Academic literature on the topic 'Axial multipole field function'
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Journal articles on the topic "Axial multipole field function"
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Russenschuck, S., G. Caiafa, L. Fiscarelli, M. Liebsch, C. Petrone, and P. Rogacki. "Challenges in extracting pseudo-multipoles from magnetic measurements." International Journal of Modern Physics A 34, no. 36 (December 11, 2019): 1942022. http://dx.doi.org/10.1142/s0217751x19420223.
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Extracting the coefficients of Fourier–Bessel series, known as pseudo-multipoles or generalized gradients, from magnetic measurements of accelerator magnets involves technical and mathematical challenges. First, a novel design of a short, rotating-coil magnetometer is required that does not intercept any axial field component of the magnet. Moreover, displacing short magnetometers, step-by-step along the magnet axis, yields a convolution of the local multipole field errors and the sensitivity (test function) of the induction coil. The deconvolution must then contend with the limited signal-to-noise ratio of the measured quantities, which are integrated voltages corresponding to spatial flux distributions. Finally, the compensation schemes, as implemented on long coils and based on scaling laws derived for the integrated field harmonics, cannot be applied to short magnetometers intercepting only a local field distribution. All this requires careful design of experiment to derive the optimal length of the induction coil, the step-size of the scan, and the highest order of pseudo-multipoles in the field reconstruction. This paper presents the theory of the measurement method, the data acquisition and deconvolution, and the design and production of a saddle-shaped, rotating-coil magnetometer.
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Usuki, Shin, Hiroyoshi Kanaka, and Kenjiro Takai Miura. "Generation and Control of Wide-Field Three-Dimensional Structured Illumination for Advanced Microscopic Imaging." Key Engineering Materials 516 (June 2012): 640–44. http://dx.doi.org/10.4028/www.scientific.net/kem.516.640.
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In a variety of practical microscopic imaging applications, many industries require not only lateral resolution improvement but also axial resolution improvement. The resolution in optical microscopy is limited by diffraction and determined by the wavelength of the incident light and the numerical aperture (NA) of the objective lens. The diffraction limit is mathematically described by a point spread function in the imaging system, and three-dimensional (3D) point spread functions describe both the lateral and axial resolutions. Thus, it is useful to focus on exceeding this limit and improving the resolution of optical imaging by the spatial control of structured illumination. Structured illumination microscopy is a familiar technique to improve resolution in fluorescent imaging, and it is expected to be applied to industrial applications. Microscopic imaging is convenient, non-destructive, and has a high-throughput performance and compatibility with a number of applications. However, the spatial resolution of conventional light microscopy is limited to wavelength scale and the depth of field is shallow; hence, it is difficult to obtain detailed 3D spatial data of the object to be measured. Here, we propose a new technique for generating and controlling wide-field 3D structured illumination. The technique, based on the 3D interference of multiple laser beams, provides lateral and axial resolution improvement, and a wide 3D field of view. The spatial configuration of the beams was theoretically examined and the optimal incident angle of the multiple beams was confirmed. Numerical simulations using the finite difference time domain (FDTD) method were carried out and confirmed the generation of 3D structured illumination and spatial control of the illumination by using the phase shift of incident beams.
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Li, Ji Hui, Li Qiang Ma, Xing Wang Xiao, Wen Jing Li, and Lei Xu. "Numerical Simulation of Multi-Impeller High Intensity Conditioning in Fine Coal Flotation." Applied Mechanics and Materials 508 (January 2014): 121–24. http://dx.doi.org/10.4028/www.scientific.net/amm.508.121.
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The numerical simulation of a mixing vessel with three layers of six 45° leaned blade disc turbine impeller was conducted by using the standard k-ε turbulence model and multiple reference frame method (MRF), the velocity field were analyzed. Results show that multi-impeller increases the fluid turbulence zone, strengthens the mixing effect and enhances the function of the axial velocity gradient of conditioning vessel.
