Semi-active Hydraulic Damper Research Articles

Semi-Active Cable Damping to Compensate for Damping Losses Due to Reduced Cable Motion Close to Cable Anchor

The relative motion of transverse cable dampers is smaller than predicted by the taut string model because of the effects of bending stiffness and fixed support conditions. As a result of the reduced damper motion, the dissipated energy per cycle is reduced as well, which may explain why damping measurements on real stay cables with transverse dampers often show lower cable damping ratios than expected from the taut string theory. To compensate for the reduced damper motion and damper efficiency, respectively, a semi-active cable damper is proposed. The controllable damper is realized by a hydraulic oil damper with real-time controlled bypass valve whereby the resulting damper force is purely dissipative. The proposed control law is clipped viscous damping with negative stiffness. The viscous coefficient is adjusted in real time to the actual frequency of vibration to generate optimum modal damping while the negative stiffness component partially compensates for the reduced damper motion due to the flexural rigidity and fixed support conditions of the cable. The measurements of the prototype semi-active hydraulic damper are used to derive a precise model of the semi-active damper force including the control force constraints due to the fully open and fully closed bypass valve. This model is used to compute the cable damping ratios of the first four cable modes, for typical damper positions, for a taut string model and for a cable model with flexural rigidity and fixed supported ends. The obtained cable damping ratios are compared to those resulting from the passive linear viscous damper being optimized to the first four cable modes. The results demonstrate that the proposed semi-active cable damper with the consideration of the minimum and maximum control force constraints significantly enhances the cable damping of the first four modes compared to the linear viscous damper.

Shaking table test and verification of development of an accumulated semi-active hydraulic damper as an active interaction control device

Semi-active control is based on the use of the emerging concept of active control and passive control. The developed accumulator semi-active hydraulic damper (ASHD) is converted to interaction element (IE) of active interaction control (AIC). Systemic equations of motion, control law and control rulers of this proposed new AIC are studied in this research. A full-scale multiple degrees of freedom shaking table is tested to verify the energy dissipation of this proposed AIC, including test building without control, with passive control added involving various stiffness ratios and also with synchronic control added involving various stiffness ratios. Shock absorption of displacement can be up to 74–81% of that of the test structure with stiffness ratio = 2.3387 and 1.790 at 1st and 2nd floor under control of synchronous switch of this proposed AIC, respectively. No matter what the test structure added with various stiffeners at 1st and 2nd floor under synchronous control, test results of shock absorption ratio of acceleration show good seismic proof capability. In addition, base shear control effects of this proposed AIC method are higher than those of the test structure with various stiffeners added under passive control. These results show that AIC with stiffeners for structural control provides the characteristics of a stabilized structure under excitation of near-fault earthquake with velocity impulse action.

Seismic Proofing Capability of the Accumulated Semiactive Hydraulic Damper as an Active Interaction Control Device with Predictive Control

The intensity of natural disasters has increased recently, causing buildings’ damages which need to be reinforced to prevent their destruction. To improve the seismic proofing capability of Accumulated Semiactive Hydraulic Damper, it is converted to an Active Interaction Control device and synchronous control and predictive control methods are proposed. The full-scale shaking table test is used to test and verify the seismic proofing capability of the proposed AIC with these control methods. This study examines the shock absorption of test structure under excitation by external forces, influences of prediction time, stiffness of the auxiliary structure, synchronous switching, and asynchronous switching on the control effects, and the influence of control locations of test structure on the control effects of the proposed AIC. Test results show that, for the proposed AIC with synchronous control and predictive control of 0.10~0.13 seconds, the displacement reduction ratios are greater than 71%, the average acceleration reduction ratios are, respectively, 36.2% and 36.9%, at the 1st and 2nd floors, and the average base shear reduction ratio is 29.6%. The proposed AIC with suitable stiffeners for the auxiliary structure at each floor with synchronous control and predictive control provide high reliability and practicability for seismic proofing of buildings.

Development of semi-active hydraulic damper as active interaction control device to withstand external excitation

Semi-automatic control systems have the characteristics of being adaptable and requiring low energy. The objective of this research was to study the performance of an improved DSHD (Displacement Semi-Active Hydraulic Damper) by converting it to AIC (Active Interaction Control Device) with the addition of an accumulator. The prototype was tested using full-scale elements for examining the structural displacement, and typical responses of the interacting interface element developed in this research, the pressure variation of the pressure storage device, and the energy dissipation hysteresis loop when the structure installed with these elements is subjected to external force of various magnitude. The laboratory results confirm that the device developed in this research is capable of applying the energy dissipation characteristics of DSHD so that these elements are appropriate for developing the proposed AIC. The mutual interaction between the subordinate structure and the main structure to be protected is capable of transforming the quake energy applied to the main structure to the subordinate structure so that the objective of minimizing the deformation of main structural can be achieved.

