基于键合图理论的动力稳定装置轮轨间动态特性分析

考虑动力稳定装置的轮轨非线性接触、轮轨间的间隙传动、夹钳油缸和水平油缸的等效刚度建立了动力稳定装置动态特性键合图模型.使用分段函数表达式实现了轮轨间的间隙传动.针对不同夹持力对于能量的传递效率与作业效果进行了深入分析与探究,确定了所需最小的水平油缸的推力.     

Whole body vibration affects the cross‐sectional area and symmetry of the m. multifidus of the thoracolumbar spine in the horse

Whole body vibration (WBV) has been used as an adjunctive therapy to improve the strength and size of paraspinal muscles as well as postural control in people with lower back pain. It has been proposed that activation of the m. multifidus plays a key role. As the function and anatomy of the m. multifidus in the horse is comparable to that in man, the authors investigated whether WBV might also be a valuable physiotherapeutic modality in horses. The effects of WBV on the cross‐sectional area (CSA) and left to right symmetry of the m. multifidus at various locations of the thoracolumbar spine of the horse was evaluated in a single‐subject quasi‐experimental time‐series design with repeated measure. Nine horses were subject to WBV, 30 min, twice daily, 5 days a week, for 60 days in addition to their regular exercise routine. The CSA of the left and right m. multifidus was measured ultrasonographically at four levels (T15–T16, T16–T17, T18–L1 and L1–L2) along the thoracolumbar spine at Days ?30, 0, 30 and 60 of the study. Changes in the CSA and CSA symmetry (left to right) of the m. multifidus were analysed using nonparametric, repeated measures, comparison of mean ranks with post‐hoc analysis as necessary. A significant increase (P<0.05) in m. multifidus CSA was found at all spinal levels after 30 and 60 days of WBV and a statistically significant improvement in m. multifidus symmetry (becoming more symmetrical) was found after 60 days of WBV, indicating that WBV may be a valuable alternative to dynamic mobilisation exercises when an increase in size and improvement in left to right symmetry of the m. multifidus is sought.     

An in vitro biomechanical comparison of the breaking strength and stiffness of polydioxanone (sizes 2, 7) and polyglactin 910 (sizes 3, 6) in the equine linea alba

OBJECTIVE: To determine failure strength, stiffness, and failure mode of 4 suture materials in equine linea alba. STUDY DESIGN: Randomized complete block design. SAMPLE POPULATION: Linea albas collected from 12 adult horses (mean weight, 475 kg; mean age, 10 years). METHODS: The ventral abdominal fascia, including the linea alba, was collected and bisected along the linea alba into right and left halves. Each half was divided into four, 5-cm sections extending from the umbilicus cranially, and randomly assigned to 1 of 4 suture materials: 2 polydioxanone (2 PD), 3 polyglactin 910 (3 PG), 6 polyglactin 910 (6 PG), and 7 polydioxanone (7 PD). A single cycle to failure test was performed on each specimen at a distraction rate of 100 mm/min. Differences in failure strength and stiffness for the materials were evaluated using a mixed linear model with significance set at P<.05. RESULTS: In 94 of 96 test sections, constructs failed by suture failure. There were significant differences in failure strength (P<.0001) and stiffness (P<.001) among the suture/tissue constructs. 7 PD had the highest breaking strength (316.8 N) followed by 6 PG (281.3 N), 3 PG (229.9 N), and 2 PD (193.0 N). Six PG had the largest stiffness (14 N/mm) followed by 3 PG (12.7 N/mm), 7 PD (10.1 N/mm), and 2 PD (7.2 N/mm). Suture breaking strength and stiffness were not affected by linea or fascia thickness, individual horse, half of the linea alba, or abdominal wall position. Eighty-five (90.4%) suture loops failed adjacent the knot. CONCLUSIONS: When tested in single cycle to failure, suture material was more likely to fail than the linea alba. Larger suture materials had higher breaking strengths than smaller suture materials and stiffness was also affected by suture material and size. CLINICAL RELEVANCE: Given its high initial breaking strength and its relatively longer in vivo strength retention, 7 PD seems an appropriate choice of suture material for closure of the equine linea alba when maximal short-term failure strength is desired.     

