A survey of parametric modelling methods for designing the head of a high-speed train

Abstract
With the continuous increase of the running speed, the head shape of a high-speed train turns out to be the critical factor to boost the speed further. In order to reduce the time required to design the head of a high-speed train and to improve the modelling efficiency, various parametric modelling methods have been widely applied in the optimization design of the head of a high-speed train to obtain an optimal head shape so that the aerodynamic effect acting on the head of a high-speed train can be reduced and more energy can be saved. This paper reviews these parametric modelling methods and classifies them into four categories: two-dimensional, three-dimensional, CATIA-based, and mesh deformation-based parametric modelling methods. Each of the methods is introduced, and the advantages and disadvantages of these methods are identified. The simulation results are presented to demonstrate that the aerodynamic performance of the optimal models constructed by these parametric modelling methods has been improved when compared with the numerical calculation results of the original models or the prototype models of running trains. Since different parametric modelling methods used different original models and optimization methods, few publications could be found which compare the simulation results of the aerodynamic performance among different parametric modelling methods. In spite of this, these parametric modelling methods indicate that more local shape details will lead to more accurate simulation results, and fewer design variables will result in higher computational efficiency. Therefore, the ability of describing more local shape details with fewer design variables could serve as a main specification to assess the performance of various parametric modelling methods. The future research directions may concentrate on how to improve such ability.

Do you want to read the rest of this article?

Request full-text
Request Full-text Paper PDF
  • Article
    Full-text available
    The head shape of high-speed trains has become a critical factor in boosting the speed further. Aerodynamic simulation-based optimization is a dominant method to obtain the optimal head shape which relies on detailed train head models defined by a lot of design variables. Since aerodynamic simulation-based optimization involves heavy calculations, too many design variables not only causes high computational costs, but also makes the optimal solution difficult to obtain. Therefore, how to use few design variables to define detailed train head model is the key to success. Partial differential equation (PDE)-based geometric modelling which creates a complicated PDE patch with few design variables provides an effective solution to this problem. In addition, it also has the advantage of naturally maintaining any high-order continuities between two adjacent surfaces which is very important in designing highly smooth train heads to achieve excellent aerodynamic performance. At the present time, PDE-based geometric modelling cannot be directly applied in computer-aided design (CAD), computer-aided manufacturing (CAM), and computer-aided engineering (CAE) since it has not become an industrial standard. In contrast, non-uniform rational B-splines (NURBS) are commonly used in CAD, CAM, CAE, and many other engineering fields. They have already become part of industry wide standards. In order to apply PDE-based geometric modelling in shape design of high-speed train heads for CAD etc., how to optimally convert PDE surfaces into NURBS surfaces must be addressed. In this paper, a new method of achieving optimal conversion of PDE surfaces representing high-speed train heads into NURBS surfaces is developed. It takes control points and weight deformations of NURBS surfaces to be design variables, and the error between NURBS surfaces and PDE surfaces as the objective function. The least squares fitting and the genetic algorithm are combined to obtain the optimal conversion between PDE surfaces and NURBS surfaces. The application examples demonstrate the effectiveness of the developed method.
  • Aerodynamic optimization of high-speed trains nose using a genetic algorithm and artificial neural network In: CFD & optimization 2011, An ECCOMAS Thematic Conference
    • J Muñoz-Paniagua
    • García García
    • Crespo Martínez
  • Article
    Two aerodynamic shape optimization geometry control methods, B-spline surface control and free-form deformation, are applied to three optimization problems and compared on the bases of optimal shape performance and problem setup ease of use. For both methods, the geometry is parameterized using B-spline surfaces with mesh movement accomplished using an efficient integrated technique. Gradients for the optimization algorithm are computed using the adjoint method. The first problem is a wing twist optimization under inviscid, subsonic flow, achieving an elliptical load distribution. The second is a lift-constrained drag minimization of a wing under transonic flow based on the Reynolds-averaged Navier–Stokes equations. The third involves lift-to-drag-ratio maximization, based on the Reynolds-averaged Navier–Stokes equations, beginning from a classically shaped blended wing–body aircraft and converging to a lifting-fuselage configuration. B-spline surface control is often found to result in slightly better performance; however, in general, both methods perform equally well. Free-form deformation provides a more general approach to problem setup, decoupling geometry control from parameterization. Overall, the results suggest that B-spline surface control is better suited for simple geometries, such as wings, whereas free-form deformation is better suited for complex geometries, such as unconventional aircraft, and for implementation with multistart algorithms and adaptive geometry control approaches.
