Jin-Ting Wang

Reflection and Transmission of Plane Waves at a Water–Porous Sediment Interface with a Double-Porosity Substrate

This paper investigates the wave propagation at the interface between the ocean and the ocean floor. The ocean floor is assumed to be composed of covered porous sediment with an underlying double-porosity substrate. For this purpose, plane wave reflection and transmission in the coupled water–porous sediment–double-porosity substrate system are analytically solved in terms of displacement potentials. Using numerical examples, the effects of the material properties of the underlying double-porosity substrate on the reflection coefficients are discussed in detail. Variations in pore and fracture fluid, fracture volume fraction, and permeability coefficients are considered. In addition, two cases of boundary conditions at the porous sediment–double-porosity substrate interface, i.e., sealed-pore boundary and open-pore boundary, are compared in the numerical calculations. Results show that material property variations in the double-porosity substrate may significantly affect the reflected wave in the overlying water if the sandwiched sediment depth is less than the critical value.

Accuracy of the half-power bandwidth method with a third-order correction for estimating damping in multi-DOF systems

A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems. This paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear systems. Damping ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves, respectively. A wide range of important parameters that characterize the shape of these response curves are taken into account. Results show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF system. In spite of this, the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.

Real-Time Dynamic Hybrid Testing Coupling Finite Element and Shaking Table

In this article, a Simulink simulation block with the finite element function is developed on the basis of S-function and implemented as the numerical substructure of real-time dynamic hybrid testing. Thereby, a real-time dynamic hybrid testing system coupling finite element calculation and shaking table testing is achieved. Using the developed system, a shear frame mounted on the soil foundation is tested, in which the shear frame is simulated as the physical model and the foundation is simulated as the finite element model with 132 degrees of freedom. Several cases of the dynamic behavior of soil-structure interaction are studied.

Simulation of large-scale numerical substructure in real-time dynamic hybrid testing

A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element (FE) numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom (DOFs). Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.

Comparison of explicit integration algorithms for real-time hybrid simulation

Real-time hybrid simulation (RTHS) combines physical experimentation with numerical simulation to evaluate dynamic responses of structures. The inherent characteristics of integration algorithms change when simulating numerical substructures owing to the response delay of loading systems in physical substructures. This study comprehensively investigates the effects of integration algorithms on the delay-dependent stability and accuracy of multiple degrees-of-freedom RTHS systems. Seven explicit integration algorithms are considered; and the discrete-time root locus technique is adopted. It is found that the stability of RTHS system is mainly determined by the time delay rather than the integration algorithms, whereas its accuracy mainly depends on the accuracy characteristic of the applied integration algorithm itself. An unconditionally stable integration algorithm cannot always guarantee good stability performance; and the inherent accuracy or numerical energy dissipation of integration algorithms should be taken into account in RTHSs. These theoretical findings are well verified by RTHSs.

Nonlinear Spectral‐Element Method for 3D Seismic‐Wave Propagation

Abstract This study extends the linear spectral‐element method (SEM) program SPECFEM3D to include nonlinear constitutive relationships. The iterations for solving the nonlinear equations are bypassed considering that the explicit integration used in the code requires a very small time increment; as a result, the high efficiency of the original linear procedure is preserved. This nonlinear code allows us to perform a deterministic seismic‐hazard analysis that considers the nonlinear behaviors of the propagation path and local site for an engineering site. After checking its accuracy against the commercial finite‐element method program ABAQUS, the extended nonlinear SEM is used to investigate the effect of noncausative faults on the seismic ground motion at the Dagangshan dam site in Southwest China. The analysis of the study case shows that the isolation effect of noncausative faults is dependent on the fault‐source relative position, and the nonlinear responses of the faults are sensitive to earthquake magnitude.

