The format of the NLDW data record is similar to the LNDW linear drum winch but without stiffness definition, which is defined by the POLY Data Record separately.
2 5 7 11 16 21 26 31 41 51 61 71 81
- --- -- ---- ----- ----- ----- ----- --------- --------- --------- --------- ---------
X| | |NLDW| | | | | | | | | |
- --- -- ---- ----- ----- ----- ----- --------- --------- --------- --------- ---------
| | | | | | | | | | |
| | | | | | | | | | |_(9)T_Max.
| | | | | | | | | | Maximum Tension (F10.0)
| | | | | | | | | |
| | | | | | | | | |_(8) Speed. Non-zero positive
| | | | | | | | | or negative winch speed (F10.0)
| | | | | | | | |
| | | | | | | | |_(7) L_End. Final Length (F10.0)
| | | | | | | |
| | | | | | | |_(6) L_Beg. Initial Length (F10.0)
| | | | | | |
| | | | | | |_(5) 2nd Node Number (I5)
| | | | | |
| | | | | |_(4) 2nd Structure Number (I5)
| | | | |
| | | | |_(3) 1st Node Number (I5)
| | | |
| | | |_(2) 1st Structure Number (I5)
| | |
| | |_(1) Compulsory Data Record Keyword (A4)
| |
| |_Optional User Identifier (A2)
|
|_Compulsory END on last data record in Data Category (A3)
(6) L_Beg: unstretched length at the beginning of the winching action. This can also be considered as the initial length and will be the length used if there is no winch action. This value must greater than 0.1m (in S.I. units) or 0.3ft (in Imperial units). Values less than this will be set to the minimum values.
(7) L_End: unstretched length at the end of the winch action. If the drum speed is positive (that is, paying out) this is the maximum length of the line and can at no time be exceeded. If this length is reached, or L_Beg is greater than L_End, then all winching action will cease for the rest of the simulation. If the drum speed is negative (that is, winding in) this is the minimum length of the line and it can at no time be less than this. If this length is reached, or L_Beg is less than L_End, all winching action will cease for the rest of the simulation.
(8) Speed: paying out (positive speed) or winding in (negative) speed. In mathematical terms the speed is dl/dt, where l is the unstretched length of line and t is time. For lines which have significant strain(ε) (this precludes steel which yields at about 0.001), you may want to consider the speed of the drum in terms of stretched length. When winding in, the line wound onto the drum will have the same tension as the free line itself at any time. This means that to wind a length of unstretched line the effective speed must be increased by a factor of (1+ε). This is done automatically. If you want to simulate a stretched line speed for winding in, then the speed specified should be input with a speed reduction factor of 1/(1+ε), where ε is the average strain. When paying out, the adjustment of speed is not straightforward. The elastic energy of the line on the drum will depend on exactly how the line was wound on the drum originally. This 'energy' stored on the drum is unknown and is assumed to be zero. Meaning the line on the drum when paying out is assumed to be unstretched. The effective winch speed (effectively with only 1 side of the line stretched) is (1+ε/2). If the user wishes to simulate a stretched line speed for paying out, then the speed specified should be input with a reduction factor of 1/(1+ε/2), where ε is the average strain.
(9) T_Max:The maximum tension causing the winch to lock. If at any time the tension exceeds this value, all winching action of the drum will cease until the tension reduces below this value.