力学学报

LARGE EDDY SIMULATION FOR INTERNAL COMBUSTION ENGINES: PROGRESS AND PROSPECTS

Zhou Lei, Xie Maozhao, Luo Kaihong, Shuai Shijin, Jia Ming

As one of the most successful methodologies for turbulence modeling in science and engineering application, large eddy simulation (LES) has become one of the most promising models for the study of turbulent flow and combustion in internal combustion engine (ICE) over the past decade, since it can provide detailed information about the three-dimensional transient turbulent in-cylinder processes with reasonable computing cost. In this paper a review of the current status and new developments of researches on LES applications in ICE is given and most significant results are presented. The basic concept, method and subgrid models of LES are outlined, and the development and achievements of LES, both domestic and international, are described with emphasis on the in-cylinder flow field, fuel injection and atomization as well as the two-phase spray turbulent combustion. Finally, existing problems in the current application of LES in ICE and possible solutions are discussed.

2013, 45(4): 467-482. doi: 10.6052/0459-1879-13-091

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OPERATIONAL SAFETY RELIABILITY OF HIGH-SPEED TRAINS UNDER STOCHASTIC WINDS

Yu Mengge, Zhang Jiye, Zhang Weihua

A new method of analyzing the crosswind stability of high-speed trains is proposed based on reliability theory, which can be the effective assessment of operational safety reliability of high-speed trains under stochastic crosswinds. Firstly, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and harmonic superposition method, and the method of the unsteady aerodynamic loads of high-speed trains under stochastic crosswind winds are presented. The standard deviation of the aerodynamic load coefficients varying with the slip angles are obtained by numerical simulation. Then the vehicle system dynamics model of high-speed trains is established, and the result computed by the model in this paper is compared with the test data to verify the correctness of the model. Finally, the stochastic winds, side fore coefficient, lift force coefficient, roll moment coefficient, yaw moment coefficient and pitch moment coefficient are dealt with as basic random variables, and the operational safety reliability and reliability sensitivity of high-speed trains under stochastic winds are calculated in this paper. This finally leads to the probabilistic characteristic wind curve. The results show that, the probability of failure increases as the vehicle speed or wind speed increases. The side force coefficient and roll moment coefficient cause the greatest impact on the operational safety of high-speed trains. Thus, when assessing the crosswind stability of high-speed trains, special attention should be paid to the variation of these two parameters. The operational safety domain computed by the traditional deterministic method is too conservative, and a more reasonable safety domain curve can be obtained using the method based on the reliability theory.

2013, 45(4): 483-492. doi: 10.6052/0459-1879-12-324

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NUMERICAL ANALYSIS FOR THE EFFECT OF THE ELECTROMAGNETIC ACTUATOR WIDTH ON FLOW STURCTURES AROUND A CRICULAR CYLINDER

Yin Jifu, You Yunxiang, Hu Tianqun, Zhao Liangming, Wang Lei, Zhou Youming, Chen Hong

The distribution of the electromagnetic force around a cylinder covered by electromagnetic actuators is obtained firstly by solving Maxwell equation system, and then such a Lorentz force is added to the momentum equation of flow governing equation system. The numerical simulation is carried out to simulate and analyze the flow structures around a circular cylinder and its lift/drag characteristics in a weakly conductive fluid under various combinations for electromagnetic interaction parameters and electromagnetic actuator widths when the Reynolds number Re=200. The results show that for the case of small electromagnetic actuator width, the separation point of the flow around a cricular cylinder is easier close to the back stagnation point, and the electromagnetic force has small influence on the total drag, but it has obvious influence on the pressure and friction. For the case of large electromagnetic actuator width, the cylinder wake is easier to become jet flow, and the total drag decreases as the electromagnetic interaction parameter and the electromagnetic actuator width increase. Moreover, for the case where the electromagnetic force is insufficient to completely inhibit periodic vortex shedding, the lift amplitude decreases as the electromagnetic interaction parameter increases, but it first has an obvious reduction and then a slight increase as the electromagnetic actuator width increases, and the lift pulsation frequency increases as electromagnetic interaction parameter and the electromagnetic actuator width increase. The results imply that the electromagnetic force can effectively improve the flow structure around a cricular cylinder to achieve the purpose of reducing the drag and inhibiting the lift fluctuation, therefore the flow structures can be improved effectively by the electromagnetic force.

