1998 Vol.(4)
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1998, (4): -.
Abstract:
In this paper the parabolic approximation model based on mild-slope equation is used to study wave propagation over a slowly varying and frictional topography under wave-current interaction. A governing equation considering the friction effects is derived by the authors for the first time. A simplified form for the rate of wave energy dissipation is presented on the basis of the wave-current action conservation equation and the bottom friction model given by Yoo and O'connor (1987). Examples reveal that the present computational method can be used for the calculation of wave elements for actual engineering projects with large water areas.
In this paper the parabolic approximation model based on mild-slope equation is used to study wave propagation over a slowly varying and frictional topography under wave-current interaction. A governing equation considering the friction effects is derived by the authors for the first time. A simplified form for the rate of wave energy dissipation is presented on the basis of the wave-current action conservation equation and the bottom friction model given by Yoo and O'connor (1987). Examples reveal that the present computational method can be used for the calculation of wave elements for actual engineering projects with large water areas.
1998, (4): -.
Abstract:
An experimental program was carried out to study the shear behavior of the reinforced concrete composite beam (RCCB) subjected to two-phase uniformly distributed load. A total of 12 reinforced concrete composite beams were tested: 10 of them were the RCCB subjected to two-phase uniformly distributed load, the other 2 were the comparative reinforced concrete beams cast at the same time as the RCCB subjected to one-phase uniformly distributed load. The interface of precast unit and recast concrete was natural and rough. The test range of the main composite factors: the ratio of precast section depth to composite section depth was from 0.35 to 0.65, the ratio of first-phase load moment to precast section ultimate bearing moment was from 0.25 to 0.65. Based on the test results, the stresses of the longitudinal reinforcements and stirrups, the load-bearing properties of the interface, the crack state and the failure characteristics of the RCCB under uniformly distributed load are discussed. The effects of the stirrups, the concrete strength and the composite factors on the shear resistance of the RCCB are analyzed, and the method for evaluating the shear resistance of the RCCB is proposed.
An experimental program was carried out to study the shear behavior of the reinforced concrete composite beam (RCCB) subjected to two-phase uniformly distributed load. A total of 12 reinforced concrete composite beams were tested: 10 of them were the RCCB subjected to two-phase uniformly distributed load, the other 2 were the comparative reinforced concrete beams cast at the same time as the RCCB subjected to one-phase uniformly distributed load. The interface of precast unit and recast concrete was natural and rough. The test range of the main composite factors: the ratio of precast section depth to composite section depth was from 0.35 to 0.65, the ratio of first-phase load moment to precast section ultimate bearing moment was from 0.25 to 0.65. Based on the test results, the stresses of the longitudinal reinforcements and stirrups, the load-bearing properties of the interface, the crack state and the failure characteristics of the RCCB under uniformly distributed load are discussed. The effects of the stirrups, the concrete strength and the composite factors on the shear resistance of the RCCB are analyzed, and the method for evaluating the shear resistance of the RCCB is proposed.
1998, (4): -.
Abstract:
The numerical simulation is based on the authors' high-order models with a dissipative term for nonlinear and dispersive wave in water of varying depth. Corresponding finite-difference equations and general conditions for open and fixed natural boundaries with an arbitrary reflection coefficient and phase shift are also given in this paper. The systematical tests of numerical simulation show that the theoretical models, the finite-difference algorithms and the boundary conditions can give good calculation results for the wave propagating in shallow and deep water with an arbitrary slope varying from gentle to steep.
The numerical simulation is based on the authors' high-order models with a dissipative term for nonlinear and dispersive wave in water of varying depth. Corresponding finite-difference equations and general conditions for open and fixed natural boundaries with an arbitrary reflection coefficient and phase shift are also given in this paper. The systematical tests of numerical simulation show that the theoretical models, the finite-difference algorithms and the boundary conditions can give good calculation results for the wave propagating in shallow and deep water with an arbitrary slope varying from gentle to steep.
1998, (4): -.
Abstract:
In order to determine the extreme sea-state encountered by oceangoing vessels, a method for the prediction of wave parameters based on the data of long-term distribution sample is developed by use of the fitting approach with the Weibull probability functions and the power functions. As an example a special calculation result is given including the analysis of wave parameters for the data of the North Atlantic Basin and the computation of motion and load encountered by two container ships CSLR and CSBV in different loading conditions. All computation results are satisfactory compared with corresponding design results.
