Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.     

Multiphysics modeling and optimization of mechatronic multibody systems

Modeling mechatronic multibody systems requires the same type of methodology as for designing and prototyping mechatronic devices: a unified and integrated engineering approach. Various formulations are currently proposed to deal with multiphysics modeling, e.g., graph theories, equational approaches, co-simulation techniques. Recent works have pointed out their relative advantages and drawbacks, depending on the application to deal with: model size, model complexity, degree of coupling, frequency range, etc. This paper is the result of a close collaboration between three laboratories, and aims at showing that for “non-academic” mechatronic applications (i.e., issuing from real industrial issues), multibody dynamics formulations can be generalized to mechatronic systems, for the model generation as well as for the numerical analysis phases. Model portability being also an important aspect of the work, they must be easily interfaced with control design and optimization programs. A global “demonstrator”, based on an industrial case, is discussed: multiphysics modeling and mathematical optimization are carried out to illustrate the consistency and the efficiency of the proposed approaches.     

MEMS光纤法珀压力传感器的设计及解调方法实现

基于外界压力引起敏感膜片形变导致腔长变化来实现压力信号传感的原理,提出了一种MEMS光纤法珀压力传感器的设计,建立了传感器敏感膜片的挠度变化与膜厚、半径及施加压力的关系理论模型,并在此基础上进行了膜片的MATLAB二维数值仿真和Comsol Multiphysics三维数值仿真,并完成了FP压力敏感头的制作,进而设计了能够应用于光纤传感的解调方法,搭建了光纤传感的压力测试系统并进行了相关实验,利用所设计的解调方法对实验数据进行处理,进而对压力传感器的性能及特性进行了测试和验证。实验结果表明,传感器测试曲线线性度良好,与数值仿真结果基本一致,在100 kPa的量程范围内其灵敏度可达62.3 nm/kPa,温度敏感系数为0.023μm/℃,测量精度3.93%,且最小压强分辨率为1.29 kPa,证实了该MEMS光纤法珀压力传感系统具有一定的可行性。     

Multiphysics coupled modeling of light water reactor fuel performance

A fuel performance code for light water reactors called CityU Advanced Multiphysics Nuclear Fuels Performance with User-defined Simulations (CAMPUS) was developed. The CAMPUS code considers heat generation and conduction, oxygen diffusion, thermal expansion, elastic strain, densification, fission product swelling, grain growth, fission gas production and release, gap heat transfer, mechanical contact, gap/plenum pressure with plenum volume, fuel thermal and irradiation creep, cladding thermal and irradiation creep and oxidation. All the equations are implemented into the COMSOL Multiphysics finite-element platform with a 2D axisymmetric geometry of a fuel pellet with cladding. Comparisons of critical fuel performance parameters for UO₂ fuel using CAMPUS are similar to those obtained from BISON, ABAQUS and FRAPCON. Additional comparisons of beryllium doped fuel (UO₂-10%volBeO) with silicon carbide, instead of Zircaloy as cladding, also indicate good agreement. The capabilities of the CAMPUS code were further demonstrated by simulating the performance of oxide (UO₂), composite (UO₂-10%volBeO), silicide (U₃Si₂) and mixed oxide ((Th_0.9,U_0.1)O₂) fuel types under normal operation conditions. Compared to UO₂, it was found that the UO₂-10%volBeO fuel experiences lower temperatures and fission gas release while producing similar cladding strain. The U₃Si₂ fuel has the earliest gap closure and induces the highest cladding hoop stress. Finally, the (Th_0.9,U_0.1)O₂ fuel is predicted to produce the lowest fission gas release and a lower fuel centerline temperature when compared with the UO₂ fuel. These tests demonstrate that CAMPUS (using the COMSOL platform) is a practical tool for modeling LWR fuel performance.     

