include nonlimited sight–distance crest vertical and sag vertical curves. These curves may present sight obstruction. A procedure to determine whether the sight line is obstructed is developed. If it does, simple formulas are applied for revising the operating-speed profile. The extended model is suitable for inclusion in the design consistency module of the interactive highway safety design model.Key words: speed profile, model, two-lane highways, alignments, design consistency.
6
Hassan, Yasser. "Improved Design of Vertical Curves with Sight Distance Profiles." Transportation Research Record: Journal of the Transportation Research Board 1851, no. 1 (January 2003): 13–24. http://dx.doi.org/10.3141/1851-02.
Full textAbstract:
Design of vertical alignment is one of the main tasks in highway geometric design. This task requires, among other things, that the designer ensure drivers always have a clear view of the road so they can stop before hitting an unexpected object in the road. Therefore, the ability to determine the required and available stopping sight distance (SSD) at any point of the vertical alignment is essential for the design process. Current design guides in the United States and Canada provide simple analytical models for determining the minimum length of a vertical curve that would satisfy the sight distance requirement. However, these models ignore the effect of grade on the required SSD. Alternative approaches and models have also been suggested but cover only special cases of vertical curves. Two specific models were expanded to determine the required SSD on crest and sag vertical curves. By comparing profiles of available SSD and required SSD on examples of vertical curves, it was shown that current North American design practices might yield segments of the vertical curve where the driver’s view is constrained to a distance shorter than the required SSD. An alternative design procedure based on the models was developed and used to determine the minimum lengths of crest and sag vertical curves. Depending on the approach grade, these new values of minimum curve length might be greater than or less than values obtained through conventional design procedures. Design aids were therefore provided in tabular form for designers’ easy and quick use.
7
Taiganidis, Ioannis. "Aspects of Stopping-Sight Distance on Crest Vertical Curves." Journal of Transportation Engineering 124, no. 4 (July 1998): 335–42. http://dx.doi.org/10.1061/(asce)0733-947x(1998)124:4(335).
Full text
8
Fambro, Daniel B., Kay Fitzpatrick, and Charles W. Russell. "Operating Speed on Crest Vertical Curves with Limited Stopping Sight Distance." Transportation Research Record: Journal of the Transportation Research Board 1701, no. 1 (January 2000): 25–31. http://dx.doi.org/10.3141/1701-04.
Full textAbstract:
Horizontal and vertical elements of a highway are designed based on an assumed design speed. This concept was developed in the 1930s as a mechanism for designing rural alignments to permit most drivers to operate uniformly at their desired speed. In 1938, AASHO recognized that drivers select a speed influenced by the roadway environment instead of an assumed design speed. Recent research suggests that design speed is no longer the speed adopted by the faster group of drivers but that it has become a value used to establish the sharpness of horizontal and vertical design elements. The objective of this study was to establish the relationship between design and operating speeds for crest vertical curves with limited sight distance. Geometric data and 3,500 paired speeds (speeds at control and crest sections) were collected at 36 sites in 3 states. The results indicated that both the 85th percentile and the mean operating speeds were well above the inferred design speeds of the crest vertical curves for the range of conditions studied and that the lower the design speed the larger the difference between the 85th percentile speed and the design speed. The mean reductions in speed between the control and crest sections tend to increase as available sight distance is decreased; however, the reduction in speed is less than that suggested by current AASHTO criteria.
9
Easa, Said M. "Length Requirements for New Single-Arc Unsymmetrical Vertical Curve." Transportation Research Record: Journal of the Transportation Research Board 2060, no. 1 (January 2008): 38–45. http://dx.doi.org/10.3141/2060-05.
Full textAbstract:
Traditional unsymmetrical vertical curves consist of two parabolic arcs smoothly connected at the point of common curvature. A new single-arc unsymmetrical vertical curve that takes the form of a cubic instead of parabolic function has been recently developed. The curve has a rate of change in grade that gradually varies between the start and end of the vertical curve. The single-arc curve eliminates the sudden change that exists in curvature of traditional two-arc unsymmetrical vertical curves. This paper first develops the sight distance (SD) relationships for the new single-arc curve (crest type). With these relationships, the SD profile for the new curve is established and its shape shows a substantial improvement over the abrupt-type SD profiles of the two-arc curves. The length requirements that satisfy stopping, passing, and decision SD guidelines of AASHTO are then presented. Some examples are used to illustrate the use of the developed design aids. The new single-arc curve builds on previously developed unsymmetrical vertical curves to improve curve characteristics that hopefully will promote road safety.
10
Easa, Said, and Essam Dabbour. "Establishing design guidelines for compound horizontal curves on three-dimensional alignments." Canadian Journal of Civil Engineering 32, no. 4 (August 1, 2005): 615–26. http://dx.doi.org/10.1139/l05-016.
Full textAbstract:
In current design guides, the minimum radii of compound horizontal curves are based on the design requirements of simple horizontal curves for each arc on flat terrain. Such a design ignores the effects of compound curvature and vertical alignment. This paper uses computer simulation software to establish the minimum radius requirements for compound curves, considering these effects. The actual lateral acceleration experienced by a vehicle negotiating a two-dimensional (2-D) simple curve is recorded as a base scenario to facilitate the analysis of a compound curve on a flat terrain or combined with vertical alignment (three-dimensional (3-D) compound curves). The vertical alignments examined include upgrades, downgrades, crest curves, and sag curves. Mathematical models for minimum radius requirements were developed for flat and 3-D compound curves. Three types of design vehicles were used. The results show that an increase in the minimum radius ranging from 5% to 26% is required to compensate for the effects of both compound curvature and vertical alignment.Key words: highway geometric design, compound horizontal alignments, side friction, vehicle simulation, 3-D alignments.
11
Shalkamy, Amr, Karim El-Basyouny, and Hai Yang Xu. "Voxel-Based Methodology for Automated 3D Sight Distance Assessment on Highways using Mobile Light Detection and Ranging Data." Transportation Research Record: Journal of the Transportation Research Board 2674, no. 5 (May 2020): 587–99. http://dx.doi.org/10.1177/0361198120917376.
Full textAbstract:
Ensuring that the available sight distance (ASD) on highways meets the minimum requirements of geometric design standards is crucial for safe and efficient operation of highways. Current practices of ASD assessment using design software or through site visits are labor intensive, time consuming, and traffic disruptive. Thus, this paper introduces a fully automated algorithm that allows large-scale assessment of ASD in three-dimensional (3D) space on highways utilizing mobile light detection and ranging (LiDAR) data. The algorithm was tested on LiDAR data of highway segments in Alberta, Canada. The results showed that the algorithm was highly accurate in detecting sight distance limitations at the defined regions and, in all cases, the driver’s vision was restricted by the pavement surface on vertical crest curves. In the case of combined vertical and horizontal curves, the vertical crest curve was found to be the controlling element in sight distance deficiencies. In addition, the assessment of historical collision data revealed clusters along the regions defined with ASD limitations, indicating that restrictions in drivers’ vision could have contributed to the collision occurrence.
12
Fitzpatrick, Kay, Daniel B. Fambro, and Angela M. Stoddard. "Safety Effects of Limited Stopping Sight Distance on Crest Vertical Curves." Transportation Research Record: Journal of the Transportation Research Board 1701, no. 1 (January 2000): 17–24. http://dx.doi.org/10.3141/1701-03.
