Journal articles on the topic 'Stochastic accelerations'
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1
Borgas, M. S., and B. L. Sawford. "A family of stochastic models for two-particle dispersion in isotropic homogeneous stationary turbulence." Journal of Fluid Mechanics 279 (November 25, 1994): 69–99. http://dx.doi.org/10.1017/s0022112094003824.
Abstract:
A family of Lagrangian stochastic models for the joint motion of particle pairs in isotropic homogeneous stationary turbulence is considered. The Markov assumption and well-mixed criterion of Thomson (1990) are used, and the models have quadratic-form functions of velocity for the particle accelerations. Two constraints are derived which formally require that the correct one-particle statistics are obtained by the models. These constraints involve the Eulerian expectation of the ‘acceleration’ of a fluid particle with conditioned instantaneous velocity, given either at the particle, or at some other particle's position. The Navier-Stokes equations, with Gaussian Eulerian probability distributions, are shown to give quadratic-form conditional accelerations, and models which satisfy these two constraints are found. Dispersion calculations show that the constraints do not always guarantee good one-particle statistics, but it is possible to select a constrained model that does. Thomson's model has good one-particle statistics, but is shown to have unphysical conditional accelerations. Comparisons of relative dispersion for the models are made.
2
Ding, Yanqiong, Yongbo Peng, and Jie Li. "A Stochastic Semi-Physical Model of Seismic Ground Motions in Time Domain." Journal of Earthquake and Tsunami 12, no. 03 (August 12, 2018): 1850006. http://dx.doi.org/10.1142/s1793431118500069.
Abstract:
A stochastic function model of seismic ground motions is presented in this paper. It is derived from the consideration of physical mechanisms of seismic ground motions. The model includes the randomness inherent in the seismic source, propagation path and local site. For logical selection of the seismic acceleration records, a cluster analysis method is employed. Statistical distributions of the random parameters associated with the proposed model are identified using the selected data. Superposition method of narrow-band wave groups is then adopted to simulate non-stationary seismic ground motions. In order to verify the feasibility of the proposed model, comparative studies of time histories and response spectra of the simulated seismic accelerations against those of the recorded seismic accelerations are carried out. Their probability density functions, moreover, are readily investigated by virtue of the probability density evolution method.
3
Kelly, Patrick, Manoranjan Majji, and Felipe Guzmán. "Estimation and Error Analysis for Optomechanical Inertial Sensors." Sensors 21, no. 18 (September 11, 2021): 6101. http://dx.doi.org/10.3390/s21186101.
Abstract:
A sensor model and methodology to estimate the forcing accelerations measured using a novel optomechanical inertial sensor with the inclusion of stochastic bias and measurement noise processes is presented. A Kalman filter for the estimation of instantaneous sensor bias is developed; the outputs from this calibration step are then employed in two different approaches for the estimation of external accelerations applied to the sensor. The performance of the system is demonstrated using simulated measurements and representative values corresponding to a bench-tested 3.76 Hz oscillator. It is shown that the developed methods produce accurate estimates of the bias over a short calibration step. This information enables precise estimates of acceleration over an extended operation period. These results establish the feasibility of reliably precise acceleration estimates using the presented methods in conjunction with state of the art optomechanical sensing technology.
4
Guo, Xiangying, Changkun Li, Zhong Luo, and Dongxing Cao. "Modal Parameter Identification of Structures Using Reconstructed Displacements and Stochastic Subspace Identification." Applied Sciences 11, no. 23 (December 2, 2021): 11432. http://dx.doi.org/10.3390/app112311432.
Abstract:
A method of modal parameter identification of structures using reconstructed displacements was proposed in the present research. The proposed method was developed based on the stochastic subspace identification (SSI) approach and used reconstructed displacements of measured accelerations as inputs. These reconstructed displacements suppressed the high-frequency component of measured acceleration data. Therefore, in comparison to the acceleration-based modal analysis, the operational modal analysis obtained more reliable and stable identification parameters from displacements regardless of the model order. However, due to the difficulty of displacement measurement, different types of noise interferences occurred when an acceleration sensor was used, causing a trend term drift error in the integral displacement. A moving average low-frequency attenuation frequency-domain integral was used to reconstruct displacements, and the moving time window was used in combination with the SSI method to identify the structural modal parameters. First, measured accelerations were used to estimate displacements. Due to the interference of noise and the influence of initial conditions, the integral displacement inevitably had a drift term. The moving average method was then used in combination with a filter to effectively eliminate the random fluctuation interference in measurement data and reduce the influence of random errors. Real displacement results of a structure were obtained through multiple smoothing, filtering, and integration. Finally, using reconstructed displacements as inputs, the improved SSI method was employed to identify the modal parameters of the structure.
5
Nava, F. Alejandro. "Assessment of possible peak accelerations through stochastic variations." Terra Nova 3, no. 3 (May 1991): 289–93. http://dx.doi.org/10.1111/j.1365-3121.1991.tb00146.x.
6
de Jager, Cornells, Joost Carpay, Alex de Koter, Hans Nieuwenhuijzen, and Erik Schellekens. "Atmospheric dynamics of luminous stars." International Astronomical Union Colloquium 113 (1989): 211–20. http://dx.doi.org/10.1017/s0252921100004474.
Abstract:
AbstractA review is given of data and theories on the motion fields in super and hypergiants with special reference to LBV’s. We show that the radiative momentum flux is incapable of driving the episodical bursts of mass loss of these stars, and that there are several indications that the LBV-phenomenon is hydrodynamically driven. The sum of turbulent and radiative accelerations in the atmospheres of the most luminous stars compensates the gravitational acceleration for stars near the Humphreys-Davidson limit. This explains their atmospheric near-instability. The motion field in the atmosphere of a typical LBV consists mainly of low-order gravity waves, while acoustic waves are rapidly damped. These gravitation waves may be stochastic rather than coherently ordered. These stochastic pulsations are assumed to be responsible for the LBV phenomenon.
7
Vajedi, S., K. Gustavsson, B. Mehlig, and L. Biferale. "Inertial-particle accelerations in turbulence: a Lagrangian closure." Journal of Fluid Mechanics 798 (May 31, 2016): 187–200. http://dx.doi.org/10.1017/jfm.2016.305.
Abstract:
The distribution of particle accelerations in turbulence is intermittent, with non-Gaussian tails that are quite different for light and heavy particles. In this article we analyse a closure scheme for the acceleration fluctuations of light and heavy inertial particles in turbulence, formulated in terms of Lagrangian correlation functions of fluid tracers. We compute the variance and the flatness of inertial-particle accelerations and we discuss their dependency on the Stokes number. The closure incorporates effects induced by the Lagrangian correlations along the trajectories of fluid tracers, and its predictions agree well with results of direct numerical simulations of inertial particles in turbulence, provided that the effects induced by inertial preferential sampling of heavy/light particles outside/inside vortices are negligible. In particular, the scheme predicts the correct functional behaviour of the acceleration variance, as a function of $St$, as well as the presence of a minimum/maximum for the flatness of the acceleration of heavy/light particles, in good qualitative agreement with numerical data. We also show that the closure works well when applied to the Lagrangian evolution of particles using a stochastic surrogate for the underlying Eulerian velocity field. Our results support the conclusion that there exist important contributions to the statistics of the acceleration of inertial particles independent of the preferential sampling. For heavy particles we observe deviations between the predictions of the closure scheme and direct numerical simulations, at Stokes numbers of order unity. For light particles the deviation occurs for larger Stokes numbers.
8
Yan, Guang Hui, and Shuo Zhang. "Research on Modeling and Optimization Control of Heavy Truck Cab Active Suspension System." Applied Mechanics and Materials 687-691 (November 2014): 359–62. http://dx.doi.org/10.4028/www.scientific.net/amm.687-691.359.
Abstract:
In order to meet the ride comfort of the heavy truck cab, the 1/2 heavy truck cab active suspension model established. Based on this model the LQG optimization control was selected for the active control of a 1/2 heavy truck cab suspension system. The road disturbance is integral white noise stochastic signal. By the example simulation in Matlab/Simulink, the results show that the cab active suspension with LQG control strategy can decrease the vertical accelerations, the roll angle and roll angle acceleration of the truck cab, the active suspension can improve both the ride comfort and driving safety.