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Zhang, Xiaolei, Yanzhong Ju, and Fuwang Wang. "Statistical Analysis of Wind-Induced Dynamic Response of Power Towers and Four-Circuit Transmission Tower-Line System." Shock and Vibration 2018 (2018): 1–18. http://dx.doi.org/10.1155/2018/5064930.
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Only one wind field model loading the transmission tower or the tower-line system was investigated in the previous studies, while the influence of two different wind field models was not considered. In addition, only one sample of the wind speed random process was used in the past numerical simulations, and the multiple dynamic response statistical analysis should be carried out. In this paper, statistical analysis of the wind-induced dynamic response of single towers and the transmission tower-line system is performed with the improved accuracy. A finite element model of the transmission tower-line system (the tower consisted of both steel tubes and angel steels) is established by ANSYS software. The analysis was performed by three statistical methods. The effects of the length of the time history and of the number of samples were investigated. The frequency histograms of samples follow the Gaussian distribution. The characteristic statistical parameters of samples were random. The displacements and the axial forces of the low tower are larger than those of the high tower. Two wind field models were applied to simulate the wind speed time history. In field 1 model, Davenport wind speed spectrum and Shiotani coherence function were applied, while in field 2 model Kaimal wind speed spectrum and Davenport coherence function were used. The results indicate that wind field 1 is calmer than wind field 2. The displacements and the axial forces of the tower-line system are less than those of single towers, which indicate damping of wind-induced vibrations by the transmission line. An extended dynamic response statistical analysis should be carried out for the transmission tower-line system.
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Wang, Xingming, Ping Chen, Wanzhi Huang, and Jiayan Zou. "Development of torque clutch drilling tool and evaluation of drag reduction performance." Advances in Mechanical Engineering 10, no. 10 (October 2018): 168781401880665. http://dx.doi.org/10.1177/1687814018806655.
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Horizontal well is one of the important methods of unconventional oil and gas resource development. As increasing length of horizontal section, there is a serious problem that axial force cannot transfer to bit. The drilling field needs a low-friction and low-cost drag reduction tool. This article summarized existing technologies of drag reduction in the horizontal and inclined well and proposes an integrated design of torque clutch. Detailed design of tool sub-systems is introduced. The tool includes three sub-systems: clutch, hydraulic system, and monitoring system. The clutch is consisted of multiple clutch units mounted in a parallel arrangement. Power of hydraulic control system adopts difference in pressure between inside and outside of drill pipes. It can efficiently reduce power consumption. The design function and minimum working pressure are validated and obtained by indoor test. According to theoretical calculation, reasonable distance from tool to bit can be obtained for an actual drilled well. During directional drilling mode, the tool can reduce more than 30% axial drag of drill string according to theoretical calculation. The tool can effectively improve the capacity of transfer weight to bit and overcome the excessive drag in horizontal drilling. No similar tools are reported in the current field.
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Kuo, Jian-Long, and Meng-Ti Chang. "Multiobjective Design of Turbo Injection Mode for Axial Flux Motor in Plastic Injection Molding Machine by Particle Swarm Optimization." Mathematical Problems in Engineering 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/974624.
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This paper proposes a turbo injection mode (TIM) for an axial flux motor to apply onto injection molding machine. Since the injection molding machine requires different speed and force parameters setting when finishing a complete injection process. The interleaved winding structure in the motor provides two different injection levels to provide enough injection forces. Two wye-wye windings are designed to switch two control modes conveniently. Wye-wye configuration is used to switch two force levels for the motor. When only one set of wye-winding is energized, field weakening function is achieved. Both of the torque and speed increase under field weakening operation. To achieve two control objectives for torque and speed of the motor, fuzzy based multiple performance characteristics index (MPCI) with particle swarm optimization (PSO) is used to find out the multiobjective optimal design solution. Both of the torque and speed are expected to be maximal at the same time. Three control factors are selected as studied factors: winding diameter, winding type, and air-gap. Experimental results show that both of the torque and speed increase under the optimal condition. This will provide enough large torque and speed to perform the turbo injection mode in injection process for the injection molding machine.