  • Article
    A 3D aerodynamic shape optimization of high-speed trains was carried out based on the multi-objective genetic algorithm NSGA-II and approximate model method. The total aerodynamic drag force in open field and the overturning moment of the head car under crosswind were set to be optimization objectives. The three-dimensional parametric model of the high-speed trains was established by the Hicks-Henne shape function. The effects of various approximate models on aerodynamic forces were analyzed and compared. Besides, the influence on aerodynamic performances of high-speed trains under multi running conditions of shape factors was analyzed. The shape factors included the head vertical contour line, the head horizontal contour line, the cross section shape of train body, the nose shape, the cowcatcher shape, the side wing shape, the height and the width of the train body. The most important optimization variables were obtained. The optimization results show that there is a tendency of the optimized train shape where the head becomes more sharp and oblate, the cross sectional area becomes smaller and the radian of the train's body side wall increases. Comparing with aerodynamic performances of the train's original shape, the maximum reduction of the aerodynamic drag force of the optimized train in open field is 17.5%, and the maximum reduction of the overturning moment the head car under crosswind is 22.9%.
  • Article
    When a train nose enters a tunnel at a high speed, an impulsive pressure wave ('tunnel sonic boom' or 'micro-pressure wave') radiates from the tunnel exit and it causes an explosive sound or an abrupt rattling of window frames of houses near the tunnel exit. Therefore it is necessary to make the nose shape of the high-speed train effective for reducing the tunnel sonic boom. In this paper, the effect of the train nose shape is investigated using numerical simulation of the tunnel entry problem. The nose shapes dealt with here are (1) fundamental nose shapes, (2) optimum nose shape obtained by nonlinear optimization method, and (5) the nose shape of the 500-series Shinkansen train which runs at 300km/h for the first time in Japan.
  • Article
    Based on three dimensional, unsteady N-S equation, influence on tunnel aerodynamic effects by oblique slope of hat oblique railway tunnel portal was simulated by the forms of numerical simulation, then micro-pressure and pressure changes of the train and tunnel were obtained. The results show that effects on the surface pressure changes of the tunnel and the train by oblique slope of hat oblique railway tunnel portal is little, and the maximum difference is about 5%; with the reduction of the oblique slope, time for the initial compression wave comes from zero up to a maximum peak becomes longer, so its largest pressure gradient becomes smaller; when oblique slope reduced from 1:1 down to 1:2, the micro-pressure waves on the place with the distance of 20 m from the tunnel exit is decreased from 66 Pa to 54 Pa, and the decrease amplitude is about 18.2%, so the reduction of the oblique slope can improve the tunnel micro-pressure waves. Results of numerical and dynamic model show good agreement, and the maximum difference is less than 5%.
  • Article
    With the train speed becoming faster and faster, the aerodynamic drag turns to be one of the essential factor that restricts the train speed ascent. However, no public literature, abroad or abroad, has dealt with the flow field and aerodynamic performance of the train with the speed reaching 500km per hour. In this paper, an optimization study is carried out to reduce the aerodynamic drag of the high speed train (HST). First of all, a grid-based method is presented to parameterize the head shape of the HST, key variables are obtained by sensitivity analysis. Next, a response surface is constructed based on computational fluid dynamics (CFD) analysis to approximate the relationship of the drag and design variables at 500KPH. Finally, the genetic algorithm is used to optimize the head shape of the HST.
  • Article
    The effect of different heights of wind barrier on double-side or single side of embankment to train aerodynamics performance was researched by numerical simulation. The results show that when wind barrier is installed, train aerodynamic coefficients are much less than those without wind barrier and that the pressure on windward surface of train changes from positive to negative, and negative pressure on roof of train decreases obviously. Different heights of wind barrier have great effect on train aerodynamic performance, the side force coefficient of train is positive when wind barrier is lower and its value decreases with the increase of height of wind barrier and it changes to negative when the height reaches certain height, while it is directly opposite to the overturning moment coefficient of train. To the single wind barrier, when its height is 1.85 m, train's overturning moment coefficient is almost equal to 0, so its reasonable height should be 1.85 m, while to the double-side wind barrier, when its height is 2.0 m, train's overturning moment coefficient is almost equal to 0, so its reasonable height should be 1.85 m.
  • Article
    This paper established an automatical calculation process for parameteric-driven aerodynamic performance optimization of the new EMU head-type. On the basis of the multi-objective genetic algorithm NSGA-II, optimal design was performed in respect of 6 key design variables including the slenderness ratio of the head type, the longitudinal line of symmetry, the maximum horizontal contour, the horizontal contour of the car bottom, the assisting hatching and the height of the nose. Then the best aerodynamic shapes of the head were selected. The multi-objective optimization design method can support design work of aerodynamic shapes and new head types which adapt to different styles and different technology needs.
  • Article
    An aerodynamic drag reduction optimization design study of high-speed train head is carried out based on the three-dimensional parametric approach of local shape function, improved ant colony algorithm and improved Kriging surrogate model. To avoid repeated generation of ten millions of meshes in the case of large deformation with complex geometry and improve the optimization efficiency of high-speed train head, we introduce mesh deformation techniques of the reduced control points based on radial basis functions (RBF). The optimization results show that: RBF mesh deformation method could largely shorten the time-consuming of mesh deformation without reducing the quality of meshes, and can be used for aerodynamic optimization design of complex geometry. Under the design space given in this article, the six key design parameters that control the nose shape have effects on the aerodynamic drag of the train with a kind of monotonically increasing relationship. After optimization under the constraints, the total aerodynamic drag of the simplify shape is reduced by 5.68%. The aerodynamic drag of leading and trailing cars reduced a lot, while the aerodynamic drag of middle car changes little.
