Comprehensive Simulation Method on Shrinkage and Creep Effects of Concrete in Structures of Bridges during Whole Time-Varying Process

2021 ◽  
Vol 15 (3) ◽  
pp. 20-29
Author(s):  
Long-fei Wang
Keyword(s):  
Simulation Method ◽  
Time Varying ◽  
Shrinkage And Creep

scholarly journals Study on hydration heat of concrete channel-box girder

2020 ◽  
pp. 257-257
Author(s):  
Xiangnan Xiao ◽  
Yunyong Peng ◽  
Guijun Luo
Keyword(s):  
Tensile Strength ◽  
Temperature Field ◽  
Casting Process ◽  
Hydration Heat ◽  
Time Varying ◽  
Bridge Structure ◽  
Box Girder ◽  
Simply Supported ◽  
Concrete Shrinkage ◽  
Shrinkage And Creep

Temperature is one of the important reasons causing the cracks on the bridge structure during the construction and operation. In this paper, the temperature field produced by hydration heat and early thermal stress of a 64m simply supported channel-box girder are simulated during casting process, considering the time-varying characteristics of concrete shrinkage and creep, elastic modulus and tensile strength. Then, various parameters influencing the temperature field are analyzed, and the corresponding measures of controlling temperature cracks are proposed.

Incorporating the Time-Varying Tail-Fatness into the Historical Simulation Method for Portfolio Value-at-Risk

2006 ◽  
Vol 09 (02) ◽  
pp. 257-274 ◽  
Author(s):  
Chu-Hsiung Lin ◽  
Chang-Cheng Chang Chien ◽  
Sunwu Winfred Chen
Keyword(s):  
At Risk ◽  
Value At Risk ◽  
Moving Average ◽  
Simulation Method ◽  
Estimation Accuracy ◽  
Time Varying ◽  
Historical Simulation ◽  
Extreme Risk ◽  
Weighted Moving Average

This study extends the method of Guermat and Harris (2002), the Power EWMA (exponentially weighted moving average) method in conjunction with historical simulation to estimating portfolio Value-at-Risk (VaR). Using historical daily return data of three hypothetical portfolios formed by international stock indices, we test the performance of this modified approach to see if it can improve the precise forecasting capability of historical simulation. We explicitly highlight the extended Power EWMA owns privileged flexibilities to capture time-varying tail-fatness and volatilities of financial returns, and therefore may promote the quality of extreme risk management. Our empirical results, derived from the Kupiec (1995) tests and failure ratios, show that our proposed method indeed offers substantial improvements on capturing dynamic returns distributions, and can significantly enhance the estimation accuracy of portfolio VaR.

A Simulation Method to Estimate Two Types of Time-Varying Failure Rate of Dynamic Systems

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Zhonglai Wang ◽  
Xiaoqiang Zhang ◽  
Hong-Zhong Huang ◽  
Zissimos P. Mourelatos
Keyword(s):  
Failure Rate ◽  
Dynamic Systems ◽  
Saddlepoint Approximation ◽  
Simulation Method ◽  
Copula Function ◽  
Type I ◽  
Time Varying ◽  
Type Ii ◽  
Time Intervals ◽  
Function Type

The failure rate of dynamic systems with random parameters is time-varying even for linear systems excited by a stationary random input. In this paper, we propose a simulation-based method to estimate two types (type I and type II) of time-varying failure rate of dynamic systems. The input stochastic processes are discretized in time and the trajectories of the output stochastic process are calculated. The time of interest is partitioned into a series of time intervals and the saddlepoint approximation (SPA) is employed to estimate the probability of failure in each interval. Type I follows the commonly used definition of failure rate. It is estimated at discrete time intervals using SPA and the correlation information from a properly selected time-dependent copula function. Type II is a proposed new concept of time-varying failure rate. It provides a way to predict the failure rate considering a virtual “good-as-old” repair action of repairable dynamic systems. The effectiveness of the proposed method is illustrated with a vehicle vibration example.

scholarly journals Fully Nonstationary Spatially Variable Ground Motion Simulations Based on a Time-Varying Power Spectrum Model

