A型地铁车内噪声分析和优化

为研究轨道车辆轻量化带来的车内振动噪声问题,基于某A型地铁车辆的有限元模型,建立其声学计算模型,以车体板件频率响应的振动位移结果作为声学激励,在车内布置ISO标准场点进行车内噪声分析.结果显示,车内各点声压级在频域上分布极不均匀,且普遍存在几个较大的峰值.分析目标板件的振动,提出几种减振降噪的优化方案.对比各方案发现,增加板件强度后振动和噪声都相应地减小;减振降噪需综合考虑优化后车体的整体强度和动力学性能.     

Numerical study of helicopter blade–vortex mechanism of interaction using large-eddy simulation

A novel approach, large-eddy simulation, is proposed for the numerical investigation of helicopter blade–vortex mechanism of interaction. The novel approach overcomes all the issues, posed by the other CFD approaches, associated with the vortex dissipation due to the turbulence modeling (RANS, URANS) and computational limitations of DNS. The influence of vertical miss distance and vortex core size on the helicopter blade–vortex mechanism of interaction is subject of investigation. It was observed that the magnitude of the aerodynamic coefficients decreases with the increase of vertical miss distance and the decrease of vortex core size.     

Parallel implementation of the fluid particle model for simulating complex fluids in the mesoscale

Dissipative particle dynamics (DPD) and its generalization—the fluid particle model (FPM)—represent the ‘fluid particle’ approach for simulating fluid‐like behavior in the mesoscale. Unlike particles from the molecular dynamics (MD) method, the ‘fluid particle’ can be viewed as a ‘droplet’ consisting of liquid molecules. In the FPM, ‘fluid particles’ interact by both central and non‐central, short‐range forces with conservative, dissipative and Brownian character. In comparison to MD, the FPM method in three dimensions requires two to three times more memory load and a three times greater communication overhead. Computational load per step per particle is comparable to MD due to the shorter interaction range allowed between ‘fluid particles’ than between MD atoms. The classical linked‐cells technique and decomposing the computational box into strips allow for rapid modifications of the code and for implementing non‐cubic computational boxes. We show that the efficiency of the FPM code depends strongly on the number of particles simulated, the geometry of the box and the computer architecture. We give a few examples from long FPM simulations involving up to 8 million fluid particles and 32 processors. Results from FPM simulations in three dimensions of the phase separation in binary fluid and dispersion of the colloidal slab are presented. A scaling law for symmetric quench in phase separation has been properly reconstructed. We also show that the microstructure of dispersed fluid depends strongly on the contrast between the kinematic viscosities of this fluid phase and the bulk phase. This FPM code can be applied for simulating mesoscopic flow dynamics in capillary pipes or critical flow phenomena in narrow blood vessels. Copyright © 2002 John Wiley & Sons, Ltd.     

CFD网格应用平台研究

CFD网格应用平台是ChinaGrid5大应用平台之一,它为各种不同的CFD应用提供了网格基础设施。平台采用了两层架构：上层基于WSRF服务,下层基于并行计算。为了无缝整合各种CFD应用,平台定义了一组包括CFD工作流模板和CFD分类码的重要概念,使用了一系列如CGNS数据可视化工具GVisual的关键技术。目前基于Service Domain的平台原型系统已经开发完成,性能测试表明CFD应用移植其到平台上后性能获得提高。     

Optimal cooperation between external criterion and data division in GMDH

The problem of cooperation between external criterion and data division is important for application and development of group method of data handling (GMDH) theory. Based on research of ‘critical noise level’ and ‘noise immunity’, this article presents the concept of ‘expected critical noise level’. The relationship between ‘expected critical noise level’ and both prediction set and model structure is expressed by a formula. According to ‘expected critical noise level’, a selection method is designed, which is able to obtain an optimal cooperation between external criterion and data division in GMDH. Finally, the corresponding algorithm and an example are given.     

