bluuebunny/crossref_metadata_2025 huggingface dataset:
LOW CYCLE FATIGUE BEHAVIOR OF Zn-22Al ALLOY IN SUPERPLASTIC REGION AND NON-SUPERPLASTIC REGION
Authors: KUSHIBE ATSUMICHI , TANAKA TSUTOMU , TAKIGAWA YORINOBU , HIGASHI KENJI
Published: March 2009

The crack propagation properties for ultrafine-grained Zn -22 wt % Al alloy during low cycle fatigue (LCF) in the superplastic region and the non-superplastic region were investigated and compared with the corresponding results for several other materials. With the Zn - 22 wt % Al alloy, it was possible to conduct LCF tests even at high strain amplitudes of more than ±5%, and the alloy appeared to exhibit a longer LCF lifetime than the other materials examined. The fatigue life is higher in the superplastic region than in the non-superplastic region. The rate of fatigue crack propagation in the superplastic region is lower than that in the other materials in the high J-integral range. In addition, the formation of cavities and crack branching were observed around a crack tip in the supereplastic region. We therefore conclude that the formation of cavities and secondary cracks as a result of the relaxation of stress concentration around the crack tip results in a reduction in the rate of fatigue crack propagation and results in a longer fatigue lifetime.
FATIGUE PROPERTIES OF AUTOMOBILE HIGH-STRENGTH BOLTS
Authors: ZHOU CONGLING , NISHIDA SHIN-ICHI , HATTORI NOBUSUKE
Published: March 2009

This study is focused on the fatigue properties of automobile high-strength bolts, including the effect of mean stress level, pre-processing schedule and the residual stresses. And the mean stress levels are 0.3, 0.5 and 0.7 times to the tensile strength (σ B ) of the material respectively. The main results obtained are as follows: 1) the fatigue strength increases under the mean stress loading, but the differences between the loading levels are not so evident; 2) most of the cases in this study are broken from the bottom of the screw thread, and the crack initiated from the impurities.
A NEW METHOD FOR VIBRATION RESPONSE OF BEAM ON FOUNDATION UNDER MOVING LOAD
Authors: YANG YOUZHE , GE XIURUN
Published: March 2009

In this research, an approach combining the precise time integration method (PTIM) and mode decomposition method is proposed to compute the response of beam structures resting on viscoelastic foundation. The PTIM has high precision, high efficiency, but it still suffers from the problem of large-size matrices when directly computing structure. And this problem can be overcome by mode superposition. Thus, the present paper integrates the PTIM and mode decomposition method together which holds the explicit recurrence form of precise algorithm. Comparing with the other numerical methods, it is found that the presented method is much more precisely and time-saving. The effect of the speed of moving load, the foundation stiffness and the length of the beam on the response of beam have also been studied. These numerical computation results show that the present method is effective and feasible.
TOP JOINT STUDY ON TEMPERATURE STRESS FOR SUPER-LONG SLAB-COLUMN STRUCTURE
Authors: DONG MINGHAI , SONG LI , SHAO YING
Published: March 2009

In this paper, top joint method is proposed to solve a practical engineering problem of temperature stress and temperature crack of super-long slab-column structure bearing temperature difference. From the study, it is shown that as for super-long slab-column structure undergoing temperature difference of inside and outside, joint located in bottom stories nearly has no influence on temperature stress and deformation while joint in top stories can significantly reduce temperature stress and deformation of super-long slab-column structures. In addition, comparison of joints located in top one story, top several stories and from bottom to top stories indicates that influences of them on temperature stress and deformation are similar. As for top joint method, among which cantilever plate method, double column method and corbel method are discussed and results indicate that influence effects of these methods on structures are similar.
A NUMERICAL SIMULATION OF STRIP PROFILE IN A 6-HIGH COLD ROLLING MILL
Authors: DU XIAOZHONG , YANG QUAN , LU CHENG , TIEU ANH KIET , KIM SHINIL
Published: March 2009

Shape control is always a key issue in the six-high rolling mill, in which the shifting of the intermediate roll and the work roll have been used to enhance the shape control capability. In this paper, a finite element method (FEM) model has been developed to simultaneously simulate the strip deformation and the roll stack deformation for the six-high rolling mill. The effects of the work-roll bending, the shifting of the intermediate roll and the work roll on the strip crown and edge drop are discussed in details. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown. The edge drop is also reduced with the bending force and the roll shifting.
FACTOR STUDY FOR THE SEPARATOR PLATE OF MCFC HAVING UNIFORM STIFFNESS AT ELEVATED TEMPERATURE
Authors: LEE SANG-WOOK , KIM JUNG-HYUN , JUN JOONG-HWAN
Published: March 2009

A molten carbonate fuel cell (MCFC) is composed of several stacks of unit cells. A unit cell is composed of two electrodes and a matrix that is inserted between separator plates. Separator plates should properly contact the electrodes to reduce the electricity loss arising from contact resistance. To this end, a pressure of about 2 kgf/cm2 is usually applied on the top of the stack, which results in the separator plates being somewhat compacted. Furthermore, the stiffness of the separator plates becomes degraded at elevated temperatures due to softening of the plate materials. Therefore, a nonuniform temperature distribution across the separator plates induced by exothermic reactions of the oxidant and reactant gases leads to a non-uniform plate stiffness. This study has firstly evaluated the change in separator plate stiffness as temperature changes by applying pressure to the plates. Secondly, using the Taguchi method, several design factors that affect stiffness have been investigated to determine which has the most influence. Based on these results, a new design for the separators, which allows for uniform stiffness at elevated temperatures, has been proposed.
TOOL PATH DESIGN OF INCREMENTAL OPEN-DIE DISK FORGING USING PHYSICAL MODELING
Authors: LEE SUNG-UK , YANG DONG-YOL
Published: March 2009

