Q. Regarding the consideration of RPM value to validate assembly.

SaiPrasad Chowdavaram · October 14, 2020, 01:33

Consider there is an exhaust assembly consists of motor and blower. Motor rpm is 3000 and blower rpm is 2500.
I am performing modal analysis to check the characterstics of vibrations based on natural frequencies. In this particular problem, which rpm has to be considered such that based on that I need to improve the natural frequencies away from operating frequency to safeguard the assembly from failure. If I consider blower operating frequency and try to improve, somewhere the coincidence of motor operating frequency happens . Which rpm has to be considered in this problem .
Please let me know ur comments on this case .
Thanku & regards
SaiPrasad Chowdavaram

karachun · October 14, 2020, 16:54

Both frequencies are important, you can not neglect one of them. Usually we try to move natural frequency +/- 10% away. Therefore your dangerous zone is 37,5-55 Hz because two dangerous zones from the engine and blower overlap.

SaiPrasad Chowdavaram · October 15, 2020, 03:49

@karachun sir, thanku for the reply. So, according to ur explaination u meant to say I need to go ahead of motor operating such that both rpm's can be compromised . Plz correct me if I wrong on ur point sir .

karachun · October 15, 2020, 17:57

Yes, if the first mode of exhaust assembly is higher than 55 Hz then structure is safe, resonance not possible.

October 14, 2020, 01:33	Q. Regarding the consideration of RPM value to validate assembly.	#1
SaiPrasad Chowdavaram New Member SaiPrasad Join Date: Dec 2017 Posts: 17 Rep Power: 8	Consider there is an exhaust assembly consists of motor and blower. Motor rpm is 3000 and blower rpm is 2500. I am performing modal analysis to check the characterstics of vibrations based on natural frequencies. In this particular problem, which rpm has to be considered such that based on that I need to improve the natural frequencies away from operating frequency to safeguard the assembly from failure. If I consider blower operating frequency and try to improve, somewhere the coincidence of motor operating frequency happens . Which rpm has to be considered in this problem . Please let me know ur comments on this case . Thanku & regards SaiPrasad Chowdavaram

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October 14, 2020, 16:54		#2
karachun Senior Member Join Date: Nov 2015 Posts: 244 Rep Power: 11	Both frequencies are important, you can not neglect one of them. Usually we try to move natural frequency +/- 10% away. Therefore your dangerous zone is 37,5-55 Hz because two dangerous zones from the engine and blower overlap.

October 15, 2020, 03:49		#3
SaiPrasad Chowdavaram New Member SaiPrasad Join Date: Dec 2017 Posts: 17 Rep Power: 8	@karachun sir, thanku for the reply. So, according to ur explaination u meant to say I need to go ahead of motor operating such that both rpm's can be compromised . Plz correct me if I wrong on ur point sir .

October 15, 2020, 17:57		#4
karachun Senior Member Join Date: Nov 2015 Posts: 244 Rep Power: 11	Yes, if the first mode of exhaust assembly is higher than 55 Hz then structure is safe, resonance not possible.