Adaptive burnup stepsize selection using control theory for 2-D lattice depletion simulations

A control theory approach is adopted to determine the temporal discretization during two-dimensional lattice physics depletion simulations. Two primary applications of automated and adaptive stepsize control are identified: (i) the presence of strong absorbers such as gadolinium, where the accurate burnout of the isotopes requires a depletion stepsize smaller than typically required, and (ii) high fidelity multiphysics simulations, e.g. loosely coupled physics, where the coupled physics are nonlinear in time and stepsize changes may be necessary to obtain an accurate coupled solution. A conventional predictor–corrector method is used to address the nonlinearity of the nuclide transmutation and neutron flux. An adaptive stepsize method is developed based on monitoring the one-group scalar neutron flux at both the predictor and corrector steps to approximate the convergence residual of the nonlinear solution. A user-specified tolerance on the L² relative error norm of the scalar neutron flux is utilized by the stepsize controller. Controllers that include integral, proportional, and/or derivative components are investigated and parameterized using Latin hypercube sampling of the controller input parameters. Three distinct fuel loadings of pressurized water reactor 17 × 17 fuel pin assemblies are considered, including no burnable absorbers, Integral Fuel Burnable Absorber, and gadolinium fuel pins. The required depletion stepsizes, as predicted throughout the cycle by the controller, are compared with a very small stepsize (0.01 MW d/kgHM) reference solution and a solution obtained by a typical rule of thumb depletion stepsize sequence.     

Development of an experimentally validated semi-empirical fully-coupled performance model of a PEM electrolysis cell with a 3-D structured porous transport layer

A semi-empirical non-isothermal model incorporating coupled momentum, heat and mass transport phenomena for predicting the performance of a proton exchange membrane (PEM) water electrolysis cell operating without flow channels is presented. Model input parameters such as electro-kinetics properties and mean pore size of the porous transport layer (PTL) were determined by rotating disc electrode and capillary flow porometry, respectively. This is the first report of a semi-empirical fully coupled model which allows one to quantify and investigate the effect of the gas phase and bubble coverage on PEM cell performance up to very high current densities of about 5 A/cm². The mass transport effects are discussed in terms of the operating conditions, design parameters and the microstructure of the PTL. The results show that, the operating temperature and pressure, and the inlet water flowrate and thickness of the PTL are the critical parameters for mitigating mass transport limitation at high current densities. The model presented here can serve as a tool for further development and scale-up effort in the area of PEM water electrolysis, and provide insight during the design stage.     

软脆铌酸锂晶体磨削的实验仿真研究

针对铌酸锂晶片在磨削加工时经常发生断裂的问题,对晶片断裂的原因进行了理论分析,并从晶体学的角度分析发现断裂与实验采用的晶片晶体结构有关。提出了基于多物理场耦合软件COMSOL Multiphysics对铌酸锂晶片磨削加工仿真的方法,为模拟铌酸锂晶片磨削减薄过程,对比分析了7种不同厚度的铌酸锂晶片在磨削加工时的应力分布和变形情况,对有外加电载荷磨削加工情况也进行了耦合仿真。研究结果表明,未施加电场时铌酸锂晶片的变形量随着晶片减薄过程逐渐减小,当铌酸锂晶片减薄至80μm时,晶片的外围出现均匀分布的4个应力集中位置,容易导致晶片产生裂纹甚至破裂;铌酸锂晶片变形量因外加电载荷而减小,因此合理施加外电场能够有效减弱晶片的应力集中趋势。     

磁选机典型开放式磁路分析与仿真

开放式磁路是一种应用最早、广泛、成熟且仍不断创新的磁路形式,对该磁路的深入研究可为目标磁路设计、工艺流程优化及工程设备选型提供有益指导。借助于COMSOL Multiphysics软件,仿真并研究若干种典型的开放式磁路,并分析磁源、磁极深度、配比、辅助极、磁化方向等相关因素对磁路的影响,之后给出几种磁路下磁性颗粒的运动轨迹。     

基于ADμC812的芯片温度控制系统的研究

介绍了一种以PID增量算法为核心,以812为硬件基础的温度控制系统,并给出了硬件电路和软件设计的总体结构。采用模拟软件COMSOL Multiphysics3.2分析控制对象的温度分布能够使控制结果与实际要求更为符合,满足芯片培养细胞的需要。     

基于动态数据的端面摩擦热-力耦合分析

为了更加准确地探索端面摩擦过程中的温度分布情况,使用端面摩擦过程中的实时动态摩擦因数和红外探头实测温度作为边界条件,在多场耦合软件COMSOL Multiphysics中进行热-力直接耦合分析,并利用红外热像仪对计算结果进行检验。结果表明:实时边界条件与数值计算相结合的方法可以准确地模拟出端面摩擦瞬态温度场;摩擦副之间的转速、载荷、摩擦因数是影响温度场分布的主要因素。