Calculation of the natural frequency of piping systems

I don’t know that either. Looking forward to experts solving this.

When calculating the natural frequencies of piping systems, generally only the first few modes are considered. The specifications require that the natural frequency be greater than 3 Hz; so, how should it be compared with that specific natural frequency?

Hehe, 3HZ is already very low; it’s probably compared to the first order!

Since this issue relates to software-related problems, it’s difficult for me to provide answers to everything; I do know some things about it, and since this topic is worth discussing, I will answer part of it. I hope that experts can provide complete answers. Hehe. 1. On the \"lumped masses\" page, the \"mass\" field is needed only when there are components with concentrated mass in the pipeline – in such cases, it’s necessary to assign a value to that concentrated mass. For example, when there is a valve, it is necessary to specify the eccentric mass of the valve. 2. Snubbers are shock absorbers that only work against vibrational loads; they have no effect on static or thermal loads. They are specialized supports used for seismic resistance, so there is certainly no need to fill in information regarding them if such supports are not used. 3) max no. of eigenvalue calculation is the maximum order of modal analysis to be considered; generally, the first 30 orders are sufficient. You can compare the results: by considering only the first 30 modes or only the first 50 modes and then performing spectral analysis, the difference in the stress values obtained should be within 5%. 4) Frequency cutoff refers to the cut-off frequency. Generally, more attention is paid to the frequencies prior to this cut-off frequency as well as the spectral analysis associated with them, since those frequencies are quite important and constitute the main part of the modal analysis and spectral analysis. My explanation may not be very professional; I welcome corrections from those who are more knowledgeable!

Thank you so much. So, does the natural frequency we’re talking about refer to the first order? I saw that the value for the first order is only around 0.2, which is much smaller than 3 Hz. When there’s a valve, it’s necessary to specify the eccentric mass of that valve. What exactly does this eccentric mass refer to? The rigid components have already been taken into account in the modeling process; is it still necessary to specify it here?

Hehe, natural frequencies are divided into the first-order natural frequency, the second-order natural frequency, and so on. The first-order natural frequency you calculated is only 0.2 Hz. I can only say that you need to check your model and constraints; if the first-order frequency is too low, the stress levels will be high when you conduct spectral analysis in the future. The eccentric mass of a valve arises because the operating rods of many valves are relatively large in size and have a mass that is comparable to or even greater than that of the valve body itself; as a result, the center of mass of the valve is not located at the geometric center of the valve body. The distance between the center of mass and the geometric center of the valve body is what is known as the eccentricity. This can be found in the technical specifications or similar documents provided by the supplier. I’m not sure what you mean by a rigid component. When modeling, for the valve body we only take into account the weight of the insulation layer and the working fluid; the element that connects the valve body to the eccentric point is a massless rigid unit. The masses of the valve body and the control lever are both assigned to the eccentric point. The rigid component you’re referring to is probably the part that connects the center of the valve body to the eccentric point.