Why Does a Marine Riser Model in ANSYS Show Excessive Displacement?

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SUMMARY

The discussion centers on the excessive displacement observed in a marine riser model simulated using ANSYS with the PIPE289 element. The model parameters include a riser length of 1000m, an outer diameter of 0.5334m, and a wall thickness of 0.0254m, subjected to ocean loads such as a current velocity of 1m/s and wave conditions of 6.5m height and 8s period. The user reports a displacement of 1000m, indicating a significant issue likely related to boundary conditions and load application. Adjustments to the current velocity were noted to have a substantial impact on the results.

PREREQUISITES
  • Understanding of ANSYS software, specifically the PIPE289 element.
  • Knowledge of marine riser dynamics and ocean load modeling.
  • Familiarity with boundary condition setup in finite element analysis.
  • Basic principles of fluid dynamics, particularly wave and current interactions.
NEXT STEPS
  • Investigate the impact of boundary conditions on displacement in ANSYS simulations.
  • Learn about the effects of varying current velocities on marine riser stability.
  • Explore advanced modeling techniques for ocean loads in ANSYS.
  • Review best practices for setting up finite element models of marine structures.
USEFUL FOR

Marine engineers, finite element analysts, and researchers involved in offshore engineering and marine riser design will benefit from this discussion.

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Homework Statement


hi,i am using pipe289 to simulate a marine riser in ansys,
the length of marine riser:1000m
the outside diameter of marine riser:0.5334m
the thickness of marine riser:0.0254
the velocity of current:1m/s
the wave peroid:8s
the wave height:6.5m
boudary conditions: ux/uy on node 1 and ux/uy/uz on node 2, a force(5e6) was applied on node 1

Homework Equations


N/A

The Attempt at a Solution


after i set the boudary conditions and ocean loads, the displacement is very large(1000m),i have tried to change the variables, i found the velocity of current has a big difference to the result, Can someone help ? Much appreciated thanks!

Mod note: The following is contained in the attached file.
Code: 
/FILENAME,RISER,1
/TITLE,RISER

DWATER=1000
H_WAVE=6.5
T_WAVE=8
V_SURFACE=1
V_MIDDLE=0.5
V_BOTTOM=0
RISMAT=1
MATWAT=2
FLUWAT=3

OD=0.5334
TW=0.0254

T_TOP=5e6

/PREP7
ET,1,PIPE289
KEYOPT,1,1,0
KEYOPT,1,4,2
KEYOPT,1,6,1
KEYOPT,1,7,0
KEYOPT,1,8,0
KEYOPT,1,9,2
KEYOPT,1,11,3  
KEYOPT,1,12,1  
KEYOPT,1,15,0 

MP,EX,1,2.1E11
MP,PRXY,1,0.3
MP,DENS,1,7850
MP,DENS,2,1030
MP,DENS,3,1200SECTYPE,SECPIPE,PIPE,,riser
SECDATA,OD,TW,16,0,3,FLUWAT,0,0
OCTYPE,BASIC
ocdata,DWATER,MATWAT,0,1,1,1,0
octable,,,0.5,0.5,,2,2
octype,curr
octable,0,V_SURFACE
octable,-500,V_MIDDLE
octable,-DWATER,0.0
octype,wave
ocdata,2
octable,H_WAVE,T_WAVE,58
CSYS,0
K,1,0,0,0
K,2,0,0,-DWATER
LSTR,1,2
LSEL,S,LINE,,1
LATT,1,1,1
LESIZE,ALL,1,,,,,,
LMESH,ALL
ALLSEL
SAVE
FINISH

/SOLU
ANTYPE,0
NSEL,S,LOC,Z,-DWATER
D,ALL,UX
D,ALL,UY
D,ALL,UZ
D,ALL,ROTZ
ALLSEL
NSEL,S,LOC,Z,0
D,ALL,UX
D,ALL,UY
ALLSEL
NSEL,S,LOC,Z,0
F,ALL,FZ,F_TOP
ALLSEL
ACEL,0,0,9.8

TIME,1 
SOLVE
SAVE 
FINISH

/POST1
SET,LAST
PLDISP,O
 

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Is there a sketch showing this riser and how it is restrained and loaded? Trying to decipher a data file is less than ideal.
 

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