A small-batch product of large-sized parts is usually manufactured using incremental open-die forging. In order to control the overall change in the shape of a part, it is essential to be able to predict the shape changes that occur during each step. This paper addresses shape changes of a material according to the forging path. Rapid prediction of metal flows for continuing incremental deformation using theoretical methods is difficult. Accordingly, instead of a theoretical approach, an experiment that tests the tendency of the metal flow for development of forming processes is required. For the sake of convenience, simulative experiments are carried out using plasticine at room temperature. In present study, the tool movement is dominant parameters to with respect to changing the shape of the workpiece.
PREDICTION OF ROLLING FORCE USING AN ADAPTIVE NEURAL NETWORK MODEL DURING COLD ROLLING OF THIN STRIP
Authors: XIE H.B. , JIANG Z.Y. , TIEU A.K. , LIU X.H. , WANG G.D
Published: March 2009

Customers for cold rolled strip products expect the good flatness and surface finish, consistent metallurgical properties and accurate strip thickness. These requirements demand accurate prediction model for rolling parameters. This paper presents a set-up optimization system developed to predict the rolling force during cold strip rolling. As the rolling force has the very nonlinear and time-varying characteristics, conventional methods with simple mathematical models and a coarse learning scheme are not sufficient to achieve a good prediction for rolling force. In this work, all the factors that influence the rolling force are analyzed. A hybrid mathematical roll force model and an adaptive neural network have been improved by adjusting the adaptive learning algorithm. A good agreement between the calculated results and measured values verifies that the approach is applicable in the prediction of rolling force during cold rolling of thin strips, and the developed model is efficient and stable.
AN INFLUENCE FUNCTION METHOD ANALYSIS OF COLD STRIP ROLLING
Authors: JIANG Z.Y. , WEI D.W. , TIEU A.K.
Published: March 2009

An influence function method has been developed to simulate the asymmetric cold rolling of thin strip with work roll kiss at edges. The numerical simulation model was obtained based on the deformation compatibility of the roll system in rolling and lateral directions. The strip plastic deformation has been considered in the formulation, which is significantly different from the traditional theory of metal rolling. The rolling mechanics and crown of the strip with work roll edge kiss, which are new findings for cold rolling of thin strip, are obtained. A comparison of the rolling force, roll edge kiss force and the strip crown after rolling has been conducted for various cross shear regions in the roll bite. Results show that the calculated strip crown is in good agreement with Ameasured value, and the rolling force and strip crown decrease with an increase of cross shear regions, as well as the work roll edge kiss force and edge wear decrease. The friction also has an influence on the profile of the rolled thin strip.
EXPERIMENTAL STUDY ON MECHANICAL PROPERTY OF STEEL REINFORCED CONCRETE L-SHAPED SHORT COLUMNS
Authors: LI ZHE , QIN HAO , DANG HUI , LI HUI , ZHANG JIAN-SHAN
Published: March 2009

The horizontal press performance of column is deteriorated because of its special-shaped section. Moreover, because the antiseismic performance of column is worse, special-shaped column is only used in regions where seismic intensity is lower. So the main problem is to enhance the ductility and shear capacity. This test study on mechanical performance has been carried out through 14 SRCLSSC and 2 RCLSSC. The study focuses on the impacts of test axial load ratio (nt), hooped reinforcement ratio (ρ v ), shear span ratio (λ) and steel ratio (ρ ss ) on the shear strength and the antiseismic performance of SRCLSSC. It can be concluded that the shear strength of SRCLSSC is increasing with the increasing of n t and ρ ss , but the degree of increasing is small when n t is a certainty value, and that the shear strength of SRCLSSC is decreasing with increasing of λ; The shear resistance formula of L-shaped column is derived through tests, the calculated results are in correspondence with those of the tests. It also can be concluded that the hysteretic loops of the SRCLSSC are full and the hysteretic behaviors are improved; the displacement ductility is increasing with increasing of ρv and ρ ss , but decreasing with the increasing of n t ; the degree of variety in high axial load ratio is larger than that in low axial load ratio. If steel bars are added, the shear strength and displacement ductility of SRCLSSC are increased in a large degree.
PREDICTION OF PLUG TIP POSITION IN ROTARY TUBE PIERCING MILL USING SIMULATION AND EXPERIMENT
Authors: LEE HYOUNG WOOK , LEE GEUN AN , KIM EUNG ZU , CHOI SEOGOU
Published: March 2009

Typical seamless tube production processes are an extrusion and a rotary tube piercing. The rotary piercing process is more competitive than the extrusion process from the viewpoint of flexibility. Main components of this equipment are twin rolling mills and a plug. Twin rolling mills are installed on a skew with proper angles in two directions. These angles are called the cross angle and the feed angle. The internal crack initiation and the growth at central area of the billet are gradually progressed due to the Mannesmann effects. The feed angle affects on the position of the crack initiation in the rotary tube piercing process. Adjustable design parameters in the equipment are the feed angle and the plug insertion depth.

