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Computing Resistance |
  
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Computing Resistance |
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Toolbar |
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Menu |
Orca3D > Speed/Power > Planing Analysis |
Command |
OrcaPlaningAnalysis |
Orca3D can compute the bare hull resistance of a planing hull for a user-defined range of speeds. The total predicted resistance, total effective power, and total propulsive power can then be calculated using a user-defined design margin and propulsive efficiency.
The process of computing the drag on a planing hull surface can be summarized as follows:
| 1. | Select the planing surface or polysurface for the analysis. Note: the selected surface or polysurface: |
| - | MUST ONLY represent the planing surface up to the chine; a hull surface that includes the topsides can be split at the chine by selecting the surface, then selecting the Surface menu > Surface Edit Tools > Split at Isocurve, finally selecting the curve representing the chine and press Enter |
| - | MUST ONLY represent half of the hull |
| - | MUST have a transverse coordinate of 0 on the centerline (for example, a multi hull ship must be positioned so that the centerline is at Y=0) |
| - | MUST be oriented with forward in the negative X-direction and up in the positive Z-direction |
| - | MUST have a surface normal direction pointing outward into the water. The surface normal direction can be verified by selecting the surface, then selecting Direction from the Rhino Analyze menu. |
| 2. | Type the command: OrcaPlaningAnalysis, select Planing Analysis from the Orca3D menu, or select the Planing Hull Analysis icon from the Orca3D toolbar to initialize the planing analysis. |
| 3. | Input the following values into the Orca Planing Analysis dialog box: |
| - | Mass and geometry properties. |
| - | Range of vessel speeds. |
| - | Margins and efficiencies. |
| 4. | Select the OK button and the results will be displayed in report form in a separate window. |
IMPORTANT: Select ONLY the planing surface to be included in the analysis. The program will use all surfaces selected in its calculations of deadrise angle, lift coefficient, effective beam, etc. If any other surfaces are selected, you will receive incorrect results.
Splitting a Surface
A hull surface can be split at a specific curve, for instance the chine line, using Rhino surface edit tools. To split a surface, select the surface to be split, then select the Surface Menu > Surface Edit Tools > Split at Isocurve. Finally, select the curve to split the surface at and press Enter.
Note: the design condition must be redefined once the surface is split in order to use the calculated design condition values in the input dialog box.
Input Dialog
Once the planing analysis is started from the command line, Orca3D Menu, or Orca3D toolbar and the planing surface is selected, the Orca Planing Analysis dialog box will open.
Mass and Geometry
Weight: the weight of the vessel at the desired condition, in the units specified.
LCG (from origin): the longitudinal center of gravity of the vessel measured from the world origin in the units specified.
VCG (from origin): the vertical center of gravity of the vessel measured from the world origin in the units specified.
Note: the weight, LCG, and VCG can be automatically filled in by Orca3D if a design condition is specified after the planing surface is split (if necessary) from the hull surface by clicking the From Design Condition box.
Propeller LCE (from origin): the longitudinal center of effort of the propeller measured from the world origin in the units specified.
Propeller VCE (from origin): the vertical center of effort of the propeller measured from the world origin in the units specified.
Shaft angle to baseline: the angle from the propeller shaft to the baseline, measured in the units specified.
Note: these values can be specified on the model by clicking the corresponding Select… button next to each input box.
Speeds
Enter the minimum speed, maximum speed, increment speed, and design speed of the vessel in the units specified for this analysis.
Note: the analysis will only give results for speeds providing a volumetric Froude number greater than 1.0.
Margins and Efficiencies
Resistance Design Margin: the margin added to the bare hull resistance to calculate total resistance and effective power. This margin can be used to account for appendages, wind, waves, shallow water, etc.
Propulsive Efficiency: the ratio of effective power to propulsive power. This efficiency can be used to account for losses in the propeller, shafting, transmission, etc and will thus determine the true definition of total propulsive power.
