Showing papers on "Damper published in 1996"

Modeling and Control of Magnetorheological Dampers for Seismic Response Reduction

Abstract: Control of civil engineering structures for earthquake hazard mitigation represents a relatively new area of research that is growing rapidly. Control systems for these structures have unique requirements and constraints. For example, during a severe seismic event, the external power to a structure may be severed, rendering control schemes relying on large external power supplies ineffective. Magnetorheological (MR) dampers are a new class of devices that mesh well with the requirements and constraints of seismic applications, including having very low power requirements. This paper proposes a clipped-optimal control strategy based on acceleration feedback for controlling MR dampers to reduce structural responses due to seismic loads. A numerical example, employing a newly developed model that accurately portrays the salient characteristics of the MR dampers, is presented to illustrate the effectiveness of the approach.

Phenomenological Model of a Magnetorheological Damper

Abstract: Semi-active 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 semi-active 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 maximum 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 magnetorheological 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 and analysis.

Design of Supplemental Dampers for Control of Structures

Abstract: A suggested method for design of supplemental dampers in multistory structures is presented. Optimal control theory using a linear quadratic regulator (LQR) is adapted to design linear passive viscous or viscoelastic devices dependent on their deformation and velocity (best represented by Kelvin model). The design is aimed at minimizing a performance cost function that produces a most suitable minimal configuration of devices while maximizing their effect. The method is fully effective using full-state static feedback. Since the active feedback action require a linear combination of all states and it cannot be supplied by passive devices, the paper introduces a methodology to eliminate the off-diagonal interactions between states using various engineering ways. This paper shows the development for velocity feedback only, for the sake of simplicity. However, the full-state formulation can be manipulated similarly to obtain a combined position-velocity feedback design. This paper shows a numerical implementation of the design methodology for a structural model prepared for further experimental considerations.

Electrorheological Dampers, Part I: Analysis and Design

Abstract: Electrorheological (ER) materials are suspensions of specialized, micron-sized particles in nonconducting oils. When electric fields are applied to ER materials, they exhibit dramatic changes (within milli-seconds) in material properties. Pre-yield, yielding, and post-yield mechanisms are all influenced by the electric field. Namely, an applied electric field dramatically increases the stiffness and energy dissipation properties of these materials. A previously known cubic equation which describes the flow of fluids with a yield stress through a rectangular duct can be applied to annular flow, provided that certain conditions on the material properties are satisfied. An analytic solution and a uniform approximation to the solution, for the rectangular duct Poiseuille flow case is presented. A numerical method is required to solve the flow in annular geometries. The approximation for rectangular ducts is extended to deal with the annular duct case.

Analysis and testing of Bingham plastic behavior in semi-active electrorheological fluid dampers

Abstract: Electrorheological- (ER-) fluid-based dashpot dampers have smart capabilities because ER fluids undergo large changes in yield stress as electric field is applied. Our objective is the development and experimental validation of quasi-steady dashpot damper models, based on an idealized nonlinear Bingham plastic shear flow mechanism, for purposes of preliminary design and performance predictions. The data required for the Bingham plastic model is normally supplied by ER fluid suppliers, that is, plastic viscosity and dynamic yield stress as a function of applied field, as determined from a shear stress versus shear strain rate diagram. As force is applied to the dashpot damper, the ER fluid flows through an annulus between the concentric inner and outer electrodes. The idealized Bingham plastic shear flow mechanism predicts that three annular flow regions develop as a function of the local shear stress. In the central pre-yield or plug region, the local shear stress is less than the dynamic yield stress, so that the plug behaves like a rigid solid. The remaining two annular regions, adjacent to the electrodes, are in the post-yield condition and correspond to the shear stress exceeding the dynamic yield stress, so that the material flows. Equivalent viscous damping performance of an ER fluid dashpot damper is strongly coupled with the plug behavior. For a constant force, as the applied field increases, so does the plug thickness and equivalent viscous damping. For a constant applied field, as the force increases, the plug thickness and equivalent viscous damping both decrease. The passive and active or field-dependent damping behavior of an ER-fluid-based dashpot damper can be designed for a specific application using these quasi-steady Bingham plastic models.

Multi-degree of freedom magnetorheological devices and system for using same

Abstract: A semi-active device (20) for damping motion between structures having multi-degrees of freedom. A magnetic field produced by a permanent magnet, a coil, or a combination thereof, change the rheological properties of an MR fluid (40) to effectively lock up the components and the structures to which they are attached to serve as a brake or damper of the associated compound motion. A system (21) employing the MR devices (20) includes a motion detection sensor (15) and a controller (19) to actuate the MR devices (20) when a predetermined motion threshold is exceeded.