9
Chen, Na, Meng Wang, Tom Alkim, and Bart van Arem. "A Robust Longitudinal Control Strategy of Platoons under Model Uncertainties and Time Delays." Journal of Advanced Transportation 2018 (2018): 1–13. http://dx.doi.org/10.1155/2018/9852721.
Abstract:
Automated vehicles are designed to free drivers from driving tasks and are expected to improve traffic safety and efficiency when connected via vehicle-to-vehicle communication, that is, connected automated vehicles (CAVs). The time delays and model uncertainties in vehicle control systems pose challenges for automated driving in real world. Ignoring them may render the performance of cooperative driving systems unsatisfactory or even unstable. This paper aims to design a robust and flexible platooning control strategy for CAVs. A centralized control method is presented, where the leader of a CAV platoon collects information from followers, computes the desired accelerations of all controlled vehicles, and broadcasts the desired accelerations to followers. The robust platooning is formulated as a Min-Max Model Predictive Control (MM-MPC) problem, where optimal accelerations are generated to minimize the cost function under the worst case, where the worst case is taken over the possible models. The proposed method is flexible in such a way that it can be applied to both homogeneous platoon and heterogeneous platoon with mixed human-driven and automated controlled vehicles. A third-order linear vehicle model with fixed feedback delay and stochastic actuator lag is used to predict the platoon behavior. Actuator lag is assumed to vary randomly with unknown distributions but a known upper bound. The controller regulates platoon accelerations over a time horizon to minimize a cost function representing driving safety, efficiency, and ride comfort, subject to speed limits, plausible acceleration range, and minimal net spacing. The designed strategy is tested by simulating homogeneous and heterogeneous platoons in a number of typical and extreme scenarios to assess the system stability and performance. The test results demonstrate that the designed control strategy for CAV can ensure the robustness of stability and performance against model uncertainties and feedback delay and outperforms the deterministic MPC based platooning control.
10
Haerendel, Gerhard. "Magnetic energy conversion in the Corona and Magnetosphere." Highlights of Astronomy 10 (1995): 302. http://dx.doi.org/10.1017/s1539299600011278.
Abstract:
Five different categories of magnetic energy conversion will be discussed, and their manifestations in the ionosphere-magnetosphere and chromosphere - corona will be compared. They are: (1) Ohmic dissipation of d.c. currents, (2) Damping of Alfvén waves, (3) Magnetic pumping, (4) Reconnection, and (5) Electrostatic acceleration parallel B. Manifestations are: (1) Ionospheric heating by Peder sen currents and generation of chromospheric faculae and plages by dissipation of field-aligned currents; (2) Generation of spicules by collisional damping of Alfvén-waves and Alfvén-wave damping in the corona by resonant absorption; (3) Drift resonance acceleration of radiation belt particles and stochastic acceleration of high-energy flare particles by Alfvén waves; (4) Reconnection at the magnetopause and in the tail, plasmoid formation and a wide variety of configuration changes and mhd instabilities in the corona for which reconnection plays a decisive role; (5) Acceleration by field-aligned potential drops as origin of auroral arcs and of > 10 MeV electron and ion beams in solar flares. Some of these mechanisms, e.g. plages, spicules, nanoflares and field-aligned electrostatic accelerations will be selected for more detailed discussion.
11
Avendaño-Valencia, Luis David, and Spilios D. Fassois. "Generalized Stochastic Constraint TARMA Models for In-Operation Identification of Wind Turbine Non-Stationary Dynamics." Key Engineering Materials 569-570 (July 2013): 587–94. http://dx.doi.org/10.4028/www.scientific.net/kem.569-570.587.
Abstract:
The identification of the operational Wind Turbine (WT) dynamics is a challenging problem, due to both the complex dynamics and the non-stationarity of the vibration response. In this study the novel class of Generalized Stochastic Constraint (GSC) Time-dependent ARMA models is used for the identification of the non-stationary characteristics of acceleration vibration signals acquired in the tower top of an operating WT, in the fore-aft and lateral directions. The results demonstrate the improved performance of GSC-TARMA models compared to their conventional Smoothness Priors (SP) and Functional Series (FS) counterparts. The obtained models confirm the presence of cyclo-stationary and broader non-stationary behavior in WT vibration. The model based frozen time-varying modes of vibration are analyzed, and the modal components of the vibration accelerations are pictorially presented on the plane defined by the fore-aft and lateral axes.
12
Zheng, Wei, Juan Han, Weijie Kong, and Lixiang Wang. "Group-SMA Algorithm Based Joint Estimation of Train Parameter and State." PROMET - Traffic&Transportation 27, no. 1 (March 2, 2015): 85–95. http://dx.doi.org/10.7307/ptt.v27i1.1499.
Abstract:
The braking rate and train arresting operation is important in the train braking performance. It is difficult to obtain the states of the train on time because of the measurement noise and a long calculation time. A type of Group Stochastic M-algorithm (GSMA) based on Rao-Blackwellization Particle Filter (RBPF) algorithm and Stochastic M-algorithm (SMA) is proposed in this paper. Compared with RBPF, GSMA based estimation precisions for the train braking rate and the control accelerations were improved by 78% and 62%, respectively. The calculation time of the GSMA was decreased by 70% compared with SMA.
13
Ruiz, X., P. Bitlloch, L. Ramírez-Piscina, and J. Casademunt. "Impact of stochastic accelerations on dopant segregation in microgravity semiconductor crystal growth." Journal of Crystal Growth 355, no. 1 (September 2012): 88–100. http://dx.doi.org/10.1016/j.jcrysgro.2012.06.027.
14
Ariaratnam, S. T., and K. C. K. Leung. "Parametric effect of vertical ground acceleration on the earthquake response of elastic structures." Canadian Journal of Civil Engineering 17, no. 2 (April 1, 1990): 209–17. http://dx.doi.org/10.1139/l90-026.
Abstract:
An analytical procedure is presented for the calculation of the statistical properties of the response of a linear elastic tall building under earthquake excitation. Emphasis is placed on the effect of the vertical ground motion. The restoring force in each story of the structural model is assumed to arise from the bending deformation of the columns whose rigidities are subjected to a general reduction due to the combined action of gravitational forces and the random variations due to vertical ground acceleration. Since earthquakes are random phenomena, stochastic modelling of ground motion seems appropriate. Both the vertical and the horizontal accelerations are treated as amplitude-modulated Gaussian random processes. With these models, the techniques developed herein, using the concept of Markov processes and Itô's stochastic differential equations, may be applied. To illustrate the application of the method, numerical results are presented for a six-story building. For computational purposes, the structural properties are evaluated using the finite element method. Within the limit of linear elastic deformation, the vertical ground acceleration is shown to be capable of causing only a slight increase of 0.08% in the lateral displacement for this moderately tall building. The percentage is expected to be larger for a taller building and much larger when the deformations exceed the elastic limit. Key words: earthquake excitation, elastic frames, random vibration, Markov process, dynamic response.
15
Picozzi, V., A. M. Avossa, and F. Ricciardelli. "Codifiable probability-based model for footbridges response to random walkers." Journal of Physics: Conference Series 2647, no. 12 (June 1, 2024): 122011. http://dx.doi.org/10.1088/1742-6596/2647/12/122011.
Abstract:
Abstract The response to the transient action of a single pedestrian or a small group of pedestrians is required for the serviceability assessment of human-induced footbridge vibrations. The approach adopted by standards and guidelines is proved to lead to a non-uniform level of reliability. This is in contrast with both the stochastic nature of pedestrian gait parameters and the probabilistic approach adopted by modern structural codes. In this paper, firstly the analysis of peak accelerations is developed according to the Eurocode for a number of simply-supported footbridges, both in vertical and lateral directions. These are shown to correspond to different level of probability of exceedance, that is larger for short-span footbridges and smaller for long-span footbridges. Then, a model for the assessment of the characteristic footbridge acceleration is provided. This is based on the prediction of the basic acceleration, i.e. the response of simply-supported footbridges to single pedestrian crossings, and the application of an acceleration ratio factor for footbridge configurations other than simply-supported.
