Prediction Of Dynamic Response Research Articles

NEURAL NETWORK-BASED PREDICTION OF CARDIOVASCULAR RESPONSE DUE TO THE GRAVITATIONAL EFFECTS

It is well-documented in the literature that the orthostatic stress during flight maneuvers induces changes in pilots' cardiovascular system by imposing dramatic changes to the blood circulation process. Research reported for prediction of cardiovascular system dynamic response during G-transition is limited. As such, more models are needed to gain insight into the behavior of cardiovascular response during G-transition. Therefore, the objective of this paper is to develop two novel models based on: (1) artificial neural network (ANN) and (2) adaptive-network-based fuzzy inference system (ANFIS) to predict the variations of the blood pressure (BP) with respect to flight maneuver's parameters, i.e., dwell time, during G-transitions. The proposed models will be used to provide operational recommendations and pilot selection for any routinepredefined flight maneuver. The training data for ANN and ANFIS are based on experimental data sets collected from a man-rated electronic tilt table that applies gigahertz-acceleration transition from +0.861 Gz (head-up (HU)) to -0.767Gz (head-down (HD)) and back to +0.861 Gz (HU) using either pitch or roll rotation. A case study is presented on how the model is intended to be used in future to predict pilot's cardiovascular response and evaluate the pilot's qualification for a specific maneuver.

The effect of loading time on flexible pavement dynamic response: a finite element analysis

Dynamic response of asphalt concrete (AC) pavements under moving load is a key component for accurate prediction of flexible pavement performance. The time and temperature dependency of AC materials calls for utilizing advanced material characterization and mechanistic theories, such as viscoelasticity and stress/strain analysis. In layered elastic analysis, as implemented in the new Mechanistic-Empirical Pavement Design Guide (MEPDG), the time dependency is accounted for by calculating the loading times at different AC layer depths. In this study, the time effect on pavement response was evaluated by means of the concept of “pseudo temperature.” With the pavement temperature measured from instrumented thermocouples, the time and temperature dependency of AC materials was integrated into one single factor, termed “effective temperature.” Via this effective temperature, pavement responses under a transient load were predicted through finite element analysis. In the finite element model, viscoelastic behavior of AC materials was characterized through relaxation moduli, while the layers with unbound granular material were assumed to be in an elastic mode. The analysis was conducted for two different AC mixtures in a simplified flexible pavement structure at two different seasons. Finite element analysis results reveal that the loading time has a more pronounced impact on pavement response in the summer for both asphalt types. The results indicate that for reasonable prediction of dynamic response in flexible pavements, the effect of the depth-dependent loading time on pavement temperature should be considered.

Improvement of dynamic response prediction of helicopters

Purpose – This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters.

Effect of lateral impact loads on failure of pressurized pipelines supported by foundation

The dynamic inelastic response and failure prediction of pipelines under lateral mass impact at the mid-span position are presented in this article. A total of 52 impact tests were carried out on seamless mild steel pipes with different internal pressure levels and foundation supports. Critical initial impact energies were obtained for each group of pipe specimens with different internal pressure levels and foundation supports. Numerical simulations of the experimental tests were carried out using three-dimensional dynamic non-linear finite element analysis, where both geometrical and material non-linearities were considered. Good agreements were achieved between the impact tests results and the numerical predictions. It has been found that the influences of the internal pressure and the foundation on the critical initial impact energy are significant. The critical initial impact energy is much less sensitive to internal pressure for the pipes with a foundation than those without a foundation.

Determination of magnetic forces in tokamaks during axisymmetric plasma disruptions

Methods are developed to infer estimates of plasma parameters from measurements of the dynamic response (e.g. displacements and support forces at critical locations) of the structure of a tokamak undergoing plasma disruptions. Simplified lumped-parameter models, based upon dynamic finite element (FE) calculations, are used to describe the mechanical response of the structure of the JET tokamak to transient forces generated during axisymmetric disruptions. These are then used in dynamic simulations, driven by parametrically-represented magnetic forces, where parameters include amplitude, duration and point of application. Estimates for these parameters are then obtained by finding values, which give the best fit, in a statistical sense, between the model's predictions of dynamic response to the measured response of the structure. These methods can then be used to help guide mechanical design of new machines so that structural loadings remain tolerable throughout the operational envelope.

