520 likes | 689 Views
UEET 601. Learning by anticipation and participation. Earthquake: Tremor effects on man-made structures. Guitar Body Vibration. Assume a Guitar String. Guitar Body Vibration. Assume a Guitar String. Guitar Vibration. Similar to a free structure beam If we anchor the beam
E N D
Guitar Vibration • Similar to a free structure beam • If we anchor the beam • Big guitar string
Tension of the string • Mass of the string • Length of string
Assume any String • How can we reduce the vibration of string?
Vibration Damping • Decrease vibration energy • Size of radiating surface • Mass • Absorption of energy
A1 A2 A3 A4 Rigid Surface Area AT Rigid Construction: Increase Mass
Energy Absorption: Damping • Opposite reaction
Assume any Building • How can we reduce the impact of an earthquake on a building?
Taipei 101 building • Damping • 730 Tons
Transamerica Pyramid • Build on Rollers • Why would rollers be effective?
Physics of Fire • Fire rectangle • Flash point • Lowest temperature to ignite • LEL vs. UEL • Lowest concentration in air for ignition • Fuel Rich Ignition Source Fuel Oxygen/Air Chain reaction (free radicals)
Physics of Surfaces Slippery?
Surfaces and the Coefficient of Friction • Friction results when one body contacts another • Frictional force is tangent to the contact surface that resists motion • No motion; static friction • Motion: kinetic friction
Friction Formula • F = uN • Where F = Force (lbs) u = Coefficient of friction N = the force acting on the normal (perpendicular) to the surface
Friction Formula: Example 1 • On a horizontal surface the normal force (N) is equal to the weight of the object N = 200 lbs 200 lbs
200 lbs Example 2How much force is required to move a 200 lbs box if the coefficient of friction is 0.75? • Recall F = uN F = 0.75 x 200 lbs F = 150 lbs
Friction Formula (continued) • On a incline plane, the normal force (N) is equal to the weight of the object times the cosine of the angle with respect to the horizontal 200 lbs
Example 3:Assume a 200 pound box rests on an incline plane of 20o. What is the resultant normal force?
200 lbs A = 20 O • N = W x Cosine A • = 200 LBS X Cosine 20 O = 200 LBS X 0.94 • = 188 lbs
Example 5How much force is required to move a 200 lbs box up an incline plane of 20o if the coefficient of friction is 0.75?
Recall F = uN and N = W x Cosine A • F = u x W x Cosine A • F= 0.75 x 200 LBS X 0.94 • F = 141 lbs 200 lbs A = 20 O
Example 6 How much force is required to move the box down the same incline plane?
200 lbs A= 20 O • Gravity is acting in the downward direction • G = w sin A = 200 sin 20 O = 68.4 lbs
200 lbs A= 20 O Recall • F = 141 to move box • G = 68.4 • Net = F – G • Net = 141 – 68.4 = 72.6 lbs
Supply/Return: Normal Operation Supply/Return: Pressurized Stairwell
Equilibrium recall Buildup at equilibrium
Time to Equilibrium Recall Rearrange 1 Rearrange 2
Recall Solve for t C = 0 at t = 0
Recall Recall at Equilibrium Substitute
Substituting and solving • Q = Air changes per hour design i.e., 4 for comfort • At 4 AC/hr • Q = 4V/hr • Q = V/15 min.
Time to Equilibrium Solving
Purging (G=0): • Vdc = G dt - QCdtbecomes • Vdc = - QCdt
Purging Example • Assume there was a chemical release in a building • Building engineer states that the ventilation rate on full exhaust is 4 air changes per hour • Air changes per hour design i.e., 6, or 4 or 2 for comfort
Purging Example • We want to purge to eliminate 99% of the toxic agent, or