16
Ágh, Csaba. "Comparative Analysis of Axlebox Accelerations in Correlation with Track Geometry Irregularities." Acta Technica Jaurinensis 12, no. 2 (April 26, 2019): 161–77. http://dx.doi.org/10.14513/actatechjaur.v12.n2.501.
Abstract:
Stochastic track irregularities influence additional dynamic forces developed in the vehicle-track interaction that lead to faster deterioration of track. For economical track maintenance it is important to understand the relationship between the irregularities recorded by conventional track geometry measuring car and the resulting dynamic vehicle responses. This paper focuses on the correlation between lateral and vertical axlebox accelerations and differently processed track geometry parameters based on a real measurement run on straight track. Decolouring of chord-offset measurement results was performed and derivatives of track geometry parameters were calculated for comparison. Those track geometry parameters have been selected which provide the most accurate information about the recorded wheelset accelerations caused by track geometry irregularities, e.g. second order derivative of cross level.
17
Zuo, Qing Lin, Li Chang Wang, and Da Hai Ji. "Vibration Test and Stochastic Analysis of Large-Span Cantilevered Floor." Applied Mechanics and Materials 188 (June 2012): 130–36. http://dx.doi.org/10.4028/www.scientific.net/amm.188.130.
Abstract:
With the study of the 3rd conference hall of Dalian International Conference Center, test and relevant calculation are applied to the structural natural frequency and floor vibration due to human excitations. The Monte Carlo stochastic analysis is applied to the cases in which the comfort for vibration due to crowd excitations may exceed the limit. The results show that the Monte Carlo stochastic method and load curves of excitations are reliable, but in the actual test the high-order harmonic effect of walking excitation is not obvious. In the stochastic analysis with the closer frequency and phase of crowd excitations or the greater population density, the discreteness of results is smaller. Compared with the population density, the differences of frequency and phase of crowd excitations lead to a bigger discreteness of results. With the bigger discreteness of frequency and phase of excitations, the peak accelerations of stochastic model are significantly smaller than the simplified model with the same frequency and phase.
18
Murböck, Michael, Petro Abrykosov, Christoph Dahle, Markus Hauk, Roland Pail, and Frank Flechtner. "In-Orbit Performance of the GRACE Accelerometers and Microwave Ranging Instrument." Remote Sensing 15, no. 3 (January 17, 2023): 563. http://dx.doi.org/10.3390/rs15030563.
Abstract:
The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided global long-term observations of mass transport in the Earth system with applications in numerous geophysical fields. In this paper, we targeted the in-orbit performance of the GRACE key instruments, the ACCelerometers (ACC) and the MicroWave ranging Instrument (MWI). For the ACC data, we followed a transplant approach analyzing the residual accelerations from transplanted accelerations of one of the two satellites to the other. For the MWI data, we analyzed the post-fit residuals of the monthly GFZ GRACE RL06 solutions with a focus on stationarity. Based on the analyses for the two test years 2007 and 2014, we derived stochastic models for the two instruments and a combined ACC+MWI stochastic model. While all three ACC axes showed worse performance than their preflight specifications, in 2007, a better ACC performance than in 2014 was observed by a factor of 3.6 due to switched-off satellite thermal control. The GRACE MWI noise showed white noise behavior for frequencies above 10 mHz around the level of 1.5×10−6 m/Hz. In the combined ACC+MWI noise model, the ACC part dominated the frequencies below 10 mHz, while the MWI part dominated above 10 mHz. We applied the combined ACC+MWI stochastic models for 2007 and 2014 to the monthly GFZ GRACE RL06 processing. This improved the formal errors and resulted in a comparable noise level of the estimated gravity field parameters. Furthermore, the need for co-estimating empirical parameters was reduced.
19
Villani, Manuela, Barbara Polidoro, Rory McCully, Thomas Ader, Ben Edwards, Andreas Rietbrock, Ziggy Lubkowski, Tim J. Courtney, and Martin Walsh. "A Selection of GMPEs for the United Kingdom Based on Instrumental and Macroseismic Datasets." Bulletin of the Seismological Society of America 109, no. 4 (July 16, 2019): 1378–400. http://dx.doi.org/10.1785/0120180268.
Abstract:
Abstract In countries with low‐to‐moderate seismicity, the selection of appropriate ground‐motion prediction equations (GMPEs) to be used in a probabilistic seismic hazard analysis (PSHA) is a challenging step. Empirical observations of ground motion are limited, and GMPEs, when available, are generally based on stochastic simulations or adjusted empirical GMPEs from elsewhere. This article investigates the suitability of recent GMPEs to the United Kingdom. To this end, the spectral accelerations obtained from available instrumental ground‐motion data in the United Kingdom with magnitude lower than 4.5 are compared with the GMPEs’ predictions through the analysis of residuals and the application of statistical tests. To compensate for the scarcity of data for the magnitude range of interest in the PSHA, a macroseismic dataset is also considered. Macroseismic intensities are converted to peak ground acceleration (PGA) and statistically compared with the PGA predicted by the GMPEs. The GMPEs are then compared in terms of median ground‐motion prediction through Sammon’s maps to evaluate their similarities. The analyses from both datasets led to six suitable GMPEs, of which three are from the Next Generation Attenuation‐West2 project, one is European, one is based mainly on a Japanese dataset, and one is a stochastic GMPE developed specifically for the United Kingdom.
20
Venglár, Michal, and Katarína Lamperová. "Effect of the Temperature on the Modal Properties of a Steel Railroad Bridge." Slovak Journal of Civil Engineering 29, no. 1 (March 1, 2021): 1–8. http://dx.doi.org/10.2478/sjce-2021-0001.
Abstract:
Abstract The article is devoted to a study of the impact of various environmental conditions on modal parameters, such as natural frequencies and damping ratios. The modal analysis has been performed using the Stochastic Subspace Identification (SSI) method of measuring data every month on the same steel bridge structures located on an important railroad route from Prague (the Czech Republic) to Košice (Slovakia). The structure is approximately 60 m long, and the bearing structure is formed by two arch trusses. The bridge was exposed to ambient vibrations as well as to vibrations caused by a train passage. Accelerations and temperatures (the temperature of the air and the structure) were logged during the measurements. Natural frequencies were obtained from these acceleration data using the SSI method and processed into graphs of the dependencies between the natural frequencies and temperatures. Some statistical procedures were also applied.
21
Wald, D., P. G. Somerville, and L. J. Burdick. "The Whittier Narrows, California Earthquake of October 1, 1987—Simulation of Recorded Accelerations." Earthquake Spectra 4, no. 1 (February 1988): 139–56. http://dx.doi.org/10.1193/1.1585469.
Abstract:
We have simulated accelerograms from many of the strong motion stations close to the mainshock of the 1987 Whittier Narrows earthquake using a semi-empirical Green's function summation technique. This method allows gross aspects of the source rupture process to be treated deterministically using a kinematic model based on first motion studies, teleseismic modeling and the distribution of aftershocks. Stochastic aspects of the rupture process are then included to simulate irregularity in both rupture and slip velocity. Gross aspects of wave propagation are modeled using theoretical Green's functions calculated with generalized rays. Detailed aspects of the source radiation at high frequencies, as well as unmodeled propagational aspects such as scattering, are included empirically by using multiple recordings of a smaller Imperial Valley earthquake as empirical source functions. Our main objective is to see how well we can predict the peak ground accelerations, time histories and response spectra of ground motions of a moderate sized earthquake within the Los Angeles Basin having limited detailed source information. We find that the simulations predict the observations accurately enough to identify which phases and amplitudes in the observed data may be due to local site response rather than source or radiation effects. Comparisons between observed and simulated accelerograms for all the stations modeled are made using peak ground acceleration, and using time histories and response spectra for the stations that have been hand-digitized to date. The Bright Avenue Whittier station has the largest simulated peak acceleration, in agreement with the recorded peak acceleration data.