2013, 45(4): 493-506. doi: 10.6052/0459-1879-12-301

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SIMULATION OF THE LIQUID COUETTE FLOW IN A NANO-CHANNEL WITH DIFFERENT WETTABILITY

Hu Haibao, Bao Luyao, Huang Suhe

The relation between characteristics of solid surfaces and properties of destiny, velocity and slip in a nanochannel with different wettabilities is explored, using molecular dynamics simulation (MDS). In these simulations, the liquid Couette flow confined between two infinite parallel planar walls is considered, and statistical ensemble is set as NVT, and the interaction between atoms is calculated using Lennard-Jones potential energy function. The hydrophobic wall which is set to rigid surface is characterized by the low solid-liquid relative energy parameter. For all simulations, velocity-rescale method is used to keep the temperature constant and the Verlet algorithm is used to solve the Newton equations. Some conclusions are presented from the simulation results in this paper. Firstly, fluid density profiles which are adjacent to solid surfaces oscillate around the value of major fluid density, and the extents of oscillation decay, the periods of oscillation remain unchanged with the hydrophobicity increase of the solid surface. Secondly, greater hydrophobic walls lead to larger slip velocity, and the hydrophilic surface even leads to negative slip. Thirdly, slip velocity increases with the accretion of velocity of the solid surface in Couette flow, and accretion of slip velocity is accelerated greatly when the flow is in layer regime. Besides, we also find the superhydrophobic walls generate smaller slippage than hydrophobic walls, which varies from the common conception, and we explain this result basing Young's equation.

2013, 45(4): 507-514. doi: 10.6052/0459-1879-12-244

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ENHANCEMENT OF STABILITY OF 3D MOVING PARTICLE SEMI-IMPLICIT METHOD BY ARTIFICIAL VISCOSITY

Feng Meiyan, Huang Shenghong

By the virtue of Lagrangian gridless particle method, the moving particle semi-implicit (MPS) method has been applied in a wide range of engineering applications. However, the built-in instability in computational algorithm has seriously limited its further development and application. In this paper, aiming at developing 3D stabilized MPS method, a comprehensive comparison of stabilizing methods proposed by different researchers has been conducted, in which many elements leading to instability are considered. Then the equations proposed in 2D are extended to 3D and an artificial viscosity model based on smooth particle hydrodynamics (SPH) is proposed to reduce instability in MPS for the first time. With the different combinations of proposed methods and models, the deforming process of a swirling cubic fluid patch and hydrostatic pressure problem are simulated comparatively. The results are also compared with those from volume of fluid (VOF) model conducted by a commercial software. The accuracy and stability of proposed methods and models are validated. It is concluded that: for 3D case, only extending and applying previous stabilizing method is still dissatisfactory, while good effects in accuracy and stability can be obtained by incorporating the artificial viscosity model proposed in present paper. And it is also revealed that no negative effects on exactness of pressure solution will be produced, and thus on the flow field.

2013, 45(4): 515-524. doi: 10.6052/0459-1879-12-247

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TURBULENCE CHARACTERISTICS IN CONSECUTIVE BENDS

Wang Hong, Wang Lianjie, Shao Xuejun, He Jianbo, Wang Xin

Measurements of turbulence characteristics are crucial to the study of bend flow. This paper presents detailed measurements of instantaneous 3D velocity at various cross-sections in consecutive bends by using a three-dimensional (3D) electromagnetic current meter. Details of turbulent flow characteristics in the bend were obtained, including turbulence spectrum, turbulence intensity, turbulent shear stress, etc. It is found out that turbulence energy is mainly carried by fluctuations below 10Hz. Turbulent flow characteristics are closely related to secondary current.

2013, 45(4): 525-533. doi: 10.6052/0459-1879-12-345

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VIBRATION ANALYSIS OF THE SELF-EXCITED OSCILLATION PULSED AIR-WATER JET

Tang Chuanlin, Hu Dong, Zhang Fenghua, Cai Shupeng

Aiming at improving the utilization ratio of jet, the self-excited oscillation pulsed air-water jet is generated by entraining air into the chamber of a self-excited oscillation pulsed water jet nozzle. The present studies focus on the actual influencing factors of oscillation frequency and hitting power of jet. Based on the theory of hydro-acoustics and fluid dynamics, a theory model which describes frequency characteristic of the self-excited oscillation pulsed air-water jet is presented. Moreover, the time domain and frequency domain characteristics of jet can be obtained by testing the vibration of cantilever beam with equalized strength caused by the jet impinging. The calculation result of the model show that the oscillation frequency of self-excited oscillation pulsed air-water jet monotonously decreases with increasing the cavity length, the relation between frequency and air hold-up is not always decreasing monotonously, but begins to go up after the minimal value. However, the sudden change of the model curve occurs at a given very low air hold-up. The theoretical result is confirmed well by experiment; it is also found that the optimal chamber length corresponding to the maximum resonance peak of the self-excited oscillation pulsed air-water jet is slightly smaller than that of the self-excited oscillation pulsed water jet, and the maximum resonance peak of the former is much higher than that of the latter.