In this research, the rotary tube piercing equipment was developed. Finite element analyses with the plug and without the plug were carried out in order to predict the internal crack initiation position under good calculation efficiency. Ductile fracture models with the one variable equation were utilized to crack initiation criteria. The forward distance of the plug was determined to be 5 mm through the analysis. It was testified by experiments of a carbon steel billet.
STUDY OF ACCURATE HIGH-SPEED TENSION TESTING METHOD
Authors: UMEDA TSUTOMU , MIMURA KOJI
Published: March 2009

The high measurement accuracy in dynamic tension testing is required for designs and numerical simulations based on the accurate modeling of stress–strain relations at various strain-rates. The non-coaxial Hopkinson bar method (NCHBM) is one of the recently proposed methods for dynamic tension tests. In this study, the direct measurement of both stress and strain was conducted by using the strain gauges affixed on the special specimen with load cell part. The stress–strain relations obtained by this revised NCHBM were compared with those obtained by the normal NCHBM. In order to verify the experimental results, some numerical models were examined by using the FEM code LS-DYNA, in which the whole finite-element model of the apparatus and the plate-type specimen were made in detail. Furthermore, new appliances for fixing specimen were examined by experiment. The target material employed in this study is SUS316.
DYNAMIC MATERIAL PROPERTIES OF THE HEAT-AFFECTED ZONE (HAZ) IN RESISTANCE SPOT WELDING
Authors: HA JI-WOONG , SONG JUNG-HAN , HUH HOON , LIM JI-HO , PARK SUNG-HO
Published: March 2009

This paper is concerned with a methodology to identify the dynamic material properties of the heat-affected zone (HAZ) near the base metal in a resistance spot weld process at various strain rates. In order to obtain the dynamic material properties of the HAZ in the spot-welded steel sheet, specimens are prepared to have similar material properties, hardness and microstructure to the actual HAZ. Such thermally simulated specimens are fabricated with the material thermal cycle simulator (MTCS) and compared with the real one for the hardness and microstructure. Dynamic tensile tests are then conducted with a high speed material testing machine. Stress–strain curves of the thermally simulated HAZ are obtained at various strain rates ranged from 0.001/sec to 100/sec. Obtained material properties are applied to the finite element analysis of the spot-welded tensile-shear specimen in order to verify validity of the proposed testing methodology and obtained results. Analysis results demonstrate that the material properties obtained are appropriate for the FE analysis of spot-welded specimens.
SHEAR STRENGTH PREDICTION OF RC BEAMS WRAPPED WITH FRP
Authors: WANG SUYAN , ZHOU YINGWU , LI HONGNAN
Published: March 2009

During past decades, substantial studies on the external bonding of fiber reinforced polymer (FRP) strips to deficient reinforced concrete (RC) beams have been carried out for the well-known superior properties of the FRP. Several shear prediction models have been established by using the effective strain of the FRP or introducing an ultimate stress discount coefficient. And the latest design concept is the use of stress distribution factor. In this paper, an equivalent effective strain model of the FRP is presented, which contains the concepts of maximum strain, stress distribution factor and critical shear crack angle influences. To develop a simple and accurate approach for such equivalent effective strain, major influenced factors are investigated and analyzed by the statistical independent hypothetic tests on a database of 128 RC beams wrapped by the FRP. Finally, a simple and rational shear design proposal is given, which is more accurate than the existing models using the above database.
THE INFLUENCE OF STRAIN PATH ON BIAXIAL COMPRESSIVE BEHAVIOR OF AZ31 MAGNESIUM ALLOY
Authors: SHIMIZU ICHIRO , TADA NAOYA , NAKAYAMA KOSUKE
Published: March 2009

The strain path dependence of the compressive flow behavior of cast AZ31 magnesium alloy was investigated. Biaxial compression tests with linear strain paths were conducted using a unique biaxial compression device. It was found that the equivalent stress-strain relations varied according to the strain paths. The work contour for linear strain paths was well described by the Logan-Hosford yield criterion. Biaxial compressions with abrupt strain path change were also carried out to investigate the influences of the prestrain amplitude and angular relation of the sequential strain paths on the flow behavior. Rapid increase in the equivalent stress was observed just after the abrupt strain path change. These specific flow behaviors were discussed with regard to the plastic anisotropy, which showed rapid evolution in the early stage of the biaxial compressions.
3D FINITE ELEMENT MODELLING OF COMPLEX STRIP ROLLING
Authors: JIANG Z. Y.
Published: March 2009

A main feature of complex strip - ribbed strip is the significant local residual deformation on a flat strip, resulting in the pulling down of rib height. The interesting issue in this paper shows a developed three-dimensional finite element model of the complex strip rolling, coupling the use of an extremely thin array of elements which is equivalent to the calculation of the additional shear deformation work rate occurred by the velocity discontinuity in the deformation zone. The 3D finite element modelling includes the consideration of the special rib inclined contact surface boundary condition has been carried out on a computer. An examination of the equivalent stress field, forward slip and rib height demonstrates the effectiveness of the developed model. The computed forward slip and rib height are in good agreement with the measured values. The effect of the rib inclined angle on the pulling down of rib height is also discussed.
AN INTEGRATED MICROMECHANICS MODELLING APPROACH FOR MICRO-FORMING SIMULATION
Authors: ZHUANG W. , LIN J.
Published: March 2009

