水下耐压结构拓扑优化设计方法探究

探究了拓扑优化设计方法在水下耐压结构设计中的应用。与固定载荷作用下结构的优化设计相比,此类问题需要正确地确定压力作用面。在拓扑优化过程中,利用变密度法得到的中间结构拓扑实际上可以看成是灰度图。基于此,提出了基于图像分割技术的压力加载面搜索方法,并利用距离正规化水平集方法(DRLSE)检测图像边界。利用数值算例验证了方法的有效性,并研究了静水压力作用下结构的拓扑优化设计问题。在给定材料约束的前提下,研究了不同边界条件下耐压壳体的最小柔顺度及最优结构拓扑形式。优化结果说明了该方法在多球交接耐压壳结构形式优化设计及复杂边界条件下耐压结构新形式探索中的工程应用价值。     

视觉定位相机标定模拟器目标靶结构优化设计

静态目标模拟器专用于飞行器视觉空间定位相机的标定,在模拟环境中为相机提供准确的模拟目标,而目标靶作为目标模拟器的核心组件其精度决定了相机的标定水平.构建目标靶标定环境下的理论模型,通过对目标靶Z向变形量h与两点位置精度△δ_(ij)的几何关系推导,确定了满足相机标定精度的h值.以计算结果为目标参数,应用Ansys软件对目标靶进行结构优化,并给出了最优结果,最后采用优化参数再建模得到了目标靶标定条件下h=5.5 μm小于理论值14 μm,验证了对目标靶结构优化的正确性.     

Metal injection molding of shape memory alloys using prealloyed NiTi powders

Metal injection molding (MIM) was applied for the production of shape memory parts using prealloyed NiTi powders with different Ni contents as starting materials. The MIM process allows the production of near-net-shape components without the occurrence of rapid tool wear as found in the case of conventional machining operations. With optimized manufacturing conditions, including feedstock preparation, injection parameters and sintering conditions, densities of more than 98% of the theoretical value could be achieved. Determination of the phase transformation behavior, as a basic requirement for the shape memory effect, was done by differential scanning calorimetry (DSC). In a first approach, tensile tests in the austenitic state showed pseudoelastic behavior. An elongation at failure of 3.8% was found. For martensite, up to 5% was obtained. Reasons for the lower strain compared to melted NiTi alloys are discussed. For martensitic samples the one-way shape memory effect (1WE) was demonstrated.     

基于吸附性能的生物质基多孔活性炭制备方案的响应面法优化

以废弃核桃壳作为原料,采用微波加热法制备生物质基多孔活性炭。基于响应面法和数值模拟方法研究活性炭前驱体进行物理活化过程中微波功率、活化时间以及磷酸质量分数对生物质基多孔活性炭吸附性能的影响,对生物质基多孔活性炭制备方案进行优化,并对最优条件下制备的生物质基多孔活性炭进行表征。结果表明,3个因素均对生物质基多孔活性炭的吸附性能有影响,其影响显著性为:微波功率磷酸质量分数活化时间。优化的制备条件为:微波加热法对活性炭前驱体进行物理活化过程中的微波功率为746W、活化时间为11.2min以及磷酸质量分数为85.9%。优化生物质基多孔活性炭的碘吸附值为1074.57mg/g,亚甲基蓝吸附值为294.4mL/g,获得率为52.1%。     

高铁车辆横向振动耦合机制及其减振技术对策

结合欧系车辆转向架技术创新特点,提出一种基于刚柔耦合仿真技术的车下质量橡胶吊挂优化设计方法。横向振动耦合机制是指以二系横向悬挂构成车体对走行部接口传递媒介的横向高频振动耦合机制,且具有抗蛇行高频阻抗、车体摇头大阻尼和"无纵梁无骨架"铝合金车体3大特殊性。因而整装车体下部1阶横向弯曲模态振动将对车体技术服役寿命30年造成十分严重的负面影响。对于车下质量橡胶吊挂来讲,比例阻尼是抑制车下质量横向振动的积极因素之一,而对中部地板横向加速度则具有极值特征,即比例阻尼取0.5%,其全频域(RMS)3σ最小。也应当注意到上述减振技术的局限性,即在走行部非常工况下,较大的车下质量存在横向耦合振动的可能性,进而造成自重楔紧失效。     

