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101.
102.
针对通过噪声的空滤器声学特性研究与改进 总被引:1,自引:0,他引:1
通过实验方法分析研究了一种中型乘用车通过噪声的特性,比较该车进、排气两侧通过噪声的声级和频谱特性,确定了进气噪声对车辆进气侧通过噪声的重要影响.为了解决该车进气噪声的问题从而达到整车降噪的目的,应用实验与边界元法计算两种手段,对该车空滤器的频率响应特性进行了研究.研究发现空滤器声系统的第一阶声固有频率与进气噪声基频相耦合是造成该车辆进气侧通过噪声高于排气侧的重要原因.基于这一研究结果,在计算和实验的基础上利用Helmholtz共振腔对空滤器的声学特性进行了改进,改进后的空滤器对降低车辆进气侧通过噪声有很好的作用. 相似文献
103.
为了提高感应电机定子绕组故障诊断的准确性,提出了一种基于Hilbert-Huang变换(HHT)的故障诊断新方法.选取断电后零序电压的基波分量作为定子故障特征,可有效避免电源不平衡和负荷波动的影响,直接反映电机定子的不对称度.利用Hilbert-Huang变换中经验模态分解(EMD)方法对断电后的零序电压进行了分解,提取出基波分量,通过计算其均方根值可以诊断出电机定子绕组故障.在一台4 kW的感应电机上进行的实验证明了该方法的可行性和有效性. 相似文献
104.
针对传统双馈风电机组(DFIG)低电压穿越(LVRT)能力不足问题,提出了储能型双馈风电场联合STATCOM的无功协调控制。该控制是在网侧变流器(GSC)原有的模型上将超级电容经隔离型DC/DC变换器并联到风机直流侧,以此吸收故障期间直流侧产生的不平衡功率;在发生低电压故障时,根据超级电容投入情况,对两侧变流器和并联在风机出口母线上的STATCOM进行无功协调控制来支撑电网电压;同时超级电容储能装置采用电压电流双闭环控制,满足了系统稳定性和经济性的要求。仿真结果表明:该方法应用在风电并网系统中可以使DFIG的LVRT能力得到极大的提升。 相似文献
105.
为了提高G102Cr18Mo高碳不锈轴承钢的洁净度、细化碳化物组织,采用真空感应熔炼、两次真空自耗重熔、大锻压比锻造的工艺路线,研究了真空处理及大锻压比锻造对化学成分、气体含量、夹杂物分布、二次枝晶间距及碳化物颗粒度的影响。研究结果表明,真空感应熔炼过程(VIM)中,随着铝含量的增加,碳的脱氧能力大幅降低,即使铝质量分数为0.003%也对碳的脱氧能力有明显的阻碍作用;真空自耗重熔过程(VAR)由于高的真空度、高的重熔温度等热力学条件以及反应动力学条件的改善,氧含量显著降低,第一次自耗重熔后氧质量分数从0.001 49%降低至0.000 57%,降低了61.7%,第二次自耗重熔后氧质量分数降低至0.000 50%。真空感应熔炼、真空自耗重熔过程,夹杂物的成分变化不大,主要以Al-Si夹杂为主,其次为Al2O3夹杂,再次为MnS夹杂、Mg-Al-Ca、Mg/Ca-Al夹杂。双真空冶炼后,钢中夹杂物主要为0~5 μm的细小夹杂物,未发现大于20 μm的夹杂,含有少量10~20 μm的夹杂,钢的洁净度大幅度提高。在真空自耗锭横断面上,从边部向芯部二次枝晶的形貌变化不大,二次枝晶间距逐渐增大,但是变化趋势缓慢,二次枝晶间距为85~95 μm,这主要得益于低的自耗重熔速度。对真空自耗锭进行大变形处理,最终锻造成40 mm的圆棒,碳化物颗粒的最大尺寸不大于20 μm,平均尺寸为15 μm,且没有碳化物聚集的现象。低的自耗重熔速度和大锻压比锻造是碳化物细化的关键。 相似文献
106.
107.
在高频感应钎焊的过程中,要获得良好的钎焊接头,必须要根据接头材料的物理性能选择合适频率的高频电源,采用计算机数值分析手段建立了感应加热电源及其频率范围的选择数值分析模型。研究表明,数值解析法可以作为高频感应钎焊感应加热设备设计的重要方法。在对高频电源电流频率等参数的选择时,利用数值解析模型所得到的解析近似解进行频率选择比传统经验公式更精确。因为后者由平面电磁波在导电媒质中的传播特性导出,更适合于板状结构感应加热时频率的选择。而对于管状或其它复杂形状,利用数值解析解可以较好地对高频电源的频率进行优化选择。 相似文献
108.
