Coupling of RANS and BEM Solvers for Simulation of Propeller Behind the Hull in Full Appended Model

To design a propeller for ship power plant,the interaction between ship hull and propeller must be taken into account.The main concern is to apply the wake effect of ship stern on the propeller performance.In this paper,a coupled BEM(Boundary Element Method)/RANS(Renolds-Averaged Navier−Stokes)solver is used to simulate propeller behind the hull in the self-propulsion test.The motivation of this work is to develop a practical tool to design marine propulsion system without suffering long computational time.An unsteady boundary element method which is also known as panel method is chosen to estimate the propeller forces.Propeller wakes are treated using a time marching wake alignment method.Also,a RANS code coupled with VoF equation is developed to consider the ship motions and wake field effects in the problem.A coupling algorithm is developed to interchange ship wake field to the potential flow solver and propeller thrust to the RANS code.Based on the difference between hull resistance and the propeller thrust,a PI controller is developed to compute the propeller RPM in every time step.Verification of the solver is carried out using the towing tank test report of a 50 m oceanography research vessel.Wake factor and trust deduction coefficient are estimated numerically.Also,the wake rollup pattern of the propeller in open water is compared with the propeller in real wake field.

Improvement of the FRP Sheet Bonded to Concrete Substrate by Silane Coupling Agent

We experimentally studied the fine lightweight aggregate with the particle size range of 3.15-4.75 mm used as functional bridge between FRP sheet and concrete substrate. However, problems would appear and how to deal with the interfacial transition zone（ITZ） and make it stronger is the key point for this concept. Considering that silane coupling agent（SCA） can provide a better bond on a silicon-containing material surface, it was introduced as a modifying material to further improve the bond quality of the ITZ between lightweight aggregate and cement paste. Results indicated that the water absorptivity of lightweight aggregate can be controlled by SCA solutions, and the pull-off bond strength, mechanical strength, and microhardness were increased, which was attributed to the optimized microstructure under the condition of an appropriate concentration of SCA.

Numerical analysis of coupled finite element with element-free Galerkin in sheet flexible-die forming

A numerical method for coupled deformation between sheet metal and flexible-die was proposed. Based on the updated Lagrangian （UL） formulation, the elastoplastic deformation of sheet metal was analyzed with finite element method （FEM） and the bulk deformation of flexible-die was analyzed with element-free Galerkin method （EFGM）. The frictional contact between sheet metal and flexible-die was treated by the penalty function method. The sheet elastic flexible-die bulging process was analyzed with the FEM-EFGM program for coupled deformation between sheet metal and bulk flexible-die, called CDSB-FEM-EFGM for short. Compared with finite element code DEFORM-2D and experiment results, the CDSB-FEM-EFGM program is feasible. This method provides a suitable numerical method to analyze sheet flexible-die forming.

Numerical modeling and deformation analysis for electromagnetically assisted deep drawing of AA5052 sheet

Electromagnetic forming(EMF)is a high-velocity manufacturing technique which uses electromagnetic(Lorentz)body forces to shape sheet metal parts.One of the several advantages of EMF is the considerable ductility increase observed in several metals,with aluminum featuring prominently among them.Electromagnetically assisted sheet metal stamping(EMAS)is an innovative hybrid sheet metal processing technique that combines EMF into traditional stamping.To evaluate the efficiency of this technique,an experimental scheme of EMAS was established according to the conventional stamping of cylindrical parts from aluminum and the formability encountered was discussed.Furthermore,a "multi-step,loose coupling" numerical scheme was proposed to investigate the deformation behaviors based on the ANSYS Multiphysics/LS-DYNA platform through establishing user-defined subroutines.The results show that electromagnetically assisted deep drawing can remarkably improve the formability of aluminum cylindrical parts.The proposed numerical scheme can successfully simulate the related Stamping-EMF process,and the deformation characteristics of sheet metal reflect experimental results.The predicted results are also validated with the profiles of the deformed sheets in experiments.