Comparison of frequency- and time-domain analyses for guyed masts in turbulent winds

Both frequency- and time-domain methods have been employed in the dynamic analysis of guyed telecommunication masts subjected to turbulent winds. Although the probabilistic frequency-domain approach offers some advantages in terms of its relative ease of implementation and in the statistical reliability of wind load descriptions, the deterministic time-domain method permits a more realistic treatment of system nonlinearities. In this study, a numerical investigation was undertaken to compare frequency- and time-domain dynamic response predictions for a selected guyed mast in gusty winds. Two different analysis techniques were employed, with the frequency-domain calculations performed using response influence lines and the time-domain analyses carried out using a stiffness-based finite element model. Good agreement was observed in root-mean-square and peak dynamic response estimates after compensation was included for differences in turbulence intensity levels assumed in the two models. In general, natural frequencies and mode shapes were also similar.Key words: guyed mast, dynamic analysis, wind, turbulence, nonlinear behaviour, finite element analysis, cables, frequency domain, time domain.

Time‐parallel implicit integrators for the near‐real‐time prediction of linear structural dynamic responses

AbstractThe time‐parallel framework for constructing parallel implicit time‐integration algorithms (PITA) is revisited in the specific context of linear structural dynamics and near‐real‐time computing. The concepts of decomposing the time‐domain in time‐slices whose boundaries define a coarse time‐grid, generating iteratively seed values of the solution on this coarse time‐grid, and using them to time‐advance the solution in each time‐slice with embarrassingly parallel time‐integrations are maintained. However, the Newton‐based corrections of the seed values, which so far have been computed in PITA and related approaches on the coarse time‐grid, are eliminated to avoid artificial resonance and numerical instability. Instead, the jumps of the solution on the coarse time‐grid are addressed by a projector which makes their propagation on the fine time‐grid computationally feasible while avoiding artificial resonance and numerical instability. The new PITA framework is demonstrated for a complex structural dynamics problem from the aircraft industry. Its potential for near‐real‐time computing is also highlighted with the solution of a relatively small‐scale problem on a Linux cluster system. Copyright © 2006 John Wiley & Sons, Ltd.

Natural Frequencies and Modal Damping Ratios Identification of Civil Structures from Ambient Vibration Data

Damping is a mechanism that dissipates vibration energy in dynamic systems and plays a key role in dynamic response prediction, vibration control as well as in structural health monitoring during service. In this paper a time domain and a time-scale domain approaches are used for damping estimation of engineering structures, using ambient response data only. The use of tests under ambient vibration is increasingly popular today because they allow to measure the structural response in service. In this paper we consider two engineering structures excited by ambient forces. The first structure is the 310 m tall TV tower recently constructed in the city of Nanjing in China. The second example concerns the Jinma cable-stayed bridge that connects Guangzhou and Zhaoqing in China. It is a single tower, double row cable-stayed bridge supported by 112 stay cables. Ambient vibration of each cable is carried out using accelerometers. From output data only, the modal parameter are extracted using a subspace method and the wavelet transform method.

Transient response of finned-tube condenser in household refrigerators

A distributed parameter model for prediction of the transient performance of a condenser is presented. The model is capable of predicting the refrigerant temperature distribution, tube wall temperature, quality of refrigerant, inventory mass of refrigerant as a function of position and time. An efficient two-level iteration method is proposed to obtain the numerical solution of the model without solving a large set of non-linear equations simultaneously. A finned tube condenser of 12 ft 3 refrigerator with R12 as working fluid was chosen as a sample and some tests were carried out to determine its transient response. The examination of results indicates that the theoretical model provides a reasonable prediction of dynamic response compared to the experimental data. Transient behavior of temperature, pressure, mass flow rate, mass of liquid and vapor of refrigerant, quality, heat transfer in household refrigerators have been presented. Also time-dependent displacement of interface between saturated and superheated regions has been shown. Extensive examinations of theoretical and experimental results show that with utilization of a controllable compressor, power consumption can be reduced.

Analytical modeling of the elastic structural response of tubes to internal detonation loading

The internal detonation loading of cylindrical shells involves loads that propagate at high speeds. Since the speed of the gaseous detonation can be comparable to the flexural-wave-group speed, the excitations of flexural waves in the tube wall become significant. Flexural waves can result in high strains, which may exceed the equivalent static strains (caused by the same nominal loading pressure) by up to a factor of 4. This paper presents a new analytical model for the transient elastodynamic structural response of cylindrical shells with finite length to internal detonation loading. It is shown that, due to the consideration of the effects of transverse shear and rotary inertia, the predictions of dynamic structural response of tubes provided by this model are in better agreement with the experimental results, than existing analytical models. The model is verified through comparison with experimental results reported in the literature.

