Parallelization strategies for resolved simulations of fluid-structure-particle interactions

Fluid-structure-particle interactions in three spatial dimensions happen in many environmental and engineering flows.This paper presents the parallel algorithms for the hybrid diffuse and sharp interface immersed boundary(IB)method developed in our previous work.For the moving structure modeled using the sharp interface IB method,a recursive box method is developed for efficiently classifying the background grid nodes.For the particles modeled using the diffuse interface IB method,a‘master-slave’approach is adopted.For the particle-particle interaction(PPI)and particle-structure interaction(PSI),a fast algorithm for classifying the active and inactive Lagrangian points,which discretize the particle surface,is developed for the‘dry’contact approach.The results show that the proposed recursive box method can reduce the classifying time from 52seconds to 0.3 seconds.Acceptable parallel efficiency is obtained for cases with different particle concentrations.Furthermore,the lubrication model is utilized when a particle approaches a wall,enabling an accurate simulation of the rebounding phenomena in the benchmark particle-wall collision problem.At last,the capability of the proposed computational framework is demonstrated by simulating particle-laden turbulent channel flows with rough walls.

激励机制下高校教师教学评价体系创新路径探究

高校教师教学评价是提高教学质量和促进教师专业发展的重要手段,而激励机制作为影响教师教学行为的重要因素之一,对教师教学评价体系的建设和完善具有重要意义。基于激励机制创新高校教师教学评价体系,不仅能够激发教师的教学热情和创新意识,提高教学质量,还能够促进教师的专业成长和发展。因而研究激励机制下高校教师教学评价体系创新路径有重要的意义。对此,通过阐述激励机制与教师教学评价体系的内在联系,进而分析激励机制下高校教师教学评价体系的创新路径,以期为高校教师教学评价体系的建设提供一定的理论指导和实践参考。

Wall-modeling for large-eddy simulation of flows around an axisymmetric body using the diffuse-interface immersed boundary method

A novel method is proposed to combine the wall-modeled large-eddy simulation(LES) with the diffuse-interface direct-forcing immersed boundary(IB) method.The new developments in this method include:(i) the momentum equation is integrated along the wall-normal direction to link the tangential component of the effective body force for the IB method to the wall shear stress predicted by the wall model;(ii) a set of Lagrangian points near the wall are introduced to compute the normal component of the effective body force for the IB method by reconstructing the normal component of the velocity. This novel method will be a classical direct-forcing IB method if the grid is fine enough to resolve the flow near the wall. The method is used to simulate the flows around the DARPA SUBOFF model. The results obtained are well comparable to the measured experimental data and wall-resolved LES results.

Wall-resolved large-eddy simulation of turbulent channel flows with rough walls

Turbulent flows over rough surfaces widely exist in nature and industry.Investigating its mechanism is of theoretical and practical significance.In this work we simulate the turbulent channel flow with rough walls using large-eddy simulation with rough elements resolved using the curvilinear immersed boundary method and compare the results obtained in this work with those in the paper by Yuan and Piomelli(J.Fluid Mech.,vol.760,pp.R1,2014),where the volume of fluid method was employed for modeling rough elements.The mean streamwise velocity profiles predicted by the two methods agree well with each other.Differences in Reynolds stresses and dispersive stresses are observed,which are attributed to the different approaches in dealing with the complex geometry of the rough surface.

Effect of chitosan/type I collagen/gelatin composites in biocompatibility and nerve repair

Chitosan, collagen I and gelatin were mixed in appropriate quantities to develop a new nerve repair material, with good arrangement and structure, as well as even aperture size. The composite material was sterilized by 60Co irradiation for 24 hours prior to implantation in the right thigh of rats following sciatic nerve damage. Results showed that the material was nontoxic to the kidneys and the liver, and did not induce an inflammatory response in the muscles. The composite material enhanced the recovery of sciatic nerve damage in rats. These experimental findings indicate that the composite material offers good biocompatibility and has a positive effect on injured nerve rehabilitation.

Effects of the Ratio of Lysine to Digestible Energy Level in the Diet on the Expression and Activity of Transcription Factors Involved in Lipogenesis in Rongchang Pigs

