基于变保真度模型的AUV流体动力参数预测

变保真度模型(Variable-fidelity modeling,VFM)作为一种有效的代理模型方法被广泛用于工程设计,其中低保真度模型(Low-fidelity modeling,LF)用于获取目标模型的整体趋势,高保真度模型(High-fidelity modeling,HF)用于校正低保真度模型的准确度,二者通过桥函数(Bridge function,BF)融合,完成对目标模型的近似。将VFM用于预测自主水下航行器(Autonomous underwater vehicle,AUV)在外界工况(速度和攻角)下的流体动力参数(阻力系数、升力系数、力矩系数),其中高低保真度模型使用径向基函数构建,桥函数使用克里金函数构建,从遗传算法交叉算子产生的候选样本集中选择变保真度模型与高保真度模型误差最大的样本进行更新,最后建立变保真度代理模型。结果显示VFM能够准确描述流体动力参数在设计空间的变化;在相同的计算条件和时间下,VFM比高保真度模型精度高;随着高保真度样本的增加,模型的精度稳步提升。

某飞行器空气流体动力参数计算与弹道仿真

为了有效指导飞行器结构设计,获得风洞试验不能获得的中间参数,减少风洞试验的次数,在现有仿真文献优点的基础上,运用Pro/Engineer、ANSA、Fluent和Matlab等软件对某飞行器的几何外形、非结构流体网格划分、流体动力参数和无动力飞行弹道数据进行处理和计算。通过MPI并行计算和JOU批处理自编程序,完成96种工况千万级网格数量下的流体动力参数高精度计算,运用Matlab自编程序结合经典四阶龙格库塔法和拉格朗日插值算法求解飞行器纵向运动方程组完成空中飞行弹道仿真。结果表明:该仿真结果能有效指导某飞行器结构设计,减少风洞试验次数,获得风洞试验不能获得的中间参数,缩短研制周期,节约研制经费。

鱼雷模拟战斗载荷排载时间的仿真研究与分析

针对空中入水鱼雷模拟战斗载荷即假雷的回收再利用,提出了假雷不扎入海底的排载时间问题。通过对假雷入水参数、衡重参数、流体动力参数等分析,给出了符合实际的仿真条件。在忽略排载冲击、低速时流体动力参数与雷体方程适应性等因素的前提下,开展了假雷非控弹道的仿真计算和分析。在给定的参考海区下,对假雷排载和不排载2种情况下深度弹道进行了对比计算,经验估算假雷排载后阻力系数增大2倍,得出了假雷不扎入海底的排载时间。

Numerical simulation of a gas pipeline network using computational fluid dynamics simulators

This article describes numerical simulation of gas pipeline network operation using high-accuracy computational fluid dynamics (CFD) simulators of the modes of gas mixture transmission through long, multi-line pipeline systems (CFD-simulator). The approach used in CFD-simulators for modeling gas mixture transmission through long, branched, multi-section pipelines is based on tailoring the full system of fluid dynamics equations to conditions of unsteady, non-isothermal processes of the gas mixture flow. Identification, in a CFD-simulator, of safe parameters for gas transmission through compressor stations amounts to finding the interior points of admissible sets described by systems of nonlinear algebraic equalities and inequalities. Such systems of equalities and inequalities comprise a formal statement of technological, design, operational and other constraints to which operation of the network equipment is subject. To illustrate the practicability of the method of numerical simulation of a gas transmission network, we compare computation results and gas flow parameters measured on-site at the gas transmission enter-prise.

Effects of expanding zone parameters of vacuum dust suction mouth on flow simulation results

Based on the parametric analysis of the expanding zone of the vacuum dust suction mouth,the flow in the vacuum dust suction mouth was simulated by computational fluid dynamics(CFD)software,Fluent.The effects of the expanding zone parameters on flow simulation were analyzed.The results show that simulation effects depend on threshold values of the expanding zone parameters of the dust suction mouth,and the threshold values of the expanding zone can be obtained according to the different structures of the vacuum dust suction mouth and be selected as the geometric parameters in calculating,and also corners of the expanding zone make unobvious difference in calculation accuracy and in computational efficiency compared with no corner.The simulation results provide practical guidance to the flow simulation on the dust suction mouth.

