Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplis...Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplished by the ship traveling from the depth h1 into the depth h2 via a step bottom. A small tsunami would be created after this transition. However, the unsteady wave-making resistance induced by this new phenomenon has not been well documented by literature. Therefore, the main purpose of the present study is to quantify the effects of an uneven bottom on the unsteady wash waves and wave-making resistance acting on the ship. An upwind differential scheme is commonly used in the Euler method to deal with the convection terms under free-surface condition to prevent waves in the upstream. Evidently, it cannot be applied to the present problem due to upstream waves generated by the ship would be dampened by the upwind scheme. The central differential scheme provides more accurate results,but it is not unconditionally stable. An MEL method is therefore employed to investigate the upstream wave generated by the ship moving over the uneven bottom. Simulation results show that the hydrodynamic interaction between the ship and the uneven bottom could initiate an upstream tsunami, as well as unsteady wave-making resistance on ships.The unsteady wave-making resistance oscillates periodically, and the amplitude and period of the oscillations are highly dependent on speed and water depth.展开更多
Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain...Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain. The free surface velocities and the bottom velocities were connected by the exact solution of the Laplace equation. Taking the velocities on half relative water depth as the fundamental unknowns, terms relating to the gradient of the water depth were retained in the inverse series expansion of the exact solution, with which the problem was closed. With enhancements of the finite order Taylor expansion for the velocity field, the application range of the present model was extended to the slope bottom which is not so mild. For linear properties, some validation computations of linear shoaling and Booij' s tests were carried out. The problems of wave-current interactions were also studied numerically to test the performance of the enhanced Boussinesq equations associated with the effect of currents. All these computational results confirm perfectly to the theoretical solution as well as other numerical solutions of the full potential problem available.展开更多
The spatial coherence of sound field in the reflection area of deep-water bottom is studied by analyzing the data of an acoustic propagation experiment conducted in the South China Sea. Some different oscillation patt...The spatial coherence of sound field in the reflection area of deep-water bottom is studied by analyzing the data of an acoustic propagation experiment conducted in the South China Sea. Some different oscillation patterns of the measured horizontal longitudinal correla- tions of acoustic field are observed for two different tracks in the flat bottom and the uneven bottom environments when the source distance ranges from 29 km to 35 km. Numerical analysis based on the ray theory is carried on to explain the causes of the differences. The experimental and mlmerical results show that the travel time differences between the one-bottom-reflection （1BR） rays, which make a major contribution to the sound field of the 1BR area in flat bottom environment, decrease gradually with increasing horizontal distance. Then the phase of the interference cyclically changes within 27r, leading to the correlations＇ periodical oscillation in deep water with flat bottom. In the uneven bottom environment, however, due to the reflection- blockage effects of the sea hill on the 1BR sound beams, the sound transmission losses （TLs） in- crease significantly in the reflection area of the sea hill. What＇s more, the horizontal-longitudinal correlations decreasing slightly in general don＇t show obvious cyclical oscillation any longer in the corresponding reflection area because of the complex interference of the relatively more eigenrays. This work is of significance to analyze the detection performance of the sonar array in deep water with the complicated bathymetry environment.展开更多
A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Ha...A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.展开更多
为精确模拟浅水波非线性演化过程中的动边界,提出一种基于位移的Hamilton变分原理,并进而导出一种基于位移的浅水方程(Shallow Water Equation based on Displacement,SWE-D).SWE-D以位移为基本未知量,可以精确满足动边界处的零水深要...为精确模拟浅水波非线性演化过程中的动边界,提出一种基于位移的Hamilton变分原理,并进而导出一种基于位移的浅水方程(Shallow Water Equation based on Displacement,SWE-D).SWE-D以位移为基本未知量,可以精确满足动边界处的零水深要求并精确捕捉动态边界位置,且解具有协调性.在Hamilton变分原理的框架下,分别采用有限元和保辛积分算法对该浅水方程进行空间离散和时间积分,可有效地处理不平水底情况,保证对非线性演化进行长时间仿真的精度.数值算例表明该方法适用于浅水动边界问题的数值模拟.展开更多
苏州河河口水闸(以下简称苏闸)运行至今出现了诸多病险问题,已严重影响安全运行。因苏闸工程的特殊性,难以使用常规的风险识别方法。为了保障水闸的安全运行,基于故障树风险分析方法,按照功能边界将苏闸划分为5个子系统;确定了各子系统...苏州河河口水闸(以下简称苏闸)运行至今出现了诸多病险问题,已严重影响安全运行。因苏闸工程的特殊性,难以使用常规的风险识别方法。为了保障水闸的安全运行,基于故障树风险分析方法,按照功能边界将苏闸划分为5个子系统;确定了各子系统存在的26项故障模式,建立了苏闸故障树(Fault Tree Analysis),通过下行法确定一阶、二阶、三阶、五阶最小割集,识别苏闸的风险源为“地基不均匀沉降”“底轴不均匀变形”以及“监测系统缺陷”。研究成果不仅为管理部门提供了水闸风险管理的建议,而且对同类工程的设计、维护、监测、管理具有重要的参考价值。展开更多
基金financially supported by Natural Scienceof University of Jiangsu Province (Grant No.22KJB580004)the Key R&D Projects in Guangdong Province (Grant No.2020B1111500001)the Jiangsu Province“Six Talents Peak”High-Level Talents Support Project (Grant No.2018-KTHY-033)。
文摘Unsteady wash waves generated by a ship with constant speed moving across an uneven bottom topography are investigated by numerical simulations based on a Mixed Euler–Lagrange(MEL) method. The transition is accomplished by the ship traveling from the depth h1 into the depth h2 via a step bottom. A small tsunami would be created after this transition. However, the unsteady wave-making resistance induced by this new phenomenon has not been well documented by literature. Therefore, the main purpose of the present study is to quantify the effects of an uneven bottom on the unsteady wash waves and wave-making resistance acting on the ship. An upwind differential scheme is commonly used in the Euler method to deal with the convection terms under free-surface condition to prevent waves in the upstream. Evidently, it cannot be applied to the present problem due to upstream waves generated by the ship would be dampened by the upwind scheme. The central differential scheme provides more accurate results,but it is not unconditionally stable. An MEL method is therefore employed to investigate the upstream wave generated by the ship moving over the uneven bottom. Simulation results show that the hydrodynamic interaction between the ship and the uneven bottom could initiate an upstream tsunami, as well as unsteady wave-making resistance on ships.The unsteady wave-making resistance oscillates periodically, and the amplitude and period of the oscillations are highly dependent on speed and water depth.
