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Numerical Simulation of Local Scour Around A Large Circular Cylinder Under Wave Action

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China Ocean Engineering 2001年第3期16卷 371-382页

作者：赵明滕斌 Slake key laboratory of coastal and Offshore Engineering Dalian University of Technology

A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by it finite element method, The results of this model are compared with those from other methods and agree well with experimental data.

关键词： local scour sediment transport wave action current numerical simulation circular cylinder

Effect of pontoons on free surface elevation around a TLP platform

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Science China(Technological Sciences) 2014年第1期57卷 163-180页

作者： CONG PeiWen GOU Ying TENG Bin State key laboratory of coastal and Offshore Engineering Dalian University of Technology

Tension leg platform(TLP)is a typical compliant offshore structure for oil/gas resources *** the design process,the prediction of the free surface elevation is of great importance for the determination of the air *** far,the existing researches for predicting the air gap of the TLPs focus on the supporting columns while pay little attention to the horizontal *** the second order diffraction problem or long incident wave condition,the velocity potential decays slowly with water depth and the effect of pontoons should not be *** the effect of pontoons on the diffracted wave field in the vicinity of a TLP platform is investigated in this *** diffraction of regular waves by a square array of truncated cylinders and a whole TLP structure is studied in detail by using both the linear and the second-order diffraction *** calculation is performed for the free surface elevation and wave run *** results show that the near-trapping phenomenon can occur inside the TLP and leads to significantly increased wave *** study the effect of pontoons on the free surface elevation comparisons are carried out between the results of these two structures with and without *** is found that pontoons have an appreciable effect on the diffracted wave field for long incident regular waves and increase the largest response notably when the near-trapping phenomenon occurs at the second-order.

关键词： TLP pontoon free surface elevation near-trapping the second-order diffraction

Rain-Flow and Reverse Rain-Flow Counting Method for the Compilation of Fatigue Load Spectrum

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China Ocean Engineering 2001年第3期16卷 429-435页

作者：宋玉普王立成李朝阳 State key laboratory of coastal and Offshore Engineering Dalian University of Technology

The rain-flow counting method is widely used to compile the fatigue load spectrum, The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reverse rain-flow counting method is proposed in this paper. In this counting method, the rule for counting of the rain-flow method is modified, so that the sequence of load-time need not be adjusted. This is a valid and useful method to count cycles and compile the load spectrum and it can be widely used in ocean engineering.

关键词： rain-flow reverse rain-flow load spectrum fatigue

Analytical approach and field monitoring for mechanical behaviors of pipe roof reinforcement

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Journal of Central South University 2009年第5期16卷 827-834页

作者：王海涛贾金青康海贵 State key laboratory of coastal and Offshore Engineering Dalian University of Technology

Considering the delay effect of initial lining and revising the Winkler elastic foundation model,an analytical approach based on Pasternak elastic foundation beam theory for pipe roof reinforcement was put forward. With the example of a certain tunnel excavation,the comparison of the values of longitudinal strain of reinforcing pipe between field monitoring and analytical approach was made. The results indicate that Pasternak model,which considers a more realistic hypothesis in the elastic soil than Winkler model,gives more accurate calculation and agrees better with the result of field monitoring. The difference of calculation results between these two models is about 7%,and Pasternak model is proved to be a better way to study the reinforcement mechanism and improve design practice. The calculation results also reveal that the reinforcing pipes act as levers,which increases longitudinal load transfer to an unexcavated area,and consequently decreases deformation and increases face stability.

关键词： tunnel heading pipe roof reinforcement Pasternak elastic foundation beam field monitoring

An experimental and numerical study of the freak wave speed

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Acta Oceanologica Sinica 2013年第5期32卷 51-56页

作者： CUI Cheng ZHANG Ningchuan KANG Haigui YU Yuxiu State key laboratory of coastal and Offshore Engineering Dalian University of Technology

The propagation speed is one of the most important characteristics for describing freak waves. The research of freak wave speed is not only helpful for understanding the generation mechanism and evolution process of freak waves, but also applicable to the prediction. A stable and accurate method is proposed for the cal- culation of the freak wave speed, in which physical model tests are carried out to measure the motion of the largest wave crest along the wave tank. The linear regression relationship between the spatial position of the largest wave crest and instantaneous moment is established to calculate the speed of totally 248 cases of experimental freak waves and 312 supplementary cases of numerical freak waves. Based on the calculate results, a semitheoretical and semiempirical formula is proposed by using a regression analysis method to predict the speed of the freak wave, and the nonlinear characteristic of the freak wave speed is also investi- gated.