压气机叶片扭曲规律的多目标三维气动优化

为了提高轴流压气机的等熵效率和总压比,采用基于人工神经网络及遗传算法的叶轮机械叶片三维优化设计方法,开发了一种高性能的动叶片。优化目标是在流量不减小的情况下,尽可能的提高转子叶片的总压比和等熵效率。优化仿真结果显示,优化后所获得的扭曲叶片可以有效地改善叶根处的流动分离,流动分离区明显后移,损失显著降低,在整个工作范围,等熵效率提高了1.27%-7.08%,流量和总压比也都得到了大幅度的提高。结果表明,对亚音叶片进行扭曲规律优化效果很明显,优化方法是获得高性能转子叶片的有效途径。     

Parametric studies of exhaust smoke-superstructure interaction on a naval ship using CFD

The prediction of flow path of exhaust plume from the ship funnels is extremely complicated since the phenomenon is affected by a large number of parameters like wind velocity and direction, level of turbulence, geometry of the structures on ship’s deck, efflux velocity of smoke etc. To complicate the matters, the entire turbulent flow field is subject to abrupt changes as the yaw angle changes. In order to understand how the smoke is brought down to ship’s deck, it is necessary to have a knowledge of the funnel exhaust behavior very early in the design spiral of the ship by undertaking parametric investigation of the interaction effect between exhaust smoke and the ship superstructure. This paper presents such a parametric investigation on representative topside configurations of a generic frigate using computational fluid dynamics (CFD). The results presented have been analysed for a total of 112 different cases by varying velocity ratios and onset wind direction for four superstructure configurations. Use of both experimental and computational approaches has been made so that they become complementary to each other. The CFD simulation has been done using the computational code FLUENT version 6.0. Closure was achieved by using the standard k-ε turbulence model. The parametric study has demonstrated that CFD is a powerful tool to study the problem of exhaust smoke-superstructure interaction on ships and is capable of providing a means of visualising the path of the exhaust under different operating conditions very early in the design spiral of a ship.     

Effects of blade tip modifications on wind turbine performance using vortex model

The effects of blade tip modifications on a wind turbine blade are studied with the design code developed previously, by taking into account the curving of the blade axis in or out of the plane of rotation. This is an area of interest for manufacturers of wind turbines to improve the aerodynamic performance, as has been done with airplane wings and also to use the swept tips to unload the blades during wind gusts by changing the local incidences with a nose-down torsional moment.The vortex model, based on Goldstein approach, treats each blade as a lifting line generating a helicoidal vortex sheet, supporting the trailed vorticity along prescribed helices whose pitch is determined to satisfy the wake equilibrium condition. As the lifting line is given sweep in the plane of rotation or dihedral in the plane containing the blade and the rotor axis, the induced velocities by the bound vortex at the lifting line are no longer zero and the blade flow is also affected by the modified vortex sheet geometry, according to the Biot-Savart formula. The study is performed with a two-bladed rotor with the NREL blade as point of reference.A series of tests is carried out with the design code, comparing the design of a rotor blade with straight axis or with a ±10% (forward or backward) sweep, dihedral or winglet. Results indicate that the aerodynamic performance are in general enhanced with these tip modifications, although the trends differ between forward and backward orientations, with some nonlinear effects associated with the wake geometry.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

Helmholtz共振腔气动噪声数值仿真

为探究出一套完整、准确的气动噪声仿真方法,用FLUENT和Actran仿真Helmholtz共振腔旁接管道系统模型.针对流场仿真,采用六面体网格建模,分析选择合适的网格密度,明确网格及边界条件的影响,以获得准确的声源信息;运用Lighthill声类比方法对声场进行仿真,采用数值计算、传声损失仿真和气动噪声仿真计算等3种方法提取管道内部场点声压级频谱曲线,分析曲线峰值频率特征,包括共振频率分析和声模态分析等.采用CFD软件与声学仿真软件相结合的方法,可以有效进行流场和声场的仿真.     