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Zhang, Jianming, Wensheng Yang, Jun Chen, and Rui Xu. "Direct Evaluation of the Stress Intensity Factors for the Single and Multiple Crack Problems Using the P-Version Finite Element Method and Contour Integral Method." Applied Sciences 11, no. 17 (August 31, 2021): 8111. http://dx.doi.org/10.3390/app11178111.
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Stress intensity factor (SIF) is one of three important parameters in classical linear elastic fracture mechanics (LEFM). The evaluation of SIFs is of great significance in the field of engineering structural and material damage assessment, such as aerospace engineering and automobile industry, etc. In this paper, the SIFs of a central straight crack plate, a slanted single-edge cracked plate under end shearing, the offset double-edge cracks rectangular plate, a branched crack in an infinite plate and a crucifix crack in a square plate under bi-axial tension are extracted by using the p-version finite element method (P-FEM) and contour integral method (CIM). The above single- and multiple-crack problems were investigated, numerical results were compared and analyzed with results using other numerical methods in the literature such as the numerical manifold method (NMM), improved approach using the finite element method, particular weight function method and exponential matrix method (EMM). The effectiveness and accuracy of the present method are verified.
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Kang, B. "Transfer Functions of One-Dimensional Distributed Parameter Systems by Wave Approach." Journal of Vibration and Acoustics 129, no. 2 (September 29, 2006): 193–201. http://dx.doi.org/10.1115/1.2424972.
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An alternative analysis technique, which does not require eigensolutions as a priori, for the dynamic response solutions, in terms of the transfer function, of one-dimensional distributed parameter systems with arbitrary supporting conditions, is presented. The technique is based on the fact that the dynamic displacement of any point in a waveguide can be determined by superimposing the amplitudes of the wave components traveling along the waveguide, where the wave numbers of the constituent waves are defined in the Laplace domain instead of the frequency domain. The spatial amplitude variations of individual waves are represented by the field transfer matrix and the distortions of the wave amplitudes at point discontinuities due to constraints or boundaries are described by the wave reflection and transmission matrices. Combining these matrices in a progressive manner along the waveguide using the concepts of generalized wave reflection and transmission matrices leads to the exact transfer function of a complex distributed parameter system subjected to an externally applied force. The transient response solution can be obtained through the Laplace inversion using the fixed Talbot method. The exact frequency response solution, which includes infinite normal modes of the system, can be obtained in terms of the complex frequency response function from the system’s transfer function. This wave-based analysis technique is applicable to any one-dimensional viscoelastic structure (strings, axial rods, torsional bar, and beams), in particular systems with multiple point discontinuities such as viscoelastic supports, attached mass, and geometric/material property changes. In this paper, the proposed approach is applied to the flexural vibration analysis of a classical Euler–Bernoulli beam with multiple spans to demonstrate its systematic and recursive formulation technique.
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Sasaki, Kenzo, Selene Piantanida, André V. G. Cavalieri, and Peter Jordan. "Real-time modelling of wavepackets in turbulent jets." Journal of Fluid Mechanics 821 (May 25, 2017): 458–81. http://dx.doi.org/10.1017/jfm.2017.201.
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Three methods are considered for estimating the downstream evolution of wavepackets in turbulent jets based on upstream measurements. The parabolised stability equations are used to compute a transfer function between axially and radially separated points in the flow, and the performance of this theoretical model is compared with that of two empirical approaches, direct transfer function calculation and autoregressive moving-average exogenous system identification, both of which require unsteady experimental data. The three approaches, which perform equally well, prove suitable for estimation of the downstream evolution of wavepackets using pressure data measured in the near-nozzle region. Over distances of the order of a couple of jet diameters, correlations of up to 80 % are observed between estimation and measurement. The performance deteriorates as axial separation between input and output is increased. While the two empirical approaches are limited in terms of both the number of input–output pairs and the number of flow variables that can be reasonably considered, the parabolised stability equations-based approach has no such limitation and can be used to perform full-field estimates comprising all of the dependent variables; in this it constitutes a potentially formidable means by which to perform single-input–multiple-output estimation. It has the further advantage of not requiring unsteady data for its construction, the only necessary ingredients being the mean flow and the linearised equations of motion.
