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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

Condition Identification Based on Vibration Measurements for Free Spanning Submarine Pipelines

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China Ocean engineering 2008年第4期22卷 561-574页

作者：胡家顺冯新李昕周晶 state key laboratory of coastal and offshore engineering Dalian University of Technology

Free spanning pipelines are suspended between two points on an uneven seaffoor. The variations of structural conditions, such as the changes in soil property, flow velocity, axial force and span length etc., directly affect working performance of the whole submarine pipeline system. But until now few researches have focused on condition identification for free span （CIFS）. A method to identify the operational conditions of free spanning submarine pipelines based on vibration measurements is proposed in this paper. Firstly, the ill-posedness of CIFS is analyzed in detail. Secondly, the framework for CIFS based on the nonlinear kernel discriminant analysis （KDA） is established. Thirdly, the internal structural characteristics of natural frequencies, normalized frequencies and frequency change ratios are studied. And then the condition feature vector for CIFS is extracted by use of the vibration measurements. Finally, the validity of the proposed approach is evaluated by a case study. The results demonstrate that the proposed approach can effectively identify each condition of free span when condition variation occurs even if under measurement noise. It is concluded that the proposed method is a promising tool for CIFS in real applications.

关键词： submasine pipelines condition identfication free span kernel discriminant analysis( KDA ) frequently structure

Uniaxial Compressive Properties of Ultra High Toughness Cementitious Composite

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Journal of Wuhan University of Technology(Materials Science) 2011年第4期26卷 762-769页

作者：蔡向荣徐世烺 state key laboratory of coastal and offshore engineering Dalian University of Technology

Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite （UHTCC） in terms of strength and toughness and to obtain its stress-strain relationships. The compressive strength investigated ranges from 30 MPa to 60 MPa. Complete stress-strain curves were directly obtained, and the strength indexes, including uniaxial compressive strength, compressive strain at peak stress, elastic modulus and Poisson＇s ratio, were calculated. The comparisons between UHTCC and matrix were also carried out to understand the fiber effect on the compressive strength indexes. Three dimensionless toughness indexes were calculated, which either represent its relative improvement in energy absorption capacity because of fiber addition or provide an indication of its behavior relative to a rigid-plastic material. Moreover, two new toughness indexes, which were named as post-crack deformation energy and equivalent compressive strength, were proposed and calculated with the aim at linking up the compressive toughness of UHTCC with the existing design concept of concrete. The failure mode was also given. The study production provides material characteristics for the practical engineering application of UHTCC.

关键词： ultra high toughness cementitious composite compressive strength compressive toughness fiber reinforcement

One-Dimensional Horizontal Boussinesq Model Enhanced for Non-Breaking and Breaking Waves

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China Ocean engineering 2008年第1期22卷 31-42页

作者：董国海马小舟滕斌 The state key laboratory of coastal and offshore engineering Dalian University of Technology

Based on a set of fully nonlinear Boussinesq equations up to the order of O（μ^2, ε^3μ^2）（where ε is the ratio of wave amplitude to water depth and ,μ is the ratio of water depth to wave length） a numerical wave model is formulated. The model＇s linear dispersion is acceptably accurate to μ ≌ 1.0, which is confirmed by comparisons between the simulat- ed and measured time series of the regular waves propagating on a submerged bar. The moving shoreline is treated numer- ically by replacing the solid beach with a permeable beach. Run-up of nonbreaking waves is verified against the analytical solution for nonlinear shallow water waves. The inclusion of wave breaking is fulfilled by introducing an eddy term in the momentum equation to serve as the breaking wave force term to dissipate wave energy in the surf zone. The model is applied to cross-shore motions of regular waves including various types of breaking on plane sloping beaches. Comparisons of the model test results comprising spatial distribution of wave height and mean water level with experimental data are presented.

