力学学报

THE OBSERVATIONS OF THE FLOW BEHAVIOR AND DISTRIBUTION OF RED BLOOD CELLS FLOWING THROUGH A MICRO-NETWORK CHANNEL

Li Fen, Hu Ruiqing, Yamada Takashi, He Ying, Ono Naoki

The structure of vascular network in solid tumor is extremely disordered and non-uniformed. These characteristics result in the complexity and diversity of the blood flow in tumor microcirculation which eventually make drug delivery and targeted therapy difficult in solid tumor. In order to investigate the influence of tumor microvascular network on the blood flow, a vertical interconnected micro-network channel was fabricated by soft lithographical method in this work, designed to simulate the expanding, multi-branched and multi-interconnected tumor vascular network. Employing the micro-flow-system, the red blood cell (RBC) suspension was injected into micro network channel at a certain speed. Inverted microscope was used to observe the migration of RBCs and the sequential images were recorded. PIV-lab package of Matlab and the tool box of the high-speed video camera were used to process the image data. The results show that, hemotocrit (Hct) level of RBC suspension is the main factor to affect the flow and distribution of RBCs in the micro-network. The trajectories of RBCs in the micro-network vary with different Hcts. When Hct level is as low as 1%, the RBCs in the micro-network flow only along the axial direction of the channels, while Hct level becomes higher, some RBCs will flow across the radial channel and the two types of RBC flow trajectories appeared. Furthermore, at the same inlet flow rate, the speeds of RBCs in the micro-network show difference with different Hct levels. The velocities of RBCs with 3% and 5% Hct levels are evidently higher than those of RBCs with 1% Hct level.

2014, 46(1): 1-9. doi: 10.6052/0459-1879-13-139

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UNCERTAINTY QUANTIFICATION AND ROBUST DESIGN OF AIRFOIL BASED ON POLYNOMIAL CHAOS TECHNIQUE

Zhao Ke, Gao Zhenghong, Huang Jiangtao, Li Jing

Robust design optimization has gained increasing concern in the engineering design process because it can provide an economical design that is insensitive to variations in the input variables without eliminating their causes. The key of robust design is uncertainty analysis. So in this paper the uncertainty analysis based on polynomial chaos was investigated and combined with CFD method to quantify the uncertainties in computational aerodynamic design. The transonic flow around RAE2822 airfoil is studied to test the presented method and analyze the effect of the polynomial order to the precision of the aerodynamic characteristic. The robust design of a supercritical airfoil based on the uncertainty of Mach number was conducted to validate the PCE method. It is shown by the optimization result that the drag coefficient was decreased at the design point while the sensitivity of the drag coefficient about the Mach number was weakened. It is proved that the PCE method can improve the efficiency of robust design and is a good choice for aerodynamic robust design.

2014, 46(1): 10-19. doi: 10.6052/0459-1879-13-127

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ANALYSIS OF MAXIMUM DISSOCIATION DEGREE OF OXYGEN DURING HYPERSONIC FLIGHT

Chen Song, Sun Quanhua

A theoretical model is established to calculate the dissociation degree of oxygen along the stagnant streamline of airflow, which is used to study the chemical nonequilibrium phenomena during hypersonic flight. The model assumes that nitrogen will not dissociate before oxygen undergoes serious dissociation. The recombination reaction in the boundary layer is also excluded in the model. It is found that, the dissociation degree of oxygen first increases and then decreases as the flight altitude increases, which is due to the competence between the equilibrium shift and nonequilibrium effect. This observation is confirmed by CFD simulations, and can be used to explain the phenomenon of the decline of real gas effects with increasing flight altitude in the literature. Using the developed model, the maximum dissociation degree of oxygen and temperature at the external edge of the boundary layer, are evaluated for hypersonic flows over a blunt body that cover a wide range of flight speeds and altitudes. The results are useful for engineering applications.

2014, 46(1): 20-27. doi: 10.6052/0459-1879-13-146

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STABILITY ANALYSIS OF SUPERSONIC BOUNDARY/MIXING LAYERS CONFLUENT FLOW

Liu Zhiyong, Yuan Xiangjiang, Liu Xiaoyong, Fei Lisen, Liu Fengjun

A compressible supersonic confluent flow composed of boundary layers and mixing layers are studied by linear stability theory. The flow is confined in a two-dimensional adiabatic channel. A slower flow lying in the center mixes with faster boundary layer flows on both sides and two mixing layers are evolved near the centerline. Different unstable modes were discovered and the first mode was found to be most unstable. Three-dimensional disturbances were investigated and comparison of instability features was made with unconfined boundary layer flows. The investigation of different widths of slow flow was also made.