An effort has been made to create an integrated Crystal Plasticity FE (CPFE) system. This enables micro-forming process simulation to be carried out easily and the important features in forming micro-parts can be captured. Firstly, based on Voronoi tessellation and the probability theory, a VGRAIN system is created for the generation of grains and grain boundaries for micro-materials. Numerical procedures have been established to link the physical parameters of a material to the control variable in a gamma distribution equation. An interface has been created, so that the generated virtual microstructure of the material can be inputted in the commercial FE code, ABAQUS, for mesh generation. Secondly, FE analyses have been carried out to demonstrate the effectiveness of the integrated system for the investigation of uncontrollable curvature and localized necking in extrusion of micro-pins and hydro-forming of micro-tubes.
THE PLASTICITY OF MONOCRYSTALLINE SILICON UNDER NANOINDENTATION
Authors: CHANG LI , ZHANG L. C.
Published: March 2009

This paper focuses on a fundamental understanding of the plastic deformation mechanism in monocrystalline silicon subjected to nanoindentation. It was found that over a wide range of indentation loads from 100 μN to 30 mN and loading/unloading rates from 3.3 μN/s to 10 mN/s, the plasticity of silicon is mainly caused by stress-induced phase transitions. The results indicate that the critical contact pressure for phase transition at unloading is almost constant, independent of the maximum indentation load ( P max ) and loading/unloading rates. However, the shape of the load-displacement curves greatly relies on the loading/unloading conditions. In general, higher P max and lower unloading/loading rates favor an abrupt volume change and thus a discontinuity in the load-displacement curve, commonly referred to as pop-in and/or pop-out events; whereas smaller P max and rapid loading/loading processes tend to generate gradual slope changes of the curves. This study concludes that the difference in the curve shape change does not indicate the mechanism change of plastic deformation in silicon.
MINIMUM WALL THICKNESS OF HOLLOW THREADED PARTS IN THREE-DIE COLD THREAD ROLLING
Authors: QI HUIPING , LI YONGTANG , FU JIANHUA , LIU ZHIQI
Published: March 2009

The cold thread rolling technology was developed rapidly in recent years due to its high efficiency, low cost and perfect mechanical properties of its production. However, researches on the precise thread rolling of the hollow parts were very few. Traditionally, the minimum thickness of the thin-walled threaded parts by thread rolling was mainly determined by the empirical (trial and error) methods. In this study, the forming process of thin-walled thread parts rolled with three thread rolling dies was analyzed. The stress state of the hollow work piece was obtained by solving the statically indeterminate problems. Then, the equations for the minimum wall thickness were derived. Experiments are also performed. The experimental results are generally in good agreement with those by the current theoretical analysis. It could be concluded that the analysis presented in this study can provide a good guidance for the thread rolling of hollow parts.
A PHENOMENOLOGICAL CONSTITUTIVE MODEL OF ALUMINUM ALLOY FOAMS AT VARIOUS STRAIN RATES
Authors: LI C. , WANG Z. H. , ZHAO L.M. , YANG G.T.
Published: March 2009

A nonlinear elasto-plastic phenomenological constitutive model for aluminum alloy foams subjected to quasi-static and dynamic compression is proposed. The six-parameter model can fully capture the three typical features of stress-strain response, i.e., linearity, plasticity-like stress plateau, and densification phases. Moreover, the parameters of the model can be systematically varied to describe the effect of initial density of foams that may be responsible for changes in yield stress and hardening-like or softening-like behavior at various strain rates. The experimental results at various loading rates are provided to validate the model. It is shown that the proposed model can be used in the selection of the optimal-density and energy absorption foam for a specific application based on certain design criteria.
BENDING BEHAVIOR OF SIMPLY SUPPOTED METALLIC SANDWICH PLATES WITH DIMPLED CORES
Authors: SEONG DAE-YONG , JUNG CHANG GYUN , YANG DONG-YOL , AHN DONG GYU
Published: March 2009

Metallic sandwich plates are lightweight structural materials with load-bearing and multi-functional characteristics. Previous analytic studies have shown that the bendability of these plates increases as the thickness decreases. Due to difficulty in the manufacture of thin sandwich plates, dimpled cores (structures called egg-box cores) are employed as a sandwich core. High-precision dimpled cores are easily fabricated in a sectional forming process. The cores are then bonded with skin sheets by multi-point resistance welding. The bending characteristics of simply supported plates were observed by the defining measure, including the radius ratio of the small dimple, the thickness of a sandwich plate, and the pattern angle (0°/90°, 45°). Experimental results revealed that sandwich plates with a thickness of 2.2 mm and a pattern angle of 0°/90° showed good bendability as the punch stroke under a collapse load was longer than other cases. In addition, the gap between attachment points was found to be an important parameter for the improvement of the bendability. Finally, sandwich plates with dimpled cores were bent with a radius of curvature of 330 mm for the sheet thickness of 2.2 mm using an incremental bending apparatus.
TWO-SCALE ANALYSIS OF HONEYCOMBS INDENTED BY FLAT PUNCH
Authors: ASADA TAKASHI , TANAKA YUJI , OHNO NOBUTADA
Published: March 2009