Portable air comfort system thermostat enabling personal localized control of room temperature

Abstract: Wireless control of an air conditioner or space heater by a portable, easily relocatable remote thermostat combined with a control signal transmitter which is placed on a table, desk or stand near an occupant of a room or office to set the operation of a cooling or heating source in order to maintain a more uniform level of air temperature comfort in the portion of the room where the thermostat is located. A wireless control receiver responsive to the transmitted control signal is included as a portion of a plug-in adapter module that plugs directly into an AC power wall receptacle. An ordinary window air conditioner or portable space heater is then merely plugged into the adapter module which provides ON and OFF control in response to the remote thermostat. A receiver is inclusible in a fixed-location wall thermostat, enabling the portable remote thermostat to maintain control of a centralized climate control system.

The Modeling and Simulation of a Proportional Solenoid Valve

Abstract: A nonlinear dynamic model of a high speed direct acting solenoid valve is presented. The valve consists of two subsystems ; a proportional solenoid and a spool assembly. These two subsystems are modeled separately. The solenoid is modeled as a nonlinear resistor/inductor combination, with inductance parameters that change with displacement and current. Empirical curve fitting techniques are used to model the magnetic characteristics of the solenoid, enabling both current and magnetic flux to be simulated. The spool assembly is modeled as a spring/mass/damper system. The inertia and damping effects of the armature are incorporated in the spool model. The solenoid model is used to estimate the spool force in order to obtain a suitable damping coefficient value. The model accurately predicts both the dynamic and steady-state response of the valve to voltage inputs. Simulated voltage, current, and displacement results are presented, which agree well with experimental results.

Damping the power-angle oscillations of a permanent-magnet synchronous generator with particular reference to wind turbine applications

Abstract: The paper describes the use of a novel permanent-magnet synchronous generator for use with a wind turbine The small pole pitch of the generator allows it to operate at low speeds, be directly coupled to the wind turbine and maintain a direct electrical grid connection The ability to couple the generator directly to the wind turbine eliminates the need for the usual gearbox, but leads to a generator design where conventional damper windings are ineffective as there is too little space The paper describes an alternative damping system whereby the stator is allowed limited rotational movement by connecting it to the wind turbine housing via a spring and a mechanical damper This arrangement allows greater damping of power-angle oscillations than is possible using conventional damper windings The response of the generator to step changes in driving torque is used to illustrate the effectiveness of such a design The behaviour of the generator on both synchronisation and during operation in a varying wind is discussed to demonstrate the feasibility of this new design

Simple ATMD Control Methodology for Tall Buildings Subject to Wind Loads

Abstract: A procedure for the design of an active tuned mass damper for vibration control in tall buildings subject to wind loads is presented. The building motions are modeled by the first mode of the response, and it is assumed that the excitation is white noise. The controller is based on complete feedback (namely, feedback of displacement, velocity, and acceleration). The controller gains that minimize the variance of the rooftop displacement are derived in closed-form. Two examples, one of a 162 m tall planar frame and the other of a 400 m tall building in a city are studied to illustrate the active damper design and to evaluate the procedure and the results. The same examples are then studied as multiple-degree-of-freedom systems subject to nonwhite excitation that better simulates the wind. Results on the reduction of the dynamic response and control effectiveness of the active damper designs are presented and discussed.

Energy input and dissipation behaviour of structures with hysteretic dampers

Abstract: This paper presents qualitative investigations on the energy behaviour of structures into which hysteretic dampers are incorporated. Emphasis was given to the ratio of the structural stiffness after the yielding of hysteretic dampers to the initial elastic stiffness, with a premise that this ratio, termed α in this study, tends to be large for structures with hysteretic dampers. Structures concerned were represented by discrete spring-mass systems having bilinear restoring force behaviour, in which the second stiffness relative to the initial stiffness is α. It was found that with the increase of α the total input energy tends to increase, but the increase is confined to a narrow range of natural periods. Both the total input energy and hysteretic energy were found to become less sensitive to the yield strength with the increase of α. A simple formula was also proposed to estimate the maximum deformation given the knowledge of the hysteretic energy. Analysis of MDOF systems revealed that, even when α is large, the total input energy and hysteretic energy for MDOF systems are approximately the same as those of the equivalent SDOF system, and the hysteretic energy can be distributed uniformly over the stories if α is large.

Disk drive test chamber

Abstract: A disk drive test chamber creates an environment for disk drives to be tested with an air circulation system that provides an even flow of air over each drive for equivalence in testing conditions. One method of providing equivalent air circulation is to have turning vanes inside air ducts to divert equal amounts of air over each shelf holding disk drives through identically sized apertures. The second method is to have apertures of varying sizes of 40, 50 and 70 percent opening per square inch in the air ducts to divert equal amounts of air. The temperature is maintained within 1/4° C. of the set point by a controller through a system of heaters, air pumps, air ducts, insulation, vents, a motorized damper and an exhaust fan. The heater generates heat to simulate the actual heat of running conditions of disk drives. The pumps send air up the side air ducts and down the center air duct. The chamber has two safety features to prevent damage to the disk drives from over temperature. Four separate techniques are employed to minimize vibration to the disk drives being tested; a steel frame, a rubber air duct transition, and neoprene pads on the brackets holding the shelves and on the leveling feet.