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Kearney, Hugh, Katherine A. Miszkiel, Marios C. Yiannakas, Daniel R. Altmann, Olga Ciccarelli, and David H. Miller. "Grey matter involvement by focal cervical spinal cord lesions is associated with progressive multiple sclerosis." Multiple Sclerosis Journal 22, no. 7 (October 2, 2015): 910–20. http://dx.doi.org/10.1177/1352458515604905.
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Background: The in vivo relationship of spinal cord lesion features with clinical course and function in multiple sclerosis (MS) is poorly defined. Objective: The objective of this paper is to investigate the associations of spinal cord lesion features on MRI with MS subgroup and disability. Methods: We recruited 120 people: 25 clinically isolated syndrome, 35 relapsing–remitting (RR), 30 secondary progressive (SP), and 30 primary progressive (PP) MS. Disability was measured using the Expanded Disability Status Scale. We performed 3T axial cervical cord MRI, using 3D-fast-field-echo and phase-sensitive-inversion-recovery sequences. Both focal lesions and diffuse abnormalities were recorded. Focal lesions were classified according to the number of white matter (WM) columns involved and whether they extended to grey matter (GM). Results: The proportion of patients with focal lesions involving at least two WM columns and extending to GM was higher in SPMS than in RRMS ( p = 0.03) and PPMS ( p = 0.015). Diffuse abnormalities were more common in both PPMS and SPMS, compared with RRMS (OR 6.1 ( p = 0.002) and 5.7 ( p = 0.003), respectively). The number of lesions per patient involving both the lateral column and extending to GM was independently associated with disability ( p < 0.001). Conclusions: More extensive focal cord lesions, extension of lesions to GM, and diffuse abnormalities are associated with progressive MS and disability.
Dissertations / Theses on the topic "Axial multipole field function"
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Horák, Michal. "Studium elektronově optických systémů s porušenou rotační symetrií." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231782.
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This thesis deals with computing of the magnetic lens with a perturbed pole piece due to manufacturing imperfections. Two possible ways of calculation are discussed - the perturbation theory and 3D computing. Three methods for evaluating axial multipole field functions from 3D fields are introduced. Beam spots in the image plane and aberration coefficients are computed and results obtained by the application of perturbation theory are compared to results evaluated from 3D simulations. Consequently, a suitability of using the perturbation theory is discussed.
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Shafer, Benjamin M. "Error Sensor Placement for Active Control of an Axial Cooling Fan." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1205.
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Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in the acoustic far field of the ANC system. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source model. The results closely matched the point source model with a loudspeaker as the primary source, and the sound power reduction was greatly reduced when error sensors were placed in non-ideal locations. A weakness of the current near-field modeling process is that a point monopole source is used to characterize the acoustic noise from an axial cooling fan, which may have multipole characteristics. A more complete characterization of fan noise may be obtained using a procedure based on the work of Martin and Roure [J. Sound Vib. 201 (5), 577--593 (1997)]. Pressure values are obtained over a hemisphere in the far field of a primary source and the contributions from point source distributions up to the second order, centered at the primary source, may be calculated using a multipole expansion. The source information is then used in the aforementioned theoretical near-field calculation of pressure. The error sensors are positioned using the complete fan characterization. The global far-field attenuation for the multipole expansion model of fan noise is compared to that of previous experiments. Results show that the multipole expansion model yields a more accurate representation the near field, but is not successful in achieving greater sound power reductions in the far field.
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Brenot, Dominique. "Transmission du son à l'intérieur d'une structure axisymétrique." Paris 6, 1986. http://www.theses.fr/1986PA066022.