Full textAbstract:
Previous studies that examined the relationship between stopping sight distance and safety have been inconclusive and inconsistent; however, the fact that a relationship has not been established does not necessarily imply that stopping sight distance is not a contributing factor in some crashes. Instead, it means that existing databases have failed to quantify any relationship that might exist. A promising approach to identifying such a relationship is a detailed examination or case study of crashes from a relatively large sample of limited sight distance roadways. If limited sight distance is a factor that contributes to crashes, it should show up in such a study. The objective of this study was to determine whether stopping sight distance was a contributing factor in crashes on roadway segments with limited sight distance crest vertical curves. This objective was accomplished by reviewing 439 narratives from crashes that occurred on 33 multilane and two-lane roadways with limited sight distance crest vertical curves. The findings suggest that the crash rates on rural two-lane highways with limited stopping sight distance are similar to the crash rates on all two-lane rural highways. They also suggest that the percentage of accidents involving large trucks and older drivers is similar on limited sight distance highways and all two-lane rural highways. Thus, for the range of conditions studied, limited stopping sight distance does not appear to be a safety problem.
13
Hassan, Yasser, Said M. Easa, and A. O. Abd El Halim. "Modeling Headlight Sight Distance on Three-Dimensional Highway Alignments." Transportation Research Record: Journal of the Transportation Research Board 1579, no. 1 (January 1997): 79–88. http://dx.doi.org/10.3141/1579-10.
Full textAbstract:
Sight distance is one of the major elements that must be considered in the geometric design to achieve safe and comfortable highways. Daytime sight distance has been extensively studied, and analytical models for two-dimensional (2-D) and three-dimensional (3-D) alignments have been developed. However, nighttime (headlight) sight distance has received less attention. Despite the higher accident rate during nighttime than during daytime, existing analytical models evaluating headlight sight distance are very primitive. Moreover, the interaction between the horizontal and vertical alignments has not been modeled. A four-phase analytical model for headlight sight distance on 3-D combined alignments is presented. The model is an application of the finite-element technique in highway geometric design. The model can determine the maximum distance that can be covered by the vehicle’s headlights and that is not obstructed by any sight obstructions including the road surface. On the basis of this analytical model, computer software was developed and used in a preliminary application for 3-D headlight sight distances on a sag or crest vertical curve combined with a horizontal curve. The application showed that the 3-D sight distance on sag vertical curves was generally lower than the corresponding 2-D value when the sag curve was overlapping with a horizontal curve. On the other hand, the overlapping of horizontal curves with crest vertical curves enhanced the 3-D sight distance. The difference between 2-D and 3-D sight distance values in both cases increased with a decrease in the horizontal curve radius and an increase in the pavement cross slope. The model was proved to be extremely valuable in establishing 3-D highway geometric design standards.
14
Papadimitriou, Eleonora, Stergios Mavromatis, and Basil Psarianos. "Stopping sight distance adequacy assessment on freeways: the case of left horizontal curves over crest vertical curves." Transportation Letters 10, no. 5 (December 2016): 269–79. http://dx.doi.org/10.1080/19427867.2016.1259759.
Full text
15
Jessen, Daniel R., Karen S. Schurr, Patrick T. McCoy, Geza Pesti, and Ryan R. Huff. "Operating Speed Prediction on Crest Vertical Curves of Rural Two-Lane Highways in Nebraska." Transportation Research Record: Journal of the Transportation Research Board 1751, no. 1 (January 2001): 67–75. http://dx.doi.org/10.3141/1751-08.
Full text
16
Guerrieri, Marco. "Two-Lane Highways Crest Curve Design. The Case Study of Italian Guidelines." Applied Sciences 10, no. 22 (November 18, 2020): 8182. http://dx.doi.org/10.3390/app10228182.
Full textAbstract:
The main purpose of the research is to evaluate the crest vertical curves radii Rv, not considering a conventional value of the opposing vehicle height h2, but the average vehicle heights h2(m) and the value of the 15th percentile of the height distribution h2(15) of the passenger car population. The study only considered car models with more than 20,000 registered vehicles in Italy. One hundred and fifteen car models belonging to different brands were taken into consideration, for a total of over 9 million vehicles. For the statistical sample analyzed, the following vehicle heights were estimated: h2(m) = 1.48 m and h2(15) = 1.39 m. The deviations between the crest radii calculated with the Italian standard (h2 = 1.10 m), and those obtained for h2(m) = 1.48 m and h2(15) = 1.39 m are up to 12%. The differences ΔHv between the values of the visible vehicle body height Hv = Hv(t) calculated using, respectively, h2(15) = 1.39 m and h2(m) = 1.48 m are modest. The value h2(m) = 1.48 m could be adopted in order to reduce the highways construction costs. In fact, the research shows that the value h2 = 1.10 m is too conservative and leads to oversizing of the crest vertical curves. Therefore, it would be necessary to make an appropriate choice of h2 value in order to take into account the current heights of passenger cars.
17
Harwood, Douglas W., and Karin M. Bauer. "Effect of Stopping Sight Distance on Crashes at Crest Vertical Curves on Rural Two-Lane Highways." Transportation Research Record: Journal of the Transportation Research Board 2486, no. 1 (January 2015): 45–53. http://dx.doi.org/10.3141/2486-06.
Full text
18
Rosey, Florence, Jean-Michel Auberlet, Jean Bertrand, and Patrick Plainchault. "Impact of perceptual treatments on lateral control during driving on crest vertical curves: A driving simulator study." Accident Analysis & Prevention 40, no. 4 (July 2008): 1513–23. http://dx.doi.org/10.1016/j.aap.2008.03.019.
Full text
19
Bijankhan, Mohammad, and Vito Ferro. "Dimensional analysis and stage-discharge relationship for weirs: a review." Journal of Agricultural Engineering 48, no. 1 (February 17, 2017): 1–11. http://dx.doi.org/10.4081/jae.2017.575.
Full textAbstract:
Deducing the weir flow stage-discharge relationship is a classical hydraulic problem. In this regard Buckingham’s theorem of dimensional analysis can be used to find simple and accurate formulas to obtain the rating curves of different weir types. At first, in this review paper the rectangular weir that is a very common hydraulic structure is studied. It is indicated that the crest shape, approach channel width, obliquity (angle between the weir crest and the direction normal to the flow motion) and vertical inclination (pivot weir) are the key-parameters affecting the flow over the rectangular weirs. The flow over the triangular, labyrinth, parabolic, circular, elliptical, and W-weirs are also studied using dimensional analysis and incomplete self-similarity concept. For all mentioned weirs the stage-discharge relationships are presented and the application limits are discussed. The results of this paper can be used and implemented by the irrigation and drainage network designers to simplify the procedure of weir design.
20
Anders, Christoph, Klaus Sander, Frank Layher, Steffen Patenge, and Raimund W. Kinne. "Temporal and spatial relationship between gluteal muscle Surface EMG activity and the vertical component of the ground reaction force during walking." PLOS ONE 16, no. 5 (May 26, 2021): e0251758. http://dx.doi.org/10.1371/journal.pone.0251758.
