共查询到20条相似文献，搜索用时 31 毫秒
1.
在薄片炸药冲击试验中,所产生的均布流场压力会对波纹板防爆墙造成中拱效果,但该作用机理尚未明确。在该试验的比较基础上,通过流固耦合法对薄片炸药所产生的流场压力变化开展研究。在分析波纹面板及空气的压力分布变化后,发现并揭示了波纹面板上出现第二次压力峰值和自由边压力耗散现象的机理。在此基础上定量分析了薄片炸药量和槽型深度对流场压力和波纹面板变形的变化规律。研究发现,随着炸药量增加,二次压力峰值将使波纹面板中拱现象愈加明显,而槽型深度会加大压力峰值。文中机理和定量分析可为海洋平台防爆结构的设计分析提供补充参考。 相似文献
2.
Corrugated stainless steel membranes have been used as the primary barriers for LNG carriers to reduce thermal stresses at cryogenic temperatures. As the capacity of the LNG cargo is increased, however, the corrugated stainless steel membranes suffer from buckling and collapse due to increased sloshing loads in large-capacity LNG cargo carriers. In this study, the pressure resistance of the corrugated part of the stainless steel membrane was evaluated using a finite element method for better design of the LNG containment system, and an experimental equipment was developed and the pressure resistance of the stainless steel corrugations was measured and compared with the calculated results. In addition, a new membrane with high-pressure resistance and its reinforcing method were developed and evaluated experimentally. 相似文献
3.
A three-dimensional general mathematical hydroelastic model dealing with the problem of wave interaction with a floating and a submerged flexible structure is developed based on small amplitude wave theory and linear structural response. The horizontal floating and submerged flexible structures are modelled with a thin plate theory. The linearized long wave equations based on shallow water approximations are derived and results are compared. Three-dimensional Green’s functions are derived using fundamental source potentials in water of finite and infinite depths. The expansion formulae associated with orthogonal mode-coupling relations are derived based on the application of Fourier transform in finite and infinite depths in case of finite width in three-dimensions. The usefulness of the expansion formula is demonstrated by analysing a physical problem of surface gravity wave interaction with a moored finite floating elastic plate in the presence of a finite submerged flexible membrane in three-dimensions. The numerical accuracy of the method is demonstrated by computing the complex values of reflected wave amplitudes for different modes of oscillation and mooring stiffness. Further, the effect of compressive force and modes of oscillations on a free oscillation hydroelastic waves in a closed channel of finite width and length for floating and submerged elastic plate system is analysed. 相似文献
4.
弹性液舱内液体晃荡实验研究 总被引：1，自引：0，他引：1
通过物理模型实验,对水平简谐激励下弹性矩形液舱内液体晃荡问题进行了研究。实验中给出了不同液深和不同激励振幅下弹性液舱内液体最低阶固有频率。采用影像采集与分析系统获得液舱内自由液面的形状和高度,通过压力采集系统得到舱壁上的压力分布。实验中分析了不同液深、不同激励频率下弹性和刚性液舱内自由液面高度和晃荡压力的变化特性。比较了弹性和刚性液舱内不同位置处自由液面高度随外界激励频率的变化规律,以及舱壁上不同位置处的压力峰值随外界激励频率的变化规律。结果表明:非共振情况下,弹性和刚性实验结果及理论值三者的波高和压力较为接近。共振情况下,弹性和刚性波高基本相等,在近舱壁处二者明显大于理论值,而在远离舱壁处二者与理论值存在一定差别;弹性压力较刚性压力略小,但二者与理论值差别较大。 相似文献
5.
In the present study, three-dimensional sloshing phenomena occurring in liquid cargo tanks are numerically simulated. The Navier-Stokes equations and continuity equation are used for the governing equations, and solved with a finite difference method in a rectangular fixed staggered mesh system. The positions of free surface are defined by the Marker density method satisfying the free-surface boundary conditions, and the flows of the gas and liquid regions are simulated simultaneously. The irregular leg length and star method is employed on the cells near the free surface for the computations of pressure. The computation results are compared with other experimental results to verify the consistency of the present numerical method, and the agreements are reasonably good. Furthermore, the flow characteristics inside a partially filled liquid tank of a real sized ship oscillating regularly and irregularly are computed to verify the possibility of practical application of the present method. 相似文献
6.
