Academic literature on the topic 'Non-linear dynamic FEM analysis of passive rubber isolator'

Building responses have become a major concern in design research. Passive control techniques are implemented to improve structure efficiency. The present research aims to assess the efficiency of base isolation system for a 2D frame and to enhance the performance of structures that are subjected to seismic ground excitations and ground vibrations induced by blast. Two moments of resistant RC frames were studied and output of the isolator (Lead / Rubber Bearing) was observed to reduce structural responses. In SAP2000 non-linear dynamic analysis is conducted to compare normal and irregular moment-resistant frames and structural responses with and without passive control techniques. Isolators are constructed based on time of isolation. Reduction of structural responses is assessed by passive control techniques, and comparative analysis is performed. Mitigating systemic retaliation is affected by the implementation of passive control system.

Application of Electromagnetic induction (EMI) based passively controlled and some local response governed MR dampers in controlling the isolator displacement in base-isolated Irregular building have been studied and compared with the Lyapunov controller. The Irregular building is hybrid isolated with elastomeric rubber bearings and a variety of sliding isolators subjected to strong near field earthquakes acting bi-directionally in horizontal plane. The shear type base-isolated Irregular building is modelled as three-dimensional linear elastic structure having three degrees-of-freedom at each floor level. Time domain dynamic analysis of the building has been carried out using constant-average acceleration Newmark-Beta method and non-linear isolation forces has been taken care by fourth-order Runge-Kutta method. It is observed that the EMI based passive controller performs better than the Lyapunov controller though it reduces less base displacement but gives lower structural response among all the controllers. Local response governed Hyperbolic and Aly’s controller require only velocity and displacement at controller locations sound simpler in application as compared to Lyapunov controller especially to civil engineering structures like Irregular building. The Hyperbolic controller restrains base displacement comparable to the Lyapunov controller but gives less base shear and story drifts to Irregular building. Variable frequency pendulum isolator (VFPI) and variable curvature friction pendulum system (VCFPS) sliding isolators perform better with MR damper control in comparison to conventional friction pendulum system (FPS) in base–isolated Irregular building.

Earthquake induced structural vibrations causes fatigue and reduction of performance of the tall steel framed structures. One of the effective ways for improving the seismic performance of a structure is the use of bracings, dampers and isolators. These devices change the stiffness and damping of the structures thereby reducing the seismic vibrations to a great extent. The main objective of this study is to compare the different types of passive energy dissipating devices in a 3 bay 10 storey steel frame building for better seismic response. The frame was modelled in SAP2000® and some of their responses to earthquake such as base shear, maximum joint displacement, inter storey drift were determined and compare during non-linear dynamic time history analysis in SAP2000®.The passive energy dissipating devices used in this study are diagonal bracing, v bracing, cross bracing, rubber base isolator and friction damper. At first a single storied shear frame model was tested in shake table and results obtained from SAP 2000® were compared. The close proximity validated the procedure. It is observed that addition of dampers to the system increases the stiffness to the frame. When compared, displacement for steel frame with dampers is reduced by 80% and that with different bracing systems are reduced up to 78% as compared to bare steel frame. For base isolators, base shear decreases up to 63.33% but an increase in the maximum joint displacement was observed. The comparison of performances of all types of dissipating mechanisms has been presented in the study.

In the fast-paced contemporary world, new inventions with rapid construction techniques came across usually built to resist the lateral forces. Among them, the demand for tall buildings has put a revolutionary impact on society. In this study, base isolation as an earthquake resisting design technique was utilized which substantially dissociate a superstructure from its substructure and increase flexibility resisting on the ground vibration areas by providing the different types of base isolators. Lead rubber bearing (LRB) isolator is a passive structural vibration control technique. In this research study, seismic behaviour of tube in tube system steel tall building in square, circular, hexagonal, and octagonal plan configurations with varying frame sections with and without LRB base isolation was analyzed for the comparative analysis on the basis of base shear, overturning moment, time period, storey displacement, storey drift and storey acceleration according to IS 1893 (part 1):2016 and UBC 1997 Earthquake code in E-TABS software by non-linear time history analysis. From the results, Octagonal shape was found to be the best option for tall buildings whereas the hexagonal shaped building showed poor performance during an earthquake.