The fully implicit incremental homogenization scheme developed by Asada and Ohno (2007) for elastoplastic periodic solids is applied to two-scale analysis of honeycomb blocks subjected to flat punch indentation. To this end, the scheme is rebuilt by introducing half unit cells based on the point-symmetric distributions of stress and strain in unit cells, so that analysis domains in unit cells are reduced by half. Then, by assuming the zigzag and armchair types of cell-arrangements, the two-scale analysis of honeycomb blocks is performed. The corresponding full-scale finite element analysis is also performed to reveal the cell-arrangement dependence of cell deformation in the honeycomb blocks. It is shown that the two-scale analysis is macroscopically successful in spite of microscopic limitations.
THE DEFORMATION OF THE MULTI-LAYERED PANEL OF SHEET METALS UNDER ELEVATED TEMPERATURES
Authors: LEE SANG-WOOK , WOO DONG-UK
Published: March 2009

A Molten Carbonate Fuel Cell (MCFC) stack consists of several layered unit cells. In each unit cell, the stiff structure of the separator plate contains the softer components, such as electrodes. When surface pressure acts on the stack over an extended period of time at elevated temperatures, the stiffness of the separator plate tends to degrade. Moreover, the demands for large electrode area (to increase the electric capacity of a unit cell) and thinner separator plates (to reduce weight) complicate the design of a separator plate with high stiffness. To evaluate the stiffness of the separator plate at elevated temperatures, we design and test a tiny, multi-layered separator plate specimen using a three-point bending tool. To determine the optimal structure of the separator plate, we investigate three design factors: angle, pitch and height. We adopt the Taguchi method to evaluate the experiments, and use finite element analysis to examine the experimental results. Based on these results, pitch is the most effective of these factors. As the pitch narrows, the stiffness of the separator plate increases. Therefore, we propose the pitch factor as a design criterion for the separator plate of the MCFC stack.
EARLY YIELDING OF LIQUID-FILLED CONICAL SHELLS
Authors: VANLAERE W. , LAGAE G. , VAN IMPE R. , BELIS J. , DELINCÉ D.
Published: March 2009

In liquid-filled conical shells, the combination of compressive meridional stresses and tensile hoop stresses can lead to instability. The present design rule for these structures is verified in this contribution by means of numerical simulations. Large axisymmetric imperfections are detrimental and may lead to failure by plastic buckling. For these shapes the design rule may be unconservative. The realism of the proposed shape deviations is questioned. However, partially or completely axisymmetric weld depressions can't be excluded from the simulations. This means that an elaborated study is needed and that the design rule must be checked even further.
THE ROLE OF THE GHOST FIELDS IN THE RENORMALIZED t–J LAGRANGIAN MODEL
Authors: ZANDRON O. S.
Published: March 2009

The present work treats the role of ghost fields in the renormalization procedure of the Lagrangian perturbative formalism of the t–J model. We show that by introducing proper ghost field variables, the propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our previous Lagrangian formalism is studied in detail, and it is shown how the thermal softening of the magnon frequency is predicted by the model. The antiferromagnetic case is also analyzed, and the results are confronted with the previous one obtained by means of the spin-polaron theories.
EXACT SOLUTION OF ISING MODEL IN 2D SHORTCUT NETWORK
Authors: SHANKER O.
Published: March 2009

We give the exact solution to the Ising model in the shortcut network in the 2D limit. The solution is found by mapping the model to the square lattice model with Brascamp and Kunz boundary conditions.
SPIN-DEPHASING ON A QUANTUM DOT WITH A NEARBY QUANTUM POINT CONTACT
Authors: ZHU FEI-YUN , TU TAO , GUO GUO-PING
Published: March 2009

We study the evolution behaviors of an electron spin on a quantum dot due to coupling to a nearby quantum point contact (QPC) as a measurement device. We obtain the dephasing time T2 of about 100 ns when the spin decoherence is only induced by the QPC. We also find that the repeated QPC measurement will slow down the transition rate between spin states which can be interpreted in terms of the quantum Zeno effect.
MONTE CARLO STUDY OF MULTILAYER FILMS USING ANISOTROPIC EXTENDED HEISENBERG MODEL WITH DIPOLAR INTERACTION
Authors: BÎRSAN E. , DOBRITA A. , CHIS R.
Published: March 2009

Using the Monte Carlo technique, we study the multilayer Heisenberg thin film with long range dipolar interactions, in order to investigate the antiferromagnetic basal layer influence on the superior layers. We find out that the basal layer's influence over the magnetic ordering of the superior layers is dependent on the distance between that layer and the basal layer, and the exchange anisotropy discontinuity has a direct effect on the critical temperatures associated with the magnetic phase transitions that can occur for different settings of the investigated system physical parameters. In the intermediate dipolar parameter region, due to antiferromagnetic ordering of the basal layer spins, we found out the mixed phase appearance in the superior layers and we relieved two phase transitions which can take place in the system, the critical temperature we obtained by studying the specific heat and the magnetic susceptibility, respectively, being in good agreement.
NUMERICAL SIMULATION OF SHOCK WAVE AND TURBULENCE INTERACTION OVER A CIRCULAR CYLINDER
Authors: XU CHANG-YUE , CHEN LI-WEI , LU XI-YUN
Published: March 2009

