When I run the GridRefinement3D example in the new version of the Palabos, several output files are generated. Seems they are sparse output option that is added to Palabos!

I could not open these separated files in Paraview for post processing!

Any helps for collecting these files as a one would be appreciated.

Cheers,

King]]>

I know the import export process is not perfected, but maybe there is a fix to this. when i load an LBM, it will work till i save and restart blender, when i restart blender, open the saved file, then try to render, i recieve this error

ERROR: Export aborted: 'bool' object has no attribute 'luxrender_texture'

its saying ""Failed to find texture "478ec31794c3cc473dfb6" in scene "" i dunno if that has anything to do with it

i should add that i delete that texture because it prohibits the rendering process and py lux from working.

Please help.

I didn't find the right solution from the Internet.

References:-

[www.luxrender.net]

Telematics Solution Video

Thanks!]]>

For velocity, in a lid driven cavity problem for instance, we use (u/Ucavity)_physical=(u/Ucavity)_LB. Where Ucavity_LB is obtained by Re and nu_LB independent from its physical value. But no such ability is available for temperature to be computed.

I have not found an answer despite so many unit conversion discussions, except natural convection case in which we can use Ra number that has deltaT term in it.]]>

Additionally, the board delay is

The primary clock (80MHz/12.5ns) of FPGA is distributed from the internal clock divider and is used to generate the clock for the ADC (f_adc_clk=40MHz).

How do I specify setup and hold times for the data port of the FPGA with respect to ADC clock? I made several attempts without success. The spreadsheet/Timing Preferences view that i used to specify INPUT_SETUP is shown in the image below

However, the problem is that I can only use clk80 as a reference which is the output of the clock divider, and there is a considerable phase shift between this clock and the clock driving the AD converter as a result of delay from the clock divider to the output pin of the FPGA. How do I take this delay into account when specifying preferences?]]>

I am in the process of converting an LBM code from simulation to physical units. I know the basics of the procedure, but I run into some difficulties when working with the Shan-Chen models for multiphase/multicomponent flows. In order to transform the

This reads: p = c_2^2*rho + c_s^2*G/2*psi(rho)^2. However, when I set G to achieve dimensional consistency, its units differ from those needed for dimensional consistency of the interaction force density. For simplicity, following Martys and Chen 1996, I set psi(rho) = rho. This gives units of G as L^5*M^{-1}*T^{-2}. Now, if I use the same effective mass (psi(rho)=rho) in the interaction strength equation, which reads F = -G*psi*sum_a(w_i*psi*e_i), G has units L^3*M^{-1}*T^{-1} ! In the force equation w_i is dimensionless and e_i has units of speed.

Has anyone had any similar problems? Any advice will be greatly appreciated.

Thank you,

Peter]]>

I am trying to understand static Smagorinsky model implemented in Palabos. As described in the documentation:

I could understand this from the relationship between the stress tensor and strain rate: PiQuoteIn the Palabos implementation, the strain-rate is computed from the stress tensor \Pi.

However, when I look at the file

.Language: C++static T computeOmega(T omega0, T preFactor, T rhoBar, Array<T,SymmetricTensor<T,Descriptor>::n> const& PiNeq) { T PiNeqNormSqr = SymmetricTensor<T,Descriptor>::tensorNormSqr(PiNeq); T PiNeqNorm = std::sqrt(PiNeqNormSqr); T alpha = preFactor * Descriptor<T>::invRho(rhoBar); T linearTerm = alpha*PiNeqNorm; T squareTerm = (T)2*alpha*alpha*PiNeqNormSqr; // In the following formula, the square-root appearing in the explicit form of // omega is developed to second-order. return omega0*(1-linearTerm+squareTerm); }

This calculation seems to be a different form compared to the one in the paper by Hou, et al. (1994)

Could anyone help explain this or provide any reference?

Thank you in advance.