2013/2014
Gli alti livelli di comfort che sono richiesti oggigiorno a bordo di navi da crociera e mega-yachts, portano i progettisti a concentrare la loro attenzione sul problema del rumore strutturale. I motori diesel quattro tempi che sono installati a bordo nave come motori principali o diesel generatori, sono tra le principali sorgenti di rumore strutturale. Per questa ragione, al fine di ridurre l’energia vibrazionale generata da queste sorgenti e trasmessa, tramite le strutture nave, ai locali alloggio, i motori diesel sono sospesi mediante elementi resilienti. Tali elementi resilienti disaccoppiano la sorgente di rumore e vibrazioni (motore diesel) dal mezzo di propagazione (le strutture nave) e isolano dunque la sorgente dalle strutture riceventi. I livelli di rumore strutturale misurati alle fondazioni del motore diesel dipendono dai livelli di velocità misurati sulla sorgente (cioè ai piedi del motore diesel), dai livelli di impedenza meccanica degli elementi resilienti e dai livelli di mobilità meccanica delle fondazioni del motore diesel. Il single-point approach è un approccio semplificato per la previsione dei livelli di rumore strutturale che trascura l’interazione tra elementi resilienti. Secondo tale teoria, al fine di ridurre il rumore strutturale trasmesso attraverso gli elementi resilienti alle strutture nave, si deve ridurre l’impedenza meccanica degli elementi resilienti così come la mobilità meccanica delle fondazioni del motore diesel. In altre parole, si devono aumentare la rigidezza dinamica degli elementi resilienti così come l’impedenza meccanica delle fondazioni del motore diesel. Ad oggi, l’impedenza meccanica degli elementi resilienti può essere ricavata solo mediante prove sperimentali in laboratorio, mentre la mobilità meccanica del motore diesel è solitamente misurata quando la nave è in costruzione. Dunque non vi è la possibilità di predire, in fase progettuale, il rumore strutturale dovuto ai motori diesel. In questa tesi, viene presentata una procedura per la simulazione del rumore strutturale dovuto a motori diesel marini. La procedura si basa su test sperimentali e simulazioni numeriche. Nella prima parte della tesi sono richiamate le basi teoriche necessarie per l’esecuzione delle procedure numeriche e delle prove sperimentali. Sono dunque presentati i risultati delle analisi numeriche per simulare la mobilità delle fondazioni dei motori diesel marini. I risultati delle analisi FEM sono stati validati mediante confronto dei risultati delle analisi numeriche con i dati ottenuti da una campagna di misure eseguite a bordo nave. Successivamente sono presentati i risultati di una serie di prove eseguite per collaudare una nuova macchina sperimentale per misurare l’impedenza meccanica degli elementi resilienti. Lo scopo del collaudo era definire una procedura per l’utilizzo della macchina e per l’esecuzione di prove sperimentali in accordo alla ISO 10846, che è considerata normativa di riferimento per questo tipo di prove. Si è dunque proceduto con l’esecuzione di prove sperimentali eseguite su un elemento resiliente per motori diesel marini. Le prove sono state eseguite a differenti carichi statici. I risultati di queste prove sperimentali sono stati utilizzati per settare un modello numerico che simuli il comportamento non-lineare del componente in gomma del resiliente. I risultati ottenuti sia dalle prove sperimentali sia dalle simulazioni numeriche sono stati utilizzati per predire il rumore strutturale generato dai motori diesel, in accordo al single-point approach. I risultati ottenuti dall’applicazione del metodo sono stati confrontati con misure eseguite a bordo e sono stati discussi per evidenziare vantaggi e svantaggi dell’applicazione del metodo. Le procedure numeriche per la simulazione del comportamento dinamico del resiliente e della fondazione costituiscono un primo passo per l’ottimizzazione del sistema di isolazione del motore diesel marino.
The high level of comfort that is required today on board cruise vessels and mega-yachts, leads the designers to focus their attention on structure-borne noise issues. Four-stroke diesel engines that are installed on board as main diesel engines for the propulsion system and as gen-sets, are usually the main sources of structure-borne noise. For this reason, the diesel engines are usually resiliently mounted in order to reduce the vibration energy generated by these sources and transmitted through the ship structures to the accommodation areas. These mounts decouple the noise and vibration source (diesel engine) from the means of wave propagation (ship structures) and so, they isolate the source from the receiving structures. The structure-borne noise levels measured at the diesel engine foundation depend on the velocity levels measured at the source (diesel engine feet), on the mechanical impedance levels of the resilient mounts and on the mechanical mobility levels of the diesel engine foundation. The simplified theory of the single-point approach neglects the interaction among the resilient mounts. According to this theory, to decrease the structure-borne noise transmitted through the resilient mounts towards the ship structures, the mechanical impedance of the resilient mounts as well as the mechanical mobility of the diesel engine foundation are to be lowered. In other words the dynamic stiffness of the resilient mounts has to be decreased and the mechanical impedance of the diesel engine foundation has to be increased. To date, the mechanical impedance of real resilient mounts can only be obtained by laboratory tests and the mechanical mobility of the diesel engine foundation is usually measured when the ship is under construction, so it is not available for predictive analyses. In the thesis, a procedure for simulating the structure-borne noise generated by marine diesel engine is discussed. The procedure is based on both experimental tests and numerical simulations. In the first part of the thesis, some notes on the theoretical background are presented. Then, the results of FE analyses for simulating the mechanical mobility of a diesel engine foundation are shown. The FE models have been validated by the results of a measurement campaign carried out on board a ship. Then, the results of a series of tests performed to tune a new test rig, designed and built up at the University of Trieste for measuring the mechanical impedance of resilient mounts, are discussed. The campaign for tuning the test rig has been carried out in order to set an experimental procedure that allows achieving results in compliance with the ISO 10846 Standard, which is a sound reference for this kind of tests. As a case study, a large resilient mount for marine diesel engines has been tested to achieve its mechanical impedance curve at different static pre-loads. The outcomes of the experimental tests have been used for tuning the best numerical model of the resilient mount that properly takes into account the nonlinear behaviour of the rubber core. The data of the experimental tests carried out on board ships as well as in laboratory and the outcomes of numerical simulations have been used to predict the structure-borne noise according to the single-point approach. The outcomes achieved by the application of the method have been compared with on board measurements and pros and cons of the method are widely discussed. Moreover, the numerical procedures for the simulation of the dynamic behaviour of the resilient mount and the diesel engine foundation, pave the way for the optimization of the decoupling system of marine diesel engines.
XXVII Ciclo
1982