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Problème de la transmission du son sur l'axe d'une structure élastique fermée à symétrie de révolution. Problème de Neumann, associé à la pression acoustique par la méthode de la phase stationnaire et problème de structure par une méthode d'éléments finis.
Books on the topic "Axial multipole field function"
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Horing, Norman J. Morgenstern. Retarded Green’s Functions. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198791942.003.0005.
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Chapter 5 introduces single-particle retarded Green’s functions, which provide the probability amplitude that a particle created at (x, t) is later annihilated at (x′,t′). Partial Green’s functions, which represent the time development of one (or a few) state(s) that may be understood as localized but are in interaction with a continuum of states, are discussed and applied to chemisorption. Introductions are also made to the Dyson integral equation, T-matrix and the Dirac delta-function potential, with the latter applied to random impurity scattering. The retarded Green’s function in the presence of random impurity scattering is exhibited in the Born and self-consistent Born approximations, with application to Ando’s semi-elliptic density of states for the 2D Landau-quantized electron-impurity system. Important retarded Green’s functions and their methods of derivation are discussed. These include Green’s functions for electrons in magnetic fields in both three dimensions and two dimensions, also a Hamilton equation-of-motion method for the determination of Green’s functions with application to a 2D saddle potential in a time-dependent electric field. Moreover, separable Hamiltonians and their product Green’s functions are discussed with application to a one-dimensional superlattice in axial electric and magnetic fields. Green’s function matching/joining techniques are introduced and applied to spatially varying mass (heterostructures) and non-local electrostatics (surface plasmons).
Book chapters on the topic "Axial multipole field function"
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Coppens, Philip. "X-ray Diffraction and the Electrostatic Potential." In X-Ray Charge Densities and Chemical Bonding. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780195098235.003.0010.
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The distribution of positive and negative charge in a crystal fully defines physical properties like the electrostatic potential and its derivatives, the electric field, and the gradient of the electric field. The electrostatic potential at a point in space, defined as the energy required to bring a positive unit of charge from infinite distance to that point, is an important function in the study of chemical reactivity. As electrostatic forces are relatively long-range forces, they determine the path along which an approaching reactant will travel towards a molecule. A nucleophilic reagent will first be attracted to the regions where the potential is positive, while an electrophilic reagent will approach the negative regions of the molecule. As the electrostatic potential is of importance in the study of intermolecular interactions, it has received considerable attention during the past two decades (see, e.g., articles on the molecular potential of biomolecules in Politzer and Truhlar 1981). It plays a key role in the process of molecular recognition, including drug-receptor interactions, and is an important function in the evaluation of the lattice energy, not only of ionic crystals. This chapter deals with the evaluation of the electrostatic potential and its derivatives by X-ray diffraction. This may be achieved either directly from the structure factors, or indirectly from the experimental electron density as described by the multipole formalism. The former method evaluates the properties in the crystal as a whole, while the latter gives the values for a molecule or fragment “lifted” out of the crystal. Like other properties derived from the charge distribution, the experimental electrostatic potential will be affected by the finite resolution of the experimental data set. But as the contribution of a structure factor F(H) to the potential is proportional to H−2, as shown below, convergence is readily achieved. A summary of the dependence of electrostatic properties of the magnitude of the scattering vector H is given in Table 8.1, which shows that the electrostatic potential is among the most accessible of the properties listed.
Conference papers on the topic "Axial multipole field function"
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Lee, Wanho, Hong-Kyu Kim, and Do Wan Kim. "Axial green function method for axisymmetric electromagnetic field computation." In 2016 IEEE Conference on Electromagnetic Field Computation (CEFC). IEEE, 2016. http://dx.doi.org/10.1109/cefc.2016.7816074.
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Boone, C., M. Fuest, K. Wellmerling, and S. Prakash. "Effect of Time Dependent Excitation Signals on Gating in Nanofluidic Channels." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53038.
