Showing papers on "Damper published in 1997"

Phenomenological model for magnetorheological dampers

Abstract: Semiactive control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semiactive control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take full advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper's intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical MR damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design an...

Passive Energy Dissipation Systems in Structural Engineering

Abstract: Fundamentals Metallic Dampers Friction Dampers Viscoeleastic Dampers Viscous Fluid Dampers Tuned Mass Dampers Tuned Liquid Dampers Future Direction Glossary Indexes

Rigidity–plasticity–viscosity: can electrorheological dampers protect base‐isolated structures from near‐source ground motions?

Abstract: The concept of seismic protection by lengthening the fundamental period of the structure has been implemented through a number of isolation systems While flexible isolation systems can effectively protect structures from earthquakes containing high frequencies and sharp accelerations, they might amplify the response of the structure when subjected to rapid, long-period motions In this case of long period excitations the stiff superstructure should be 'locked' to the ground, rather than be supported on flexible bearings This paper shows through a comprehensive analytical study that a practical solution to this problem is to provide additional rigidity to the structure using a friction-type mechanism (rigid-plastic behaviour) The presence of friction-type forces reduce substantially the relative displacements of a single-degree-of-freedom structure by keeping accelerations at low levels; however, they are responsible for the presence of permanent displacements Accordingly, the use of controllable fluid dampers is proposed and it is shown that they can be a practical solution to the problem The response of a single-degree-of-freedom base-isolated structures is investigated, and the feasibility of a proposed electrorheological damper to deliver the required forces is discussed

Optimal damper placement for minimum transfer functions

Abstract: The purpose of this paper is to propose an efficient and systematic procedure for finding the optimal damper placement to minimize the sum of amplitudes of the transfer functions evaluated at the undamped fundamental natural frequency of a structural system subject to a constraint on the sum of the damping coefficients of added dampers. Optimality criteria are derived and the optimal damper placement is determined based upon those criteria without any indefinite iterative operation. The present procedure can be applied to any structural system so far as it can be modelled with finite-element systems. The present procedure also enables one to treat structural systems with an arbitrary damping system (for example, proportional or non-proportional) in a unified manner. Due to employment of a general dynamical property, i.e. the amplitude of a transfer function, the results are general and are not influenced by characteristics of input motions. © 1997 John Wiley & Sons, Ltd.

Modulated homogeneous friction : A semi-active damping strategy

Abstract: A control strategy for semi-active friction devices leading to efficient hysteretic dissipaters is proposed. The control algorithm makes the contact force between the sliding surfaces of the damper proportional to the absolute value of the prior local peak of the damper deformation. This control logic leads to a non-linear force–deformation relation that satisfies homogeneity of degree one; this means that, like in a linear viscoelastic damping model, when the deformation is scaled by a constant, the force results are scaled by the same constant. The closed-loop system shows rectangular hysteresis loops which enclose an area proportional to the square of the deformation of the damper. Some characteristics of the dynamic response of structures incorporating this type of semi-active damper are investigated. It is demonstrated that in the case of single-degree-of-freedom models, the period of vibration and decay ratio are independent of the amplitude of vibration. In the case of multi-degree-of-freedom models with this type of nonlinearity, the free-vibration response can exhibit natural modes of vibration. A linearization method is proposed and modelling tools for the delay associated with actuator dynamics and for the flexibility of the brace connecting the damper to the structure are presented. © 1997 by John Wiley & Sons, Ltd.

Seismic testing of a building structure with a semi-active fluid damper control system

Abstract: This paper describes shaking table tests of a multi-storey scale-model building structure subjected to seismic excitation and controlled by a semi-active fluid damper control system. The semi-active dampers were installed in the lateral bracing of the structure and the mechanical properties of the dampers were modified according to control algorithms which utilized the measured response of the structure. A simplified time-delay compensation method was developed to account for delays within the control system. The results of the shaking table tests are presented and interpreted and analytical predictions are shown to compare reasonably well with the experimental results. © 1997 John Wiley & Sons, Ltd.

A comparison of semi-active control strategies for the MR damper

Abstract: Because the behavior of semi-active devices is often highly nonlinear, one of the main challenges in the application of this technology is the development of appropriate control algorithms. In this paper, a number of recently proposed semi-active control algorithms are evaluated for use with the magnetorheological (MR) damper, an innovative semi-active control device that appears to be particularly promising for civil engineering applications. The performance of the resulting control systems are compared through simulation, and the advantages of each algorithm are discussed. The results demonstrate that the performance of the control system is highly dependent on the choice of algorithm employed.

