An unsteady three-dimensional eutrophication model in Tolo harbour, Hong Kong     

Chau KW 《Marine pollution bulletin》2005,51(8-12):1078-1084

The eutrophication phenomenon often leads to undesirable water quality. This paper delineates an unsteady three-dimensional finite difference numerical model for eutrophication dynamics in the coastal waters of Tolo harbour, Hong Kong, employing the numerically generated, boundary-fitted, orthogonal curvilinear grid system as well as a grid “block” technique. It models the transport and interaction of nine water quality constituents. Adjustments of values of some kinetic coefficients in the model are effected through calibration with field data. It is demonstrated that the model can reasonably reproduce the interactions amongst all the water quality constituents, the eutrophication processes and, in particular, the featured bottom water anoxic condition during the summer in Tolo harbour.  相似文献   

豚尾的摆动推进     

程健宇  庄礼贤  童秉纲 《海洋科学》1992,16(4):22-27

采用非定常势流理论,对高游速海洋动物所具有的新月形尾推进进行了分析,着重考虑了推进力能量的频率特性,并理论估算了一种海豚的实际游动状况。  相似文献   

一维河网不稳定流模型在黄河下游枯季水量调度中的应用     

任汝信  童国庆  李静 《湖泊科学》2004,16(Z1):111-115

随着黄河下游工农业生产的不断发展,人民群众生活质量不断提高,黄河水资源供需矛盾越来越突出.确保黄河不断流必然面临着越来越大的压力,必须提高水量调度的快速反映能力.本文讨论了一维河网不稳定流数值计算模型在黄河下游枯水演进中的数学基础、 实现方法和在此基础上建立的枯季水量调度软件的应用.从对八十年代以来的枯水年份的模拟情况来看,流量拟合结果均能达到乙级以上,这对于水资源短缺的黄河下游的引黄调度具有重要的参考价值.  相似文献   

DEPTH-AVERAGE ANALYSIS OF HYSTERESIS BETWEEN FLOW AND SEDIMENT TRANSPORT UNDER UNSTEADY CONDITIONS   总被引：1，自引：0，他引：1  

Weiming WU Mustafa ALTINAKAR Sam S. Y. WANG 《国际泥沙研究》2006,21(2):101-112

1 INTRODUCTION Flow and sediment transport in natural rivers are generally unsteady, and exhibit temporal and spatial lags. Traditionally, in most hydraulic engineering problems the unsteady flow and sediment transport are approximately treated as steady …  相似文献   

On the hydrodynamic loading of marine cycloidal propeller during maneuvering     

《Applied Ocean Research》2019

In marine cycloidal propeller (MCP), the inflow velocity vector to the propeller blade continuously changes at different blade orbit angle. Earlier marine cycloidal propellers were installed on ships that mainly performed towing operations. Recently marine cycloidal propellers are being installed on large naval vessels, which spend lot of their operating hours in cruising. Therefore, the hydrodynamic loading on the blades both during cruising maneuvers need to be investigated. The flow characteristics around the propeller blade are computed numerically by panel method. Viscous effects on the flow are then estimated by boundary layer technique. The effect of rotating disc on viscous fluid is also investigated. The corrected flow characteristics are then used for estimating the hydrodynamic loading. The operating conditions that are critical for the loading of the blade and the support structure and some aspects of the maneuvering simulation at cruising speed are investigated.  相似文献   

A two-dimensional dam-break flood plain model     

T.V. Hromadka  C.E. Berenbrock  J.R. Freckleton  G.L. Guymon 《Advances in water resources》1985,8(1):7-14

A simple two-dimensional dam-break model is developed for flood plain study purposes. Both a finite difference grid and an irregular triangle element integrated finite difference formulation are presented. The governing flow equations are approximately solved as a diffusion model coupled to the equation of continuity. Application of the model to a hypothetical dam-break study indicates that the approach can be used to predict a two-dimensional dam-break flood plain over a broad, flat plain more accurately than a one-dimensional model, especially when the flow can break-out of the main channel and then return to the channel at other downstream reaches.  相似文献   