2014, 46(1): 28-36. doi: 10.6052/0459-1879-13-066

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SUBHARMONIC INTERACTION OF SPATIALLY-DEVELOPING COMPRESSIBLE MIXING LAYERS

Yang Wubing, Shen Qing, Wang Qiang

A phenomenological model of collective interaction of primary vortex of mixing layers is built on the linear stability theory. The model can be used to determine the influence of the phase shift of the subharmonic disturbance wave on the nonlinear evolving process of the primary vortex. The results indicate that there are three classes of subharmonic interaction to the short subharmonic wavelength, which are tearing, symmetric collective interaction and asymmetrical collective interaction, respectively. And to the long subharmonic wavelength, there always occurs asymmetrical collective interaction.

2014, 46(1): 37-43. doi: 10.6052/0459-1879-13-065

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LATTICE BOLTZMANN SIMULATION OF A POWER-LAW FLUID PAST A CIRCULAR CYLINDER

Dong Bo, Li Weizhong, Feng Yujing, Sun Tao

Based on the interpolation-supplemented lattice Boltzmann method and constitutive equation for power-law fluid, a lattice Boltzmann model for power-law fluid in body-fitted coordinates is proposed and applied to simulate steady and unsteady flows of a power-law fluid past a circular cylinder, respectively. The non-equilibrium extrapolation boundary scheme is adopted for the non-slip velocity at the circular cylinder surface. The drag coefficient and lift coefficient are calculated by integrating the total stresses on the boundary of the circular cylinder, respectively, and the results are in good agreement with those obtained by using the conventional lattice Boltzmann method and finite volume method. After performing the grid sensitivity tests, in terms of steady flow, the effects of power-law index on the wake length, separation angle, viscosity distribution over cylinder surface, pressure coefficient and drag coefficient are further analyzed. Moreover, as for unsteady flow, the influences of power-law index on the flow field, drag coefficient, lift coefficient and Strouhal number are investigated. The validation and capability of the model are demonstrated by the good agreement between the simulation results and the ones obtained by other numerical simulation methods. The simulations show that the interpolation-supplemented lattice Boltzmann method can be used to study power-law fluid flow in flow field with complex boundaries, and it can be further applied to study other types of non-Newtonian fluid flow problems by using different constitutive equations.

2014, 46(1): 44-53. doi: 10.6052/0459-1879-13-299

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PARALLEL-BEAM TOMOGRAPHY BASED ON TDLAS

Li Fei, Yu Xilong, Lin Xin, Zhang Shaohua, Zhang Xinyu

Tunable diode laser absorption spectroscopy (TDLAS) has been one of the most powerful techniques for combustion diagnostics in high speed flow. In order to improve its spatial solution, a new method called TDLAT (tunable diode laser absorption tomography) has been developed combining with computed tomography (CT). This study reports a TDLAT system composed of six parallel beams and a motorized?rotation?stage. Two water vapor absorption lines, 7185.6cm^-1 and 7444.3cm^-1, were utilized in each beam. Temperature and concentration distribution can be deduced after the reconstruction of absorbance of the line-pair using algebraic reconstruction technique (ART). A verification?experiment was performed using a premixed CH₄/Air flat burner. Comparing with thermocouple measurement, the good temperature reconstruction indicates that this TDLAT can capture the primary characteristic of this flame. More researches about TDLAT are undergoing. The future improved TDLAT system will be used to measure the temperature and concentration distributions in a scramjet facility.

2014, 46(1): 54-59. doi: 10.6052/0459-1879-13-068

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NUMERICAL METHODS AND TRANSITION INVESTIGATION OF TRANSIENT FLOWS AROUND A PITCHING HYDROFOIL

Wu Qin, Wang Guoyu, Huang Biao

In order to investigate the numerical method for transient flows around a pitching hydrofoil, the numerical simulations for a NACA66 hydrofoil are performed by using the standard k-ω SST turbulence model and revised γ-Re_θ transition model respectively. The simulation results are compared with the experimental results, and the hydrodynamic property and the fluid structure during the pitching process are studied. It is revealed that, compared with the standard k-ω SST turbulence model, the revised -Re transition model is able to present the hydrodynamic property and the fluid structure of the transient flow around a pitching hydrofoil more accurately, and better predict the separation and transition process in the boundary layer. The transient flow process around a pitching hydrofoil can be divided into 5 parts. At small angle of attack, transition is observed at the leading edge of the foil, resulting in the inflection of dynamic property curves. As the angle of attack increases, a clockwise trailing edge vortex expands toward the leading edge of the foil. At high angles of attack, large-scale load fluctuations are observed due to the stall caused by separation of the leading edge vortex. The transition from turbulent flow to laminar flow occurs during the downward pitching process.

