Topology Optimization of Metamaterial Microstructures for Negative Poisson’s Ratio under Large Deformation Using a Gradient-Free Method

Negative Poisson’s ratio(NPR)metamaterials are attractive for their unique mechanical behaviors and potential applications in deformation control and energy absorption.However,when subjected to significant stretching,NPR metamaterials designed under small strain assumption may experience a rapid degradation in NPR performance.To address this issue,this study aims to design metamaterials maintaining a targeted NPR under large deformation by taking advantage of the geometry nonlinearity mechanism.A representative periodic unit cell is modeled considering geometry nonlinearity,and its topology is designed using a gradient-free method.The unit cell microstructural topologies are described with the material-field series-expansion(MFSE)method.The MFSE method assumes spatial correlation of the material distribution,which greatly reduces the number of required design variables.To conveniently design metamaterials with desired NPR under large deformation,we propose a two-stage gradient-free metamaterial topology optimization method,which fully takes advantage of the dimension reduction benefits of the MFSE method and the Kriging surrogate model technique.Initially,we use homogenization to find a preliminary NPR design under a small deformation assumption.In the second stage,we begin with this preliminary design and minimize deviations in NPR from a targeted value under large deformation.Using this strategy and solution technique,we successfully obtain a group of NPR metamaterials that can sustain different desired NPRs in the range of[−0.8,−0.1]under uniaxial stretching up to 20% strain.Furthermore,typical microstructure designs are fabricated and tested through experiments.The experimental results show good consistency with our numerical results,demonstrating the effectiveness of the present gradientfree NPR metamaterial design strategy.

Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Theoretical analyses on bed topography responses in large depth-to-width ratio river bends with constant curvatures

Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-width ratio, a theoretical model is established with the coupling of Navier-Stokes （N-S）~ sediment transport, and bed deformation equations. The flow characteristics and bed response of river are obtained with the perturbation method. The research results show that, under the effect of two- dimensional flow disturbance, the bars and pools present the regular response. For a given sinuousness, the amplitude of the bed response can be used as a criterion to judge the bedform stability. The effects of the Reynolds number, disturbance wavenumber, sinuousness, and bed morphology gradient on the bed response development are described.

Research on the squeeze cast technology of the castings with large ratio of height to thickness

The squeeze cast technology is only applicable, at present, to the castings with a ratio of height to thickness less than 3.5. Researching the squeeze cast technology for castings with a large ratio of height to thickness will broaden the applicable range of the advanced casting technology. This paper describes a study of the temperature distribution during solidification for castings with a ratio of height to thickness of 7 by the methods of experiment and computer simulation. The shrinkage porosity distribution in the castings and the mechanical properties of the castings were also researched. The experimental and simulated results show that increasing squeeze force, or enhancing mold temperature, cannot reduce the shrinkage porosities in the castings. When castings solidify in a sequential manner and the squeeze force effectively acts on the surface of the liquid metal, the shrinkage porosities in the castings are eliminated and mechanical properties are clearly improved.

Systemic immune inflammation index, ratio of lymphocytes to monocytes, lactate dehydrogenase and prognosis of diffuse large Bcell lymphoma patients

