Strategies for mitigating wind-induced motion in tall buildings through aerodynamic and damping modifications

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 50-55).The advent of modern structural systems, spurred by advances in construction methodology and high strength materials, has driven the height of modern skyscrapers beyond what was once deemed possible. Although science and technology has been able to increase the strength of building materials such as steel and concrete, their material stiffness has remained virtually unchanged. The end result is a wave of taller, slender and more flexible skyscrapers that are very susceptible to wind-induced excitations. Ever mindful of the fact that human comfort levels are affected by perceived structural responses, engineers must employ various strategies to satisfy serviceability constraints. This thesis presents an overview, in addition to successful applications, of the various aerodynamic and damping modifications that are used to control wind-induced motion in tall buildings. Finally, a modified gyrostabilizer, akin to those used in luxury yachts, is proposed as a possible active control mechanism. The feasibility of this device was studied using simple statics and rigid body dynamics.by Nnabuihe Nnamani.M.Eng

STRUCTURAL CONTROL OF A SMALL-SCALE TEST-BED SHAKER STRUCTURE USING A SPONGE-TYPE MAGNETO-RHEOLOGICAL FLUID DAMPER

Semi-active damping devices have been shown to be effective in mitigating unwanted vibrations in civil structures. These devices impart force indirectly through real-time alterations to structural properties. Simulating the complex behavior of these devices for laboratory-scale experiments is a major challenge. Commercial devices for seismic applications typically operate in the 2-10 kN range; this force is too high for small-scale testing applications where requirements typically range from 0-10 N. Several challenges must be overcome to produce damping forces at this level. In this study, a small-scale magneto-rheological (MR) damper utilizing a fluid absorbent metal foam matrix is developed and tested to accomplish this goal. This matrix allows magneto-rheological (MR) fluid to be extracted upon magnetic excitation in order to produce MR-fluid shear stresses and viscosity effects between an electromagnetic piston, the foam, and the damper housing. Dampers for uniaxial seismic excitation are traditionally positioned in the horizontal orientation allowing MR-fluid to gather in the lower part of the damper housing when partially filled. Thus, the absorbent matrix is placed in the bottom of the housing relieving the need to fill the entire device with MR-fluid, a practice that requires seals that add significant unwanted friction to the desired low-force device. The damper, once constructed, can be used in feedback control applications to reduce seismic vibrations and to test structural control algorithms and wireless command devices. To validate this device, a parametric study was performed utilizing force and acceleration measurements to characterize damper performance and controllability for this actuator. A discussion of the results is presented to demonstrate the attainment of the damper design objectives

Temperature sensitive controller performance of MR dampers

Magnetorheological (MR) dampers can experience large temperature changes as a result of heating caused by energy dissipation, but control systems are often designed without consideration of this fact. Furthermore, due to the highly nonlinear behavior of MR dampers, many control strategies have been proposed and it is difficult to determine which is the most effective. This paper aims to address these issues through a numerical and experimental study of an MR mass isolator subject to temperature variation. A dynamic temperature dependant model of an MR damper is first developed and validated. Control system experiments are then performed using hardware-in-the-loopsimulations. Proportional, PID, gain scheduling, and on/off control strategies are found to be equally affected by temperature variation. Using simulations incorporating the temperature dependant MR damper model, it is shown that this is largely due to a change in fluid viscosity and the associated movement of the lower clipped optimal' control bound. This zero-volts condition determines how close any controller can perform to the ideal semiactive case, thus all types of controller are affected. In terms of relative performance, proportional and PID controllers perform equally well and outperform the on/off and gain scheduling strategies. Gain scheduling methods are superior to on/off control

