英文工程流体力学第二章.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,*,*,White,:Chapter 2,Chapter 2,Pressure Distributionin a fluid,(,Fluid Statics,Basic,),1,Definition:,Unit:,(SI),(,P,ound per,S,quire,I,nch),Vertical to the surface and point into it.,At any point,pressure is independent of orientation.,Properties of Pressure,Pressure,2,At any point in a static fluid,pressure is independent of orientation.,Verification:,When,(up),Forces on left and up surface:,3,Fluid Mechanics,Aerodynamics,Fluid,at rest,Fluid Statics,Fluid Dynamics,Fluid,in motion,4,Pressure is the only surface force.,Pressure distribution relates,to body force only.,Dams,（,水坝）,Buoyancy,related instrument,（,利用浮力的装置）,Fluid power system,（,液压驱动系统,）,Connected vessel,（,连通器）,Applications:,2.1 Fluid rest,5,Consider a cube in a static fluid,Pressure at the center is,p;,Body forces are,dx,dy,dz,2.2,Equilibrium of a Fluid Element,6,dx,dy,dz,dx,dy,dz,Pressure:,Body force:,7,In x direction:,Force on left surface,Force on right surface,Body force in x direction,Euler Equilibrium Equations,(Euler 1775),8,Pressure increase in the direction of body force.,Surfaces in fluid with same pressure,vertical to body force everywhere,in gravity field it is a horizontal plane.,Equipressure surface,（,等压面）,9,x,z,z,h,z,0,p,0,1,Basic rule:,General solution,2,Boundary condition:,2.3,Pressure Distribution under Gravity,10,Pressure at free surface,Pressure due to weight on top,Any point with the same depth,h,under free surface has the same pressure.,equipressure surface,（,等压面）,Free surface is an equipressure surface,11,p,0,Water manometer,（水柱压力计）,p,h,Pressure source,Connected water tube,Application?,Absolute pressure,（绝对压力）,Relative pressure,（,相对压力）,Gauge pressure,（,表压力）,Vacuum degree（,真空度）,Pressure measurement,h,(mmH,2,O),h+p,0,(mmH,2,O),p,A,绝压,p,G,表压,12,P2.7,Homework:,13,Centroid,（,形心，重心）,h,c,y,c,C,h,y,x,A,y,x,p,0,Find total force,P,2.4 Hydrostatic Force on Plane Surface,14,h,c,:,depth of centroid,The force on a submerged plane equals the pressure at the plate center times the plate area,independent of,the shape of the plate,or the,angle,.,Center of pressure,Is the center of pressure at centroid?,h,c,y,c,C,h,d,y,d,D,h,y,x,A,y,x,p,0,15,h,c,y,c,C,h,d,y,d,D,h,y,x,A,y,x,p,0,Moment to x axis,16,Example,The gate is 5m wide,is hinged at point B,and rest against a smooth wall at point A.,Find,The force on the gate exerted by seawater pressure,The horizontal force,P,x,exerted by the wall at point A,17,(a)Centroid:3m above B,Solution:,(b),L,c,L,18,Hoover Dam,Channel,Select a,dA,and find the three forces on it,Integration,2.5 Hydrostatic Forces on Curved Surfaces,19,Conclusion:,x,1.Horizontal forces:,x,O,z,A,A,x,2.Vertical forces:,O,z,V,20,Example:,Find the forces acting on the hemi-spherical covers.,R,F,O,x,y,H,45,o,Solution:,21,2.6.1 Uniform Linear Acceleration,（,恒加速度直线运动）,a,X=-a,g,x,Gravity,Body force,Inertia Force,2.6 Fluid in rigid body motion,22,Boundary condition:,At free surface,（,自由液面）,Equipressure surface,（,等压面）,Euler Equilibrium Equations,23,A cup of coffee is 7cm deep at rest.,1.Whether it will spill out while a,x,=7m/s,2,?,2.Gage pressure of point A?,Example:,Solution:,It will not spill out!,24,2.6.2 Rigid body rotation,（,整体旋转）,g,2,r,z,f,O,2,y,x,y,R,O,f,2,x,r,y,x,Body force:,Equipressure surface:,dp=0,25,Parabola dish,（,抛物面）,Free surface:,g,2,r,z,f,O,z,0,How to find,z,0,?,旋转抛物面体的体积是同底面积和高的圆柱体积的一半。,26,P2.64,P2.97(selective),P2.147,P2.152,Homework:,27,