22
Hu, Zhaohui, and Dongbin Zhao. "Adaptive Cruise Control Based on Reinforcement Leaning with Shaping Rewards." Journal of Advanced Computational Intelligence and Intelligent Informatics 15, no. 3 (May 20, 2011): 351–56. http://dx.doi.org/10.20965/jaciii.2011.p0351.
Abstract:
This paper proposes a Supervised Reinforcement Learning (SRL) algorithm for the Adaptive Cruise Control system (ACC) to comply with human driving habit, which can be thought of as a dynamic programming problem with stochastic demands. In short, the ACC problem can be deemed as the host vehicle adopting different control parameters (accelerations in the upper controller, brakes and throttles in the bottom controller) in the process of following or other driving situations according to the driver’s behavior. We discretize the relative speed as well as the relative distance to construct the two-dimensional states and map them to a one-dimensional state space; discretize the acceleration to generate the action set; and design additional speed improvement shaping reward and distance improvement shaping reward to construct the supervisor. We apply the SRL algorithm to the ACC problem in different scenarios. The results show the higher robustness and accuracy of the SRL control policy compared with traditional control methods.
23
Wang, Nan, Rumi Takedatsu, Kim B. Olsen, and Steven M. Day. "Broadband Ground‐Motion Simulation with Interfrequency Correlations." Bulletin of the Seismological Society of America 109, no. 6 (October 29, 2019): 2437–46. http://dx.doi.org/10.1785/0120190136.
Abstract:
Abstract Ground‐motion simulations can be viable alternatives to empirical relations for seismic hazard analysis when data are sparse. Interfrequency correlation is revealed in recorded seismic data, which has implications for seismic risk (Bayless and Abrahamson, 2018a). However, in many cases, simulated ground‐motion time series, in particular those originating from stochastic methods, lack interfrequency correlation. Here, we develop a postprocessing method to rectify simulation techniques that otherwise produce synthetic time histories deficient in an interfrequency correlation structure. An empirical correlation matrix is used in our approach to generate correlated random variables that are multiplied in the frequency domain with the Fourier amplitudes of the synthetic ground‐motion time series. The method is tested using the San Diego State University broadband ground‐motion generation module, which is a broadband ground‐motion generator that combines deterministic low‐frequency and stochastic high‐frequency signals, validated for the median of the spectral acceleration. Using our method, the results for seven western U.S. earthquakes with magnitude between 5.0 and 7.2 show that empirical interfrequency correlations are well simulated for a large number of realizations without biasing the fit of the median of the spectral accelerations to data. The best fit of the interfrequency correlation to data is obtained assuming that the horizontal components are correlated with a correlation coefficient of about 0.7.
24
Bae, Gihwan, and Yoshiyuki Suzuki. "Stochastic Identification of Building Structure using Response Accelerations of the 1995 Hyogoken-Nanbu Earthquake." Proceedings of the ISCIE International Symposium on Stochastic Systems Theory and its Applications 1996 (May 5, 1996): 19–24. http://dx.doi.org/10.5687/sss.1996.19.
25
Pimenta, Francisco, João Pacheco, Sérgio Pereira, and Filipe Magalhães. "Reconstructing the bending moments time history of wind turbine tower from acceleration measurements using Gaussian processes." Journal of Physics: Conference Series 2265, no. 3 (May 1, 2022): 032080. http://dx.doi.org/10.1088/1742-6596/2265/3/032080.
Abstract:
Abstract The proper estimation of the fatigue damage accumulated over time for a given wind turbine is a key information when evaluating the remaining lifetime of the structure. While the most obvious way to do so is to instrument the structure with strain gauges, not only this is a demanding task, it also only provides information about the sections that are being monitored. In this work we propose a new methodology to estimate the fatigue damage in any section of the tower based on the accelerations time series and a single instrumented section with strain gauges. We argue that accelerations and displacements of a linear structure under stochastic loading share a well defined covariance structure. This conclusion allow us to define a Monte Carlo Markov Chain (MCMC) algorithm to constrain the parameters that best describe this structure, as well as to use all the machinery associated with gaussian processes to convert accelerations into displacements, and these into bending moments. Using artificial experimental data obtained from a previously validated numerical model as input to our method, we obtained a good agreement between the simulated and reconstructed response. The results concerning fatigue damage were also in reasonable agreement, although presenting higher deviations that must be analysed in future studies.
26
Cao, Hui, and Tong Liu. "Damage Identification of Beams Based on Improved Element Damage Variable with Reconstructed Modal Rotations." International Journal of Computational Methods 12, no. 04 (August 2015): 1540007. http://dx.doi.org/10.1142/s0219876215400071.
Abstract:
Damage identification of structures is always attractive to researchers because it plays an important role in the health monitoring in many civil engineering structures. When carrying out a health monitoring, sensors are usually laid on a beam to record acceleration signals, in which the modes of the beam can be extracted to construct indicators for detecting damage of the investigated beam. It should be noted that it is difficult to measure rotational signals of the beam at a position where sensors are laid, thus only the modal translations are available. Although the modal translations can be used to construct indicators without modal rotations and often it is the case, an indicator taking into account modal rotations is suggested in application to resist the effect of noise on the accuracy of measurement. In this paper, modal rotations were reconstructed by modal translations using the principle of static condensation and QR decomposition. Then both modal translations and rotations were used to build an indicator based on element modal strain energy with the help of data fusion theory. The modal translations were extracted from accelerations recorded on a beam using stochastic subspace identification (SSI). Studies were carried out on choosing values of parameters in SSI in order to eliminate the effect of noise as nearly as possible. The simulation given by a FEM model and analyses of accelerations recorded on a reinforced concrete beam show that the proposed damage indicator with the efforts of eliminating noise is able to detect the locations of damage in the investigated beams.
27
Osei, Jack Banahene, Mark Adom-Asamoah, Ahmed Ali Awadallah Ahmed, and Eugene Boasiako Antwi. "Monte Carlo Based Seismic Hazard Model for Southern Ghana." Civil Engineering Journal 4, no. 7 (July 10, 2018): 1510. http://dx.doi.org/10.28991/cej-0309191.
Abstract:
Seismic hazard assessment involves quantifying the likely ground motion intensities to be expected at a particular site or region. It is a crucial aspect of any seismic hazard mitigation program. The conventional probabilistic seismic hazard assessment is highly reliant on the past seismic activities in a particular region. However, for regions with lower rates of seismicity, where seismological data is scanty, it would seem desirable to use a stochastic modelling (Monte Carlo based) approach. This study presents a Monte Carlo simulation hazard model for Southern Ghana. Six sites are selected in order to determine their expected ground motion intensities (peak ground acceleration and spectral acceleration). Results revealed that Accra and Tema as the highly seismic cities in Southern Ghana, with Ho and Cape Coast having relatively lower seismicities. The expected peak ground acceleration corresponding to a 10% probability of exceedance in 50 years for the proposed seismic hazard model was as high as 0.06 g for the cities considered. However, at the rather extreme 2% probability of exceedance in 50 years, a PGA of 0.5 g can be anticipated. Evidently, the 2% in 50 years uniform hazard spectrum for the highly seismic cities recorded high spectral accelerations, at a natural vibrational period within the ranges of about 0.1-0.3 sec. This indicates that low-rise structures in these cities may be exposed to high seismic risk.
28
Zhu, Jian, and Ping Tan. "Vulnerability Analysis of Small High-Rise Shear Wall Buildings." Advanced Materials Research 255-260 (May 2011): 416–20. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.416.
Abstract:
In order to evaluate seismic reliability and vulnerability of the typical small high-rise shear wall buildings in Western China region, the sample finite element analytical small high-rise shear wall structure has been built in considering of fiber element model and fiber wall element model. Meantime stochastic response spectrum of accelerations with 5% damping ratio have being set up based on China Seismic Code as input seismic excitation, dynamic history analysis was being used to determine earthquake resistant capability of sample structures. Vulnerability curves of four performance levels are also be drawn after carefully analysis based PGA index.
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Bittner, M., L. Fritsch, B. Hirzinger, M. Broggi, and M. Beer. "Efficient time-dependent reliability analysis for a railway bridge model." Journal of Physics: Conference Series 2647, no. 6 (June 1, 2024): 062002. http://dx.doi.org/10.1088/1742-6596/2647/6/062002.