Semiactive control algorithms for structures with variable dampers

Abstract: Semiactive control systems combine the following features of active and passive control to reduce the response of structures to various dynamic loadings: (1) active variable stiffness, where the stiffness of the structure is adjusted to establish a nonresonant condition between the structure and excitation; and (2) active variable damper, where the damping coefficient of the device is varied to achieve the most reduction in the response This study is concerned with examining the effectiveness of variable dampers for seismic applications Three algorithms for selecting the damping coefficient of variable dampers are presented and compared They include a linear quadratic regulator algorithm; a generalized linear quadratic regulator algorithm with a penalty imposed on the acceleration response; and a displacement-acceleration domain algorithm, where the damping coefficient is selected by examining the response on the displacement-acceleration plane and assigning different damping coefficients accordingly Two single-degree-of-freedom structures subjected to 20 ground excitations are analyzed using the three algorithms The analyses indicate that, unlike passive dampers (where for flexible structures, an increase in damping coefficient decreases displacement but increases the acceleration response), variable dampers can be effective in reducing both the displacement and acceleration responses The algorithms are used to compute the seismic response of two structures: (1) an isolated bridge modeled as a single-degree-of-freedom system; and (2) a base-isolated six-story frame modeled as a multi-degree-of-freedom system The results indicate that variable dampers significantly reduce the displacement and acceleration responses

Harmonic Balance Vibration Analysis of Turbine Blades With Friction Dampers

Abstract: Although considerable effort has been devoted to the formulation of predictive models of friction damper behavior in turbomachinery applications, especially for turbine blades, the problem is far from being solved due to the complex nonlinear behavior of the contact surfaces. This paper primarily focuses on analytical and numerical aspects of the problem and addresses the problem in the frequency domain while exploring the viability of equivalent time-domain alternatives. The distinct features of this work are: (i) the modelling of nonlinear friction damper behavior as an equivalent amplitude-dependent complex stiffness via a first-order harmonic balance method (HBM), (ii) the use of sine sweep excitation in time-marching analysis, (iii) the application of the methodology to numerical test cases, including an idealised 3D turbine blade model with several friction dampers, (iv) the verification of the numerical findings using experimental data, and (v) a detailed assessment of the suitability of HBM for the analysis of structures with friction dampers.

Turbine blade damper and seal

Abstract: A damper for a turbine blade in a gas turbine engine includes a main body and may include at least one extended end which is adapted to clear radially inner surfaces of two adjacent blade platforms, to enhance the damping profile of the damper and radial support for a seal. An associated seal for the turbine blade includes supported and sealing portions and may further include a locator that interfaces with a catch structure on the blade to maintain the seal in the proper axial position with respect to the radially inner surfaces of the adjacent platforms. The seal may further include a projection adapted to provide interference with the blade in the event that the damper and seal are installed improperly with respect to each other to prevent such improper assembly.

Combined air exchange and air conditioning unit

Abstract: The combined air exchange and air conditioning unit is used for conditioning air from a conditioned space. The unit comprises an exhaust air chamber, a return air chamber, a supply air chamber, and a fresh air chamber. A supply blower is used for drawing air from inside the supply air chamber to the outside and an exhaust blower is used for drawing air from inside the exhaust air chamber. A central plate damper is provided for regulating air transfers between the chambers. The damper plate is movable within a position range defined between two extreme positions, the first position allowing a connection of the return air chamber with the supply air chamber and a connection of the fresh air chamber with the exhaust air chamber, the second extreme position allowing a connection of the return air chamber with the exhaust air chamber and a connection of the fresh air chamber with the supply air chamber. The unit is further provided with a heat pump for reversibly transferring heat between air to be drawn by the exhaust blower means, and air to be drawn by the supply blower means. The unit combines an air exchange device and an air conditioning device in a very compact housing.

On the current status of magnetorheological dampers: seismic protection of full-scale structures

Abstract: Because of their mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness, magnetorheological (MR) fluid dampers have been shown to be semi-active control devices that mesh well with application demands and constraints to offer an attractive means of protecting civil infrastructure systems against severe earthquake and wind loading. Following an overview of the essential features of MR fluids, this paper discusses the current status of this new technology for seismic protection of structures, including presentation of recent laboratory studies employing a seismically-excited, scale-model building and preliminary analyses of a prototype full-scale MR damper.