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Nanofluidic field effect devices feature a gate electrode embedded in the nanochannel wall. The gate electrode creates local variation in the electric field allowing active, tunable control of ionic transport. Tunable control over ionic transport through nanofluidic networks is essential for applications including artificial ion channels, ion pumps, ion separation, and biosensing. Using DC excitation at the gate, experiments have demonstrated multiple current states in the nanochannel, including the ability to switch off the measured current; however, experimental evaluation of transient signals at the gate electrode has not been explored. Modeling results have shown ion transport at the nanoscale has known time scales for diffusion, electromigration, and convection. This supports the evidence detailed here that use of a time-dependent signal to create local perturbation in the electric field can be used for systematic manipulation of ionic transport in nanochannels. In this report, sinusoidal waveforms of various frequencies were compared against DC excitation on the gate electrode. The ionic transport was quantified by measuring the current through the nanochannels as a function of applied axial and gate potentials. It was found that time varying signals have a higher degree of modulation than a VRMS matched DC signal.
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Kamal, Abhishek, Gagan Chandra Das, Vinayak Kulkarni, and Niranjan Sahoo. "Comparative Study of Force Prediction Techniques Using Multi Component Accelerometer Force Balance for High Enthalpy Ground Testing." In ASME 2019 Gas Turbine India Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gtindia2019-2666.
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Abstract Large wave drag and high surface heating are the major concerns of hypersonic flows. Hence, development of force measurement technique or prediction of force has always remained a promising research topic in this field. Present studies also deal with force prediction techniques and force balance calibration methodology for ground testing in an impulse test facility. A blunt double cone model is fabricated along with a three component accelerometer force balance. Impulse hammer hits are made on different locations of this test model. In these calibration experiments, the applied impulse and acceleration responses from three accelerometers are recorded. These calibration tests are repeated multiple times to apply hammer hits of different magnitude. All the input and corresponding output singles are then processed first to arrive at the impulse response function or correlation between input and outputs. Then the force recovery techniques are applied to recover the axial and normal forces generated during application of one of the calibration forces. The experimentally recovered force signals from different techniques are compared and then the accuracy of these predictions is estimated using different error estimation techniques. Such studies are found essential not only in defining the most accurate force prediction technique but also in understanding the time required for prediction by a particular technique. Additionally, such studies essentially helps to improve a force prediction algorithm.
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Wu, Tingcheng, Luis San Andrés, and Xueliang Lu. "CFD Analysis of the Influence of Gas Content on the Rotordynamic Force Coefficients for a Circumferentially Grooved Annular Seal for Multiple Phase Pumps." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-58631.
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Abstract Pumping efficiency and rotordynamic stability are paramount to subsea multiphase pump operation since, during the life of a well, the process fluid transitions from a pure liquid to a mixture of gas in liquid to just gas. Circumferentially grooved seals commonly serve as balance pistons in pumps while also restricting secondary flow. Prior experimental results obtained with a grooved seal operating with a mixture of air and mineral oil show the seal rotordynamic force coefficients vary significantly with the gas volume fraction (GVF). This paper, complementing an exhaustive experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a circumferentially grooved seal supplied with air in oil mixture with a GVF varying from 0 to 0.7. The test seal has fourteen grooves, an overall axial length of 43.6 mm and a radial clearance of 0.211 mm. The 127 mm diameter rotor spins at constant angular speed (Ω = 3,500 rpm). The mixture enters the seal at a supply pressure (Pin) of 2.9 bar(a), and the seal exit pressure (Pout) is 1 bar(a). The CFD two-phase flow simulations utilize the Euler-Euler multiphase model to predict the mass flow rate and the pressure field as a function of the operating conditions. Using a multi-frequency shaft orbit motion method, the CFD simulations deliver the variations of reaction force on the rotor with respect to the excitation frequency. For a pure liquid condition (GVF = 0), both the CFD and experimental results produce constant stiffness, damping and added mass coefficients. The experimental and CFD results demonstrate the seal rotordynamic force coefficients are quite sensitive to the gas volume fraction (GVF). When introducing a small amount of air into the oil (GVF = 0.1), the direct damping coefficient increases by approximately 10%. For operation with a mixture with inlet GVF > 0.1, the cross-coupled stiffness coefficients develop strong frequency dependent characteristics. In contrast, the direct damping coefficient has a negligible variation with excitation frequency. The CFD predictions, as well as the experimental results, evidence that air injection in a liquid stream can significantly change the seal rotordynamic characteristics, and thus can affect the rotordynamic stability of a pump. An accurate CFD analysis thus enables engineers to design reliable grooved seals operating under two-phase flow conditions.