This study was conducted to determine the effects of varying the ratio of lysine to digestible energy level On the activity and gene expression of the transcription factors peroxisome proliferator-activated receptor-γ （PPAR-γ） and CCAAT/enhancer-binding protein-or and -β （C/EBP-α and C/EBP-β） to better understand the regulatory mechanisms controlling adipogenesis in fat and muscle tissue of the Rongchang pig. A total of 144 castrated Rongchang pigs weighing approximately 20 kg were used in a 2 ×2 factorial design experiment. Diets were formulated to contain a high （14.22 MJ/kg） or low （13.11 MJ/kg） digesti- ble energy （DE） level. Within each energy level, pigs were fed diets containing a high lysine： DE ratio （0.67,0. 53, or 0. 42） or a low lysine ： DE ratio （0.49,0.38 ,or 0.30） during the periods from 20 to 50 kg, 50 to 80 kg, and 80 kg to slaughter, respectively. Each diet was fed to six replicate pens, each containing nine pigs. When the pigs reached average live weights of 20,35,60, and 90 kg ,one pig from each of the replicates was chosen at random and slaughtered.Samples of back fat and longissimus dorsi muscle were collected for the assessment of transcriptional factor. The results showed that feeding a high DE level significantly increased （ P 〈 0.05 ） the expression of PPAR-T at 60 and 90 kg in muscle and at 35,60, and 90 kg in back fat. Energy level also significantly increased the expression of C/EBP-fl at 35 and 60 kg in both muscle and back fat （ P 〈 0.05 ）. Higher dieta- ry lysine increased the expression of C/EBP-fl in muscle at 35 and 90 kg （ P 〈 0.05）, but decreased the expression in back fat at 35 （P = 0.03 ） and 90 kg （P = 0.09）. The lysine level increased the expression of PPAR-3~ in muscle at 60 kg only. Energy level and lysine content had no significant effects on promote the activity of PPAR-γ, C/EBP-α, or C/EBP-β either in muscle or in back fat at any level of the body weights tested. Collectively, these data indicated that dietary energy density and lysine level were equally important for lipid deposition in muscle tissue, whereas dietary energy density was more important than lysine level for fat deposition in fat tissue.

Towards multi-fidelity simulation of flows around an underwater vehicle with appendages and propeller

Flow around a real-life underwater vehicle often happens at a high Reynolds number with flow structures at different scales from the boundary layer around a blade to that around the hull. This poses a great challenge for large-eddy simulation of an underwater vehicle aiming at resolving all relevant flow scales. In this work, we propose to model the hull with appendages using the immersed boundary method, and model the propeller using the actuator disk model without resolving the geometry of the blade. The proposed method is then applied to simulate the flow around Defense Advanced Research Projects Agency(DARPA) suboff. An overall acceptable agreement is obtained for the pressure and friction coefficients. Complex flow features are observed in the near wake of suboff. In the far wake, the core region is featured by a jet because of the actuator disk, surrounded by an annular region with velocity deficit due to the body of suboff.

On the capability of the curvilinear immersed boundary method in predicting near-wall turbulence of turbulent channel flows

The immersed boundary method has been widely used for simulating flows over complex geometries.However,its accuracy in predicting the statistics of near-wall turbulence has not been fully tested.In this work,we evaluate the capability of the curvilinear immersed boundary(CURVIB)method in predicting near-wall velocity and pressure fluctuations in turbulent channel flows.Simulation results show that quantities including the time-averaged streamwise velocity,the rms(root-mean-square)of velocity fluctuations,the rms of vorticity fluctuations,the shear stresses,and the correlation coefficients of u'and v"computed from the CURVIB simulations are in good agreement with those from the body-fitted simulations.More importantly,it is found that the time-averaged pressure,the rms and wavenumber-frequency spectra of pressure fluctuations computed using the CURVIB method agree well with the body-fitted results.

How far the wake of a wind farm can persist for?

With the increased penetration of wind energy in our nation’s energy portfolio, wind farms are placed in a way close to each other. Thus, their wakes have to be fully considered in the design and operation of a wind farm. In this study, we investigate the wake of a wind farm using large-eddy simulation with wind turbine rotor modelled by the actuator disk model. The simulated results show that the wake of a wind farm can persist for a long distance in its downstream. For the considered wind farm layout, the velocity in the wake recovers 95% of that of the undisturbed inflow at 55 rotor diameters downstream from its last row, suggesting that the wake of a wind farm should be fully considered in the optimal design and operation for its downstream wind farms.

Editorial: Fluid mechanics problems in wind energy

Wind energy is growing as the key energy resource in many countries.Wind turbines convert the kinetic energy of moving air into electricity,in which fluid mechanics plays a vital role,from the aerodynamics of wind turbine blades,wind turbine wakes to atmospheric turbulence.Last one hundred years have seen the dramatic improvement on the performance of wind turbines,that the current designs are featured with higher power efficiency,larger rotor and higher tower when compared with those in 1980s.The growing wind power industry poses new requests for wind technologies,such as the design and control of floating offshore wind turbine(FOWT),the micro-sitting of wind turbines in complex terrains,and many others,which rely heavily on the advancements from the fluid mechanics aspect.

