改进的基于附加已知质量的模型修正方法

基于附加已知质量块的有限元模型修正方法是一种新的富有实用前景的模型修正算法，但是当测试模态数目太少时，这一方法的修正精度不能满足工程要求。然而在工程实际中，受技术条件的制约，测试模态数目有限是不可避免的。为了提高测试模态数目不足情况下算法的修正精度，提出了一些改进措施。对于满秩情况，应用所提出的迭代算法，可以有效地逐次提高修正精度，但是缺点在于试验成本高。基于工程实际中有限元模型误差分布局部性的特点，提出利用误差局部性进行修正方程的约简。结果表明，改进后的方法对于实现模型局部误差修正，具有良好的精度，并且可操作性好。此外还分析了修正方程非满秩产生的原因，提出应用缩聚的方法来保证修正方程的满秩。最后以一个长直机翼结构为例，进行了算法验证，结果表明局部修正算法精度高，满足应用需求。     

带附加气室空气悬架剪式座椅振动特性试验研究

基于HY-Z04型剪式座椅,以SK37-6型膜式空气弹簧作为弹性元件,构建了带附加气室空气悬架座椅振动试验系统。试验研究了节流孔开度、簧上质量及激励频率等因素对座椅振动特性的影响规律,研究结果表明,座椅悬架的固有频率随节流孔的增大而减小;节流孔产生的阻尼随节流孔的增大先变大后变小;当激励频率较低时,节流孔开度对座椅加速度的影响不大,当激励频率高于某值后,节流孔开度越大,对应的加速度均方根值越小;节流孔对加速度均方根值的影响具有明显的非线性。     

考虑流体附加质量的输流管道振动特性分析

针对管内流体激励(flow-induced vibrations,FIV)引起的结构振动问题,考虑单向流固耦合作用,通过引入附加质量分析内流流速对结构振动特性的影响.以两端固定支撑输流直管作为研究对象,利用数值方法模拟不同流速下管内的流动状态,获取流体压力系数、湍动能及管道结构位移响应.基于单向耦合振动机理,建立管道流...     

周期附加质量充液管路减振特性研究

以充液管路振动控制为目标研究周期附加质量的新型声子晶体管路振动传播特性。利用传递矩阵法建立周期附加质量充液管路带隙理论模型,深入分析影响带隙特性关键因素,包括附加质量尺寸、安装位置及材料阻尼。数值计算表明,声子晶体管路存在低频振动带隙可有效抑制振动传播,且设计方法简单、操作方便、减振效果明显,以期为充液管路减振设计提供新思路。     

结构在静流场中振动时的附加质量分布

结构在静流场中振动时,附加质量的分布形式对其振动特性有非常大的影响,尤其是对较为轻薄的结构,但截至目前,对附加质量显式分布的研究甚少。基于三维问题的边界元法,在合适的Dirichlet及Neumann条件下,提出了一种较简单的方法,可求解结构以任意给定模式在不可压缩单相静流场中振动时的附加质量显式分布。数值计算表明,该方法的求解结果与理论解及实验结果吻合良好,可较好地应用于复杂形状结构在有界或无界静流场中振动时的附加质量分布计算。     

弹体落水过程中附加质量变化影响研究

基于势流理论,建立弹体边界元模型,研究了弹体刚体运动、弹性振动引起的附加质量随弹体浸湿长度的变化规律,以及砰击力的变化.并在结构多自由度系统运动方程中计及附加质量的变化影响,得到附加质量变化不仅引起系统质量阵变化,还将影响阻尼系数阵.     

三维结构振动诱导流场附加质量的数值分析

在流体环境中,结构的振动会诱导周边的流体一起运动从而产生附加质量的影响,这也是结构工程中大跨度柔性结构耦合风振理论模型的重要组成部分。根据势流理论,采用奇点配置法利用空间点源(汇)及偶极子基本解推导了三维情形下结构振动诱导流场附加质量的计算式。数值分析结果表明:该方法能有效地计算复杂结构边界条件下流场的附加质量;其中索穹顶结构的数值算例也表明,在这类大跨度柔性结构的风振分析中附加质量的影响是很大的,必须引起足够的重视。     

具有中间支承的薄膜固有振动分析

把具有中间支承的薄膜固有振动转化为多个集中载荷作用下的薄膜强迫振动，然后采用Laplace变换求得了具有中间支承薄膜固有振动振型的解析解，并通过实例计算说明了该方法的应用。     

PVC薄膜质量的研究

文中介绍了不同型号聚氯乙烯的力学性能、耐老化性能的差别，及其对薄膜制品质量造成的影响。     

连续变密度圆形和环形薄膜的轴对称振动

本文采用打靶法数值分析了质量密度沿径向连续变化的圆形和环形薄膜的轴对称横向自由振动。针对密度以半径的二次函数变化的情形,计算了系统的一阶大有频率,并与文献（７）中分别用Ｄｉｆｆｅｒｅｎｔｉａｌ Ｑｕａｄｒａｔｕｒｅ Ｍｅｔｈｏｄ和Ｒａｙｌｅｉｇｈ’ｓ Ｑｕｏｔｉｅｎｔ Ｍｅｔｈｏｄ所得结果进行了比较,显示出本文结果的精确性和方法的优越性。然后,数值求解了密度沿半径以指数函数变化的非均匀圆形和环形膜     