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Jáuregui, Juan Carlos, and Oscar M. González. "Modeling Axial Vibrations in Herringbone Gears." In ASME 1999 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/detc99/vib-8109.
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Abstract This paper addresses the axial vibrations of herringbone gears. Theoretically, herringbone gears balance their axial loads due to their symmetry; however, in practice, they present high vibrations. The reasons are manufacturing deviations such as lead angle errors, pitch error differences between each side of the gear, misalignment between pinion and gear axes, etc. These errors can be represented as an error function of sinusoidal form acting as forced vibrations over the teeth. Although axial and lateral motions of a gear pair are generally coupled, the symmetric geometry of herringbone gears makes possible to analyze the axial and lateral stiffness as uncoupled functions. It is viable then to represent the axial motion as a single degree of freedom model. The effect of each parameter of the error function is analyze individually in order to determine which has the greater effect in the system. Results are compared to field data showing good agreement.
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Chilla, M., G. Pullan, and S. Gallimore. "Reducing Instrumentation Errors Caused by Circumferential Flow Field Variations in Multi-Stage Axial Compressors." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90839.
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Abstract The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an 8-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180deg sector (half-annulus) model of the compressor is used. It is shown that the time-mean flow field in the stator leading edge planes is circumferentially non-uniform. The circumferential variations in stagnation pressure and stagnation temperature respectively reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while towards the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%. Recognizing that data from large-scale unsteady calculations is rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equi-spaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.
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Borello, D., and F. Rispoli. "Improved Non-Equilibrium Turbulence Closure Modeling for Axial Flow Compressors Simulation." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38672.
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The present paper investigates the predictive attitude of three non conventional turbulence closures in simulating the physics pertinent to decelerating turbomachinery flows. The performance of a cubic k-ε model and an algebraic Reynolds stress model adopting a non-linear link between turbulence and velocity gradients have been exploited with reference to their capabilities in predicting anisotropy effects and the sensibility to streamlines curvature. In addition, a modification of the kinetic energy production term in standard isotropic model has been also tested, in accord with Kato and Launder formulation. To put in evidence the predictive capabilities of such models a comparison with the standard Launder and Sharma turbulence closure will be carried out. The authors adopt a multi-level parallel solver developed in the framework of a finite element (FE) method based on a stabilized Petrov-Galerkin formulation. The FE method is here applied on mixed Q2-Q1 element shape functions. The solution scheme is based on a Multigrid (MG) solver properly developed to operate in a parallel environment. To increase the performance of MG schemes in solving self-adjoint elliptic problems a remedial strategy consisting of a LFMG-type scheme named Hybrid Linear Full Multi-Grid technique (HLFMG) has been proposed. The parallel algorithm follows a Single Program Multiple Domains (SPMD) scheme. The subdomains fields for Reynolds Averaged Navier-Stokes problem are generated by the adoption of an original overlapping domain decomposition technique. In the present paper we analyze a two-dimensional leading edge and both a DCA (2D) and NACA65 (3D) compressor cascades. The flows considered for model benchmarking are highly challenging because of the possibly transitional nature of the flow and the existence of three-dimensional phenomena and of significant separation regions. The potential of non-standard closures has been investigated in terms of both velocity and turbulent variables. In the leading edge test-case, the cubic k-ε model is shown to provide a better base-line for nonequilibrium effects simulation with respect to the algebraic stress model. The Kato and Launder modification has shown poor predictive attitude in representing the flow downstream the impingement and it has not adopted for the other test-cases. In the DCA simulation the presence of large transition regions leads to a degradation of the predictions of the cubic model. Algebraic stress model has shown performances comparable to the cubic model ones. The 3D linear cascade flow simulations put in evidence that the standard and algebraic Reynolds stress approaches have similar performance, clearly worse respect to the cubic model.