Full textAbstract:
Background Optimized temporal and spatial activation of the gluteal intermuscular functional unit is essential for steady gait and minimized joint loading. Research question To analyze the temporal relationship between spatially resolved surface EMG (SEMG) of the gluteal region and the corresponding ground reaction force (GRF). Methods Healthy adults (29♀; 25♂; age 62.6±7.0 years) walked at their self-selected slow, normal, and fast walking speeds on a 10 m walkway (ten trials/speed). Bilateral paired eight-electrode strips were horizontally aligned at mid-distance of the vertical line between greater trochanter and iliac crest. Concerning the ventral to dorsal direction, the center of each strip was placed on this vertical line. Initially, these signals were monopolarly sampled, but eight vertically oriented bipolar channels covering the whole gluteal region from ventral to dorsal (P1 to P8) were subsequently calculated by subtracting the signals of the corresponding electrodes of each electrode strip for both sides of the body. Three vertical bipolar channels represented the tensor fasciae latae (TFL; P2), gluteus medius (Gmed, SENIAM position; average of P4 and P5), and gluteus maximus muscles (Gmax; P7). To determine the interval between SEMG and corresponding GRF, the time delay (TD) between the respective first amplitude peaks (F1) in SEMG and vertical GRF curves was calculated. Results Throughout the grand averaged SEMG curves, the absolute amplitudes significantly differed among the three walking speeds at all electrode positions, with the amplitude of the F1 peak significantly increasing with increasing speed. In addition, when normalized to slow, the relative SEMG amplitude differences at the individual electrode positions showed an impressively homogeneous pattern. In both vertical GRF and all electrode SEMGs, the F1 peak occurred significantly earlier with increasing speed. Also, the TD between SEMG and vertical GRF F1 peaks significantly decreased with increasing speed. Concerning spatial activation, the TD between the respective F1 peaks in the SEMG and vertical GRF was significantly shorter for the ventral TFL position than the dorsal Gmed and Gmax positions, showing that the SEMG F1 peak during this initial phase of the gait cycle occurred earlier in the dorsal positions, and thus implying that the occurrence of the SEMG F1 peak proceeded from dorsal to ventral. Significance Tightly regulated spatial and temporal activation of the gluteal intermuscular functional unit, which includes both speed- and position-dependent mechanisms, seems to be an essential requirement for a functionally optimized, steady gait.
21
Sarhan, Mohamed, and Yasser Hassan. "Three-Dimensional, Probabilistic Highway Design." Transportation Research Record: Journal of the Transportation Research Board 2060, no. 1 (January 2008): 10–18. http://dx.doi.org/10.3141/2060-02.
Full textAbstract:
The potential usefulness of reliability analysis has recently been stressed in many engineering applications. Given the variability in the design parameters, a reliability-based probabilistic approach is well suited to replace the current deterministic highway design practice. However, progress in this regard is generally slow. In this study, the reliability analysis was used to estimate the probability of hazard (POH) that might result from insufficiency of sight distances. As an application, the available sight distance was checked against required stopping sight distance on an assumed road segment. Variation of the design parameters was addressed with Monte Carlo simulation using 100,000 sets of design parameters based on distributions available in the literature. A computer program was developed to use these sets of design parameters to calculate the profiles of available and required stopping sight distances in two- and three-dimensional projections as well as the profile of POH. The approach was applied to a horizontal curve overlapping with flat grade, crest curves, and sag curves in a cut section where the side slope would restrict the sightline. The analysis showed that the current deterministic approach yields very conservative estimates of available and required stopping sight distance, resulting in very low POH. The application example also showed the change of POH with the change of vertical alignment parameters.
22
Kazemzadehazad, Sanaz, Saeed Monajjem, Grégoire S. Larue, and Mark J. King. "Evaluating new treatments for improving driver performance on combined horizontal and crest vertical curves on two-lane rural roads: A driving simulator study." Transportation Research Part F: Traffic Psychology and Behaviour 62 (April 2019): 727–39. http://dx.doi.org/10.1016/j.trf.2019.03.002.
Full text
23
Jiang, Lei, Chao-Lung Ting, Marc Perlin, and William W. Schultz. "Moderate and steep Faraday waves: instabilities, modulation and temporal asymmetries." Journal of Fluid Mechanics 329 (December 25, 1996): 275–307. http://dx.doi.org/10.1017/s0022112096008920.
Full textAbstract:
Mild to steep standing waves of the fundamental mode are generated in a narrow rectangular cylinder undergoing vertical oscillation with forcing frequencies of 3.15 Hz to 3.34 Hz. A precise, non-intrusive optical wave profile measurement system is used along with a wave probe to accurately quantify the spatial and temporal surface elevations. These standing waves are also simulated by a two-dimensional spectral Cauchy integral code. Experiments show that contact-line effects increase the viscous natural frequency and alter the neutral stability curves. Hence, as expected, the addition of the wetting agent Photo Flo significantly changes the stability curve and the hysteresis in the response diagram. Experimentally, we find strong modulations in the wave amplitude for some forcing frequencies higher than 3.30 Hz. Reducing contact-line effects by Photo-Flo addition suppresses these modulations. Perturbation analysis predicts that some of this modulation is caused by noise in the forcing signal through ‘sideband resonance’, i.e. the introduction of small sideband forcing can generate large modulations of the Faraday waves. The analysis is verified by our numerical simulations and physical experiments. Finally, we observe experimentally a new form of steep standing wave with a large symmetric double-peaked crest, while simulation of the same forcing condition results in a sharper crest than seen previously. Both standing wave forms appear at a finite wave steepness far smaller than the maximum steepness for the classical standing wave and a surface tension far smaller than that for a Wilton ripple. In both physical and numerical experiments, a stronger second harmonic (in time) and temporal asymmetry in the wave forms suggest a 1:2 resonance due to a non-conventional quartet interaction. Increasing wave steepness leads to a new form of breaking standing waves in physical experiments.
24
Saville, Thorndike. "AN APPROXIMATION OF THE WAVE RUN-UP FREQUENCY DISTRIBUTION." Coastal Engineering Proceedings 1, no. 8 (January 29, 2011): 4. http://dx.doi.org/10.9753/icce.v8.4.
Full textAbstract:
The distribution of wave steepness (H/T ) for fully developed sea is obtained from Bretschneider's joint distribution of wave height and wave period. This steepness distribution is used with standard wave runup curves to develop a frequency curve of wave run-up. Use of this run-up distribution curve will permit more accurate estimation of the variability in wave run-up for design cases, and particularly the percent of time in which run-ups will exceed that predicted for the significant wave. The distribution may also be used with normal overtopping procedures to determine more accurate estimates of overtopping quantities. Wave run-up may be defined as the vertical height above mean water level to which water from a breaking wave will rise on a structure face. Accurate design data on the height of wave run-up is needed for determination of design crest elevations of protective structures subject to wave action such as seawalls, beach fills, surge barriers, and dams. Such structures are normally designed to prevent wave overtopping with consequent flooding on the landward side and, if of an earth type, possible failure by rearface erosion. Because of the importance of wave run-up elevations in determining structure heights and freeboards, a great deal of work has been done in the past six years in an attempt to relate wave run-up to incident wave characteristics, and slope or structure characteristics. Compilations based largely on laboratory experimental work have been made and have fe-?* suited in curves similar to those shown in Figure 1 which is reprinted from the U. S. Beach Erosion Board Technical Report No. 4. Such curves most frequently have related the dimensionless ratio of relative run-up (R/H ) to incident wave steepness in deep water (H /T ), as a function of structure type or slope. (H is the equivalent deep water wave height.) The curves shown in Figure 1 are of this type, and pertain to structures having a depth of water greater than three wave heights at the toe of the structure; this depth limitation in effect means that the wave breaks directly on the structure. The curves shown in Figure 1 are a portion of a set of five separate figures, covering different structure depths (d/H ). All are published in Beach Erosion Board Technical Report Number 4. These curves were derived primarily from small scale laboratory tests. Further laboratory tests with much larger waves (heights two to five feet) have shown that a scale effect exists for some conditions.
25
Khoury, John, Kamar Amine, and Rima Abi Saad. "An Initial Investigation of the Effects of a Fully Automated Vehicle Fleet on Geometric Design." Journal of Advanced Transportation 2019 (May 26, 2019): 1–10. http://dx.doi.org/10.1155/2019/6126408.