关键词： Boussinesq model surf zone wave breaking wave run- up

Multilevel Optimal Design of Prestressed Lightweight Concrete-Steel Platform Structures

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China Ocean engineering 2002年第1期17卷 69-78页

作者：王立成宋玉普康海贵王兴国 state key laboratory of coastal and offshore engineering Dalian University of Technology

The concrete-steel platform structure is rather complicated because it involves such materials as concrete, reinforcing bars, steel, and so on. If the traditional dimension optimization method is employed, the optimal design of the platform will meet many handicaps, even it cannot be implemented at all. The multilevel optimal design approach is an efficient tool for the solution of large-scale engineering structures. In this paper, this approach is applied to the optimal design of a concrete-steel platform, which is formulated as a system level optimal design problem and a set of uncoupled substructure level optimal design problems. The process of optimization is a process of iteration between system level and substructure level until the objective function converges. An illustrative example indicates that this method is effective in the optimal design of concrete-steel platforms.

关键词： concrete-steel platform multilevel optimal design objective function design constraints

Static and Dynamic Analysis of Mooring Lines by Nonlinear Finite Element Method

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China Ocean engineering 2010年第3期24卷 417-430页

作者：杨敏冬滕斌 state key laboratory of coastal and offshore engineering Dalian University of Technology

This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two nodes is briefly presented on the basis of the total Lagrangian formulation. The static and dynamic equilibrium equations of mooring lines are established. An incremental-iterative method is used to determine the initial static equilibrium state of cable systems under the action of self weights, buoyancy and current. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method, and examine the effect of various parameters.

关键词： geometrically nonlinear finite element mooring line incremental iteration method

Tensile and Flexural Properties of Ultra High Toughness Cemontious Composite

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Journal of Wuhan University of Technology(Materials Science) 2009年第4期24卷 677-683页

作者：李贺东徐世烺 state key laboratory of coastal and offshore engineering Dalian University of Technology

The tensile and flexural properties of polyvinyl alcohol （PVA） fiber reinforced ultra high toughness cementitious composite （UHTCC） were investigated. The composite, tested at the age of 14 d, 28 d and 56 d, shows extremely remarkable pseudo strain hardening behavior, saturated multiple cracking and ultra high ultimate strain capacity above 4% under uniaxial loading. Also, the corresponding crack widths are controlled under 50 um even at 56 days age. In the third point bending tests on thin plate specimens, the composite shows ultra high flexural ductility and multiple cracking on the tension surface. The high ultimate flexural strength/first tensile strength ratio of about 5 verifies the pseudo strain hardening behavior of UHTCC. SEM observation on fracture surfaces provides indirect evidence of optimal design for the composite.

关键词： pseudo strain hardening cementitious composite multiple cracking ductility SEM

Longshore Currents of Random Waves on Different Plane Beaches

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海洋工程：英文版 2003年第2期17卷 265-276页

作者：邹志利王淑平邱大洪王艳王风龙董国海 state key laboratory of coastal and offshore engineering Dalian University of Technology

Model tests and numerical calculation of longshore currents and wave heights produced by irregular waves on two beaches with slopes of 1:100 and 1:40 are studied. The cross-shore distributions of longshore current velocities and wave heights are given and the influences of wave heights, wave periods, and beach slopes on longshore currents are discussed. The discussion is also made on the influences of different eddy viscosity coefficients on the numerical results of longshore current velocities.

关键词： coast current current coasts wave breaking

Strain analysis of buried steel pipelines across strike-slip faults

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Journal of Central South University 2011年第5期18卷 1654-1661页

作者：王滨李昕周晶 state key laboratory of coastal and offshore engineering Dalian University of Technology

Existing analytical methods of buried steel pipelines subjected to active strike-slip faults depended on a number of *** study the failure mechanism more accurately,a refined strain analytical methodology was proposed,taking the nonlinear characteristics of soil-pipeline interaction and pipe steel into *** on the elastic-beam and beam-on-elastic-foundation theories,the position of pipe potential destruction and the strain and deformation distributions along the pipeline were *** with existing analytical methods and three-dimensional nonlinear finite element analysis,the maximum axial total strains of pipe from the analytical methodology presented are in good agreement with the finite element results at small and intermediate fault movements and become gradually more conservative at large fault *** position of pipe potential failure and the deformation distribution along the pipeline are fairly consistent with the finite element results.

关键词： strike-slip fault buffed pipeline nonlinear pipe-soil interaction analytical formula strain analysis