碱性条件下Fe-P-B合金电镀

研究了碱性溶液中镀液组成、阴极电流密度、温度、pH值对Fe-P-B合金电镀层沉积速率和组成的影响,优化了工艺,在最佳工艺条件下获得Fe-P-B镀层,并对镀层的耐腐蚀性、结构和结合力进行了分析.结果表明:提高镀液中硫酸亚铁铵含量、溶液pH值、温度和电流密度,镀层沉积速率增加;提高镀液中次亚磷酸钠、丙二酸和硼氢化钠含量,镀层沉积速率先增后降低,出现一个极大值;镀层中B含量的增加会使P含量降低,但提高电流密度和镀液温度时二者都有所增加;在最佳工艺条件下获得的Fe-P-B合金镀层为非晶态结构,和基体结合力优良,耐蚀性良好,在15%NaoH溶液中的耐腐蚀性优于在5%NaCl溶液中.     

Maximizing production rates of the Linde-Hampson machine

In contrast to the ideal case of unlimited size recuperator, any real Linde-Hampson machine of finite size recuperator can be optimized to reach the extreme rates of performance. The group of cryocoolers sharing the same size recuperator is optimized in a closed form by determining the corresponding flow rate which maximizes its rate of cold production. For a similar group of liquefiers an optimal flow rate is derived to maximize the rate of production of liquid cryogen. The group of cryocoolers sharing a constant and given flow rate is optimized by shortening the recuperator for reaching a maximum compactness measured by the cooling power per unit size of the recuperator. The optimum conditions are developed for nitrogen and argon. The relevance of this analysis is discussed in the context of practice of fast cooldown Joule-Thomson cryocooling.     

Pre-oxidation of an extremely polluted industrial wastewater by the Fenton's reagent

The pre-oxidation of an extremely polluted pharmaceutical wastewater (chemical oxygen demand (COD) value of 362,000mg/l) using the Fenton's reagent has been systematically studied using an experimental design technique. The parameters influencing the COD removal of the wastewater, namely temperature, ferrous ion and hydrogen peroxide concentrations have been optimized to achieve a COD global reduction of 56.4%.The total range of the proposed experimental design, however, could not be tested because under some conditions (hydrogen peroxide concentration over 5M) the Fenton's reaction became violent and could not be controlled, probably due to the high exothermic effect associated with COD oxidation. For the tested conditions, the optimal values of hydrogen peroxide and ferrous ion concentration were 3 and 0.3M, respectively, whereas temperature only showed a mild positive effect on COD removal. In addition, during the first 10min of Fenton's reaction, more than 90% of the total COD removal can be achieved.Fenton's reaction has proved to be a feasible technique for the pre-oxidation of the wastewater under study, and can be considered a suitable pre-treatment for this type of wastewaters.     

测量过程控制图参数的自助最大熵融合优化

Shewhart控制图是核查数据分析的主要工具,在核查数据为小样本情况下Shewhart控制图容易导致“误发警报”。针对这一问题,提出一种自助最大熵融合方法,优化Shewhart控制图控制参数。首先,通过自助法充分挖掘核查数据自身特征,扩大样本容量。在此基础上,应用最大熵原理,描述出核查数据概率分布参数的密度函数,估计核查数据样本的均值和方差,从而优化Shewhart控制图控制参数。实验表明,经自助最大熵优化后的Shewhart控制图控制参数更加接近理论值,降低了发生“误发警报”的概率。     

Optimization of a predictive controller for closed-loop adaptive optics

For closed-loop adaptive optics systems limited by time delay and measurement noise, we demonstrate that the ideal rejection transfer function is proportional to the frequency signal-to-noise ratio of the wave-front input. We describe a new modal linear predictive controller that approaches this ideal transfer function. Its parameters are optimized by minimization of the residual wave-front error with a modified recursive least-squares algorithm. The optimization can be performed with closed-loop data in the case of evolving turbulent conditions. We present numerical simulations to show the significant improvements brought by the predictor.     