Experimental and numerical analysis of secondary disasters induced by oxygen rich combustion within a tunnel

Various physical parameters, including gas concentrations (O2, CO, CH4, and H2) and temperatures at dif- ferent air velocities, were determined for full scale wood fires in the Chongqing Coal Research Institute fire test tunnel. Both experimental measurements and numerical simulations are discussed. The numer- ical analysis was performed with the computational fluid dynamics software package ''FLUENT''. The results show that the experimental data agree with the simulation results. The results verify that Roberts' theory of burning is correct. They also prove that the air velocity is the key factor that determines the type of combustion. Also, it is shown that secondary disasters are unlikely for oxygen rich combustion with a limited fire load.

Numerical simulation of effect of bionic V-riblet non-smooth surface on tire anti-hydroplaning

Inspired by the idea that bionic non-smooth surfaces(BNSS) can reduce fluid adhesion and resistance, and the effect of bionic V-riblet non-smooth structure arranged in tire tread pattern grooves surface on anti-hydroplaning performance was investigated by using computational fluid dynamics(CFD). The physical model of the object(model of V-riblet surface distribution, hydroplaning model) and SST k-ω turbulence model were established for numerical analysis of tire hydroplaning. With the help of a orthogonal table L16(45), the parameters of V-riblet structure design compared to the smooth structure were analyzed, and obtained the priority level of the experimental factors as well as the best combination within the scope of the experiment. The simulation results show that V-riblet structure can reduce water flow resistance by disturbing the eddy movement in boundary layers. Then, the preferred type of V-riblet non-smooth structure was arranged on the bottom of tire grooves for hydroplaning performance analysis. The results show that bionic V-riblet non-smooth structure can effectively increase hydroplaning velocity and improve tire anti-hydroplaning performance. Bionic design of tire tread pattern grooves is a good way to promote anti-hydroplaning performance without increasing additional groove space, so that tire grip performance and roll noise are avoided due to grooves space enlargement.

SPH-FEM simulations of microwave-treated basalt strength

Microwave precondition has been highlighted as a promising technology for softening the rock mass prior to rock breakage by machine to reduce drill bit/cutter wear as well as inverse production rate.To numerically explore the effect of numerical parameters on rock static strength simulation,and determine the numerical mechanical parameters of microwave-treated basalts for future drilling and cutting simulations,numerical models of uniaxial compression strength(UCS)and Brazilian tensile strength(BTS)were established with the coupling of smoothed particle hydrodynamics and finite element method(SPH-FEM).To eliminate the large rock strength errors caused by microwave-induced damage,the cohesion and internal friction angle of microwave-treated basalt specimens with the same microwave treatment parameters were calibrated based on a linear Mohr-Coulomb theory.Based on parametric sensitivity analysis of SPH simulation of UCS and BTS,experimental UCS and BTS values were simultaneously captured according to the same set of calibrated cohesion and internal friction angle data,and the UCS modeling results are in good agreement with experimental tests.Furthermore,the effect of microwave irradiation parameter on the basalt mechanical behaviors was evaluated.

A CFD Based Investigation of the Unsteady Hydrodynamic Coefficients of 3-D Fins in Viscous Flow

The motion of the fins and control surfaces of underwater vehicles in a fluid is an interesting and challenging research subject.Typically the effect of fin oscillations on the fluid flow around such a body is highly unsteady, generating vortices and requiring detailed analysis of fluid-structure interactions.An understanding of the complexities of such flows is of interest to engineers developing vehicles capable of high dynamic performance in their propulsion and maneuvering.In the present study, a CFD based RANS simulation of a 3-D fin body moving in a viscous fluid was developed.It investigated hydrodynamic performance by evaluating the hydrodynamic coefficients (lift, drag and moment) at two different oscillating frequencies.A parametric analysis of the factors that affect the hydrodynamic performance of the fin body was done, along with a comparison of results from experiments.The results of the simulation were found in close agreement with experimental results and this validated the simulation as an effective tool for evaluation of the unsteady hydrodynamic coefficients of 3-D fins.This work can be further be used for analysis of the stability and maneuverability of fin actuated underwater vehicles.