  • Article
    Aiming at shortening the design period and improve the design efficiency of the nose shape of high speed trains, a parametric shape optimization method is developed for the design of the nose shape has been proposed in the present paper based on the VMF parametric approach, NURBS curves and discrete control point method. 33 design variables have been utilized to control the nose shape, and totally different shapes could be obtained by varying the values of design variables. Based on the above parametric method, multi-objective particle swarm algorithm, CFD numerical simulation and supported vector machine regression model, multi-objective aerodynamic shape optimization has been performed. Results reveal that the parametric shape design method proposed here could precisely describe the three-dimensional nose shape of high speed trains and could be applied to the concept design and optimization of the nose shape. Besides, the SVM regression model based the multi-points criterion could accurately describe the non-linear relationship between the design variables and objectives, and could be generally utilized in other fields. No matter the simplified model or the real model, the aerodynamic performance of the model after optimization has been greatly improved. Based on the SVR model, the nonlinear relation between the aerodynamic drag and the design variables is obtained, which could provide guidance for the engineering design and optimization.
  • Article
    The height of wind-break wall is an important factor that must be considered when the wind-break wall is built. If the height is too low, the wall will produce no wind-proof effects under strong cross-wind. If it is too high, the vehicle will trend to overturn toward the wall. Take the super-thin wind-break wall for example, the simulation and analysis of the box wagon in strong cross-wind on lines with the wind-break wall is carried through by FLUENT, which is based on 2D, stable and incompressible Navier-Stokes equation and k-ε two equations turbulent model. The reasonable height was determined by the smallest sum of overturning moments of the vehicle when it locates on the first and second track. Thus the position of the wind-break wall is fixed. Research shows that when the position of wind-break wall changes, its reasonable height varies, too. And these two are found to be approximately cubic polynomial relations.
  • Article
    Based on the concepts of niche count and crowding distance, a modified multi-objective particle swarm optimization (MPSO) is introduced. The niche count and crowding distance are used to determine the globally best particle across four test cases using an external file. A comparative analysis was carried out between MPSO and non-dominated sorting multiobjective adaptive genetic algorithms, both real-coded and binary-coded. The results show that MPSO based on the crowding distance is best for getting the Pareto front, especially for problems with high-dimensional and non-continuous Pareto fronts. In order to verify the efficiency of MPSO in solving engineering problems, the optimal design of the aerodynamic nose shape of high-speed trains was undertaken using a modified vehicle modeling function (MVMF) parametric method. Taking the aerodynamic drag of the whole train (Cd) and the aerodynamic lift of the trailer car (Cl) as the optimization goals, the Kriging surrogate model was introduced to reduce the computational time, and the MPSO based on crowding distance was used to find the Pareto front. The optimization results show that MPSO is efficient at getting the Pareto front; compared to the original shape, the Cd and Cl of the optimal shape are reduced by 1.6% and 29.74%, respectively.
  • Article
    A method for estimating the aerodynamic drag of a train, particularly the aerodynamic drag of a Shinkansen train, is presented. In addition to estimating the aerodynamic drag, an evaluation of the accuracy of the estimate is made in terms of the total resistances to be measured in the open and in a tunnel. As a result, the contributions of the Shinkansen train configuration and the track type to the total resistance are clarified.
  • Article
    When a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the tunnel exit, an impulsive pressure wave (micro-pressure wave) is radiated from the tunnel exit. Improving the train nose shape is one of the techniques for suppressing the micro-pressure wave. Furthermore, tunnel entrance hoods are required for long concrete slab tunnels in order to suppress the micro-pressure wave. The effect of the tunnel entrance hood on the compression wave generated by the train can be evaluated by means of a rapid computational scheme devised and validated experimentally by Howe et al. In this study, the optimal longitudinal distribution of the cross-sectional area of the train nose shape was determined by using the rapid computational scheme and a genetic algorithm. The effect of the nose shape optimization was confirmed through experiments using scale models.
  • Article
    When a compression wave generated by a train entering a tunnel propagates through the tunnel and arrives at the tunnel exit, an impulsive pressure wave (micro-pressure wave or tunnel sonic boom) is radiated from the tunnel exit. Since the impulsive wave is closely related to the form of the compression wave arriving at the tunnel exit, improvement of the train nose shape is one means of reducing the impulsive wave. In this work, numerical optimization of the train nose shape for reducing the impulsive wave is performed by nonlinear programming combined with numerical simulation. The cross-sectional area distribution of the train nose is determined by the nonlinear programming, while the effect of the train nose shape on the form of the compression wave is estimated by the numerical simulation which solves the unsteady axisymmetric compressible Euler equations by finite volume method, TVD scheme and sliding grid method. The effect of the nose shape obtained by the optimization is confirmed by experiments using models.
  • Article
    With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces (moments), possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objectives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load reduction factor was reduced by up to 1.72%.