BACKGROUND In malignant tumors,inflammation plays a vital role in the development,invasion,and metastasis of cancer cells.Diffuse large B-cell lymphoma(DLBCL),the most common malignant proliferative disease of the lymphatic system,is commonly associated with inflammation.The international prognostic index(IPI),which includes age,lactate dehydrogenase(LDH),number of extranodal lesions,Ann Arbor score,and Eastern Cooperative Oncology Group(ECOG)score,can evaluate the prognosis of DLBCL.However,its use in accurately identifying highrisk patients and guiding treatment is poor.Therefore,it is important to find novel immune markers in predicting the prognosis of DLBCL patients.AIM To determine the association between the systemic immune inflammation index(SII),ratio of lymphocytes to monocytes(LMR),ratio of LMR to LDH(LMR/LDH),and prognosis of patients with DLBCL.METHODS A total of 68 patients diagnosed with DLBCL,treated in our hospital between January 2016 and January 2020,were included.χ2 test,Pearson’s R correlation,Kaplan Meier curves,and Cox proportional risk regression analysis were used.The differences in the SII,LMR,and LMR/LDH among patients with different clinicopathological features were analyzed.The differences in progression-free survival time among patients with different SII,LMR,and LMR/LDH expressions and influencing factors affecting the prognosis of DLBCL patients,were also analyzed.RESULTS The LMR and LMR/LDH in patients with Ann Arbor stage III–IV,ECOG score≥2,and SII,IPI score 2–5 were significantly higher than those of patients with Ann Arbor stage I-II and ECOG score<2(P<0.05).Patients with high SII,LMR,and LMR/LDH had progression-free survival times of 34 mo(95%CI:32.52–38.50),35 mo(95%CI:33.42–36.58)and 35 mo(95%CI:33.49–36.51),respectively,which were significantly lower than those with low SII,LMR,and LMR/LDH(P<0.05);the SII,LMR,and LMR/LDH were positively correlated(P<0.05).Cox proportional risk regression analysis showed that the SII,LMR,and LMR/LDH were influencing factors for the prognosis of DLBCL patients(hazard ratio=1.143,1.665,and 1.704,respectively;P<0.05).CONCLUSION The SII,LMR,and LMR/LDH are related to the clinicopathological features of DLCBL,and they also influence the prognosis of patients with the disease.

A multicomponent multiphase lattice Boltzmann model with large liquid–gas density ratios for simulations of wetting phenomena

A multicomponent multiphase（MCMP） pseudopotential lattice Boltzmann（LB） model with large liquid–gas density ratios is proposed for simulating the wetting phenomena. In the proposed model, two layers of neighboring nodes are adopted to calculate the fluid–fluid cohesion force with higher isotropy order. In addition, the different-time-step method is employed to calculate the processes of particle propagation and collision for the two fluid components with a large pseudoparticle mass contrast. It is found that the spurious current is remarkably reduced by employing the higher isotropy order calculation of the fluid–fluid cohesion force. The maximum spurious current appearing at the phase interfaces is evidently influenced by the magnitudes of fluid–fluid and fluid–solid interaction strengths, but weakly affected by the time step ratio.The density ratio analyses show that the liquid–gas density ratio is dependent on both the fluid–fluid interaction strength and the time step ratio. For the liquid–gas flow simulations without solid phase, the maximum liquid–gas density ratio achieved by the present model is higher than 1000：1. However, the obtainable maximum liquid–gas density ratio in the solid–liquid–gas system is lower. Wetting phenomena of droplets contacting smooth/rough solid surfaces and the dynamic process of liquid movement in a capillary tube are simulated to validate the proposed model in different solid–liquid–gas coexisting systems. It is shown that the simulated intrinsic contact angles of droplets on smooth surfaces are in good agreement with those predicted by the constructed LB formula that is related to Young＇s equation. The apparent contact angles of droplets on rough surfaces compare reasonably well with the predictions of Cassie＇s law. For the simulation of liquid movement in a capillary tube, the linear relation between the liquid–gas interface position and simulation time is observed, which is identical to the analytical prediction. The simulation results regarding the wetting phenomena of droplets on smooth/rough surfaces and the dynamic process of liquid movement in the capillary tube demonstrate the quantitative capability of the proposed model.