Experimental investigation of oil retention in air conditioning systems

In air conditioning and refrigeration systems a small amount of oil is carried with the refrigerant and is retained in the system components. Oil retention characteristics in the condenser, evaporator, liquid and suction lines were measured and are presented and discussed here. Refrigerants R22, R410A, and R134a with miscible and non-miscible lubricants were considered to investigate oil retention physics in the widest possible range of transport properties. A parametric analysis in the suction line showed that oil retention depends on the oil mass fraction, vapor refrigerant mass flux, mixture viscosity ratio and orientation of the pipe. In the suction line, an increase in mixture viscosity of about 55% caused a rise in oil retention in the range of 50%, depending on the oil mass fraction. Oil retention in the upward vertical suction line is about 50% higher than in the horizontal line at similar conditions.     

A hybrid solar air conditioner: Experimental investigation

The removal of moisture from the supply air using conventional air conditioners (A/C) represents a considerable portion of the air conditioning load in hot and humid regions. Desiccant assisted A/Cs are used to address this issue. In this work, the performance of a hybrid A/C, which consists of a desiccant wheel, an enthalpy wheel, and a vapor compression cycle (VCC), is investigated experimentally. The effect of the process air stream's temperature and humidity, and the effect of the ventilation rate on the hybrid A/C performance are investigated. The experimental results show that the hybrid A/C is more effective than the standalone VCC in maintaining the indoor conditions within the comfort zone. The simulation of the complete hybrid solar A/C that uses a concentrating photovoltaic/thermal collector shows that a system coefficient of performance higher than unity is possible.     

Experimental investigation of air cooling of a conductive calorimeter

The spatial inhomogeneity of thermal fluxes on the surface of the heat-dissipation unit of a KTS-2 calorimeter and a system consisting of an additional thermistor and stepped turbulizers for equalization and intensification of the heat transfer are investigated experimentally. Institute of Technical Thermophysics of the National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 3, pp. 409–411, May–June, 1999.     

Experimental investigation of mass recovery adsorption refrigeration cycle

The study investigates the performance of silica gel–water adsorption refrigeration cycle with mass recovery process by experimental prototype machine. In an adsorption refrigeration cycle, the pressures in adsorber and desorber are different. The mass recovery cycle utilizes the pressure difference to enhance the refrigerant mass circulation. Moreover, novel cycle was proposed for improvement of cooling output. In our previous study, simulation analysis shows that mass recovery cycle has the advantage over conventional single-stage. Experiments with prototype machine were conducted to investigate the performance improvement of mass recovery cycle in the present paper. Specific cooling power (SCP) and coefficient of performance (COP) were calculated with experimental data to analyze the influences of operating conditions. The proposed cycle was compared with the single-stage cycle in terms of SCP and COP. The results show that SCP of mass recovery cycle is superior to that of conventional cycle and mass recovery cycle is effective with low temperature heat source.     

蒸发式冷凝器传热传质性能研究

建立单级压缩制冷循环蒸发式冷凝器实验台,研究逆流状态下,迎面风速和喷淋密度对传热传质的性能影响。通过调节水泵和风机的频率改变风水量的配比关系,得出蒸发式冷凝器的传热传质性能变化情况。分析数据得出,当迎面风速为2.96 m/s,喷淋密度为0.057 kg/(m·s)时,总传热系数达最优值628 W/(m2·K),传质系数随风速的增大而增大,随喷淋密度的变化不明显。此外,通过实验数据回归得到传质系数计算关联式。     

螺杆式空气源热泵机组压缩机油位试验研究

分析压缩机吸气回液、外置油分离器油分离效率对螺杆式空气源热泵机组压缩机油位的影响,提出改进翅片换热器分液、优化气液分离器结构、改善油分离器分离方式等改进措施,并对螺杆式空气源冷（热）水机组进行试验。结果表明,所提改进措施不仅能够提高压缩机运行过程中的油位,而且能够提高机组运行稳定性。     

Experimental investigation on air bubble dynamics during fine powder discharge in a silo

An unstable discharge rate occurs during dry fine powder discharge from a silo due to significant two–phase solid/gas interactions that occur in powder flows. In addition, the air bubble phenomenon may occur in a silo during fine powder discharge. The bubble dynamics seriously influence the fine powder discharge stability in the silo. Therefore, for some industrial applications with silo discharge of fine material, it is important to understand it. In this study, we experimentally investigate the effect of air bubbles on fine powder discharge behavior, including the discharge mass flow rate and variation in pressure inside the silo. An initial collapse of the powder bed in the silo is observed at the beginning of the discharge process, causing the pressure to change rapidly. Moreover, the dependence of the bubble size, bubble rising velocity, number of bubbles, and frequency of bubble generation on the size of the fine powder are analyzed in detail. The air–loss index for different particle sizes is calculated to investigate the proportion of the air flowing into the silo that disperses into the voids between the powders and does not become part of a bubble. The bubble properties in the experimental cases that use different particle sizes are consistent with the Geldart particle classification of the used powders. The results of this study successfully illustrate the bubble dynamics and the discharge behavior of fine powder.