k-Wave

1. mohsen
   

   Member
   Joined: Dec '14
   Posts: 10

   tanx a lot for your nice guidances

   i am trying to solve a 1-D propagation of photoacustic wave in multi layers media analytically.

   firs i am too confused about my boundary conditions in first and end points. what B.C s should be used for my model.

   another thing is that how could i extend k-wave model for multi layer medias?

   my ultimate question, for photoacustic model what is considered source term in your model because it was not implied about derivative of heat equation that is source term of photoacustic wave.

   best

   mohsen

   Posted 10 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi Mohsen,

   Do you mean the boundary conditions between the layers? In this case, both the acoustic pressure and the particle velocity normal to the surface must remain continuous across the boundary. You can already use k-Wave for modelling layered media. A good place to start is to work through the examples included in the toolbox, starting with the Initial Value Problems (you can open these via the help browser in MATLAB). I'd also advise taking a look at the k-Wave manual. This includes a description of the source terms used in k-Wave.

   Brad.

   Posted 10 years ago #

3. mohsen
   

   Member
   Joined: Dec '14
   Posts: 10

   thnak you brad

   Posted 10 years ago #

4. mohsen
   

   Member
   Joined: Dec '14
   Posts: 10

   brad i am solving this equation analytically too. indeed i will vallidated my method by k-wave toolbox. i was meaning about boundaru condition indeed, first and end points. what is considered in k-wave or what do i consider in my model. another thing initial value problem that is considered in k-wave is divided(p(x,0)==0 --> p(x,0)^1/2=-p(x,0)^-1/2).how about my model, should i make it like that?

   really i need help i am confused,so much.

   another thing, could i substitute coeficient cariable with temperature in k wave tool box?

   thank you so much

   Posted 10 years ago #

5. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi mohsen,

   k-Wave uses a perfectly matched layer (PML) at the edges of the domain to simulate free field conditions, so you could consider a Sommerfeld radiation condition.

   "k-wave is divided(p(x,0)==0 --> p(x,0)^1/2=-p(x,0)^-1/2)"

   That's not quite right. k-Wave solves three first-order equations rather than the wave equation. This means it solves for acoustic pressure, density, and particle velocity. Because a time-staggered grid is used, odd symmetry is applied to the particle velocity (rather than the pressure) when using source.p0 to ensure the particle velocity is zero at t = 0.

   k-Wave currently only includes models for wave propagation. If you want to model heat diffusion, you will need to solve the diffusion equation.

   Hope that helps,

   Brad.

   Posted 10 years ago #

6. mohsen
   

   Member
   Joined: Dec '14
   Posts: 10

   hello brad

   I am trying to run this code
   % based on Heterogeneous Propagation Medium Example

   % 3rd April 2012

   clear all;

   % create the computational grid
   Nx = 512; % number of grid points in the x (row) direction
   dx = 1e-3; % grid point spacing in the x direction [m]
   kgrid = makeGrid(Nx, dx);

   % define the properties of the propagation medium
   region1 = (kgrid.x > -Nx/3*dx) .* (kgrid.x < 0);
   region2 = (kgrid.x >= 0) .* (kgrid.x < 0.25*Nx/4*dx);
   medium.sound_speed = 1500*ones(Nx,1); % [m/s]
   medium.sound_speed(region1==1) = 2000;
   medium.sound_speed(region2==1) = 2200;
   medium.density = 1000*ones(Nx,1); % [kg/m^3]
   medium.density(region1==1) = 1500;
   medium.density(region2==1) = 1800;

   % define the initial pressure distribution
   mua = 10;
   p0 = exp(-mua*kgrid.x).*region2;
   source.p0 = p0;

   %define a sensor
   sensor.mask = zeros(Nx,1);

   % run the simulation
   sensor_data = kspaceFirstOrder1D(kgrid, medium, source, sensor);

   but i am encountered with this error !!!

   Error using kspaceFirstOrder_inputChecking (line 523)
   sensor.mask must be a binary grid with at least one element set to 1

   Error in kspaceFirstOrder1D (line 433)
   kspaceFirstOrder_inputChecking;

   Error in k_wave_example_for_Mohsen_201412 (line 64)
   sensor_data = kspaceFirstOrder1D(kgrid, medium, source, sensor);

   what is its problem?

   thnx for your kindly guidance and merry chrismass

   best wishes

   Posted 10 years ago #

7. bencox
   

   Developer
   Joined: Mar '10
   Posts: 292

   Hi mohsen,

   As the error message says, your sensor.mask is all zeros and k-Wave requires it to have at least one 1. If, for some reason, you don't want to use a sensor then just leave it out and run: kspaceFirstOrder1D(kgrid, medium, source, []);.

   Ben

   Posted 9 years ago #

8. mohsen
   

   Member
   Joined: Dec '14
   Posts: 10

   hello dr brad

   how could i change in step time value?

   our how much is step time value in above code?

   thanx

   Posted 9 years ago #

9. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi Mohsen,

   You can define the time step by setting kgrid.t_array. This is introduced in the Recording The Particle Velocity Example, and is also discussed in more detail in Section 3.2 of the k-Wave manual (page 30).

   Brad.

   Posted 9 years ago #

10. mohsen
    

    Member
    Joined: Dec '14
    Posts: 10

    hello dr brad

    so far i was successful with your guidance in understanding of this problem.

    so one point for me is missing

    is that this code so for normilized problem?

    because when i try to run with normal values ,outputs are completely deferent

    best

    mohsen

    Posted 9 years ago #

11. Bradley Treeby
    

    Developer
    Joined: Mar '10
    Posts: 1,643

    Hi Mohsen,

    The code is not normalised in any way. If your source is defined in units of pressure [Pa], then your output will also be in units of pressure.

    Brad.

    Posted 9 years ago #

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