进气结构对扫气性能的影响机理研究

为探究多种进气结构对扫气性能的影响,基于进气口壁厚、进气口形状、进气口偏移量、进气口数量4种气口结构参数,开展正交试验。试验结果表明:直流扫气对置活塞二冲程柴油机的进气结构通过影响进气气流的旋流强度和流通阻力对综合性能产生影响;通过改变进气结构的进气倾角、斜面长度、斜面宽度对进气气流的旋流强度进行调整;通过改变进气结构的进气倾角、总气口接触面对流通阻力产生影响;改变进气旋流强度可以调整扫气性能,改变进气流通阻力可以抑制废气回流。研究发现进气口壁厚为调节对置活塞二冲程柴油机扫气性能的显著因素。

土壤草铵膦污染诱导赤子爱胜蚓蛋白质氧化损伤

为评价施用草铵膦(GLA)可能给土壤生态环境带来的潜在风险,将制备的GLA人工污染土壤[0(对照)、10、20、40、80 mg·kg^(-1)]于室内老化3个月后置入赤子爱胜蚓,培养30 d后研究蚯蚓体内蛋白质的氧化损伤及其解毒机制。结果表明:与对照组比较,20、40 mg·kg^(-1) GLA污染土壤明显上调了蚯蚓体内NADPH氧化酶和CAT同工酶活性,同时促进了GSH的合成(P<0.05)。当GLA浓度增至80 mg·kg^(-1)时,SOD、APX、POD同工酶活性明显升高,而HSP70的合成和蚯蚓的体质量受到显著抑制。免疫印迹显示,在GLA浓度为10~40 mg·kg^(-1)时,蚯蚓体内蛋白羰基化产物明显增加,诱导了潜在的解毒机制。泛素和20S蛋白酶体的蛋白丰度总体上随着土壤GLA浓度的增加趋于升高。在GLA浓度为40~80 mg·kg^(-1)时,20S蛋白酶体、总蛋白酶、EPs同工酶和GSTs酶活性显著升高(P<0.05)。研究表明,土壤GLA污染诱导了赤子爱胜蚓蛋白质的氧化损伤,泛素-20S蛋白酶体、EPs同工酶、总蛋白酶和GSTs是其重要的解毒机制。

拧紧工艺对压气机轴端预紧力的影响研究

增压器是一种高速旋转机械,工作环境十分复杂。在装配过程中,压气机轴端螺母的拧紧工艺会影响所获得预紧力的均匀程度,如果轴端螺母松动,会导致增压器故障。针对这一问题,首先,采用压气机轴端螺母预紧力范围评价模型,结合压气机热力计算结果,确定预紧力范围;然后,根据设计值确定扭矩法及扭矩-转角法拧紧试验规范;最后,基于自主开发的紧固试验装置,开展压气机轴端连接结构模拟样件拧紧试验,研究了不同拧紧工艺对轴端预紧力的影响。结果表明:保证压气机轴端结构正常工作所需轴端预紧力范围为18.16~31.03 kN;采用扭矩-转角法拧紧得到的预紧力标准差约为扭矩法的25%,使用扭矩-转角法有利于降低预紧力分散程度,且采用扭矩-转角法拧紧更接近设计中值,有利于提高预紧力控制精度。

基于Strohmeyer模型的金属材料P-S-N曲线表征方法研究

基于Strohmeyer模型提出一种考虑置信度的金属材料P-S-N曲线通用表征方法,利用非线性最小二乘法(NLS)拟合得到高精度P-S-N曲线。考虑金属材料寿命及测试应力分散性,提出单一寿命模型和改进三参数分散度模型,结合对数寿命标准差与应力的相关性分析数据离散度,分别利用2A12铝合金和BSM590钢材料验证了可行性。研究结果表明:利用所提出的表征方法预测疲劳极限,误差小于10%,分散度模型调整系数提高超过0.4,拟合精度显著提高,对结构件的精细化可靠性设计提供了技术支撑。

基于Lyapunov直接法双驱永磁运动载体的应用研究

中小型管道特别是热力管道内部质量在线检测不便,实现难度较大。为解决此问题,针对所需环境要求,设计一种将永磁吸附双半球式应用于钢板质量及厚度检测的运动载体。通过分析其在不同平面和曲面上的受力,建立动力学和运动学模型、设计控制率。利用Lyapunov直接法验证该机构的行走稳定性。设计物理样机,并在不同曲面和平面上进行实验,实验结果和仿真效果几乎相同,验证了双驱永磁运动载体的可行性和实用性。

合成孔径雷达图像的地面目标检测与伪装效果评估

地面目标伪装效果评估是基于目标在探测频段下伪装前后检测概率的变化,合成孔径雷达能够全天候工作,分辨率较高,已经成为对地侦查的主要手段。对于SAR图像的目标检测概率通常采用专家判读和特征模板匹配等方式获取,这些方法主观性较强或对算法设计的依赖度较高,因此需要一种科学客观的评判方法。随着神经网络在图像识别领域的快速发展,目标特征提取和识别结果愈加准确,现采用YOLO-V3(You Only Look Once)算法模型,对MSTAR目标背景合成图像进行机器学习,自动获取目标特征进行识别。训练后的模型在测试集的识别准确度为97.87%,用训练好的模型对未伪装样本与伪装后样本分别进行检测概率计算,通过比较检测概率的变化从而量化某类目标的伪装效果。