In order to determine the extreme sea-state encountered by oceangoing vessels, a method for the prediction of wave parameters based on the data of long-term distribution sample is developed by use of the fitting approach with the Weibull probability functions and the power functions. As an example a special calculation result is given including the analysis of wave parameters for the data of the North Atlantic Basin and the computation of motion and load encountered by two container ships CSLR and CSBV in different loading conditions. All computation results are satisfactory compared with corresponding design results.
1998, (4): -.
Abstract:
This paper analyzes the pipe network system of oil- gas collection and transportation for offshore oilfield development. A "0-1" integer linear programming model is constructed to optimize the investment of seabed pipe network. The mathematical model is solved by the spanning tree method of graph theory and network analysis. All spanning trees of a network graph compose all the feasible solutions of the mathematical model. The optimal solution of the model is the spanning tree with the minimum cost among all spanning trees. This method can be used to optimize the seabed pipe network system and give a minimum cost plan for the development of offshore marginal oilfield groups.
This paper analyzes the pipe network system of oil- gas collection and transportation for offshore oilfield development. A "0-1" integer linear programming model is constructed to optimize the investment of seabed pipe network. The mathematical model is solved by the spanning tree method of graph theory and network analysis. All spanning trees of a network graph compose all the feasible solutions of the mathematical model. The optimal solution of the model is the spanning tree with the minimum cost among all spanning trees. This method can be used to optimize the seabed pipe network system and give a minimum cost plan for the development of offshore marginal oilfield groups.
1998, (4): -.
Abstract:
In the designing of the flexible fender pile, M-method is usually adopted. But M-method is usable only in the case that the value of the force (moment M and shear force Q) exerted on the pile above the soil is known. In practical cases, only the percussive energy of the ship can be found, while the exact value of the percussive force cannot be computed directly. In this paper, a method is introduced which can be used to calculate the inner force of flexible fender piles by a computer in these cases. First, according to the known docking dynamic energy of a ship, the absorbed energy can be found from the deformation of the pile and the rubber fender respectively, at the same time the value of the force acting on the fender piles and the reaction of fenders can be calculated. Then the inner force and displacement of the fender piles can also be calculated further by M-method. The whole computing process is realized by a computer program and the results obtained are reasonable. In this paper, the computation, the iteration method and the computer program are all expounded in detail. This method can be applied to the design of fender piles and type selection of rubber fenders in practical projects.
In the designing of the flexible fender pile, M-method is usually adopted. But M-method is usable only in the case that the value of the force (moment M and shear force Q) exerted on the pile above the soil is known. In practical cases, only the percussive energy of the ship can be found, while the exact value of the percussive force cannot be computed directly. In this paper, a method is introduced which can be used to calculate the inner force of flexible fender piles by a computer in these cases. First, according to the known docking dynamic energy of a ship, the absorbed energy can be found from the deformation of the pile and the rubber fender respectively, at the same time the value of the force acting on the fender piles and the reaction of fenders can be calculated. Then the inner force and displacement of the fender piles can also be calculated further by M-method. The whole computing process is realized by a computer program and the results obtained are reasonable. In this paper, the computation, the iteration method and the computer program are all expounded in detail. This method can be applied to the design of fender piles and type selection of rubber fenders in practical projects.
1998, (4): -.
Abstract:
The olTshore platform with bucket foundations is a new type of offshore platform that distinguishes from traditional template platforms by replacing driven piles with bucket foundations. The suction penentration of bucket foundation is a complicated hydro-dynamic process. The key of this process is the seepage field caused by the difference of pressure applied on purpose inside and outside the bucket. The appearance and developement of seepage field has a decisive influence on the suction penetration process. In this study, the finite element analysis method is applied to the dynamic simulation of the seepage field of suction penetration of bucket foundation. A criterion is suggested to distinguish the hydro-dynamic stability of the soil inside the bucket according to the critical hydraulic gradient method. The reliability of the model and its applicability to engineering practice have been proved through comparison between the results of model test and finite element calculation.
