为探究浅埋薄基岩超长工作面液压支架群组的承载特性,构建了工作面煤壁-支架-顶板的弹性基础梁力学模型,研究了7种因素对支架阻力的影响。理论计算与实测结果吻合良好。研究结果表明:支架工作阻力呈单峰值与“M”形三峰值两种分布形式;工作面长度、基本顶厚度和弹性模量影响支架阻力分布曲线形状和高阻力范围;采高和上覆岩层载荷影响曲线值;支架刚度影响高阻力范围;巷帮刚度影响靠近巷道侧的支架阻力。基于此,提出了包括确定适当面长、支架分区调控、煤壁协同控制、巷帮主动强化等手段在内的浅埋薄基岩超长工作面关键安全管控措施。研究成果可为浅埋薄基岩超长工作面支架阻力设计与灾害预防提供理论依据。

为了研究列车与分离式三箱梁之间的气动干扰,进行了一系列风洞试验,重点研究了气动干扰对主梁和列车的三分力系数及主梁涡振性能的影响。采用列车和主梁的节段模型进行静力三分力测试和涡振试验。结果表明分离式三箱梁与列车之间存在显著的气动干扰效应。当单列车存在时,列车和主梁之间的相对水平位置对主梁的三分力系数影响不大。当双列车会车时,主梁的阻力系数较无列车和单列车时显著减小,且背风侧列车受到的气动力先突降后陡增,气动力的剧烈波动会引起列车的振动,对行车安全及舒适性不利。停靠在主梁上的列车对分离式三箱梁的涡振性能产生不利影响,会引起分离式三箱梁新的竖向涡振,且当列车位于迎风侧轨道上时,主梁扭转涡振振幅显著增加。

本文采用风洞试验研究分离式狭缝控制下单箱梁气动力及流场特征。以Great Belt East Bridge主梁为研究对象,几何缩尺比为1125制作单箱梁模型。狭缝连接单箱梁模型的迎风和背风面风嘴。控制原理为来流从迎风面狭缝口进入狭缝再从背风面吹出,从而改变旋涡的脱落模式。试验中来流风速固定在10 m/s,对应的雷诺数为2.3×104。通过对单箱梁表面压力进行测量,结果表明本控制方法能显著降低作用在主梁上的表面压力脉动值和非定常气动力。通过对升力时程做频谱分析,发现分离式狭缝能加速单箱梁尾部旋涡脱落。采用粒子图像测速技术测得了单箱梁尾流场。结果表明控制工况上表面形成的分离涡向下方移动,尾流的宽度缩小,表明降低了作用于主梁的阻力。POD分析结果表明控制工况的前两阶模态能量占比较低,表明更多的能量被转移到高阶模态,小尺度涡结构的...

公铁同层桁架桥内的列车所处风环境复杂,随着公铁同层桥梁桥面越来越宽,侧风作用下列车的安全问题越来越突出。为研究风屏障对公铁同层桁架桥-列车系统气动特性影响,对某大跨度公铁同层桁架悬索桥进行节段模型风洞试验,以30%透风率风屏障为例,测试了不同风屏障布置形式(单、双侧)、布置位置(内、外侧)和4种高度(2.5 m、3.0 m、3.5 m和4.0 m)条件下车桥系统气动特性。结果表明下游内侧风屏障对车桥系统气动特性几乎无影响,但下游外侧风屏障会增大主梁阻力系数,同时减小列车升阻力系数,影响列车背风面负压区甚至列车其余各面风压;风屏障布置在外侧时对主梁阻力系数的影响大于风屏障布置在内侧时,对列车的遮挡效果也优于风屏障布置在内侧时;随着风屏障高度增加,主梁阻力系数逐渐增大,列车升阻力系数逐渐减小,但车桥气动力系数随风屏障的...