Analysis and Design of ER Damper for Seismic Protection of Structures

Abstract: An electrorheological (ER) fluid damper suitable for vibration and seismic protection of civil structures has been designed, constructed, and tested. The damper consists of a main cylinder and a piston rod that pushes an ER fluid through a stationary annular duct. The behavior of the damper can be approximated with Hagen-Poiseille flow theory. Under the presence of electric field, the ER fluid exhibits a finite yield stress of the order of 1.8 kPa at 3kV/mm and manifests some elastic behavior before yielding. An elastic-viscoplastic law is proposed that predicts satisfactorily the fluid behavior obtained from viscometric tests at different frequencies. The contribution from the elasticity of the fluid is insignificant to the global response of the damper at the flow rates of interest, and it is shown that the damper response can be satisfactorily predicted with a simple rigid-viscoplastic law. Experimental results on the damper response with and without the presence of electric field are presented. As the rate of deformation increases viscous stresses prevail over yield stresses and a smaller fraction of the total damper force can be controlled. Some design recommendations on ER dampers for seismic protection applications are provided.

Performance of Particle Dampers Under Random Excitation

Abstract: An experimental and analytical study is made of the performance of particle dampers under wide-band random excitation. A small model, provided with a nonlinear auxiliary mass damper, was used to investigate the major system parameters that influence the performance of particle dampers: total auxiliary mass ratio, particle size, container dimension, and the intensity and direction of the excitation. It is shown that properly designed particle dampers, even with a relatively small mass ratio, can considerably reduce the response of lightly damped structures. An approximate analytical solution, which is based on the concept of an equivalent single unit-impact damper, is presented. It is shown that the approximate solution can provide an adequate estimate of the root-mean-square response of the randomly excited primary system when provided with a particle damper that is operating in the vicinity of its optimum range of parameters.

Response of impact dampers with granular materials under random excitation

Abstract: This paper presents the results of an experimental and analytical study of the performance of granular material dampers with tungsten powder, as an impacting mass, under wide-band random excitation. The influence of some of the major system parameters such as the total auxiliary mass ratio, container dimensions and intensity of the excitation are investigated using a small building model under base excitation. An approximate analytical solution based on the concept of an equivalent single-unit impact damper is presented. Comparison between the experimental and analytical results shows that, with the proper use of the equivalent single-particle impact damper approach, reasonably accurate estimates of the rms response of a primary system under stationary random excitation can be obtained.

Low-cost wireless HVAC systems

Abstract: Communication between the various elements of HVAC systems is effected by means of low-cost, low-power, narrow-band AM SAW-stabilized transmitters 21, 27, 39, 86 and receivers 18, 28, 47, 89. A residential embodiment (FIG. 1) transmits temperature information from each room of the house to a master control 24, which is used to control the HVAC demand and to control the damper in the corresponding room. In a first commercial building embodiment (FIGS. 2 and 3), thermostat/transceiver 61-66 assemblies transmit not only demand and control information from the corresponding thermostat 78 (with switches), but relay information transmitted from other thermostat/transceiver assemblies, whereby messages are retransmitted from one floor to the next to overcome the high attenuation of commercial building construction in reaching rooftop HVAC systems 71-76. In a second commercial building embodiment (FIG. 4), messages are transmitted from a thermostat/transceiver assembly 92 in each floor to a relaying transceiver assembly 96 in a stairwell, the transmissions to rooftop units 93, 97 being made with little attenuation through the stairwell and the roof. Message protocols with or without acknowledgement may be used. Relative humidity and CO 2 level may be controlled as well as temperature.

Controllable seat damper system and control method therefor

Abstract: A controllable fluid damper (22) is employed in a seat suspension system. A microprocessor (42) receives successive signals from a displacement sensor (44) and computes a rate of displacement. This displacement rate is used to determine an appropriate control signal for the damper (22) to provide the desired isolation of the seat occupant from the vibration input to the frame. A rate control method is disclosed as a preferred control technique for providing the desired isolation.

Air handling unit including control system that prevents outside air from entering the unit through an exhaust air damper

Abstract: A control system for controlling an air handling unit. The control system links the position of an exhaust air damper and a recirculation air damper so as the exhaust air damper is opened, the recirculation air damper is closed the same amount, and vice versa. An outside air damper remains completely open at all times. The relative positions of the exhaust air damper and the recirculation air damper control the amount of outside air that is emitted into the air handling unit through the outside air damper. For each of the control states of heating with minimum outside air, cooling with outside air, mechanical cooling with maximum outside air, and mechanical cooling with minimum outside air, the outside air damper remains completely open, and the position of the exhaust air damper and the recirculation air damper are controlled based on a particular state. Sequencing strategies are employed for transitions between the control states that utilize these positions of the dampers.