Modeling and Testing of a Semiactive Hydraulic Damper in Periodic Working Regimes

This paper presents analytical and experimental studies of a modified semiactive hydraulic damper operating in periodic working regimes. This work was completed as a part of the Rotor Embedded Actuator Control Technology project sponsored by the Technology Strategy Board in the United Kingdom. The damper tested is based on modifications to an industrially employed helicopter damper. The work presented covers the relevant aspects of the model development, damper modification, test planning, and analysis, as well as a model-simulation correlation study. The model of the damper directly reflects the actual hydraulic modification, enabling a semiactive mode of operation. Pressure-flow representations used in the damper modeling are based on a novel testing methodology using triangular piston excitation waveforms. A specific test structure based on varying the relative phase difference between two harmonic input signals is used to assess the damper properties in periodic working regimes. The test configuration with a base harmonic piston excitation combined with a harmonic modulation at a frequency 3 times higher than the base frequency leads to significant changes in the second and fourth harmonic components of the resulting periodic damper forces. A successful model-simulation correlation study suggests that a simple one-state dynamic model of this damper features good predictive properties, equally applicable in the extended simulation contexts.

Validity of the displacement dependent semi-active hydraulic damper used in a structure

In structural engineering, the damping device is the best way to equip the structure for resisting earthquakes. The newly developed displacement dependent semi-active hydraulic damper (DSHD) is a kind of hydraulic damper to reduce the structural response. The DSHD is a fixture connecting the brace and the structure. At a seismic loading, the DSHD is functioned to dissipate the energy at the transition of bracing from the tensile constraint to the compressive constraint or in reverse. When a structure suffers a large seismic excitation, the overflow function is triggered to prevent the failure of a bracing member. That is, at the stress in the linked brace reaching a certain value, it will start the opening of the overflow valve maintaining an aptotic pressure for confining the bracing deformation within the design value. This DSHD provides availability for resisting excessive vibration in the structural design. In this paper, the analysis modeling is set up for simulating the nonlinear behavior of DSHD. The performance of DSHD is investigated in the nonlinear analysis for seismic evaluation.

A Linearization Model for the Displacement Dependent Semi-active Hydraulic Damper

In earthquake engineering, a hydraulic damper is a kind of energy-dissipating device to reduce the structural response. Newly developed Displacement Dependent Semi-Active Hydraulic Damper (DSHD) is one of the hydraulic dampers. For this damper, the hydraulic cylinder is acting as a damper connector. This damper connector is like a flexible switch with tight-loose and close-open functions and is used to connect a structure and a resistance component. For a DSHD-added structure, to linearize the nonlinear behavior of DSHD is required for preliminary design. Using the damping ratio as a parameter, the DSHD is modeled as a fixture of a linear spring and linear viscous damper. This approach is valid for application in the engineering practice.

Control of Fixed Offshore Jacket Platform Using Semi-Active Hydraulic Damper

Semi-active control of fixed offshore jacket platforms in shallow water depth using semi-active hydraulic damper (SHD) is presented. The semi-active control uses Bang Bang control algorithm to provide the required control command to the SHDs. In the control strategy, SHDs are installed in the bracings, making it an attractive proposition for the use in jacket structures. Although the main objective of providing semi-active control devices is to control the acceleration response of the deck for smooth operation and comfort condition, the reduction in base shear and displacement are also considered as important. In particular, great reduction in foundation cost can be achieved by base shear control under extreme sea state. The effectiveness of the control scheme is investigated by varying some important parameters such as the damper capacity, the maximum damping coefficient, and the distribution of dampers along the height of the structures under various sea states. A four legged steel jacket platform in a water depth of 122 m is considered as an example problem for finding out the controlled responses. Three wave conditions are considered, namely, operating wave, extreme wave, and irregular sea state. Results of the study indicate that significant control in acceleration response can be achieved by semi-active control using SHDs. Further, considerable reduction in base shear is also possible by providing SHDs of adequate capacity at the bottom-most level of the jacket.

Fluid formulae for damping changeability conceptual design of railway semi-active hydraulic dampers

Damping changeability design and evaluation is the most fundamental issue at the beginning of any new railway semi-active hydraulic damper development. Therefore, physical fluid mechanics for the calculation of basic structure and resistance parameters of the damper should be carefully studied in the conceptual phase. Fluid formulae for changeable damping performance evaluation of two commercial railway semi-active hydraulic dampers are established. Simulation results show that the damper switched by high-speed solenoid valves obtains a wide range of changeable damping coefficients, which guarantees the absorption of a wide spectrum of vibrations; however, a different low cost damper regulated with an inversely proportional relief valve, whose Force–velocity characteristics share the same rising curve, is relatively limited in damping ability. In order to overcome the drawback of the latter one with no obvious cost increase, a new semi-active hydraulic damper which is regulated by a simple proportional throttle valve is proposed. Continued fluid formulation and simulation suggests that the damper can change its damping force rising curves or “effective” damping coefficients continuously, within a considerably wide range. Thus, fluid formulae explicitly established in this study are of significance in the damping changeability conceptual design, further refinement and control design for the three semi-active hydraulic dampers. The proposed new damper, which has both a simple configuration and an easy-to-control ability, might be feasible for industry applications.

