排气消声器声学及阻力特性数值仿真研究

对某一轻型卡车所装配的消声器,利用声学软件SYSNOISE对消声器声学性能进行数值仿真计算;利用计算流体动力学软件FLUENT对消声器的阻力特性进行数值仿真计算。模拟结果清楚地反映了消声器内的流场和声场的情况,结果表明数值方法能准确的模拟排气消声器的性能。通过仿真模拟,综合考虑消声器内部的声学性能和空气动力性能,表明运用数值方法预测排气消声器的阻力及声学性能在工程中是有效的,为消声器的改进设计和优化设计提供了依据。     

往复式压缩机吸气消声器的设计与优化

传统内插式吸气消声器腔室之间密封性差,影响消声器消声性能和阻力特性,为解决这一问题,设计一种新结构吸气消声器,通过初步实验对比,证明新吸气消声器腔室密封性好,且具有较好的声学性能和阻力特性,可使压缩机声功率级降低1.87 dB,制冷量提高7.4 W,性能系数提高0.016。为进一步提高新消声器的消声性能,利用声学分析软件LMS Virtual. Lab 进行声学仿真模拟,分析其引流管长度、引流管通流截面宽度、扩张孔位置和出口内插管长度等内部结构参数对传递损失的影响,优化内部结构参数。最终,压缩机声功率级降低2.51 dB,制冷量提高5.63W,性能系数提高0.015。     

往复式压缩机吸气消声器的设计与优化

传统内插式吸气消声器腔室之间密封性差，影响消声器消声性能和阻力特性，为解决这一问题，设计一种新结构吸气消声器，通过初步实验对比，证明新吸气消声器腔室密封性好，且具有较好的声学性能和阻力特性，可使压缩机声功率级降低1.87 dB，制冷量提高7.4 W，性能系数提高0.016。为进一步提高新消声器的消声性能，利用声学分析软件LMS Virtual. Lab 进行声学仿真模拟，分析其引流管长度、引流管通流截面宽度、扩张孔位置和出口内插管长度等内部结构参数对传递损失的影响，优化内部结构参数。最终，压缩机声功率级降低2.51 dB，制冷量提高5.63W，性能系数提高0.015。     

冰箱压缩机消声器声学特性的数值分析

分析全封闭往复活塞冰箱压缩机的消声器消声性能。利用软件建立不同结构形状进气消声器的有限元模型,通过导入声学软件进行计算,获得一腔室,两腔室消声器和复杂形状消声器内部声场的声压分布及传递损失。分析结构参数对消声性能的影响。     

消声器中频声学性能的计算测量方法

传统的消声器声学性能计算和实验测量都是在消声器进出口管道作为平面波声场的条件下进行,当进出口管道内出现有高阶模态激发的三维声场时,这些计算方法和实验测量方法就不再适用。由此,采用消声器进出口管道内加径向隔板的方法来计算消声器的声学性能,当原来管道声场中出现高阶模态时,仍然可以用平面波方法计算消声器的传递损失。应用该方法对进气滤清消声器进行传递损失数值计算,在原来进出口管道的平面波声场范围内,计算结果与传统方法计算结果均接近实验的测量结果,验证了该方法预测消声器声学性能的可行性。进而在所设计的消声器中频声学性能实验测试台架上,用声波分解法对阻性消声器进行传递损失测试,实验测量结果和有限元仿真结果也吻合良好。     

复杂结构消声器消声特性的数值分析及结构优化

由于复杂结构消声器的内部声场比较复杂，平面波理论无法准确预测其分布，为了计算复杂结构消声器的消声特性，并进一步提高消声器的声学性能，在基本假设的前提下，合理处理进出口及壁面的边界条件。建立消声器内部声场的三维有限元模型，计算消声器的传递损失（TL）。然后，分析了不同的结构参数（隔板位置、内插管位置、进口管位置）对消声器的传递损失的影响，并优化了消声器的结构参数，有效地提高了消声器的消声性能，使得压缩机整机噪声降低了3．2dB，验证了该分析方法的可行性，为复杂结构消声器的设计提供了参考依据。     

装载机消声器的消声性能的仿真计算与分析

采用三维声学有限元法研究消声器的进出气口轴向角度对消声器声学性能的影响规律。结果表明,在中低频段,轴向角度对消声器传递损失影响很大,当轴向角度为60度时,对传递损失的影响最为显著;改进后的消声器改善了原消声器的消声性能。由于消声器进出气口轴向角度对消声性能的影响,这为消声器的设计提供了借鉴。     

抗性消声器声学性能分析与结构优化

针对某抗性消声器消声量不足的问题,采用Virtual. Lab声学有限元AML自动匹配边界条件方法进行声学分析,得到消声器传递损失频域分布。利用数值分析方法模拟计算消声器内部流场,分析消声器消声效果和2次噪声产生原因。在控制一定压力损失的前提下,优化消声器内部结构,达到提高消声器消声性能的优化目标,为消声器声学性能和空气动力学性能研究提供一种可行的数值分析方法。     

基于计算流体动力学的内燃机排气消声器声学特性仿真

用计算流体动力学方法对消声器的声学特性进行了仿真计算,并将计算结果和有限元方法计算结果及实验测试结果进行了对比.结果表明,计算流体动力学方法在计算消声器声学特性时,能够考虑声场中流场耗散效应的影响,在对结构较为复杂的消声器进行仿真时具有有限元方法所不具备的优势.在此基础上进一步计算了流速对消声器声学特性的影响,计算结果表明,在流速影响下整个频率范围内消声量均有所降低,且消声频率向高频方向发展.     

电冰箱压缩机吸气消声器流动与声学性能分析

分别对电冰箱压缩机半直接吸气消声器和直接吸气消声器的流场和声场进行数值模拟,对其流动特性和声学性能进行对比分析。研究成果可用于预测电冰箱压缩机消声器的综合性能,为消声器的设计、选型及结构优化提供理论依据。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。