  • Conference Paper
    To reduce a micro-pressure wave and an aerodynamic drag of a high-speed train, two-step optimization is performed on the train nose shape using the vehicle modeling function. In the first step, the cross-sectional area distribution of a train nose is optimized to reduce a micro-pressure wave. The optimized cross-sectional area distributions of a train nose have an extremely blunt front end and a negative gradient around a middle section. The steep change of the cross-sectional area from the positive to negative gradient causes a strong expansion effect. This phenomenon divides one large compression wave into two small waves. Compared to the previous optimization results, the optimized shapes reduce the maximum micro-pressure wave by 12-19%. To generate 3-D nose shapes from the optimized cross-sectional area distribution, the vehicle modeling function is proposed. This mathematical function makes a simple curve with a rounded front end, and the curve shape is controlled by two parameters. Modeling of a complex curve can be achieved by a combination of several functions. To make the 3-D nose shape, the 2-D side and top view shapes are defined firstly, and the cross sections are produced along the length of a train. One of the most important features of the vehicle modeling function is that it can make various 3-D nose shapes for a given cross-sectional area. The 3-D nose shape optimization is done with the optimized cross-sectional area distribution. Through the second optimization, the aerodynamic drag force is reduced by 5.6% preserving the minimum micro-pressure wave.
  • Conference Paper
    The objective of this work is to demonstrate the possibility of using adaptive surrogate models for optimization problems which require expensive computations. A hybrid GA - PSO algorithm is combined with a kriging based surrogate model. The suggested method was used to find the optimum shape of a two dimensional nose shape of a high speed train traveling at 350 Km/hr considering both the induced aerodynamic drag and the generated aerodynamic noise. Since the prediction of aerodynamic drag and aerodynamic noise requires computational fluid dynamic simulations, to limit the number of computer simulations required for optimization, a surrogate model identical to the kriging model was used. The accuracy of the surrogate model is checked using the parameter EIV there by updating the surrogate model whenever necessary. The results show that the combined shape optimization algorithm requires a small number of simulations to identify the optimum shape compared with other methods. The suggested method not only requires a small number of simulations but is also robust. This makes the study on the effect of different weights on the optimum shape feasible without the need for additional simulations. The results show that the nose shape should be slightly short and pointed to get the best aerodynamic performance in terms of induced drag and the nose shape should be slightly long and little bit blunt for the least aerodynamic noise generated. The optimum nose shapes fall between these two shapes based upon the choice of the weights. Regarding the choice of the weights for the given two dimensional test geometry the best compromise would be to choose 50% drag and 50 % noise. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
  • Article
    The optimization of the nose shape of a high-speed train entering a tunnel has been performed using genetic algorithms (GA). This optimization method requires the parameterization of each optimal candidate as a design vector. The geometrical parameterization of the nose has been defined using three design variables that include the most characteristic geometrical factors affecting the compression wave generated at the entry of the train and the aerodynamic drag of the train. A large set of three-dimensional, turbulent, compressible, unsteady simulations of realistic train models have been done, and this information has been used to fit a metamodel. The metamodel is used by the GA to evaluate each optimal candidate in a more efficient way. The optimal designs that minimize the maximum pressure gradient and the aerodynamic drag are in good agreement with the literature. To complete this single-objective optimization, a multi-objective optimization has been developed, and a Pareto front has been obtained. The use of metamodels has permitted to analyze the influence of each design variable.
  • Article
    South Korea is proposing to construct a new public transportation system. The Great Train eXpress (GTX) will be built underground as the present subway system. However, the cruise speed will be 200 km/h. When the train speed increases in a tunnel, the aerodynamic drag significantly increases. Therefore, it is important to estimate the aerodynamic drag of the train before construction. In this study, an analysis to estimate the aerodynamic drag of the GTX is performed using Computational Fluid Dynamics (CFD). When the cruise speed increases from 100 km/h to 200 km/h, the aerodynamic drag is estimated. The effects of the train nose length and the tunnel cross-sectional area on the aerodynamic drag are also evaluated. When the train speed increases by a factor of two, the aerodynamic drag is increased approximately four times. The aerodynamic drag is reduced up to approximately 50% by changing of the nose from a blunt to a streamlined shape. The aerodynamic drag decreases up to approximately 50% again when the cross-sectional area of the tunnel increases. The tunnel cross-sectional area for construction of the proposed GTX should be larger than the current tunnel cross-sectional area. These results are applicable for the basic design of the proposed GTX and tunnel system.
  • Article
    With the speed upgrade of the high-speed train, the aerodynamic drag becomes one of the key factors to restrain the train speed and energy saving. In order to reduce the aerodynamic drag of train head, a new parametric approach called local shape function (LSF) was adopted based on the free form surface deformation (FFD) method and a new efficient optimization method based on the response surface method (RSM) of GA-GRNN. The optimization results show that the parametric method can control the large deformation with a few design parameters, and can ensure the deformation zones smoothness and smooth transition of different deformation regions. With the same sample points for training, GA-GRNN performs better than GRNN to get the global optimal solution. As an example, the aerodynamic drag for a simplified shape with head + one carriage + tail train is reduced by 8.7%. The proposed optimization method is efficient for the engineering design of high-speed train.