A method combining boundary and finite element approaches as well as modal analysis to solve the acoustical scattering from elastic obstacle in infinite fluid is described. An elastic cylinder with finite length immersed in water is chosen as an example for numerical demonstration. The computed frequency response and direction pattern of the backscattering target strength of the cylinder are conformable to those measured. 相似文献
7.
The paper considers the hydroelastic interaction involved in panel-water impacts for high-speed craft. Hydroelastic panel-water impacts are simulated by using the finite element code LS-DYNA and a simplified in-house developed method. The mechanisms involved are studied through a systematic series of simulations comprising different impact velocities, deadrise angles, boundary conditions, membrane effects, and panel properties. The terms inertial hydroelastic effects and kinematic hydroelastic effects are introduced to categorize the different mechanisms involved in the hydroelastic problem. It is shown that hydroelastic effects can both increase and reduce the panel responses depending on the impact envelope considered, and it is made clear that the impact envelope has to be carefully considered when establishing the significance of hydroelasticity in a hull-water impact problem. Membrane effects are shown to have large influences on the hydroelastic effects even for moderate panel deflections. The results generated are further used to evaluate and discuss hydroelastic criterion and methods for hydroelastic characterization. 相似文献
8.
The hydrodynamic problem of a two dimensional wedge tank filled with liquid entering a calm water surface is analysed based on the incompressible velocity potential theory. The motion effect of inner liquid on the entry process is investigated through comparison with the result containing equivalent solid mass or the liquid being frozen. The problem is solved through the boundary element method in the time domain. Two separated computational regions are constructed. One is the inner domain for the internal liquid, and the other is the outer open domain for the open water. The former is solved in the physical coordinate system, and the latter is solved in a stretched coordinate system. The solutions of two separated domains are connected through the motion of the body. The auxiliary function method is extended to decouple the nonlinear mutual dependence between fluid loads from two separated domains and the body motion. Detailed results for wedge motion, external impact pressure and free surface, and for internal pressure, free surface deformation and liquid motion are provided. Through comparison with the results of a wedge tank with frozen ice, in-depth discussion on the effect of the inner liquid is provided. 相似文献
9.
The laboratory and field experiments so far have shown that when a wave breaks directly on a vertical faced coastal structure, the resulting impact pressures may become very severe in magnitude and short in duration. Some experimental evidence in the literature suggests that the structural response to the extremely high magnitude impact forces is only limited. This study is mainly concerned with the comparison of the theoretical and experimental results of a vertical wall response under the wave impact loading. In the dynamic analysis of the wall the classical elastic plate theory is used and the numerical results for the dynamic values of the transverse displacement are obtained by employing the method of finite elements. In the theoretical analyses the experimental pressure histories are used and the theoretical wall deflection histories are compared with the experimental results. The computational and experimental deflection histories exhibit similar patterns. The theoretical maximum wall deflections are mostly found to be slightly smaller than the experimental values. 相似文献
10.
Shen Huishen
Professor 《中国海洋工程》1996,(4)
- posthuckling analysis is presented for the stilTened cylindrical shell of finite length subjected to combined loading of external liquid pressure and axial compression. The formulations are based on a boundary layer theory of shell buckling, which includes the effects of nonlinear prebuckling deformations, nonlinear large deflections in the postbuckling range and initial geometrical imperfections of the shell. The "smeared stifl'cner" approach is adopted for the stiffencrs. In the analysis a singular perturbation technique is used (o determine the interactive buckling loads and the postbuckling paths. Numerical examples cover the performance of perfect and imperfect, stringer and ring stiffened cylindrical shells. Typical results arc presented in the dimcnsionless graphical form. 相似文献
11.