2014, 46(1): 60-69. doi: 10.6052/0459-1879-13-080

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RESEARCH ON NONSTEADY SHAPE FACTOR OF CROSS FLOW IN LOW PERMEABILITY FRACTURED RESERVOIRS

Shu Weibing, Xu Hehua, Liu Tangwei, Wan Juying

The mass transfer shape factor between matrix and fracture is one of the most important parameters in the numerical simulation research on porous flow in fractured reservoirs. For the purpose of indicating the nonlinear and nonsteady characteristics of mass transfer between fracture and matrix in low permeability fractured reservoirs, this paper firstly analyzed the inapplicability of pseudo-state shape factor and existing nonsteady shape factor used in low permeability fracture reservoirs, then the variable coefficient of apparent permeability was introduced based on the fitting analysis results of the v-!-abla p curve of 23 core samples, and then a nonlinear diffusivity equation was developed based on the variable coefficient to govern the mass transfer between fracture and low permeability matrix. Integral method and method of moments were applied to deduce semi-analytical solution of zero dimension nonlinear diffusivity equation at the earlier and later stages, to lead the nonsteady shape factor and the new mass transfer function. By comparison with the pseudo-state mass transfer model, which was restricted to describe the mass exchange in the systems whose pressure changes quite slowly, the new shape factor was effective to simulate the nonlinear and nonsteady mass transfer between matrix and fracture in low permeability fractured reservoirs, and the fine grid finite element numerical model verified the reliability and availability of the nonsteady shape factor and the new transfer function.

2014, 46(1): 70-77. doi: 10.6052/0459-1879-13-154

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STUDY ON NUMERICAL MANIFOLD METHOD BASED ON FINITE DEFORMATION THEORY

Wei Wei, Jiang Qinghui, Zhou Chuangbing

The large deformation of structure calculated by original numerical manifold method (NMM) is cumulated by small deformation calculated in each time step. However, when the structure undergoes large deformation and large rotation, the calculation strategy used in original NMM will lead to calculation error. In order to solve this problem, in this study, combining the interpolation function of NMM, the Numerical Manifold Method based on finite deformation theory is deduced from integral weak form of the momentum conservation equation and the stress boundary conditions. The comparison between the iteration schemes of original NMM and improved NMM points out the sources of error calculated by original NMM for the large deformation problem. Finally, examples of large deformation cantilever and rotation block are employed to exam the improved NMM. The numerical result shows that the improved NMM handles the problem involving in large deformation and large rotation very well. The result calculated by the improved NMM eliminates the errors caused by rotation of structure and is coincide with the analytical solution and Abaqus numerical solution very well.

2014, 46(1): 78-86. doi: 10.6052/0459-1879-13-081

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THE EXPLICIT RELATION BETWEEN THE M-INTEGRAL AND THE ELASTIC MODULI OF INCLUSION/DAMAGES

Yu Ningyu, Li Qun

The M-integral represents the energy release rate due to the self-similar expansion of defects in material configurational mechanics while the reduction of effective elastic moduli is an inner damage parameter in traditional damage mechanics. This study will focus on the inherent relation between them in order to build the bridge of material configurational mechanics and damage mechanics. The explicit expression of M-integral is derived by using Muskhelishvili complex potential for the infinite plane with a circle inclusion. And the explicit expression of M-integral reveals the explicit relation between M-integral and the elastic moduli of the inclusion. A finite element method analysis is then performed to simulate the complex defects embedded in an elastic-plastic plane. The results reveal the inherent relation between the reduction of the effective elastic moduli for damaged area and the M-integral. In conclusion, the M-integral as an outer variable is believed to be capable of replacing the inner variable (reduction of the effective moduli) to describe the defects evolution in damaged material.