Abstract:
Abstract This paper proposes a framework for efficient time-dependent reliability analysis for a parametrized stochastic dynamic system, namely a train bridge load model with uncertain design properties. The Probability Density Evolution Method is utilized to explore the multidimensional random space, identify specific failure paths contributing to the failure region, and provide a full probabilistic output of the desired target quantity. The framework is tested on an uncertain railway bridge subjected to train transit (moving loads). The peak acceleration as a function of the train speed in a certain interval is analysed and utilised as performance criteria. The main sources of uncertainties are the damping and the bridge’s moment of inertia. The full evolutionary Probability Density Function of the bridge’s maximum deck acceleration is obtained, the reliability is assessed and a probability of failure estimated. The results show that in the considered speed intervals, the velocities contributing to the failure region are depending on the underlying sampling method. The Probability Density Evolution Method offers additional insight on the evolution of the critical peak accelerations while at the same time performing a reasonable amount of full model evaluations. The study concludes that further discussion is needed to determine the appropriate prediction of the train speeds that may or may not significantly contribute to the probability of failure in this bridge train model.
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Gerlici, Juraj, Olena Nozhenko, Ganna Cherniak, Mykola Gorbunov, Rostyslav Domin, and Tomáš Lack. "The development of diagnostics methodological principles of the railway rolling stock on the basis of the analysis of dynamic vibration processes of the rail." MATEC Web of Conferences 157 (2018): 03007. http://dx.doi.org/10.1051/matecconf/201815703007.
Abstract:
The paper discusses the preconditions of the methodology development of diagnosis system for assessing dynamic impact of the rolling stock on the basis of processing and analysis of data obtained in operation on the results of measurement of parameters that characterize dynamic vibration processes of the mechanical system of “rolling stock – track”. On the basis of usage of the processing methods of time series and stochastic processes there has been established the relationship between these dynamic processes and wheel defects, and designed experimental data processing algorithms, which in the future will be an integral part of the intellectual systems of decision making when assessing the impact level of the rolling stock on the track. The article presents some results of the experimental and theoretical research of the rail accelerations data, which have been registered during passing of the train. The computational algorithm of the specialized pre-processing of the multidimensional signal recorded by this system is described. The advantage of this algorithm is that it does not require additional information about the train speed on the section equipped with the monitoring system, about the number of wheel pairs of locomotives and train cars, and about the distances between the wheel pairs. Based on the processing results of accelerations of the rails there have been set the parameters of increase in all statistical indicators with increase in the train speed. It is noted that the level of indicators for accelerations of the rails in the vertical direction is twice as high as the corresponding parameters in the horizontal direction.
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Stokes, C. L., D. A. Lauffenburger, and S. K. Williams. "Migration of individual microvessel endothelial cells: stochastic model and parameter measurement." Journal of Cell Science 99, no. 2 (June 1, 1991): 419–30. http://dx.doi.org/10.1242/jcs.99.2.419.
Abstract:
Analysis of cell motility effects in physiological processes can be facilitated by a mathematical model capable of simulating individual cell movement paths. A quantitative description of motility of individual cells would be useful, for example, in the study of the formation of new blood vessel networks in angiogenesis by microvessel endothelial cell (MEC) migration. In this paper we propose a stochastic mathematical model for the random motility and chemotaxis of single cells, and evaluate migration paths of MEC in terms of this model. In our model, cell velocity under random motility conditions is described as a persistent random walk using the Ornstein-Uhlenbeck (O-U) process. Two parameters quantify this process: the magnitude of random movement accelerations, alpha, and a decay rate constant for movement velocity, beta. Two other quantities often used in measurements of individual cell random motility properties—cell speed, S, and persistence time in velocity, Pv—can be defined in terms of the fundamental stochastic parameters alpha and beta by: S =square root (alpha/beta) and Pv = 1/beta. We account for chemotactic cell movement in chemoattractant gradients by adding a directional bias term to the O-U process. The magnitude of the directional bias is characterized by the chemotactic responsiveness, kappa. A critical advantage of the proposed model is that it can generate, using experimentally measured values of alpha, beta and kappa, computer simulations of theoretical individual cell paths for use in evaluating the role of cell migration in specific physiological processes. We have used the model to assess MEC migration in the presence of absence of the angiogenic stimulus acidic fibroblast growth factor (aFGF). Time-lapse video was used to observe and track the paths of cells moving in various media, and the mean square displacement was measured from these paths. To test the validity of the model, we compared the mean square displacement measurements of each cell with model predictions of that displacement. The comparison indicates that the O-U process provides a satisfactory description of the random migration at this level of comparison. Using nonlinear regression in these comparisons, we measured the magnitude of random accelerations, alpha, and the velocity decay rate constant, beta, for each cell path. We consequently obtained values for the derived quantities, speed and persistence time. In control medium, we find that alpha = 250 +/− 100 microns 2h-3 and beta = 0.22 +/− 0.03h-1, while in stimulus medium (control plus unpurified aFGF) alpha = 1900 +/− 720 microns 2h-3 and beta = 0.99 +/− 0.37h-1.(ABSTRACT TRUNCATED AT 400 WORDS)
32
Cesare, Valentina. "Dark Coincidences: Small-Scale Solutions with Refracted Gravity and MOND." Universe 9, no. 1 (January 16, 2023): 56. http://dx.doi.org/10.3390/universe9010056.
Abstract:
General relativity and its Newtonian weak field limit are not sufficient to explain the observed phenomenology in the Universe, from the formation of large-scale structures to the dynamics of galaxies, with the only presence of baryonic matter. The most investigated cosmological model, the ΛCDM, accounts for the majority of observations by introducing two dark components, dark energy and dark matter, which represent ∼95% of the mass-energy budget of the Universe. Nevertheless, the ΛCDM model faces important challenges on the scale of galaxies. For example, some very tight relations between the properties of dark and baryonic matters in disk galaxies, such as the baryonic Tully–Fisher relation (BTFR), the mass discrepancy–acceleration relation (MDAR), and the radial acceleration relation (RAR), which see the emergence of the acceleration scale a0≃1.2×10−10 m s−2, cannot be intuitively explained by the CDM paradigm, where cosmic structures form through a stochastic merging process. An even more outstanding coincidence is due to the fact that the acceleration scale a0, emerging from galaxy dynamics, also seems to be related to the cosmological constant Λ. Another challenge is provided by dwarf galaxies, which are darker than what is expected in their innermost regions. These pieces of evidence can be more naturally explained, or sometimes even predicted, by modified theories of gravity, that do not introduce any dark fluid. I illustrate possible solutions to these problems with the modified theory of gravity MOND, which departs from Newtonian gravity for accelerations smaller than a0, and with Refracted Gravity, a novel classical theory of gravity introduced in 2016, where the modification of the law of gravity is instead regulated by a density scale.
33
Zhang, Rui, and Yimin Zhang. "Dynamic model and analysis of the traction unit gear system in long wall coal shearer." Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 234, no. 3 (April 14, 2020): 546–67. http://dx.doi.org/10.1177/1464419320913698.
Abstract:
The present work contributes to the analysis of dynamic behavior of long wall coal shearer traction unit through dynamic model of geared drives. In contrast to the majority of the models in the literature, complete machine dynamic model of coal shearer is introduced for obtaining dynamic gear loads for traction unit. A new stochastic coal cutting loads model is presented. Predicted vibration accelerations were compared with coal cutting experiments. It is demonstrated that the predictions match very well with experimental data. Forced vibrations of traction unit gear system are studied to investigate the influence of some of the key design parameters. Frequency coupling phenomenon and cutting rock interlayer process are also investigated in this paper.
34
Botshekan, Meshkat, Erfan Asaadi, Jake Roxon, Franz-Josef Ulm, Mazdak Tootkaboni, and Arghavan Louhghalam. "Smartphone-enabled road condition monitoring: from accelerations to road roughness and excess energy dissipation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2246 (February 2021): 20200701. http://dx.doi.org/10.1098/rspa.2020.0701.
