Laboratory 3 Hydrostatic Forces Brad Peirson Laboratory Group Nick O Brien EGR 365 Fluid Mechanics Instructor Prof Fleischmann School of Engineering Padnos College of Engineering and Computing Grand Valley State University May 29 2007 1 Purpose The purpose of this lab is to experimentally determine the hydrostatic force on a submerged planar surface and to compare those experimental results to theoretical predictions 2 Background Place the diagram of the apparatus here see appendix A for diagram The diagram will cover the variables in the equations used for this lab Brief explanation of derivation of necessary equations Full derivation to be included in Appendix B Provide necessary equations Closing Moment M RT sin 2 0 5L mg sin 1 Opening Moment M gw0 5d2 cosL 1 d 3 cos2 1 Explanation of derivation of theoretical model Appendix C Reference Appendices D through G for answers to questions 3 Results Reference Appendix A for data tables The plot of depth versus weight for the experimental and theoretical models would be listed here currently in Appendix A Compare theoretical model from appendix B with experimental model from appendix A Theoretical from Excel chart for the range of interest d 0 0029W 3 0 1805W 2 5 9281W 23 42 Experimental d 0 1844W 3 1 4291W 2 6 3055W 50 133 4 Discussion Conclusions There is a significant difference between the experimental results and the theoretical prediciton for a given depth The theoretical result is much higher than that of the experimental result There are several factors that increase the closing moment of the experiemntal apparatus that aren t accounted for in the theoretical model 1 Friction in the pulley neglected in experimental model will require greater water pressure to overcome and thus decrease the amount of weight required Door seal adds a seal to the door as well as friction between mating portions of the seal will add to the amount of force required to open the door and decrease the weight required Hinges assumed frictionless in the model friction force will create a concentrated moment tending to close the door and decreasing the weight required 2 A Excel Data Sheets B Derivation of Necessary Equations C Question 1 Response What would be the advantage of using loose pin hinges and drilling the opening slightly Loose pins drilled openings minimize the friction in the hinge If this were not the case then the friction would cause a concentrated moment at the hinge that would tend to close the door D Derivation of Theoretical Model E Question 2 Response Why does the gasket help If it were removed would more or less depth be required to open the door The gasket forms a seal around the door that allows it to open clearly when the opening moment exceed the closing moment Without the gasket so much water would trickle in around the door that the actual opening point could be missed In reality the seal creates a closing moment that the water pressure must overcome to open the door Removing the seal would decrease the actual force required to open the door F Question 3 Response How many points are required to fit a cubic How many should you take 4 points are required But technically the plot can do whatever it wants between points More points added when fitting a line constrain the line between points therefore the more data points the better G Question 4 Response Can and should electronic sensors be added to the apparatus Proximity sensor Atttach to the door to give an exact response when the door opens Hall effect sensor Set at a known height from the bottom of the door to measure the precise water depth Set it to store the depth value at the moment that the door sensor triggers