2014 ◽  
Vol 2014 ◽  
pp. 1-10
Author(s):  
Huiguo Chen ◽  
Yingmin Li ◽  
Junru Ren
Keyword(s):  
Power Spectrum ◽  
Ground Motion ◽  
Response Spectrum ◽  
Power Spectra ◽  
Response Spectra ◽  
Simulation Method ◽  
Time Varying ◽  
Time Frequency ◽  
Response Characteristics ◽  
Spectrum Model

By analyzing the evolutionary spectrum method for multivariate nonstationary stochastic processes, a simulation method for fully nonstationary spatially variable ground motion is proposed based on the Kameda time-varying power spectrum model. This method can properly simulate nonstationary spatially variable ground motion based on a target response spectrum. Two numerical examples, in which the Kameda time-varying power spectra are calculated for different conditions, are presented to demonstrate the capabilities of the proposed method. In the first example, the nonstationary spatially variable ground motion that satisfies the time-frequency characteristics and response characteristics of the original ground motion is simulated by identifying the parameters of the given time-varying power spectrum. In the second example, the ground motion that satisfies the design response spectra is simulated by defining the parameters of the time-varying power spectrum directly. The results demonstrate that the method can effectively simulate nonstationary spatially variable ground motion, which implies that the proposed method can be used in engineering applications.

Transient Analysis of a Flexible Pin-on-Disk System and Its Application to the Research Into Time-Varying Squeal

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Lijun Zhang ◽  
Jun Wu ◽  
Dejian Meng
Keyword(s):  
Harmonic Wave ◽  
Frictional Coefficient ◽  
Low Frequency ◽  
Simulation Method ◽  
Time Varying ◽  
Disk System ◽  
Leading Role ◽  
Deformation Features ◽  
Coupling Mode ◽  
Pin On Disk

In this paper, a flexible pin-on-disk system is used to simulate how squeal noise can be generated in frictional contact. As the research object, the modeling process and transient simulation method of the flexible pin-on-disk system are introduced. By means of numerical simulation, the time-varying frictional squeal reappears by introducing periodic frictional coefficient generated from rotation. Afterward, the features of time-varying squeal are studied including time-domain features, frequency-domain features, transient deformation features of the disk and the pin on the occurrence of squeal, as well as energy features. Finally, the conception and mathematical expressions of modal contribution factor are defined, and the transient modal contribution factor features of every mode are studied to make clear the function of every mode. The relationship between mode contribution factors and the vibration is revealed. It reveals that modal contribution factors between squeal and not are quite different from each other. On no occurrence of squeal, the modal contribution factors of sine and cosine modes of the disk fluctuate in the way similar to harmonic wave, and the phase difference between the contribution factors of sine and cosine mode with the same nodal circle and the same nodal diameter is 90 deg. During squeal, the coupling mode may play the most important role but not all the time. At any time, the low-frequency modes play the leading role.

scholarly journals Time-Dependent Reliability Modeling and Analysis Method for Mechanics Based on Convex Process

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Lei Wang ◽  
Xiaojun Wang ◽  
Ruixing Wang ◽  
Xiao Chen
Keyword(s):  
Monte Carlo ◽  
Product Life Cycle ◽  
Process Model ◽  
Limit State ◽  
Simulation Method ◽  
Time Dependent ◽  
Structural Safety ◽  
Time Varying ◽  
Modeling And Analysis ◽  
Convex Process

The objective of the present study is to evaluate the time-dependent reliability for dynamic mechanics with insufficient time-varying uncertainty information. In this paper, the nonprobabilistic convex process model, which contains autocorrelation and cross-correlation, is firstly employed for the quantitative assessment of the time-variant uncertainty in structural performance characteristics. By combination of the set-theory method and the regularization treatment, the time-varying properties of structural limit state are determined and a standard convex process with autocorrelation for describing the limit state is formulated. By virtue of the classical first-passage method in random process theory, a new nonprobabilistic measure index of time-dependent reliability is proposed and its solution strategy is mathematically conducted. Furthermore, the Monte-Carlo simulation method is also discussed to illustrate the feasibility and accuracy of the developed approach. Three engineering cases clearly demonstrate that the proposed method may provide a reasonable and more efficient way to estimate structural safety than Monte-Carlo simulations throughout a product life-cycle.

scholarly journals Dynamics Simulation of Stirling Engine for Solar Energy Based on the Time-Varying Support Stiffness