Influence of Flux Creep on Dynamic Behavior of Magnetic Levitation Systems With a High-<tex>$T_c$</tex>Superconductor

Significant flux creep may be generated in some high-T/sub c/ superconductors with weak pinning, which could yield an influence on the dynamic behavior of a high-T/sub c/ superconductor-magnet levitation system. To investigate this influence, this article presents a numerical analysis of dynamic features of the levitation generated by an interaction between a high-T/sub c/ superconductor (HTSC) and a permanent magnet (PM) after the flux creep in the superconductor is taken into account in a macro-model of superconductivity. The influence is comprehensively displayed by comparing the predictions of dynamic responses of such systems in which the flux creep in the superconductor is and is not taken into account. The obtained results show that whether or not the flux creep results in a noticeable influence to the levitation of superconductor-magnet systems is mainly dependent upon properties of superconductivity and applied excitation, e.g., critical current density of superconductors, and amplitude and frequency of external excitations. When the critical current density is less than 4.5/spl times/10/sup 8/ A/m/sup 2/, and the system is subjected to a periodic excitation, the influence of flux creep should be taken into account in the theoretical analysis.

Dynamic analysis of composite plate with multiple delaminations based on higher-order zigzag theory

In a recent paper, Cho and Kim [Journal of Applied Mechanics] proposed a higher-order cubic zigzag theory of laminated composites with multiple delaminations. The proposed theory is not only accurate but also efficient because it work with a minimal number of degrees of freedom with the application of interface continuity conditions as well as bounding surface conditions of transverse shear stresses including delaminated interfaces. In this work, we investigate the dynamic behavior of laminated composite plates with multiple delaminations. A four-node finite element based on the efficient higher-order zigzag plate theory of laminated composite plates with multiple delaminations is developed to refine the prediction of frequencies, mode shape, and time response. Through the dynamic version of the variational approach, the dynamic equilibrium equations and variationally consistent boundary conditions are obtained. Natural frequency prediction and time response analysis of a composite plate with multiple delaminations demonstrate the accuracy and efficiency of the present finite element method. To prevent penetration violation at the delamination interfaces, unilateral contact constraints by Lagrange multiplier method are applied in the time response analysis. The present finite element is suitable for the prediction of dynamic response of thick composite plates with multiple and arbitrary shaped delaminations.

Numerical simulation of stochastic road process using white noise filtration

To carry out the dynamic response prediction of a vehicle subjected to excitation from a stochastic road in a time domain, it is necessary to simulate time series of road irregularities. Based on the frequency domain model, power spectral density (PSD) function of roads, this study focuses on regenerating the time domain model of roads by using a white noise filtration method, especially on the temporally and spatially correlative bilateral track model by taking the coherence between the road tracks into consideration. As a typical time series of road irregularity, the resulting model was theoretically discussed and numerically simulated. A numerical example showed that the method was highly efficient and accurate, even when very long sequences were simulated. Finally, several conclusions were drawn.

Experimental and analytical studies on dynamic characteristics of a large span cable-stayed bridge

An analytical and experimental modal analysis has been carried out on the Qingzhou cable-stayed bridge in Fuzhou, China. Its main span of 605 m is currently the longest span among the completed composite-deck cable-stayed bridges in the world. An analytical modal analysis is performed on the developed three-dimensional finite element model starting from the deformed configuration to provide the analytical frequencies and mode shapes. The field ambient vibration tests on the bridge deck and all stay cables were conducted just prior to the opening of the bridge. The output-only modal parameter identification is then carried out by using the peak picking of the average normalized power spectral densities in the frequency-domain and stochastic subspace identification in the time-domain. A good correlation is achieved between the finite element and ambient vibration test results. It is demonstrated that the analytical and experimental modal analysis provide a comprehensive study on the dynamic properties of the bridge. The ambient vibration tests are sufficient to identify the most significant modes below 1.0 Hz of this kind of large span cable-stayed bridge. The validated finite element model with respect to ambient vibration test results can serve as the baseline for a more precise dynamic response prediction and long-term health monitoring of the bridge.

Shaking table test and dynamic response prediction on an earthquake-damaged RC building

This paper presents the results from shaking table tests of a one-tenth-scale reinforced concrete (RC) building model. The test model is a protype of a building that was seriously damaged during the 1985 Mexico earthquake. The input ground excitation used during the test was from the records obtained near the site of the prototype building during the 1985 and 1995 Mexico earthquakes. The tests showed that the damage pattern of the test model agreed well with that of the prototype building. Analytical prediction of earthquake response has been conducted for the prototype building using a sophisticated 3-D frame model. The input motion used for the dynamic analysis was the shaking table test measurements with similarity transformation. The comparison of the analytical results and the shaking table test results indicates that the response of the RC building to minor and the moderate earthquakes can be predicated well. However, there is difference between the predication and the actual response to the major earthquake.

