• Structural Engineering and Mechanics
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• v.14 no.1
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• pp.57-70
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• 2002

This work presents an iterative mesh partitioning approach to improve the efficiency of parallel substructure finite element computations. The proposed approach employs an iterative strategy with a set of empirical rules derived from the results of numerical experiments on a number of different finite element meshes. The proposed approach also utilizes state-of-the-art partitioning techniques in its iterative partitioning kernel, a cost function to estimate the computational cost of each submesh, and a mechanism that adjusts element weights to redistribute elements among submeshes during iterative partitioning to partition a mesh into submeshes (or substructures) with balanced computational workloads. In addition, actual parallel finite element structural analyses on several test examples are presented to demonstrate the effectiveness of the approach proposed herein. The results show that the proposed approach can effectively improve the efficiency of parallel substructure finite element computations.

• Earthquakes and Structures
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• v.17 no.1
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• pp.101-113
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• 2019

Earthquake-induced pounding is one of the major reasons for structural failure in earthquake prone cities. An accurate description of the pounding phenomenon of two buildings requires the consideration of systems with a large number of degrees of freedom including adequate contact impact formulations. In this paper, firstly, a node to surface formulation for the realization of state-of-the-art pounding models for structural beam elements is presented. Secondly, a hierarchical substructure technique is introduced, which is adapted to the structural pounding problem. The numerical accuracy and efficiency of the method, especially for the contact forces, are verified on an academic example, applying four different impact elements. Error estimations are carried out and compared with the classical modal truncation method. It is demonstrated that the hierarchical substructure method is indeed able to significantly speed up the numeric integration procedure by preserving a required level of accuracy.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.2
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• pp.188-197
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• 2016

Offshore substructures have been developed to support structures against complex offshore environments. The load at offshore substructures is dominated by waves, and deformation of waves caused by interactions with the current is an important phenomena. Wave load simulation of fixed offshore substructures in waves with the presence of uniform current was carried out by numerical wave tank technique using the commercial software, FLUENT. The continuity and Navier-Stokes equations were applied as the governing equations for incompressible fluid motion, and numerical wavemaker was employed to reproduce offshore wave environment. Convergence test against grids number was carried out to investigate grid dependency and optimized conditions for numerical wave generation were derived including investigation of the damping effect against length of the damping domain. Numerical simulation of wave and current interactions with fixed offshore substructure was carried out by computational fluid dynamics, and comparison with other experiments and simulations results was conducted.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.359-368
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• 2018

Dynamic analysis of complex and large structures may be costly from a numerical point of view. For coupled vibroacoustic finite element models, the importance of reducing the size becomes obvious because the fluid degrees of freedom must be added to the structural ones. In this paper, a component mode synthesis method is proposed for large vibroacoustic interaction problems. This method couples fluid subdomains and dynamical substructuring of Craig and Bampton type. The acoustic formulation is written in terms of the velocity potential, which implies several advantages: coupled algebraic systems remain symmetric, and a potential formulation allows a direct extension of Craig and Bampton's method to acoustics. Those properties make the proposed method easy to implement in an existing finite element code because the local numerical treatment of substructures and fluid subdomains is undifferentiated. Test cases are then presented for axisymmetric geometries. Numerical results tend to prove the validity and the efficiency of the proposed method.

• Earthquakes and Structures
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• v.13 no.3
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• pp.299-307
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• 2017

High Damping Rubber bearings (HDR bearings) have been used in the seismic design of bridge structures widely in China. In earthquakes, structural natural periods will be extended, seismic energy will be dissipated by this kind of bearing. Previously, cyclic loading method was used mainly for test studies on mechanical properties of HDR bearings, which cannot simulate real seismic responses. In this paper, Real-Time Substructure (RTS) test study on mechanical properties of HDR bearings was conducted and it was found that the loading rate effect was not negligible. Then the influence of peak acceleration of ground motion was studied. At last test results were compared with a numerical simulation in the OpenSees software framework with the Kikuchi model. It is found that the Kikuchi model can simulate real mechanical properties of HDR bearings in earthquakes accurately.