关键词： freak wave speed regression analysis Stokes wave

A modified method for simulating non-stationary multi-point earthquake ground motion

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Earthquake Engineering and Engineering Vibration 2010年第2期9卷 201-211页

作者： Li Minggao,Li Xin and Zhou Jing State key laboratory of coastal and Offshore Engineering,Dalian University of Technology,Dalian 116024,China State key laboratory of coastal and Offshore Engineering Dalian University of Technology Dalian China

A spectral-representation-based algorithm is proposed to simulate non-stationary and stochastic processes with evolutionary power,according to a prescribed non-stationary cross-spectral density matrix. Non-stationary multi-point seismic ground motions at different locations on the ground surface are generated for use in engineering applications. First,a modified iterative procedure is used to generate uniformly modulated non-stationary ground motion time histories which are compatible with the prescribed power spectrum. Then,ground motion time histories are modeled as a non-stationary stochastic process with amplitude and frequency modulation. The characteristic frequency and damping ratio of the Clough-Penzien acceleration spectrum are considered as a function of time in order to study the frequency time variation. Finally,two numerical examples are presented to validate the efficiency of the proposed method,and the results show that this method can be effectively applied to the dynamic seismic analysis of long and large scale structures.

关键词： multi-support excitation spatial correlation power spectrum-compatibility non-stationary ground motion simulation

A 3-D Numerical Model for the Calculation of Water Wave Transformation in Large Area

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China Ocean Engineering 2001年第3期16卷 445-452页

作者：孙大鹏李玉成葛岚 The State key laboratory of coastal and Offshore Engineering Dalian University of Technology

Based on the integral equation transformed from three dimensional Laplace equation and by the adoption of the division manner of sub-region boundary element method, the numerical computations of the velocity potential of each sub-region are given considering the continuity conditions of potential and normal derivatives at the interface of sub-regions, Therefore, computation of wave deformation in offshore flow field is realized. The present numerical model provides a good solution for the application of boundary element method to the calculation of wave deformation in large areas.

关键词： Laplace equation wave deformation sub-region boundary element method

Study on Failure Mechanism and Bearing Capacity of Three-Dimensional Rectangular Footing Subjected to Combined Loading

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China Ocean Engineering 2008年第2期22卷 313-330页

作者：张其一栾茂田王忠涛 State key laboratory of coastal and Offshore Engineering Dalian University of Technology

This paper presents two kinematic failure mechanisms of threc-dimensional rectangular footing resting on homogeneous undrained clay foundation under uniaxial vertical loading and uniaxial moment loading. The failure mechanism under vertical loading comprises a plane strain Prandti-type mechanism over the central part of the longer side, and the size of the mechanism gradually reduces at the ends of the longer side and over the shorter side as the corner of rectangular footing is being approached where the direction of soil motion remains normal to each corresponding side respectively. The failure mechanism under moment loading comprises a plane strain scoop sliding mechanism over the central part of the longer side, and the radius of scoop sliding mechanism increases linearly at the ends of the longer side. On the basis of the kinematic failure mechanisms mentioned above, the vertical ultimate bearing capacity and the ultimate bearing capacity against moment or moment ultimate bearing capacity are obtained by use of upper bound limit analysis theory. At the same time, numerical analysis results, Skempton＇ s results and Salgado et al. ＇s results are compared with this upper bound solution. It shows that the presented failure mechanisms and plastic limit analysis predictions are validated. In order to investigate the behaviors of undrained clay foundation beneath the rectangular footing subjected to the combined loadings, numerical analysis is adopted by virtue of the general-purpose FEM software ABAQUS, where the clay is assumed to obey the Mohr-Coulomb yielding criterion. The failure envelope and the ultimate bearing capacity are achieved by the numerical analysis results with the varying aspect ratios from length L to breadth B of the rectangular footing. The failure mechanisms of rectangular footing which are subjected to the combined vertical loading V and horizontal loading H （Vertical loading V and moment loading M, and horizontal loading H and moment loading M

关键词： rectangular footing upper bound limit analysis failure mechardsm failure envelope combined loading

Experimental Study on Performance of Plain Concrete Due to Triaxial Variable-Amplitude Tension-Compression Cyclic Loading

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Journal of Wuhan University of Technology(Materials Science) 2005年第3期20卷 104-109页

作者：曹伟 State key laboratory of coastal and Offshore Engineering Dalian University of Technology

An experimental study on performance of plain concrete under triaxial constant-amplitude and variable amplitude tension- compression cyclic loadings was carded out. The low level of the cyclic stress is 0. 2f and the upper level ranges between 0. 20f and 0. 55f., while the constant lateral pressure is 0. 3 f . The specimen failure mode, the three-stage evolution rule of the longitudinal strains and the damage evolution law under cyclic loading were analyzed. Furthermore, Miner＇s rule is proved not to be applicable to the cyclic loading conditions, hereby, a nonlinear cumulative damage model was established. Based on the model the remaining fatigue life was evaluated. The comparison whh the experiment resuhs shaws that the model is of better precision and applicability.

关键词： concrete triaxial tension-compression Cyclic loading three-stage evolution rule nonlinear cumulative damage model