Statistical Linearization Model for the Response Prediction of Nonlinear Stochastic Systems Through Information Closure Method

A new linearization model with density response based on information closure scheme is proposed for the prediction of dynamic response of a stochastic nonlinear system. Firstly, both probability density function and maximum entropy of a nonlinear stochastic system are estimated under the available information about the moment response of the system. With the estimated entropy and property of entropy stability, a robust stability boundary of the nonlinear stochastic system is predicted. Next, for the prediction of response statistics, a statistical linearization model is constructed with the estimated density function through a priori information of moments from statistical data. For the accurate prediction of the system response, the excitation intensity of the linearization model is adjusted such that the response of maximum entropy is invariant in the linearization model. Finally, the performance of the present linearization model is compared and supported by employing two examples with exact solutions, Monte Carlo simulations, and Gaussian linearization method.

Transient response of dry expansion evaporator in household refrigerators

A distributed parameter model for prediction of the transient performance of an evaporator is presented. The model is capable of predicting the refrigerant temperature distribution, tube wall temperature, quality of refrigerant, inventory mass of refrigerant as a function of position and time. An efficient two-level iteration method is proposed to obtain the numerical solution of the model without solving a large set of non-linear equations simultaneously. A round bound evaporator of 12 ft3 refrigerator with R12 as working fluid were chosen as a sample and some tests were carried out to determine its transient response. The results indicate that the theoretical model provides a reasonable prediction of dynamic response compared with the experimental data. Transient behaviour of temperature, pressure, mass flow rate, mass of liquid and vapour of refrigerant, quality, heat transfer in household refrigerators have been presented. Also time dependent displacement of interface between saturated and superheated regions has been shown. Extensive investigation of theoretical and experimental results shows that with a controllable compressor, power consumption can be reduced.

An Original Definition of the Profile of Compliant Foil Journal Gas Bearings: Static and Dynamic Analysis

This article deals with a numerical analysis of the static and dynamic performance of a compliant journal gas bearing. The common approach found in foil bearing literature consists in calculating the carrying capacity for a given shaft position. In this study the external load is fixed (magnitude and direction) and the related shaft position is investigated. Nevertheless, a rigid profile, able to support high imposed loads, is no longer valid if one considers that the bearing becomes compliant. An original calculation method of the initial profile considering rigid surfaces is proposed to overcome this problem. The prediction of nonlinear dynamic behavior, i.e., stability and response to external excitation, is investigated. Finally, a viscous damping model is introduced into the dynamic model in order to obtain the amount of structural damping necessary to increase the stability of the compliant journal gas bearing.

The Steady-state Sinusoidal Dynamic Behaviour of Peach and Pear

Foods are frequently subjected to dynamic loading during harvesting, handling, transportation, and processing. Accurate prediction of dynamic responses of foods under these loading conditions requires better understanding of their dynamic visco-elastic properties. In this article, dynamic equilibrium was determined according to sinusoidal stress–strain. When a visco-elastic specimen is subjected to a sinusoidal varying stress, the resulting strain will be a sinusoidal response of the same frequency as the stress, out of phase by a lag angle. Experiments were conducted to measure the complex modulus of intact Daguanshan peaches and Luyu pears, the phase angle by which the strain lags the stress, and their relationship with initial pre-loading and vibration input power over a range of frequencies. Both the complex modulus and the phase angle increased as the frequency increased from 20 to 200 Hz. Initial pre-loading had a significant effect on the complex modulus, but not on the phase angle. Vibration input power had no significant effect on the complex modulus and phase angle. The phase angle depends not only on internal friction but also on the inertia of intact fruit.

Dynamic Analysis Of Slender Towers Made OfNo-tension Material With Limited CompressiveStrength

This paper deals with a simplified non-linear model of continuous cantilever beams that, while it can make it easier to represent the dynamic response of masonry columns and slender structures with simple geometry and flexural behaviour, is able to account for the main mechanical characteristics of the material. A non-linear elastic constitutive law is defined in terms of generalized stress and strain, assuming the material has no resistance to tension and has limited compressive strength, which has been formulated in previous work for rectangular cross-section beams and generalized, in the ongoing work, to the case of hollow rectangular sections, in order to study the dynamic behaviour of various types of towers, bell towers and similar structures. Therefore, this relationship has been used to develop a numerical method that allows one to analyse the non-linear dynamic behaviour of masonry isolated towers under multi-component earthquake excitations or different dynamic loads. Some numerical examples are presented in order to show: (i) the difference in prediction of dynamic response obtained by means of the developed model with respect to the linear elastic one, (ii) the influence of the material’s compressive strength on non-linear response, (iii) information provided by the model on damage spread in masonry structures.