# Why Fx produced is negative?

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August 26, 2014, 04:00
Why Fx produced is negative?
#1
New Member

Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 5
Hi,

My Fx produced from fine marine for in wave resistance contain negative, below is the result that i captured from monitor. May i know why the Fx is negative? It should be positive in my opinion.

Thanks
Attached Files
 Forces Problem.docx (85.9 KB, 15 views)

 August 26, 2014, 06:15 #2 Member   Romain Join Date: May 2009 Posts: 40 Rep Power: 10 Hi, Can you give more information, namely the coordinate system you are using (is the bow towards +X axis or -X), the direction of the boat, the direction of the waves... Take a screen shot of the free surface in cfview also. It looks like the boat wasn't moving at all since the drag is very close to 0 before it sees the first waves. Maybe it would make more sense to run a first case without waves so that the boat reaches its nominal speed, and a steady-state solution. Then create another run which is a restart from the steady state solution with the wave maker on.

August 28, 2014, 01:02
#3
New Member

Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 5
Hi Rombzh,

My bow is towards -X and my Vx shown is -1.029754m/s. While in flow setting, i setup the simulation with following information;

Wave generator:
i) Wave depth of 4.572m with period 1.397s and wave height of 0.2m.
ii) Direction of propagation is X = 1, Y = 0.
iii) Reference point is X = -12.192m (on the inlet patch) Y = 0.

Body Motion:
I activate Cardian angle
Tx(Imposed and 1/2 sinusoidal ramp)
Tz(Solved)
Ry1(Solved)
Dynamic parameters(Solve using Domhydro)

I will try out your suggestion. If there is still not understand about my setting information, i can sent the file to let you check out but through your email because the file is so big that cant upload through the forum. Now i just simply use this model as testing to understand how to run in wave resistance simulation especially in body motion part.

Thanks
Attached Files
 Trimaran.igg_computation_1.zip (594 Bytes, 8 views)

 August 30, 2014, 03:31 #4 Member   Romain Join Date: May 2009 Posts: 40 Rep Power: 10 Hi, I'm not sure why you attached a .cfv file as it is quite useless. Open Cfview, and open your .cfv file and plot wave elevation on the free surface to see what's going on. Export the file as a .png and maybe post it here.

August 30, 2014, 10:59
#5
New Member

Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 5
Hi Rombzh,

So sorry that i send you the wrong file. Then the .png file you suggested to be exported is too big that it can't be uploaded here so i try to upload as JPEG file. Is this the information you want? Actually i am not really good in CFView so if the file wrong please let me know and i try do it again. Again appologize to you if i make you inconvenient.
Attached Images
 Wave Elevation.jpg (44.4 KB, 12 views)

 September 1, 2014, 08:31 #6 Member   Romain Join Date: May 2009 Posts: 40 Rep Power: 10 Hi, I meant plot the wave elevation as a color contour on the free surface. The different Fine Marine tutorials explain how to do it.

 September 1, 2014, 11:26 #7 New Member   Lim Pei San Join Date: Mar 2014 Posts: 25 Rep Power: 5 Hi Rombzh, Ok, i will try to find the tutorial on how to plot it. Thanks a lot that you thought me a lot of fine marine things. After that, now i am doing resistance simulation with turbulence model. I am sure that fine marine is a dedicate software to simulate the resistance, but my result still have around 50% error in getting accurate answer. I am sure there is some mistake i made in setting procedure but i dont know where is the problem that cause the result came out inaccurate. Any suggestions to make an ideal or standard setting for resistance simulation in turbulence model which used to compare with experimental result? Thanks

September 3, 2014, 00:23
#8
New Member

Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 5
Hi Rombzh,

Is this the wave elevation with colour contour that you want?
Attached Images
 Wave Colour Contour 2.jpg (29.1 KB, 18 views) Wave Colour Contour 1.jpg (26.8 KB, 15 views)

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