General Mechanical

Simulating vibration on microscopic slide, observe how acoustic wave propagates

• ocyee627
Subscriber

Hello everyone,
I am trying to simulate a scenario whereby a vibration source is applied at one end of a microscopic slide.
I am interested in observing how the microscopic slide would behave,  or in technical terms, how the acoustic wave is able to propagate from the source of vibration to the other end of the microscopic slide.

Would like to ask what kind of analysis system is recommended for such simulation? And also how would I set the vibration condition to be an oscillatory boundary condition? Is there any ways to able to visualize how the wave propagates through the microscopic slide? Would appreciate the help and guidelines provided as I am a new user of Ansys workbench.

Regards,
OCY

• peteroznewman
Subscriber

Hello OCY,

Acoustic waves travel by compression and decompression of the pressure of the fluid in the direction the wave is traveling.

A long plate of solid material can be excited to generate a compression longitudinal wave along the length of the material, similar to an acoustic wave, but solids can also carry shear waves that are lateral displacements of material as the wave passes. These lateral shear waves have lower wave speeds than the longitudinal compression waves.

The analysis system to visualize a single wave (either compression or shear) traveling along the length of a solid plate is Transient Structural. Here is a discussion.

You are interested in the steady state condition of a structure subject to a constant oscillation force (or displacement), so use a Harmonic Response analysis. In that analysis, any applied force (or displacement) is assumed to be the amplitude of a sinusoidal force (or displacement). The results assume a sinusoidal response and you can plot the amplitude of displacement or stress. This analysis is done over a range of input frequencies. Therefore, you can plot how the response of a point on the model changes as the input frequency sweeps from low to high values of the frequency range requested.

• ocyee627
Subscriber

Thank you for the recommendations! However, if I want to add a droplet on top of the glass slide to see how the droplet behaves correspond to the waves from the glass slide, will that be the same? How can i do this? Please advise and your help would be much appreciated. Thank you in advance!

• peteroznewman
Subscriber

Ouch, you just increased the complexity of the model by several orders of magnitude.
Now instead of solving a Structural problem in the Mechanical APDL solver, you also need to solve a Computational Fluid Dynamics (CFD) problem in the Fluent solver. I would guess that the fluid motion will not affect the structural motion, so this could be a 1-way coupled simulation. That means you solve the mechanical model, then use the motion of the surface as an input to the CFD model. The next level of complexity is when there is a 2-way coupling, where the motion of the structure is changed by the presence of the fluid.

One way this could be done is with the VOF approach. That means making a block of cells on top of the slide to model the air and water. At the start of the simulation, you would assign a blob of cells to be water and the rest would be air. To quote Karthik, "The VOF approach in Fluent uses surface tension (interfacial tension). It is capable of handling contact dynamics near the wall using what is referred to as the wall adhesion approach. Users can specify contact angles to model the movement of the solid-liquid-gas contact line."

Here is a simple explanation of contact angle and surface tension. A published paper is attached to this post.
I am not a CFD expert, but one of them might reply if you are lucky.