  • Article
    As the running speed of high-speed trains increases, aerodynamic drag becomes the key factor which limits the further increase of the running speed and energy consumption. Aerodynamic lift of the trailing car also becomes the key force which affects the amenity and safety of the train. In the present paper, a simplified CRH380A high-speed train with three carriages is chosen as the model in order to optimize aerodynamic drag of the total train and aerodynamic lift of the trailing car. A constrained multi-objective optimization design of the aerodynamic head shape of high-speed trains based on adaptive non-dominated sorting genetic algorithm is also developed combining local function three-dimensional parametric approach and central Latin hypercube sampling method with maximin criteria based on the iterative local search algorithm. The results show that local function parametric approach can be well applied to optimal design of complex three-dimensional aerodynamic shape, and the adaptive non-dominated sorting genetic algorithm can be more accurate and efficient to find the Pareto front. After optimization the aerodynamic drag of the simplified train with three carriages is reduced by 3.2%, and the lift coefficient of the trailing car by 8.24%, the volume of the streamlined head by 2.16%; the aerodynamic drag of the real prototype CRH380A is reduced by 2.26%, lift coefficient of the trailing car by 19.67%. The variation of aerodynamic performance between the simplified train and the true train is mainly concentrated in the deformation region of the nose cone and tail cone. The optimization approach proposed in the present paper is simple yet efficient, and sheds lights on the constrained multi-objective engineering optimization design of aerodynamic shape of high-speed trains.
  • Article
    Railway train aerodynamic problems are closely associated with the flows occurring around train. Much effort to speed up the train system has to date been paid on the improvement of electric motor power rather than understanding the flow around the train. This has led to larger energy losses and performance deterioration of the train system, since the flows around train are more disturbed due to turbulence of the increased speed of the train, and consequently the flow energies are converted to aerodynamic drag, noise and vibrations. With the speed-up of train, many engineering problems which have been neglected at low train speeds, are being raised with regard to aerodynamic noise and vibrations, impulse forces occurring as two trains intersect each other, impulse wave at the exit of tunnel, ear discomfort of passengers inside train, etc. These are of major limitation factors to the speed-up of train system. The present review addresses the state of the art on the aerodynamic and aeroacoustic problems of high-speed railway train and highlights proper control strategies to alleviate undesirable aerodynamic problems of high-speed railway train system.
  • Article
    Noise barriers are an efficient way of reducing the noise from railways, particularly the noise produced in the region of the rails and wheels. Several designs of noise barrier have been suggested in the literature which aim to improve the insertion loss over that obtainable from a plane screen of the same height. The positioning of these barriers is governed by the limitations imposed by the structure gauge of the railway. Scale modeling has been carried out in a humidity‐controlled anechoic chamber at a scale of 1:20. Appropriate materials have been selected to model the impedance of the track ballast, absorbing barrier surfaces and grassland at the reduced scale. To model the interaction between the side of the train and the barrier realistically, models appropriate for a high‐speed train cross section have been used. Experimental results for the insertion loss of shaped and multiple‐edge barriers are compared with the results from numerical modeling. The efficiency of each of the designs is assessed. The generation of time histories for the passage of trains and the calculation of noise indices are considered.
  • Article
    As train velocity increases, aerodynamic problems become increasingly important for railways. In open sections, passing of a train nose, train tail and pantograph shield generate pressure variation along the wayside to cause environmental problems, such as rattling of window frames and shutters of houses near the railway. These phenomena are classified as infrasound. It is necessary to solve the problem of operating high-speed trains in the densely populated residential areas along the railways. This paper describes the results of recent researches conducted to develop effective countermeasures to reduce the pressure variation. We investigated the effect of the pressure barrier and train nose configuration as countermeasures.
  • Article
    The tunnel booming noise generated during the train-tunnel interaction has been one of the most serious constraints in the development of the high-speed trains. It is well known that the nose shape of the train has the significant influence on the intensity of the booming noise. In this study, the nose shape has been optimized by using the response surface methodology and the axi-symmetric compressible Euler equations. The parametric studies are also performed with respect to the slenderness ratio, the blockage ratio and the train speed to investigate their sensitivities to the optimization results. The results show that it is possible to befine more general design space by introducing the Hicks-Henne shape functions, resulting in the more effective nose shape than that of Maeda. The mechanism and the aspects of the train-tunnel interaction were also investigated discussed from the results of the parametric study.
