Home > List of Keywords > *LMU
*LMU
Data format:
A single line comprising 9 values, as follows:
ID NODE1 NODE2 IPRO1 IPRO2 IPRO3 H D1 D2
Status :
Optional
Restriction :
Nodes NODE1, NODE2 and the spring properties IPRO1, IPRO2 and IPRO3 must have been previously defined.
Purpose :
To define simplified Leg Mating Units devices.
Details:
| Parameter | Description |
|---|---|
| ID | Identificaiton number of the LMU element among all other elements of the model |
| NODE1 | Identification number of the node defining LMU end node P. P node orientation gives the LMU frame. |
| NODE2 | Identification number of the node defining LMU end node Q. |
| IPRO(1) | Identification number of spring property to be considered for translations along the X-axis. The spring property must have been previously defined with the *SPRINGPRO keyword. |
| IPRO(2) | Identification number of spring property to be considered for translations along the Y-axis. The spring property must have been previously defined with the *SPRINGPRO keyword. |
| IPRO(3) | Identification number of spring property to be considered for translations along the Z-axis. The spring property must have been previously defined with the *SPRINGPRO keyword. |
| H | LMU cone definition. |
| D1 | LMU cone definition. Note: D1 shall be the smallest diameter, D2 the biggest. |
| D2 | LMU cone definition. Note: D1 shall be the smallest diameter, D2 the biggest. |
A description of this simplified LMU model can be found in a paper presented by SAIPEM UK Ltd. Numerical modelling of installation aids for platform installation.
The LMU element is defined by:
-
Point P belongs to the upper part of the LMU (usually the topside)
-
Point Q belongs to the lower part of the LMU (usually the jacket leg)
-
Three force-displacement laws acting in the local frame (x,y,z) defined with respect to P in order to simulate the axial and lateral shock absorbers
-
Its height H and two diameters D1 and D2.
The model is based on the following general idea:
- if the vertical distance dz is positive then a vertical force is produced between P and Q given by a pure vertical deflection of the vertical spring, z_def_z=dz;
- if the total horizontal (radial) distance between P and Q is such that the two LMU sections intersect laterally then both a horizontal and a vertical force are produced since the global contact force produced by a horizontal deflection has to be normal to the LMU lateral contact surface.
Note
The spring properties give the reaction force variation with respect to the contact penetration. This penetration is expressed in absolute values, i.e. it is useless to define negative displacements.
As far as the LMU is concerned, there is no reaction force as soon as the two pieces are not in contact.
D1 shall be the smallest diameter, D2 the biggest.