A discontinuous Galerkin method with block cyclic reduction solver for simulating compressible flows on GPUs

An optimized implementation of a block tridiagonal solver based on the block cyclic reduction (BCR) algorithm is introduced and its portability to graphics processing units (GPUs) is explored. The computations are performed on the NVIDIA GTX480 GPU. The results are compared with those obtained on a single core of Intel Core i7-920 (2.67 GHz) in terms of calculation runtime. The BCR linear solver achieves the maximum speedup of 5.84x with block size of 32 over the CPU Thomas algorithm in double precision. The proposed BCR solver is applied to discontinuous Galerkin (DG) simulations on structured grids via alternating direction implicit (ADI) scheme. The GPU performance of the entire computational fluid dynamics (CFD) code is studied for different compressible inviscid flow test cases. For a general mesh with quadrilateral elements, the ADI-DG solver achieves the maximum total speedup of 7.45x for the piecewise quadratic solution over the CPU platform in double precision.     

On addressing noise constraints in the design of wind turbine blades

Power production from wind energy has been increasing over the past decades, with more areas being used as wind farms and larger wind turbines (WTs) being built. With this development, awareness of the impact of wind energy on the environment and on human health has also raised. There has been a large interest in developing fast turnaround WT blade design frameworks, capable of predicting both aerodynamic and aeroacoustic performance to handle ever stricter noise criteria constraints dictated by site or local authorities. In this work, a blade element momentum theory model is used to predict the aerodynamic performance of a wind turbine, coupled to an empirical aeroacoustic noise model and boundary layer corrections. The aeroacoustic prediction code developed was validated against measurement data of the AOC 15/50 WT and included in an optimization framework using a genetic algorithm. The blade shape was parametrized using NURBS curves for the cross sectional airfoil shapes and Bézier curves for the twist and chord distributions, totaling up to 62 design variables. Two multi-objective optimization cases, both single- and multi-operating point, were performed. Optimal solutions selected from the Pareto fronts are discussed in detail. These solutions ranged from an increase in annual energy production of 15 % to a reduction in noise levels of 9.8 %. It was demonstrated that substantial noise reduction could be obtained at an expense of a minor aerodynamic penalty.     

一种新型离心风机的气动噪声数值仿真

以一种新型离心风机为例,运用Lighthill声比拟理论和计算流体动力学技术对离心风机的非定常流场和气动噪声进行数值模拟。首先以风机内部静压脉动随时间的波动判断离心风机的主要噪声源的位置,然后,以噪声频谱图和1／3倍频程图分析离心风机的噪声组成,判断离心风机噪声的产生机理。并以实验结果作为根据,验证仿真结果的正确性。结果表明：在非定常流场中,离心风机的噪声源主要分布在叶片与蜗壳之间的狭窄区域,在气动噪声成分中涡流噪声所占的比例最大,其产生的主要原因是由于叶片尾缘漩涡脱落造成的压力脉动形成的。     

An efficient evolutionary optimisation framework applied to turbine blade firtree root local profiles

In this paper, an efficient evolutionary optimisation of a turbine blade firtree root local profile is presented. The firtree geometry is designed using an intelligent rule-based computer-aided design system (ICAD) and analysed using an industrial-strength finite element code. A large number of geometric and mechanical constraints drawn from past experience are incorporated in the design of the model. The high computational cost associated with finding optimal designs using high-fidelity codes is addressed using a surrogate-assisted genetic algorithm. The initial surrogate model is first built based on points sampled with a design-of-experiment method. A database of designs analysed using the high-fidelity code is built and augmented while the genetic algorithm progresses. In the procedure for deciding whether the high-fidelity code should be run, a simple 3 principle is used instead of searching for the point with maximum expected improvement. This is combined with an appropriate ranking of the design points within the database. Some benchmark test problems are first used to illustrate the effectiveness and efficiency of the framework. When applied to the problem of local shape optimisation of a turbine blade firtree root, significant improvement is achieved using a limited computational budget.     

