一种变温环境下水听器灵敏度校准系统的设计

针对缺少在变温条件下校准水听器灵敏度方法的问题,设计了一套基于动圈换能器声管的变温水听器灵敏度校准系统。建立模型分析声管内的声压分布,并计算了变温后对灵敏度校准结果的补偿量;利用Comsol仿真不同声管厚度对声场的影响,分析了底面非均匀振动和不同尺寸的水听器对校准结果的影响,确定了合适的声管尺寸和测量方法。分别在常温与变温条件下对不同尺寸的水听器进行校准并将校准结果与标准值比较。结果表明,此系统在常温下的校准结果与标准值的偏差低于0.5 dB,变温条件下的测量结果与标准值偏差低于0.6 dB,整体系统的扩展不确定度约为1.0 dB。     

高纯氢中痕量杂质变温浓缩装置及方法

为解决高纯氢中痕量杂质的分析问题,对变温浓缩样品气前处理装置进行探讨,介绍了装置的工作原理、气路设计和部件选择等;研究装置的浓缩方法,确定样品气流量、浓缩体积、脱附温度等操作条件,并对方法的可靠性做了评价。     

动态质量法燃油流量标准装置的研究及不确定度分析

针对某动态质量法液体流量标准装置进行研究,详细介绍了其工作原理,根据结构特点,分析了压力及流量调节、气动系统和称重系统等关键技术;介绍了后期技术改造,变温系统、自动化改造;最后进行了不确定度分析。     

直冷冰箱变温控制技术

本文提出了一种实现直冷冰箱变温控制的方法 ,并依据该方法制作了直冷变温冰箱。该冰箱的变温室温度可以在 5℃到 - 18℃之间调节 ,使变温室可以作为冷藏室、冰温室、微冻室和冷冻室使用。变温室作为冷藏室、冷冻室等不同功能间室使用时 ,对直冷变温冰箱的储藏温度和耗电量也进行了测试 ,测试结果表明该方法是可行的     

低品位热能驱动的热化学吸附变温器冷热复合储能研究

本文介绍了一种基于热化学吸附变温器原理的冷热复合储能技术,在此基础上采用热化学吸附工质对NaBr-NH3搭建了低品位热能驱动的热化学吸附储能实验测试系统,对其变温吸附储热和吸附储冷性能进行了理论及实验研究。研究结果表明:变温吸附储热模式时,在变温15℃的工况下储热密度为258kJ/kg;吸附储冷模式时,在制冷温度7℃的工况下储冷密度可达525kJ/kg,COP为0.3,SCP可达175W/kg,实验数据分析表明热化学吸附变温器在低品位热能高效回收利用和能量储存方面具有很好的发展潜力,可同时实现热量和冷量的复合储存。     

全温润滑油流量标准装置稳定性测试

此流量标准装置具有全变温的特性,变温范围为-35℃-150℃。本文对装置原理和特性进行了介绍,根据其特性制定了稳定性测试的方法并通过实际测试确定了装置稳定性。     

变温环境下精密调谐机构频率补偿原理的有限元分析

对精密调谐机构进行了精细的有限元建模,采用等效建模方法对机构的连接弹簧、调谐螺钉、配合关系进行了处理,就精密调谐机构在0～+65 ℃的变温环境下进行了计算,分析了调谐机构在高温环境下的频率补偿原理。实际的测试结果表明了计算分析的正确性。     

Parafilm的结构及热稳定性研究

目的采用红外光谱法研究Parafilm的分子结构。方法采用变温傅里叶变换衰减全反射红外光谱(ATR-FTIR)技术,分别研究Parafilm的一维变温光谱、二阶导数变温光谱、四阶导数变温光谱及去卷积变温光谱。结果 Parafilm主要存在着CH_3不对称伸缩振动模式、CH_2不对称伸缩振动模式、CH_2对称伸缩振动模式、CH_2变角振动模式、CH_3不对称变角振动模式、CH_3对称变角振动模式、C—C骨架伸缩振动模式和CH_2面内摇摆振动模式等8种红外吸收模式,最终确定Parafilm的主要分子结构为聚异丁烯。采用变温ATR-FTIR技术(293~393 K)进一步开展Parafilm热稳定性研究,研究发现Parafilm的热稳定较差,而其临界使用温度为313 K。结论该研究拓展了变温ATR-FTIR技术在高分子包装材料的结构及热稳定性方面的研究范围。     