Full textAbstract:
This paper investigates the potential changes in the geometric design elements in response to a fully autonomous vehicle fleet. When autonomous vehicles completely replace conventional vehicles, the human driver will no longer be a concern. Currently, and for safety reasons, the human driver plays an inherent role in designing highway elements, which depend on the driver’s perception-reaction time, driver’s eye height, and other driver related parameters. This study focuses on the geometric design elements that will directly be affected by the replacement of the human driver with fully autonomous vehicles. Stopping sight distance, decision sight distance, and length of sag and crest vertical curves are geometric design elements directly affected by the projected change. Revised values for these design elements are presented and their effects are quantified using a real-life scenario. An existing roadway designed using current AASHTO standards has been redesigned with the revised values. Compared with the existing design, the proposed design shows significant economic and environmental improvements, given the elimination of the human driver.
26
Ismail, Karim, and Tarek Sayed. "Risk-based framework for accommodating uncertainty in highway geometric design." Canadian Journal of Civil Engineering 36, no. 5 (May 2009): 743–53. http://dx.doi.org/10.1139/l08-146.
Full textAbstract:
The development of highway standard design models involves various assumptions regarding design inputs and the road environment. This paper suggests an improvement to the treatment of uncertainty in design inputs by replacing the current deterministic approach with a reliability-based framework. Reliability theory deals with the propagation of quantified variability in design inputs throughout the design process. In such a framework, each design output corresponds to a theoretical probability of noncompliance to design requirements. These probabilities can be used to assess and compare the a priori safety level associated with various design scenarios. This paper proposes that such a priori safety level of standard design outputs should be consistent and close to a prespecified target level. A set of methods is proposed to determine a target value for design safety. A general framework for calibrating standard design models is presented. To demonstrate the concept, the paper presents an application of the calibration framework to the standard design model of crest vertical curves. Calibrated design charts are constructed to yield a consistent design safety level.
27
Monajjem, Saeed, Sanaz Kazemzadehazad, and Gregoire Larue. "The Effect of New Treatments and On-Coming Traffic on Driver Performance on Combined Horizontal and Crest Vertical Curves of Two-Lane Rural Roads: A Driving Simulator Study." Iranian Journal of Science and Technology, Transactions of Civil Engineering 43, no. 3 (November 23, 2018): 521–31. http://dx.doi.org/10.1007/s40996-018-0211-3.
Full text
28
Mavromatis, Stergios, Nikiforos Stamatiadis, Basil Psarianos, and George Yannis. "Controlling Crest Vertical Curvature Rates Based on Variable Grade Stopping Sight Distance Calculation." Transportation Research Record: Journal of the Transportation Research Board 2521, no. 1 (January 2015): 31–44. http://dx.doi.org/10.3141/2521-04.
Full textAbstract:
Stopping sight distance (SSD) is a key control element that directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many design policies ignore the grade effect during vehicle braking on variable grades. Such a case occurs during the determination of crest vertical curvature rates in which the relevant SSD values are extracted assuming leveled road geometry. This paper investigates a possible deficiency of such an approach with regard to cases in which the length of the vertical curve exceeds the control SSD values. SSD calculation on variable grades during the braking process was addressed through a recently developed process that related the point mass model and the laws of mechanics. For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative ending grade values related to the control crest vertical curve rates adopted by AASHTO. The process revealed numerous SSD shortage areas for which revised crest vertical curvature rates were provided to grant SSD adequacy throughout the vehicles' braking process. This paper also aimed to provide designers with ready-to-use vertical design tools associated with amended vertical curvature rates to AASHTO's road functional classification as a function of the crest vertical curve's exit grade value.
29
Easa, Said M., Yasser Hassan, and A. O. Abd El Halim. "Sight distance evaluation on complex highway vertical alignments." Canadian Journal of Civil Engineering 23, no. 3 (June 1, 1996): 577–86. http://dx.doi.org/10.1139/l96-866.
Full textAbstract:
Sight distance (stopping, passing, and decision) is a key element in highway geometric design. Existing models for evaluating sight distance on vertical alignments are applicable only to simple, isolated elements such as a crest vertical curve, a sag vertical curve, and a reverse vertical curve (a sag curve following a crest curve, or vice versa). This paper presents an analytical methodology for evaluating sight distance on complex vertical alignments that involve any combination of vertical alignment elements. The methodology can be used for evaluating passing sight distance on two-lane highways, and stopping sight distance and decision sight distance on all highways. Sight distance controlled by the headlight beam can also be evaluated. The locations of sight-hidden dips, which may develop when a sag vertical curve follows a crest vertical curve with or without a common tangent, can be determined. Also, sight distances obstructed by overpasses are evaluated. A profile of the available sight distance can be established and used to evaluate sight distance deficiency and the effect of alignment improvements. A software was developed and can be used for determining the available sight distance accurately. The software may replace the current field and graphical practice for establishing the no-passing zones and evaluating stopping and decision sight distances on complex vertical alignments. Key words: sight distance, vertical alignment, highway, passing zones.
30
Hansen, Regan, and Kevin Chang. "Horizontal and Vertical Curvature and its Effects on Driver Passing Choice." Transportation Research Record: Journal of the Transportation Research Board 2673, no. 2 (February 2019): 734–42. http://dx.doi.org/10.1177/0361198119827531.
Full textAbstract:
Passing maneuvers on rural two-lane highways require drivers to enter the opposing traffic lane to overtake an impeding vehicle. A successful maneuver requires the driver to correctly judge the time it will take to complete the pass, and the distance to and speed of the oncoming vehicle. Previous studies have shown that the type and speed of impeding vehicle, traffic volume, roadway cross-section, and driver characteristics influence gap-acceptance behavior, but have not considered vertical curvature or specified directionality in the horizontal curvature. This paper describes a driving simulation experiment in which these geometric, situational, and driver characteristic variables were collected for 643 passing attempts. A logistic regression model was developed to infer the effects of horizontal and vertical curvature on driver passing decisions. This study uniquely quantified that drivers were: more likely to pass if the road curved to the left than if it was straight and less likely to pass if the road curved to the right; more likely to pass if there was a sag curve than if the road was flat and less likely to pass if there was a crest curve; and less likely to pass when traveling uphill than if the road was level. As the influence of roadway geometry on gap-acceptance decisions is not currently implemented in overtaking models, the results of this study have practical implications for microsimulation of rural two-lane highways, highway design, and highway safety, and the inclusion of roadway geometry variables may improve future modeling of roadway capacity and passing locations along two-lane highways.
31
Misra, Shubhra, Muthukumar Narayanaswamy, Atilla Bayram, and Fengyan Shi. "OPTIMIZATION OF CAISSON BREAKWATER SUPERSTRUCTURE GEOMETRY USING A 2DV RANS-VOF NUMERICAL MODEL." Coastal Engineering Proceedings 1, no. 32 (January 30, 2011): 49. http://dx.doi.org/10.9753/icce.v32.structures.49.