Active suspension control to improve vehicle ride and handling

Abstract: SUMMARY In practice most active vehicle suspension work can be traced to two sources, Lotus' modal control and Karnopp's skyhook damper. A model is developed which allows comparison of different active suspension control algorithms. The Lotus modal control algorithm is reviewed, and compared with Karnopp's skyhook damper. It is shown that a tight inner closed loop allows the Lotus algorithm to achieve the inertial damping described by Kamopp for a single comer or quarter car. It is suggested that to achieve simultaneously high inertial damping and good disturbance rejection an inner force loop is desirable. A vehicle control scheme is presented which combines the Lotus modal decomposition with Karnopp's skyhook damper, allowing nearly optimal ride and simultaneously permitting modification of vehicle handling properties.

Active and semi-active control of structures under seismic excitation

Abstract: Considerable effort has been devoted to develop passive and active methods for reducing structural response under seismic excitations. Passive control approaches have already found application in practice. Active control methods, on the other hand, are being vigorously examined for application to civil structures. This paper investigates the application of active and semi-active control schemes to structures subjected to seismic excitations, and it focuses on the use of the sliding-mode control approach for the development of the control algorithms. The possibility of control redundancy with respect to the number of sliding constraints is taken into account in the controller design. Several sets of numerical results are obtained for a realistic 10-storey shear building, subjected to earthquake-induced ground motions and controlled by active or semi-active control schemes. It is observed that both active and semi-active control schemes can be used to reduce the dynamic response. Active control performs very effectively in reducing the structural response, but the required control force values can be quite large to limit its practical application in the case of large and massive buildings. Active regulation of linear viscous dampers was found unnecessary for this type of structural system, as it did not induce any significantly more reduction in the response than the dampers acting passively. On the other hand, it is shown that active regulation of stiffness can be used with advantage to reduce the response. © 1997 by John Wiley & Sons, Ltd.

Wireless air conditioning control system

Abstract: A wireless air conditioning control system is provided. A thermostat assembly measures ambient temperature in an area to which an air conditioning system provides conditioned air. It compares the measured ambient temperature with a predetermined target temperature and wirelessly transmits air conditioning request signals to an air conditioning control assembly responsively to the comparison. The thermostat assembly and the air conditioning control assembly may be automatically mated with one another so that the air conditioning control assembly responds to air conditioning request signals only from a particular thermostat assembly. Where a plurality of transmitters are present, their transmissions are staggered to avoid data collision. The control assembly includes a freeze protection mechanism to protect against freezing conditions in the absence of air conditioning request signals. A battery powered thermostat assembly is intermittently partially shut down to reduce power consumption. The transmitter assembly predicts temperature to account for thermal inertia.

Design rules for MR fluid actuators in different working modes

Abstract: The behavior of actuators based on magnetorheological fluids is determined by a variety of parameters. The magnetorheological properties of the MR suspension, the working mode (shear mode, flow mode, squeeze mode) and the design of the magnetic circuit consisting of MR fluid, flux guide and coil all considerably influence the properties of the actuator. This paper presents design rules for MR fluid actuators in different working modes. The behavior of MR fluids in the three working modes was investigated by using a rotational viscometer, a flow mode damper and a new measuring technique working in the squeeze mode. The measurement results for various magnetic flux densities are reported and the results of the different working modes are compared. High dynamic damping forces dependent on the magnetic field can be achieved especially in the squeeze mode. The design of the magnetic circuit of an MR fluid actuator is analyzed by using finite-element-methods. The advantages of integrating permanent magnets into the magnetic circuit of an MR fluid actuator are pointed out. The working point of the actuator can be adjusted by permanent magnets without consuming any power and the maximum power required to drive the actuator can be reduced. From these results design rules for MR fluid actuators are developed.

Magneto-rheological fluid damper

Abstract: A controllable magneto-rheological damper includes a housing; a piston moly disposed in the housing; a cavity defined by the housing and the piston; a passage fluidically coupled to the cavity; a magneto-rheological fluid contained within the cavity, wherein motion of the piston is damped by flow of the magneto-rheological fluid through the passage; and a magnet disposed to produce a magnetic field within the passage with field lines essentially parallel to the passage.

Numerical Modelling for the Hydraulic Performance Prediction of Automotive Monotube Dampers

Abstract: SUMMARY A computer model of an automotive monotube damper is developed based on fundamental principles of mechanics. The model can identify the required damper valve and/or size for the desired performance and hence speed the design process. Also, a parametric study can be easily conducted to understand the effects of parameters on the performance. A typical monotube damper is introduced and numerical formulations are described. Satisfactory agreement is achieved between model results and test data for a wide range of parameters including stroke conditions, valve combinations, and gas charge pressure. Some of these results are presented including the correlation at low and high speed strokes, cavitation simulation, and thermal effects on the performance.