咬合干扰与颞下颌关节紊乱病的相关性研究

目的:通过临床检查分析安氏Ⅱ类1分类颞下颌关节紊乱(temporomandibular disorders,TMD)患者的咬合特点,探讨咬合干扰与颞下颌关节紊乱的相关性。方法:选取安氏Ⅱ类1分类TMD患者60例为实验组,无TMD安氏Ⅱ类1分类患者60例为对照组。采用目前国际上通用的视觉模拟尺分级评分测量法(visual analog scale VAS)对口面部不舒适程度进行评价;按照Fricton指数所包括的内容计算颞下颌功能障碍指数(temporomandibular dysfunction index DI),[DI=(MM+JN+JP)/26(0~1)],该指数包括下颌运动(MM)、关节杂音(JN)及关节压诊(JP)等。结果:实验组有咬合干扰者45例,对照组有咬合干扰者42例,二组间差异无显著性(P>0.05);实验组中存在咬合干扰的患者与无咬合干扰患者相比较,DI指数以及疼痛相关视觉模拟分数(VAS)均偏高,二者间差异有统计学意义(P<0.01),其中女性患者DI指数高于男性。结论:咬合干扰(occlusal interferences,OI)与TMD虽无直接联系,但OI与TMD共存可加重TMD患者临床症状,OI的存在对口颌系统的健康可能构成威胁。

Time-dependent Vibration Frequency Reliability Analysis of Blade Vibration of Compressor Wheel of Turbocharger for Vehicle Application

Blade vibration failure is one of the main failure modes of compressor wheel of turbocharger for vehicle application. The existing models for evaluating the reliability of blade vibration of compressor wheel are static, and can not reflect the relationship between the reliability of compressor wheel with blade vibration failure mode and the life parameter. For the blade vibration failure mode of compressor wheel of turbocharger, the reliability evaluation method is studied. Taking a compressor wheel of turbocharger for vehicle application as an example, the blade vibration characteristics and how they change with the operating parameters of turbocharger are analyzed. The failure criterion for blade vibration mode of compressor wheel is built with the Campbell diagram, and taking the effect of the dispersity of blade natural vibration frequency and randomness of turbocharger operating speed into account, time-dependent reliability models of compressor wheel with blade vibration failure mode are derived, which embody the parameters of blade natural vibration frequency, turbocharger operating speed, the blade number of compressor wheel, life index and minimum number of resonance, etc. Finally, the rule governing the reliability and failure rate of compressor wheel and the method for determining the reliable life of compressor with blade vibration is presented. A method is proposed to evaluate the reliability of compressor wheel with blade vibration failure mode time-dependently.

Method for Evaluating the Reliability of Compressor Impeller of Turbocharger for Vehicle Application in Plateau Area

As turbocharging diesel engines for vehicle application are applied in plateau area, the environmental adaptability of engines has drawn more attention. For the environmental adaptability problem of turbocharging diesel engines for vehicle application, the present studies almost focus on the optimization of performance match between turbocharger and engine, and the reliability problem of turbocharger is almost ignored. The reliability problem of compressor impeller of turhocharger for vehicle application when diesel engines operate in plateau area is studied. Firstly, the rule that the rotational speed of turbocharger changes with the altitude height is presented, and the potential failure modes of compressor impeller are analyzed. Then, the failure behavior models of compressor impeller are built, and the reliability models of compressor impeller operating in plateau area are developed. Finally, the rule that the reliability of compressor impeller changes with the altitude height is studied, the measurements for improving the reliability of the compressor impellers of turbocharger operating in plateau area are given. The results indicate that when the operating speed of diesel engine is certain, the rotational speed of turbocharger increases with the increase of altitude height, and the failure risk of compressor impeller with the failure modes of hub fatigue and blade resonance increases. The reliability of compressor impeller decreases with the increase of altitude height, and it also decreases as the increase of number of the mission profile cycle of engine. The method proposed can not only be used to evaluating the reliability of compressor impeller when diesel engines operate in plateau area but also be applied to direct the structural optimization of compressor impeller.

RW-splint在安氏Ⅱ类1分类错畸形诊断设计中的应用

目的探讨在正畸前戴用RW-splint是否可引导或确定下颌处于正中关系位,以期为后期诊断设计提供帮助。方法选择安氏Ⅱ类1分类错畸形患者20例,在固定矫治前进行RW-splint治疗,测量前牙覆盖量的变化。结果治疗前的前牙覆盖量为(6.792±0.795)mm,治疗后半年的前牙覆盖量为(7.720±0.930)mm,治疗前和治疗后半年前牙覆盖量差异有统计学意义(t=6.319,P<0.01),治疗后半年与治疗前前牙覆盖量变化值为(0.928±0.657)mm。结论正畸前戴用RW-splint可引导或确定下颌处于正中关系位,为后期诊断设计提供帮助。