Seismic Performance of Tuned Liquid Column Dampers for Structural Control Using Real-Time Hybrid Simulation

This article presents real-time hybrid simulation (RTHS) in a single-degree-of-freedom (SDOF) steel frame incorporated with tuned liquid column damper (TLCD). The SDOF steel frame is numerically simulated, and the TLCD alone is physically experimented on a shaking table. The delay-dependent stability of RTHS system for TLCD investigation is first assessed; and the delay-dependent accuracy is verified by comparing the responses obtained through the RTHS, the conventional shaking table test, and an analytical solution. Then, RTHSs are carried out to evaluate the effects of mass ratio, structural damping ratio, structural stiffness, and peak ground acceleration on the reduction effectiveness of STLCD. The nonlinear behavior of the STLCD is experimentally captured. Finally, the structural responses under STLCD and multiple TLCDs (MTLCD) control are compared. It is found that the performance of STLCD strongly depends on structural parameters and properties of earthquakes; both MTLCD and STLCD induce approximately the same response reductions, and the former can enhance the control performance in certain cases. These results presented here may contribute to improve the design and application of TLCDs in practical engineering.

Efficiency analysis of numerical integrations for finite element substructure in real-time hybrid simulation

Finite element (FE) is a powerful tool and has been applied by investigators to real-time hybrid simulations (RTHSs). This study focuses on the computational efficiency, including the computational time and accuracy, of numerical integrations in solving FE numerical substructure in RTHSs. First, sparse matrix storage schemes are adopted to decrease the computational time of FE numerical substructure. In this way, the task execution time (TET) decreases such that the scale of the numerical substructure model increases. Subsequently, several commonly used explicit numerical integration algorithms, including the central difference method (CDM), the Newmark explicit method, the Chang method and the Gui-λ method, are comprehensively compared to evaluate their computational time in solving FE numerical substructure. CDM is better than the other explicit integration algorithms when the damping matrix is diagonal, while the Gui-λ (λ = 4) method is advantageous when the damping matrix is non-diagonal. Finally, the effect of time delay on the computational accuracy of RTHSs is investigated by simulating structure-foundation systems. Simulation results show that the influences of time delay on the displacement response become obvious with the mass ratio increasing, and delay compensation methods may reduce the relative error of the displacement peak value to less than 5% even under the large time-step and large time delay.

Seismic damage analysis of the outlet piers of arch dams using the finite element sub-model method

This study aims to analyze seismic damage of reinforced outlet piers of arch dams by the nonlinear finite element (FE) sub-model method. First, the dam–foundation system is modeled and analyzed, in which the effects of infinite foundation, contraction joints, and nonlinear concrete are taken into account. The detailed structures of the outlet pier are then simulated with a refined FE model in the sub-model analysis. In this way the damage mechanism of the plain (unreinforced) outlet pier is analyzed, and the effects of two reinforcement measures (i.e., post-tensioned anchor cables and reinforcing bar) on the dynamic damage to the outlet pier are investigated comprehensively. Results show that the plain pier is damaged severely by strong earthquakes while implementation of post-tensioned anchor cables strengthens the pier effectively. In addition, radiation damping strongly alleviates seismic damage to the piers.

Seismic stability assessment of an arch dam-foundation system

A seismic stability assessment of arch dam-foundation systems is presented using a comprehensive approach, in which the main factors that significantly influence the seismic response of an arch dam-foundation system are considered. A large scale finite element model with over 1 million degrees of freedom is constructed for the Baihetan arch dam (289 m high), which is under construction in the Southwest of China. In particular, the complicated geological conditions with faults intersecting interlayer shear weakness zones at the dam base and the dam abutment resisting force body is modeled in the analysis. Three performance indices are adopted to assess the seismic stability of the arch dam. The results demonstrate that the opening of the joints of the Baihetan arch dam is small and the water stop installed between the joints would not be torn during a design earthquake. The yielding formed in the interface between the dam and foundation does not reach the grouting curtain that would remain in an elastic state after an earthquake. The yielding zones occurring on the upper portion of the dam faces extend 1/8 thickness of block section into the dam body and thus cantilever blocks need not be concerned with sliding stability. The faults and interlayer shear weakness zones in the near field foundation exhibit severe yielding, and a potential sliding surface is penetrated. Although the factor of safety against sliding of the surface fluctuates with a decreased trend during an earthquake, the minimum instantaneous value reaches 1.02 and is still larger than 1.0. Therefore, a conclusion is drawn that the Baihetan arch dam-foundation system will remain stable under the design earthquake.