Harmonic Load
Harmonic loads can be loads from any sinusoidal loading, such as from rotating equipment or reciprocating pumps on a line. The magnitude of the loading should be determined before analysis. If only one compressor is on a line, then only one harmonic load is input. If more than one load is acting on the same line, then the phase (angle) or the separation in timing of application of each harmonic load becomes important (consider for example that the two loads may be equal and opposite thus canceling out any dynamic imbalance, or the two loads can be in the same direction, say +X and separated by 30° phase angle). So, the situation must be carefully analyzed before imposing these loads.
Harmonic analyses of linear structures are generally performed to determine the steady-state response to long-duration loads, which vary sinusoidally (harmonically) with time, thus enabling you to verify whether your designs will successfully overcome resonance, fatigue, and other harmful effects of harmonic vibrations. In a harmonic analysis, all long-duration loads and the structural response vary sinusoidally at the same frequency.
Various parameters for harmonic analysis are specified in this dialog shown above.
Damping
CAEPIPE applies this factor to all the modes. Enter value of critical damping as a percent, not as a fraction (Example: For 5%, enter 5, not 0.05).
Combination
CAEPIPE combines modal responses using one of two methods: Root mean square (RMS) or Absolute sum (which may be too conservative). Pick one.
After you input the data here, then apply Harmonic loads at the Data column of the corresponding nodes of interest in the piping model. Then, select Harmonic under the menu Loads > Load cases for analysis.
The Harmonic Load dialog is shown below:
The harmonic load can be imposed as a Force (FX/FY/FZ) at a specified frequency and phase angle. You may be able to get more information on the harmonic loading (mass, rpm, eccentricity, etc.) from the manufacturer of the equipment.
Since a harmonic load response is unsigned, results do not have signs (+ or –).