基金Project supported by the National Natural Science Foundation of China (No. 10172058)the Special Fund for PhD Program of Education Ministry of China (No.2000024817)
文摘Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain. The free surface velocities and the bottom velocities were connected by the exact solution of the Laplace equation. Taking the velocities on half relative water depth as the fundamental unknowns, terms relating to the gradient of the water depth were retained in the inverse series expansion of the exact solution, with which the problem was closed. With enhancements of the finite order Taylor expansion for the velocity field, the application range of the present model was extended to the slope bottom which is not so mild. For linear properties, some validation computations of linear shoaling and Booij' s tests were carried out. The problems of wave-current interactions were also studied numerically to test the performance of the enhanced Boussinesq equations associated with the effect of currents. All these computational results confirm perfectly to the theoretical solution as well as other numerical solutions of the full potential problem available.
基金supported by the National Natural Science Foundation of China(11434012,41561144006,11404366)
文摘The spatial coherence of sound field in the reflection area of deep-water bottom is studied by analyzing the data of an acoustic propagation experiment conducted in the South China Sea. Some different oscillation patterns of the measured horizontal longitudinal correla- tions of acoustic field are observed for two different tracks in the flat bottom and the uneven bottom environments when the source distance ranges from 29 km to 35 km. Numerical analysis based on the ray theory is carried on to explain the causes of the differences. The experimental and mlmerical results show that the travel time differences between the one-bottom-reflection （1BR） rays, which make a major contribution to the sound field of the 1BR area in flat bottom environment, decrease gradually with increasing horizontal distance. Then the phase of the interference cyclically changes within 27r, leading to the correlations＇ periodical oscillation in deep water with flat bottom. In the uneven bottom environment, however, due to the reflection- blockage effects of the sea hill on the 1BR sound beams, the sound transmission losses （TLs） in- crease significantly in the reflection area of the sea hill. What＇s more, the horizontal-longitudinal correlations decreasing slightly in general don＇t show obvious cyclical oscillation any longer in the corresponding reflection area because of the complex interference of the relatively more eigenrays. This work is of significance to analyze the detection performance of the sonar array in deep water with the complicated bathymetry environment.
基金This project was supported by the National Outstanding Youth Science Foundation of China under contract! No. 49825161.
文摘A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.
文摘为精确模拟浅水波非线性演化过程中的动边界,提出一种基于位移的Hamilton变分原理,并进而导出一种基于位移的浅水方程(Shallow Water Equation based on Displacement,SWE-D).SWE-D以位移为基本未知量,可以精确满足动边界处的零水深要求并精确捕捉动态边界位置,且解具有协调性.在Hamilton变分原理的框架下,分别采用有限元和保辛积分算法对该浅水方程进行空间离散和时间积分,可有效地处理不平水底情况,保证对非线性演化进行长时间仿真的精度.数值算例表明该方法适用于浅水动边界问题的数值模拟.
文摘苏州河河口水闸(以下简称苏闸)运行至今出现了诸多病险问题,已严重影响安全运行。因苏闸工程的特殊性,难以使用常规的风险识别方法。为了保障水闸的安全运行,基于故障树风险分析方法,按照功能边界将苏闸划分为5个子系统;确定了各子系统存在的26项故障模式,建立了苏闸故障树(Fault Tree Analysis),通过下行法确定一阶、二阶、三阶、五阶最小割集,识别苏闸的风险源为“地基不均匀沉降”“底轴不均匀变形”以及“监测系统缺陷”。研究成果不仅为管理部门提供了水闸风险管理的建议,而且对同类工程的设计、维护、监测、管理具有重要的参考价值。