基于流场恶化理论和声学类比理论建立了一套声学优化设计方法,并应用于高速列车排障器的声学优化设计中。结果表明,头尾车流线体是最重要的声源,分别占总声能的23.7%和33.7%。与尾车流线型部位相比,头车流线型部位声源能量更偏向高频。车体A计权辐射噪声呈现宽频带噪声(主要在1~4 kHz范围内)和峰值特征(尤其在2 kHz)。在四种方案中,最大伸缩长度的排障器能缓和2 k Hz的强峰值效应,降低总声能,并表现出最佳的声辐射性能。通过风洞试验验证了数值计算模型的正确性。

为探究列车底部转向架区域结构对列车底部流场以及列车气动性能的影响,本文采用SST k-ω湍流模型对不同简化程度转向架、雷诺数Re=2.25×106下的三车编组高速列车周围流场进行仿真分析,并结合风洞试验结果验证数值方法的正确性。分析结果表明与原始带转向架的列车模型相比,移除转向架并光顺列车车身的简化模型,可实现列车减阻38.2%;将转向架区域进行全包裹并光顺风挡区域,列车气动阻力减少30.3%;而当移除转向架并保留转向架腔外形时,列车气动阻力不减反增10.2%。因此,在进行高速列车气动外形减阻设计时,可考虑封闭转向架腔的方式,实现列车整车气动减阻。

The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine(HFPE) were introduced. The basic vibration equation of free piston assembly(FPA) was established based upon the energy conversion between the injected fuel and the friction together with the load. Both the theoretical and numerical results show that the vibration system of FPA is a nonlinear conservative autonomous system in one cycle. The FPA vibration is symmetric with constant amplitude when FPA is only driven by the compression pressure in the compression accumulator and that in the combustion chamber. When considering the friction and load, FPA could still achieve a stable vibration after a few cycles' adjustment whether the input energy is equal to the consumed energy or not. The vibration characteristics are different when FPA vibrates in the compression stroke and the expansion stroke, which is the unique feature of the single-piston HFPE.

A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow characteristics of VHT, such as its instantaneous flow rates, average flow rates, and flow pulsations in the ports, are investigated. Matlab software is used to simulate and calculate. There are five controlled angles of the port plate that can help to define the flow characteristics of VHT. The relationships between the flow characteristics and the structure in VHT are shown. Also, the plus-minus change of the average flow rates and the continuity of the instantaneous flow rates in the ports are presented. The results demonstrate the performance laws of VHT when the controlled angles of the port plate and of the swash plate change. The results also reveal that the special principle of the flow pulsation in the ports and the jump points of the instantaneous curves are th...

For the backfill hydraulic support as the key equipment for achieving integration of backfilling and coal mining simultaneously in the practical process, its characteristics will directly influence the backfill body's compression ratio. Horizontal roof gap, as a key parameter of backfilling characteristics, may impact the backfilling effect from the aspects of control of roof subsidence in advance, support stress, backfilling process and the support design. Firstly, the reason why Horizontal roof gap exists was analyzed and its definition, causes and connotation were introduced, then adopting the Pro/E 3D simulation software, three typical 3D entity models of backfill hydraulic supports were built, based on the influence of Horizontal roof gap on backfilling effect, and influence rules of four factors, i.e. support height, suspension height, suspension angle and tamping angle, were emphatically analyzed on Horizontal roof gap. The results indicate that, the four factors all have sign...

A new electro-hydraulic exciter that consists of rotary valve and micro-displacement double-functioned hydraulic cylinder was proposed to realize different kinds of waveforms.Calculated fluid dynamics(CFD) simulation of rotary valve orifice reveals that orifice exists the two-throttle phenomenon.According to the finding,the revised flow area model was established.Vibration waveforms analysis was carried out by means of mathematic model and the related experiments were validated.Furthermore,as a new analysis indicator,saturation percentage was introduced first.The experimental results indicate that the revised flow area model is more accurate compared to the original one,and vibration waveforms can be optimized through suitable spool parameters and the revised cylinder structure.