Enhanced thermal stability of VCSEL array by thermoelectric analysis-based optimization of mesas distribution

The thermal stability of a vertical-cavity surface-emitting laser(VCSEL) array is enhanced by redesigning the mesa arrangement. Based on a thermoelectric coupling three-dimensional(3D) finite-element model, an optimized VCSEL array is designed. The effects of this optimization are studied experimentally. Power density characteristics of VCSEL arrays with different mesa configuration are obtained under different thermal stress in which the optimized device shows improved performance. Optimized device also shows better stability from measured spectra and calculated thermal resistances. The experimental results prove that our simulation model and optimization is instructive for VCSEL array design.     

聚焦光束大气传输光束扩展定标规律的数值分析

选取多种典型激光传输条件下的计算参量，对平台光束聚焦大气传输湍流热晕相互作用引起的光束扩展进行了数值分析.热畸变的产生是在快速变化的湍流扩束作用之后，在此假定的基础上，建立了描述聚焦光束大气传输光束扩展与大气传输特征物理参量的定标关系.在了解激光发射系统的特征参量和大气传输效应的特征参量之后，即可由定标关系迅速判断激光大气传输的效果，从而为激光工程系统的参量优化设计及其应用效能评估提供依据. 关键词： 湍流效应 热晕效应 光束扩展 定标规律     

碳遮光石英气凝胶传热机制与热性能数值模拟

建立了碳遮光石英气凝胶传热机制及热性能数值模拟方法,在交叉立方阵列导热模型、热辐射传输谱带模型、辐射导热耦合传热模型基础上,采用蒙特卡罗方法与有限体积法数值模拟了气凝胶内的热辐射传输及辐射导热耦合传热,并以表观导热系数描述气凝胶传热性能.以某石英气凝胶为例,定量模拟了热性能、各种传热方式的作用及温度依赖性,分析了应用Rosseland扩散近似引起的误差.     

低温发电用翅片管换热器传热特性的数值模拟分析

为了深入研究低温余热发电系统用翅片管换热器的传热特性,文中建立了翅片管换热器计算模型,对工质R123在翅片管换热器内的传热性能进行数值模拟,比较管内工质R123在不同流速与温度时的换热特性,利用最小二乘法原理,对烟气侧和工质侧的换热关联式进行了拟合,得到了二者的换热准则方程,此外,利用实验方法对模拟结果进行验证。     

高斯叠代法研究相控阵非线性声场

相控阵在聚焦超声治疗应用中不可避免地受到非线性影响,提出了采用高斯叠代法计算相控阵的非线性声场。在该方法中,利用预设焦点参数并应用伪逆矩阵算法得到阵元的激励参数;然后将阵元近似拟合成一组高斯声束的叠加,通过高斯声束叠代计算非线性声场。数值计算中以64阵元一维相控阵为研究对象;线性条件下,高斯叠代法结果与菲涅耳积分结果的误差低于0.5%,验证了该方法的可行性;单焦点及双焦点模式的相控阵非线性声场结果表明非线性效应能提高焦点聚焦性能,并且非线性效应与激励声压及激励频率成正比。      

The focusing performance with a horizontal time- reversal array at different depths in shallow water

The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation.It is observed that the focusing performance of a bottom-mounted horizontal time-reversal array is much better than that of a horizontal time-reversal array at other depths in shallow water.The normal mode modeling is used to explain this result.The absolute values of the modes at different depths are compared.It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than that at other depths.It means that the horizontal time-reversal array deployed at the bottom can sample more modes,obtain more information of the probe source and achieve better focusing performance.The numerical simulations of time-reversal focusing performance under various conditions,such as different sound speed profiles,and different bottom parameters,lead to similar results.     