Full textAbstract:
This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied confidently to reduce the level of uncertainty from empirical guidance and provide for a deterministic quantification of the hydraulic response associated with any arbitrary Caisson breakwater superstructure geometry. The RANS-VOF model used for this paper is first satisfactorily validated against laboratory measurements (surface elevation, overtopping and pressure) of a caisson breakwater on a rubble-mound foundation and then applied to several prototype caisson breakwater superstructure geometries. Numerical simulations presented in this paper for prototype geometries demonstrate that curved/inclined parapets, when compared with vertical face caisson breakwaters with the same crest elevation, can lead to large increases in overtopping as well as downward forces. Expectedly, the landward forces are reduced by the implementation of a curved or recessed and inclined parapet when compared to a caisson with a completely vertical face. During large overtopping events, the model results show that much larger short-duration seaward loads can be generated for curved and inclined superstructures when compared to vertical face geometries. This is in general agreement with previous laboratory experiments as well as field observations of seaward caisson sliding and failure resulting from large overtopping events. Further, numerical experiments indicate that the overtopping response of a superstructure can vary noticeably due to small changes in the recessed length of an inclined or curved parapet. The numerical model also easily provides for the quantification of the variation of instantaneous and peak overtopping discharges along the crest of the caisson superstructure, and which can provide for useful guidance in the design of various crest infrastructure components, such as drainage systems, flow deflectors, wave power devices etc.
32
Easa, Said. "Length requirements for single-arc asymmetrical sag vertical curve for highways." Canadian Journal of Civil Engineering 37, no. 6 (June 2010): 834–41. http://dx.doi.org/10.1139/l10-037.
Full textAbstract:
This paper presents the length requirements for a single-arc asymmetrical vertical curve (sag type) for highways that complements two other papers on the curve development and the length requirements (crest type) that have been published. The single-arc, asymmetrical curve takes the form of a cubic instead of parabolic function and its rate of change in grade gradually varies between the start and the end of the curve. The paper presents the length requirements of the single-arc asymmetrical curve based on the headlight, comfort, and overpass criteria. For the headlight criterion, sight distance (SD) relationships are first developed for the new curve considering different locations of the driver and object. The SD profile and minimum sight distance are then examined. Design aids are then established. The results show that the length requirements based on the comfort criteria are about 60% of those of the headlight criteria. The new single-arc asymmetrical curve improves curve characteristics, and as such would be of interest to the highway design community.
33
Gibreel, Gamal M., Ibrahim A. El-Dimeery, Yasser Hassan, and Said M. Easa. "Impact of highway consistency on capacity utilization of two-lane rural highways." Canadian Journal of Civil Engineering 26, no. 6 (December 1, 1999): 789–98. http://dx.doi.org/10.1139/l99-042.
Full textAbstract:
Consistent highway design is expected to provide safe, economical, and smooth traffic operation. Several studies have been performed to investigate the effect of highway consistency on traffic safety. However, the relationship between design consistency and highway capacity and level of service has not been addressed in current research work and design practices. In addition, the effect of the three-dimensional (3D) nature of highway alignments was not considered, and design consistency was studied based solely on two-dimensional (2D) analysis of highway horizontal alignments. This paper presents a methodology to determine the effect of highway design consistency on highway capacity utilization based on 3D analysis. This methodology will help road designers to estimate highway capacity more accurately. The study was performed on two-lane rural highways in Ontario, where two types of 3D combinations were considered: a horizontal curve combined with a sag vertical curve (sag combination) and a horizontal curve combined with a crest vertical curve (crest combination). An additional adjustment factor that reflects the effect of highway design consistency on capacity utilization was developed. Different statistical models are introduced to estimate this factor based on geometric or traffic data. In addition, typical values of the consistency factor were developed based on an overall consistency evaluation criterion and can be easily used in capacity analysis.Key words: three-dimensional, alignments, capacity, geometric design, operating speed, design consistency.
34
Calvi, Alessandro. "Investigating the effectiveness of perceptual treatments on a crest vertical curve: A driving simulator study." Transportation Research Part F: Traffic Psychology and Behaviour 58 (October 2018): 1074–86. http://dx.doi.org/10.1016/j.trf.2018.06.002.
Full text
35
Hassan, Yasser, and Tarek Sayed. "Effect of driver and road characteristics on required preview sight distance." Canadian Journal of Civil Engineering 29, no. 2 (April 1, 2002): 276–88. http://dx.doi.org/10.1139/l02-002.
Full textAbstract:
Highway geometric design is a complex process that is closely related to human perception and behaviour. Among the human perception issues that can affect highway geometric design is the preview sight distance, which has been defined as the distance required to perceive a horizontal curve and react properly to it. Previous attempts to quantify preview sight distance included measurement on actual roads, physical modelling, and computer animation. This paper presents a computer animation experiment that was designed to examine the effects of geometric parameters and driver characteristics on preview sight distance and to statistically model preview sight distance. Statistical analysis showed that preview sight distance depends on geometric parameters such as the horizontal curve radius, use of spiral curve and its length, presence of crest vertical curve, algebraic difference of vertical grades, vertical curvature, and road delineation. On the other hand, driver characteristics were mostly found to be insignificant parameters. Finally, statistical models were developed to predict the value of preview sight distance using linear regression analysis. The models vary in simplicity and accuracy and were formulated as a function of the general alignment configuration or as a function of the exact geometric parameters.Key words: highway geometric design, sight distance, driver characteristics, three-dimensional alignment.
36
Castro, María, Alejandro de Blas, Roberto Rodríguez-Solano, and José Angel Sánchez. "Finding and characterizing hidden dips in roads." Baltic Journal of Road and Bridge Engineering 10, no. 4 (December 15, 2015): 340–45. http://dx.doi.org/10.3846/bjrbe.2015.43.
Full textAbstract:
Sometimes when connecting a crest vertical curve, followed by a sag and another crest, a road disappears from the view of a driver to reappear later. Then, there is a loss of path or a hidden dip in a road. It is essential to avoid losses when they hide dangerous points, such as intersections or unexpected changes in direction. In addition, this loss disrupts drivers and its effect depends on quantitative relationships between the variables involved in the problem. This paper presents a quantitative procedure for studying hidden dips in roads. The method is based on calculating the sections visible and hidden by a driver using a Geographic Information System. An application to a Spanish road is presented. Procedure results were compared with in situ carried out studies and with a video of the highway recorded using a Global Positioning System equipped video camera embarked in a vehicle. The main quantitative issues related to hidden dips are discussed.
37
Huebner, Richard Scott, David A. Anderson, John C. Warner, and Joseph R. Reed. "PAVDRN: Computer Model for Predicting Water Film Thickness and Potential for Hydroplaning on New and Reconditioned Pavements." Transportation Research Record: Journal of the Transportation Research Board 1599, no. 1 (January 1997): 128–31. http://dx.doi.org/10.3141/1599-16.
Full textAbstract:
PAVDRN is a computer model that determines the speed at which hydroplaning will be initiated on a section of highway pavement. It is intended to be used by highway engineers before final geometric design to (a) indicate the location of the worst incidence of hydroplaning that is likely to occur on a given section and (b) to rapidly assess different geometric configurations of a section and pavement materials to select a design that will minimize hydroplaning potential. The model is based upon a one-dimensional, steady-state form of the kinematic wave equation. This equation is used in conjunction with relationships for Manning's n that account for the nature of the shallow flow over highway pavements. Ultimately, water-film thickness along a maximum flowpath length is used in empirical expressions to determine the speed at which hydroplaning is likely to occur along this path. The path is determined by analyzing the geometry of the pavement section. Five different geometric sections can be analyzed: ( a) tangent section, ( b) superelevated curve, ( c) transition section, ( d) vertical crest curve, and ( e) vertical sag curve. The user interface was written in Microsoft Visual Basic Version 3.0. It uses context-sensitive help screens. The algorithms for water-film thickness and hydroplaning potential were written in FORTRAN 77.
38
Jiang, Chong, Wen-yan Wu, Jia-li He, and Lu-jie Chen. "Computation Method for the Settlement of a Vertically Loaded Pile in Sloping Ground." Advances in Civil Engineering 2020 (July 23, 2020): 1–10. http://dx.doi.org/10.1155/2020/2109535.
