1997 Vol.(4)
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1997, (4): -.
Abstract:
A new numerical finite difference iteration method for refraction-diffraction of waves in water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the dissipation term is briefly described, together with some analysis and comparison of computational results of the model with measurements in a hydraulic scale model (Berkhoff et al., 1982). An example of practical use of the method is given, showing that the present model is useful to engineering practice.
A new numerical finite difference iteration method for refraction-diffraction of waves in water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the dissipation term is briefly described, together with some analysis and comparison of computational results of the model with measurements in a hydraulic scale model (Berkhoff et al., 1982). An example of practical use of the method is given, showing that the present model is useful to engineering practice.
1997, (4): -.
Abstract:
A boundary element method is developed for calculating the flare ship hull slamming problem. The nonlinear free surface elevation and the linear element assumption are employed. The method has been verified by comparisons with results for the water entry of wedges with various deadrise angles. Numerical results show that the pressure distribution varies greatly with the ship hull with different curvilinear equations, and the slamming features are also different. From the numerical simulation, the authors found that the structural damage of the flare hull might be caused by the increasing hydrodynamic pressure over an extensive area on the flare when the upper part of the flare comes into contact with water.
A boundary element method is developed for calculating the flare ship hull slamming problem. The nonlinear free surface elevation and the linear element assumption are employed. The method has been verified by comparisons with results for the water entry of wedges with various deadrise angles. Numerical results show that the pressure distribution varies greatly with the ship hull with different curvilinear equations, and the slamming features are also different. From the numerical simulation, the authors found that the structural damage of the flare hull might be caused by the increasing hydrodynamic pressure over an extensive area on the flare when the upper part of the flare comes into contact with water.
1997, (4): -.
Abstract:
In previous and this studies it appears that the linear and nonlinear wave theory can not accurately and easily predict the water particle velocities. Therefore, different from the theoretical considerations, in this study we have attempted to determine the transfer function empirically. Laboratory experiments were performed under various wave conditions. The empirical formulas of the transfer function of the wave height, angular frequency and water particle velocity were obtained on the basis of these test data by dimensional analysis and regression analysis. In intermediate and deep water depth conditions, the transfer function was only a function of a nondimensional parameter which is composed of the angular frequency, the depth of the velocity gauge under the still water level, water depth and the acceleration of gravity. Finally, the empirical formulas were compared with experimental data and observational data form present and Cavaleri's (1978) studies. The empirical formulas were found to be in sufficient correltion with these data.
In previous and this studies it appears that the linear and nonlinear wave theory can not accurately and easily predict the water particle velocities. Therefore, different from the theoretical considerations, in this study we have attempted to determine the transfer function empirically. Laboratory experiments were performed under various wave conditions. The empirical formulas of the transfer function of the wave height, angular frequency and water particle velocity were obtained on the basis of these test data by dimensional analysis and regression analysis. In intermediate and deep water depth conditions, the transfer function was only a function of a nondimensional parameter which is composed of the angular frequency, the depth of the velocity gauge under the still water level, water depth and the acceleration of gravity. Finally, the empirical formulas were compared with experimental data and observational data form present and Cavaleri's (1978) studies. The empirical formulas were found to be in sufficient correltion with these data.
1997, (4): -.
Abstract:
1997, (4): -.
Abstract:
In consideration of the effects of transverse shear deformation and structure-fluid interaction, the analytical expression of fluid force between a floating laminated composite plate and liquid surface is obtained. By expanding the displacements into Fourier series, the structure- fluid coupling dynamic response is solved. The effects of lamination angle, layer number, depth of fluid region and loading forms on dynamic response are investigated.
In consideration of the effects of transverse shear deformation and structure-fluid interaction, the analytical expression of fluid force between a floating laminated composite plate and liquid surface is obtained. By expanding the displacements into Fourier series, the structure- fluid coupling dynamic response is solved. The effects of lamination angle, layer number, depth of fluid region and loading forms on dynamic response are investigated.
1997, (4): -.
Abstract:
1997, (4): -.
Abstract:
As the solution of the two equations for determining the existing fifth order Stokes wave derived by Skjelbreia is complex and tedious, the two equations are simplified into one equation for determining d/ L, i. e., f(H, T, d / L) = 0. According to this simplified method, three cases of the solution for the Skjelbreia equations have been found: one accurate solution; more than one accurate solution and no accurate solution (but there exists the optimum approximate solution in the area of satisfying Skjelbreia equations). As to the case of more than one accurate solution, the reasonable solution can be judged from the method of variational principle, by means of which an optimum solution improved from the solution of Skjelbreia equations in the area of satisfying the original mathematical equations of non-vortex and nonlinear wave theory, i. e., the optimum fifth order Stokes wave, is given.