Study on Simulation Method of Pipeline Networks' Dynamic Characteristic in Hydraulic Manifold Block

In the design of Hydraulic Manifold Blocks (HMB), dynamic performance of inner pipeline networks usually should be evaluated. To meet the design requirements, dynamic characteristic simulation is often needed. Based on comprehensive study on the existing simulation methods, a new method combined of Power Bond Graph(PBG) and Computational Fluid Dynamic (CFD) is proposed. In this method, flow field of typical channels inside HMB is analyzed with CFD to obtain the local resistance coefficients. Then, with these coefficients, a new sectional lumped-parameter model including kinetic friction factor is developed using PBG. A typical HMB design example is given and the comparison between the simulation and the experimental results demonstrates the feasibility and effectiveness of the proposed method.

Comparative study of experiment and numerical analysis of secondary disasters induced by wood fire in tunnel

Studied the changes of heat physical parameters, gas concentration of O_2, CO,CH_4 and H_2, and temperature through full scale wood fire experiments in a tunnel and simulationby FLUNET, a kind of computational fluid dynamics software.The results showthat the wood fire experiment and simulation are both oxygen-enriched combustions,which show that the simulation results coincide with the experiment.The results also provethat it is difficult for oxygen-enriched combustion to cause secondary disasters.Somesuggestions were put forward to prevent the occurrence of secondary disasters effectively.

Use of Computational Fluid Dynamics to Simulate the Effects of Design and Operating Parameters on the Overall Performance

With around 10 tonnes of waste being generated for every maul woman and child each year across the globe, safe disposal of it all has become an urgent environmental problem. In 1993, Western Europe,the United States, Canada, Japan, Australia and New Zealand produced a total of 480 millon tonnes of industrial waste and & billion tonnes from activities such as energy production, agriculture, mining and sewage disposal. The emission to the atmosphere of both heavy metals and acid gases and perhaps more important in the longer term, the Dioxins/Furans (PCDDs/PCDFs), promises to be one of the key issues facing not only the industry but the society as a whole over the next decade and more.Although it is increasingly likely that measures to control toxic emissions will have to be directed at a wider target than just the waste incinerators, it is equally certain that both public opinion and legislation will, at least in the first instance, see the incinerators as one of the most obvious candidates for tighter regulation.These days, virtually all the new research and development techniques in combustion technology involve the application of computational fluid dynamics (CFD) to combustor design. This seems to be the best approach to solving design problems. Mathematical modelling thus is seen as an inherent part of.practically all combustion research programmes. The new discipline of computational fluid dynamics can also be used to help minimize flame generated pollutants released to the atmosphere. These pollutants include; CO2, CO, SO2, NOx, HC1, Hydrocarbons, soot, particulates, heavy metals and dioxins/furans. CFD studies of their release to the atmosphere must include not only their source in the flame, but also their removal from the fine gases by scrubbing and other techniques. The governing differential equations for the process being studied must be defined and solved simultaneously if the parameters in the equations are interacting. At present, this procedure can give valuable insight into the effect of design parameters on the flow field and concentrations of major species. In the case of many pollutants, the equations governing their production does not affect the flow field or concentrations of major species. Thus the equations are effectively decoupled and the pollutant formation, convection and diffusion can be calculated in a post-processor.This paper presents and discusses the results of our CFD modelling work at two large municinal and a newly commissioned 5 MW clinical incinerator plants in UK.

Analysis of the Water Film Behavior and its Breakup on Profile using Experimental and Numerical Methods

This paper deals with the description of water film behaviour on the airfoil NACA0012 using experimental and numerical methods. Properties of the water film on the profile and its breakup into droplets behind the profile are investigated in the aerodynamic tunnel and using CFD methods. The characteristic parameters of the water film, like its thickness and shape for different flow modes are described. Hereafter are described droplets drifted by the air, which water film is broken behind the profile.