2013, 45(4): 534-540. doi: 10.6052/0459-1879-12-239

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DETERMINATIONS OF SURFACE ELASTIC PARAMETERS OF FCC-METALS BY USING THE CAUCHY-BORN RULE

Liu Jianyun, Song Jingru, Wei Yueguang

First, fundamental relations on the surface energy density and surface elastic constitutive equations are derived based on the trans-scale mechanics theory considering both strain gradient and surface effects through energy variation. Second, a new method to determine both surface energy density and surface elastic parameters is developed based on a simple quasi-continuity scheme, Cauchy-Born rule. Furthermore, taking the face-centre-cubic (FCC) metals as examples, we systematically obtain the values of the surface elastic parameters for typical fcc metals which are consistent with others results by using the molecular dynamic simulations.

2013, 45(4): 541-547. doi: 10.6052/0459-1879-12-372

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POISSON BRACKET METHOD AND ITS APPLICATIONS TO QUASICRYSTALS, LIQUID CRYSTALS AND A CLASS OF SOFT MATTER

Fan Tianyou

This paper gives an introduction on the Poisson bracket method in condensed matter physics, Lie group and Lie algebra and their some applications to quasicrystals, liquid crystals and a class of soft matter. It introduces not only derivation on hydrodynamic or elasto-hydrodynamic equations of the materials, but also solutions of relevant equations, some among them explore the mistakes of well-known classic solutions, in addition, the equations and solutions on soft matter quasicrystals are observed for the first time.

2013, 45(4): 548-559. doi: 10.6052/0459-1879-12-346

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APPROXIMATE THEORY AND ANALYTICAL SOLUTION FOR RECTANGULAR PLATES WITH IN-PLANE STIFFNESS GRADIENT

Li Yaochen, Nie Guojun, Yang Changjin

Approximate theory for rectangular plates with in-plane stiffness gradient subjected to transverse loading is established. In this theory, Reissner-Mindlin assumption is introduced, and the shear deformation in the mid-surface of the plate is considered. Material properties of the plates vary exponentially in the direction parallel to one pair of edges. Analytical solution in the cases that one pair of edges of the plate is simply supported and the other pair is fixed or simply supported is obtained. It is indicated that this solution can degenerate into the classical solution of thin plates based on the well-known Kirchhoff assumption if the shear deformation in the mid-surface is ignored. The numerical results of this solution are given and compared with those from 3D finite element solution by means of PATRAN code. It shows that the precision of this solution is still high even for thick plates.

2013, 45(4): 560-567. doi: 10.6052/0459-1879-12-318

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REGIONAL IMPORTANCE MEASURE OF THE BASIC VARIABLE AND ITS SPARSE GRID SOLUTION

Li Luyi, Lü Zhenzhou

To improve the stability and convergence of the existing contribution to sample mean (CSM) regional importance measure (RIM), a new RIM is proposed to estimate the contribution to the mean of the model output by the different regions of basic variable, and it is named as improved contribution to sample mean (ICSM). An extended version of the ICSM, which is named as contribution to first order variance (CFOV), is developed to analyze the effect of the different regions of the basic variable on its corresponding first order variance in the variance decomposition. The properties of the two proposed RIMs are analyzed and their relationships with the existing CSM and contribution to sample variance (CSV) RIM are derived. Furthermore, based on the characteristics of the proposed RIMs, their highly efficient sparse grid integration (SGI) solutions are also established. Several numerical and engineering examples show that the newly defined ICSM can act as effectively as the CSM, but the convergence and stability of ICSM is better than those of CSM. The proposed CFOV can provide more detailed information than the existing CSV, which can effectively instruct the engineer on how to achieve a targeted reduction of the main effect of each basic variable. The established SGI-based method can improve the efficiency of the regional importance analysis considerably in case of acceptable accuracy.