Study on Training Innovation Ability of Forestry and Agricultural Mechanical Post-graduates

For training forestry and agricultural mechanical post-graduates' innovation ability. This paper studied some problems hindering students improvement,mean value and standard deviation of time management tendency of students were researched. The results showed,graduate enthusiasm should be mobilized,curriculum should be optimized,new teaching methods should be introduced,practice should be strengthened and paid more attention,a strict system of management and evaluation should be established.     

Spatially resolved protein hydrogen exchange measured by subzero-cooled chip-based nanoelectrospray ionization tandem mass spectrometry

Mass spectrometry has become a valuable method for studying structural dynamics of proteins in solution by measuring their backbone amide hydrogen/deuterium exchange (HDX) kinetics. In a typical exchange experiment one or more proteins are incubated in deuterated buffer at physiological conditions. After a given period of deuteration, the exchange reaction is quenched by acidification (pH 2.5) and cooling (0 °C) and the deuterated protein (or a digest thereof) is analyzed by mass spectrometry. The unavoidable loss of deuterium (back-exchange) that occurs under quench conditions is undesired as it leads to loss of information. Here we describe the successful application of a chip-based nanoelectrospray ionization mass spectrometry top-down fragmentation approach based on cooling to subzero temperature (-15 °C) which reduces the back-exchange at quench conditions to very low levels. For example, only 4% and 6% deuterium loss for fully deuterated ubiquitin and β(2)-microglobulin were observed after 10 min of back-exchange. The practical value of our subzero-cooled setup for top-down fragmentation HDX analyses is demonstrated by electron-transfer dissociation of ubiquitin ions under carefully optimized mass spectrometric conditions where gas-phase hydrogen scrambling is negligible. Our results show that the known dynamic behavior of ubiquitin in solution is accurately reflected in the deuterium contents of the fragment ions.     

Nondestructive readout in thick magnetic film devices

To study the nondestructive readout properties of thick magnetic film devices, sense voltages are computed for triangular interrogate word pulses. Eddy currents are assumed to be the exclusive damping mechanism. For a given pulse rise time one can obtain a maximum signal peak value with a given optimum film thickness, and the read signal of an optimized film can be approximated by simple analytical functions. In an attempt to describe the nondestructive readout stability, a relation is developed between pulse widths, angle of rotation of the magnetization, and reversibility threshold.     

Bootstrap method for nonlinear filtering of EM-ML reconstructions of PET images

Reconstructions of positron emission tomography images are obtained with the iterative expectation maximization (EM) algorithm. The EM algorithm is halted according to a cross-validation procedure. For the cases studied, this method yields a reconstruction with high variability about its expected value. The variability of the reconstruction about its expected value is reduced by computing its bootstrap expectation. Based on the reconstruction computed from the observed projection data, synthetic projection data sets are simulated. Reconstructions of the synthetic projection data sets are averaged to yield the bootstrap expectation. This bootstrap procedure is a nonlinear filtering method. The procedure is automatic; no smoothing kernel or bandwidth parameter need be specified. For simulated data, the bootstrap method yielded somewhat sharper reconstructions than did an optimized linear approach. The method is applied to real data from a fluorodeoxiglucose study of the human brain. Near the boundaries, the resampling procedure yielded a sharper reconstruction. © 1996 John Wiley & Sons, Inc.     