Full textAbstract:
Based on the hyperbolic curve tangent modulus method and the wedge stress theory, this paper proposes a calculation method for the settlement of a vertically loaded single pile in sloping ground. By establishing the relationship between the initial tangent modulus and the compression modulus of the slope soil, the tangent modulus of the slope soil is obtained combining with Mindlin-Geddes solution and Hansen formula, and the solution of the pile settlement in sloping ground is derived. Then, a series of numerical analyses are carried out to examine the feasibility of the proposed method. Finally, the effect of parameters is discussed in detail, including the slope angle, the distance of the pile from the slope crest, and the soil properties around the pile. The results show that the pile settlement will increase by increasing the slope angle or decreasing the distance of the pile from the slope crest, and the effect of the two parameters on the pile settlement is coupling-related. Besides, the compression modulus, cohesion, and internal friction angle of the soil around the pile are negatively related to the pile settlement and it is found that the compression modulus of the soil is the more influential parameter.
39
Kvapil, Jiří, Jaroslava Plomerová, Hana Kampfová Exnerová, Vladislav Babuška, and György Hetényi. "Transversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian Massif." Solid Earth 12, no. 5 (May 11, 2021): 1051–74. http://dx.doi.org/10.5194/se-12-1051-2021.
Full textAbstract:
Abstract. The recent development of ambient noise tomography, in combination with the increasing number of permanent seismic stations and dense networks of temporary stations operated during passive seismic experiments, provides a unique opportunity to build the first high-resolution 3-D shear wave velocity (vS) model of the entire crust of the Bohemian Massif (BM). This paper provides a regional-scale model of velocity distribution in the BM crust. The velocity model with a cell size of 22 km is built using a conventional two-step inversion approach from Rayleigh wave group velocity dispersion curves measured at more than 400 stations. The shear velocities within the upper crust of the BM are ∼0.2 km s−1 higher than those in its surroundings. The highest crustal velocities appear in its southern part, the Moldanubian unit. The Cadomian part of the region has a thinner crust, whereas the crust assembled, or tectonically transformed in the Variscan period, is thicker. The sharp Moho discontinuity preserves traces of its dynamic development expressed in remnants of Variscan subductions imprinted in bands of crustal thickening. A significant feature of the presented model is the velocity-drop interface (VDI) modelled in the lower part of the crust. We explain this feature by the anisotropic fabric of the lower crust, which is characterised as vertical transverse isotropy with the low velocity being the symmetry axis. The VDI is often interrupted around the boundaries of the crustal units, usually above locally increased velocities in the lowermost crust. Due to the north-west–south-east shortening of the crust and the late-Variscan strike-slip movements along the north-east–south-west oriented sutures preserved in the BM lithosphere, the anisotropic fabric of the lower crust was partly or fully erased along the boundaries of original microplates. These weakened zones accompanied by a velocity increase above the Moho (which indicate an emplacement of mantle rocks into the lower crust) can represent channels through which portions of subducted and later molten rocks have percolated upwards providing magma to subsequently form granitoid plutons.
40
Fambro, Daniel B., Kay Fitzpatrick, and Rodger J. Koppa. "New Stopping Sight Distance Model for Use in Highway Geometric Design." Transportation Research Record: Journal of the Transportation Research Board 1701, no. 1 (January 2000): 1–8. http://dx.doi.org/10.3141/1701-01.
Full textAbstract:
Stopping sight distance is an important design parameter in that it defines the minimum sight distance that must be provided at all points along the highway. Thus, it influences geometric design values, construction costs, and highway safety. Stopping sight distance is defined as the sum of two components—brake reaction distance and braking distance. The basic model for calculating stopping sight distances was formalized in 1940, and the model’s parameters have been altered to compensate for changes in eye height, object height, and driver behavior over the past 50 years. Recent studies, however, question whether the model’s parameters and assumptions represent real-world conditions. A new model for determining stopping sight distance requirements for geometric design of highways is presented. This model is based on parameters describing driver and vehicle capabilities that can be validated with field data and defended as safe driving behavior. More than 50 drivers, 3,000 braking maneuvers, 1,000 driver eye heights, and 1,000 accident narratives were used to develop the recommended parameter values for the new model. The recommended values are attainable by most drivers, vehicles, and roadways. This model results in stopping sight distances, sag vertical curve lengths, and lateral clearances that are between the current minimum and desirable requirements and crest vertical curve lengths that are shorter than current minimum requirements.
41
Balachandar, Ram, B. S. Hyun, and V. C. Patel. "Effect of depth on flow over a fixed dune." Canadian Journal of Civil Engineering 34, no. 12 (December 2007): 1587–99. http://dx.doi.org/10.1139/l07-068.
Full textAbstract:
Laser Doppler velocimeter (LDV) measurements were carried out to study the effect of depth on the flow over a train of fixed two-dimensional dunes. Conventionally averaged velocity and turbulence parameters reveal large peaks in the streamwise and vertical components of turbulent intensities and shear stress, along the shear layer emanating from the dune crest. A secondary peak in the streamwise turbulence profiles some distance beyond the shear layer indicates maintenance of turbulence generated on the previous dune and convection of the flow history from one dune to the next. Analyses based on triple products and quadrant decomposition of velocity fluctuations reveals the central role of the shear layer in dictating the flow properties over the entire depth. The depth influences the flow in the near-bed region and the length of the separation zone is longer at a shallower depth. The streamwise mean profiles collapse onto a single curve in the outer region beyond the shear layer, indicating a degree of similarity and independence from the near-bed flow. The profiles of the vertical component of turbulence reveal a systematic dependence on flow depth, with lower turbulence intensity at larger depths. The quantitative effect of flow depth is evident in the measurements at all levels, including triple products and quadrant decomposition.
42
Cho, Yong Jun. "Numerical Analysis of Modified Seabed Topography Due to the Presence of Breakwaters of Varying Reflection Characteristics using Physics-based Morphology Model [SeoulFoam]." Journal of Korean Society of Coastal and Ocean Engineers 33, no. 4 (August 31, 2021): 168–78. http://dx.doi.org/10.9765/kscoe.2021.33.4.168.
Full textAbstract:
Numerical simulations were implemented to look into the modified seabed topography due to the presence of breakwaters of varying reflection characteristics. The numerical model was composed of OlaFlow, an OpenFoam-based tool box, and a physics-based morphology model [Seoul Foam]. In doing so, the interaction between the seabed, which undergoes deformation due to siltation and scouring, and the incoming waves was described using Dynamic Mesh. The rubble-mound, vertical, and curved slit caisson breakwaters with varying reflection characteristics resulted in standing waves that differ from each other, shown to have a significant influence on the seabed topography. These results are in line with Nielsen’s study (1993) that sands saltated under the surface nodes of standing waves, where the near-bed velocities are most substantial, convected toward the surface antinodes by boundary-layer drift. Moreover, the crest of sand waves was formed under the surface antinodes of standing waves, and the trough of sand waves was formed under the surface antinodes. In addition, sand wave amplitude reaches its peak in the curved slit caisson with a significant reflection coefficient, and the saltation of many grains of sand would cause this phenomenon due to the increased near-bed velocity under the nodes when the reflection coefficient is getting large.
43
Muhumuza, K. "A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise." International Journal of Geophysics 2020 (February 3, 2020): 1–11. http://dx.doi.org/10.1155/2020/5269537.