The interaction of shock wave and turbulence for transonic flow over a circular cylinder is investigated using detached-eddy simulation (DES). Several typical cases are calculated for free-stream Mach number M∞ from 0.85 to 0.95, and the physical mechanisms relevant to the shock wave and turbulence interaction are discussed. Results show that there exist two flow states. One is unsteady flow state with moving shock waves interacting with turbulent flow for M∞ < 0.9 approximately, and the other is quasi-steady flow with stationary shocks standing over the wake of the cylinder for M∞ > 0.9, suppressing the vortex shedding from the cylinder. Moreover, local supersonic zones are identified in the wake of the cylinder and generated by two processes, i.e., reverse flow and shock wave distortion induced the supersonic zone. Turbulent shear layer instabilities are revealed and associated with moving shock wave and traveling pressure wave.
THE EFFECT OF SURFACE CURVATURE ON UNDEX-INDUCED HULL CAVITATION
Authors: XIE WENFENG , LIU TIEGANG , YOUNG YIN-LU
Published: March 2009

Hull cavitation evolution induced by an underwater explosion (UNDEX) near a deformable steel structure is numerically investigated using a multiphase compressible fluid solver1-3 coupled with an unsteady one-fluid cavitation model4,5. A series of computations are conducted with varying structure surface curvature. Results suggest that structure surface curvature influence the peak pressures generated from the shock impact and cavitation collapse; a concave-designed surface not only causes local shock focus but also enhances the subsequent cavitation reload.
NUMERICAL SIMULATION OF THE DETONATION OF CONDENSED EXPLOSIVES
Authors: WANG CHENG , YE TING , NING JIANGUO
Published: March 2009

Detonation process of a condensed explosive was simulated using a finite difference method. Euler equations were applied to describe the detonation flow field, an ignition and growth model for the chemical reaction and Jones-Wilkins-Lee (JWL) equations of state for the state of explosives and detonation products. Based on the simple mixture rule that assumes the reacting explosives to be a mixture of the reactant and product components, 1D and 2D codes were developed to simulate the detonation process of high explosive PBX9404. The numerical results are in good agreement with the experimental results, which demonstrates that the finite difference method, mixture rule and chemical reaction proposed in this paper are adequate and feasible.
THE LATTICE BOLTZMANN METHOD BASED ON QUADTREE MESH
Authors: CHEN Y. , CAI Q. D.
Published: March 2009

A lattice Boltzmann method (LBM) based on nonuniform quadtree mesh is proposed. For the two steps in LBM, the collision step is a local procedure and can be implemented in the same way for both uniform and nonuniform mesh grids, while the streaming step is equivalent to solving several linear advection equations. On quadtree mesh (and some other nonuniform meshes), it is usually trivial to construct a first order interpolation scheme for the streaming step. Then the back and forth error compensation and correction (BFECC) method is employed to improve the accuracy order, such that a second order scheme is obtained in streaming step. Several numerical test cases are carried out to prove the accuracy and efficiency of our method.
NUMERICAL INVESTIGATION ON THE INTERACTION OF CYLINDER AND SHOCKWAVE BASED ON THE IMMERSED BOUNDARY METHOD
Authors: JIANG XIAOHAI , CHEN ZHIHUA , LI HONGZHI
Published: March 2009

The immersed boundary method (IBM) is an innovative approach for modeling flow with complex geometries and is more efficient than traditional method. In the present investigation, the shock wave propagation over one circular cylinder is simulated numerically with the Ghost-Body Immersed Boundary Method and high-resolution Roe scheme. To validate the IBM, a plane incident shock wave passing through a square cylinder is predicted and good agreement with previous experiments was obtained. Then based on our calculation, the reflection and diffraction processes of a shock wave passing through a circular cylinder were visualized and discussed in detail.
BOUNDARY LAYER STABILITY WITH MULTIPLE MODES IN HYPERSONIC FLOWS
Authors: GUO XIN , TANG DENGBIN , SHEN QING
Published: March 2009

Inviscid and viscous boundary layer stabilities in hypersonic flows, which are different from those in low speed flows, are investigated, and have actually multiple unstable modes due to inherent mathematic characters. Numerical integration with the singularity point is implemented by expanding calculation region onto the complex plane, and can avoid the difficulty in solving the inviscid stability equations. The high accurate numerical method of the parabolic stability equation (PSE) is used in spatial marching to solve the viscous stability equations. Computed results show good agreement with relevant data.
NUMERICAL SIMULATION OF UNSTEADY FLOW FIELD AROUND HELICOPTER IN FORWARD FLIGHT USING A PARALLEL DYNAMIC OVERSET UNSTRUCTURED GRIDS METHOD
Authors: TIAN SHULING , WU YIZHAO , XIA JIAN
Published: March 2009

A parallel Navier-Stokes solver based on dynamic overset unstructured grids method is presented to simulate the unsteady turbulent flow field around helicopter in forward flight. The grid method has the advantages of unstructured grid and Chimera grid and is suitable to deal with multiple bodies in relatively moving. Unsteady Navier-Stokes equations are solved on overset unstructured grids by an explicit dual time-stepping, finite volume method. Preconditioning method applied to inner iteration of the dual-time stepping is used to speed up the convergence of numerical simulation. The Spalart-Allmaras one-equation turbulence model is used to evaluate the turbulent viscosity. Parallel computation is based on the dynamic domain decomposition method in overset unstructured grids system at each physical time step. A generic helicopter Robin with a four-blade rotor in forward flight is considered to validate the method presented in this paper. Numerical simulation results show that the parallel dynamic overset unstructured grids method is very efficient for the simulation of helicopter flow field and the results are reliable.
NUMERICAL SIMULATION ON FLAPPING MOTION OF SUBMERGED PLANE WATER JETS
Authors: ZHAO LI-QING , SUN JIAN-HONG , ZHOU PEI-PEI
Published: March 2009

