|
[Sponsors] |
Velocity and runout distance in offshore slopes |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
June 10, 2017, 20:37 |
Velocity and runout distance in offshore slopes
|
#1 |
New Member
Binoy Debnath
Join Date: Sep 2016
Posts: 13
Rep Power: 9 |
Hello Everyone,
I am working on modeling offshore submarine slope in CFX. I am trying to validate a model by using CFX which is previously done by finite element method. A soft soil block sliding along an inclined rigid seabed. The rigid base is fixed with an inclination of 5 degree. The soil block is initially stationary and begins to slide due to self weight. I am trying to compare the soil block's front toe velocity and run-out distance of front toe with time. For my case in CFX I gave no slip boundary condition at bottom layer of domain to represent the rigid seabed. After simulation I got the results that are not consistent with the FE model. In FE model they found maximum runout distance is 22 m at 10s, maximum velocity is 4 m/s and slide becomes stationary at 10s. But in CFX I got maximum runout distance is 20 to 22m at 20 s, maximum velocity is 1.5 m/s. And slide becomes stationary after 25s. It seems runout distance is almost close to the FE model but velocity remains lower than FE model. I also tried with fine mesh at the bottom boundary, but it changes max velocity up to 1.9 m/s. I tried by many ways but every-time i got lower velocity than FE model. Here I have attached an image and output file of the model. I am sorry for my grammatical and spelling mistakes. I hope someone can help me to figure out the problem. Thanks in Advance. Best regards, Binoy |
|
June 11, 2017, 06:08 |
|
#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
* You appear to be using a continuous fluid model for the clay in a multiphase model.
* You have no model for clay maximum packing, siltation, etc * The clay strain rate is set to a discontinuous and apparent arbitrary function * You have defined an apparent arbitrary time step size, and presumably mesh size and convergence tolerance All these points are assumptions you have made which appear dubious to me. |
|
June 11, 2017, 19:14 |
|
#3 |
New Member
Binoy Debnath
Join Date: Sep 2016
Posts: 13
Rep Power: 9 |
Thanks Glenn for your reply.
Can't I use a continuous fluid model for the clay block in a multiphase model? For the modelling of clay maximum packing I have to use dispersed solid or dispersed fluid to model the clay block. I will try to do by this way. Clay shear strain rate: One of my previous model I faced this problem also and you suggested to me to use tanh function to define the clay shear strain rate. I am still struggling with this and couldn't figure out how to use the function. Also I don't know the limit of minimum and maximum shear strain rate of clay for this particular problem, it varies with different problem, I guess. Please give me suggestion. Time step size, mesh size and convergence tolerance: Please give me suggestion about the using of time step size. Using which relation I need to use time step size. I know one relation which is related with maximum node velocity and minimum element size. But for this model I know only minimum element size. And also give me suggestion about the mesh size and convergence tolerance. Once again, thank you for your time. Binoy |
|
June 12, 2017, 06:16 |
|
#4 | ||
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
Quote:
Quote:
Mesh Size: Do a sensitivity analysis Convergence: Do a sensitivity analysis. |
|||
|
|