The olTshore platform with bucket foundations is a new type of offshore platform that distinguishes from traditional template platforms by replacing driven piles with bucket foundations. The suction penentration of bucket foundation is a complicated hydro-dynamic process. The key of this process is the seepage field caused by the difference of pressure applied on purpose inside and outside the bucket. The appearance and developement of seepage field has a decisive influence on the suction penetration process. In this study, the finite element analysis method is applied to the dynamic simulation of the seepage field of suction penetration of bucket foundation. A criterion is suggested to distinguish the hydro-dynamic stability of the soil inside the bucket according to the critical hydraulic gradient method. The reliability of the model and its applicability to engineering practice have been proved through comparison between the results of model test and finite element calculation.
1998, (4): -.
Abstract:
By means of nonlinear pushover collapse analysis approach, the aseismic reliability analyses of two offshore jacket platforms in the Bohai Gulf in China are studied according to their ocean location and environmental loadings there. On the basis of those analyses, an aseismic reliability analysis approach is presented. The results show that the aseismic reliability of those platforms is high. Also it is proved that this aseismic reliability analysis approach is simple, practical and reliable.
By means of nonlinear pushover collapse analysis approach, the aseismic reliability analyses of two offshore jacket platforms in the Bohai Gulf in China are studied according to their ocean location and environmental loadings there. On the basis of those analyses, an aseismic reliability analysis approach is presented. The results show that the aseismic reliability of those platforms is high. Also it is proved that this aseismic reliability analysis approach is simple, practical and reliable.
1998, (4): -.
Abstract:
Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m under the ground. The wave velocity method, bender element method, LDT and the formula derived by the authors are used, focus is put on the pre-failure mechanical behavior of the clay. The analysis shows that, (i) pore-pressure coefficient B is less than 1.0, (ii) the relationship between shear modulus and Poisson's ratio is not in agreement with that reported before, (iii) the modulus measured with LDT is still less than that measured with bender element method, and (iv) there are two threshold strains, within which the clay can be considered as elastic, and both of them are larger than that reported before.
Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m under the ground. The wave velocity method, bender element method, LDT and the formula derived by the authors are used, focus is put on the pre-failure mechanical behavior of the clay. The analysis shows that, (i) pore-pressure coefficient B is less than 1.0, (ii) the relationship between shear modulus and Poisson's ratio is not in agreement with that reported before, (iii) the modulus measured with LDT is still less than that measured with bender element method, and (iv) there are two threshold strains, within which the clay can be considered as elastic, and both of them are larger than that reported before.
1998, (4): -.
Abstract:
On the basis of ice- induced forced vibration model, ice- induced displacement responses of offshore fixed platforms are investigated in both time domain and frequency domain. The relationships of ice-induced displacement responses with ice breaking modes, ice acting directions and platform structures are analyzed and determined. The results lead to an important conclusion obtained for the first time that ice breaking frequency and the natural frequency of the first mode of the platform are the two main factors that dominate the degree of vibration. The present work provides a firm basis for both design and operation of fixed platforms against ice loading.
On the basis of ice- induced forced vibration model, ice- induced displacement responses of offshore fixed platforms are investigated in both time domain and frequency domain. The relationships of ice-induced displacement responses with ice breaking modes, ice acting directions and platform structures are analyzed and determined. The results lead to an important conclusion obtained for the first time that ice breaking frequency and the natural frequency of the first mode of the platform are the two main factors that dominate the degree of vibration. The present work provides a firm basis for both design and operation of fixed platforms against ice loading.
1998, (4): -.
Abstract:
The retaining wall made of large successive cylinders is a kind of structure which draws much attention in coastal engineering of China. The earth pressure on the arched back of large successive cylinders is different from that on the plane back of a general wall. On the basis of equilibrium offerees on the strip element taken from the soil between two cylinders, the differential equation is established and the analytic solution to the equation is obtained. The formulas of earth pressure on large successive cylinders are given in this paper. The distribution of earth pressure around the circle given by the present formulas is different from that given by the formulas commonly used at present, but it is identical with that measured in the model test.
The retaining wall made of large successive cylinders is a kind of structure which draws much attention in coastal engineering of China. The earth pressure on the arched back of large successive cylinders is different from that on the plane back of a general wall. On the basis of equilibrium offerees on the strip element taken from the soil between two cylinders, the differential equation is established and the analytic solution to the equation is obtained. The formulas of earth pressure on large successive cylinders are given in this paper. The distribution of earth pressure around the circle given by the present formulas is different from that given by the formulas commonly used at present, but it is identical with that measured in the model test.
1998, (4): -.
Abstract:
When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.
When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.
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