Abstract:
We develop a framework to address the shortcomings of current smartphone-based approaches for road roughness sensing and monitoring through combining vehicle dynamics, random vibration theory and a two-layer inverse analysis. The proposed approach uses in-cabin recordings of the vehicle’s vertical acceleration measured by a smartphone positioned inside the car for the estimation of road roughness. The mechanistic road roughness–vehicle interaction model at the core of the proposed framework links the frequency spectrum of the vehicle’s vertical acceleration to the road roughness power spectral density and lends itself to the quantitative characterization of roughness-induced energy dissipation. We demonstrate that the measure of roughness provided by the stochastic model of car dynamics interacting with a rough road is fully compatible, in a statistical sense, with the spatial but deterministic definition of road roughness, and validate the identification strategy that originates from it against laser measurements of road roughness. The critical crowdsourcing features of the proposed framework, such as the marginal impact of phone position and transferability, are examined and its utility to meld with big data analytics to identify the class of vehicles travelling on a roadway network is demonstrated.
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Lasser, Martin, Ulrich Meyer, Daniel Arnold, and Adrian Jäggi. "Stochastic noise modelling of kinematic orbit positions in the Celestial Mechanics Approach." Advances in Geosciences 50 (October 20, 2020): 101–13. http://dx.doi.org/10.5194/adgeo-50-101-2020.
Abstract:
Abstract. Gravity field models may be derived from kinematic orbit positions of Low Earth Orbiting satellites equipped with onboard GPS (Global Positioning System) receivers. An accurate description of the stochastic behaviour of the kinematic positions plays a key role to calculate high quality gravity field solutions. In the Celestial Mechanics Approach (CMA) kinematic positions are used as pseudo-observations to estimate orbit parameters and gravity field coefficients simultaneously. So far, a simplified stochastic model based on epoch-wise covariance information, which may be efficiently derived in the kinematic point positioning process, has been applied. We extend this model by using the fully populated covariance matrix, covering correlations over 50 min. As white noise is generally assumed for the original GPS carrier phase observations, this purely formal variance propagation cannot describe the full noise characteristics introduced by the original observations. Therefore, we sophisticate our model by deriving empirical covariances from the residuals of an orbit fit of the kinematic positions. We process GRACE (Gravity Recovery And Climate Experiment) GPS data of April 2007 to derive gravity field solutions up to degree and order 70. Two different orbit parametrisations, a purely dynamic orbit and a reduced-dynamic orbit with constrained piecewise constant accelerations, are adopted. The resulting gravity fields are solved on a monthly basis using daily orbital arcs. Extending the stochastic model from utilising epoch-wise covariance information to an empirical model, leads to a – expressed in terms of formal errors – more realistic gravity field solution.
36
Gorini, Antonella, Sandro Marcucci, Paolo Marsan, and Giuliano Milana. "Strong Motion Records of the 2002 Molise, Italy, Earthquake Sequence and Stochastic Simulation of the Main Shock." Earthquake Spectra 20, no. 1_suppl (July 2004): 65–79. http://dx.doi.org/10.1193/1.1764784.
Abstract:
The far field radiation inferred from accelerometric data recorded by the Italian Strong Motion Network (RAN) during the October 31, 2002, Molise, Italy, earthquake indicates a strong anisotropy in PGA distribution that presents its maximum values in the eastern part of the epicentral area. This study explores an interpretation of source directivity using a stochastic approach to produce synthetic seismograms accounting for source dimensions and rupture evolution. An E-W strike-slip fault, with a dip close to 90° and a fault plane size of (8×6) km2, reproduces satisfactorily both peak accelerations and spectral shapes of the recorded data when the rupture enucleates from the western edge at a depth of about 20 km and propagates eastward. This approach allows us to put constraints on seismic source characteristics and can be used to simulate ground motion for the most damaged areas where strong motion data are not available.
37
Semak, Matthew R., Jeremiah Schwartz, and Gary Heise. "Examining Human Unipedal Quiet Stance: Characterizing Control through Jerk." Computational and Mathematical Methods in Medicine 2020 (January 4, 2020): 1–15. http://dx.doi.org/10.1155/2020/5658321.
Abstract:
We investigated the quality of smoothness during human unipedal quiet stance. Smoothness is quantified by the time rate of change of the accelerations, or jerks, associated with the motion of the foot and can be seen as an indicative of how controlled the balance process is. To become more acquainted with this as a quantity, we wanted to establish whether or not it can be modeled as a (stationary) stochastic process and, if so, explore its temporal scaling behavior. Specifically, our study focused on the jerk concerning the center-of-pressure (COP) for each foot. Data were collected via a force plate for individuals attempting to maintain upright posture using one leg (with eyes open). Positive tests for stochasticity allowed us to treat the time series as a stochastic process and, given this, we took the jerk to be proportional to the increment of the force realizations. Detrended fluctuation analysis was the primary tool used to explore the scaling behavior. Results suggest that both the medial-lateral and anterior-posterior components of the jerk display persistent and antipersistent correlations which can be modeled by fractional Gaussian noise over three different temporal scaling regions. Finally, we discussed certain possible implications of these features such as a jerk-based control over the force on the foot’s COP.
38
Decký, Martin, Matúš Kováč, and Peter Kotek. "The Comparison of Measured and Simulated Dynamic Responses of Vehicles Indicated by Road Pavement Unevenness." Civil and Environmental Engineering 11, no. 1 (May 1, 2015): 10–20. http://dx.doi.org/10.1515/cee-2015-0002.
Abstract:
Abstract The article presents the comparison of measured and simulated dynamic responses of heavy vehicle which are indicated by road pavement unevenness. This unevenness was represented by speed control bumps, potholes and stochastic pavement unevenness. The objective simulations were realized through the medium Quarter- Car Simulation by means of application of simulated theory of dynamic systems. The reliability of used model was verificated with comparison of measured and simulated values of sprung mass T815 vehicle accelerations. In the article, there are presented courses of total vertical forces of Quarter-Car Simulation for the first, the second and the fourth classification degree of unevenness, which was considered through the world's respected parameter IRI (International Roughness Index). Obtained simulated dynamic effects of the vehicle on the pavement were used for modification of a relevant Slovak design method of asphalt pavements.
39
Kvåle, Knut Andreas, and Ole Øiseth. "Dynamic Response of an End-Supported Pontoon Bridge due to Wave Excitation: Numerical Predictions versus Measurements." Shock and Vibration 2021 (May 31, 2021): 1–18. http://dx.doi.org/10.1155/2021/8842812.
Abstract:
Herein, numerical predictions of the dynamic response of an existing floating pontoon bridge are compared with the measured dynamic response. Hydrodynamic coefficients that describe the fluid-structure interaction and the wave transfer functions are obtained by applying linear potential theory. The results obtained from the hydrodynamic analysis are combined with a beam model of the bridge in a finite element method (FEM) framework to enable stochastic response prediction through the power spectral density method. The standard deviations of the predicted accelerations are compared with the standard deviations of the measured accelerations, and the overall quality of the prediction model is discussed. Predictions with sea states related to the serviceability limit state (SLS) and ultimate limit state (ULS) conditions used in design of the bridge are emphasized. To investigate the behaviour more in depth, a measurement segment is chosen and predictions of the displacement response power spectral density due to excitation characterized by the recorded sea surface elevation are compared with those obtained from the corresponding response measurements. A decent agreement is obtained for both cases when using the model as it is and with waves as the only excitation source, but significant discrepancies are present, in particular, for the torsional components. By including preliminary contributions from wind action and relying on a model optimized against measured modal parameters, a satisfactory agreement is obtained. The effect on the response of an uncertain structural damping is also quantified and concluded to be significant within realistic damping levels.
40
Wang, Yen Po, Yi Ting Lin, and Gang Huang. "Damage Localization of Output-Only Frame Systems Using Stochastic Subspace Identification." Advanced Materials Research 446-449 (January 2012): 1352–59. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.1352.
