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The Optimal Design of TMD for Offshore Structures

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China Ocean Engineering 1999年第2期14卷 133-144页

作者： sau lon james hu Tomotsuka TAKAYAMA Dept. of Ocean Engrg. University of Rhode Island RI02881 Professor Professor Disaster Prevention Res. Inst. Kyoto Univ. Gokasho Uji Kyoto 611-0011 Japan.

This paper presents the optimal design procedure of Tuned Mass Damper (TMD) for reducing vibration of an actual steel jacket offshore platform excited by random wave loading. In this study, a frequency domain is taken. The force on the structure is determined by use of the linearized Morison equation for an input Power Spectral Density (PSD) of wave elevation. The sensitivity of optimum values of TMD to characteristic parameters of random wave spectrum is analyzed. An optimized TMD design for the modeled platform is given based on design conditions and the findings of the study.

关键词： tuned mass damper design Morison equation power spectral density offshore structures

Multiple-Step Predictive Control for Offshore Structures

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China Ocean Engineering 1999年第3期14卷 231-246页

作者：李华军 sau-lon james hu College of Engrg. Ocean University of Qingdao Professor Member of ASCEDepartment of Ocean EngrgUniversity of Rhode IslandNarragansett

Ocean wave propagation is slow, visible and measurable, so a wave theory can be used to approximately predict the imminnent wave force on an offshore structure based on measured, real-time wave elevation near the structure. This predictability suggests the development of a more efficient algorithm, than those that have been developed for structures under wind and seismic loads, for the active vibration control of offshore structures. The present study delveops a mutiple-step predictive optimal control (MPOC) algorithm that accounts for multiple step external loading in the determination of optimal control forces. The control efficiency of the newly developed MPOC algorithm has been Investigated under both regular (single-frequency) and irregular (multiple-frequency) wave loads, and compared with that of two other well-known optimal control algorithms: classical linear optimal control(CLOC) and instantaneous optimal control(IOC).

关键词： active control offshore structure predictive control control algorithm wave load vibration

Fundamental modeling issues on benchmark structure for structural health monitoring

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Science China(Technological Sciences) 2009年第7期52卷 1999-2008页

作者： hu sau-lon james Department of Ocean Engineering University of Rhode Island Narragansett RI 02882-1197 USA

The IASC-ASCE Structural Health Monitoring Task Group developed a series of benchmark problems, and participants of the benchmark study were charged with using a 12-degree-of-freedom (DOF) shear building as their identification model. The present article addresses improperness, including the parameter and modeling errors, of using this particular model for the intended purpose of damage detec- tion, while the measurements of damaged structures are synthesized from a full-order finite-element model. In addressing parameter errors, a model calibration procedure is utilized to tune the mass and stiffness matrices of the baseline identification model, and a 12-DOF shear building model that preserves the first three modes of the full-order model is obtained. Sequentially, this calibrated model is employed as the baseline model while performing the damage detection under various damage scenarios. Numerical results indicate that the 12-DOF shear building model is an over-simplified identification model, through which only idealized damage situations for the benchmark structure can be detected. It is suggested that a more sophisticated 3-dimensional frame structure model should be adopted as the identification model, if one intends to detect local member damages correctly.

关键词： benchmark structural health monitoring damage detection modeling error

Employing incomplete complex modes for model updating and damage detection of damped structures

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Science China(Technological Sciences) 2008年第12期51卷 2244-2258页

作者： hu sau-lon james Department of Ocean Engineering University of Rhode Island

In the study of finite element model updating or damage detection,most papers are devoted to undamped ***,their objective has been exclusively restricted to the correction of the mass and stiffness *** contrast,this paper performs the model updating and damage detection for damped structures.A theoretical contribution of this paper is to extend the cross-model cross-mode(CMCM) method to simultaneously update the mass,damping and stiffness matrices of a finite element model when only few spatially incomplete,complex-valued modes are *** studies are conducted for a 30-DOF(degree-of-freedom) cantilever beam with multiple damaged elements,as the measured modes are synthesized from finite element *** numerical results reveal that applying the CMCM method,together with an iterative Guyan reduction scheme,can yield good damage detection in *** the measured modes utilized in the CMCM method are corrupted with irregular errors,assessing damage at the location that possesses larger modal strain energy is less sensitive to the corrupted modes.