Conversion of coalbed methane surrogate into hydrogen and graphene sheets using rotating gliding arc plasma

The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surrogate.Based on a previous investigation of discharge properties,product distribution and energy efficiency,the operating parameters such as CH4 concentration,applied voltage and gas flow rate can effectively affect the CH4 conversion rate,the selectivity of H2 and the properties of solid generated carbon.Nevertheless,the basic properties of RGA plasma and its role in CH4 conversion are scarcely mentioned.In the present work,a 3D RGA model,with a detailed nonequilibrium CH4/Ar plasma chemistry,is developed to validate the previous experiments on CBM conversion,aiming in particular at the distribution of H2 and other gas products.Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection,electron migration and electron diffusion,and is prominently determined by the variation of the gas flow rate and applied voltage.Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction,taking into consideration the formation and loss pathways of crucial targeted substances(such as CH4,C2H2,H2 and H radicals)and corresponding contribution rates.Additionally,the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM)and Raman spectroscopy.The results show that increasing the applied voltage and decreasing CH4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets,while the size of the graphene sheets is slightly affected by the change in gas flow rate.

基于鼓泡-引射耦合的柴油初次雾化

针对斯特林发动机小负荷燃油雾化不良问题,提出了基于鼓泡-引射耦合的雾化方式.基于VOF(Volume of Fluid)仿真研究了鼓泡喷嘴内气液流态,并依据时间线性稳定性分析,对射流液膜失稳和破碎进行数学描述,建立了鼓泡-引射耦合下的初次雾化模型.分析了气液质量比RGL(gas-liquid mass ratio)、负荷对初次雾化的影响,并与传统雾化方式比较.结果表明:增大RGL会促进射流失稳、减小液滴粒径.相较于传统雾化方式,鼓泡-引射耦合下小负荷索特平均直径SMD减小约62%,雾化质量显著提高.

冰碛地层围岩隧道注浆材料组分优化与作用机理

冰碛层隧道围岩的地质组成情况复杂,整体胶结性差,结构不均匀,隧道在开挖过程中易出现围岩垮塌、涌水等问题。因此,以硅酸盐水泥为主材料,添加氧化镁、黄原胶、膨润土及水玻璃进行组分优化,通过析水率试验、凝固试验、流动度试验、力学试验、膨胀率试验及抗渗性能试验,研究一种适用于冰碛层围岩注浆条件的新型水泥基注浆材料,并分析注浆材料的微观形貌与固结机理。结果表明:新型注浆材料孔隙和缝隙基本被充填,结构紧密,抗渗性能相对较好。向材料中引入Mg^(2+)可形成Mg(OH)_(2)晶体以填补材料微孔结构,完善材料抗渗机制。大量纤维状水化硅酸钙(C—S—H)凝胶将钙矾石(AFt)、Ca(OH)_(2)、Mg(OH)_(2)等晶体和黄原胶螯合体胶结包裹成整体,可大幅提高材料抗渗能力。通过现场试验,验证了注浆材料的优良性能,材料可有效固结冰碛松散地层,确保隧道开挖安全。

基于ABAQUS的钛合金管板焊接过程模拟仿真

针对蒸汽发生单元钛合金管板焊接过程中焊接变形预测与控制问题,开展了焊接过程有限元仿真研究。基于顺序耦合的热弹塑性有限元法,采用ABAQUS对典型管板结构进行了不同焊接顺序下的焊接仿真分析,利用校核后的组合热源定义热流密度函数,计算得到焊接温度场、应力场及变形。结果显示,采用高斯热源与椭球体组合热源可以较为精确模拟熔池形貌,管板焊缝区域存在应力集中,且应力峰值位于管板被夹持区域,大小为631.2 MPa,超过材料屈服极限。单个环焊缝在不同路径下的应力分布因受到周围焊缝热输入的影响而出现复杂波动。采用从上至下的对称焊接顺序可以有效减小焊接变形量,最大变形量降幅可达24.3%,为后续工艺优化提供了参考依据。