  • Article
    Large-eddy simulation (LES) is made of the flow around a generic train model at two different yaw angles of 90∘ and 35∘. The Reynolds numbers, based on the freestream velocity and the height of the train, are 3×105 and 3.7×105 for the yaw angles of 90∘ and 35∘, respectively. The primary objective is to investigate the influence of the nose shape and yaw angles on the flow structures and the train aerodynamics. Both the time-averaged and instantaneous flows are explored. In the case of the 90∘ yaw angle, the LES results show that the influence of the three-dimensional flow from the nose of the train on the time-averaged wake flow is limited to a region of a length of 3.5 train heights from the tip of the nose in the direction of the length of the train. The instantaneous flow shows an unsteady vortex shedding due to the shear layer instabilities on the periphery of the recirculation region and the exterior flow. In the case of the 35∘ yaw angle, weak vortex shedding is found in the wake. Instead, unstable vortices are found in the lower part of the recirculation region. These vortices detach from and reattach to the train surface in a regular fashion leaving disturbances on the train surface and hence affecting the aerodynamic coefficients. The influence of the shape of the nose on the flow structures is investigated by repeating the simulations at the 90∘ yaw angle on a short nose model. The short nose model is identical to the long nose model whilst the length of its nose is half that of the long nose. The short-nose simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear layer instabilities.
  • Article
    Experimental studies and numerical modelling of the flow over a train in a crosswind have, until recently, focused on the cases of yaw angles up to about 40°, in which use was often made of the slender body analogy. As the yaw angle is increased above 40° it is generally agreed that the flow changes from that associated with a slender body to unsteady vortex shedding. The mechanism of this transition between these two types of flow and its effect on the aerodynamic forces on the train, however, have not been investigated in detail. The present paper reports a series of experiments of the flow at yaw angles above 60°, which reveal detailes of the wake structure. The transition mechanism and its effects on the aerodynamic loads are hence deduced. The present observations complete the understanding of the flow over the entire yaw angle range from 0° to 90°.
  • Article
    This paper reports numerical computations of the train–tunnel interaction at a tunnel entrance with real dimensions. Simulations were carried out by the FEM using the three-dimensional compressible Euler equation. The train speed was 300km/h. For a single-track tunnel, four kinds of tunnel entrance shapes were studied to investigate the formation of the compression wave front at the tunnel entrance. This study shows the possibility of a partial change in the compression wave front by means of the optimal combination of the degree of the tunnel entrance slopes and holes in the tunnel entrance ceiling. The results can be used for countermeasures against the boom noise at the tunnel exit, for the air tightness design of the train body shell and fatigue damage of the tunnel wall and structure. The compression wave fronts at the tunnel entrance directly affected the pressure drop in the tunnel and the booming noise intensity at the tunnel exit.
  • Article
    Experiments were carried out in an anechoic chamber using a 1:20 scale model of a high-speed train to determine the insertion loss of various forms of track-side noise barrier. All the barriers investigated had the upper edge level with the bottom of the train windows and were positioned as close as possible to the train, within the limitations of the structure gauge. They thus provided attenuation of noise from sources in the lower portion of the train, in the region of the rails and wheels. The measured performance of plane screens with rigid and sound-absorbing surfaces is compared with values predicted by standard prediction methods for railway noise and the results of a numerical model. The effect of barrier shape and absorptive surfaces upon screening performance is investigated. Results are presented in terms of the insertion loss of the peak SPL of the pass-by profile for a single bogie noise source and for the whole train, and also insertion loss based onLAeq,1 h . Results for these three measures show similar trends. For the conditions tested insertion loss values for all the screens were lower when the ground behind the barrier was absorbing than when the ground was rigid. The relative changes in insertion loss for the different forms of barrier were similar for the two ground types. Insertion loss values for rigid screens were between 6 and 10 dB lower than those for similar screens with complete sound absorbing surfaces. The application of absorbing areas on rigid screens significantly increases the insertion loss by between 3 and 6 dB. The least efficient screen was a corrugated barrier with a rigid surface. The most efficient screens tested were plane and curved barriers with absorbing surfaces and a multiple edge screen with a part-absorbing surface.
  • Article
    Sound barriers have been widely adopted and installed to reduce noise levels at locations adjacent to Shinkansen tracks. A number of different types of sound barriers with specific configurational features have been developed, but a quantitative evaluation of their advantages has yet to be clarified. In this paper, scale-model experiments were conducted on sound barrier configurations, the positioning of sound-absorbing materials, and a new type sound barrier that was fitted with an acoustic tube array on its upper surface. Sound barriers with effective configurations (Y-shaped sound barriers with absorbing materials and acoustic tube arrays) were proposed based on the experimental results. Furthermore, the authors verified the effectiveness of the proposed barriers by means of field tests with running Shinkansen vehicles.