The comparison between laser screw welding and resistant spot welding of lap joint with large thickness ratio

The present paper investigates the welding forming,microstructure and shear tensile test of lap joints with large thickness ratio which were fabricated by laser screw welding(LSW)and resistant spot welding(RSW).The comparison was conducted on two kinds of lap joints,galvanized sheet and hot pressed steel(GS-HPS),galvanized sheet and high strength steel(GS-HS).The microstructure and fracture morphology were analyzed by optical microscope.It was demonstrated that with large thickness ratio the sound lap joint of GS-HS could be obtained by LSW regardless of the irradiation of laser beam from thick metal to sheet or otherwise,and the morphology shows it is better when the laser is irradiated on the thick metal.Nevertheless,when the laser beam was applied on thick metal of HPS,blind hole or blowhole was formed in the center of joint,which is attributed to the shrinkage during solidification of the molten pool.Small pores or dispersed porosity appeared on the faying face of the joint without predetermined gap which provides the degassing.However,the increase of predetermined gap could reduce the shear strength and nugget size.Two kinds of joints made by LSW have superior shear strength than those made by RSW when the laser were applied on galvanized sheet.

Investigation of short-channel design on performance optimization effect of Hall thruster with large height–radius ratio

In this study,the neutral gas distribution and steady-state discharge under different discharge channel lengths were studied via numerical simulations.The results show that the channel with a length of 22 mm has the advantage of comprehensive discharge performance.At this time,the magnetic field intensity at the anode surface is 10%of the peak magnetic field intensity.Further analysis shows that the high-gas-density zone moves outward due to the shortening of the channel length,which optimizes the matching between the gas flow field and the magnetic field,and thus increases the ionization rate.The outward movement of the main ionization zone also reduces the ion loss on the wall surface.Thus,the propellant utilization efficiency can reach a maximum of 96.8%.Moreover,the plasma potential in the main ionization zone will decrease with the shortening of the channel.The excessively short-channel will greatly reduce the voltage utilization efficiency.The thrust is reduced to a minimum of 46.1 m N.Meanwhile,because the anode surface is excessively close to the main ionization zone,the discharge reliability is also difficult to guarantee.It was proved that the performance of Hall thrusters can be optimized by shortening the discharge channel appropriately,and the specific design scheme of short-channel of HEP-1350 PM was defined,which serves as a reference for the optimization design of Hall thruster with large height–radius ratio.The shortchannel design also helps to reduce the thruster axial dimension,further consolidating the advantages of lightweight and large thrust-to-weight ratio of the Hall thruster with large height–radius ratio.

Rational cutting height for large cutting height fully mechanized top-coal caving

Large cutting height fully mechanized top-coal caving is a new mining method that improves recovery ratio and single-pass production. It also allows safe and efficient mining. A rational cutting height is one key parameter of this technique. Numerical simulation and a granular-media model experiment were used to analyze the effect of cutting height on the rock pressure of a fully mechanized top-coal caving work face. The recovery ratio was also studied. As the cutting height increases the top-coal thickness is reduced. Changing the ratio of cutting to drawing height intensifies the face pressure and the top-coal shattering. A maximum cutting height exists under a given set of conditions due to issues with surrounding rock-mass control. An increase in cutting height makes the top-coal cave better and the recovery ratio when drawing top-coal is then improved. A method of adjusting the face rock pressure is presented. Changing the cutting to drawing height ratio is the technique used to control face rock pressure. The recovery ratio when cutting coal exceeds that when caving top-coal so the face recovery ratio may be improved by over sizing the cutting height and increasing the top-coal drawing ratio. An optimum ratio of cutting to drawing height exists that maximizes the face recovery ratio. A rational cutting height is determined by comprehensively considering the surrounding rock-mass control and the recovery ratio. At the same time increasing the cutting height can improve single pass mining during fully mechanized top-coal caving.