2014, 46(1): 87-93. doi: 10.6052/0459-1879-13-097

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CDM MODEL FOR INTRALAMINAR PROGRESSIVE DAMAGE ANALYSIS OF COMPOSITE LAMINATES

Wu Yitao, Yao Weixing, Wu Fuqiang

Based on continuum damage mechanics (CDM), a model was proposed for predicting intralaminar progressive damage of composite laminates, including damage description, damage model judgment and damage evolution. Four different damage modes existent within lamina, namely, fiber tension fracture (FFT), fiber compression fracture (FFC), inter fiber tension fracture (IFFT) and inter fiber compression fracture (IFFC), were considered, and damage state variables corresponding to these four modes were also defined. Material constitutive relationship being in the damaged states in the material principal axes was derived compared to that of undamaged states. The onset of the damage was estimated with Puck's criteria and the evolution of the damage was controlled by the strain energy release density within the characteristic length. Assuming that the material was exhibited linear strain-softening behavior, a new damage evolution law associating damage state variables with equivalent strain on fracture plane was established in this paper. The proposed model can predict damage initiation, damage evolution and final failure of composite laminates. Failure analyses of [45/0/-45/90]_2S notched laminates under tension and compression were performed with the present model and showed that it is capable to predict the strength of the composite laminate and analyze the failure process.

2014, 46(1): 94-104. doi: 10.6052/0459-1879-13-106

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SPECIAL HYBRID STRESS SOLID ELEMENT WITH DRILLING DEGREES OF FREEDOM AND A TRACTION-FREE CIRCULAR BOUNDARY

Wang Anping

New 8-node special hybrid stress elements with drilling degrees of freedom have been developed based on the principle of minimum complementary energy. These elements are used jointly with conventional displacement elements for the analysis of stress concentrations around different holes and notches. The assumed stress fields in the elements satisfy the equilibrium equations, the traction-free boundary conditions and the compatibility equations. The examples of these special elements have been shown that these present special elements are far superior in predicting the stress concentration factors, the distributions of circumferential stresses and the normal stress when only very coarse meshes are used near holes and notches.

2014, 46(1): 105-113. doi: 10.6052/0459-1879-13-104

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THE BUCKLING ANALYSIS OF SHEAR MEMBRANE BASED ON STABILITY THEORY

Ma Rui, Yang Qingshan, Wang Xiaofeng

Based on the Large Deflection Post-buckling Theory, wrinkling parameters of membranes were deduced in this paper, considering the influence of the tensile stress along the wrinkles. Then, the formulas were simplified according to the experimental results and used to analyze the buckling of a membrane under shear. The results are compared with the related documents and the numerical results of ABAQUS to verify the validity and rationality of the formulas.

2014, 46(1): 114-119. doi: 10.6052/0459-1879-13-159

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DYNAMIC RESPONSE OF DOUBLE RING-STIFFENED CYLINDRICAL SHELL WITH INTERNAL FLUID

Xiao Wei, Zhang A-Man, Wang Yu

In this paper, a numerical model on fluid-structure interaction is established and the validation of the model is carried out. The doubly asymptotic approximation for external domain is used to model the external fluid, the doubly asymptotic approximation for internal domain is used to model the internal fluid and the nonlinear finite element software ABAQUS is employed to model the structure. Based on the numerical model, the influence of internal fluid to the dynamic response of double ring-stiffened cylindrical shell is investigated. The main results are as follows. Compared with the analytic solution, the oscillation period and amplitude of late time response obtained by the first order doubly asymptotic approximation decrease. But, the solution of the second order doubly asymptotic approximation agrees well with the analytic solution. The existence of internal fluid makes the plastic deformation and velocity response of double ring-stiffened cylindrical shell decrease.

2014, 46(1): 120-127. doi: 10.6052/0459-1879-13-196

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PARAMETER IDENTIFICATION OF FLEXIBLE PLATE BASED ON THE ACCELERATION OUTPUT

Xie Yong, Liu Pan, Cai Guoping

This paper studies the parameter identification using a flexible plate as research object. An eigensystem realization algorithm (ERA) based on the output of acceleration sensors is investigated and the optimal positions of sensors on the plate are studied using the particle swarm optimization (PSO). Simulation results indicate that the PSO may effectively determine the optimal positions of sensors on the plate, and the plate parameter may be identified accurately using the ERA.