Finite-element simulation of moving induction heat treatment 总被引:1,自引:0,他引:1
K. F. Wang S. Chandrasekar H. T. Y. Yang 《Journal of Materials Engineering and Performance》1995,4(4):460-473
An efficient finite-element procedure with a remesh scheme has been developed for the analysis of the moving induction heat
treatment process, wherein relative motion occurs between the coil and the workpiece. In this procedure, the magnetic field
is first simulated by using an updated mesh that tracks the moving coil position; the moving heat source within the workpiece
material is derived from the magnetic field. The heat equation is then solved to obtain the temperature field created by the
heat source. The procedure has been applied to calculate the temperature distributions in 1080 carbon steel cylinders during
induction heating. The calculations have been validated by comparison with analytical solutions for the temperature distribution
obtained using Green’s function methods. Finally, the temperature, residual stress, and microstructure distributions in quenched
1080 steel cylinders have been obtained using the finite-element procedure. Quenching of the heated cylinders, by both a moving
cooling ring and a stationary liquid bath, has been analyzed. The finite-element procedure presented incorporates temperature-dependent
material properties, phase transformations occurring in the 1080 steel, the change in magnetic permeability of the 1080 steel
at the Curie temperature, and an elastoplastic stress model based on a mixed hardening rule. The simulation results demonstrate
that the finite-element procedure could be applied to a variety of moving induction heat treatment problems to determine the
residual stress and microstructure distributions in the heat-treated component. It also could be used in the design of process
parameters and coils. 相似文献
109.
110.
Soluble sugars are essential nutrients generally perceived as phagostimulants to most insects studied. However, tannins are known as digestibility reducers, hence deleterious to caterpillar development, and as deterrents as well. Previous work demonstrated that larvae of the polyphagous oblique-banded leafroller, Choristoneura rosaceana, performed better when reared on a control + 0.5% tannic acid diet than on the standard control diet and that larvae reared on a control + 5% glucose diet had slower development and reduced survival. This study was designed to elucidate the behavioral and neurophysiological components of the larval responses to tannic acid and glucose. C. rosaceana larvae were reared individually from the first to the sixth instar on one of four different artificial diets: (1) control; (2) control + 5% glucose; (3) control + 0.5% tannic acid; (4) control + 5% glucose + 0.5% tannic acid. After 14 days, larvae reared on the control + 5% glucose diet had not developed past the fourth instar, whereas a considerable proportion of larvae reared on the control + 0.5% tannic acid diet had already attained the pupal stage. Insects reared on the control or the control + 5% glucose + 0.5% tannic acid diet had intermediate development, with most larvae in the fifth instar. In addition, once the mid-sixth instar was reached, the feeding preferences to 25 and 300 mM glucose, 25 mM tannic acid, and 25 mM glucose + 25 mM tannic acid over water were assessed in two-choice tests. Feeding affected preference. Control-reared insects preferred feeding on treatments containing glucose and were not deterred by tannic acid. However, larvae that had been exposed to tannic acid during their development were deterred by tannic acid and their glucose discrimination was impaired. The sensitivity to glucose was also examined from neurophysiological recordings by stimulating the sugar-sensitive cell (cell 1) on the lateral styloconic sensillum of the maxillary galea with increasing concentrations of glucose (1, 10, 25, 50, 100, 200, 300, and 500 mM). We also determined whether tannic acid was phagostimulatory, since insects develop relatively quickly on a diet containing this compound, by testing 1 mM tannic acid, 1 mM tannic acid + 300 mM glucose, and 300 mM glucose on the lateral styloconic sensilla. The traces indicated that 1 mM tannic acid was not detected by any of the four chemosensory cells in these sensilla. The combination of tannic acid and glucose produced no spikes from the sugar-sensitive cell, whereas a prominent spike activity resulted with 300 mM glucose. We concluded that, although C. rosaceana larvae develop faster on a tannic acid diet, this compound is not a phagostimulant. The converse is true for glucose; i.e., it stimulates the sugar-sensitive cell in the lateral styloconica in a concentration-dependent fashion. Previous dietary experience changes the sensory and behavioral responses of C. rosaceana to glucose. Our findings imply that not all compounds that are phagostimulatory are necessarily beneficial to an insect's fitness. Therefore, developmental studies should be interpreted in conjunction with behavioral and physiological data. 相似文献