深部顺槽巷道稳定性控制及效果评估

为解决基于传统支护参数对深部顺槽巷道支护面临的片帮、顶板下沉及底鼓等问题,在对3号煤层回采巷道地质条件和支护现状进行分析的基础上,基于锚网索耦合理论对支护参数进行优化实现支护手段与巷道围岩的二次耦合,同时在现场布置4个观测点对支护效果进行综合监测,并综合分析其社会效益。

基于单片测量的新型B-H复合传感结构设计

基于标准单片测量法,针对H线圈法和B线圈法等一系列传统磁特性测量方法的不足进行改进,提出一种新型B-H复合传感结构的设计方法;该设计方法基于一种自主设计的旋钮控制的夹紧装置,通过霍尔元件代替H线圈法测量磁场强度H,通过切向线圈传感器代替B线圈法或探测针法测量磁通密度B,同时装置于夹紧装置的温度传感器可用来测量样片温升变化、压力传感器可用来探究样片磁致伸缩现象对磁特性的影响。通过仿真软件搭建测量模型和多物理场耦合模型,验证新型复合传感结构设计用来进行磁特性测量的可行性。通过一系列数据验证说明该复合装置具有可行性与实用性,且结构简易、易于拆解、可测量多种材料且测量精度较高。

用于不锈钢薄板切割的直接半导体激光源

针对高功率半导体激光器存在的光束质量差、单元功率低的缺点,利用合束技术来提高激光功率及光束质量,配合QBH光纤前端帽优化聚焦镜以实现高效耦合。采用11个条宽5.4 mm的迷你线阵合束,通过光束整形、空间合束、偏振合束和波长合束,聚焦耦合进200μm/0.2光纤。在50 A电流下,实现连续386 W输出,功率密度为1.23 MW/cm2,电光效率为43.6%。在200 W的功率下,该激光器可以切割厚度为1 mm的不锈钢薄板。

基于松散耦合法的电磁平板成形3D有限元仿真

数值模拟提供一种手段去分析电磁成形中的多物理场耦合过程,但是目前的电磁成形模拟大多局限于2D模型或者将复杂的多物理场耦合数值模型简化为单独的多个物理场分别进行求解。为提供一种能够适用于复杂3D模型的多场耦合模拟方法,采用松散耦合法对平板电磁自由胀形过程进行3D有限元模拟分析。对工件网格采用拉格朗日算法,空气网格采用任意拉格朗日欧拉算法。从而使空气3D网格能够与板料变形随动而不产生畸变,实现磁场—结构场的迭代耦合分析。动态而无畸变的六面体网格能够在磁场分析模块与塑性成形模块间准确传递数据,既提高了运算速度又可获得精确计算结果。与实际数据比较证明,模拟的板料变形规律与试验结果一致。

PP/CaCO_3低发泡片材的开发研究

聚丙烯与其他聚烯烃共混改性 ,可明显提高熔体强度 ,采用 40 %CaCO3填充聚丙烯后用RA发泡剂发泡 ,可制得PP/Ca CO3低发泡片材 (密度为 0 .90 4g/cm3)。该片材具有良好的可降解性 ,用于替代聚苯乙烯 (PS)或纸浆制备一次性餐具 。

镁合金板材温热冲压成形热力耦合数值模拟

采用Gleeble3500热模拟试验机进行单向拉伸试验,获取了材料的力学性能参数,分析了AZ31镁合金板材的力学性能特点.采用热力耦合技术对镁合金板材温热冲压过程中的温度场进行了数值模拟,研究了冲压过程中温度场的分布规律,并对差温拉延工艺进行了分析.结果表明:差温拉延工艺可以提高镁合金板材的温热成形性能;采用热力耦合技术的数值模拟更能反映AZ31镁合金板材的温度敏感特性.