  • Article
    The work presented in this paper concerns the first compression wave generated in a tunnel when a high-speed train enters it. This wave is the first of successive compression and expansion waves which propagate back and forth in the tunnel. Once generated at the tunnel entrance, its amplitude and gradient vary according to the train and tunnel characteristics. These waves provoke: (a) an aural discomfort for train passengers, (b) mechanical stresses on train and tunnel structures, and (c) emission of impulsive noises outside the tunnel. A reduced-scale test method, using low-sound-speed gas mixtures, has been developed and validated by using newly available European full-scale test-results. It can reproduce quite well the three-dimensional effects due to the train geometry and its position in the tunnel. The study also clearly points out that three-dimensional effects on the front of the first compression wave are attenuated with distance from the tunnel entrance and that the wave front can be considered well established and planar for distances larger than four times the tunnel diameter. Characteristics of the planar wave are in good agreement with Japanese results. The reduced-scale train Mach number has been extended up to 0.34 to determine its test domain. Our study clearly shows that, as far as the characteristics of the wave front of well-established planar first compression wave are concerned, axially symmetrical models can advantageously replace three-dimensional models, provided that the longitudinal cross-sectional area profile is the same for both configurations. This feature yields the following train nose design procedure: first determine the cross-sectional profile of a train nose against train–tunnel interactions by means of axially symmetrical configuration, then give a three-dimensional shape for drag and stability optimisation.
  • Article
    An analysis is made of the compression wave generated when a high-speed train enters a tunnel with a flared portal. Nonlinear steepening of the wavefront in a very long tunnel is responsible for an intense, environmentally harmful, micro-pressure wave , which propagates as a pulse from the distant tunnel exit when the compression wave arrives, with amplitude proportional to the maximum gradient in the compression wavefront. The compression wave profile can be determined analytically for train Mach numbers M satisfying M2⪡1, by regarding the local flow near the tunnel mouth during train entry as incompressible . In this paper, the influence of tunnel portal flaring on the initial thickness of the compression wave is examined first in this limit. The shape of the flared portal is “optimal” when the pressure gradient across the front is constant and an overall minimum, so that the pressure in the wavefront increases linearly . This linear behaviour is shown to occur for a flared portal extending a distance ℓ into the tunnel from the entrance plane (x=0) only when the tunnel cross-sectional area S (x) satisfiesS (x)A=1[A/AE−(x/ℓ)(1−A/AE)], −ℓ
  • Article
    Full-text available
    The rapid development of very high speed trains and the increasing operational speeds of conventional passenger and freight rolling stock are the cause of a growing interest in railways aerodynamics. Environmental issues, comfort demands and reduction of energy consumption are the key points to which aerodynamic improvements can largely contribute. Railways aerodynamics has to be performed on the complete system and the influence of the many individual shape parameters is strongly coupled. It is therefore very difficult to systematically predict how a given parameter will affect the aerodynamic properties and, more generally, what combination of the parameters yields the best performance. An optimization procedure using a genetic algorithm and relying on a commercially available CFD software for the flow simulations has been developed to bring out train shapes with lowest possible aerodynamic drag. Results are presented for a first two-dimensional application, showing the efficiency and the flexibility of the method.
  • Article
    The paper deals with the nose shape design of high-speed railways to minimize the maximum micropressure wave, which is known to be mainly affected by train speed, train-to-tunnel area ratio, slenderness and shape of train nose, etc. It is advantageous to develop a proper approximate metamodel for replacing the real analysis code in the context of approximate design optimization. The study has adopted a newly introduced regression technique; the central of the paper is to develop and examine the support vector machine (SVM) for use in the sequential approximate optimization process. In the sequential approximate optimization process, Owen’s random orthogonal arrays and D-optimal design are used to generate training data for building approximate models. The paper describes how SVM works and how efficiently SVM is compared with an existing Kriging model. As a design result, the present study suggests an optimal nose shape that is an improvement over current design in terms of micropressure wave.
  • Article
    Optimization of the cross-sectional area distribution of a high-speed train nose is conducted for various nose lengths in order to minimize the micro-pressure wave intensity at a tunnel exit. To this end, an inviscid compressible flow solver is adopted with an axi-symmetric patched grid system. To improve the shape of the train nose, multi-step design optimization is performed using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm with a response surface model. The optimization reveals that the optimal nose shapes differ for different nose lengths. For a short nose, the shape has an extremely blunt front end, and the cross-sectional area decreases in the middle section. As the nose length increases, the nose shape flattens around the middle section. These optimal shapes divide one large compression wave into two small waves by causing a strong expansion effect between the front and rear ends. As a result, through the nose shape optimization, the intensity of the micro-pressure wave is reduced by 18–27% compared to a parabolic nose, which has a minimum variation of the cross-sectional area change. The optimized distribution of the cross-sectional area can be used as a guideline for the design of three-dimensional nose shapes of high-speed trains, further improving their aerodynamic performance. KeywordsHigh-speed train-Cross-sectional area distribution-Nose shape-Design optimization-Micro-pressure wave
  • Article
    Aiming at optimizing the head shape of the CRH3 high speed train, an efficient optimization approach is proposed. The CFD analysis by solving Navier-Stokes equations is coupled with optimization calculation based on the multi-objective genetic algorithm, meanwhile the arbitrary shape deformation technique (ASD) is also introduced into the design flow, which greatly shortens the time consumption for geometry regeneration and flow field remeshing. As a result, the efficiency of the optimization calculation is highly improved. Statistical analysis is done to the designs in the design space, and the correlation between the design variables and the objective is studied to find out the key variables that most affect the objective. Response surface analysis is also performed to get the nonlinear relationship between the key design variables and the objective with the Kriging algorithm. Finally, after the optimization, an aerodynamic performance comparison between the optimal shape and the original shape reveals that the original shape of CRH3 high speed train owns a very stable aerodynamic performance and can be trustingly used in industry. Keywordsaerodynamic shape design-optimization-arbitrary shape deformation-response surface analysis-Kriging algorithm
  • Chapter
    A new procedure for optimization of aerodynamic properties of trains is presented. Instead of large number of evaluations of Navier-Stokes solver, simple polynomial response surface models are used as a basis for optimization. The suggested optimization strategy is demonstrated on two flow optimization cases: optimization of the train’s front for the crosswind stability and optimization of vortex generators for purpose of drag reduction. Besides finding global minimum for each aerodynamic objective, a strategy for finding a set of optimal solution is demonstrated. This is based on usage of generic algorithms onto response surface models. The resulting solutions called Pareto-optimal help to explore the extreme designs and to find tradeoffs between design objectives. The paper shows that accuracy of the polynomial response surfaces is good and suitable for optimization of train aerodynamics.