Optimizing loading path and die linetype of large length-to-diameter ratio metal stator screw lining hydroforming

In order to meet the high temperature environment requirement of deep and superdeep well exploitation, a technology of large length-to-diameter ratio metal stator screw lining meshing with rotor is presented. Based on the elastic-plasticity theory, and under the consideration of the effect of tube size, material mechanical parameters, friction coefficient and loading paths, the external pressure plastic forming mechanical model of metal stator screw lining is established, to study the optimal loading path of metal stator lining tube hydroforming process. The results show that wall thickness reduction of the external pressure tube hydroforming(THF) is about 4%, and three evaluation criteria of metal stator screw lining forming quality are presented: fillet stick mold coefficient, thickness relative error and forming quality coefficient. The smaller the three criteria are, the better the forming quality is.Each indicator has a trend of increase with the loading rate reducing, and the adjustment laws of die arc transition zone equidistance profile curve are acquired for improving tube forming quality. Hence, the research results prove the feasibility of external pressure THF used for processing high-accuracy large length-to-diameter ratio metal stator screw lining, and provide theoretical basis for designing new kind of stator structure which has better performance and longer service life.

Research on Large Depth Diameter Ratio Ultra-precision Aspheric Grinding System

In this paper, the factors of affecting surface roughness and profiles accuracy of the machined larege depth diamter ratio aspheric surfaces in ultra-precision grinding process are analyzed theoretically. An ultra-precision aspheric grinding system is then designed and manufactured. Aerostatic form is adopted to build the spindle of the workpiece, transverse guideway, longitudinal guideway and the spindle of the grinder in this system. The following specification is achieved, such as the turning accuracy of the spindle of the workpiece is 0.05 μm, radial rigidity of the spindle is GE 220N/μm, axial rigidity is GE 160 N/μm, radial rigidity of the guideway is GE 200N/μm, the highest rotational speed of the grinder is 80 000 rev/min and its turning accuracy is 0.1 μm, the resolution of linear displacement of the transverse and longitudinal guideway is 4.9 nm. Adjusting range of this adjusting mechanism is 2 mm in the Y direction, the adjusting accuracy of the precise adjusting mechanism is 0.1 μm. Micro displacement measuring system of this ultra-precision aspheric grinding adopts two-backfeed strategy, and angle displacement back-feed is realized by photoelectric encoder, it’s resolution is 655 360 pulse/rev. after 4 frequency multiplication, it’s angle displacement resolution is achieved 2 621 440 pulse/rev. Straight-line displacement is monitored by single frequency laser interferometer (DLSTAX LTM-20B, made in Japan). This CNC system adopts inimitable bi-arc step length flex CN interpolation algorithm, it’s CN system resolution is 5 nm.So this aspheric grinding system ensures profile accuracy of the machined part. The resolution of this interferometer is 5 nm. Finally, lots of ultra-precision grinding experiments are carried out on this grinding system. Some optical aspheric parts, with profiles accuracy of 0.3 μm, surface roughness less than 0.01 μm, are obtained.

Floquet instability of a large density ratio liquid-gas coaxial jet with periodic fluctuation

By numerical simulation of basic flow, this paper extends Floquet stability analysis of interracial flow with periodic fluctuation into large density ratio range. Stability of a liquid aluminum jet in a coaxial nitrogen stream with velocity fluctuation is investigated by Chebyshev collocation method and the Floquet theory. Parametric resonance of the jet and the influences of different physical parameters on the instability are discussed. The results show qualitative agreement with the available experimental data.

Experimental and Numerical Research on Deformation Behavior of Thin-Walled and Large Expansion Ratio Guide Vane Liner in Hydroforming Process

Some tube hydroforming process tests and further research work were conducted to manufacture hollow guide vane liners( made of super alloy GH3030).The relative thickness( t0/ OD) of the tubular blank is approximately 0. 01,and the maximum expansion ratio( Dmax/ OD) of the needed part is more than 40%,and the length to diameter ratio of the expansion regionis more than 3. 0. It is very hard to manufacture this kind of ultra-thin-wall,curved axis and large expansion ratio tubular part without fracture and wrinkles. The success of the process is highly dependent on useful wrinkles with appropriate internal pressure and axial feeding. A simplified finite element model and a theoretical model are used for detecting the deformation behavior and forming laws. Further study results demonstrate that the useful wrinkles do not appear at the same time and middle-wrinkles need bigger axial force than tube-end-wrinkles and feeding-wrinkles. The wrinkles can transfer bigger axial force after its wave peak has come into contact with the die inner surface. The thickness thinning rate of the element at the peak is bigger than that at the trough. With the increase of the axial and hoop stress ratio,the critical buckling stress also increases. Microstructure examination results show that the grain size in the maximum thinning zone has been stretched and refined after the large deformation and annealing treatment.The process is feasible and the finished part is qualified.