EVOLUTIONARY MODEL OF VISCOELASTIC DAMPERS FOR STRUCTURAL ApPLICATIONS

Abstract: Th 7 effe~ts oftempe~atureon the energy dissipation of viscoelastic dampers for seismic mitigation of structures are mvestigated. To Simulate the damper behavior, an evolutionary model is proposed to describe ~e dependence o~ ~e ~echanical propertie~ of th~ damper on the deformation frequency and the temperature mcre~e due to diSSipation. Thermorheologlcally Simple materials are considered and the influence of the de­ formatio~ frequency on the storage and loss moduli is modeled using fractional derivative operators. The effect of m~tenal temperature on the for~e-~eformation relation is modeled using the concept of evolutionary transfer func~0!1' and the proposed model IS Implemented using a step-by-step technique in the frequency domain. The p~edictions. of the proposed. model in the case of sinusoidal and seismic deformations show good agreement with e~penmental results. Fmally, the response spectra of single-degree-of-freedom structures with added vis­ coelastic ~pers and subjected to seismic excitation are computed using the proposed evolutionary model; the results obtained show that the thermal effect due to energy dissipation is not always negligible.

Air distribution fan and outside air damper recycling control

Abstract: A system for controlling the operation of an air distribution fan and the operation of a motorized outside air damper of an air conditioning system, having heating and/or cooling and/or humidifying and/or dehumidifying operating modes. The system includes a fan recycling control for periodically energizing and de-energizing an air distribution fan in an air conditioning system in order to operate the air distribution fan for a first selectable time period after a second selectable time period from the end of the last operation of the air distribution fan. The last operation of the air distribution fan could have been due to the heating or cooling or humidifying or dehumidifying or constant fan modes of the air conditioning system, or due to fan operation initiated by the fan recycling control. The system includes an outside air damper recycling control that can open a motorized outside air damper, for the purpose of drawing in ventilation air, each time the air distribution fan operates, and for as long as the air distribution fan continued to operate, can cycle, periodically close then open, the outside air damper based on selectable time periods since it was last opened or closed, respectively. The outside air damper recycling control can de-energize the motorized outside air damper at the end of each operation of the air distribution fan.

Effect of eddy current dampers on the vibrational properties in superconducting levitation using melt-processed YBaCuO bulk superconductors

Abstract: The effect of eddy current dampers on the vibrational properties in superconducting levitation has been investigated using melt-processed YBaCuO bulk superconductors. In vertical vibration, the damping was about 100 times improved by inserting eddy current dampers into the gap between a superconductor and a magnet. On the other hand, in horizontal vibration, eddy current dampers did not greatly affect the vibrationaal properties of superconducting levitation up to a given thickness of eddy current dampers.

Zone control for HVAC system

Abstract: A control assembly for a HVAC system serving a plurality of zones within a structure, having ducting including a damper situated in an outlet of the ducting leading to each zone, a biasing element biasing the damper in a normally open position, and a motor coupled to each damper for closing each damper. A standard manual or automatic change-over thermostat is situated in each of the zones which includes at least a heating signal output and a cooling signal output. The control assembly formed by a collection of diodes and relays includes a pair of relays having a set of normally open contacts coupled between the damper motors and a source of power, one of the pair of relays having a coil coupled to the heating signal outputs of all of the thermostats and another of the pair of relays having a coil coupled to the cooling signal outputs of all of the thermostats so that, upon initiation of a heating or cooling signal from any of the thermostats, power is applied to the motor coupled to each damper for closing each damper. The control assembly includes individual zone controls each of which are formed by a collection of diodes and relays including a first additional relay which has a set of normally closed contacts coupled between the damper motor in the zone and the source of power, and a coil coupled to the heating and cooling signal outputs of the thermostat in the zone so that the initiation of a heating or cooling signal by the zone thermostat opens the normally closed contacts of the first additional relay thus preventing power from being applied to the damper motor leading to the zone thereby permitting the damper to remain open under influence of the biasing element. A second additional relay has a set of normally closed contacts coupled between the cooling signal output of all the thermostats and a control unit controlling the application of power to the cooling unit, and a coil coupled to the heating signal output of all the thermostats so that initiation of a signal from a heating signal output of any of the thermostats prevents the application of power to the cooling unit thus achieving automatic change-over between heating and cooling.