Time-domain calculation method of improved hysteretic damped system based on frequency-dependent loss factor

2020 ◽  
Vol 488 ◽  
pp. 115658
Author(s):  
Panxu Sun ◽  
Hong Yang ◽  
Yin Zhao
Keyword(s):  
Time Domain ◽  
Calculation Method ◽  
Loss Factor ◽  
Frequency Dependent ◽  
Damped System

Frequency-Dependent Resistances and Inductances in Time-Domain Transient Simulations of Power Transformers

2019 ◽  
Vol 55 (9) ◽  
pp. 1-5
Author(s):  
Matthias K. Bucher ◽  
Thomas Franz ◽  
Michael Jaritz ◽  
Jasmin Smajic ◽  
Jens Tepper
Keyword(s):  
Time Domain ◽  
Power Transformers ◽  
Frequency Dependent ◽  
Transient Simulations

Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI

2008 ◽  
Author(s):  
Mansour Tabatabaie ◽  
Thomas Ballard
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Time Domain ◽  
Soil Structure ◽  
Wave Radiation ◽  
Far Field ◽  
Frequency Dependent ◽  
Nonlinear Springs ◽  
Mat Foundation ◽  
The Time Domain

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.

Application of a General Technique for Prediction of Riser Vortex-Induced Response in Waves and Current

1989 ◽  
Vol 111 (2) ◽  
pp. 82-91 ◽  
Author(s):  
G. J. Lyons ◽  
M. H. Patel
Keyword(s):  
Time Domain ◽  
Calculation Method ◽  
Prediction Method ◽  
Induced Response ◽  
Flow Properties ◽  
General Technique ◽  
Prediction Technique ◽  
Combined Action ◽  
Semi Empirical ◽  
Surface Vessel

This paper describes applications of an extension to a recently developed calculation method for vortex-induced response of risers and tethers. The vortex-induced vibration response for the excited modes is generated using a semi-empirical formulation which is applied within a time domain calculation. This makes it possible to take account of the variation of flow properties along the riser length, as well as in time. The calculation method has been verified by comparison with model test data for vortex-induced response to surface vessel motions in still water. This paper presents applications of the technique for vortex shedding due to the combined action of current, surface vessel motions and waves. The mathematics of the extended prediction technique is described and results are illustrated by presenting typical vortex-induced responses for single-tube risers. The results of the prediction method are used to highlight the relative magnitudes and nature of vortex-induced response excited by currents, surface vessel motions and waves.

A high order finite-difference scheme for time-domain modelling of time-varying seismoelectric waves

Geophysics ◽  
2021 ◽  
pp. 1-49
Author(s):  
Yanju Ji ◽  
Li Han ◽  
Xingguo Huang ◽  
Xuejiao Zhao ◽  
Kristian Jensen ◽  
...  
Keyword(s):  
Porous Media ◽  
Finite Difference ◽  
Time Domain ◽  
Calculation Method ◽  
High Order ◽  
Difference Approximation ◽  
Time Varying ◽  
Time Step ◽  
Static Approximation ◽  
High Order Finite Difference

Simulation of the seismoelectric effect serves as a useful tool to capture the observed seismoelectric conversion phenomenon in porous media, thus offering promising potential in underground exploration activities to detect pore fluids such as water, oil and gas. The static electromagnetic (EM) approximation is among the most widely used methods for numerical simulation of the seismoelectric responses. However, the static approximation ignores the accompanying electric field generated by the shear wave, resulting in considerable errors when compared to analytical results, particularly under high salinity conditions. To mitigate this problem, we propose a spatial high-order finite-difference time-domain (FDTD) method based on Maxwell's full equations of time-varying EM fields to simulate the seismoelectric response in 2D mode. To improve the computational efficiency influenced by the velocity differences between seismic and electromagnetic waves, different time steps are set according to the stability conditions, and the seismic feedback values of EM time nodes are obtained by linear approximation within the seismic unit time step. To improve the simulation accuracy of the seismoelectric response with the time-varying EM calculation method, finite-difference coefficients are obtained by solving the spatial high-order difference approximation based on Taylor expansion. The proposed method yields consistent simulation results compared to those obtained from the analytical method under different salinity conditions, thus indicating its validity for simulating seismoelectric responses in porous media. We further apply our method to both layered and anomalous body models and extend our algorithm to 3D. Results show that the time-varying EM calculation method could effectively capture the reflection and transmission phenomena of the seismic and EM wavefields at the interfaces of contrasting media. This may allow for the identification of abnormal locations, thus highlighting the capability of seismoelectric response simulation to detect subsurface properties.

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