arun7328
Marine/Ocean
- Mar 30, 2015
- 1
Dear Sir,
I am carrying out coupling of a containership using Star-CCM+ and Abaqus to predict the dynamic response in waves. I am having a problem with the bending moment calculation. I am comparing Abaqus results to experimental and 2-D hydroelastic strip theory.
I have attached two graphs for the explanation below and would be grateful if you could help me.
1st graph of Bending moment shows 2 plots one with no current velocity and one with current ( to model fwd velocity of the ship). The current velocity is given as an input in the CFD model. If we look at the bending moments the reference axis about which the response oscillates or say the mean of oscillations have changed. For the no current case and only wave, BM oscillates with respect to the still water BM that was calculated for that element (see 2nd graph called still water). For the simulation with current and wave, it oscillates about a lower value, which is now the steady still water bending moment. However, please note that the peak-to-peak magnitude is nearly the same for both. Steady still water bending moment means the bending moment of the ship at still water with just a current (no waves) which is equal to the ship speed.
Please refer to the 2nd graph named still water. The still water bending moment at amidships is about 155 Nm and for steady case is about 140 Nm. The bending moments for with and without current oscillates with respect to these values. Now the difference between static and steady is 15 Nm. If I compare the bending moment with current to the experimental value it falls short by about 14-15 Nm. The experimental measurements say that they have included the steady still water Bending moment. But in my case for the co-simulations with current it oscillates about the steady case and I suspect it does not include steady bending moment it in the calculation. I am not sure of this. I did another case where there is a lot of green water. I observe the same problem even there. When I add 15Nm, I get closer values. But it feels weird to just simply add a constant value to an oscillatory response. Is there anyone who has experienced this? Could you please help me? I am sure somehow this is the problem but don't know how to solve this.
Thank You
Regards
Arun
I am carrying out coupling of a containership using Star-CCM+ and Abaqus to predict the dynamic response in waves. I am having a problem with the bending moment calculation. I am comparing Abaqus results to experimental and 2-D hydroelastic strip theory.
I have attached two graphs for the explanation below and would be grateful if you could help me.
1st graph of Bending moment shows 2 plots one with no current velocity and one with current ( to model fwd velocity of the ship). The current velocity is given as an input in the CFD model. If we look at the bending moments the reference axis about which the response oscillates or say the mean of oscillations have changed. For the no current case and only wave, BM oscillates with respect to the still water BM that was calculated for that element (see 2nd graph called still water). For the simulation with current and wave, it oscillates about a lower value, which is now the steady still water bending moment. However, please note that the peak-to-peak magnitude is nearly the same for both. Steady still water bending moment means the bending moment of the ship at still water with just a current (no waves) which is equal to the ship speed.
Please refer to the 2nd graph named still water. The still water bending moment at amidships is about 155 Nm and for steady case is about 140 Nm. The bending moments for with and without current oscillates with respect to these values. Now the difference between static and steady is 15 Nm. If I compare the bending moment with current to the experimental value it falls short by about 14-15 Nm. The experimental measurements say that they have included the steady still water Bending moment. But in my case for the co-simulations with current it oscillates about the steady case and I suspect it does not include steady bending moment it in the calculation. I am not sure of this. I did another case where there is a lot of green water. I observe the same problem even there. When I add 15Nm, I get closer values. But it feels weird to just simply add a constant value to an oscillatory response. Is there anyone who has experienced this? Could you please help me? I am sure somehow this is the problem but don't know how to solve this.
Thank You
Regards
Arun