Numerical Simulation of a New 3D Isolation System Designed for a Facility with Large Aspect Ratio

This paper proposes a novel three-dimensional(3D)isolation system for facilities and presents the numerical simulation approach for the isolated system under earthquake excitations and impact effect using the OpenSees(Open System for Earthquake Engineering Simulation)software frame work.The 3D isolators combine the quasi-zero stiffness(QZS)system in the vertical direction and lead rubber bearing in the horizontal direction.Considering the large aspect ratio of the isolated facility,linear viscous dampers are designed in the vertical direction to diminish the overturning effect.The vertical QZS isolation system is characterized by a cubic force-displacement relation,thus,no elements or materials can model this mechanic behavior in the existing finite element software.This study takes advantage of the open source feature of the OpenSees to create a new material to represent the mechanic properties of the QZS system.Then the user-defined material is combined with the rubber isolator element to model the 3D isolator.Considering different soil types and input magnitudes,six sets of natural seismic records and artificial waves and half sine pulses are selected as the input excitations.A finite element model for the 3D isolated facility is established based on the combined element and the simulation is performed to calculate the time history response.The numerical simulation reveals the flexibility of the OpenSees to deal with new engineering problems,and the results prove that the new 3D isolation system can have an optimal isolation effect in both horizontal and vertical directions.The maximum acceleration response at the top of the facility is below the target limit,and the maximum deformation and the overturning motion of the isolation system can be controlled in a safe range.

Fabrication and Property of SiC Ceramic with Large Thickness/Diameter Ratios

Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.

The Lower Peripheral Blood Lymphocyte to Monocyte Ratio Following Completion of First Line Chemotherapy Is a Risk Factor for Predicting Relapse in Patients with Diffuse Large B-Cell Lymphoma

Background and objective: During routine follow up, there is no specific predictor to ascertain relapse after standard first line chemotherapy in diffuse large cell lymphoma. Therefore, this study was designed to assess the prognostic significance of the ratio between absolute lymphocyte and monocyte counts (LMR) in the peripheral blood to verify relapse in diffuse large B cell lymphoma. Patients and methods: A total of 139 patients with newly diagnosed diffuse large B cell lymphoma (DLBCL) were evaluated and treated with CHOP or R-CHOP between the years 2009 and 2016. Three months following completion of first line therapy, Lymphocyte/monocyte ratio (LMR) was calculated from the routine automated complete blood cell count (CBC) attained a plateau after the bone marrow recovery after first line chemotherapy. The absolute lymphocyte count/absolute monocyte count ratio (LMR) was calculated by dividing the ALC by the AMC. Results: ROC curve analysis of 139 patients established 2.8 as cutoff point of LMR for relapse with AUC of 0.97 (95% CI 0.93 - 0.99, P ≤ 0.001). Cox regression analysis was performed to identify factors predicting relapse. In univariate regression analysis, ALC (95% CI 0.003 - 0.03, p ≤ 0.001), AMC (95% CI 15.4 - 128.8, p ≤ 0.001), LMR (95% CI 0.001 - 0.01, p ≤ 0.001), and LDH (95% CI 0.1 - 0.5, p ≤ 0.001) following completion of therapy are significant factors for relapse. Other significant factors for relapse are Ann Arbor stage (95% CI 1.1 - 6.9, P = 0.03), extranodal sites (95% CI 1.2 - 6.1, P = 0.01), age (95% CI 1.3 - 6.5, P = 0.01) and treatment of CHOP protocol (95% CI 0.05 - 0.6, P = 0.007). In a multivariate analysis LMR following completion of therapy was predictive for relapse (95% CI 0.001 - 0.2, P = 0.005). ALC was also significant in multivariate analysis (95% CI 0.01 - 0.8, P = 0.03). LDH following completion of therapy (95% CI 0.2 - 14.9, P = 0.5), AMC following completion of therapy (95% CI 0.3 - 43.1, P = 0.3), age (95% CI 0.9 - 205.4, P = 0.06), extra-nodal sites (95% CI 0.04 - 9.8, P = 0.8), Ann Arbor stage (95% CI 0.3 - 28.7, P = 0.3), and Treatment of CHOP protocol (95% CI 0.01 - 2.4, P = 0.2) were not statistically significant. Conclusion: This study observed that LMR assessed after first line chemotherapy during routine follow up is an independent predictor of relapse and clinical outcome in DLBCL patients. LMR at follow up can be used a simple inexpensive biomarker to alert clinicians for relapse during follow up after standard first line chemotherapy in DLBCL patients.

