Seismic response of tuned systems

1987 ◽  
Vol 14 (6) ◽  
pp. 780-787
Author(s):  
A. Ghobarah ◽  
T. S. Aziz
Keyword(s):  
Seismic Response ◽  
Coupled System ◽  
Coupled Analysis ◽  
System Response ◽  
Primary System ◽  
Mass Ratio ◽  
Secondary System ◽  
Seismic Behaviour ◽  
Yield Level ◽  
Key Words Dynamic

A study is made of the seismic behaviour of tuned equipment–structure systems where one or both of the system components experience inelastic deformation. The response is determined using coupled and decoupled models of the system. The effect of various parameters such as mass ratio and yield level on the system response is evaluated.It was found that the mass ratio and yield level of the tuned inelastic system are the key parameters affecting the response of the coupled system. The response of the primary system is found to be insensitive to the variation of the yield level of the secondary system. In addition, the response obtained using uncoupled analysis of the equipment and structure system is generally higher than the response obtained using coupled analysis and may result in grossly overdesigned systems. Key words: dynamic, seismic, response, tuned, coupled, equipment, structure, earthquake, inelastic.

Seismic Design of Jumpers: The Coupling Conundrum

2017 ◽  
Author(s):  
Marcello Cademartori ◽  
Omar Zanoli ◽  
Eric J. Parker
Keyword(s):  
Coupled Model ◽  
Coupled Systems ◽  
Complete Analysis ◽  
Coupled Analysis ◽  
Primary System ◽  
Plant Design ◽  
Efficient Design ◽  
Secondary System ◽  
Coupled Models ◽  
Natural Period

Subsea developments in seismically active areas present a number of engineering challenges. One such item, which is frequently underestimated, is design of jumpers to resist earthquake loading. Jumpers connect quite dissimilar pieces of subsea equipment, for example heavy manifolds on deep foundations, PLETs on mudmats and wellheads supported on slender well casings. If the structures connected have a different dynamic response (e.g. manifold, PLET and wellheads with different fundamental periods), the jumpers receive additional loads from the out of phase structure movements. Such “seismic coupling” is particularly an issue for high pressure high temperature (HPHT) fields, where stiff heavy jumpers are combined with large manifolds. This paper discusses possible approach to evaluate coupling, and provides practical advice for subsea designers. Specifically we address coupling from a point of view of the fundamental period of the connected structures and jumpers, making reference to results of dynamic modeling and codified experience from nuclear power plant design. Differentiation between cases which require fully coupled treatment, and those in which a more straightforward separation and analysis of the individual subsystems is very important to producing an efficient design in reasonable time frame. These aspects are illustrated using a case history from our project files. Coupled dynamic analysis of primary (supporting) and secondary (supported) systems may not be always feasible or desirable. The number of supported structures may be such that a coupled analysis may create computational difficulties. In addition to this, data regarding the secondary system may be not available at the time of the analysis of the primary system with the result that development of a coupled model would be not applicable. In cases where an attempt is made to develop complex coupled systems, sanity checks of such a system may be not an easy task. For these and other reasons, complete analysis of complex coupled systems is rarely performed. The objective of this paper is to explore the conditions under which an uncoupled analysis is justified and to give simplified indication to check the results of coupled models. The paper presents a case study of a manifold-jumper-PLET. The system is evaluated using a standard uncoupled approach in which seismic actions are computed for the manifold, jumper and PLET considered as separate structures. The resulting actions are compared to those from a “coupled analysis” in which the full system is analyzed. The standard uncoupled analysis is found to be unconservative in cases where the jumper’s natural period of vibration is similar to that of the manifold or PLET. This approach shows promise as a means of identifying cases where coupled analysis is required to correctly assess seismic forces.

scholarly journals Dynamical Behavior of a Pseudoelastic Vibration Absorber Using Shape Memory Alloys

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Hugo De S. Oliveira ◽  
Aline S. De Paula ◽  
Marcelo A. Savi
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Dynamical Behavior ◽  
Vibration Reduction ◽  
Hysteretic Behavior ◽  
System Response ◽  
Vibration Absorber ◽  
Primary System ◽  
Secondary System ◽  
Tuned Vibration Absorber