2013, 45(4): 568-579. doi: 10.6052/0459-1879-12-260

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CHARACTERISTICS OF FRAGMENT SIZE DISTRIBUTION OF DUCTILE MATERIALS FRAGMENTIZED UNDER HIGH STRAINRATE TENSION

Zheng Yuxuan, Chen Lei, Hu Shisheng, Zhou Fenghua

Finite Element Method has been used to simulate the fracture and fragmentations of ductile metallic rings undergoing high rate expansions. In this paper, the numerical fragments obtained from the FEM simulations were collected for statistical analysis. It is found that: (1) The cumulative distributions of the normalized fragment sizes at different initial expansion velocities are similar, and collectively the fragment size distributions are modeled as a Weibull distribution with an initial threshold. Approximately, this distribution can be further simplified as a Rayleigh distribution, which is the special case with the Weibull parameter to be 2; (2) The cumulative distribution of the fragment sizes exhibits a step-like nature, which means that the fragment sizes may be "quantized". A Monte-Carlo model is established to describe the origination of such quantization. In the model, the fractures occur at the sites where the tensioned material necks. The spacing of the necking sites follows a narrow Weibull distribution. As the fragment size is the sum of several (a random integer) necking spacing, the distributions of the fragment sizes automatically inherit the quantum properties of the random integers as long as the spacing distributions are not so wide. The experimental results conducted on Al L04 and on OFHC agree with the analysis.

2013, 45(4): 580-587. doi: 10.6052/0459-1879-12-338

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STRUCTURAL TOPOLOGY OPTIMIZATION AND FREQUENCY INFLUENCE ANALYSIS UNDER HARMONIC FORCE EXCITATIONS

Liu Hu, Zhang Weihong, Zhu Jihong

In this paper, structural topology optimization is studied under harmonic force excitations. The displacement amplitude at the specified location of a structure is defined as the objective function subjected to the volume constraint. The displacement amplitude is calculated based on modal superposition method and the corresponding sensitivity analysis is derived. In order to avoid localized modes, the polynomial interpolation scheme is introduced to relate material properties to pseudo density variables. In the meantime, the influences of the excitation frequency and direction upon the displacement response are investigated and how the eigen-modes vary in the optimization process is highlighted. Topology optimization of structure under harmonic excitation with high frequency is specially analyzed. More constraints on the static displacements are applied to generate clear structural topology. Numerical optimization examples are finally solved to demonstrate the validity of the proposed optimization procedure.

2013, 45(4): 588-597. doi: 10.6052/0459-1879-12-253

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EXPERIMENTAL STUDY ON HIGH TEMPERATURE THERMAL-VIBRATION CHARACTERISTICS FOR HOLLOW WING STRUCTURE OF HIGH-SPEED FLIGHT VEHICLES

Wu Dafang, Zhao Shougen, Pan Bing, Wang Yuewu, Wang Jie, Mu Meng, Zhu Lin

During long time and high speed flight, high-speed aircraft structure, such as the wing and rudder, bears not only prolonged serious vibration, but also harsh aerodynamic heating. The high temperatures caused by aerodynamic heating can greatly change the elasticity properties of the materials in a high-speed flight vehicle, leading to an alteration in the vibration characteristics of high-speed flight vehicle structures. Knowledge of the vibration characteristics of these key structures is critical to the safety design of high-speed flight vehicles. In this paper, vibration excitation was exerted to a hollow wing under controlled thermal environments by combining a self-developed transient aerodynamic heating device with a vibration test system. A self-designed extension configuration withstanding high temperature is used to transfer the vibration signals to the non-high temperature zone for vibration data acquisition. With this novel method, accurate measurements of various vibration characteristics parameters, such as natural frequency and vibration modal, can be achieved in a thermal-mechanical environment with a highest temperature up to 900℃. Experimental results provide an important basis for the dynamic characteristic analysis and safety design of the hollow wing structure used in a long-range high-speed flight vehicles under high-temperature thermal-vibration conditions.

2013, 45(4): 598-605. doi: 10.6052/0459-1879-12-360

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THE MOTION STABILITY ANALYSIS OF A ROTATING BEAM WITH A RIGID BODY ON ITS END

Zhao Jie, Yu Kaiping, Xue Zhong

Discretization method may lead to the phenomenon of "dynamic stiffening", which is commonly used in the analysis of the stability and other dynamic behavior of complex spacecraft with flexible components. In this paper, the beam is treated as a subsystem with distributed parameters (infinite degrees of freedom). Based on Rumyancev theorem, the steady motion of the system can be derived by calculating the first-order variation of relative potential energy functional of the system. Then the system stability analysis of steady state motion becomes to solve the isolation minimum problem of the system potential energy functional. The differential equations of the system's motion are not necessary in the analysis; consequently the modeling process is simplified. The sufficient condition for steady motion stability can be obtained by determining the positive definiteness of the second variation of the system relative potential energy functional variational. What's more, this condition is the most extensive one among those obtained by analyzing the stability of motion based on Liyapunov direct method.