Optimum viscous dampers for stiffness design of shear buildings

Abstract: The problem in this paper is to find the optimum sets of story stiffnesses and of damping coefficients of the dampers of an elastic planar shear building with viscous dampers (SBVD model) subject to constraints on maximum interstory drifts due to a set of spectrum-compatible earthquake motions, on upper bounds for each damping coefficient of dampers, and on the sum of damping coefficients of dampers. Two basic characteristics of an ordered set of optimum SBVD designs have been disclosed: (1) greater damping coefficients are distributed within the specified upper bounds among the dampers placed on stories with greater interstory drifts; (2) the effect on stiffness reduction of the optimization of the damping coefficients of dampers from an initial design of an SBVD model with uniform dampers is greater when non-uniform maximum interstory drifts with larger differences between the minimum and maximum values are specified. A design guideline for the effective configuration of viscous dampers for stiffness design of an SBVD model is proposed.

Method for controlling motion using an adjustable damper

Abstract: The relative motion and force between two interconnected elements can be controlled by a semi-active damper to minimize the instances of the motion exceeding acceptable limits, while maximizing isolation between the elements. Applying an algorithm to the control parameters of the damper provides excellent isolation from input vibration and shocks. The dampers and control algorithms are useful in primary vehicle suspension systems, cab mounts, seat mounts, and engine mounts.

Dynamic modelling of an ER vibration damper for vehicle suspension applications

Abstract: In this paper, the authors describe the development of a mathematical model of a controllable vibration damper intended for eventual application to ground-vehicle suspension systems. The damper under investigation employs electro-rheological (ER) fluid as the working medium which enables a continuously variable damping force to be provided in response to an electrical control signal. There are some difficulties inherent in characterizing the ER damper's behaviour which the present study attempts to overcome. The paper begins by describing a novel form of non-dimensionalization which drastically reduces the number of variables required to characterize the quasi-steady behaviour of the ER fluid. The construction of the ER damper is described and, on the basis of physical reasoning, it is shown how a dynamic model can be derived by taking account of ER fluid inertia and compressibility. A recently developed iterative scheme is introduced in order to solve the resulting non-linear equations of motion. The paper concludes with a case study involving the application of the ER damper to controlling the lateral vibrations of a rail vehicle.

Closed loop finite-element modeling of active/passive damping in structural vibration control

Abstract: A three-dimensional (3D) finite-element closed loop model has been developed to predict the effects of active/passive damping on a vibrating structure. The example used is a cantilever structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric actuator and the base structure. This hybrid arrangement is called an active constrained layer damper (ACLD). A piezoelectric sensor is also embedded in the structure. The finite-element analysis includes a control algorithm to close the loop between the sensor and the actuator. The parametric study considers different types of control as well as geometric parameters related to the ACLD. Comparisons are made between active constrained layer and passive constrained layer, and active damping only. The results obtained here reiterate that ACLD is better for vibration suppression than either the purely passive or active system and provides higher structural damping with less control gain when compared to the purely active system. This is the first attempt at a detailed 3D finite-element model that makes no approximations about the piezoelectric devices and includes closed loop modeling.

Damper for brake noise reduction

Abstract: An apparatus for reducing unwanted brake noise has a ring damper affixed around a periphery of a brake rotor in a disk brake system in a manner that permits relative motion and slippage between the ring damper and the rotor when the rotor vibrates during braking. In a preferred embodiment, the ring damper is disposed in a groove formed in the periphery of the disk and is pre-loaded against the rotor both radially and transversely. The ring damper is held in place by the groove itself and by the interference pre-load or pre-tension between the ring damper and the disk brake rotor.

Dampers for internal applications and articles damped therewith

Abstract: The present invention provides a damper comprising a compressible and resilient shaft and at least one constrained layer damping section attached to the exterior of the shaft via an adhesive. The damper can be compressed and inserted into a cavity or hollow in an article to be damped whereupon it can expand and provide vibration damping properties as well as optional acoustic absorbing properties. The present invention also provides the damped article and a method of damping the article.

Regenerative control of active vibration damper and suspension systems

Abstract: A new energy regenerative type vibration damper and suspension systems are introduced. It is intended for active damper to reduce energy consumption without losing damping efficiency. An electro-dynamic actuator is used for the regenerative damper. The electric energy is regenerated during the high-speed motion of the actuator. For low-speed motion, an active or passive control algorithm is applied to the same actuator to achieve a good damping performance. This idea is applied to a single degree-of-freedom vibrating system. The experimental results show that the system has better performance than the pure passive damper system and can regenerate vibration energy.