The tuned vibration absorber (TVA) provides vibration reduction of a primary system subjected to external excitation. The idea is to increase the number of system degrees of freedom connecting a secondary system to the primary system. This procedure promotes vibration reduction at its design forcing frequency but two new resonance peaks appear introducing critical behaviors that must be avoided. The use of shape memory alloys (SMAs) can improve the performance of the classical TVA establishing an adaptive TVA (ATVA). This paper deals with the nonlinear dynamics of a passive pseudoelastic tuned vibration absorber with an SMA element. In this regard, a single degree of freedom elastic oscillator is used to represent the primary system, while an extra oscillator with an SMA element represents the secondary system. Temperature dependent behavior of the system allows one to change the system response avoiding undesirable responses. Nevertheless, hysteretic behavior introduces complex characteristics to the system dynamics. The influence of the hysteretic behavior due to stress-induced phase transformation is investigated. The ATVA performance is evaluated by analyzing primary system maximum vibration amplitudes for different forcing amplitudes and frequencies. Numerical simulations establish comparisons of the ATVA results with those obtained from the classical TVA. A parametric study is developed showing the best performance conditions and this information can be useful for design purposes.

scholarly journals Accuracy of Analytical Models to Predict Primary and Secondary System Response in Seismically Isolated Buildings

2021 ◽  
Author(s):  
Cengiz Ipek ◽  
Eric D. Wolff ◽  
Michael C. Constantinou
Keyword(s):  
Seismic Isolation ◽  
Response Spectra ◽  
Analytical Models ◽  
System Response ◽  
Primary System ◽  
Secondary System ◽  
Viscous Dampers ◽  
Floor Response Spectra ◽  
Analytical Results ◽  
Seismically Isolated

Abstract Seismic isolation is generally considered an effective earthquake protection strategy. As application of seismic isolation increases, decisions on the use of one particular isolator versus another isolator increasingly depend on computed responses with complex analytical models. Accordingly, validation of analytical models to predict primary (structural) and secondary system (non-structural component) response in seismically isolated buildings becomes very important. This paper presents comparisons of experimental and analytical results on the primary and secondary system response of a building model in order to provide information on the accuracy of the predicted response. The tested model was configured as a 6-story building at quarter length scale in a moment-frame configuration, and with the following seismic isolation systems: a) Low damping elastomeric bearings with and without linear or nonlinear viscous dampers, b) Single Friction Pendulum (FP) bearings with and without linear or nonlinear viscous dampers, and c) Lead-rubber bearings. Response quantities compared include story drifts and isolator shear forces and displacements for the primary system, and peak floor total velocities and floor response spectra that relate to secondary system response. This paper presents samples results out of a total of 288 comparisons of experimental and analytical results presented in an MCEER report. It is shown that the primary and secondary system response is computed with sufficient accuracy by the analytical models but some response quantities may be underestimated or overestimated by significant amounts.

Effectiveness of Location and Number of Multiple Tuned Mass Damper for Seismic Structures

2020 ◽  
Vol 9 (6) ◽  
pp. 780-783
Keyword(s):  
Seismic Response ◽  
Software Tool ◽  
Tuned Mass Damper ◽  
Structure Study ◽  
Structural Performance ◽  
Mass Ratio ◽  
Tuned Mass Dampers ◽  
Maximum Reduction ◽  
Mass Damper ◽  
Earthquake Data

Tuned mass dampers (TMD) are one of the most reliable devices to control the vibration of the structure. The optimum mass ratio required for a single tuned mass damper (STMD) is evaluated corresponding to the fundamental natural frequency of the structure. The effect of STMD and Multiple tuned mass dampers (MTMD) on a G+20 storey structure are studied to demonstrate the damper’s effectiveness in seismic application. The location and number of tuned mass dampers are studied to give best structural performance in maximum reduction of seismic response for El Centro earthquake data. The analysis results from SAP 2000 software tool shows damper weighing 2.5% of the total weight of the structure effectively reduce the response of the structure. Study shows that introduction of 4-MTMD at top storey can effectively reduce the response by 10% more in comparison to single tuned mass damper. The use of MTMD of same mass ratio that of STMD is more effective in seismic response.

