If this data record is used the RNDD option (Administration and Calculation Options for the Aqwa Suite) is also needed in the preliminary data category.

      2   5  7   11
    - --- -- ---- ----- -----
   |X|   |  |SC1/|     |XXXXX|
    - --- -- ---- ----- -----
       |  |   |     |
       |  |   |     |_(1)Scale Factor (I5) (default implies constant drag coefficients)
       |  |   |
       |  |   |
       |  |   |_Compulsory Data Record Keyword (A4)
       |  |
       |  |_Optional User Identifier (A2)
       |
       |_Compulsory END on last data record in Data Category (A3)

(1) This scale factor applies to all elements on all structures but in the present version of the program only affects Morison TUBE elements on those structures.

If this data record is omitted the program assumes that the Reynolds Number is sufficiently large for the drag coefficient to be considered constant. If this is not a reasonable assumption then this data record should be input with a value of unity.

The user should read the following sections before using this facility.

Effect of the Scale Factor on Reynolds Number

Experimental evidence shows that the Reynolds Number is not a simple function of the velocity and diameter for cylinders with arbitrary orientation to the direction of the fluid flow. However, considerable improvement in agreement with model tests has been obtained by using the Scale Factor to obtain a local Reynolds Number and interpolating from classic experimental results,

where

Local Reynolds Number = (U.D/ν)/(Scale Factor^3/2)

U = Local velocity transverse to the axis of the TUBE

D = The diameter of the TUBE

ν = Kinematic viscosity of water

Effect of the Scale Factor on Hydrodynamic Coefficients

If this data record is omitted then the drag coefficients used are those input in Data Category 4 by the user, or default coefficients assumed by the program if the user inputs zero. However, when this data record is input, these coefficients for all Morison tube elements on all structures are ignored. The program will instead interpolate coefficients from the Wieselburger graph of drag coefficient versus Reynolds Number (as shown below) for a smooth cylinder, where the Reynolds number is calculated in the manner shown above.

Drag Coefficient Variation with Reynolds Number

Note that the following curve is only used when the SC1/ data record is defined in data category 17 and is only for TUBE elements. The relative flow velocity normal to the tube is used in the calculation of the Reynolds Number Re.