NUMERICAL SIMULATION OF SEDIMENT TRANSPORT IN DYNAMIC FLOW CONDITIONS     

Farhad YAZDANDOOST 《国际泥沙研究》2005,20(4):358-365

1 INTRODUCTION Rivers as a source of life can at the same time impose devastating conditions on the environment. It is , therefore, imperative to analyse and predict river behaviour for different given conditions and engineering activities. Therefore, the use of simulation tools in this field has become a necessity. Many computational tools for simulation of sediment transport in rivers are now available that can be used for prediction and design under different flow conditions. However, …  相似文献   

Drag and inertia coefficients for a circular cylinder in steady plus low-amplitude oscillatory flows     

《Applied Ocean Research》2017

Computer simulations of steady plus low-amplitude oscillatory flow about a circular cylinder are reported at a fixed Reynolds number of 150 based on the steady component. The conventional Keleugan–Carpenter number based on the oscillatory component is fixed at π/5. The oscillation frequency is varied so as to study a wide spectrum of flows where inertial forces dominate at one end and viscous drag forces at the other as a function of the modified Keleugan–Carpenter number. The hydrodynamic force on the cylinder in-line with the flow direction is represented by Morison's equation and an extended version with three terms. The drag and inertia coefficients in Morison's equation are determined by least-squares fits to data directly computed from integration of skin friction and pressure distributions around the periphery of the cylinder. The root-mean-square value of the residue of reconstructed minus directly-computed forces varies between 2 and 41% depending on the flow parameters. Comparable results can be obtained with a semi-theoretical approach using inviscid inertia and quasi-steady viscous drag terms. Physical explanations for the variation of the force coefficients are provided and implications for pertinent flow–structure interactions are discussed.  相似文献   

On the fluid structure interaction of a marine cycloidal propeller     

《Applied Ocean Research》2017

Marine cycloidal propulsion system is efficient in maneuvering ships like tugs, ferries, etc. It is capable of vectoring thrust in all direction in a horizontal plane. When used in pair, the system enables a vessel to perform maneuvers like moving sideways, perform rotation about a point, i.e. turning diameter of its own length, etc. In this system, the propeller blades have to change their angle of attack at different angular position of the disc. Due to this reason, the inflow velocity vector to propeller blades changes continuously. The propeller blade oscillates about a vertical axis passing through its body and at the same time rotates about a point. Superposed on these motions is the dynamics of the ship on which the propulsion system is installed. This results in a formidable and challenging hydrodynamics problem. Each of the propeller blade sections could be considered as an aerofoil operating in combined heave and pitch oscillation mode. Due to the constantly varying inflow velocity, the hydrodynamic flow is unsteady. The unsteady hydrodynamic flow is simulated by incorporating the effect of shed vortices at different time instant behind the trailing edge. Due to the kinematics of the problem, the blade is subjected to higher structural deformation and vibration load. The structural deformation and vibration when coupled with the hydrodynamic loading add another level of complexity to the problem. In this paper, the variation of hydrodynamic load on the propeller blade due to steady and unsteady flow is compared. We also model the structural dynamics of the blade and study its effect on the hydrodynamic loading. Finally, we couple the structural dynamics with hydrodynamics loading and study its influence on the propeller blade for different operating regimes.  相似文献   

Analysis of radial movement of a confined aquifer due to well pumping and injection     

Jiang Li 《Hydrogeology Journal》2007,15(3):445-458

Three aspects of radial motion of an aquifer solid matrix, driven by hydraulic forces due to well recharge and discharge, have been investigated mathematically. Firstly, the analytic solutions in the velocity and displacement fields were found using the definition of bulk mass flow, conservation of water and solid mass, the Darcy-Gersevanov law, and the drawdown of hydraulic head for unsteady flow. Secondly, the radial velocity and displacement of aquifer solid matrix were investigated with respect to time and location in response to three pumping-injection schemes (i.e., linear, nonlinear, and sinusoidal well flow rates). Aquifer movement was found to be more responsive to linear and nonlinear pumping rates than to constant pumpage. Aquifer movement in response to periodic well discharge and recharge was governed by an integral sinusoidal function. Finally, the potential risk of earth fissuring at a given location caused by tensile stress, in turn induced by well discharge-recharge activity, has been discussed using the analytic solution. The deformation compression and extension zones derived from analysis of the results indicated the possible occurrence of tensile stress that may cause earth fissures. Sample computations, using assumed parameters, provided a first-hand evaluation of the location of potential fissuring in relation to the well.  相似文献