磁性流体を用いたバックドライブ可能な油圧アクチュエータの開発

早大学位記番号:新7478早稲田大

Modelling and design of a dual channel magnetorheological damper

© Cranfield UniversityA limitation with the current analytical models for predicting the performance of a magnetorheological (MR) damper is that they fail to capture the hysteretic variation of force versus velocity variation correctly. This can significantly underestimate the damper force and overestimate the dynamic range of the device. In this work a transient analytical fluid dynamics model is developed by using a combination of Laplace and Weber transform and Duhamel’s superposition of velocity boundary condition, to overcome these limitations. The solution of the system of nonlinear simultaneous equations, obtained by applying mass flow balance, velocity compatibility conditions and force equilibrium of Bingham plastic plug flow, gives the damper force. This method is shown to generate direct and inverse model of an MR device. The proposed model has been validated against a commercially available MR damper at low speed, to a range of test signals. The mean error using the above model has been shown to be 5% for all the test signals. This compares well with three conventional models which give; transient constant velocity model 35%, quasi static model 35% and phenomenological model 35%. The phenomenological model gives 10% mean error for a sinusoidal input signal. The application of the proposed analytical model has been demonstrated by the design of a novel dual channel damper. The design of the electromechanical components has been shown to be np-hard problem and the optimisation using genetic algorithm has been applied to minimise the volume and electrical time constant. The performance of the dual channel damper has been simulated for various combinations of values of shear yield stress for two channels. Compared to the conventional single channel damper the novel design is shown to give 30% higher damper force, 50% improved dynamic range and limits the effect of transients to within 10% of the damper force. The dual channel damper is an effective solution to resist the onset of turbulent flow in the channels up to 20m/s piston velocity

R&D on control of vibrations under covicocepad during 2007-2008

This paper provides information on the latest R&D within COVICOCEPAD project approved in the framework of Eurocores program. It addresses the use of TLD, base isolation devices, MR dampers and a hybrid technique using both devices together. Some results are provided associated with calibration of a MR damper at FEUP, as well as its inclusion in a small scale laboratory set-up with proper equations of motion of the controlled smart structure. An application of semi-active control technique to a bridge is outlined. Further remarks and details on future tests to be performed in LNEC shaking table, within COVICOCEPAD project, are provided

On dynamic control of structural vibrations research activities conducted within the covicocepad project

This paper provides an overview on the latest research and development (R&D) activities carried out under the project entitled Comparison of Vibration Control in Civil Engineering Using Passive and Active Dampers (COVICOCEPAD) which was executed within the framework of the Eurocores project, as a part of the sixth European program. The general interest of the paper relies upon the variety of presented highlights relevant to structural control research streams currently under development in a number of European universities, addressing the use of tuned liquid dampers (TLD), base isolation devices, magneto-rheological (MR) dampers and a hybrid technique using both devices together. The paper also provides details of a few new testing equipments which are in use of the relevant laboratories. Finally, research projects in the field of structural control at the involved research institutes are reviewed.info:eu-repo/semantics/publishedVersio

A study of a piezoelectric energy harvesting system using magnetorheological fluids

This thesis reports the study of a piezoelectric energy harvesting system using a thin layer of magnetorheological fluid as a soft impact mechanism to enhance the frequency of the energy generator. Currently, the major bottleneck of vibration energy harvesting is the dynamic nature of vibrations in the environment which necessitates that vibration energy harvesters change their frequency to match that of the source. This work used the variable rheological properties of magnetorheological fluids to tune the frequency of a piezoelectric energy harvester. The study employed both numerical and experimental studies to investigate the effect of using the fluid in vibration energy harvesting. The results obtained show an increase in the output voltage and frequency of the device by 9.7% and 36%, respectively. For the first time, a soft impact frequency-increased piezoelectric energy harvesting system using magnetorheological fluid is studied in this thesis

Innovative magnetorheological devices for shock and vibration mitigation

Vibration and impact protection have been a popular topic in research fields, which could directly affect the passengers’ and drivers’ comfort and safety, even cause spines fracture. Therefore, an increasing number of vehicle suspensions and aircraft landing gears are proposed and manufactured. Magnetorheological fluids (MRFs), as a smart material, are growly applied into the above device owing to its unique properties such as fast response, reversible properties, and broad controllable range, which could improve the vibration/impact mitigation performance. MRF was utilized to achieve adaptive parameters of the vehicle suspensions by controlling the magnetic field strength of the MRF working areas. Generally, the magnetic field is provided by a given current, subsequently, it would consume massive energy from a long-term perspective. Thus, a self-powered concept was applied as well. This thesis reports a compact stiffness controllable MR damper with a self-powered capacity. After the prototype of the MR damper, its property tests were conducted to verify the stiffness controllability and the energy generating ability using a hydraulic Instron test system. Then, a quarter-car test rig was built, and the semi-active MR suspension integrated with the self-powered MR damper was installed on a test rig. Two controllers, one based on short-time Fourier transform (STFT) and a classical skyhook controller was developed to control the stiffness. The evaluation results demonstrate that the proposed MR damper incorporated with STFT controller or skyhook controller could suppress the response displacements and accelerations obviously comparing with the conventional passive systems