大口径LD泵浦的激光放大器热沉积特性

 通过分析LD阵列端面泵浦片状放大器的工作特点，建立了对增益介质Nd:YLF进行热特性研究的有限元模型。针对泵浦能量空间均匀分布、高斯分布、超高斯分布三种情况，计算出了LD泵浦功率56 kW，脉冲宽度520 μs，重复频率10 Hz状态下晶体瞬时3维温度和热应力分布。研究结果表明：由于脉冲工作方式，晶体各节点温度随时间呈锯齿形变化，经过一段时间后吸热和冷却效果达到平衡，介质温度呈周期性变化；在相同泵浦峰值功率条件下，超高斯泵浦能量分布引起的温升和热应力最小，其最大值分别为103.3 ℃和47.6 MPa；有效泵浦功率密度达到10 kW/cm²量级时，介质极可能发生热致断裂。     

脉冲磁场中波导管涡流影响的数值模拟

 提出了脉冲磁场中波导管涡流影响的数值模拟方案，编制了EDDYC程序，研究了波导管电导率、管径、壁厚和激励电流角频率等对波导管涡流的影响，对将在二极管-速调管实验中使用的不锈钢（1Cr18Ni9Ti）波导管的涡流影响进行了模拟。     

对旋轴流水轮机的非定常数值模拟研究

为了研究采用对旋转轮的新型轴流式水轮机的非定常性能,应用三维非定常数值计算方法,对该新型水轮机进行了数值模拟研究.数值计算中,采用了全三维全流道的数值计算方法,基于DES(Detached Eddy Simulation)方法获得了对旋轴流水轮机的非定常流场和能量性能.计算结果显示,该新型水轮机在一个转动周期的不同时刻,其内部流场存在显著的非定常特性.     

大气湍流和热晕效应对列阵合成激光传输特性和光束质量影响的理论研究进展

介绍了大气湍流效应和热晕效应对列阵合成激光传输特性和光束质量影响的理论研究进展。主要介绍了合成激光在大气中传输的解析和数值模拟研究方法,大气湍流效应对列阵合成光束的光强分布、远场发散角、方向性、曲率半径和湍流距离的影响,以及大气热晕效应对列阵合成光束的光强分布、传输效率、重心偏移、热晕时间尺度和焦移的影响。研究结果表明,大气湍流效应和热晕效应对合成激光光束质量的影响与光束合成方式、合成光束参数以及大气参数密切相关。     

An optimization method for designing SENSE imaging RF coil arrays

An optimization method in RF coil array design for SENSE imaging is described. Using this method the optimized RF coil geometries can be calculated numerically given the required SENSE imaging performance. Although this method can be applied to optimize the RF coil arrays for both 1D and 2D SENSE imaging, to demonstrate the potential applications of this method, we designed RF coil arrays for 2D SENSE imaging and compared their performance by simulation. An optimized 4-channel receive-only RF coil array designed for 2D SENSE imaging was implemented and tested to demonstrate the feasibility of the proposed technique. Imaging results showed reasonable agreement with the simulations, thus the method can be applied to RF coil array designs for SENSE imaging when optimum imaging performance is desired.     

次声管道降噪滤波器优化设计

提出了基于声学响应模型与群差分进化算法的次声管道降噪滤波器优化设计方法,在理想条件和工程实践两种情景下设计了管道滤波器的结构参数并仿真分析了降噪性能表现。结果表明:（1）理想条件下的设计结果在约0.1～0.8 Hz的频带内取得了5 dB以上的降噪性能提升,最大提升达到12 dB。（2）工程实践情景的设计结果在各种环境风速中最大可以取得约3dB的性能提升。（3）大风速条件的优化设计可应用于环境风速未知或变化较大的场景。分析结果表明所提设计方法可以有效设计管道滤波器,优化设计的管道滤波器在降噪性能上优于传统管道滤波器。      

Analysis of the RATAN-600 radiotelescope antenna with a multilevel Physical Optics algorithm

The RATAN-600 antenna is a flexible multireflector system composed of reflectors of very large dimensions. An extended system, with improved performance in the millimetric range, includes a focal receiver array. Accurate electromagnetic analysis of such a system, and simulation of three-dimensional (3D) patterns, represents a substantial computational challenge. A fast Physical Optics method based on a multilevel subdivision of the surfaces of integration is proposed to address this problem. This method allows to perform Physical Optics integrals with a computational complexity comparable to that of the Fast Fourier Transform. The algorithm and initial numerical results of its application to the RATAN-600 antenna system are presented.     

