How can we optimise the parameters in a tuned liquid column damper for an mdof system? I have developed the psdf of windecitation force. How can I find rms value?
You may find the following articles useful
Mousavi, S. A., Bargi, K., & Zahrai, S. M. (2013). Optimum parameters of tuned liquid column–gas damper for mitigation of seismic‐induced vibrations of offshore jacket platforms. Structural Control and Health Monitoring, 20(3), 422-444.
Gao, H., Kwok, K. C. S., & Samali, B. (1997). Optimization of tuned liquid column dampers. Engineering Structures, 19(6), 476-486.
Gao, H., Kwok, K. S. C., & Samali, B. (1999). Characteristics of multiple tuned liquid column dampers in suppressing structural vibration. Engineering structures, 21(4), 316-331.
Yalla, S. K., & Kareem, A. (2000). Optimum absorber parameters for tuned liquid column dampers. Journal of Structural Engineering, 126(8), 906-915.
You can do this either in time domain or frequency domain. The former calls for a comprehensive parametric study in which dominant wind parameters (periods, turbulence intensity, etc.) as well as TLCD's parameters (frequency, area ratio, head loss, etc.) should be accounted for. Structural properties (period, inherent damping, etc.) can also be considered. Note that such parametric study might call for significant number of runs (in the order of 10,000 to 1 million). The latter technique can be done through some stochastic analyses. Anyway, time domain analyses are more accurate as structural nonlinearities as well as nonlinear damping of the TLCD can be explicitly addressed. RMS value in the time domain analyses can be easily obtained from obtained time histories. In case of stochastic analyses standard deviation (not RMS) can be obtained form the power spectral density (PSD).
tanku behrouz :)
tanku seyed:)
seyed, since i dont have details of forces in time domain..i simulated the psdf of the wind force acting at the structure Sff(w)..so frequecy domain will be easier for me i hope..
actually i plan to compare tlcd with rheoligical fluid and magnetic rhelogical tlcd..so in
'Magneto-rheological tuned liquid column dampers
(MR-TLCDs) for vibration mitigation of tall
buildings: modelling and analysis of open-loop control
J.Y. Wang a,1, Y.Q. Ni a,*, J.M. Ko a,2, B.F. Spencer Jr. b,3'
they are assuming coefficient of headloss as 30 in conventional tlcd (in most of the papers results comes around 30 also) and using the same value in MR-TLCD also..is it fine if we fix the coefficient of headloss and using it for both???
Absolute value of the head loss coefficient strictly depends on the derived form of the equation of motion. So care should be exercised in selecting its value. Head loss coefficient can have noticeable effect on the efficiency of the TLCD (about 10% to 20%) and adopting a predefined constant value for the head loss coefficient is a little questionable.
You should not use the same head loss coefficient for TLCD and MRTLCD. Note that polarized MR fluid acts as a semi-solid material and lead to significant head loss. In other words, in MRTLCD required head loss is provided mainly through the induced magnetic field. Accordingly initially provided head loss (through orifice, elbows, etc) should not be the same for a fair comparison.
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