电大液压气动技术课程作业解答(一)小抄参考

1、液压气动技术课程作业解答（一）一、判断题1通常把既无黏性又不可压缩的液体称为理想液体。（）注：无黏性、不可压缩是理想液体必须具有的两个假定条件，缺一不可。2真空度是以绝对真空为基准来测量的液体压力。（）注：真空度是以大气压力为基准来测量的液体的相对压力，此时液体压力小于大气压力。而以绝对真空为基准来测量的压力应是液体的绝对压力。3连续性方程表明恒定流动中，液体的平均流速与流通圆管的直径大小成反比。（）注：恒定流动中，由于液体的不可压缩性，通过管道截面的液体流量相等，液体的平均流速与流通圆管的面积成反比，即应与流通圆管直径的平方成反比。4流经薄壁小孔的流量与液体的密度和黏度有关。（）注：薄壁小孔

2、的流量公式是要求熟记的内容，从公式中所含各项参数可知，小孔流量与液体密度有关，而与液体的黏度无关。5重力作用下的静止液体的等压面是水平面。（）注：判定等压面是否为水平面，也要求满足上述两项条件。二、填空题1负载 运动速度 功率2内摩擦力340 46mm2/s4.平均流速v 圆管直径d 运动黏度5.沿程压力损失 局部压力损失三、计算题1如图所示，有一直径为d、质量为m的活塞浸在液体中，并在力f的作用下处于静止状态。若液体的密度为,活塞浸入的深度为h，试确定液体在测压管内的上升高度。 解：由等压面概念，活塞底部平面的液体压力为 （1）活塞的受力平衡方程 （2）由（1）式代入（2）得2.如图所示用一

3、倾斜管道输送油液，已知h15m，p10.45mpa，p20.25mpa，d10mm，l20m，900kg/m3，运动黏度4510-6m2/s，求流量q。 解：分别在管道两端取流通截面1、2由伯努利方程其中，1=2， v1=v2，h1=0， h2=h=15m这里，h为油液流经管道的沿程压力损失，代入求流量：3.有一阀门，测得入口压力p10.25mpa，出口压力p20.06mpa，当通过阀门的流量q132 l/min时，求阀门的开口面积。解：液体流经阀门的特性可按流经薄壁小孔考虑由薄壁小孔流量公式 式中，代入计算4如图所示，已知某液压系统输出流量为25 l/min，吸油管直径为25mm，油液密度为

4、900kg/m3，运动黏度为20mm2/s，液压泵吸油口距油箱液面的高度h0.4m，若仅考虑吸油管中的沿程损失，试求液压泵入口处的真空度。解：分别取油箱油面及液压泵入口为流通截面1、2，列出伯努利方程其中，p1=pa=0.1013mpa， v1=0 h1=0h2=h=0.4m判断管道中油液流态油液在管中为层流，2=2沿程损失 代入计算 =0.47104pa=4.710-3mpa5如图所示的圆柱滑阀，已知阀心直径d=2cm，进口压力p1=9.8mpa，出口压力p2=0.9mpa，油液密度=900kg/m3，流量系数cd=0.65，阀口开度x=0.2cm，求通过阀口的流量。 解：圆柱滑阀当阀口开度

5、较小时，油液流经阀口的流动特性相当于薄壁小孔。过流面积 adx压差 pp1pmpa代入流量公式 winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against us

6、a.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with ei

7、ght.but it is recently named rugby league international federation player of the year sonny bill williams who has attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league

8、 and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associatio

9、ns 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa

10、 hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures co

11、mplaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be v

12、ery calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.8

13、5 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet (

14、 then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history

15、has repeated itself here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a team under-cooked - but i have been impressed by the kangaroos focus in their games since then.they have been concentrating on the s

16、ort of stuff that wins you tough, even contests - strong defence, especially on their own goal-line, completing sets and a good kick-chase. theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.it is as though their entire tournament has been preparation for the final.in johnathan thurston, cooper cronk, cameron smith and either billy slater or greg inglis at full-back they have a spine that is unmatched in rugby league. they have played in so many high-pressure games - a priceless asset going into saturday.