2014, 46(1): 128-135. doi: 10.6052/0459-1879-13-124

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PROBABILITY DENSITY EVOLUTION ANALYSIS OF NONLINEAR RESPONSE OF STRUCTURES WITH NON-UNIFORM RANDOM PARAMETERS

Chen Jianbing, Zhang Shenghan

The probability density evolution method (PDEM) provides a feasible approach for nonlinear stochastic response analysis of multi-degree-of-freedom systems. In the present paper, the point evolution, ensemble evolution and the partition of probability-assigned space are firstly revisited. The criterion for point selection is then explored. The concept of generalized F-discrepancy (GF-discrepancy), which avoids the NP-hard problem of computation, is introduced for random variables of general non-uniform, non-Gaussian distribution as an index to measure the quality of a point set. The relationship between GF-discrepancy and EF-discrepancy is explored and the error bound is studied by the extended Koksma-Hlawka inequality. Based on the GF-discrepancy, a new strategy for point-selecting and space-partitioning is proposed. The numerical example shows that the proposed method enables highly accurate probability density evolution analysis of nonlinear structures involving dozens of non-uniform random variables. Problems to be further studied are discussed.

2014, 46(1): 136-144. doi: 10.6052/0459-1879-13-174

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BIOMECHANICAL INVESTIGATION ON HOST RESPONSE OF ACELLULAR DERMAL MATRIX IN LAMELLAR CORNEAL TRANSPLANTATION

Ji Jing, Liu Ziyuan, Zhang Jing, Li Xuemin, Wang Wei

The biocompatibility, biological changes and tissue structure of acellular dermal matrix (ADM) in lamellar corneal transplantation (LCT) as a substitute are experimentally investigated in order to evaluate its possibility as a supporting material in corneal tissue engineering. The microstructure of ADM was observed with light microscope (LM), fluorescence microscope, polarizing microscope, and transmission electron microscope (TEM). In the implantation experiment, the ADM was processed with 3 different methods and implanted into rabbit corneal stroma. The ocular surface condition was observed with slit lamp microscope (SLM) postoperatively. The rabbits were sacrificed and morphology structures of the corneal grafts were studied by LM and polarizing microscope at 1 week, 4 weeks, 12 weeks and 24 weeks after transplantation. It was found that the ADM were composed mainly of Type-I and III collagens organized loosely and disorderly. No cellular structure was observed. There were inflammatory responses after implantation. Some implants turned to be transparent. Histological study evidenced both the growth of cells into the implant and the reconstruction collagen fiber. The results showed that the ADM with compact structure and proper pretreatment could stably exist in corneal stroma after implantation and, therefore, could be used as a potential scaffold in corneal tissue engineering.

2014, 46(1): 145-154. doi: 10.6052/0459-1879-13-439

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SHOCK TUBE STUDY OF ETHYLENE IGNITION DELAY CHARACTERISTICS AT LOW DILUTION

Liang Jinhu, Hu Honghao, Wang Su, Zhang Shengtao, Fan Bingcheng, Cui Jiping

Ignition delay characteristics of ethylene/O₂/Ar mixtures have been studied behind reflected shock waves in a shock tube by monitoring the steepest rise of the characteristic emission of OH radical at 306.5nm. Experiments were conducted with low argon dilution, covering a temperature range of 800～1650K, at pressures of 0.2, 0.7 and 1.2MPa, and with equivalence ratios of 0.5, 1 and 2. The oxygen content of the test mixtures was about 20%. The correlation formula of ignition delay dependence on temperature, pressure, equivalence ratios and fuel and oxygen mole fraction was obtained. The transition of ethylene ignition to detonation was observed with different initial temperatures, and the influence of initial temperature on ignition delay characteristics of ethylene was also discussed.

2014, 46(1): 155-159. doi: 10.6052/0459-1879-13-027

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A TRANSITION PREDICTION METHOD BASED ON TURBULENCE KINETIC EQUATION

Zhang Yang, Xu Jinglei, Bai Junqiang, Hua Jun

Transition is a chief obstacle for high-accuracy prediction of drag. The γ-θ transition model proposed by Menter and Langtry increases the adaptability by inducing vorticity Reynolds number and intermittency factor, but there are lots of empirical formulae that cannot be told the lodgments of theory. The dissipation term of kinetic energy can be sufficiently constructed with the first and second order correlations of velocity. Transition phenomena can be caught by adding some dissipation terms into the turbulent kinetic energy equation. The method is tested by a natural transition and two bypass transition test cases. The results approve that this method can be applied in engineering turbulence flows simulation.

2014, 46(1): 160-164. doi: 10.6052/0459-1879-13-231

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