With best,

Song

[1] Hou, et al. 1994, "A lattice Boltzmann subgrid model for high Reynolds number flows"

[2] Krafczyk 2003 "LARGE-EDDY SIMULATIONS WITH A MULTIPLE-RELAXATION-TIME LBE MODEL"]]>

For

Re = PhyL * PhyU / PhyNu = Resolution * LatticeU / LatticeNu

Usually we use LatticeU= PhyU / M.

1. Must LatticeU be proportionable with PhyU? Can it be any value? And according to the comments of the code, it should be “proportional to Mach number”. I’ve no idea what it means.

2. In some of my cases of High Re with smagorinsky model, If I make my deltaX halved, I found that the original LatticeU can not be used in the new case for the simulating divergent. In this situation, I have to make my latticeU smaller. Why this happened?

3. I found that if the M is different in the same case (means LatticeU different), there are some differences in the results velocity. Was it right? If so, how should we determine the value of latticeU?

4. During the iteration, we use averaged rho to monitor the simulation. Usually it should be drifted around 1. But if the latticeU is not suitable, the ave rho will continually grow up, even from 1 to 4. Why will this happen? As we know that rho is the sum of the distribution functions, if it grow up, does it suit the mass conservation? And is this kind of result correct？

Maybe some of the questions are so primitive，thank you for your focus.

with best wishes,

steed188]]>

I have been recently trying to incorporate thermal effects to my multiphase simulations. I am still using the shan chen lbm as i am not able properly incorporate wall interaction when using other equations of state. in shan chen, i take T=1/G and use a separate mesh to model the transport of temperature as we usually do in thermal LBM. It works perfectly in single phase but doesnt work in multiphase. The simulation goes to NaN at the interfaces. I read in various papers about a heat source term which took phase change into account (involving rho, cv and delta t). But how do i implement this formula? I tried Cv=5.1 as given in one paper i saw, but it didnt work. I also tried converting Cv directly into lattice units but it still didnt solve my problem. Can anybody tell me what value to take for Cv and if it is fine to calculate delta T similar to how we calculate psi?

Thanks in Advance,

Regards,

Githin]]>

Please introduce me some research works on the area multi-block multi-phase LB (Shan Chen Method) simulation.

any help is appreciated

Thanks in advance]]>

I will be soon working on developing an unstructured LBM solver based on the paper given below:-

Finite volume TVD formulation of lattice Boltzmann simulation on unstructured mesh, Dhiraj V. Patil, K.N. Lakshmisha *

All the papers i found on unstructured LBM are on simple SCSP LBM. Are there any papers extending the unstructured LBM to multiphase simulations? If yes, it would be a great help if you could name a few. If no, is it possible to do this? Any ideas on how?

Thanks a lot in advance,

Githin]]>

I have a question about of U_ {LB} at palabos. I simulated a channel 2D (D2Q9) and 3D (D3Q27), where the initial velocity initial is zero, and I used a model with external force term. At the case 2D, my simulation woked with U_ {LB} 0.02, but at the case 3D this value does not work. I changed this value for 0.3.

The choice of these values was to see the examples of the website of Palabos.

But at this moment I still can not explain why it is necessary to make that change.

Can someone tell me the reason, or where can I find literature about this topic?

Thanks for your help]]>

My question is, when I modified resolution number's without changed my problem physical (physical velocity, Reynolds number and characteristic length) my velocity profile changed.

According to consistency of problem, this doesn't must change the solution because I would to change the resolution number, but that the effect of this change is increasing accuracy.

Please community someone can tell me why do it happen this, or where can I found literature about of this topic.

Thank you]]>

I have started working on an LBM model with medium range repulsive force to simulate emulsions of heavy phase. I was inspired by the works of Chibbaro, 2008 (Phys Rev E 77, 036705) and Falcucci, 2010 (Soft Matter, 2010, 6, 4357–4365). For those of you who do not know what the repulsion model does, it is essentially incorporating a realistic component of repulsion between particles of the same phase, reducing the effective surface tension and promoting the formation of emulsions. This is compared to the original Shan-Chen model that only features short-range attractive forces.