Abstract:
Assurance of integrity of structures is the main task of structural health monitoring. The condition (health) of a structure may be revealed from its dynamic characteristics in response to natural or man-made loads. As the measurement of the natural or operating forces on actual real-life structures is generally formidable, dynamic characteristics of the structures have to be extracted from the available output signals only. The stochastic subspace identification (SSI) technique is adopted in this study to identify the equivalent system parameters of the discrete-time state equation using covariance functions of the measured output signals. With the system parameters realized, the method of damage locating vector (DLV) is then considered for further assessment. Members with nearly zero stress under the loadings of DLVs are considered potentially damaged, whereas the DLVs are derived from singular value decomposition of the change in flexibility matrix of the structure before and after the damage state. In this study, the feasibility of DLV method for damage detection of a planar structure is explored based on its seismic responses. To comply with the desired output-only scenario, the information of ground motion is discarded in the stage of SSI analysis. Despite the non-stationary nature of earthquakes, the proposed scheme has been proved sufficient for damage localization of structures from global responses (floor accelerations). The damaged locations can be identified when the structure is fully observed, regardless of single or multiple damages. In the case of partial but co-located observation (damaged floors observed), the damaged locations can still be identified with acceptable accuracy and reliability.
41
ALBEVERIO, SERGIO, and WOLFGANG ALT. "STOCHASTIC DYNAMICS OF VISCOELASTIC SKEINS: CONDENSATION WAVES AND CONTINUUM LIMITS." Mathematical Models and Methods in Applied Sciences 18, supp01 (August 2008): 1149–91. http://dx.doi.org/10.1142/s0218202508002991.
Abstract:
Skeins (one-dimensional queues) of migrating birds show typical fluctuations in swarm length and frequent events of "condensation waves" starting at the leading bird and traveling backward within the moving skein, similar to queuing traffic waves in car files but more smooth. These dynamical phenomena can be fairly reproduced by stochastic ordinary differential equations for a "multi-particle" system including the individual tendency of birds to attain a preferred speed as well as mutual interaction "forces" between neighbors, induced by distance-dependent attraction or repulsion as well as adjustment of velocities. Such a one-dimensional system constitutes a so-called "stochastic viscoelastic skein." For the simple case of nearest neighbor interactions we define the density between individualsu = u(t, x) as a step function inversely proportional to the neighbor distance, and the velocity function v = v(t, x) as a standard piecewise linear interpolation between individual velocities. Then, in the limit of infinitely many birds in a skein of finite length, with mean neighbor distance δ converging to zero and after a suitable scaling, we obtain continuum mass and force balance equations that constitute generalized nonlinear compressible Navier–Stokes equations. The resulting density-dependent stress functions and viscosity coefficients are directly derived from the parameter functions in the original model. We investigate two different sources of additive noise in the force balance equations: (1) independent stochastic accelerations of each bird and (2) exogenous stochastic noise arising from pressure perturbations in the interspace between them. Proper scaling of these noise terms leads, under suitable modeling assumptions, to their maintenance in the continuum limit δ → 0, where they appear as (1) uncorrelated spatiotemporal Gaussian noise or, respectively, (2) certain spatially correlated stochastic integrals. In both cases some a priori estimates are given which support convergence to the resulting stochastic Navier–Stokes system. Natural conditions at the moving swarm boundaries (along characteristics of the hyperbolic system) appear as singularly perturbed zero-tension Neumann conditions for the velocity function v. Numerical solutions of this free boundary value problem are compared to multi-particle simulations of the original discrete system. By analyzing its linearization around the constant swarm state, we can characterize several properties of swarm dynamics. In particular, we compute approximating values for the averaged speed and length of typical condensation waves.
42
Liang, Jinfan, Xun Huang, Qiwang Xu, Yu Liu, Jingfan Zhang, and Jie Huang. "A Novel UAV-Assisted Multi-Mobility Channel Model for Urban Transportation Emergency Communications." Electronics 12, no. 14 (July 9, 2023): 3015. http://dx.doi.org/10.3390/electronics12143015.
Abstract:
With the increasing requirements for unmanned aerial vehicle (UAV) communication in various application scenarios, the UAV-assisted emergency communication in urban transportation scenario has received great attention. In this paper, a novel UAV-assisted UAV-to-vehicle (U2V) geometry-based stochastic model (GBSM) for the urban traffic communication scenario is proposed. The three-dimensional (3D) multi-mobilities of the transmitter (Tx), receiver (Rx), and clusters are considered by introducing the time-variant acceleration and velocity correspondingly. The velocity variation of the clusters is used to simulate the motion of vehicles around the Rx. Moreover, to describe the vehicles’ moving states, Markov chain is adopted to analyze the changes in cluster motion states, including survival, death, dynamic, and static states. By adjusting the scenario-specific parameters, such as the vehicle density (ρ) and dynamic–static ratio (Ω), the model can support various urban traffic scenarios. Based on the proposed model, several key statistical properties, namely the root mean square (RMS) delay spread, temporal autocorrelation function (ACF), level-crossing rate (LCR), power delay profile (PDP), and stationary interval, under different clusters and antenna accelerations are obtained and analyzed. The accuracy of the proposed model is verified by the measured data. The results demonstrate the usability of our model, which can be provided as a reference for the design, evaluation, and optimization of future communication networks between UAV and vehicles in urban transportation emergency communications.
43
Astakhov, Sergei, and Vasily Biryukov. "Stochastic Mechanism of Shock Disturbances of Rocket Sleigh Supports during High-Speed Track Testing of Aviation Equipment." E3S Web of Conferences 446 (2023): 01005. http://dx.doi.org/10.1051/e3sconf/202344601005.
Abstract:
Tests of ballistic aircraft on rail tracks in conditions close to real ones are an economically viable alternative to flight tests. Rocket rail tracks exist in the USA, Canada, France, China and a number of other countries. The article con-siders potentially self-oscillating mechanical systems that have a threshold mechanism for the transition from a noise vibrational stable state to a self-oscillatory one, depending on the mode parameters. An algorithm for estimating the damping coefficient of the harmonic components of a particular mode of a complex process is proposed. As an indicator of energy loss of the oscillatory component during resonant interaction, the value of the density of the power spectrum related to the width of the frequency range is taken. Based on the solution of the Fokker-Planck equation for a stochastic process, estimates of the “drift” and “diffusion” coefficients are obtained. A technique for estimating the state of potentially self-oscillatory systems in the form of a set of probabilistic stochastic characteristics is proposed. According to the experimental data of vibration accelerations for the structural elements of the rocket sled with the test object, according to the proposed method, it is possible to make the contribution of the self-oscillations of the elements, if they are pre-sent in a complex vibration process, and also to make estimates of their vibration strength at resonances.
44
Liang, Wei, Jin Huang, Jie Zhang, Xiaodong Tang, and Youran Zhang. "Reconstruction of vibration-deformation-induced pointing error via optimized acceleration measurement points for large reflector antennas." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, no. 10 (December 20, 2018): 3417–28. http://dx.doi.org/10.1177/0954406218818609.
Abstract:
As large reflector antennas have a low natural frequency and primarily operate in open air without a radome, factors such as the stochastic wind disturbance and the moving platform obviously increase the vibration-deformation pointing error. Moreover, in the actual working operation of large reflector antennas, the traditional measurement method can only sense the pointing error at the hinge via encoders and cannot sense the vibration-deformation-induced pointing error of the main reflector. This paper presents a reconstruction method of the vibration-deformation-induced pointing error for the main reflector via optimized acceleration measurement points. First, an entire working condition model of the main reflector for vibration-deformation-induced pointing error observation is established to provide the general relations among the acceleration, location, number of measurement points, and vibration-deformation-induced pointing error. In this model, the vibration-deformation-induced pointing error is reconstructed based on the best-fitting paraboloid theory and the frequency-domain integration approach. Furthermore, a Tikhonov regularization scheme is adopted to mitigate the ill-posedness due to random noise in the measured accelerations. Second, to obtain a well-reconstructed vibration-deformation-induced pointing error with certain accuracy, this study proposes a novel four-symmetric-point dynamic optimization algorithm for optimization of the sensor layout is proposed. Finally, a wind disturbance simulation of a 7.3 m antenna is undertaken. The results show that under the accuracy constraint of 5%, a well-reconstructed vibration-deformation-induced pointing error is obtained from the 20 optimized measurement points. Compared with the effective independence method, four-symmetric-point dynamic optimization algorithm has higher precision in observing the vibration-deformation-induced pointing error and is more convenient for arranging the sensors.