• Smart Structures and Systems
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• v.12 no.6
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• pp.619-640
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• 2013

It is highly desirable to explore efficient algorithms for detecting structural damage of large size structural systems with limited input and output measurements. In this paper, a new structural damage detection algorithm based on substructure approach is proposed for large size structural systems with limited input and output measurements. Inter-connection effect between adjacent substructures is treated as 'additional unknown inputs' to substructures. Extended state vector of each substructure and its unknown excitations are estimated by sequential extended Kalman estimator and least-squares estimation, respectively. It is shown that the 'additional unknown inputs' can be estimated by the algorithm without the measurements on the substructure interface DOFs, which is superior to previous substructural identification approaches. Also, structural parameters and unknown excitation are estimated in a sequential manner, which simplifies the identification problem compared with other existing work. Structural damage can be detected from the degradation of the identified substructural element stiffness values. The performances of the proposed algorithm are demonstrated by several numerical examples and a lab experiment. Measurement noise effect is considered. Both the simulation results and experimental data validate that the proposed algorithm is viable for structural damage detection of large size structural systems with limited input and output measurements.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.252-261
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• 2016

A spar-type floating substructure that is being widely used for offshore wind power generation is vulnerable to resonance in the heave direction because of its small water plane area. For this reason, the stable dynamic response of this floating structure should be ensured by accurately identifying the resonance characteristics. The purpose of this study is to analyze the characteristics of the combination resonance between the excitation frequency of a regular wave and natural frequencies of the floating substructure. First, the nonlinear equations of motion with two degrees of freedom are derived by assuming that the floating substructure is a rigid body, where the heaving motion and pitching motions are coupled. Moreover, to identify the characteristics of the combination resonance, the nonlinear term in the nonlinear equations is approximated up to the second order using the Taylor series expansion. Furthermore, the validity of the approximate model is confirmed through a comparison with the results of a numerical analysis which is made by applying the commercial software ANSYS AQWA to the full model. The result indicates that the combination resonance occurs at the frequencies of ${\omega}{\pm}{\omega}_5$ and $2{\omega}_{n5}$ between the excitation frequency (${\omega}$) of a regular wave and the natural frequency of the pitching motion (${\omega}_{n5}$) of the floating substructure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.666-671
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• 2002

For a large structure, substructure based SDM(structural dynamics modification) method is very effective to raise its dynamic characteristics. Dividing into smaller substructures has a major advantage in the aspect of computation especially for getting sensitivities, which are in the core of SDM process. But quite often, non-matching nodes problem occurs in the process of synthesizing substructures. The reason is that, in general, each substructure is modelled separately, then later combined together to form a entire structure model under interface constraint conditions. Without solving the non-matching nodes problem, the substructure based SDM can not be processed. In this work, virtual node concept is introduced. Lagrange multipliers are used to enforce the interface compatibility constraint. The governing equation of whole structure is derived using hybrid variational principle. The eigenvalues of whole structure are calculated using determinant search method. The number of degrees of freedom of the eigenvalue problem can be drastically reduced to just the number of interface degree of freedom. Thus, the eigenvalue sensitivities can be easily calculated, and further SDM can be efficiently performed. Some numerical problems are tested to show the effectiveness of handling non-matching nodes.

• Computational Structural Engineering : An International Journal
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• v.3 no.1
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• pp.1-7
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• 2003

For system identification of large structures, it is not practical to identify the entire structure due to the prohibitive computational time and difficulty in numerical convergence. This paper explores the possibility of performing system identification at substructure level, taking advantage of reduction in both the number of unknowns and the number of degrees of freedom involved. Another advantage is that different portions (substructures) of a structural system can be identified independently and even concurrently with parallel computing. Two substructural identification methods are formulated on the basis whether substructural approach is used to obtain first-order or second-order model. For substructural first-order model, identification at the substructure level will be performed by means of the Observer/Kalman filter Identification (OKID) and the Eigensystem Realization Algorithm (ERA) whereas identification at the global level will be performed to obtain second-order model in order to evaluate the system's stiffness and mass parameters. In the case of substructural second-order model, identification will be performed at the substructure level throughout the identification process. The efficiency of the proposed technique is shown by numerical examples for multi-storey shear buildings subjected to random forces, taking into consideration the effects of noisy measurement data. The results indicate that both the proposed methods are effective and efficient for damage identification of large structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.517-522
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• 2002

The frequency response function(FRF) of each substructure is used for the transfer function synthesis method(TFS). The dynamic characteristics of the full system are obtained by synthesizing FRFs of each substructure. The validation of TFS depends on accuracy for FRF of each substructure. Impact hammer testing is widely used to obtain the modal characteristics of structures. However, the FRF obtained from impact hammer testing contains several errors, such as finite record length error and leakage error of which characteristic depends on data acquisition time which we call record length. In this paper, a method to remove these errors is proposed so as to enhance results of TFS. Numerical examples show that the FRF of full structure can be predicted exactly by the method proposed in this paper.