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Res Propulsion | Propeller | Engines

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Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX CHAPTER 4 RESISTANCE AND POWERING 59 Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX 4. RESISTANCE CALCULATION 4.1 Introduction The resistance of a ship at a given speed is the force required to tow the ship at that speed in smooth water, assuming no interference from the towing ship. If the hull has no appendages this is called bare hull resistance. The resistance will be equal to the components of fluid
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     Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX   59 CHAPTER 4RESISTANCE AND POWERING       Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX   60 4. RESISTANCE CALCULATION4.1 Introduction The resistance of a ship at a given speed is the force required to tow theship at that speed in smooth water, assuming no interference from the towing ship. If the hull has no appendages this is called bare hull resistance. The resistance will beequal to the components of fluid forces acting parallel to the ship centreline.The resistance of a DAT can be given by:Total resistance R T (DAT) = R bare + R bow thrusters + R pod   4.1.2 Resistance Calculation of POD:  R pod can be calculated by using the equation: (from proceedings of 24 th ITTC –Vol. III, Specialist committee on Azimuthing podded propulsion)R pod = R body + R fin  Where,R body = ½ ρ V 2 S body [C body (1+ k body ) +  Δ C F body ]R fin = ½ ρ V 2 S fin [C fin (1+ k fin ) +  Δ C Ffin ]The parameters of podded propulsion system can be assumed from the parent shipdata. The approximate values are:S body = 136.4 m 2 (approx.)Diameter of shaft = 1.0 m.S fin = 8.4 m 2 (approx.)C F body = C fin = 0.001556 (from ITTC-57 line)  Δ C F body =  Δ C fin =[105(k s /L) 1/3 – 0.64] x 10 -3 = 0.00358(for k s = 0.015 m and L is the length of the ship)K body = K fin = 0.7 (from VTT, Finland)(The form factor, k, which is defined in pod setup and test location, is given only asqualitative information of the test results and the hull. The numerical value of formfactor, k = 0.7, is rather high if it is compared with conventional hull forms. However,form factor values of this range are fairly common for icebreaking hull forms     Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX   61 R body = 24.81 KNR fin = 1.52 KNThe sum of the separately measured nominal total resistance (bare hull + poddrag) compared to the directly measured total resistance deviate only approximately  2 % from each other. Thus it can be concluded that there are no significant pod -hull interaction despite the rather large sized pod units. (Source: VTT technicalresearch center of Finland.)Therefore,R pod = R body + R fin = 26.33 KN (for V = 15.0 Knots)For bare hull and bow thrusters resistance calculation, we can follow differentmethods of calculating resistance and assume the maximum of all to decide thepowering requirements. The ship stern shape is considered to be normal, and thebow has a U-shape. Saltwater properties and the speed range are detailed in thevessel condition section of NAVCAD.The input parameters for calculating resistance by any of the methods given inNAVCAD v3.1e. [X]Bare-hull: Holtrop-1984 method [X]Appendage: Holtrop-1988 methodTechnique: Prediction [ ]Wind :Cf type : ITTC [ ]Seas :Align to : [ ]Channel :File : [ ]Barge :Correlation allow(Ca): 0.00012 [ ]Net :[X]Roughness: 0.15mm dCa: %-7.5[X]3-D corr : Form factor(1+k): 1.1307 [ ]Speed dependent correction---------- Prediction results -----------------------------------------Vel Fn Rn Cf [Cform] [Cw] Cr Ctkts----- ----- ------ -------- -------- -------- -------- --------10.00 0.100 1.21e9 0.001495 0.000195 0.000963 0.001159 0.00277411.00 0.109 1.33e9 0.001478 0.000193 0.000942 0.001135 0.00273312.00 0.119 1.45e9 0.001462 0.000191 0.000927 0.001118 0.00270113.00 0.129 1.57e9 0.001448 0.000189 0.000923 0.001113 0.00268114.00 0.139 1.69e9 0.001435 0.000188 0.000935 0.001123 0.00267815.00 0.149 1.81e9 0.001424 0.000186 0.000970 0.001156 0.00270016.00 0.159 1.93e9 0.001413 0.000185 0.001035 0.001220 0.00275317.00 0.169 2.05e9 0.001403 0.000183 0.001138 0.001322 0.00284418.00 0.179 2.18e9 0.001393 0.000182 0.001294 0.001476 0.00298919.00 0.189 2.30e9 0.001384 0.000181 0.001503 0.001684 0.003188     Department of Ship Technology, CUSAT, B.Tech (NA$SB), Batch – XXIX   62 Vel Rw/W Rr/W Rbare/W Rw Rr Rbare PEbarekts kN kN kN kW----- ------- ------- ------- ------- ------- ------- -------10.00 0.00014 0.00017 0.00041 257.59 309.86 741.88 3816.611.00 0.00017 0.00021 0.00049 304.81 367.32 884.46 5005.112.00 0.00020 0.00024 0.00058 357.14 430.76 1040.21 6421.613.00 0.00023 0.00028 0.00068 417.35 502.91 1211.80 8104.214.00 0.00027 0.00033 0.00078 490.33 588.68 1404.08 10112.515.00 0.00033 0.00039 0.00091 583.82 695.79 1624.72 12537.416.00 0.00040 0.00047 0.00105 708.83 835.25 1884.68 15513.017.00 0.00049 0.00057 0.00123 879.95 1021.64 2198.50 19227.118.00 0.00063 0.00071 0.00145 1121.08 1278.86 2590.03 23983.719.00 0.00081 0.00091 0.00172 1451.57 1626.25 3078.59 30091.5Vel Rapp Rwind Rseas Rchan Rother Rtotal PEtotalkts kN kN kN kN kN kN kW----- ------- ------- ------- ------- ------- ------- -------10.00 5.60 0.00 0.00 0.00 0.00 747.49 3845.411.00 6.76 0.00 0.00 0.00 0.00 891.22 5043.312.00 8.02 0.00 0.00 0.00 0.00 1048.23 6471.113.00 9.38 0.00 0.00 0.00 0.00 1221.18 8167.014.00 10.85 0.00 0.00 0.00 0.00 1414.94 10190.715.00 12.43 0.00 0.00 0.00 0.00 1637.15 12633.316.00 14.11 0.00 0.00 0.00 0.00 1898.79 15629.117.00 15.90 0.00 0.00 0.00 0.00 2214.40 19366.118.00 17.79 0.00 0.00 0.00 0.00 2607.82 24148.419.00 19.78 0.00 0.00 0.00 0.00 3098.37 30284.8Condition dataWater type: CustomMass density: 1008 kg/m3Kinematic visc: 1.16e-06 m2/s---------- Hull data --------------------------------------------------Primary: Secondary:Length between PP: 263.000 m Trim by stern: 0.000 mWL aft of FP: 0.000 m LCB aft of FP: 126.820 mLength on WL: 272.500 m Bulb ext fwd FP: 6.150 mMax beam on WL: 48.700 m Bulb area at FP: 42.000 m2Draft at mid WL: 16.750 m Bulb ctr abv BL: 6.150 mDisplacement bare: 182642.0 t Transom area: 15.000 m2Max area coef(Cx): 0.985 Half ent angle: 52.000 degWaterplane coef: 0.920 Stern shapes: U-shapeWetted surface: 20052.0 m2 Bow shape: NormalLoading: Load draftParameters: Holtrop-1984 methodFn(Lwl) [0.10..0.80] 0.10*Fn-high [0.10..0.80] 0.19Cp(Lwl) [0.55..0.85] 0.83Lwl/Bwl [3.90..14.90] 5.60Bwl/T [2.10..4.00] 2.91
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