scholarly journals Elastic Response of Acoustic Coating on Fluid-Loaded Rib-Stiffened Cylindrical Shells

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Christopher Gilles Doherty ◽  
Steve C. Southward ◽  
Andrew J. Hull
Keyword(s):  
Cylindrical Shell ◽  
Cylindrical Shells ◽  
Coupled System ◽  
Elastic Response ◽  
System Response ◽  
Elastic Cylindrical Shell ◽  
Fluid Environment ◽  
Reinforcing Ribs ◽  
Double Index ◽  
Stress Boundary Conditions

Reinforced cylindrical shells are used in numerous industries; common examples include undersea vehicles, aircraft, and industrial piping. Current models typically incorporate approximation theories to determine shell behavior, which are limited by both thickness and frequency. In addition, many applications feature coatings on the shell interior or exterior that normally have thicknesses which must also be considered. To increase the fidelity of such systems, this work develops an analytic model of an elastic cylindrical shell featuring periodically spaced ring stiffeners with a coating applied to the outer surface. There is an external fluid environment. Beginning with the equations of elasticity for a solid, spatial-domain displacement field solutions are developed incorporating unknown wave propagation coefficients. These fields are used to determine stresses at the boundaries of the shell and coating, which are then coupled with stresses from the stiffeners and fluid. The stress boundary conditions contain double-index infinite summations, which are decoupled, truncated, and recombined into a global matrix equation. The solution to this global equation results in the displacement responses of the system as well as the exterior scattered pressure field. An incident acoustic wave excitation is considered. Thin-shell reference models are used for validation, and the predicted system response to an example simulation is examined. It is shown that the reinforcing ribs and coating add significant complexity to the overall cylindrical shell model; however, the proposed approach enables the study of structural and acoustic responses of the coupled system.

Transient Response of MDOF Systems With Inerters to Nonstationary Stochastic Excitation

2017 ◽  
Vol 84 (10) ◽  
Author(s):  
Sami F. Masri ◽  
John P. Caffrey ◽  
Hui Li
Keyword(s):  
Degrees Of Freedom ◽  
Broad Band ◽  
Primary System ◽  
Mean Square ◽  
Stochastic Excitation ◽  
Mass Ratio ◽  
Tuning Parameters ◽  
Mdof Systems ◽  
Mean Square Response ◽  
Arbitrary Location

Explicit, closed-form, exact analytical expressions are derived for the covariance kernels of a multi degrees-of-freedom (MDOF) system with arbitrary amounts of viscous damping (not necessarily proportional-type), that is equipped with one or more auxiliary mass damper-inerters placed at arbitrary location(s) within the system. The “inerter” is a device that imparts additional inertia to the vibration damper, hence magnifying its effectiveness without a significant damper mass addition. The MDOF system is subjected to nonstationary stochastic excitation consisting of modulated white noise. Results of the analysis are used to determine the dependence of the time-varying mean-square response of the primary MDOF system on the key system parameters such as primary system damping, auxiliary damper mass ratio, location of the damper-inerter, inerter mass ratio, inerter node choices, tuning of the coupling between the damper-inerter and the primary system, and the excitation envelope function. Results of the analysis are used to determine the dependence of the peak transient mean-square response of the system on the damper/inerter tuning parameters, and the shape of the deterministic intensity function. It is shown that, under favorable dynamic environments, a properly designed auxiliary damper, encompassing an inerter with a sizable mass ratio, can significantly attenuate the response of the primary system to broad band excitations; however, the dimensionless “rise-time” of the nonstationary excitation substantially reduces the effectiveness of such a class of devices (even when optimally tuned) in attenuating the peak dynamic response of the primary system.

Sign in / Sign up

Export Citation Format

Share Document