As the solution of the two equations for determining the existing fifth order Stokes wave derived by Skjelbreia is complex and tedious, the two equations are simplified into one equation for determining d/ L, i. e., f(H, T, d / L) = 0. According to this simplified method, three cases of the solution for the Skjelbreia equations have been found: one accurate solution; more than one accurate solution and no accurate solution (but there exists the optimum approximate solution in the area of satisfying Skjelbreia equations). As to the case of more than one accurate solution, the reasonable solution can be judged from the method of variational principle, by means of which an optimum solution improved from the solution of Skjelbreia equations in the area of satisfying the original mathematical equations of non-vortex and nonlinear wave theory, i. e., the optimum fifth order Stokes wave, is given.
1997, (4): -.
Abstract:
The first-yield collapse of submarine pipelines with an initial out-of-roundness imperfection under combined bending and external pressure load is formulated by means of the Von. Mises yield criterion. The formula reduces to Timoshenko and Gere's expression in the case of external pressure load alone. The influence curves of various parameters on the yield strength are presented, the collapse of submarine pipelines in a deep water region is numerically predicted, and the effect of pre-yield nonlinear bending on the yield strength is also examined.
The first-yield collapse of submarine pipelines with an initial out-of-roundness imperfection under combined bending and external pressure load is formulated by means of the Von. Mises yield criterion. The formula reduces to Timoshenko and Gere's expression in the case of external pressure load alone. The influence curves of various parameters on the yield strength are presented, the collapse of submarine pipelines in a deep water region is numerically predicted, and the effect of pre-yield nonlinear bending on the yield strength is also examined.
1997, (4): -.
Abstract:
This paper presents a series of design curves to aid in the selection of turret mooring systems for tankers based Floating Production Storage and Offloading (FPSO) systems. These curves are appropriate to water depths ranging from 100 m to 600 m. The curves can be used as a preliminary design tool, allowing the designer to quickly evaluate alternative mooring system configurations, including the number of mooring lines, the characteristics of chain and wire rope to be deployed and the initial tension. With a knowledge of the total environmental force and vessel motion characteristics, the designer can determine the appropriate system for closer evaluation.
This paper presents a series of design curves to aid in the selection of turret mooring systems for tankers based Floating Production Storage and Offloading (FPSO) systems. These curves are appropriate to water depths ranging from 100 m to 600 m. The curves can be used as a preliminary design tool, allowing the designer to quickly evaluate alternative mooring system configurations, including the number of mooring lines, the characteristics of chain and wire rope to be deployed and the initial tension. With a knowledge of the total environmental force and vessel motion characteristics, the designer can determine the appropriate system for closer evaluation.
1997, (4): -.
Abstract:
In this paper, the maneuvering characteristics of a low speed submersible are investigated. First, the captive model tests are carried out to obtain the hydrodynamic forces acting on the submersible using a Planar Motion Mechanism (PMM). For the hydrodynamic forces within a wide range of attack angles, the hydrodynamic coefficients whictuare usually used in the conventional maneuvering motion are quite difficult to be applied. In this case, a Fourier series is adopted to represent the hydrodynamic forces and it fits the experimental data well. Then, based on the experimental results the simulation calculations are made to predict some of the maneuvering performance of the low speed submersible.
In this paper, the maneuvering characteristics of a low speed submersible are investigated. First, the captive model tests are carried out to obtain the hydrodynamic forces acting on the submersible using a Planar Motion Mechanism (PMM). For the hydrodynamic forces within a wide range of attack angles, the hydrodynamic coefficients whictuare usually used in the conventional maneuvering motion are quite difficult to be applied. In this case, a Fourier series is adopted to represent the hydrodynamic forces and it fits the experimental data well. Then, based on the experimental results the simulation calculations are made to predict some of the maneuvering performance of the low speed submersible.
1997, (4): -.
Abstract:
According to the field test data of laterally loaded steel piles at home and abroad, an empirical formula for evaluating the modulus of subgrade reaction under static load in layered soil is proposed. The suggested formula takes account of not only non-linearity of K5 with the depth but also its variation with the load. It is shown that the computed bending moments along the pile shaft and the deflection at the pile top are consistent with the measured ones.
According to the field test data of laterally loaded steel piles at home and abroad, an empirical formula for evaluating the modulus of subgrade reaction under static load in layered soil is proposed. The suggested formula takes account of not only non-linearity of K5 with the depth but also its variation with the load. It is shown that the computed bending moments along the pile shaft and the deflection at the pile top are consistent with the measured ones.
1997, (4): -.
Abstract:
The groyne has been used widely in bank protection and river regulation. The plane layout and structural style of groyne are closely related to the stability of the groyne itself and the effect of bank protection. In this paper, based on the preliminary summary of the design of bank protection in the bore surging area of Qiantang River, some problems regarding the structure of groyne are pointed out and an improved plan is put forward. Site experiment was carried out combined with an emergency repair. The results of the experiment indicate that the improved project is reliable and successful.
The groyne has been used widely in bank protection and river regulation. The plane layout and structural style of groyne are closely related to the stability of the groyne itself and the effect of bank protection. In this paper, based on the preliminary summary of the design of bank protection in the bore surging area of Qiantang River, some problems regarding the structure of groyne are pointed out and an improved plan is put forward. Site experiment was carried out combined with an emergency repair. The results of the experiment indicate that the improved project is reliable and successful.
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