多级立式大温差吸收式变温器性能分析

对现有吸收式换热器存在占地面积大、成本高、一次侧热水回水温度高等问题的原因进行了分析,指出问题根源在于吸收机内部存在大量“三角形”传热过程。介绍了全新的多级立式大温差发生-冷凝和蒸发-吸收基本单元,分析了其不仅能消除原吸收式换热器内不匹配的传热现象,而且做到结构紧凑的原理。由以上基本单元构建了新型吸收式换热器,称之为多级立式大温差吸收式变温器。建立了吸收式变温器的模拟分析模型,将其性能与传统单级吸收式换热器进行了比较。结果表明：吸收式变温器可制取的最低一次侧热水回水温度更低,从26℃降至20℃以下;总传热面积更小,当一次侧回水温度为26℃时,吸收式变温器的总KA（传热系数K与传热面积A的乘积）比单级吸收式换热器减小25%~32%,与此同时溶液泵总功率比单级吸收式换热器高出19%~48%,并没有显著增加。吸收式变温器相对于单级吸收式换热器具有明显性能优势。     

变温结晶法制备高分散性纳米氢氧化镁

以轻烧粉与氯化铵反应得到的精制氯化镁溶液为原料,氨气为沉淀剂,通过改变反应温度控制反应体系过饱和度,变温反应制备出高分散纳米氢氧化镁,并利用扫描电镜(SEM)、X射线衍射(XRD)和激光粒度分布仪对产品进行了表征。实验研究了变温反应与恒温反应产品形貌和粒径的区别,结合液相体系中OH-浓度随反应温度的变化过程,分析讨论了变温法制备高分散纳米氢氧化镁的机理。     

空调系统变水温调节的特性实验及节能分析

针对中、小型中央空调系统，根据空调系统大多数时间处于部分负荷下运行的特点，通过实验，分析了变水温调节时冷水机组和空调系统的运行特性：以实验结果为依据，对中央空调系统的节能潜力进行了分析。     

基于DEA的评价模型及其输入输出指标确定

产品包装方案的评价是一个多目标规划问题.应用数据包络分析原理(DEA),通过对包装设计方案的横向比较,构建产品包装方案的评价模型.采用两步法对评价模型求解,首先对输入变量进行比例收缩(或对输出变量进行比例扩张),求出各方案的相对效率;然后计算各方案每项指标的松弛变量.结合包装行业的特点,将越小越好的指标作为输入指标、越大越好的指标作为输出指标,建立了相应的输入输出指标体系.     

Numerical comparison of some explicit time integration schemes used in DEM,FEM/DEM and molecular dynamics

Discontinua simulations are becoming an important part of Computational Mechanics to the extent that Computational Mechanics of Discontinua is becoming a separate subdiscipline of Computational Mechanics. Among the most widely used methods of Computational Mechanics of Discontinua are Discrete Element Methods, Molecular Dynamics Methods, Combined Finite‐Discrete Element Methods, DDA, Manifold Methods, etc. The common feature of all these methods is time discretization of the governing equations and the resulting mostly explicit time integration schemes. A wide range of time integration schemes is available in the literature. In this paper a comparative study of some of the most commonly used explicit time integration schemes is made in terms of accuracy, stability and CPU efficiency. The study has been performed using numerical experiments based on a one degree of freedom mass‐spring system. The results are presented as charts that can be used when deciding which scheme to use for a particular discontinua problem. Copyright © 2004 John Wiley & Sons, Ltd.     

On comparing finite difference schemes applied to a nonlinear multi-region heat and mass transfer problem

 A three-time-level scheme is employed to obtain numerical solutions of heat and mass transfer potentials for the nonlinear Luikov system. Relative errors are examined when the numerical solutions are compared to the analytical solutions for a single layer linear problem using different finite difference techniques. As a final example, comparisons also are made when the numerical schemes are used to solve a two-layer multi-region nonlinear approach, considering that the thermal conductivity and mass conductivity of the material are dependent on temperature and moisture transfer potential respectively. Received 6 September 2000     

An enthalpy formulation based on an arbitrarily deforming mesh for solution of the Stefan problem