Stiffness optimization of vehicle engine magneto-rheological fluids mounts

As important tool for engine semi-automatic isolation system, the magneto-rheological fluids (MRC) can’t achieve tunable stiffness but damping. Therefore, the MRC’s initial stiffness affects the performance of isolation system. To obtain the better isolation effect of MRC in wide frequency, it is necessary to optimize the initial stiffness. As motor unbalanced force and isolation damping are not considered in traditional mount optimization, the feature of semi-automatic control can not be reflected. For a four-cylinder four-cycle in-line diesel engine, a new method which is suitable for stiffness optimization on vehicle engine isolation is presented by using Genetic Algorithm. The optimal isolation system has small absolute force transmissibility in abroad frequency range and small vibration intensity with impact load by using the new method.     

发动机配气机构弹簧有限元分析

气门弹簧是发动机配气机构的重要组件之一,气门弹簧是否符合技术要求是发动机能否正常工作的关键。对弹簧进行强度、刚度、抗疲劳强度以及模态分析,分别采用耦合式有限元分析法和夹板式有限元分析法对弹簧进行了对比分析,发现弹簧内侧为弹簧的易疲劳区,弹簧的强度、刚度、抗疲劳强度满足技术要求,没有共振现象。研究还表明,夹板式有限元分析法比耦合式准确。     

城市静态小水体生态修复措施与生态服务价值评估研究

城市静态小水体污染是城市环境污染的重要问题之一。针对城市静态小水体的特点,依据稳态转换理论和生物操纵理论,形成适应于城市静态小水体的生态修复措施,并运用于武汉市青山区倒口湖水生态修复工程。工程实施后湖水水质得到明显改善,其中,水体透明度由0.2~0.4m提高至1.0~1.5m,溶解氧浓度由1.82~2.35mg/L上升至5.21~6.28mg/L,CODMn浓度由14.96~16.3mg/L降低至3.56~5.01mg/L,TN浓度由2.61~2.99mg/L降至1.27~1.6mg/L,TP浓度由0.43~0.62mg/L降至0.06~0.12mg/L。进一步对倒口湖水生态系统的供给、调节、文化以及支持4方面的服务价值进行评估,通过对水生态系统服务价值评价指标计算得出,工程实施前后水生态系统服务价值分别为299.34万元和645.62万元,新增服务价值346.28万元。在增量价值中固碳释氧、净化水质指标占比最大,表明在水生系统动植物的协同作用下,倒口湖的水质条件得到明显改善。     

钢桁架混凝土梁试验研究

The present paper studies the applicability of composite concrete beams to building and bridge structures. The ultimate flexural and shearing strength, the flexural stiffness, and the width of cracks of a series of composite concrete beams are analysed an     

装载机工作装置结构有限元分析

装载机工作装置设计水平的高低直接影响其作业性能的好坏,进而影响整机工作效率。本文基于有限元分析理论,研究了工作装置的静力分析问题,建立了有限元模型,对6种典型载荷工况进行了分析,为工作装置的设计提供了依据。采用自由度耦合模拟销轴的铰接为类似结构边界条件的处理提供了一种实用方案。     

考虑初始静力荷载效应的框架结构部分底层柱失效时的瞬时动力分析

为研究高层建筑结构整体性问题中连续倒塌问题,采用有限元方法模拟高层结构底层边柱突然失效时的瞬时动力响应。从计算结果可以看出,动力分析的水平位移比静力作用的最大水平位移大很多并以静力位移为中心上下波动,并在阻尼作用下收敛到静力位移。初始静力荷载效应使瞬时动力响应的振幅比无初始静力荷载效应的结构的水平和竖向位移振幅小。初始静力效应对结构瞬态响应的影响与刚度、质量、阻尼等因素有关,刚度越小,质量、阻尼越大时,初始静力荷载效应对结构最大位移影响越小。在对底层边柱突然失效的高层结构进行分析时,必须计算结构的瞬时动力响应。建议以较为简单的无初始静力荷载效应时的瞬时动力响应作为结构设计依据,其结果趋于安全。