关键词： incomplete complex modes model updating damage detection CMCM damped structures

A Novel Approach for Evaluating Nonstationary Response of Dynamic Systems to Stochastic Excitation

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Journal of Ocean University of China 2020年第4期19卷 781-789页

作者： CAO Qianying hu sau-lon james LI Hewenxuan College of Engineering Ocean University of ChinaQingdao 266100China Department of Ocean Engineering University of Rhode IslandNarragansettRI 02882USA College of Engineering University of Rhode IslandKingstonRI 02881USA

The transient state of a dynamic system,such as offshore structures,to random excitation is always *** studies have contributed to evaluating response covariances at the transient state of a linear multi-degree-of-freedom(MDOF)system to random excitations,but a closed-form solution was not available unless the excitation was assumed to be a physically unrealizable white noise *** study derives explicit,closed-form solutions for the response covariances at the transient state by using a pole-residue(PR)approach operated in the Laplace domain when the excitations are assumed to be stationary random processes described by physically realizable spectral density *** using the PR method,we can analytically solve the triple integral in evaluating the nonstationary response *** this approach uses the poles and residues of system transfer functions,rather than the conventional mode superposition technique,the method is applicable to MDOF systems with non-classical damping *** application of the proposed method is demonstrated for multi-story shear buildings to stochastic ground acceleration characterized by the Kanai–Tajimi spectral density function model,and a numerical example is provided to illustrate the detailed *** numerical integrations are required for computing the response covariances as the exact closed-form solution has been *** correctness of the proposed method is numerically verified by Monte Carlo simulations.

关键词： linear systems transient state nonstationary response pole residue

Model updating based on incomplete modal data

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Science China(Technological Sciences) 2011年第7期54卷 1737-1747页

作者： LI huaJun WANG JunRong hu sau-lon james Shandong Provincial Key Lab of Ocean Engineering Ocean University of China Qingdao 266100 China CNOOC Research Institute China National Offshore Oil Corporation Beijing 100027 China Department of Ocean Engineering University of Rhode Island Narragansett RI 02882-1197 USA

The objective of model updating is to improve the accuracy of a dynamic model based on the correlation between the measured data and the analytical (finite element) model. In this paper, we intend to update the mass and stiffness matrices of an analytical model when only modal frequencies or spatially incomplete modal data are available. While the proposed method is systematic in nature, it also preserves the initial configuration of the analytical model, and physical equality and/or inequality constraints can be easily incorporated into the solution procedure. Numerical examples associated with a simple 5-DoF (degree of freedom) mass-spring system are chosen to illustrate the detailed procedure and the effectiveness of the proposed method. Numerical scenarios ranging from the updating for stiffness terms only to that for all mass and stiffness terms based on various kinds of incomplete modal data are studied. The obtained model updating results are excellent when the measured modal data are noise-free. Uncertainty studies are also conducted based on simulations of corrupted modal data, but a thorough theoretical analysis of the noise effect on the proposed method is still needed.

关键词： model updating model reduction modal expansion incomplete mode

Stress Wave Propagation Analysis on Vortex-Induced Vibration of Marine Risers

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China Ocean Engineering 2017年第1期31卷 30-36页

作者： LI hua-jun WANG Chao LIU Fu-shun hu sau-lon james Shandong Provincial Key Lab of Ocean Engineering Ocean University of China Department of Ocean Engineering University of Rhode Island

To analyze the stress wave propagation associated with the vortex-induced vibration（VIV） of a marine riser, this paper employed a multi-signal complex exponential method. This method is an extension of the classical Prony＇s method which decomposes a complicated signal into a number of complex exponential components. Because the proposed method processes multiple signals simultaneously, it can estimate the “global” dominating frequencies（poles） shared by those *** complex amplitude（residues） corresponding to the estimated frequencies for those signals is also obtained in the process. As the signals were collected at different locations along the axial direction of a marine riser, the phenomena of the stress wave propagation could be analyzed through the obtained residues of those signals. The Norwegian Deepwater Program（NDP） high mode test data were utilized in the numerical studies, including data sets in both the in-line（IL） and cross-flow（CF） directions. It was found that the most dominant component in the IL direction has its stress wave propagation along the riser being dominated by a standing wave, while that in the CF direction dominated by a traveling wave.

关键词： Vortex exponential utilized reconstructed riser directions interpolation dominated residues processed