FAIR项目Super-FRS超导二极磁铁测试线圈的三维失超数值模拟

国际反质子与离子研究装置(FAIR)项目中的Super-FRS超导二极磁铁是一个大型温铁结构的超导磁体,由中国负责设计、研制和测试。为了研究超导线圈的性能和其设计的可靠性,前期研制了一个测试线圈。建立了一个基于ANSYS和OPERA 3D的三维失超模型,不仅将模拟结果和实验数据进行对比,更可以获得失超过程的更多细节。模型将环氧浸渍的超导线圈简化为各项异性连续介质。将ANSYS求解器用于瞬态传热过程的分析,OPERA 3D用于磁场计算,并采用ANSYS脚本语言（APDL）进行焦耳热的计算和保护电路方程的求解。模拟得到了温度、电压、电流随时间的变化曲线和失超传播过程。最后将模拟结果和测试线圈的测试结果进行了比较。     

0.22 THz二维电磁带隙波导和阵列天线设计

基于二维电磁带隙（EBG）结构,设计了工作在0.22 THz的直波导传输线和90弯波导传输线。数值模拟结果显示:直波导和弯波导的S21参数在0.22 THz处均大于10-5 dB,20 GHz模拟频带内的S21参数分别大于-0.001 dB和-0.003 5 dB。EBG结构很好地阻止了电磁波在电磁带隙内部的传播。基于EBG结构波导,设计了3 dB功分器和H面扇形喇叭阵列天线。数值模拟结果显示:功分器的S21参数在0.22 THz处为-3 dB,阵列天线方向性为17.1 dBi,具有较小的旁瓣和后瓣,E面和H面方向图均具有良好对称性。     

Materials,technologies, and circuit concepts for nanocrossbar-based bipolar RRAM

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO₂, WO₃, GeSe, SiO₂ and MSQ thin films were integrated into nanojunctions of 100×100 nm². The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10¹⁰ bit.     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

脉管制冷机性能数值模拟方法的研究进展及发展方向

本文对于脉管制冷机性能的数值模拟方法的发展过程进行了简要的回顾,指出,有限容积法是目前大多数研究者所采用的软件的基本框架。对于作者研究组在过去2年中的主要成果作了简要介绍,包括采用一维模型研究脉管的最佳长径比,最佳混合工质的摩尔配比,以及锥形脉管制冷机的最佳锥角等问题。介绍了对回热器的2维模拟以及对脉管中的自然对流3维计算的主要结果。最后对于进一步发展脉管制冷机数值模拟方法问题提出了作者的见解。     

一先进跨音速离心压气机叶轮内部粘性流动数值模拟

随着计算机和计算技术的发展，三元粘性数值计算被广泛地应用于叶轮机械内部流场分析，本文使用三元Ｎ－Ｓ方程对这一先进跨音速离心压气机叶轮内部流场进行数值模拟，一是对这一成功设计进行分析验证。二是使用数值方法进行内部流场细节的模拟掌握其内部粘性流动特点，为今后设计和改进高压比跨音速离心压气机提供经验。     

Thermal emission properties of 2D and 3D silicon photonic crystals

We present measurements of the thermal emission properties of 2D and 3D silicon photonic crystals with and without substrate heated resistively as well as passively with an aluminium hotplate. The out-of-plane and in-plane emission properties were recorded and compared to numerical simulation. It turned out that for the in-plane 2D photonic crystal and out-of-plane 3D photonic crystal emission a photonic stop gap effect is visible. For the out-of-plane 2D photonic crystal emission, no photonic bandgap effect is observable but instead strong silicon oxide emission from native oxide inside the pores of silicon are observable. A model for the modified thermal emission is presented.