Light-driven soft actuator based on graphene and WSe2 nanosheets composite for multimodal motion and remote manipulation

Remote controlled soft actuators have attracted ever-increasing interest in industrial,medical,robotics,and engineering fields.Soft actuators are charming than normal tools in executing dedicate tasks due to small volume and flexible body they have.However,it remains a challenge to design soft actuator that can adapt to multi-environments under remote stimuli with promising nano materials.Herein,we have developed a kind of near-infrared laser driven soft actuators with multi locomotive modes based on WSe2 and graphene nanosheets heterojunction.Different locomotion modes are driven by photothermal effect induced deformation to adapt to different working conditions.Moreover,the specially designed gripper driven by pulsed laser can lift a heavy load which is four times of its weight.This work broadens the choice of advanced nanomaterials for photothermal conversion of soft actuators.It is promising to realize applications including photothermal therapy and complex environment detection through the combination of the intelligent robot design and optical fiber system.

退化高寒草地土壤真菌群落与土壤环境因子间相互关系

【目的】为探究祁连山高寒草地退化过程中土壤真菌群落分布特征与土壤环境因子间的相互关系。【方法】利用Illumina Miseq PE250高通量测序技术对轻度、中度和重度退化草地土壤真菌群落结构变化及其多样性进行分析,并对土壤真菌群落与土壤环境因子的相互关系进行冗余分析(RDA)。【结果】随着退化程度加剧,土壤pH呈现出升高趋势,电导率呈现出先升高后降低趋势,土壤含水量、有机碳、全氮、全磷和全钾含量均逐渐降低。高通量测序共得到750575条有效序列和5788个OTUs;各试验点样地中真菌群落Chao1指数和Shannon-Wiener指数变化各异。在门分类水平上,子囊菌门(Ascomycota)、担子菌门(Basidiomycota)、接合菌门(Zygomycota)、球囊菌门(Glomeromycota)和壶菌门(Chytridiomycota)是各草地土壤的优势类群。RDA分析表明,土壤速效钾、全氮、速效氮和有机碳是祁连山不同退化高寒草地土壤真菌群落分布的主要驱动因子。【结论】祁连山不同退化高寒草地土壤真菌群落间差异明显,土壤环境因子是影响土壤真菌群落分布的重要因素。

An Improved Algorithm for Optimizing MapReduce Based on Locality and Overlapping

MapReduce is currently the most popular programming model for big data processing, and Hadoop is a weU-known MapReduce implementation platform. However, Hadoop jobs suffer from imbalanced workloads during the reduce phase and inefficiently utilize the available computing and network resources. In some cases, these problems lead to serious performance degradation in MapReduce jobs. To resolve these problems, in this paper, we propose two algorithms, the Locality-Based Balanced Schedule （LBBS） and Overlapping-Based Resource Utilization （OBRU）, that optimize the Locality-Enhanced Load Balance （LELB） and the Map, Local reduce, Shuffle, and final Reduce （MLSR） phases. The LBBS collects partition information from input data during the map phase and generates balanced schedule plans for the reduce phase. OBRU is responsible for using computing and network resources efficiently by overlapping the local reduce, shuffle, and final reduce phases. Experimental results show that the LBBS and OBRU algorithms yield significant improvements in load balancing. When LBBS and OBRU are applied, job performance increases by 15% from that of models using LELB and MLSR.

Fabrication of 4H-SiC n-channel IGBTs with ultra high blocking voltage

Owing to the conductivity modulation of silicon carbide（Si C） bipolar devices, n-channel insulated gate bipolar transistors（n-IGBTs） have a significant advantage over metal oxide semiconductor field effect transistors（MOSFETs） in ultra high voltage（UHV） applications. In this paper, backside grinding and laser annealing process were carried out to fabricate 4 H-Si C n-IGBTs. The thickness of a drift layer was 120 μm, which was designed for a blocking voltage of 13 k V. The n-IGBTs carried a collector current density of 24 A/cm^2 at a power dissipation of300 W/cm^2 when the gate voltage was 20 V, with a differential specific on-resistance of 140 mΩ·cm^2.

Hybrid Diffuse and Sharp Interface Immersed Boundary Methods for Particulate Flows in the Presence of Complex Boundaries

A coupling framework that leverages the advantages of the diffuse and sharp interface immersed boundary(IB)methods is presented for handling the interaction among particles and particles with the static complex geometries of the environment.In the proposed coupling approach,the curvilinear IB method is employed to represent the static complex geometries,a variant of the direct forcing IB method is proposed for simulating particles,and the discrete element method is employed for particle-particle and particle-wall collisions.The proposed approach is validated using several classical benchmark problems,which include flow around a sphere,sedimentation of a sphere,collision of two sedimenting spheres,and collision between a particle and a flat wall,with the present predictions showing an overall good agreement with the results reported in the literature.The capability of the proposed framework is further demonstrated by simulating the interaction between multiple particles and a wall-mounted cylinder,and the particle-laden turbulent flow over periodic hills.The proposed method provides an efficient way to simulate particle-laden turbulent flows in environments with complex boundaries.