2014 ◽  
Vol 8 (1) ◽  
pp. 710-715
Author(s):  
Junzhou Huo ◽  
Hanyang Wu ◽  
Jing Chen
Keyword(s):  
Damping Ratio ◽  
Simulation Method ◽  
Stirling Engine ◽  
Output Shaft ◽  
Dynamics Simulation ◽  
Time Varying ◽  
Vibration Displacement ◽  
Constant Stiffness ◽  
Simulation Results ◽  
Stiffness And Damping

In order to simulate the Stirling engine more easily, the stiffness and damping ratio of the crankshaft bearing are assumed to be steady-state in the research before, but this assumption is contrary to the real condition. Therefore, in this paper, a time-varying stiffness and damping ratio of the crankshaft bearing simulation method has been proposed. Compared with the simulation results of the crankshaft bearings with constant stiffness, the speed fluctuation coefficient of output shaft and crankshaft in time-varying stiffness model is increased by 10%, 24.6% and 13.7%; the vibration displacement of the center mass of output shaft is decreased by 3.0%; the average dynamic load on airframe is increased by 47.9%. From the simulation results, it is found that the time-varying stiffness and damping ratio of the crankshaft bearing is significant to the characteristics of the Stirling engine dynamic response.

A NOVEL DRIVING STRATEGY FOR DYNAMIC SIMULATION OF HOISTING ROPE WITH TIME-VARYING LENGTH

2013 ◽  
Vol 04 (03) ◽  
pp. 1350009 ◽  
Author(s):  
JINJIE WANG ◽  
GUOHUA CAO ◽  
YANDONG WANG ◽  
RONGHUA WU
Keyword(s):  
Equations Of Motion ◽  
Simulation Method ◽  
Time Varying ◽  
Concentrated Mass ◽  
Lagrange’S Equation ◽  
Simulation Efficiency ◽  
Runge Kutta Method ◽  
Adams Simulation ◽  
Varying Length ◽  
Hoisting System

A simulation method for investigating the vibration behavior of hoisting rope with time-varying length is improved. By previously creating markers in the MSC.ADAMS software package, the parametric model of the rope wound along helix is established based on the concentrated-mass theory with multi-degree of freedom (multi-DOF). A novel driving strategy, cooperating fixed joints with angle sensors under the control of driving script, is proposed to substitute conventional contact force. Researching on the hoisting rope in the sinking winch mechanism, an equivalent discretization model is obtained with complicated boundary conditions considered. The differential equations of motion of the hoisting system are formulated employing Lagrange's equation and numerically solved using Runge–Kutta method. The simulation indicates that the horizontal swing is decreased in principle and the simulation with 800 discrete ropes is not performed more than 61 min. Therefore, this feasible strategy could not only guarantee the accuracy but also promote simulation efficiency and stability. The motion curves exported from ADAMS simulation coincide with one in numerical simulation, which validates both the numerical model and the driving strategy.

A Simulation Method to Estimate the Time-Varying Failure Rate of Dynamic Systems

2014 ◽  
Author(s):  
Zhonglai Wang ◽  
Xiaoqiang Zhang ◽  
Hong-Zhong Huang ◽  
Zissimos P. Mourelatos
Keyword(s):  
Failure Rate ◽  
Dynamic Systems ◽  
Saddlepoint Approximation ◽  
Planning Horizon ◽  
Simulation Method ◽  
Probability Of Failure ◽  
Small Time ◽  
Time Interval ◽  
Time Varying ◽  
Time Step

The failure rate of dynamic systems with random parameters is time-varying even for linear systems excited by a stationary random input. In this paper, we propose a simulation-based method to estimate this time-varying failure rate. The input and output stochastic processes are discretized using a small time step to calculate the trajectories of the output stochastic process accurately through simulation. The planning horizon (time of interest) is then partitioned into a series of longer correlated time intervals and the Saddlepoint approximation (SPA) is employed to estimate the distribution of maximum response and thus obtain the probability of failure in each time interval. Using the same simulated trajectories with SPA, a time-dependent copula is built to provide the correlation between the response in each time interval and the response up to that time interval. The time-varying failure rate is finally estimated at each discrete time, using the probability of failure in each time interval and the correlation information from the estimated copula. The effectiveness of the proposed method is illustrated with a vehicle vibration example.

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