45
Marzbanrad, Javad, Goodarz Ahmadi, Yousef Hojjat, and Hassan Zohoor. "Optimal Active Control of Vehicle Suspension System Including Time Delay and Preview for Rough Roads." Journal of Vibration and Control 8, no. 7 (July 2002): 967–91. http://dx.doi.org/10.1177/107754602029586.
Abstract:
An optimal preview control of a vehicle suspension system traveling on a rough road is studied. A three-dimensional seven degree-of-freedom car-riding model and several descriptions of the road surface roughness heights, including haversine (hole/bump) and stochastic filtered white noise models, are used in the analysis. It is assumed that contact-less sensors affixed to the vehicle front bumper measure the road surface height at some distances in the front of the car. The suspension systems are optimized with respect to ride comfort and road holding preferences including accelerations of the sprung mass, tire deflection, suspension rattle space and control force. The performance and power demand of active, active and delay, active and preview systems are evaluated and are compared with those for the passive system. The results show that the optimal preview control improves all aspects of the vehicle suspension performance while requiring less power. Effects of variation of preview time and variations in the road condition are also examined.
46
Lebedev, Anatoliy, Mykhailo Shuliak, and Andriy Stelmakh. "ANALYSIS OF METHODS AND DEVICES FOR EVALUATION OF THE TRACTION PROPERTIES TRACTOR." Bulletin of the National Technical University «KhPI». Series: Automobile and Tractor Construction, no. 2 (March 19, 2023): 108–17. http://dx.doi.org/10.20998/2078-6840.2022.2.12.
Abstract:
The article presents analysis of the methods and means of evaluating of the traction properties tractor. In the previous researches, it was propose to evaluate of the traction properties tractor on their supporting-coupling properties without taking into account the stochastic modes of exploitation and modes of operation. Experimental methods of definitions the traction of tractor require conducting a large number of experiments. Therefore, it is necessary to carry out an analysis of the methods and the means of improving the results of the definitions of the traction of tractor and justify ways to increase the speed of their implementation The conducted analysis made it possible to justify, that method evaluating the traction properties of tractor on the measurement of its accelerations on moving is the best method. Based on the results of experimental research, a conclusion was made about the need for a theoretical research of the effectiveness of tractor ballasting.
47
Wang, Yanzhi, Zheng Zhan, Liang Zhao, Jian Tang, Siyue Wang, Jiayu Li, Bo Yuan, Wujie Wen, and Xue Lin. "Universal Approximation Property and Equivalence of Stochastic Computing-Based Neural Networks and Binary Neural Networks." Proceedings of the AAAI Conference on Artificial Intelligence 33 (July 17, 2019): 5369–76. http://dx.doi.org/10.1609/aaai.v33i01.33015369.
Abstract:
Large-scale deep neural networks are both memory and computation-intensive, thereby posing stringent requirements on the computing platforms. Hardware accelerations of deep neural networks have been extensively investigated. Specific forms of binary neural networks (BNNs) and stochastic computing-based neural networks (SCNNs) are particularly appealing to hardware implementations since they can be implemented almost entirely with binary operations.
Despite the obvious advantages in hardware implementation, these approximate computing techniques are questioned by researchers in terms of accuracy and universal applicability. Also it is important to understand the relative pros and cons of SCNNs and BNNs in theory and in actual hardware implementations. In order to address these concerns, in this paper we prove that the “ideal” SCNNs and BNNs satisfy the universal approximation property with probability 1 (due to the stochastic behavior), which is a new angle from the original approximation property. The proof is conducted by first proving the property for SCNNs from the strong law of large numbers, and then using SCNNs as a “bridge” to prove for BNNs. Besides the universal approximation property, we also derive an appropriate bound for bit length M in order to provide insights for the actual neural network implementations. Based on the universal approximation property, we further prove that SCNNs and BNNs exhibit the same energy complexity. In other words, they have the same asymptotic energy consumption with the growth of network size. We also provide a detailed analysis of the pros and cons of SCNNs and BNNs for hardware implementations and conclude that SCNNs are more suitable.
48
Pavlenko, V. A., and O. V. Pavlenko. "Stochastic Simulation and Development of the Ground Motion Prediction Equation for the Baikal Rift Zone." Физика земли 2023, no. 1 (January 1, 2023): 54–66. http://dx.doi.org/10.31857/s0002333723010039.
Abstract:
To obtain realistic and correct estimates of seismic effects in the Baikal Rift Zone (BRZ), a ground motion prediction equation has been developed based on the records of local earthquakes (magnitudes mb ~ 3.4–5.5, hypocentral distances R ~ 15–220 km) obtained by Ulan-Ude and Severomuisk seismic stations. At the first step, in our previous works, using stochastic simulation of the accelerograms of the recorded local earthquakes we estimated the regional parameters of radiation and propagation of seismic waves (stress drop in an earthquake source, quality function of the medium, geometrical spreading, wave attenuation at high frequencies, local site amplification, etc. These parameters were then used to generate a set of earthquake accelerograms over a wide range of magnitudes (Mw ~ 4.0–8.0) and distances (R ~ 1–200 km) on a rock site, and a ground motion prediction equation (GMPE) describing the dependence of peak ground accelerations (PGA) and peak ground velocities (PGV) on magnitude and distance are constructed. The obtained PGA estimates are compared with those estimated from GMPE recommended for BRZ by the international Global Earthquake Model (GEM) project. The scatter of the estimates obtained based on GEM GMPE indicates the relevance of developing the own GMPEs for Russian regions based on the records of local earthquakes. The GMPE derived in this work can be used for seismic hazard assessment in the BRZ eastern part and will be updated as new data are acquired.
49
Ma, C. F., Y. H. Zhang, P. Tan, and F. L. Zhou. "Seismic Response of Base-Isolated High-Rise Buildings under Fully Nonstationary Excitation." Shock and Vibration 2014 (2014): 1–11. http://dx.doi.org/10.1155/2014/401469.
Abstract:
Stochastic seismic responses of base-isolated high-rise buildings subjected to fully nonstationary earthquake ground motion are computed by combining the pseudoexcitation and the equivalent linearization methods, and the accuracy of results obtained by the pseudoexcitation method is verified by the Monte Carlo method. The superstructure of a base-isolated high-rise building is represented by a finite element model and a shear-type multi-degree of freedom model, respectively. The influence of the model type and the number of the modes of the superstructure participating in the computation of the dynamic responses of the isolated system has been investigated. The results of a 20-storey, 3D-frame with height to width ratio of 4 show that storey drifts and absolute accelerations of the superstructure for such a high-rise building will be substantially underestimated if the shear-type multi-degree of freedom model is employed or the higher modes of the superstructure are neglected; however, this has nearly no influence on the drift of the base slab.
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Çavdar, Ö. "Probabilistic sensitivity analysis of two suspension bridges in Istanbul, Turkey to near- and far-fault ground motion." Natural Hazards and Earth System Sciences 12, no. 2 (February 28, 2012): 459–73. http://dx.doi.org/10.5194/nhess-12-459-2012.
Abstract:
Abstract. The aim of this paper is to compare the near-fault and far-fault ground motion effects on the probabilistic sensitivity dynamic responses of two suspension bridges in Istanbul. Two different types of suspension bridges are selected to investigate the near-fault (NF) and far-fault (FF) ground motion effects on the bridge sensitivity responses. NF and FF strong ground motion records, which have approximately identical peak ground accelerations, of the Kocaeli (1999) earthquake are selected for the analyses. Displacements and internal forces are determined using the probabilistic sensitivity method (PSM), which is one type of stochastic finite element method. The efficiency and accuracy of the proposed algorithm are validated by comparison with results of the Monte Carlo Simulation (MCS) method. The displacements and internal forces obtained from the analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that there is more seismic demand on displacements and internal forces when suspension bridges are subjected to NF and FF ground motion.