Full textAbstract:
This work assesses the feasibility of the direct use of surface-wave dispersion curves from seismic ambient noise to gain insight into the crustal structure of Bransfield Strait and detect seasonal seismic velocity changes. We cross-correlated four years of vertical component ambient noise data recorded by a seismic array in West Antarctica. To estimate fundamental mode Rayleigh wave Green’s functions, the correlations are computed in 4-hr segments, stacked over 1-year time windows and moving windows of 3 months. Rayleigh wave group dispersion curves are then measured on two spectral bands—primary (10–30 s) and secondary (5–10 s) microseisms—using frequency-time analysis. We analyze the temporal evolution of seismic velocity by comparing dispersion curves for the successive annual and 3-month correlation stacks. Our main assumption was that the Green’s functions from the cross-correlations, and thus the dispersion curves, remain invariant if the crustal structure remains unchanged. Maximum amplitudes of secondary microseisms were observed during local winter when the Southern Ocean experiences winter storms. The Rayleigh wave group velocity ranges between 2.1 and 3.7 km/s, considering our period range studied. Interannual velocity variations are not much evident. We observe a slight velocity decrease in summer and increase in winter, which could be attributed to the pressure melting of ice and an increase in ice mass, respectively. The velocity anomalies observed within the crust and upper mantle structure correlate with the major crustal and upper mantle features known from previous studies in the area. Our results demonstrate that the direct comparison of surface wave dispersion curves extracted from ambient noise might be a useful tool in monitoring crustal structure variations.
44
Tian, Su Gui, Ben Jiang Qian, Fu Shun Liang, An An Li, and Xing Fu Yu. "Creep Behaviors of a Single Crystal Nickel-Based Superalloy Containing 4.2%Re." Materials Science Forum 689 (June 2011): 276–81. http://dx.doi.org/10.4028/www.scientific.net/msf.689.276.
Full textAbstract:
By the measurement of creep curves and microstructure observation, an investigation has been made into the creep behaviors and microstructure evolution of a single crystal nickel-based superalloy containing 4.2%Re. Results show that the superalloy displays an obvious sensibility on the applied temperatures and stresses in the range of the applied temperatures and stresses. During the initial creep, the cubical g¢ phase in the alloy is transformed into an N-type rafted structure along the direction vertical to the applied stress axis. After crept up to fracture, the rafted g¢ phase in the region near fracture is transformed into a twisted configuration. The dislocation climbing over the rafted g¢ phase is considered to be the main deformation mechanism of the alloy during the steady creep state, and dislocations shear into the rafted g¢ phase is the main deformation mechanism of the alloy in the later stage of creep.
45
Zhang, Ping, Lin Ma, Jin Ping Yuan, Xiao Nan Yin, and Zhi Hai Cai. "The Finite Element Simulation Research on Stress-Strain Field of Laser Cladding." Key Engineering Materials 373-374 (March 2008): 322–25. http://dx.doi.org/10.4028/www.scientific.net/kem.373-374.322.
Full textAbstract:
The tensile plastic strains and the residual tensile stresses caused by heat input during the laser cladding process are the main reasons for the cracking. In this paper, the laser cladding process on a type 1045 steel plate with Ni60 powder feeding was investigated and simulated by finite element method to analyze the temperature field and stress-strain field of the laser cladding process. In the temperature field model, the main considerations were given to the heat source data and the thermal boundary conditions. The interactions of laser, powders and base metal were mainly considered in the application of the heat source data. The relationship between the heat convection coefficient of work piece surface and the temperature variation was mainly considered in the application of thermal boundary conditions. In the stress-strain field model, the main consideration was given to the elastic-plastic characteristics of the materials, and the materials were assumed to be linear strain-strengthened. Moreover, the thermal stresses could be solved through the temperature field and were subsequently applied directly to the stress-strain field model as loads. Besides the temperature variations, the stress variations and the strain variations of some critical points (including the crest point of the cladded layer and intersection point of cladded layer and plate) were also obtained through the finite calculation. The temperature variations show that the heating curve is approximately a straight line while the cooling curve is like an arm of a hyperbola. The strain variations show that the thermal strain has a variation trend similar to the temperature variations. The elastic strain of each point is very low when compared to the plastic strain. The calculated results show that the tensile plastic strain of the crest point on the coating is the greatest in the cladding direction and the tensile stress in this direction of this point is great too. As a result, transverse crack can be easily initiated at the crest of the coating. While the tensile plastic strain at the intersection point of the base metal and coating is the greatest in the direction vertical to the plate thickness, the stress at this point (in the same direction) is compressive. Therefore, the intersection points tend to form a limited toe crack which can not grow.
46
Sarvandani, Mohamadhasan Mohamadian, Emanuel Kästle, Lapo Boschi, Sylvie Leroy, and Mathilde Cannat. "Seismic Ambient Noise Imaging of a Quasi-Amagmatic Ultra-Slow Spreading Ridge." Remote Sensing 13, no. 14 (July 17, 2021): 2811. http://dx.doi.org/10.3390/rs13142811.
Full textAbstract:
Passive seismic interferometry has become very popular in recent years in exploration geophysics. However, it has not been widely applied in marine exploration. The purpose of this study is to investigate the internal structure of a quasi-amagmatic portion of the Southwest Indian Ridge by interferometry and to examine the performance and reliability of interferometry in marine explorations. To reach this goal, continuous vertical component recordings from 43 ocean bottom seismometers were analyzed. The recorded signals from 200 station pairs were cross-correlated in the frequency domain. The Bessel function method was applied to extract phase–velocity dispersion curves from the zero crossings of the cross-correlations. An average of all the dispersion curves was estimated in a period band 1–10 s and inverted through a conditional neighborhood algorithm which led to the final 1D S-wave velocity model of the crust and upper mantle. The obtained S-wave velocity model is in good agreement with previous geological and geophysical studies in the region and also in similar areas. We find an average crustal thickness of 7 km with a shallow layer of low shear velocities and high Vp/Vs ratio. We infer that the uppermost 2 km are highly porous and may be strongly serpentinized.
47
Egorushkin, I. I., I. Yu Koulakov, N. M. Shapiro, E. I. Gordeev, A. V. Yakovlev, and I. F. Abkadyrov. "Structure of the Upper Crust beneath the Klyuchevskoy Group of Volcanoes Revealed from Ambient Noise Tomography." Russian Geology and Geophysics 62, no. 1 (January 1, 2021): 68–82. http://dx.doi.org/10.2113/rgg20204238.
Full textAbstract:
Abstract ––The Klyuchevskoy group of volcanoes (KGV) located in the central part of Kamchatka is a unique complex that demonstrates exceptional variety and intensity of volcanic manifestations. These features of the eruptive activity of the KGV are determined by a complex system of magmatic sources in the crust and mantle. While the structure of deep anomalies is quite reliably determined by tomography techniques based on body waves, the structure of the upper crust can only be determined using ambient noise tomography. We present the results of processing data from the KISS temporary network. This network consisted of more than 100 seismic stations that were installed from 2015 to 2016 over a large area covering the Klyuchevskoy group of volcanoes and its surroundings. To retrieve Rayleigh surface waves, cross-correlation of continuous seismic noise records from pairs of stations was used. We obtained the dispersion curves of the group velocities of these Rayleigh surface waves using frequency–time analysis (FTAN) of the calculated correlograms. These curves served as input data for performing ambient noise tomography. Tomography was performed in two stages: (1) computation of two-dimensional group velocity maps for different frequencies and (2) calculation of a three-dimensional model of the shear wave velocity to a depth of about 8 km based on the inversion of local dispersion curves obtained from these maps. The resulting models revealed the structural features of individual volcanic systems of the KGV. High velocities were observed at shallow depths beneath the large basaltic edifices of the Ushkovsky and Tolbachik volcanoes. At greater depths, while the velocity structure beneath Ushkovsky remained unchanged, we detected low velocities beneath Tolbachik. This fact illustrates the difference between dormant and active magmatic systems. Velocity anomalies of a complex shape are observed beneath the Klyuchevskoy, Kamen, and Bezymianny volcanoes, varying both laterally and with depth. Absolute velocities in vertical sections show that the edifices of these volcanoes are relatively low-velocity bodies located on a horizontal high-velocity basement. A low-velocity anomaly was discovered under the Bezymianny Volcano at a depth of 6 km, which is presumably associated with a shallow magma reservoir. An intense low-velocity anomaly was found beneath the Udina Volcano. It was interpreted as an image of a magma reservoir experiencing strong seismic unrest that began in December 2017 and continues to this day.