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Adamczyk, John J. "Wake Mixing in Axial Flow Compressors." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-029.
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Over the years it has been speculated that the performance of multi-stage axial flow compressors is enhanced by the passage of a wake through a blade row prior to being mixed-out by viscous diffusion. The link between wake mixing and performance depends on the ability to recover the total pressure deficit of a wake by a reversible flow process. This paper shows that such a process exists, it is unsteady, and is associated with the kinematics of the wake vorticity field. The analysis shows that the benefits of wake total pressure recovery can be estimated from linear theory and quantified in terms of a volume integral involving the deterministic stress and the mean strain rate. In the limit of large reduced frequency the recovery process is shown to be a direct function of blade circulation. Results are presented which show that the recovery process can reduce the wake mixing loss by as much as seventy percent. Under certain circumstances this can lead to nearly a point improvement in stage efficiency, a nontrivial amount.
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Dorney, D. J., D. L. Sondak, P. G. A. Cizmas, V. E. Saren, and N. M. Savin. "Full-Annulus Simulations of Airfoil Clocking in a 1-1/2 Stage Axial Compressor." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-023.
Full textAbstract:
Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects. It has been shown, both experimentally and computationally, that airfoil clocking can be used to improve the efficiency and reduce the unsteadiness in multiple-stage axial turbomachines with equal blade counts in alternate blade rows. While previous investigations have provided an improved understanding of the physics associated with airfoil clocking, more research is needed to determine if airfoil clocking is viable for use in modern gas-turbine compressors. This paper presents the results of a combined experimental/computational research effort to study the physics of airfoil clocking in a high-speed axial compressor. Computational simulations have been performed for eight different clocking positions of the stator airfoils in a 1-1/2 stage high-speed compressor. To accurately model the experimental compressor, full-annulus simulations were conducted using 34 IGV, 35 rotor and 34 stator airfoils. It is common practice to modify blade counts to reduce the computational work required to perform turbomachinery simulations, and this approximation has been made in all computational clocking studies performed to date. A simulation was also performed in the present study with 1 inlet guide vane, 1 rotor airfoil, and 1 stator airfoil to model blade rows with 34 airfoils each in order to examine the effects of this approximation. Time-averaged and unsteady data (including performance and boundary layer quantities) were examined. The predicted results indicate that simulating the full annulus gives better qualitative agreement with the experimental data, as well as more accurately modeling the interaction between adjacent blade rows.
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Oates, William S., and Ralph C. Smith. "Multi-Axial Homogenized Energy Model for Ferroelectric Materials." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13733.
Full textAbstract:
A multi-axial homogenized energy model is developed to account for nonlinear and hysteretic ferroelectric constitutive behavior induced by multi-axial electric field loading. The modeling approach extends a one-dimensional multi-scale modeling framework developed for ferroic materials [1, 2]. A three-dimensional energy function is introduced at the mesoscopic length scale and subsequently approximated as piecewise polynomial approximations to improve computational efficiency. Multi-scale field relations are then developed by introducing a distribution of effective electric fields and coercive fields that govern the nucleation of localized domain switching in polycrystalline ferroelectric materials. The distribution of field relations is used to relate the localized domain switching processes to observed macroscopic behavior by utilizing a stochastic homogenization technique. It is demonstrated that a simplified stochastic distribution of effective fields and coercive fields is sufficient to predict multi-axial ferroelectric switching in ferroelectric ceramics. Examples are given to validate the model in comparison to multi-axial loading experiments given in the literature. The model reduction provides a simple and efficient multi-scale modeling approach that is important for developing reliable piezoelectric actuator systems as well as implementation in model-based control of two and three dimensional structures.