1. What is Holtrop’s method?1.1 Empirical Prediction of ResistanceIt easy to predict the resistance of similar ships based on model ships and actual previous ships. And it can be applied for hull form design using optimum design variables.But It has limitation to prediction the resistance of a completely new hull form or the local variation of hull form1.2 Holtrop’s methodHoltrop (1984)It was extended using 334 model test results including Series 64 hull form (Yeh, 1965) based on Holtrop et. al (1982).It was calculated below formulation.�!"= �#(1 + �)+�$%%+�& + �'+�!(+�)�# : friction resistance of ITTC19571+k: form factor, �#(1 + �) is viscous resistance � *�$%%: appendage resistance�&: wave-making resistance(�&is divided into �&+), �&+', and �& according to the Froud number. Froud number at the ship speed we will use is all less than 0.4, so we must calculate the �&+))�' : additional pressure resistance due to bulbous bow�!( : additional pressure resistance due to submerged transom stern�) : model-ship correlation allowance
1. Draw Kelvin wave with wave elevation contour and oblique 3D view according to the variation of the submerged depth of source and inflow speed, and discuss the difference of the wave systems according to the conditions.– Computation domain : X[0, 30], y[-10, 10]– Submerged depth of source : 1.0, 2.0– Inflow speed : 3.0, 4.0, 5.0Theory1-1 Potential flow-uniform flowParalle to x axis u = V, v=0Velocity potential =>-SourceEmission to all directionSource strength : volumetric flow rate per unit lengthFlow speedVelocity potential : integration of flow speed1-2 Potential flow for the wave systemThe wave height can be obtained by using the positive flow. - Coordinate : fixed at pressure point Pressure point moves to -x direction with the speed of U In the fixed coordinate at pressure point, uniform flow U flows to the pressure point toward +x direction +y axis : starboard, +z axis : upward - Velocity potential - Boundary condition : nonlinear kinematic/dynamic boundary condition × Uniform flow �� + disturbed potential due to an object �× In small slenderness ratio �� >> �Boundary condition : nonlinear kinematic/dynamic boundary condition
Theory (procedures)Q) From the given data, compare total resistance (R) and effective horse power (EHP) of full-scale ship using Froude method, ITTC 1957 for 2D method and Hughes, ITTC 1978 for 3D method. The temperature of sea water is 15°C. (1) Froude Method1.The model ship with the accumulation ratio � is towed to satisfy Expression .2. If towed, obtain the measured total resistance3. The value of the frictional resistance of the model ship is calculated assuming that the length of the model ship is the same and the surface area of the flooding surface is the same as the frictional resistance of the plate.4. The residuary resistance of the model ship is 5. obtained using the law of comparison of residuary resistance of ship (�� �� density ratio of ship and model ship)6. is obtained by a flat plate having the same length as the ship and the surface area of flooding.7. Calculate as The price of A from here is .[p is density of water, g is gravity acceleration, S is flooding surface area, V is ship speed, c is resistance factor (0.1392+ (0.258/2.68+L)]
저항론 과제4_Self Propulsion Test