Based on volume of fluid (VOF) technique, the flapping motion of submerged turbulent plane jet in shallow water impinging vertically onto the free water surface was simulated. To study further on the flapping motion, the power spectrum density, the centerline velocity decay, as well as the mean velocity profiles of the jet were all investigated in this paper. The results are in great agreement with those of theoretical analyses, and the results show that the flapping motion is a new flow pattern of submerged turbulent plane jets.
A HYBRID RECONSTRUCTION STRATEGY FOR FULLY ADAPTIVE MULTI-RESOLUTION SCHEME
Authors: DENG FENG , WU YI-ZHAO
Published: March 2009

In this paper we propose a second order hybrid reconstruction strategy for the fully adaptive multi-resolution scheme based on the second order finite volume method. The fully adaptive multi-resolution scheme is an adaptive grid method for solving the hyperbolic conservation laws. To improve its robustness, the third order central reconstruction is replaced by the second order hybrid reconstruction, i.e. the anti-ENO (essentially non-oscillatory) reconstruction and the ENO reconstruction have been adopted for the multi-resolution analysis and the inverse multi-resolution analysis, respectively. Several numerical examples indicate that this new hybrid reconstruction strategy is much less sensitive to the tolerance than the central reconstruction.
ON EVOLUTION OF TURBULENT SPOTS WITH INITIAL MULTIPLE DISTURBANCE MODES
Authors: YANG YINGZHAO , TANG DENGBIN , CHEN LIN
Published: March 2009

The formation and nonlinear evolution of turbulent spots in the near wall shear flow are researched by the direct numerical simulation of Navier-Stokes equations, and the initial multiple disturbance models with the pulse form are proposed. A group of three-dimensional coupling difference schemes with high accuracy and resolution are used to simulate evolution processes of turbulent spots, and the computed results show clearly basic characteristic of turbulent spots, specially, interaction properties between turbulent spots.
ESTIMATION OF CONVECTION SPEED THROUGH PIV MEASUREMENTS IN TURBULENT PLANAR MIXING LAYER
Authors: LI CHIUAN-TING , CHANG KEH-CHIN , WANG MUH-RONG
Published: March 2009

The spatio-temporal correlations in a turbulent planar mixing layer are acquired using the particle image velocimetry. Estimation of convection speed is recommended to be made with the spatio-temporal correlations of fluctuating vorticity. The spatial correlation can be deduced from the temporal correlation through the use of the Taylor's hypothesis when applied to the region without apparent dominant frequency.
ANALYSIS OF THE EFFECTS OF MASS-INJECTION AT THE LEADING EDGE ON CAVITY FLOW CHARACTERISTICS
Authors: WU JI FEI , FAN ZHAO LIN , LUO XIN FU
Published: March 2009

An experimental investigation was conducted in a high speed wind tunnel to explore the effects of mass-injection on cavity flow characteristics. Detailed static-pressure and fluctuating pressure measurements were obtained at the cavity floor to enable the effects of the mass-injection at the leading edge to be determined. Results indicate that varying mass-injection hole number and the flux rate of mass-injection has no significant effect on cavity flow characteristics. However, mass-injection can reduce the cavity static pressure gradient when the cavity flow type is transitional-cavity flow. The study also indicates that Mach number can influence the effect of mass-injection on cavity fluctuating pressure distributions, and at supersonic speeds, mass-injection can suppress the cavity tones effectively.
IMPACT OF INFLOW AND AMBIENT CONDITIONS ON DENSITY-INDUCED CURRENT IN A STRATIFIED RESERVOIR
Authors: GU ROY R.
Published: March 2009

The effects of inflow boundary conditions, ambient stratification, and geometry on the behavior of a density-induced current in a stratified reservoir are quantified through numerical experiments with a validated two-dimensional (2D) simulation model. Model results are analyzed to evaluate the sensitivity of reservoir flow variables to changes in the parameters characterizing inflow and ambient water. Quantitative evidence is presented to show that reservoir flow is more sensitive to Froude and Reynolds numbers than to other parameters. A critical value for each parameter is identified, which divides significant and insignificant effects on flow and dilution.
UNCERTAINTY BASED ROBUST OPTIMIZATION IN AERODYNAMICS
Authors: TANG ZHILI
Published: March 2009

The Taguchi robust design concept is combined with the multi-objective deterministic optimization method to overcome single point design problems in Aerodynamics. Starting from a statistical definition of stability, the method finds, Nash equilibrium solutions for performance and its stability simultaneously.
NUMERICAL INVESTIGATIONS OF PSEUDO-SHOCK WAVES IN VARIABLE CROSS-SECTION DUCTS
Authors: WANG CHENGPENG , TIAN XUANG , CHENG KEMING
Published: March 2009