钢材表面硅烷处理后的防腐蚀性能研究

采用硫酸铜点滴、线性极化、交流阻抗等试验对比研究了经硅烷偶联剂(SCA)和铬酸盐表面处理后冷轧板的耐蚀性能。结果表明,经硅烷偶联剂表面处理后不但提高了基材的防腐蚀性能,并且还提高了基材与涂层的结合力,明显增强了钢材的耐蚀性。SCA处理能够起到和铬酸盐钝化相同的防护效果,有望取代造成环境污染的铬酸盐钝化工艺。

板料电磁成形顺序耦合三维有限元仿真

电磁成形有限元模拟涉及多场耦合作用,其中结构场与电磁场之间的不同耦合方法对模拟结果影响显著。与松散耦合方法相比,顺序耦合方法考虑了板料变形对电磁场的影响,从而能够更精确的描述电磁成形过程。以ANSYS仿真软件为平台,建立板料电磁成形的顺序耦合三维有限元模型。通过不同耦合方法的模拟结果与实验结果对比表明,采用顺序耦合模型得到的板料变形与实验接近,而采用松散耦合模型得到的板料变形明显大于实验值。由此可见,顺序耦合模型是适合于电磁成形模拟的可靠模型。采用顺序耦合模型研究发现,放电电流的加载时间对板料电磁成形中板料变形的影响显著。当取放电时间为电流曲线的1.5个周期时,模拟结果与实验数据吻合最好。综合考虑计算效率与精度,板料电磁成形中放电电流的加载时间取1.5个周期为宜。

氨基硅烷偶联剂对铝板/聚丙烯粘接件拉伸剪切变形的影响

研究了不同浓度γ-氨丙基三乙氧基硅烷(γ-APS)乙醇溶液处理铝板/聚丙烯粘接试样的拉伸剪切断面形貌和力-位移曲线特征,分析了γ-APS的作用。不用γ-APS处理铝板时,拉伸剪切断面上塑料经历了较为剧烈的塑性流动,但γ晶降低了塑料的强度和韧性及其整体协调变形能力,最大载荷时变形位移仅为0.13mm。经过γ-APS处理后,最大载荷时变形位移明显增大,γ-APS在溶液中的体积分数为3%时达到最大值0.63mm,断面上塑料因拉伸剪切而形成与剪切方向基本平行的薄片状,这表明γ-APS在马来酸酐接枝聚丙烯(PP-g-MAH)的基础上起到了明显的界面改性作用。

一体式厌氧平板膜生物反应器处理酒厂废水的研究

研究了容积负荷、水力停留时间对一体式厌氧平板膜生物反应器处理高浓度酒厂废水效果的影响。试验结果表明,CODCr负荷为5．2～8 kg／(m3·d),水力停留时间3～5 d时,CODCr平均去除率为95％。正常运行时的碱度与VFA的比为2．5～4．5。当CODCr负荷超过10 kg／(m3·d),系统 VFA出现累积,COD去除率下降。水力停留时间对一体式厌氧平板膜生物反应器处理效果有重要影响,水力停留时间应大于70 h。

钢板桩轧制过程充型模拟及轧制力有限元分析

采用二辊可逆式轧机和万能轧机组轧制钢板桩(/%:0.12～0.22C、0.15～0.55Si、0.80～1,50Mn)。通过热模拟试验得出该钢在980～1 030℃、变形速率0.5～5.0^(-1 )时的应力-应变曲线。借助ABAQUS软件,采用弹塑性有限元法对钢板桩轧制过程进行了三维热力耦合模拟。针对生产中出现的轧机过载问题,分析了轧制过程各道次的轧制力,通过改变相关道次孔型辊缝改善了充型和降低轧制力。

一体式厌氧膜生物反应器膜材质选择的试验研究

厌氧膜生物反应器作为一种处理高浓度有机废水行之有效的工艺,膜材质选择是保证其良好运行的关键之一.试验研究了一体式厌氧膜生物反应器中三种不同材质的膜PAN、PES和PVDF膜过滤特性.并通过数据拟合得出不同的膜通量和膜阻力随时间的数学模型表达式.结果表明,在相同的操作条件下,PAN膜通量维持在一个较高水平,膜污染速度增长缓慢,PAN膜是本试验条件下厌氧膜生物反应器的最佳膜材质.