THE EFFECTS OF VELOCITY RATIO ON THE LARGE SCALE COHERENT STRUCTURES IN FREE SHEAR LAYERS

The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.

Saturation Ion Current Densities in Inductively Coupled Hydrogen Plasma Produced by Large-Power Radio Frequency Generator

An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.

Investigation on the width-to-depth ratio effect on turbulent flows in a sharp meandering channel with periodic boundaries using large eddy simulations

As one of the most common river patterns in nature,meandering river has very complex flow structures in its curved channel bends,including secondary flow structure and primary flow velocity redistributions.To date,most of the studies have been carried out on the flow structures in channel bends with unavoidable influences from inlet and outlet boundaries,while a streamwise periodic boundary can overcome this shortcoming elegantly.In this paper,large eddy simulations(LES)are employed to investigate the complex flow structures in periodically continuous sharp sine-generated bends.The influence of width-to-depth ratios and dimensionless curvature radiuses are studied.The results highlight two additional vortex structures beyond the commonly known secondary currents:The recirculation zone(RZ)and the inner bank cell(IBC).The width-to-depth ratio shows the determining effect on the recirculation zone.The size of recirculation zone is usually bigger in sine-generated-curve(SGC)channel with large width-to-depth ratios.The biggest recirculation zones appear between the zero-curvature section and the apex section.The inner bank cell only forms in SGC channels with small width-to-depth ratios and low curvature.For SGC channel with large width-to-depth ratios,only one circulation cell is observed near the inner bank.The spatial variations of turbulent features are also revealed by statistical analysis based on the LES sampling data.Results highlight remarkable effect of width-to-depth ratio and dimensionless curvature radius on the turbulent kinetic energy(TKE)and bed shear stress in SGC channels.

A hybrid algorithm based on tabu search and large neighbourhood search for car sequencing problem

The car sequencing problem(CSP)concerns a production sequence of different types of cars in the mixed-model assembly line.A hybrid algorithm is proposed to find an assembly sequence of CSP with minimum violations.Firstly,the hybrid algorithm is based on the tabu search and large neighborhood search(TLNS),servicing as the framework.Moreover,two components are incorporated into the hybrid algorithm.One is the parallel constructive heuristic(PCH)that is used to construct a set of initial solutions and find some high quality solutions,and the other is the small neighborhood search(SNS)which is designed to improve the new constructed solutions.The computational results show that the proposed hybrid algorithm(PCH+TLNS+SNS)obtains100best known values out of109public instances,among these89instances get their best known values with100%success rate.By comparing with the well-known related algorithms,computational results demonstrate the effectiveness,efficiency and robustness of the proposed algorithm.