摘要：以金属纤维多孔材料为研究对象（厚度≤3 mm）,以在狭小空间内用于吸声减振为背景,针对材料的制备工艺、结构参数等因素对其进行结构优化。结果表明,烧结温度较低、无烧结结点形成的结构,其吸声性能较好;而且在不同频率范围内,平均孔径和丝径可以通过最优搭配得到性能较好的吸声材料。通过结构优化设计,在烧结温度为850℃,当频率范围为50~6400 Hz时,丝径为Φ12μm,平均孔径分别为10、30、40μm的样品吸声性能较好。

摘要：目的:探索长时间停流情况下高扬程虹吸管中空气累积现象的发生发展及其对虹吸持续工作的危害,并给出应对该现象的工程预防措施。创新点:利用物理模型实验,结合理论解析推导,得到高扬程虹吸管内空气累积的原因及关键影响因素,突破高扬程虹吸排水在少雨地区的使用局限,给出其长期适用的工程设计条件,对其在实际边坡工程中的推广应用提供理论技术指导。方法:通过物理模型试验,揭示长期停流虹吸管内出现空气累积的必然性;利用理论公式推导,对不同因素的影响结果进行对比分析,得出影响空气累积的主要因素。结论:1.溶于水的空气因压力降低而析出、管端空气溶入扩散到虹吸管顶部及温度变化引起空气析出等现象是无法避免的;其中,原有空气的析出及温度变化引起的空气累积是主要因素;2.边坡虹吸排水设计时进水端口距控制水位至少应预留2.05 m的地下水位上升余量,或者保持出水口的高程比进水口高程低4.1 m来保证析出空气段处于下水管中。

摘要：Precision planting is one key point of precision agriculture.A doorframe type swing seedling pick-up device for the automatic precise field transplanter was designed and tested in a *** seedling device could automatically extract seedlings from growing trays,transfer them,and release them into the planting unit where they were to be precisely transplanted into the *** consisted of a path manipulator and two *** path manipulator for seedling extraction was constructed with creative design ofⅡ-type mechanism combination in *** consisted of an oscillating guide linkage mechanism and a grooved globoidal cam *** to the planned seedling pick-up trajectory,the design of the path manipulator for seedling extraction was finished with a set of the closed loop vector *** gripper was a pincette-type mechanism using the pick-up pins to penetrate into the root mass for seedling *** consisted of multiple pick-up pins,U-type pull rod,shaft,stop block,compression spring and *** mechanical dimensions of the gripper were determined by the tray size and plant characteristic with a set of rectangular equations and the boundary constraint *** final gripper was developed on the basis of cultural practice for vegetable seedling in china.A prototype of the seedling pick-up device was constructed to examine whether its working efficacy was satisfactory or *** to the analysis on the work process,the seedling pick-up device could precisely complete a work cycle of approaching,penetrating,extracting,transferring,erecting and discharging a *** pepper seedlings,tomato seedlings and cucumber seedlings as the transplanting objects,the performance tests were conducted to evaluate the practicality and adaptability of the pick-up *** laboratory evaluation showed that the pick-up device equipped with two grippers could extract 70 seedlings per minute with an average success ratio of 90.49%.T