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MECH 221 FLUID MECHANICS (Fall 06/07) Tutorial 2. FLUID STATICS. Two Basic Properties of Fluid Statics. There is no shear stress in a fluid at rest The pressure/normal stress at a point in a fluid at rest is same in all direction
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MECH 221 FLUID MECHANICS(Fall 06/07)Tutorial 2 FLUID STATICS
Two Basic Properties of Fluid Statics • There is no shear stress in a fluid at rest • The pressure/normal stress at a point in a fluid at rest is same in all direction • Please refer to chapter two lecture notes or text book for above two properties proofs
Resolve stress into any three perpendicular directions • Stress tensor is a mathematical tool to handle a real three dimensional physics Fluid Element Fluid Body Stress Tensor Stress Analysis in Fluid Statics
Stress Analysis in Fluid Statics • The two basic properties in fluid statics is converted into mathematical form by stress tensor • Mathematical form is more accurate or rigorous • Engineering is quantitative science • Then we can use these two basic properties to calculate fluid pressure engineering problem accurately
z g y 0 x Basic Equation of Fluid Statics • Fluid static pressure is due to the gravity (g) in our daily life • For fluid at rest the pressure change pre unit distance (gradient) in the vertical direction at any point in a fluid depends ONLY on the specific weight ( ) of the fluid at that point
g z 0 y x Basic Equation of Fluid Statics • This implies that there is no pressure change pre unit distance in the horizontal direction (perpendicular to body force “g” direction) • If we set the z-axis of coordinate system in a same direction to the body force “g”, the sign of the left hand side equation will change from negative to positive
Basic Equation of Fluid Statics • For incompressible fluid (density is constant) and not a very large vertical distance variation, the basic equation is reduced to • For many kind medium across z direction:
Basic Equation of Fluid Statics • If we select the horizontal level across the two sides of U tube and the medium is same in the enclosed end section, then the two tubes pressure on the horizontal level are same