The Pseudo-Shock Wave (PSW), which appears when supersonic flow in duct decelerates to subsonic, is a complicated process due to the interaction between boundary layer and shock wave. It significantly affects the performance and efficiency of flow devices. In this paper, PSW in two kinds of variable cross-section ducts, edge-varied and corner-varied, was investigated through CFD numerical simulation. Compared to the rectangular duct, a shorter and wider separation region is appeared in the corner of the edge-varied duct while the strongest separation is laterally propagated across the entire plane of the corner-varied duct's side wall. This makes the performances of varied ducts different from traditional constant cross-section ducts.
CALCULATION OF THE UNSTEADY AIRLOADS ON WIND TURBINE BLADES UNDER YAWED FLOW
Authors: SI HAI-QING , WANG TONG-GUANG
Published: March 2009

A dynamic stall model is coupled with the blade element momentum theory to calculate the cyclic variation of the aerodynamic characteristics of the wind turbine in yawed flow. In the dynamic stall model, unsteady effects under attached flow conditions are simulated by the superposition of indicial aerodynamic responses. The movement of the unsteady flow separation point is related to the static separation based on the Kirchhoff flow model via a deficiency function, in which the unsteady boundary layer response and the leading edge pressure response are taken into consideration. The induced vortex force and the associated pitching moment are represented empirically in a time-dependent manner during dynamic stall. The required input of the inflow velocity and incidence to the dynamic stall model is calculated using the improved blade element momentum theory. The calculated results are compared well with the NREL UAE Phase VI experimental data. For completeness, possible factors causing the difference between calculated and experimental results are analyzed and discussed in detail in this paper.
EULERIAN NUMERICAL METHOD FOR SIMULATION OF EXPLOSION PROBLEMS
Authors: MA TIANBAO , NING JIANGUO , WANG CHENG
Published: March 2009

This paper presents an adaptive grid subdivision algorithm based on the Youngs' interface reconstruction algorithm to treat the advection of the mixed grids in the multi-material Eulerian method. The advantage of this algorithm is that it only needs to calculate the advection between pure grids, escaping the complexity encountered in the advection of mixed grids with two materials. In addition, this algorithm is a multi-dimensional advection algorithm, and it can decrease the error encountered in the direction-split advection algorithm. In order to verify the efficiency of the proposed adaptive grid subdivision algorithm in the actual physical field, it is added to the indigenously developed EXPLOSION-2D simulation software, and some numerical tests are performed to demonstrate the utility of this algorithm. The simulation results verify that the adaptive grid subdivision algorithm is simple and efficient.
The A563T variation of the renal epithelial calcium channel TRPV5 among African Americans enhances calcium influx
Authors: Na Tao , Zhang Wei , Jiang Yi , Liang Youyou , Ma He-Ping , Warnock David G. , Peng Ji-Bin
Published: March 2009

The transient receptor potential cation channel, subfamily V, member 5 ( TRPV5) gene, which encodes the Ca2+channel in the apical membrane of distal convoluted tubule and connecting tubule of the kidney, exhibits an unusually high frequency of nonsynonymous single nucleotide polymorphisms (SNPs) among African Americans. To assess the functional impacts of the nonsynonymous SNP variations in TRPV5, these variants were analyzed with radiotracer45Ca2+influx assay and the voltage-clamp technique using Xenopus laevis oocytes. Among the variations tested, including A8V, R154H, A563T, and L712F, the latter two significantly increased TRPV5-mediated Ca2+influx. The A563T variant, which exists in African Americans with relative high frequency, exhibited increased Ca2+influx at extracellular Ca2+from 0.01 to 2 mM despite a lower expression level at the plasma membrane. This variant also exhibited a reduction in Na+current as a result of increased sensitivity to extracellular Mg2+. By substituting threonine-563 (Thr563) with serine or valine residue, the bulky side chain of Thr563was shown to facilitate Ca2+transport, whereas the hydroxyl group of Thr563is likely related to Mg2+sensitivity. The A563T variant was capable of increasing TRPV5-mediated Ca2+influx, even when it was expressed under conditions mimicking heterozygous or compound state with other variants. In conclusion, the A563T variant of TRPV5 significantly increased Ca2+influx by affecting the Ca2+permeation pathway. Thus the A563T variation in TRPV5 may contribute to the superior ability of renal Ca2+conservation in African Americans.
A Strategic Framework for Rural Micro-Enterprise Development: The Integration of Information Communication Technology (ICT), E-Commerce, Marketing, and Actor-Network Theory
Authors: Rhodes Jo
Published: March 2009

Using a contextualist, interpretivist research method anchored in a South African rural women's organization, this paper contributes to the discourse on ICT-enabled rural microeconomic development. A conceptual framework, encapsulating rural socioeconomic development, ICTs (e-commerce through a government-sponsored telecentre), and marketing (as a particular business process) is probed using an in-situ participative action research project in cooperation with the organization's management team; and analyzed through Actor-Network Theory. The results reveal key barriers experienced by a rural development organization exploring ICT-enabled migration paths from development (self-help projects) to micro-enterprise. These barriers include the impact of traditional practices on a modern organization; the struggle to align marketing principles with cultural constraints; the conceptual confusion of relating development principles to business practices in a community isolated from regional and national levels of development; the consequences of leapfrogging the phases of institutionalization when implementing ICTs; and the consequences of the transitory mobilization of actors.