Comparison of methods for the determination of key reactions in chemical systems: Application to Titan’s atmosphere

A new paradigm is emerging in the field of photochemistry modeling in giant planets and Titan atmospheres. The emphasis is placed on the accurate predictions of the models and the quantification of their uncertainties. In order to improve photochemical models predictions, it is necessary to identify in chemical schemes the key reactions that should be studied in priority at conditions relevant to planetary atmospheres.     

一种新型微谐振陀螺及其灵敏度改进型(英文)

设计的新型微机械陀螺采用了谐振敏感原理,其具有直接准数字式频率输出、高灵敏度、结构设计灵活、自解耦等优点。由于灵敏度是谐振式陀螺的一个重要指标且对其他指标有重要影响,本文重点对其进行优化设计。从仿真结果可以看出,在保证其他性能的前提下,起始结构方案、改进结构方案1、改进结构方案2和最终方案的灵敏度值分别为0.080、0.210、0.341和0.5447Hz/(°/s)。通过对比可得,每次改进过程,灵敏度都有较大提高。经分析,驱动方向上DETF的振幅减到外质量块振幅的1.16×10-4。测量范围为±300°/s,在测量范围内,线性度为6.41×10-7。     

磁悬浮飞轮优化设计与实验

针对在轨磁悬浮飞轮转子系统,考虑发射主动段振动工况,提出一种基于灵敏度分析的多学科优化设计方法。通过比较分析内、外锁紧方案对锁紧状态飞轮转子系统共振频率的影响,得到了较优的抱式外锁紧方案。在此基础上,对飞轮转子进行灵敏度分析,并选择高灵敏度结构参数作为优化设计变量。考虑其结构强度、转动惯量、控制性能、自由状态和锁紧状态一阶共振频率,以飞轮转子质量最小为优化目标,利用序列二次规划法对其进行多学科优化设计。优化结果表明,在满足发射振动工况下,飞轮转子极转动惯量与质量的数值比达到最大为0.0070,比初始值0.0064提高了9.4%。该优化方法提高了飞轮转子设计的可靠性和效率,其首次在轨实验成功对我国磁悬浮飞轮空间应用具有重要意义。     

改进模拟退火算法的喷管动力学模型修正

为获得液体火箭发动机喷管高精度的结构动力学有限元模型，提出一种基于改进模拟退火算法（Improved Simulation Annealing Algorithm，ISAA）的有限元模型修正方法。首先，将复杂的薄壁夹层板喷管等效为复合材料层合壳，建立喷管的参数化有限元模型；在此基础上，以结构模态参数为参考基，构造出联合使用模态频率及模态振型的目标函数，并运用灵敏度分析提取设计变量，从而建立其优化模型；提出带记忆、局部搜索功能的改进模拟退火算法，运用ISAA在设计空间进行多目标全局寻优；最后，采用基于MSC Patran/Nastran软件平台二次开发的结构动力学模型修正软件ZDXZ V1.0进行模型修正，并对模型修正方法的有效性进行了校验。结果表明，修正后喷管的前3阶计算模态频率与试验值相对误差小于2%，振型相关性最小MAC值大于0.9，大大提升了喷管模型的动力学符合性，模型精度满足工程应用要求；表明所述模型修正策略的有效性，该方法具有高效、强鲁棒性等特点，适合于大型复杂结构的模型修正。     

100kHz~1MHz频率范围水听器灵敏度激光法校准及其验证

激光法校准水听器灵敏度是一种绝对校准方法，本文介绍了激光法水声声压校准装置的校准原理及主要系统构成，采用激光法对TC4034和BK8103水听器的灵敏度在100kHz~1MHz频率范围进行了校准实验研究，分析了激光法校准装置的测量不确定度，校准结果与三换能器互易法对校准结果进行了对比。结果表明两种校准方法的结果总体上是一致的，校准结果偏差小于两套装置的合成不确定度。本文对导致二者之间偏差的原因进行了分析。     

皮卫星星箭分离动力学模拟及其灵敏度分析

皮卫星能源有限、姿控能力差等特点决定其对星箭分离初始姿态要求较高。在采用自主研发的皮卫星星箭分离机构的基础上，以多体动力学理论为基础，采用ADAMS软件建立了皮卫星及其星箭分离机构虚拟样机模型，分别就皮卫星质心偏离量、分离弹簧与舱门扭簧弹性系数对入轨初始姿态影响展开了分析。分析结果表明：质心偏心量对分离姿态影响最明显，分离弹簧与舱门扭簧弹性系数对其影响次之，合理配置分离弹簧与舱门扭簧弹性系数有利于卫星保持良好的姿态分离。在轨分离试验显示：分离时刻皮卫星滚动角速度、俯仰角速度、偏航角速度分别为-0.18（°）/s，-1.6（°）/s，0.95（°）/s，与在轨环境下仿真结果基本相符；入轨初始姿态能满足皮卫星的姿控要求，为其后续工作提供了保障。     