48
Pastor-Galán, Daniel, Gabriel Gutiérrez-Alonso, and Arlo B. Weil. "The enigmatic curvature of Central Iberia and its puzzling kinematics." Solid Earth 11, no. 4 (July 8, 2020): 1247–73. http://dx.doi.org/10.5194/se-11-1247-2020.
Full textAbstract:
Abstract. The collision between Gondwana and Laurussia that formed the latest supercontinent, Pangea, occurred during Devonian to early Permian times and resulted in a large-scale orogeny that today transects Europe, northwest Africa, and eastern North America. This orogen is characterized by an “S” shaped corrugated geometry in Iberia. The northern curve of the corrugation is the well-known and studied Cantabrian (or Ibero–Armorican) Orocline and is convex to the east and towards the hinterland. Largely ignored for decades, the geometry and kinematics of the southern curvature, known as the Central Iberian curve, are still ambiguous and hotly debated. Despite the paucity of data, the enigmatic Central Iberian curvature has inspired a variety of kinematic models that attempt to explain its formation but with little consensus. This paper presents the advances and milestones in our understanding of the geometry and kinematics of the Central Iberian curve from the last decade with particular attention to structural and paleomagnetic studies. When combined, the currently available datasets suggest that the Central Iberian curve did not undergo regional differential vertical-axis rotations during or after the latest stages of the Variscan orogeny and did not form as the consequence of a single process. Instead, its core is likely a primary curve (i.e., inherited from previous physiographic features of the Iberian crust), whereas the curvature in areas outside the core is dominated by folding interference from the Variscan orogeny or more recent Cenozoic (Alpine) tectonic events.
49
Wang, An, and James H. Duncan. "The controlled vertical impact of an inclined flat plate on a quiescent water surface." Journal of Fluid Mechanics 879 (September 27, 2019): 468–511. http://dx.doi.org/10.1017/jfm.2019.630.
Full textAbstract:
The generation of spray during the vertical impact of a flat plate (length $L=1.22~\text{m}$, width $B=0.38~\text{m}$) on a quiescent water surface is studied experimentally. The plate is held in an orientation tilted up from horizontal by angles $\unicode[STIX]{x1D6FD}$ ranging from $10^{\circ }$ to $25^{\circ }$ about one of its long edges, which is positioned close to a vertical wall. The plate motion, which is driven by a servo motor system, is set to maintain a constant speed, $W_{0}$, until the trailing (upper) long edge of the plate passes the still water level (SWL) and then to decelerate to a stop. The impact Froude numbers $\mathit{Fr}$ ($=W_{0}/\sqrt{gB}$, where $g$ is the gravitational acceleration) range from 0.21 to 0.63. The evolution of the water surface underneath the plate and outboard of its trailing edge is measured with a cinematic laser induced fluorescence technique. As the plate’s leading (low) edge passes the SWL, the local water surface rises and develops into a thin spray sheet that travels along the plate’s lower surface toward the trailing edge. The horizontal speed of the under-plate spray tip is approximately $2.25W_{0}/\tan \unicode[STIX]{x1D6FD}$, as high as $15~\text{m}~\text{s}^{-1}$. In agreement with published similarity theory for the flow during the vertical water entry of a wedge, the under-plate surface profiles scaled by $W_{0}t$ nearly collapse on a single curve for each $\unicode[STIX]{x1D6FD}$. As the under-plate spray passes the plate’s trailing edge, it develops into the leading portion (called herein the Type I spray) of the outboard spray system. As the trailing edge of the plate passes through the local water surface, a crater develops and a large nearly vertical spray sheet (called the Type II spray) is generated from the outer edge (called the outboard spray root) of the crater. The characteristic horizontal length scale of the crater is found to expand in time following a power law with an exponent of approximately 0.77 for all conditions. A short time after its formation, the outboard spray root becomes the crest of a gravity wave whose propagation speed is of the order of $1~\text{m}~\text{s}^{-1}$ for all $\unicode[STIX]{x1D6FD}$ and $\mathit{Fr}$. The dimensionless envelope of the Type II spray profiles collapse to a single curve at high $\mathit{Fr}$ for each $\unicode[STIX]{x1D6FD}$. The connecting spray sheet between the Type I and Type II sprays tends to break up at small $\unicode[STIX]{x1D6FD}$ and large $\mathit{Fr}$.
50
Neukirch, Maik, Antonio García-Jerez, Antonio Villaseñor, Francisco Luzón, Jacques Brives, and Laurent Stehly. "On the Utility of Horizontal-to-Vertical Spectral Ratios of Ambient Noise in Joint Inversion with Rayleigh Wave Dispersion Curves for the Large-N Maupasacq Experiment." Sensors 21, no. 17 (September 4, 2021): 5946. http://dx.doi.org/10.3390/s21175946.
Full textAbstract:
Horizontal-to-Vertical Spectral Ratios (HVSR) and Rayleigh group velocity dispersion curves (DC) can be used to estimate the shallow S-wave velocity (VS) structure. Knowing the VS structure is important for geophysical data interpretation either in order to better constrain data inversions for P-wave velocity (VP) structures such as travel time tomography or full waveform inversions or to directly study the VS structure for geo-engineering purposes (e.g., ground motion prediction). The joint inversion of HVSR and dispersion data for 1D VS structure allows characterising the uppermost crust and near surface, where the HVSR data (0.03 to 10s) are most sensitive while the dispersion data (1 to 30s) constrain the deeper model which would, otherwise, add complexity to the HVSR data inversion and adversely affect its convergence. During a large-scale experiment, 197 three-component short-period stations, 41 broad band instruments and 190 geophones were continuously operated for 6 months (April to October 2017) covering an area of approximately 1500km2 with a site spacing of approximately 1 to 3km. Joint inversion of HVSR and DC allowed estimating VS and, to some extent density, down to depths of around 1000m. Broadband and short period instruments performed statistically better than geophone nodes due to the latter’s gap in sensitivity between HVSR and DC. It may be possible to use HVSR data in a joint inversion with DC, increasing resolution for the shallower layers and/or alleviating the absence of short period DC data, which may be harder to obtain. By including HVSR to DC inversions, confidence improvements of two to three times for layers above 300m were achieved. Furthermore, HVSR/DC joint inversion may be useful to generate initial models for 3D tomographic inversions in large scale deployments. Lastly, the joint inversion of HVSR and DC data can be sensitive to density but this sensitivity is situational and depends strongly on the other inversion parameters, namely VS and VP. Density estimates from a HVSR/DC joint inversion should be treated with care, while some subsurface structures may be sensitive, others are clearly not. Inclusion of gravity inversion to HVSR/DC joint inversion may be possible and prove useful.