【Weekly Question】Question Collection Theme Post (Issue 2, 2009)
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Issue 2 of 2009: Please attach in the comments the questions you would like to know the answers to! I also hope that more relevant professionals will get involved, exchange ideas with each other, and work together to improve everyone’s skills!
I have a question regarding pipe dynamics: The situation is roughly as follows – there is a row of hollow pipes, with saturated water at around 300 degrees inside them. One end of each pipe is fixed, while the other end is subjected to forced displacement vibrations of 25 mm at 30 Hz by a device; we need to calculate the stress conditions in these pipes. Regarding dynamic problems, I believe that the current pipeline calculation softwares, CII and AUTOPIPE, do not have very strong capabilities in this area. In the dynamic analysis of computing devices, we generally use ANSYS software. However, the case of pipes is a bit special: in harmonic response analysis, all loads must be harmonic loads (that vary sinusoidally over time). In the example given above, the forced displacement is a harmonic load, but the pressure and temperature inside the pipe are steady-state loads (they remain almost constant during resonance). So, how does the software handle dynamic and static loads during harmonic analysis? I consulted the technicians at AUTOPIPE (which is the software we use), and their advice was: 1. First, conduct a static analysis of temperature and pressure conditions. 2. Perform a harmonic response analysis with forced displacement again. 3. Combination of the first two operating conditions. What concerns me about this method is that if the static and dynamic loads are calculated separately, then the effect of the static load on the dynamic load is not taken into account. The stress generated by the static load affects the stiffness matrix of the structure, and the stiffness matrix in turn influences the frequency and response of the structure. I haven’t conducted any comparisons yet to determine how large the error is in this processing method. How do you guys handle such issues?
In terms of pipeline dynamic analysis, it’s one problem. If you have any other questions of interest, please reply in the comments!
Let me give an example: when designing large-diameter above-ground pipelines in northern regions, it is necessary to take into account the impact of snow loads, but there is no input for snow loads in C2. So, which method should be used to simulate the snow load?