The paper presents a theoretical and an experimental investigation into the plastic collapse of circular steel corrugated cylinders under external hydrostatic pressure. The experimental investigation gives a detailed study of 9 steel corrugated cylinders which were tested to destruction. Six of these cylinders failed by plastic non-symmetric bifurcation buckling and three failed by plastic axisymmetric deformation. The results of these tests were used, together with the results obtained from previous tests, to present a design chart for the plastic collapse of these vessels. The design chart was obtained by a semi-empirical approach, where the thinness ratios of the vessels were plotted against their plastic knockdown factors. The process of using the design chart is to calculate the theoretical elastic instability pressure for a perfect vessel by the finite element method and also to calculate the thinness ratio for this vessel. Using the appropriate value of the thinness ratio, the plastic knockdown factors are obtained from the design chart. To obtain the actual collapse pressure of the vessel, the theoretical elastic instability pressure for a perfect vessel is divided by the plastic knockdown factor. This work is of importance in ocean engineering. A large safety factor must also be introduced. 相似文献
12.
Shape optimization of two-dimensional cavitators in supercavitating flows, using NSGA II algorithm 总被引：1，自引：0，他引：1
The reduction of energy consumption of high speed submersible bodies is an important challenge in hydrodynamic researches. In this paper, shape optimization of two-dimensional cavitators in supercavitating flows is studied. A two dimensional supercavitation potential flow passes a symmetric two dimensional cavitator, which is placed perpendicular to the flow in a channel of infinite length and immediately a cavity is formed behind the cavitator. This is because of the generation of a gas or vapor cavity between the body and the surrounding liquid due to the change in a high speed flow direction passing the cavitator. Drag force acting on this supercavitating body dictates the thrust requirements for the propulsion system, to maintain a required cavity at the operating speed. Therefore, any reduction in the drag force, by modifying the shape of the cavitator, will lead to decrease this force. This study concentrates on the optimization of two dimensional cavitators in order to decrease drag coefficient for a specified after body length and velocity in a potential flow. To achieve this goal a multi-objective optimization problem is defined to optimize cavitator shapes in supercavitating flow. The so-called NSGA II (Non-dominated Sorting Genetic Algorithm) algorithm is used as an optimization method. Design parameters and constraints are obtained according to supercavitating flow characteristics and cavitator modeling and objective functions are generated using Linear Regression Method. The obtained results are compared with other classic optimization methods, like the weighted sum method, for validation. 相似文献
13.
基于粘性流模型的筒型基础防波堤波浪力数值分析 总被引：3，自引：0，他引：3
筒型基础防波堤是一种新型港口海岸工程结构,其基础上部是由连续排列的圆筒构成的直立防浪墙.采用粘性流数值模型,研究连续圆筒防波堤上波浪力竖向分布、水平(沿圆筒环向)分布和波浪力合力特性,并对粘性流数值模型计算的平面直墙波浪力与海港水文规范方法计算结果;粘性流数值模型计算的连续圆筒墙面波浪力与平面直墙波浪力;无限长连续圆筒墙面波浪力与有限长连续圆筒墙面波浪力进行比较分析.针对所选工程算例,建议按<海港水文规范>中平面直墙波浪力计算方法确定连续圆筒防波堤上的波浪力时,波峰时考虑0.90左右的折减系数,波谷时考虑0.95左右的折减系数. 相似文献
14.
A two-dimensional finite wedge entering water obliquely in freefall with three degrees of freedom is considered through the velocity potential theory for the incompressible liquid. The problem is solved by using the boundary element method in the time domain. The scheme of the stretched coordinate system is adopted at the initial stages when only a small part of the wedge near its tip has entered water. The auxiliary function method is adopted to decouple the nonlinear mutual dependence between the body motions in three degrees of freedom and the fluid flow. When the liquid has detached from the knuckle of the wedge, the free jet is treated through the momentum equation. The developed method is verified through existing results for one degree of freedom in vertical motion. Various case studies are undertaken for a wedge entering water vertically, obliquely and with rotational angles. Results are provided the accelerations, velocities, pressure distribution and free surface deformation, and the physical implications are discussed. 相似文献
15.