Application of Compact Schemes to Large Eddy Simulation of Turbulent Jets

We present 3-D large eddy simulation (LES) results for a turbulent Mach 0.9 isothermal round jet at a Reynolds number of 100,000 (based on jet nozzle exit conditions and nozzle diameter). Our LES code is part of a Computational Aeroacoustics (CAA) methodology that couples surface integral acoustics techniques such as Kirchhoff's method and the Ffowcs Williams– Hawkings method with LES for the far field noise estimation of turbulent jets. The LES code employs high-order accurate compact differencing together with implicit spatial filtering and state-of-the-art non-reflecting boundary conditions. A localized dynamic Smagorinsky subgrid-scale (SGS) model is used for representing the effects of the unresolved scales on the resolved scales. A computational grid consisting of 12 million points was used in the present simulation. Mean flow results obtained in our simulation are found to be in very good agreement with the available experimental data of jets at similar flow conditions. Furthermore, the near field data provided by the LES is coupled with the Ffowcs Williams–Hawkings method to compute the far field noise. Far field aeroacoustics results are also presented and comparisons are made with experimental measurements of jets at similar flow conditions. The aeroacoustics results are encouraging and suggest further investigation of the effects of inflow conditions on the jet acoustic field.     

Feedforward into local loops of plant modifying cascaded feedback systems

Horowitz and Wang (1979) have proposed a quantitative synthesis technique for plant modifying SISO feedback design. In essence, inner loops are designed to reduce ‘[tdot]feedback loop bandwidths and effect of sensor noise, at the cost of increase in plant internal signal levels.’ The major effort of this design goes into achieving ‘[tdot]desired trade-off between increased plant signal level and cost of feedback.’ In this paper it is shown that by a very simple use of available feedforward ‘degrees of freedom’, the above trade-off problem diminishes significantly for practically important classes of systems and the overall design simplifies considerably.     

On the development of high-performance C++ object-oriented code with application to an explicit edge-based fluid dynamics scheme

Object-oriented techniques are investigated and algorithms constructed for developing efficient explicit edge-based finite-volume code. C++ was the chosen programming language and the developed algorithms include effecting reduced data trafficking and balanced dynamic–static polymorphism as well as a proposed novel caching technique. These are implemented into an actual object-oriented computational fluid dynamics (CFD) code and numerical experiments conducted on PC and SGI platforms to assess improved performance. Significant reductions in both required memory and computational times are demonstrated for computational meshes ranging from small to large.     

KDDML‐G: a grid‐enabled knowledge discovery system

KDDML‐G is a middleware language and system for knowledge discovery on the grid. The challenge that motivated the development of a grid‐enabled version of the ‘standalone’ KDDML (Knowledge Discovery in Databases Markup Language) environment was on one side to exploit the parallelism offered by the grid environment, and on the other side to overcome the problem of data immovability, a quite frequent restriction on real‐world data collections that has principally a privacy‐preserving purpose. The last question is addressed by moving the code and ‘mining’ the data ‘on the place’, that is by adapting the computation to the availability and localization of the data. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of noise on signal detection

Twelve subjects were tested twice in visual vigilance tasks which lasted 40?min. Employing a two-category confidence rating scale they detected increments in light level from displays of five lights. The display was flashed on simultaneously for 0·5 s every 3·5?s. The subjects performed the task on different days under two conditions of continuous white noise: ‘quiet’ (70?dB) and ‘noise’ (l00?dB). Half of the subjects had the noise treatment in the order of quiet-noise and half in the reverse order. No effects of noise either upon the overall performance or upon the vigilance decrement were observed. For the risky criterion results showed mainly that during a run under the two conditions the percentage of correct and false responses decreased, d' remained unchanged and β partly increased as a function of time. For the cautious criterion only β increased during a run under the two conditions. The results were interpreted in terms of arousal theory     

Modified genetic algorithm strategy for structural identification

Genetic algorithms (GA) have proved to be a robust, efficient search technique for many problems. As the number of variables involved increases, classical GA will often have difficulty and/or require long computational time in obtaining acceptable results. In this paper, a modified GA strategy is proposed to improve the accuracy and computational time for parameter identification of multiple degree-of-freedom (DOF) structural systems. The strategy includes multiple populations or ‘species’, a search space reduction procedure and new operators designed to provide a robust and reliable identification. Average absolute error in the estimated stiffness values of 1.4% is achieved for a 20-DOF unknown mass system with 5% noise, and even more importantly the maximum error is reduced to only 3.8%.