  • A technique is presented for deforming solid geometric models in a free-form manner. The technique can be used with any solid modeling system, such as CSG or B-rep. It can deform surface primitives of any type or degree: planes, quadrics, parametric surface patches, or implicitly defined surfaces, for example. The deformation can be applied either globally or locally. Local deformations can be imposed with any desired degree of derivative continuity. It is also possible to deform a solid model in such a way that its volume is preserved.The scheme is based on trivariate Bernstein polynomials, and provides the designer with an intuitive appreciation for its effects.
  • Article
    Abstract Due to their simplicity and intuitiveness, swept surfaces are widely used in many surface modelling applications. In this paper, we present a versatile swept surface technique called the boundary constrained swept surfaces. The most distinct feature is its ability to satisfy boundary constraints, including the shape and tangent conditions at the boundaries of a swept surface. This permits significantly varying surfaces to be both modelled and smoothly assembled, leading to the construction of complex objects. The representation, similar to an ordinary swept surface, is analytical in nature and thus it is light in storage cost and numerically very stable to compute. We also introduce a number of useful shape manipulation tools, such as sculpting forces, to deform a surface both locally and globally. In addition to being a complementary method to the mainstream surface modelling and deformation techniques, we have found it very effective in automatically rebuilding existing complex models. Model reconstruction is arguably one of the most laborious and expensive tasks in modelling complex animated characters. We demonstrate how our technique can be used to automate this process.
  • Article
    Although the control-point based parametric approach is used most widely in free-form surface modelling, complementary techniques co-exist to meet various specialised requirements. The partial differential equation (PDE) based modelling approach is especially suitable for satisfying surface boundary constraints. They are also effective for the generation of families of free-form surfaces, which share a common base and differ in their secondary features. In this paper, we present a fast surface modelling method using a sixth order PDE. This PDE provides enough degrees of freedom not only to accommodate tangent, but also curvature boundary conditions and offers more shape control parameters to serve as user controls for the manipulation of surface shapes. In order to achieve real-time performance, we have constructed a surface function and developed a high-precision approximate solution to the 6th order PDE. Unlike some existing PDE-based techniques, this resolution method can satisfy the boundary conditions exactly, and is able to create free-form surfaces as fast and almost as accurately as the closed-form (analytical) solutions. Due to the fact that it has sufficient degrees of freedom to accommodate the continuity of 3-sided and 4-sided surface patches at their boundaries, this method is able to model complex surfaces consisting of multiple patches. Compared with existing PDE-based modelling methods, this method is both fast and can solve a larger class of surface modelling problems. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curves, surfaces, solid, and object representations; physically based modelling
  • Article
    The aesthetic features of some free form surfaces, such as vases, despite being adjunct, can prove tedious and time consuming to create by the conventional surface models, such as NURBS. In this paper, we propose a new method that is able to rapidly generate complex free form surfaces, such as vases together with their accessory features using the fourth order partial differential equations (PDEs) with three vector-valued shape parameters. Vases of different shapes can be easily produced by altering the shape parameters, force functions and boundary conditions of the proposed PDE. As computational performance is of paramount significance for interactive computer graphics applications, an analytical solution to the PDE has been derived. The effects of the shape parameters, boundary conditions and force functions on the final surface shape have also been studied. r 2002 Publishedby Elsevier Science Ltd .
  • Article
    Since the advent of computer-based geometric modeling, designers have tried to develop modeling and deformation tools that allow users to emulate the ease with which sculptors work with clay. T.W. Sederberg and S.R. Parry (1986) demonstrated the application of free-form deformations. FFDs let the user conceptually embed an object in a clear pliable solid and apply deformations to the solid, which then carry through to the encased object. We describe a technique that logically extends current FFDs by basing them on nonuniform rational B-splines. The resulting NURBS-based FFDs (NFFDs) offer flexibility and control not achieved in prior implementations. We conclude by describing a straightforward combination of this technique with global and local deformations of solid primitives used to animate a lifelike surface model of the human leg.< >