A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation. 相似文献
16.
Further developments and applications of the 2D harmonic polynomial cell (HPC) method proposed by Shao and Faltinsen [22] are presented. First, a local potential flow solution coupled with the HPC method and based on the domain decomposition strategy is proposed to cope with singular potential flow characteristics at sharp corners fully submerged in a fluid. The results are verified by comparing them with the analytical added mass of a double-wedge in infinite fluid. The effect of the singular potential flow is not dominant for added mass and damping, but the error is non-negligible when calculating mean wave loads using direct pressure integration. Then, the double-layer nodes technique is used to simulate a thin free shear layer shed from lifting bodies, across which the velocity potential is discontinuous. The results are verified by comparing them with analytical results for steady and unsteady lifting problems of a flat plate in infinite fluid. The latter includes the Wagner problem and the Theodorsen functions. Satisfactory agreement with other numerical results is documented for steady linear flow past a foil and beneath the free surface. 相似文献
17.
A surface panel method treating a boundary-value problem of the Dirichlet type with the free surface is presented to design a three-dimensional body corresponding to a prescribed pressure distribution. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by four-point finite difference scheme. Sample designs for submerged spheroids and Wigley hull are carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but also by experiment. 相似文献
18.
The purpose of the present paper is to develop a potential-based panel method for determining the steady potential flow about three-dimensional hydrofoil under free surface. The method uses constant-strength doublets and source density distribution over the foil body surface and thereby Dirichlet-type boundary condition is used instead of Neumann-type condition. On the undisturbed free surface source density is used to meet the free surface condition that is linearised in terms of double-body model approach and is discretised by a one-side, upstream, four-point finite difference operator. After solving the doublets on the foil and sources on the free surface, the numerical results of pressure, lift and resistance coefficients and also wave profiles can then be calculated for different Froude number and depth of submergence to demonstrate the influence of free surface and aspect ratio effects on performance of the hydrofoil. 相似文献
19.
Alexander Korobkin 《Ocean Engineering》1998,25(8):687-714
The impact of an elastic plate onto the compressible fluid without free surface deformation is considered. The ability of the liquid volume to be deformed is geometrically limited which leads to severe impact conditions. The present analysis is focused on the stresses in the plate and the hydrodynamic loads under the impact. The motivation for this research comes from ship hydrodynamics, where the hulls of a catamaran restrict the liquid outflow and the water impacts onto the wetdeck. The influence of the air on the impact process is investigated. The analysis did not reveal any great advantage of utilizing the air-cushion effect or ejection of air into the water near the impact region to prevent high stresses in the elastic plate. It was found that in the problem considered, the stress peaks far from the plate centre and the one-mode approximation does not provide correct information about the stress level. 相似文献
20.
《Marine Geology》2006,225(1-4):1-4
The depth of the free methane gas horizon in Eckernförde Bay, Western Baltic Sea, was monitored over 4 months in 1-h intervals with an echo sounder mounted on a tower at the seafloor. The depth to the top of the free gas varied between 50 cm and 100 cm below seafloor. Short-term fluctuations of free gas depth are related for the most part to changes of total pressure (air pressure and water level), the observation period was too short to demonstrate the effect of the annual temperature cycle.The correlation of gas depth changes and total pressure agrees well with theory which predicts a linear influence of pressure fluctuations on gas solubility. Since the methane content in the pore water of Eckernförde Bay is at the saturation limit environmental changes (pressure and temperature variations) cannot be buffered and have an instant impact on free gas presence.The implications of this observation are manifold. Geo-technically, the bearing strength of the seafloor is altered by the presence of gas bubbles. Similarly, sonar systems are influenced by the presence of gas bubbles which alter the acoustic seafloor properties. Of ecological interest is that pressure drops can trigger a sudden ebullition of the greenhouse gas methane from the seafloor into the atmosphere. 相似文献