混凝土裂缝化学灌浆压力模拟与合适压力探讨

在混凝土裂缝灌浆过程中,为了解灌浆压力在裂缝中的分布情况,将混凝土裂缝化学灌浆看作一个流体力学问题来求解。根据流体力学的基本原理,采用目前国际上广泛应用的fluent软件,对灌浆过程中裂缝不同部位的压力分布状况进行了数值模拟。结果显示,在不同灌浆方式和离灌浆口不同距离的条件下,灌浆压力的沿程衰减和压力大小是不同的,据此对合适灌浆压力进行了探讨。该成果可在一定程度上用于指导灌浆施工。     

导流板对海底管道绕流影响的数值模拟与试验研究

采用试验研究和数值模拟相结合的方法为对海底管道添加导流板后的绕流特性进行了研究。数值模型利用有限体积法进行离散,湍流模型采用标准kε湍流模型。通过对比分析,数值模拟结果与试验结果吻合较好。同时对不同间隙比下导流板对迎流面前驻点、流速分布、管道表面压力分布、升阻力系数及床面剪应力的影响进行了分析,为海底管道冲刷及防护技术的进一步研究奠定了基础。     

长江洪水期三峡工程对长江口水动力特性及污水稀释扩散影响的数值模拟研究

运用ECOMSED建立了长江口的水动力模型。潮位和流速的验证结果表明模型能够较好地反应长江口的水动力特性,可以应用于长江口的实际计算。对2010年7月长江发生的大洪水对长江口的水动力特性的影响进行了模拟。模型计算结果表明,由于三峡工程的蓄水作用,使得长江口附近的流速发生明显的减小,对污水的稀释扩散和水环境也会产生一定的影响。上海三个排污口分别排出稀释度为1000的污水时,由于三峡工程的蓄水,上游来水量相应减少,不利于上海排出污水的稀释扩散。     

赣江尾闾河网地形变化对洪季水动力的影响北大核心CSCD

为探明在新水沙条件和人类活动的影响下赣江尾闾河网地形变化与洪季水动力特征变化的关系,以1998—2020年为研究时段,基于1998、2013、2020年河道地形,分别建立一维河网数学模型,复演赣江98特大洪水,研究不同时期地形变化对洪季水动力特征的影响。结果表明:赣江尾闾河网的整体下切使水位流量关系右移,洪期各支洪峰流量整体增加,相同水位下,外洲站来流增幅超过50%。1998—2020年期间,南支地形下切幅度大于其他各支,地形不均匀下切导致尾闾河网节点分流比改变,整体上主支与南支分流增多、中支与北支分流减少。各支流速变化剧烈,主支下游流速增幅超过1 m/s。本研究可为河道整治规划、堤坝防护和灾害预防提供一些技术参考。     

The condition of the least‐squares finite element matrices

A universal, practical, a priori, numerical procedure is presented by which to realistically bind the spectral condition number of the global stiffness matrix generated by the finite element least‐squares method. The procedure is then applied to second and fourth‐order problems in one and two dimensions to show that the condition of the global stiffness matrix thus generated is, in all instances, proportional to but the diameter of the element squared. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels

Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal‐plane about desired position and heading co‐ordinates defined by the operator. A three degrees‐of‐freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi‐submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust‐induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work‐over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co‐ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi‐submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.     

Current variability in a wide and open lacustrine embayment in Lake Geneva (Switzerland)

Field measurements and numerical simulations were used to determine the effects of dominant meteorological conditions on the hydrodynamics of a wide (aspect ratio ~ 2), relatively deep (seasonally stratified) and open lake embayment (Vidy Bay, Lake Geneva). A three-dimensional hydrodynamic model (Delft3D-FLOW) was employed to simulate flow in the lake. High-resolution maps of wind, temperature and humidity (over the lake) were applied as input to drive the model. Because wind was the main force driving flow in the lake, currents in the embayment were investigated systematically for different wind conditions and seasonal stratification. Satisfactory model validation was achieved using drifter and moored measurements within the embayment. Markedly different circulation patterns were measured within the embayment, with the transition from one pattern to another occurring abruptly for small changes in wind direction. These distinct patterns resulted from relatively small changes in the large gyre of Lake Geneva's main basin, especially the angle between the current in front of the embayment and the embayment shoreline. The boundary between the embayment and the pelagic zone was defined by the largest gyre within the embayment. This study shows that, (i) in a large lake, complex current patterns can occur even within a minor embayment, and (ii) that these patterns can transition rapidly over a small range of wind directions. Near-shore gyre can occur for lengthy periods, which has implications for flushing of discharges within the embayment.     

UUV海底定点停驻受力特性及稳定性分析

在简单介绍海底定点停驻UUV概念及工作过程的基础上,建立了其在海底时的稳定性分析模型,并推导出了航行器负浮力、主轴与两支撑点之间的半角θ、流体动力Fx、Fy之间的关系。为了研究航行器在海底时的流体动力特性,采用Ansys ICEM对其离海底不同距离及海底有不同倾角时的情况进行结构化的网格划分,并应用CFX软件对其在不同水流速度下的外围流场进行数值仿真,得到了其在海底时所受侧向力、升力随距海底的距离、海水流速及海底倾角的变化趋势。最后,对航行器在海底时的稳定性进行了分析并得到了一组能够保证航行器海底稳定的较好参数。     

Meshfree method for fluctuating hydrodynamics

In the current study a meshfree Lagrangian particle method for the Landau–Lifshitz Navier–Stokes (LLNS) equations is developed. The LLNS equations incorporate thermal fluctuation into macroscopic hydrodynamics by the addition of white noise fluxes whose magnitudes are set by a fluctuation–dissipation theorem. The study focuses on capturing the correct variance and correlations computed at equilibrium flows, which are compared with available theoretical values. Moreover, a numerical test for the random walk of standing shock wave has been considered for capturing the shock location.     

TRANSPORT OF BICOMPONENT CONTAMINANT IN FREE-SURFACE WETLAND FLOW

This paper presents a theoretical analysis of a pulsed bicomponent contaminant emission into a free-surface wetland flow.The basic equations are for the bicomponent contaminant transport in the wetland flow under the combined action of advection,mass dispersion,and ecological reaction at the phase averaged scale.The effect of the ecological reaction is separated from the hydro-dynamic effect via a set of widely used transforms.The analytical solution for the evolution of the depth-averaged concentration is rigorously derived,with a limiting case covering the known solution for the single component contaminant transport.It is found that the depth-averaged species concentration of the bicomponent contaminant can approach an equilibrium state determined by the distri-bution coefficient.