My question is this. The repulsive model features two G parameters, uncoupling density ratio and surface tension. How are the values of these parameters determined? Does anyone have any experience? The expressions given in the two papers above as well as in other places differ significantly in both value and sign! Any help will be most appreciated.

Best Regards,

Peter]]>

I want to simulate a droplet in fully periodic 2D domain using MCMP Shan-Chen method. initialization is performed by inserting a square of one of the fluid in the center of the domain (rhoW = 1,rhoO=0.01), while the other fluid applied out of this square (rhoW = 0.01,rhoO=1). for a system size of 100x100 and relaxation time of 1 for both fluids, results of simulation converge to a circle of a droplet in the middle of system. Also the the initialization is a square with length 20 in the center of system. the selected G is 1.5. and psi function for force calculation is equal to density.

I want to get same results for a system size of 50x50 or 200x200, how it can be possible?

is there any grid in-dependency check for multi phase multi component simulation using Shan-Chen LB method in the literature?

please help me in this issue

Thanks in advance]]>

that is, using reduced variables. rho_cr_lbm is the critical density in LB units which in this case is 200. and rho_cr_phy is 322.

this leads to a liquid density of 850 which is somewhat near the real value of 1000 but the vapor density becomes around 130 which is nowhere near the actual value.

What am I doing wrong here?

I appreciate any help provided.

Thanks in advance

Githin]]>

I am currently attempting to model 2D incompressible flow over a flat plate using the standard D2Q9 lattice Boltzmann method. I am comparing my results with the Blasius solution i.e. the similarity variable (eta) vs. the non-dimensionalised u and v velocity components at various positions along the plate. I am getting errors of approximately 50% when compared to the Blasius solution.

I was just wondering if anybody had any tips on why this might be happening? I have set up the problem as follows:

1. The plate is situated at bottom of the domain with a small section of open flow before the plate. I am simulating the section before the plate using half-way free-slip or symmetrical boundary conditions. I am using half-way bounceback boundary conditions to simulate no-slip conditions for the plate.

2. I have a constant u velocity at the inlet and I am using the equilibrium scheme to simulate this (constant density of 1 and v velocity set to 0).

3. The equilibrium scheme is also used at the top of the domain using the same parameters as the inlet. The top of the domain is situated far above the maximum boundary layer thickness so that the boundary conditions do not cause any unphysical effects.

4. Zero gradient conditions are used for the outlet.

Is there anything that I am doing that immediately seems incorrect? I would sincerely appreciate any help with this. I am currently implementing a GPU code to drastically increase the mesh density and determine whether this improves accuracy (my current meshes are in the order of 100 x 1000, 200 x 2000 etc. in x and y respectively), but I just wanted to check if my overall approach to the problem is correct as well.

Thanks in advance,

Gerald]]>

2. for calculating the interaction force, the effective mass (e.g. psi(x)) for the neighbor nodes (e.g. psi(x+e) & psi(x-e)) should be known. In the case of inlet velocity, the function psi(x-e) a is out of the computational domain. How can I compute the interaction force for inlet boundary nodes?

for the left boundary condition:

rho_in=2.05

ux_in=1.0d0-(ff(2,1,y)+ff(4,1,y)+ff(0,1,y)+2.0d0*(ff(6,1,y)+ff(3,1,y)+ff(7,1,y)))/rho_in

rho_in=(ff (2,1,y)+ff (4,1,y)+ff1(0,1,y)+2.0d0*(ff (6,1,y)+ff (3,1,y)+ff (7,1,y)))/(1-ux_in)

ff(1,1,y)=ff1(3,1,y)+2.0d0/3.0d0*rho_in1*ux_in1

ff(5,1,y)=ff(7,1,y)-(ff(2,1,y)-ff(4,1,y))/2.0d0+1.0d0/6.0d0*rho_in1*ux_in

ff(8,1,y)=ff(6,1,y)+(ff(2,1,y)-ff(4,1,y))/2.0d0+1.0d0/6.0d0*rho_in1*ux_in

For the right boundary condition:

rho_out=2.0

ux_out=-1.0d0+(ff(2,lx,y)+ff(4,lx,y)+ff(0,lx,y)+2.0d0*(ff(1,lx,y)+ff(5,lx,y)+ff(8,lx,y)))/rho_out

ff(3,lx,y)=ff(1,lx,y)-2.0d0/3.0d0*rho_out*ux_out

ff(6,lx,y)=ff1(8,lx,y)-(ff(2,lx,y)-ff(4,lx,y))/2.0d0-1.0d0/6.0d0*rho_out*ux_out

ff(7,lx,y)=ff(5,lx,y)+(ff(2,lx,y)-ff(4,lx,y))/2.0d0-1.0d0/6.0d0*rho_out*ux_out]]>

Assignment help Uk]]>

1.I have studied Double distribution function, But Actually i don't know how to establish in my code,

2.should I understand the derive of formula in LBM totally? Because I try to my best to study the math ,some detail derive i couldn't hadle the all

3.Can anyone give me a good advise to tell me and if you have the example or tech code for compressible problem can you share to me ?

Thanks everyone~

,]]>

I am trying to simulate mixed convection problem using Lattice Boltzmann method, and trying to make it grid independent.

I have assigned the values in the following way:

grid size: nx=200, ny=200

alpha=0.0141

visco=0.01

Prandtl number=0.71

tauf=(3*visco+0.5).........for momentum distribution function

taug=(3*alpha+0.5)........for thermal distribution function

u_top=(Re*visco)/(sqrt(3)*nx)

Ma=u_top*(sqrt(3))

Now, this top lid velocity(u_top) is used in the iterations to calculate the macroscopic variables. Since, u_top is depending on grid size, so every time this input parameter gets changed with changing grid size.Hence, I am facing problem with this grid independence test. It would be a great help if anyone can suggest me any solution.

Shikha]]>

In the standard LBM it holds that

tau = nu / c_s^2 + 1/2 (Eq 1)

where tau is the relaxation time, nu the kinematic dynamic viscosity, and c_s the speed of sound.

It also holds that

nu = mu / rho (Eq 2)

where mu is the regular (non-kinematic) dynamic viscosity and rho the macroscopic mass density.

Substituting Eq 2 in Eq 1 gives

tau = mu / rho / c_s^2 + 1/2 (Eq 3)

For an isothermal incompressible flow we assume the regular dynamic viscosity 'mu' is constant. We may not assume the kinematic dynamic viscosity 'nu' is constant. So, I would say the relaxation time 'tau' is not constant but depends on the locally computed mass density 'rho', just like Eq 3 makes clear. Still, most LBM papers state that the relaxation time 'tau' is constant. Can anybody shed light on this?]]>

I'm struggling to get a working LBM reaction-diffusion implementation. I have a pretty weak mathematics and physics background, and thus I'm having a hard time understanding the notations around the BGK operator. I would like to know if I understood the basics correctly.

Right now, what I'm doing is the following (v is the diffusive species I'm interested in), on a D2Q5 grid, in pseudo-code:

v[0, :] = initial_condition t = 0 while t < t_max: for each node x: compute a pseudo (pre-collision?) dv[x]/dt using the forward euler method for each node x: real dv[x]/dt = 1/3 * dv[x]/dt + 1/6 * dv[left of x]/dt + 1/6 * dv[right of x]/dt + 1/6 * dv[above x]/dt + 1/6 * dv[below x]/dt (if x is on a domain boudary, use bounce-back condition) v[t, x] += dv[x]/dt t += dt

Is this correct, theory-wise, or am I missing something?

Thanks for any help. I'm happy to share my code if anyone wants to go this far to help me. Once I'll have it working (probably in python), I will distribute it without conditions, so it could for instance be added to the example sections of palabos.]]>

What I can see is that the whole bounding box of the voxel mesh is produced, and if the flag can be used to produce only the shape of the geometry as it is represented in stl, no position shift and 1:1 (scaling factor = 1), how can it be done?

Any example of codes?

Regards,

Jinstone]]>