Traditionally schemes for dealing with the Stefan phase change problem are separated into fixed grif or front tracking (deforming grid) schemes. A standard fixed grid scheme is to use an enthalpy formulation and track the movement of the phase front via a liquid fraction variable. In this paper, an enthalpy formulation is applied on a continuously deforming finite element grid. This approach results in a general numerical scheme that incorporates both front tracking and fixed grid schemes. It is shown how on appropriate setting of the grid velocity a fixed or deforming grid solution can be generated from the general scheme. In addition an approximate front tracking scheme is developed which can produce accurate non-oscillatory predictions at a computational cost close to an efficient fixed grid scheme. The versatility of the general scheme and the approximate front tracking scheme are demonstrated on solution of a number of Stefan problems in both one and two dimensions.     

Computational efficiency of the continuous cell-to-cell mapping technique as a function of integration schemes

The continuous cell-to-cell mapping technique (CCCMT) is a recently proposed Markovian approach which can be used for the dynamic reliability and safety analysis of process control systems, as well as for the global analysis of nonlinear dynamic systems in general. A parametric study is performed on the computational efficiency of CCCMT as a function of various integration schemes. The results show that a variable stepsize scheme is desirable with a sufficient required precision. Among the integration schemes considered, a fourth order Runge-Kutta scheme seems to be preferable for short term simulations and the mid-point implicit scheme seems to be preferable for long term simulations or to obtain the steady-state system behavior.     

分户计量式集中供暖换热机组控制方案研究

简要介绍了集中供暖换热机组的基本原理,结合实际应用,详细阐述了分户计量式集中供暖换热机组的多种控制方案,包括热水温度控制、热水流量控制(工频控制、温差变频控制、压差变频控制)和热水系统压力(补水)控制,并对相关控制方案进行了对比分析,最后给出了相应的结论.     

New centralised adaptive load-shedding algorithms to mitigate power system blackouts

Conventional under-frequency load-shedding scheme is designed to retrieve the balance of generation and consumption following a disturbance. In the conventional load-shedding method, frequency settings, timedelay settings and the amount of load to be shed in each step are constant values. The loads to be shed by this scheme are also constant load feeders and not selected adaptively. This constant non-adaptive load-shedding algorithm is not the most efficient scheme for all power system disturbances. Application of centralised loadshedding algorithms could enhance adaptability of the load-shedding schemes. Two centralised adaptive loadshedding algorithms are proposed. The first algorithm is response-based and the second one is a combination of event-based and response-based methods. The proposed methods are capable of preserving power system instability even for large disturbances and combinational events. They use both frequency and voltage variables to select appropriate amount of load shedding. Parameters of the suggested schemes are also selected adaptively based on the magnitude of the disturbance. Performances of the proposed algorithms are evaluated by the application of the adaptive algorithms to the distributed and dynamic simulated model of a real power system. Obtained simulation results confirm that by using these algorithms various power system blackouts may be prevented.     

对流占优扩散方程的改进特征差分算法

将特征线方法和有限差分方法相结合，给出了一种求解对流占优扩散方程数值解的新的隐式特征差分格式，并研究了新算法的收敛性，新算法的优点是适应性强，特别适用于变系数方程，数值试验的结果表明在消除数值震荡方面更有效。     

Robust audio watermarking using frequency-selective spread spectrum

A novel audio watermarking scheme based on frequency-selective spread spectrum (FSSS) technique is presented. Unlike most of the existing spread spectrum (SS) watermarking schemes that use the entire audible frequency range for watermark embedding, the proposed scheme randomly selects subband(s) signal(s) of the host audio signal for watermark embedding. The proposed FSSS scheme provides a natural mechanism to exploit the band-dependent frequency-masking characteristics of the human auditory system to ensure the fidelity of the host audio signal and the robustness of the embedded information. Key attributes of the proposed scheme include reduced host interference in watermark detection, better fidelity, secure embedding and improved multiple watermark embedding capability. To detect the embedded watermark, two blind watermark detection methods are examined, one based on normalised correlation and the other based on estimation correlation. Extensive simulation results are presented to analyse the performance of the proposed scheme for various signal manipulations and standard benchmark attacks. A comparison with the existing fullband SS-based schemes is also provided to show the improved performance of the proposed scheme.