船舶结构强度(1,2,3).ppt

2. Still water and wave-induced bending moment and shear force 2.1 Static loading on a ship afloat in still water 2.1.1 Buoyancy forces The resultant of the hydrostatic pressure distribution over the immersed external area of the ship and directed upwards. Buoyancy is dependent on the immersion of the ship along its length. Gravity forces, or weights The weights are body forces distributed throughout the ship and its contents, and the direction of the weight forces is always vertically downward. Weight is dependent on conditions of loading as well as location of equipment (arrangement), structure etc. Static load components on hull Ship at static equilibrium showing resultant weight and distributed resultant buoyant forces An uneven loading along the ship causes shear force and bending moment. 2.1.1 Buoyancy distribution curve The local buoyancy per unit length is = area of the immersed section * density of sea water. The section area is the area below each waterline. The curve of area below the respective waterline is the section area or Bonjean curve. Consider a section If we assume the ship is immersed to a mean draft, say at midships, with an angle of trim, this will determine the immersion of each station along the length. Total buoyancy = total weight and lcb (xb)=lcg (xg) The assumed value of mean draft and trim angle is then adjusted until B = W and lcb (xb)=lcg (xg). The procedure solving for the balance position of a ship in still water Step 1: Given displacement mean draft, dm longitudinal center of buoyancy, xb longitudinal metacentric radius, R area of waterplane, A center of flotation aft of amidships, xf Hydrostatic curves If , then static equilibrium obtained. Otherwise turn to step 2. 船名：诺克耐维斯（Knock Nevis） 净重吨位(DWT)：564,763吨（经重建后） 船长：458m. 船宽：68.86m 吃水：24.61m The external surface of the hull, or shell, must be a complex three-dimensional curved surface. Difficulties in analysis and construction. 1.2