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Recent content by pilafa

  1. pilafa

    Obtain ABSOLUTE acceleration value in a Response Spectrum Analysis

    @FEA way: I am using Inventor-NASTRAN @driftLimiter: Imagine a simple frame fixed on the ground with a MOTOR on it. The motor has a maximum allowable acceleration in its specs. I want to check that the acceleration "seen" by the motor will be lower than that. I then need the ABSOLUTE...
  2. pilafa

    Obtain ABSOLUTE acceleration value in a Response Spectrum Analysis

    Hi, I am running a Response Spectrum Analysis (it us actually a DDAM analysis, a "special type" of Spectrum Analysis). I understand that the acceleration values that I obtain as result in my structure are RELATIVE acceleration values (I see in the postproc that the acceleration at the base of...
  3. pilafa

    Piezoelectric transducer pressure

    Hi, Does anyone know if there is an equation to calculate the pressure produced by a piezoelectric transducer (maybe in function of electrical power, density of media, etc). Thanks, pilafa
  4. pilafa

    Impedance value on water-air free surface

    - My FEA program has an option to automatically define a "far field". - Yes, I am modelling an air volume above the tank - I will try the time-domain test when I have a chance - Any comment on the previous post (how to choose alpha values)? Thanks
  5. pilafa

    Impedance value on water-air free surface

    Hi, In order to assess my doubt, I built three simple models: M1: - Tank of water with oscillating pressure in the bottom - Surrounding air outside the tank (on the top) with far-field condition on the air domain M2: - Only the tank, with a rigid-wall boundary condition on the...
  6. pilafa

    Impedance value on water-air free surface

    Thanks for your answer btrueblood. In my FEA, I need to input some Z value. So, I found this formula (I guess it is equivalent to yours): (Source) In this formula, alpha is the "absorption coefficient" (I assume that: alpha+R=1) So, when: alpha = 1 -> Z=rho_0*C0 -> the energy is perfectly...
  7. pilafa

    Impedance value on water-air free surface

    Hi, I have an open tank filled with water, with an ultrasound source in it. I calculate the pressure in the water with FEA. I would like to study only the water, and avoid meshing surrounding air (which I think is not necessary anyway). For that, I impose an impedance value on the free...
  8. pilafa

    Acoustic fundamental. Part 1: Real and complex part of Pressure

    No GregLocock, I think hacksaw agrees with you (see previous answers). To summarize hacksaw's answers (correct me if I am wrong): - When working in the frequency domain (with Helmholtz equation): physical pressure is the magnitude of the pressure vector {Re,Im} - When working in time...
  9. pilafa

    Acoustic fundamental. Part 1: Real and complex part of Pressure

    Hi, Thanks for your help. Ok...but how to interpret it then? Maybe it does not have a physical interpretation itself, but has sense only for computing the magnitude of P. Yes, I confirmed with a simple test. I work with lossless flow. I have a source of pressure in a closed box. If all the...
  10. pilafa

    Acoustic fundamental. Part 1: Real and complex part of Pressure

    Hi, There is a series of acoustic concept I would like to review. My background is rather in the fields of elasticity and CFD. I read good references explaining the maths. I can understand them, but most of those references don't link it with practical application. 1) Complex and Real part...
  11. pilafa

    Mixture law for a concrete slab (vibration)

    Hi Doug, Thank you for your answer. Since it's a "noise vibration" problem, I am confident that the amplitudes will be very small. Now my concern about using the Rule of Mixture is that the properties of a reinforced concrete beam are not isotropic. I am thinking about using the Rule of...
  12. pilafa

    Load for a dynamic study: displacement to the base or acceleration field?

    Hi, I want to study the dynamic response of a structure subjects to a sine wave acceleration signal. For that, I will perform an harmonic FEA simulation. To simplify, let's say that the structure is a column fixed on the ground, and that the ground is moving. To apply the loads, I am...
  13. pilafa

    Mixture law for a concrete slab (vibration)

    Hi, I want to study vibration on a simple reinforced concrete structure with FEA. The amplitudes are small, so all the materials stay in the linear domain. I wonder if it is acceptable to use a Rule of Mixtures to calculate an equivalente Young Modulus (Ec= Ef*Vf+ Em*Vm). Thanks, Pierre
  14. pilafa

    Error message with hyperelastic Mooney-Rivlin option

    Hi, I’m doing some analysis with SOLID186 and the Mooney-Rivlin hyperelastic material option (TB,HYPER,1,,5,MOONEY). I have a tetrahedral mesh. Ansys gives me this error: ‘Error related to regular shapes of 3D elements with mixed u/P formulation, it should never happen.’ By the way...
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