2013, 45(4): 606-613. doi: 10.6052/0459-1879-12-343

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THE OPTIMIZED REFERENCE ENTHALPY METHOD USING IN HIGH-SPEED TURBULENT CHANNEL FLOWS

Chen Xiaoping, Li Xinliang, Zhong Fengquan

Direct numerical simulations of high-speed turbulent channel flows have been performed. The classic reference enthalpy method was evaluated and optimized by using the data with inflow Mach numbers of 3, 5, 6, 7, and 10. In fully developed turbulent flow, studies have shown that the classic reference enthalpy method is not applicable in high-speed channel flows. The wall heat flux predicted by the optimized reference enthalpy methods I and II are much better than the classic reference enthalpy method; moreover, the optimized reference enthalpy method II is more suitable, whose errors are within 10% compared with DNS. At the same time, the optimized reference enthalpy method II has been verified based on the experiment data of thermal environment of supersonic combustor.

2013, 45(4): 614-618. doi: 10.6052/0459-1879-12-308

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THE SCALED BOUNDARY COORDINATE INTERPOLATION METHOD AND ITS APPLICATION TO SPECTRAL ELEMENT METHOD: NUMERICAL SIMULATION OF THE EULER EQUATIONS OVER UNBOUNDED DOMAINS

Wu Zeyan, Wang Lifeng, Wu Zhe

A new infinite element,by combining the scaled boundary coordinate interpolation method and spectral element method, named scaled boundary spectral element (SBSE), to solve Euler equations over infinite domains directly is presented in this paper. The usage of SBSE and the procedures for solving Euler equations using Runge-Kutta discontinuous Galerkin (RKDG) method are described. Two typical subsonic flow cases, around a circular cylinder and around NACA0012 airfoil, are simulated, which illustrate the correctness of this method. When one solve Euler equations over infinite domains directly with SBSE, the solution domain need be divided into 2 sub-domains at most, avoiding the trouble of dividing the solution domain into 9 or 27 sub-domains when one do the same thing with spectrum methods. The numerical results demonstrate that SBSE provides an available choice for solving Euler equations over infinite domains directly.

2013, 45(4): 619-623. doi: 10.6052/0459-1879-13-026

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DAMAGE ANALYSIS METHOD FOR LAMINATES BASED ON PERIDYNAMIC THEORY

Hu Yile, Yu Yin, Wang Hai

A new method for progressive damage analysis of fiber-reinforced composite laminates based on peridynamic theory was proposed. The basic parameters, micromodulus and critical stretch for peridynamic modeling were deduced based on elasticity and composite mechanics. The concept of off-axial modulus was introduced into the bonds' definition to establish a pairwise force function for anisotropic materials. This approach was able to analyze three types of damages: fiber fracture, matrix fracture and delaminations. Based on this approach, laminate with an open hole was subjected to a tensile load to simulate the progressive damage process. The predictions showed good agreements with experimental results.

2013, 45(4): 624-628. doi: 10.6052/0459-1879-12-368

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STRUT AND TIE MODEL OF ANCHORAGE ZONE BASED ON MULTI-NODE MICRO TRUSS ELEMENT

Zhong Jitao, Liu Zhao

At present the strut and tie models of D-regions in concrete girder bridges are often obtained qualitatively according to stress trace and integration, by which the location of members is random to some extent. To solve this problem, a multi-scale evolutionary optimization algorithm is proposed, taking post-tensioned anchorage zone as research objects. First, the equivalent ground structure is built by a multi-node pattern of micro-truss element. Then the algorithm is used to analyze the ground structure subjected to different eccentric loads in order to generate the strut and tie model of anchorage zone. Finally, the models are compared with those in AASHTO bridge design specifications. The research shows that the algorithm can identify definitely the position of struts and ties of models, and the distribution of ties are found to be in good agreement with finite element analysis.

2013, 45(4): 629-633. doi: 10.6052/0459-1879-13-030

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A BRIEF INTRODUCTION OF COMPLETED KEY PROGRAM PROJECTS ON MECHANICS IN 2012

Zhang Panfeng, Zhan Shige, Wang Lifeng, Xu Xianghong

The paper brief introduced the completion and evaluation of 12 NSFC key program projects on mechanics in 2012. The detail projects list and the evaluation assessments provided by expert committee are given.

2013, 45(4): 634-638. doi: 10.6052/0459-1879-13-216

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