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Sound speed in water

Posted 8 oct. 2013, 14:37 UTC−4 Version 4.3b 5 Replies

Ying Zhang
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I need the exact sound speed in water. However, the material contents show it is a function of temperature as cs(T[1/K)). Firstly, how can I read this function? Then how can I set the temperature or the initial temperature? I
am dealing with wave propagation problem, in which temperature should not change.

Thanks
5 Replies Last Post 9 oct. 2013, 09:38 UTC−4
Jesus Lucio
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Posted: 1 decade ago 8 oct. 2013, 18:50 UTC−4
Hi, Ying,

That property can be reached by something similar to:
mod1.mat1.def.cs(300) ,
where "mod1" is the identifier for the model (not necessary if you are going to call that property from inside the model), "mat1" is the identifier of the material (in this case it should be water), and the rest is the name of the node where the property is located. You can see this by opening the nodes inside the material (there is a node with its basic properties). In the example I have set temperature to 300 K.

In the Model Builder you can find the selected temperature in the field "Model Inputs", inside the physics node (for instance, "Pressure Acoustics Model"): there one field has the actual value of temperature (by default 293.15[K]).

Regards.
Jesus.
Hi, Ying, That property can be reached by something similar to: mod1.mat1.def.cs(300) , where "mod1" is the identifier for the model (not necessary if you are going to call that property from inside the model), "mat1" is the identifier of the material (in this case it should be water), and the rest is the name of the node where the property is located. You can see this by opening the nodes inside the material (there is a node with its basic properties). In the example I have set temperature to 300 K. In the Model Builder you can find the selected temperature in the field "Model Inputs", inside the physics node (for instance, "Pressure Acoustics Model"): there one field has the actual value of temperature (by default 293.15[K]). Regards. Jesus.
Ying Zhang
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Posted: 1 decade ago 8 oct. 2013, 19:50 UTC−4
Thanks, Jesus

But I still cannot find "Model inputs". Could you tell me more accurately where it is?

In addition, even I set temperature, I still cannot know what value Comsol uses for calculations. Is there any way to figure this out?

Thanks,

Ying
Thanks, Jesus But I still cannot find "Model inputs". Could you tell me more accurately where it is? In addition, even I set temperature, I still cannot know what value Comsol uses for calculations. Is there any way to figure this out? Thanks, Ying
Jesus Lucio
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Posted: 1 decade ago 9 oct. 2013, 05:03 UTC−4
Hi,

"Model inputs" is (if needed) inside the main domain node belonging to the corresponding physics.

About the exact value of the speed of sound, you can see a plot of the function in its node (look inside "Materials" node, then the node of your material, then the node for basic functions and then the node to the function you need): there you can click on "Plot" or else press F8. In the graphics window you will see a graph of the function. You can get also numeric values at: "Results / Derived Values / Global Evaluation": there you can type: "mod1.mat1.def.cs(300)", where I took 300[K] as the temperature. The result is given in a Table.

Regards,
Jesus.
Hi, "Model inputs" is (if needed) inside the main domain node belonging to the corresponding physics. About the exact value of the speed of sound, you can see a plot of the function in its node (look inside "Materials" node, then the node of your material, then the node for basic functions and then the node to the function you need): there you can click on "Plot" or else press F8. In the graphics window you will see a graph of the function. You can get also numeric values at: "Results / Derived Values / Global Evaluation": there you can type: "mod1.mat1.def.cs(300)", where I took 300[K] as the temperature. The result is given in a Table. Regards, Jesus.
Ying Zhang
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Posted: 1 decade ago 9 oct. 2013, 09:14 UTC−4
Thanks, Jesus. And how can I model infinite or semi-infinite field?

Thanks, Jesus. And how can I model infinite or semi-infinite field?
Jesus Lucio
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Posted: 1 decade ago 9 oct. 2013, 09:38 UTC−4
Hi,

There are theoretical expressions for that (problem known as "absorbing" or "low-reflecting boundary condition" or "open boundary condition"), but you could resolve it easier using some of the special boundary conditions present in some physics/modules (for instance, "scattering boundary conditions" in case of RF Module). You can also use Infinite Element Domains or Perfectly Matched Layers, also present only in some modules. Please, look for them in the documentation (page 330 in COMSOL Ref. Manual, v. 4.3b).

Regards,
Jesus.
Hi, There are theoretical expressions for that (problem known as "absorbing" or "low-reflecting boundary condition" or "open boundary condition"), but you could resolve it easier using some of the special boundary conditions present in some physics/modules (for instance, "scattering boundary conditions" in case of RF Module). You can also use Infinite Element Domains or Perfectly Matched Layers, also present only in some modules. Please, look for them in the documentation (page 330 in COMSOL Ref. Manual, v. 4.3b). Regards, Jesus.

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