超声速来流基元叶型前缘加工误差气动敏感性分析

为研究叶型前缘加工误差对叶栅气动性能敏感性,以NASA Rotor 67转子70%叶高截面基元级叶型为研究对象,选择Clamped型非均匀B样条曲线实现叶型前缘数学描述。采用单因素法建立叶型前缘加工误差模型,提炼出叶片弦长误差、前缘轮廓度误差、几何进气角误差三个误差模型;随后结合L9(34)正交实验及数值模拟方法研究超声速来流条件下三维直列叶栅不同前缘误差类型对叶栅气动性能的敏感性。正交实验极差分析及显著性分析均表明:前缘轮廓度误差FP是影响叶栅气动性能的主要影响因素(75%以上可能性),叶栅性能随前缘轮廓度增加呈现恶化趋势,即叶型前缘越厚,叶栅总压损失越大,扩压能力越小。进一步分析轮廓度误差对叶栅性能影响机制得出:激波损失是叶栅性能随轮廓度误差加大而恶化的重要原因。     

Topology optimization of joint load control with geometrical nonlinearity

This paper presents an extended topology optimization approach considering joint load constraints with geo-metrical nonlinearity in design of assembled structures. The geometrical nonlinearity is firstly included to reflect the structural response and the joint load distribution under large deformation. To avoid a failure of fastener joints, topology optimization is then carried out to minimize the structural end compliance in the equilibrium state while controlling joint loads intensities over fasteners. During nonlinear analysis and optimization, a novel implementation of adjoint vector sensitivity analysis along with super element condensation is introduced to address numerical instability issues. The degrees of freedom of weak regions are condensed so that their influences are excluded from the iterative Newton-Raphson (NR) solution. Numerical examples are presented to validate the efficiency and robustness of the proposed method. The effects of joint load constraints and geometrical nonlinearity are highlighted by comparing numerical optimization results.     

Conceptual design,modeling and compliance characterization of a novel 2-DOF rotational pointing mechanism for fast steering mirror

In this paper, a novel 2-DOF rotational pointing mechanism (RPM) is designed inspired by the guidelines of the graphical approach. The mechanism integrates with a fast steering mirror (FSM) for compensating pointing errors of a laser beam. The design intends to achieve an angular travel of ±10 mrad and steers a 25 mm mirror aperture. A planar flexure with beam flexures accompanied in parallel with an axial flexure build-up mechanism configuration. Compliant mechanism-based RPM ensures high precision and compactness. Compliance characteristics are established based on the stiffness matrix method for four different planar flexure layouts. One layout with best in-plane rotational compliance is then assessed for performance sensitivity to mechanism dimension parameters and parasitic error, thus informing the design space. Rotational stiffness in both the in-plane rotational axes and stress is determined based on finite element analysis (FEA). The wire electrical discharge machining (EDM) is employed for developing the proof of concept for the RPM and is then assembled in FSM. Experiments are conducted to determine the rotational stiffness and angular travel about both in-plane rotational axes. Comparison among theoretical, numerical and experiments reveal excellent linearity of rotational stiffness along the rotational travel range. The maximum theoretical error is less than 5.5% compared with FEA while, the experimental error has a mean of 5% and 3% for both rotational axes thus satisfying the intended design requirement.     

γ-TiAl合金铣削加工表面残余应力研究

为了探索高温理想结构材料γ-Ti Al合金铣削表面残余应力特性,结合正交试验数据处理方法中的极差分析法,建立各工艺因素情况下不同水平对表面残余应力的关系曲线,并对其工艺过程中的热力影响机理进行分析;同时建立面向残余应力的各因素灵敏度数学模型,进而确定以获取较大残余压应力为目标的工艺参数优选区间。研究表明:在试验参数限定范围内,步进方向以及进给方向均呈现为残余压应力,主要原因是冷塑性变形占主导作用。通过对灵敏度数学模型进行分析,发现残余应力对设计变量中的铣削速度变化最敏感,对每齿进给量、铣削深度和铣削宽度的敏感程度近似相同,为Ti Al金属间化合物铣削表面残余应力控制研究提供了理论依据。