超深孔一次爆破成井施工工艺研究

用超深孔一次或分段爆破成并技术全深度一次钻孔,机械化程度高;不需井筒内爆破施工作业,安全程度高,是目前比较先进的筒状硐室施工方法.但是在施工工艺方面,存在钻孔、联线施工质量要求高,装药、封堵难度大,排矸与支护衔接困难等问题,制约着此技术的推广使用.立足于切实可行的一次成井施工工艺,结合实践经验,对钻孔、装药、联线、排矸...     

Superior prospect of chemically activated electrospun carbon fibers for hydrogen storage

In this study, the capacity of hydrogen storage was evaluated by using electrospun activated carbon fibers prepared by electrospinning and chemical activation based on the comparison with other carbon materials such as active carbon, single walled carbon nanotube, and graphite. For an improved hydrogen storage system, the optimized conditions of carbon materials were investigated with studying their specific surface area, pore volume, size, and shape. The hydrogen adsorption capacity of chemically activated electrospun carbon fiber itself is better than that of other porous carbon materials. This is attributed to the optimized pore structure of electrospun activated carbon fibers that might provide better sites for hydrogen adsorption than other carbon materials.     

电沉积制备Ni-S涂层电极的研究

以泡沫镍为基体电沉积制备了Ni-S涂层电极.通过对电流密度、电沉积温度、电沉积时间和镀液pH值等条件对涂层析氢性能影响的研究,确定了适宜的电沉积工艺条件;电极涂层的XRD、SEM测试结果表明涂层为非晶态结构、表面颗粒大小均匀且具较大表面积;电解过程中出现了Ni3S2由非晶态向晶态的转变,由于Ni3S2具有较强的吸附氢能力,是析氢反应的催化活性中心,电解过程中Ni3S2的出现降低了电极的析氢电位.模拟电解水实验结果表明泡沫镍基Ni-S涂层电极较Raney-Ni电极具有更好的析氢活性.     

Faceted concentrators optimized for homogeneous radiation

For technical reasons, large three-dimensional compound parabolic concentrators (CPC's) are often built from facets with either no or only one-dimensional curvature. We analyze CPC approximations made with various numbers of axial and circumferential subdivisions. Incident radiation within half-angles of 10 degrees and 30 degrees is considered. The reflectivity of the mirrors is assumed to be 90% or 95%. The performance of faceted concentrators can be significantly improved by optimization as compared with heuristic CPC approaches. The highest increase in transmission that we observed was 19% greater as compared with that of a heuristic CPC approximation. The shapes of the optimized concentrators differ from that of a classic CPC, and most of the optimized concentrators are longer than a classic CPC. For practical concentrators with a small number of facets, the optimized geometry provides better performance than a heuristic approximation of the CPC shape.     

采用改进遗传神经网络的多载荷振动信号故障诊断

根据柴油机气阀机构运动规律,利用小波包分解提取缸盖振动信号的特征向量;针对多种载荷混合诊断的问题,采用二进制与实数混合编码的方式对使用遗传算法的误差反向传播（BP）神经网络的隐层结点数目、权值和阈值进行优化。通过实验检测,证明该方法在多种载荷混合振动信号诊断上,较一般方法学习、收敛速度快,检测准确率高。     

Stress-Strain Behaviour Simulation of Vanadium Microalloyed Steel with the Internal Defects During two Different Heating Strategies

This paper is focused on the explanation of a linkage between two different heating strategies and a grow of the internal casting defects, that are already present in continuously cast blooms made from vanadium micro-alloyed Cr-Mo steel. Internal defects initiation and propagation can be associated to unsuitable casting and heating conditions. Small casting voids surrounded by ferrite-bainite network enriched by carbides forming elements produce perfect conditions for crack grow during the bloom straightening, heating in the soaking pit and/or heat treatment. Moreover, we simulated the stress-strain behaviour of continuously cast round bloom during heating in soaking pit using the FEM software. It is shown that optimized heating strategy led to significantly lower rates of the plastic strain as a crucial value for the crack propagation.