Enhancing the collaboration of earthquake engineering research infrastructures

Towards stronger international collaboration of earthquake engineering research infrastructures International collaboration and mobility of researchers is a means for maximising the efficiency of use of research infrastructures. The European infrastructures are committed to widen joint research and access to their facilities. This is relevant to European framework for research and innovation, the single market and the competitiveness of the construction industry.JRC.G.4-European laboratory for structural assessmen

Element and system design for active and passive vibration isolation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2005.Includes bibliographical references (p. 277-294).This thesis focusses on broadband vibration isolation, with an emphasis on control of absolute payload motion for ultra-precision instruments such as the MIT/Caltech Laser-Interferometric Gravitational Wave Observatory (LIGO), which is designed to measure spatial strains on the order of 10-²¹. We develop novel passive elements and control strategies as well as a framework for concurrent design of the passive and active elements of single-stage and multi-stage isolation systems. In many applications, it is difficult to construct passive isolation systems compliant enough to achieve specifications on low-frequency ground transmission without introducing hysteresis as well as high-frequency transmission resonances. We develop and test a compliant support that employs a post-buckled structure in con- junction with a compliant spring to attain a low-frequency, low-static-sag mount in a compact package with a large range of travel and very clean dynamics. Most passive damping techniques increase ground transmission at high frequency, but tuned-mass dampers are decoupled from the ground. We explore the tuned-mass damper as a passive realization of the skyhook damper, obtain the optimal designs for multiple-SDOF systems of dampers, propose the concept of a multi-DOF damper, and show that MDOF dampers that couple translational and rotational motion have the potential to provide performance many times better than that traditional tuned-mass dampers. Active control can be used to improve low-frequency performance, but high-gain control can amplify sensor and actuator noise or cause instability. We study several control strategies for uncertain plants with high-order dynamics.(cont.) In particular, we develop a novel control strategy, "model-reaching" adaptive control, that drives the system onto a dynamic manifold defined directly in terms of the states of the target. The method can be used to robustly increase the apparent compliance of an isolation mount and maintain a -40 dB/decade roll-off above the resulting corner frequency.by Lei Zuo.Ph.D

Active noise control in a luxury vehicle

Structure-borne road noise is a critical sound attribute for the overall Noise Vibration& Harshness (NVH) performance of modern luxury vehicles. Currentpassive NVH solutions require structural design modifications, in order to controllow frequency sources that cause structure-borne noise. Active Road NoiseControl (ARNC) has been demonstrated to several commercial vehicles as analternative solution that does not compromise other performances of the car,especially vehicle dynamics. Automotive manufacturers of luxury vehicles, suchas Bentley Motors Limited, are expected to build cars that meet high standardsof driving performance and refinement levels. This thesis focuses on the developmentof an active sound technology for road noise with the use of NVHanalysis methods, which are a common practice in the vehicle development process.Modern NVH methods of road noise analysis reveal the locations of themost predominant structure-borne noise sources. There are significant advantagesin using NVH analysis techniques for the design of ARNC systems, sincethey o_er integrated solutions to the automotive industry in terms of time andcost reduction. A method for defining the accelerometer sensors number andtheir locations on the axles has been developed as an alternative to existingmethodologies, which are applied from the early stages of the NVH development.A physical road noise simulator was developed for replicating road noise.Four random uncorrelated forces were applied on the tyres for analysing andevaluating ARNC systems. In terms of feedforward control, a computer modelof a causal adaptive feedforward system was used to investigate the relationshipbetween the locations, DoF and the performance of the control system.An adaptive system was installed on a Bentley vehicle for conducting the ARNCmeasurements. The adaptive ARNC system was tested on the physical road noisesimulator. The vehicle's tyres were excited by broadband random forces andmaximum 10 dB(A) reduction at the centre frequency of the tyre cavity resonancewas achieved. When the control was focused on the road rumble, then overall3 dB(A) up to 500 Hz were removed from the noise levels measured at the rearheadrests. In terms of road noise testing, a portable multichannel controller wasintegrated with the vehicle electrical system for road noise data acquisition andreal-time ARNC. Finally, the performance of the portable controller is predictedbased on data acquired by the same multichannel system and therefore highlightthe potential use of this system as an ARNC controller

Magnetic Bearings

The term magnetic bearings refers to devices that provide stable suspension of a rotor. Because of the contact-less motion of the rotor, magnetic bearings offer many advantages for various applications. Commercial applications include compressors, centrifuges, high-speed turbines, energy-storage flywheels, high-precision machine tools, etc. Magnetic bearings are a typical mechatronic product. Thus, a great deal of knowledge is necessary for its design, construction and operation. This book is a collection of writings on magnetic bearings, presented in fragments and divided into six chapters. Hopefully, this book will provide not only an introduction but also a number of key aspects of magnetic bearings theory and applications. Last but not least, the presented content is free, which is of great importance, especially for young researcher and engineers in the field

Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, part 2

A collection of papers presented at the Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems is given. The papers address modeling, systems identification, and control of flexible aircraft, spacecraft and robotic systems

Design of a small fast steering mirror for airborne and aerospace applications

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 177-181).This thesis presents the analysis and design of a small advanced fast steering mirror (sAFSM) for airborne and aerospace platforms. The sAFSM provides feedback-controlled articulation of two rotational axes for precision optical pointing. The design, useful for both disturbance rejection and high-speed scanning applications, incorporates a flux steering actuator with a ring core magnetic configuration. The novel magnetic concept enables a dramatic size reduction compared with heritage systems. The moving armature is supported with a combination of elastomer sheets and active position control. Local angular and mirror-normal displacement is sensed with integrated capacitive sensors. Analysis content includes specification of performance requirements based on a realistic deep-space laser communication mission, magnetic equivalent circuit and three-dimensional magnetostatic finite element analysis of the actuator, and a 3D structural optimization of the moving armature modal frequencies. The resulting design is one iteration removed from a flight -ready model. The sAFSM hardware is in fabrication, and anticipated performance exceeds 10 krad/s2 angular acceleration, 10 mrad range, and 9 kHz closed-loop bandwidth.by Michael Thomas Boulet.S.M