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  1. pjhype

    Element Size-Any effect to solution other than accuracy?

    You probably deleted the elements but kept the nodes with the constraints. These nodes are not necessarily connected to the model, resulting in the error. If the nodes of the refined model match the nodes of the coarse model, you could perform a coincident node check and keep the constraints...
  2. pjhype

    Element Size-Any effect to solution other than accuracy?

    What is the error message? pj
  3. pjhype

    viscous damping in NE/Nastran?

    Brad, I don't understand your distinction between "independent of frequency" and "constant w.r.t. frequency". Perhaps you could clarify. The damping force due to structural damping is equal to: i*G*k*u where i=sqrt(-1) G=structural damping coefficient...
  4. pjhype

    viscous damping in NE/Nastran?

    Chad, In linear finite element analyses, there are three types of damping: (1) structural damping, which creates damping forces that are constant w.r.t. frequency, (2) viscous damping, which creates damping forces that increase linearly w.r.t. frequency, and (3) modal damping, which...
  5. pjhype

    wahts the reason of a peak at 50Hz in the spectrum

    I once knew a guy who traveled all over the world "measuring" vibration levels in semiconductor facilities. When I analyzed the data, I found only peaks at 50 and 60 Hz. It turned out that he was using ICP accelerometers and forgot to turn on the ICP power supply in his analyzer! pj
  6. pjhype

    Eigenvalue analysis

    Mass Normalization means that each eigenvector is scaled to a unit value of generalized mass, that is, (PHI-transpose)* M * (PHI) = 1.0 Where PHI is the eigenvector and M is the modal mass matrix. This is done in order to simplify computational and storage requirements in the finite element...
  7. pjhype

    25 lbs preload spring

    mpoc, I cannot tell you the amplification factor without seeing some test data. I would recommend that you perform a test where you would put an accelerometer on the armature and subject the motor to a sine sweep in the frequency range of interest. This will give you the transmissibility of...
  8. pjhype

    Termal loads

    I think you can perform your thermal analysis, save the output and make the output set current, then go to Model, Load, From Output, and FEMAP will automatically define your nodal temperature loads. You should then use these nodal temperature loads in your structural analysis to perform a...
  9. pjhype

    25 lbs preload spring

    mpoc, f = [1/(2*pi)]*sqrt(k/m) where k = 620 lb/in m = (1.3 / 386.4) sl This yields a result of 68 Hz for the 1.3 lb mass. This is valid only if you can model the armiture as being supported on the preload spring as a single degree-of-freedom oscillator. pj
  10. pjhype

    25 lbs preload spring

    mpoc, Could it be that during vibration testing you are exciting the natural frequency of the armature on the preload spring? According to the numbers you are providing, the 1.3lb armature will vibrate at 68 Hz and the 2.2lb armature will vibrate at 53 Hz. If you can provide the value of the...
  11. pjhype

    FEM, Earthquake vs. thermal exp.

    If you are performing a linear static analysis using the peak g-loading from the earthquake, and if you are calculating the steady-state thermal expansion, you can analyze the loads separately then combine the results in your post-processor. You could then determine the maximum allowable...
  12. pjhype

    Elastomer-metal Interface stresses

    You should look at the stress gradients to determine which stresses look more reasonable. Keep in mind that the nodal stresses are average stresses obtained through the interpolation of the stress field defined by the element integration points. In real life, there are plenty of applications...
  13. pjhype

    Elastomer-metal Interface stresses

    Biomedman, What you have "discovered" is a known singularity in the mathematical theory of linear elasticity that occurs at the interfaces of dissimilar materials (boundary layer effect). The singularity is due to the fact shear stress is being transferred between the two materials...
  14. pjhype

    Novice at FEA: needs advice

    Regarding the finite element books, check out the following web site: http://www.solid.ikp.liu.se/fe/index.html pj
  15. pjhype

    Solutions for U.S. Unemployment and the Loss of Manufacturing Jobs:

    QCE: No, I never said that engineering cannot change the world. The statement meant that engineering cannot (directly) change people's values. If someone feels that they can improve their quality of life with material things, it is engineering's role to supply these things. You cannot...
  16. pjhype

    Solutions for U.S. Unemployment and the Loss of Manufacturing Jobs:

    Scott, I sense that you're thought process is in the middle of a dichotomy with an outcome where you cannot possibly win. On one hand, you are an engineer, who is (presumably) on the forefront of technology and developing products for the betterment of mankind. This includes making...
  17. pjhype

    How to connecting solid interface meshes together?

    The reason for the singularity is not obvious based on what you described. I am assuming that the mesh on the upper cube matches the mesh on the lower cube one-to-one across the interface. I am also assuming that you are using AUTOSPC. You might try constraining the independent nodes on the...
  18. pjhype

    Solutions for U.S. Unemployment and the Loss of Manufacturing Jobs:

    swertel, I’d like to quote from another well-known movie, Wall Street, where the main character makes the point that “greed is good”. Why should we be penalized for wanting a better life? Hasn’t this been the driving force for our economy since the industrial revolution? Are you willing to...
  19. pjhype

    Designing and Testing to Meet Standard Vibration Test Curves

    This is a HUGE area. You might want to start by familiarizing yourself with the testing methodology. A good place to start would be MIL-STD-810F, Method 514.5 (available on-line) that explains some of the basic concepts for testing of payloads on fixed wing aircraft. You should also pay...
  20. pjhype

    qualification for an acoustic engineer

    It depends on what industry you are interested in. The qualifications are different if you plan on a career in architectural, automotive, audio equipment, environmental, underwater, or aerospace acoustics. Some of the fundamental qualifications include understanding the mechanics (physics)...

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