[Weekly Question] (Issue 2, 2009) – “Dynamic Analysis – Harmonic Analysis””

I’ll follow up with a post explaining the differences between the two software programs. For pipeline systems, the most common types of vibration are those in the pipelines of reciprocating compressors and reciprocating pumps. This back-and-forth motion can often be represented by a force or displacement in sine form, known as harmonic loading. Harmonic analysis transforms vibration problems into a simple static force resolution process, and using this method as much as possible brings great convenience. 　　AutoPSA7.0 supports multiple harmonic loads acting on the piping system simultaneously, including harmonic forces and harmonic displacements, as well as cases with damping. Additionally, the combined effect of multiple harmonic loads with different frequencies and phases can be calculated, and resonance phenomena can be examined using frequency increments. However, the relative error between the two remains less than 0.13%. This post was last edited by skybiue123 on 2009-2-16 15:40.]

I was hoping for some examples such as reciprocating compressors, to study them first and then discuss them; I wonder what the moderators think?

Piping system dynamic analysis actually involves two aspects: the calculation of the natural frequencies of the fluid within the pipes and the pressure non-uniformities, as well as the calculation of the natural frequencies and dynamic responses of the piping system structure. Reducing pressure pulsations can lower the amplitude of the excitation force and prevent excessive vibration displacements; however, sometimes, even with very small pressure pulsations, the piping system may still experience significant mechanical vibrations due to being close to a mechanical resonance state. Therefore, during the design process, in addition to analyzing pressure pulsations, it is also necessary to analyze the vibration of the piping structure, calculate and adjust its natural frequencies to avoid mechanical resonance, and verify that the vibration displacements and stresses of the piping under pressure pulsations remain within acceptable limits. For the compressor outlet pipeline, the lowest natural frequency of the piping structure shall not be lower than 8 Hz. Regarding the control of the natural frequency of piping systems, foreign companies are more stringent than domestic ones; generally, it is required that this natural frequency be no less than twice the machine’s excitation frequency. In conducting analyses, the natural frequency of the piping systems should be kept at least 1.2 times higher than the machine’s excitation frequency

1. There are two scenarios: for pipes that have already been designed, the issue is to address vibration problems; for new systems, the goal is to prevent vibration from occurring. 2. Pipe systems have mechanical frequencies (i.e., natural frequencies), which are related to the stiffness and mass of the pipes. The softer the pipe, the poorer its stability, and its first natural frequency will be low. The fluid inside the pipe also has its own frequency, determined by the properties of the fluid, the layout of the pipes, and the size of the connected equipment. If the frequency of the fluid matches the mechanical frequency of the pipe, resonance occurs. 3. The effects of the fluid on the pipes include water hammer, steam hammer, and other impacts on the pipes; pulsations in the fluid flowing through compressors, resonance in the pipes, and vibrations in rotating equipment can all lead to pipe vibrations; additionally, large nearby equipment can also cause vibrations. 4. It is often difficult to obtain information about the equipment, which results in less accurate analyses

CAESARII includes various dynamic analysis modules to simulate mechanical problems caused by different dynamic loads. Natural frequency analysis of the gas (liquid) column in reciprocating compressor (pump) pipelines-----Preventing gas (liquid) column resonance ； (Modal analysis) Analysis of pressure pulsations in the pipelines of reciprocating compressors (pumps) – Controlling pressure pulsation levels ； (Resonance analysis) Analysis of pipeline natural frequencies – Preventing resonance in pipeline systems ； Analysis of forced vibration response in pipelines-----Controlling pipeline vibration and stress ； Stress analysis of pipelines under impact loads-----Preventing pipeline vibration and excessive stress ； (Response spectrum or time-history analysis) Pipe **analysis-----to prevent excessive pipe **forces. (Response spectrum or time-history analysis)

:)It seems the person upstairs is a customer of Changsha Youyi