ISSN  0890-5487 CN 32-1441/P

1998 Vol.(3)

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Dynamic Analysis and Numerical Simulation of a Kind of Arrestor Arresting Buckle Propagation by FEM
1998, (3): -.
[Abstract](593)
Abstract:
For exact estimation of efficiency of a buckle arrester, it is necessary to take the effect of structural inertia into account in the analysis of buckle propagation on elastic structures after meeting arresters. Under this consideration, this paper deals with the dynamics of buckle arrest and its numerical simulation on the basis of the beam system model used by Chater and Hutchinson (1983). The FEM combined with an improving arc-length control method is adopted to solve the dynamic equations describing the arresting of buckle propagation. A new group of parameters for arrester design which differs greatly from that by the quasi-static analysis is obtained. The present results support the conclusion that the inertia of the beam cannot be neglected in such analysis.
Dynamic Structure-Fluid Interaction Response of a Composite Cylindrical Shell Submerged in Water
1998, (3): -.
[Abstract](433)
Abstract:
This paper analyzes the dynamic structure-fluid interaction response of a submerged composite cylindrical shell. Dynamic equations based on the first-order shear deformation theory include the initial stresses and structure-fluid interaction forces due to fluid. The field equation is solved by expanding the velocity potential into series similar to transverse deflection of the cylindrical shell and the structure-fluid interaction force is obtained. The dynamic response is investigated by means of series expansion method. The effects of structure-fluid interaction on dynamic response are discussed.
Estimating Directional Distribution for Co-Existent Field of Incident and Reflected Waves
1998, (3): -.
[Abstract](421)
Abstract:
In the nearshore, the wave field contains reflected and incident waves in which there is correlation between their phases due to the effect of reflection by some obstacles. Based on the extended eigenvector method (EEV) derived by Guan et at., a modified method (MEEV) is proposed as a general and practical approach to estimating directional spectra for the co-existent field of incident and reflected waves and a formula is given for direct calculation of the reflection coefficient. The results of numerical simulations show that MEEV is superior to EEV in resolution power, and the computed reflection coefficient agrees well with the real value within a certain range of incident angle.
Ice Induced Low Temperature Fatigue Crack Propagation in Offshore Structural Steel A131
1998, (3): -.
[Abstract](431)
Abstract:
To investigate the low temperature fatigue crack propagation behavior of offshore structural steel A131 under random ice loading, three ice failure modes that are commonly present in the Bohai Gulf are simulated according to the vibration stress responses induced by real ice loading. The test data are processed by a universal software FCPUSL developed on the basis of the theory of fatigue crack propagation and statistics. The fundamental parameter controlling the fatigue crack propagation induced by random ice loading is determined to be the amplitude root mean square stress intensity factor ATarm. The test results are presented on the crack propagation diagram where the crack growth rate da/ dN is described as the function of Karm. It is evident that the ice failure modes have great influence on the fatigue crack propagation behavior of the steel in ice-induced vibration. However, some of the experimental phenomena and test results are hard to be physically explained at present. The work in this paper is an initial attempt to investigate the cause of collapse of offshore structures due to ice loading.
Nonlinear Coupled Motions for a Given Two-Point Tension Mooring System
1998, (3): -.
[Abstract](446)
Abstract:
The nonlinear behaviors of plane coupled motions for a given two-point tension mooring system, are discussed in the present paper. For a cylinder moored by two taut lines under the action of gravity, buoyance and forces due to wave-current and mooring lines, a mathematical model of motions with three degrees of freedom is established. The steady solution and stability are analyzed. By integrating the equations of motions, history, phase map and Poincare map are obtained. The Liapunov exponents are also computed. The numerical results show that: the horizontal movement will increase, and stability will also increase as the steady force increases. The amplitude of responses will decrease as time-dependent forces decrease. Because of the geometric nonlinearity, there exist many windows bifurcating to pseudo-periodic or multi-periodic solution. The bifurcating patterns may be different. The behaviors are very complex. Under wave excitation alone, the motions are nonsymmetrical but still symmetrical statistically.
Structural Types of Sea Embankment and Their Stability Analysis
1998, (3): -.
[Abstract](460)
Abstract:
In this paper based on investigation on the structural types of sea embankments in the southeast coastal area of China, as well as the related tidal stages, waves and strength of marine soils, the finite element method (FEM) calculations for seepage flow stability, including the overall stability against sliding and local stability of sloping surface under the action of tidal stage and waves are carried out. A comparison of the computational results of FEM for single circular slip, composite circular slip and geogrid reinforcement against sliding shows that for calculation of stability against sliding of marine soft soil foundation it is even more reasonable to use the composite circular slip. The stability of sloping type sea embankment against sliding is slightly better than that of the vertical face type; for the combination of three defences (wave, scour and seepage defences) the sea embankment structural type of a composite cross section with a platform should be a good one, but it still should be suitable to local conditions. For the local stability of riprap slope blocks and wall face loose masonry blocks, according to the analyses of wave-induced seepage flow fields, calculating formulas are given and they are verified by model test on block stability of breakwtwers.
A Three-Dimensional Prediction Method for Thermal Diffusion
1998, (3): -.
[Abstract](426)
Abstract:
A three-dimensional, first order turbulence closure, thermal diffusion model is described in this paper. The governing equations consist of an equation of continuity, three components of momentum, conservation equations for salt, temperature and subgridscale energy, and an equation of state. In the model, according to the hypothesis of Kolmogorov and Prandtl, the viscosity coefficient of turbulent flow of homogeneous fluid is related to the local turbulent energy, and the horizontal and vertical exchange coefficients of mass, heat and momentum are computed with the introduction of subgridscale turbulence energy. The governing equations are solved by finite difference techniques. This model is applied to the Jiaozhou bay to predict thermal pollution by the Huangdao power plant. An instantaneous tidal current field is computed, then the distribution of temperature increment is predicted, and finally the effect of wind stress on thermal discharge is discussed.
The Statistical Distribution of the Horizontal Velocities of Water Particles at Wave Surface Maxima
1998, (3): -.
[Abstract](418)
Abstract:
Computation of Long-Term Statistical Properties of Wave Agitation in Harbors
1998, (3): -.
[Abstract](413)
Abstract:
In this paper, the long-term statistical properties of wave height in an idealized square harbor with a partial opening are studied. The incident waves are propagated into the harbor numerically by the finite/infinite element method using three different wave models: (1) monochromatic wave train, (2) long-crested random wave train, and (3) short-crested random wave train. This study shows that for a given incident wave, the wave height in the harbor is affected by the wave model used. For long-term estimation of wave height exceedance probability, it is recommended that the waves be propagated into the harbor using the random wave model, and that wave heights be computed by use of the Rayleigh probability distribution.
Study on Current-Random Wave Forces Acting on a Framework
1998, (3): -.
[Abstract](421)
Abstract:
The forces of random wave plus current acting on a simplified offshore platform (jacket) model have been studied numerically and experimentally. The numerical results are in good agreement with experiments. The mean force can be approximated as a function of equivalent velocity parameter and the root-mean-square force as a function of equivalent significant wave height parameter.

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