空压机并网运行自稳压控制系统改造

针对某厂空压机并网改造后运行效果不理想的问题,介绍了空压机并网运行自稳压控制系统的二次改造方案。该方案将2台空压机储气罐串联,既增大了储气罐的容量,又保证了输出的压缩空气流量和压力的可靠性、稳定性;可预先设定2台空压机的循环运行间隔时间;当一台空压机故障时,另一台空压机可自动投入工作;设有急停开关、2台空压机的启动及停止开关,可直接控制2台空压机的启动或停止运行。实际应用表明,二次改造后的空压机组运行稳定、正常。     

基于异形梁模型的海洋柔性管缆防弯器数值模拟

为防止海洋柔性管缆在自重和环境载荷作用下的局部曲率过大而发生结构失效,在连接部位安装防弯器增加管缆弯曲刚度,并使管缆曲率分布均匀.分析防弯器力学性能和在位特点,阐述计算难点和几种数值建模方法的可行性与效果,并具体讨论用梁单元建立防弯器异形梁有限元模型的优势.利用平面异形梁单元特点,采用等效弯曲刚度进行防弯器结构分析,从而形成一套简洁高效的数值分析方法.通过数值算例评价该计算方法的适用性.     

Numerical simulation of combined screw compressor–expander machines for use in high pressure refrigeration systems

Recent interest in natural refrigerants has created a new impetus for studies of CO₂ as a working fluid in vapour compression systems for refrigeration and air conditioning. Two major drawbacks to its use are the very high pressure differences required across the compressor and the large efficiency losses associated with the throttling process in the refrigeration cycle. It is shown how these disadvantages can be minimised by the use of a screw machine both to compress the gas and use the expansion process to recover power. Both these functions can be performed simultaneously, using only one pair of rotors, in a configuration that partially balances out the forces induced by the pressure difference and hence, reduces the bearing loads to an acceptable level. A further feature is the use of rotors, which seal on both contacting surfaces so that the same profile may be used for the expander and the compressor sections. This enables the rotors performing both these functions to be machined or ground in the same cutting operation and then separated by machining a parting slot in them. Computational Continuum Mechanics comprising both, fluid flow and structural analysis is used in this paper for the investigation of fluid-solid interaction in such machines.     

轿车乘员舱内气流对气动阻力影响的数值模拟

为揭示轿车侧窗开启程度和乘员舱内布置对气动阻力的影响规律,建立1∶1阶背式英国汽车研究协会(Motor Industry Research Association,MIRA)标准模型;基于FLUENT,在30 m/s风速下采用可实现k-ε湍流模型对不同侧窗开度的模型进行三维稳态数值模拟,得到气动阻力因数随侧窗开启程度的增大而增大的变化趋势.在侧窗全开时,改变舱内布置,得到气动阻力因数随假人个数的变化规律;对比不同情况下模型的流场分布发现,当考虑乘员舱内气流时,气动阻力的大小不仅与进气量有关,而且受舱内流场分布的影响.     

浅埋厚煤层地表漏风对采空区煤自燃影响数值模拟研究

西部矿区浅埋厚煤层通常采用抽出式通风方式,地表漏风不仅使风流紊乱,而且其中的O 2贯穿采空区,与采空区遗煤共同作用使其氧化,从而发生煤自燃,并且产生的CO等有害气体超标,严重影响矿井的正常开采。目前一般采用现场实测、理论分析及实验研究方法对地面漏风引起的采空区内煤自燃的气体浓度场和温度场等进行研究,然而地表裂隙漏风自然发火实验复杂程度较高,理论分析及实验研究方法难以从三维角度认识地表漏风对采空区内煤自燃的影响规律。针对上述问题,根据我国西北矿区埋深浅、煤层厚等特点,建立三维数值计算模型,采用数值模拟与现场实测相结合的方法研究了浅埋厚煤层条件下导气裂隙采空区“三带”分布情况及不同工况下采空区O 2浓度场、CO浓度场、温度场、压力场等的分布规律,并采用ZD5煤矿火灾多参数监测装置进行现场验证。结果表明:采空区内“三带”分布规律和O 2浓度场分布受地表漏风影响明显,采空区顶部O 2容易聚集,改变了采空区内气体流场分布规律,采空区内高体积分数O 2(体积分数为18%~23%)聚集范围为沿采空区走向0~270 m、沿采空区竖直方向3~20 m,特别是在沿采空区走向0~80 m、沿采空区竖直方向3~8 m空间O 2充足、有一定遗煤且热量不容易散失,该区域煤自然发火危险程度较高;采空区内回风隅角压力最小,为-10 Pa,回风口压力最低,进风口压力最大,沿倾向、竖直方向及走向压力均逐渐增大;采空区内温度和CO分布规律类似,在采空区底部受顶部漏风影响很小,主要受工作面进风隅角影响,热量积聚和CO聚集规律与不漏风时基本一致,而从采空区中部开始,温度和CO主要受顶部漏风影响,在中部区域温度和CO均呈现“O”形圈分布,采空区顶部,温度和CO在每个断裂带与采空区交接处达到极大值,并向两侧递减,在最深部的断裂带与采空区交接处出现最大值。     

Numerical simulation on the effect of welding parameters on welding residual stresses in T92/S30432 dissimilar welded pipe

Dissimilar welded joints are commonly used in fossil power plants to connect martensitic steel components and austenitic stainless steel piping systems. The integrity for such welded structures is depended on residual stresses induced by manufacturing process. In this paper, the characteristics of residual stresses on the dissimilar welded pipe between T92 steel and S30432 steel were investigated using finite element method. Moreover, the effects of heat input, groove shape and layer number on the residual stress distribution were studied to find the approach to reduce the residual stress. The numerical results revealed that the hoop and axial stress in heat affected zone (HAZ) of T92 steel side of the dissimilar welded joint had sharp gradients. By decreasing the groove angle, the peak values of the hoop and axial stress on T92 steel side were reduced greatly while the peak values in welded metal and HAZ of S30432 steel side differed little. Furthermore, more layer number and less heat input decreased the peak value of the tensile residual stress on welded metal and S30432 steel side, but had little effect on the residual stress in T92 steel side.