Numerical Analysis for Shock Absorption Performance of Accumulated Semi-Active Hydraulic Damper

The semi-active control does not consume a huge quantity of electricity because its controlling force comes from the oscillation of the structure system. Furthermore, it is adaptable that the control over the structure can be changed. Therefore, the optimum solutions are available to resolve the problems of the electric power system conditions and the adaptability of the controlling force, commonly found in other control methods. The damper used in this research is the Accumulated Semi-Active Hydraulic Damper, ASHD, developed on the basis of the Displacement Dependent Semi-Active Hydraulic Damper by means of installing the accumulator. The damper and the bracing series are connected together to the structure; the displacement of structure can drive the bracing series distortion to engender the action power of ASHD. When the action power passes through ASHD, the energy dissipation behaviors occur, which can form the fullest hysteresis loop. This research establishes the mathematical analysis model to analyze its energy dissipation capability based on the hysteresis loop of ASHD, obtained from the experiment. The analysis results show that no matter what energy dissipation period, ASHD perform high energy dissipation capability.

Evaluation method for the optimum seismic energy dissipation performance of displacement dependent seismic-active hydraulic damper

The objective of design, manufacturing and usage of semi-active hydraulic damper are the maximum ratio of energy dissipation, appropriate ratio of bracing stiffness and structural stiffness, the ratio of energy dissipation approaching 1 under large shake of earthquake, value of resistance force becoming stable in increase of amplitude and the optimal ratio of energy dissipation under different loading amplitude. In accordance with unilateral and bilateral specifications of semi-active hydraulic damper, the purpose of this research is to develop one integrated process capability model that measure the manufacturing quality characteristics of semi-active hydraulic damper with larger-the-better, smaller-the-better and nominal-the-better precisely. The integrated process capability model can be used to evaluate the energy dissipation efficiency of semi-active hydraulic damper in the process of manufacturing. Separately, the variation analysis of this model can be used to assess the effect of energy dissipation for each element of hydraulic damper. And then, component parts of hydraulic damper can be improved timely to reach optimum seismic energy dissipation capability.

THE ENERGY DISSIPATION BEHAVIOR OF DISPLACEMENT DEPENDENT SEMI-ACTIVE HYDRAULIC DAMPER

The functionalities and energy dissipation capability of Displacement dependent semi-active hydraulic damper, DSHD are analyzed and discussed with complete experiment which involves the factors to affect time-delay of DSHD, and the reasons to cause sliding of the oil cylinder under the dynamic state. The test results show that 1) Time-delay occurs in unloading period because of the hysteresis phenomenon. Herein, Kelvin solid is approved to simulate this process and shows that stiffness of the brace and damping coefficient of oil will lead time-delay; 2) It's important to avoid sliding of the cylinder, caused by insufficient oil pressure and residual air in the oil cylinder and pipe, for achieving excellent performance of DSHD. These phenomena can be improved by applying appropriate pre-pressure to the oil tank.

Reliability of Applied Semiactive Structural Control System

Research on semiactive control of structures has been carried out actively since the middle of the 1990s. After a theoretical and experimental study, a semiactive structural control system has been applied to an actual five-story building in 1998 by use of a continuous-variable semiactive hydraulic damper that has a maximum damping force of 1,000 kN. For application of the system, health monitoring, fail-safe operation, possibility of power failure, sensor malfunction, control device operation, computer, and communication system, etc., need to be considered. In this paper, reliability of an operational semiactive structural control system is discussed from the view points of health monitoring of the system and fail-safe functions. Power failures, abnormal outputs of sensors, valve damages, and communication errors, are focused as main problems. Dynamic load and forced vibration tests were carried out to determine fail-safe functions. After completion of the system installation, monitoring for earthquake excitation was initiated. Results presented show the effectiveness of functioning of the system. Finally, reliability of the system is confirmed and satisfactory performance is demonstrated.

Resetting Semiactive Stiffness Damper for Seismic Response Control

Recently, a semiactive hydraulic stiffness damper operating in the resetting mode, referred to as the resetting semiactive stiffness damper (RSASD), was shown to be effective in reducing the structural response due to dynamic loads. In this paper, a general resetting control law based on the Lyapunov theory is proposed for an RSASD. The performance of such a resetting controller and of a switching control method are investigated through extensive numerical simulations using different types of earthquake excitations. Simulation results indicate that an RSASD is more effective in suppressing the building response subject to earthquakes than a switching semiactive stiffness damper. Likewise, the performance of a particular control method depends on the types of earthquake excitations.

Dynamic loading test and simulation analysis of full-scale semi-active hydraulic damper for structural control

A semi-active hydraulic damper (SHD) for a semi-active damper system, which is useful for practical structural control especially for large earthquakes, has been developed. Its maximum damping force is set to 1 or 2 MN, and it is controlled by only 70 W of electric power. An SHD with a maximum damping force of 1 MN was applied to an actual building in 1998. This paper first presents the results of a dynamic loading test to confirm the control performance of the SHD. Next, an analytical model of SHDs (SHD model) is constructed with the same concept for two kinds of SHDs based on the test results. Through simulation analyses of the test results using the proposed SHD model, the dynamic characteristics of the SHD can be well represented within practical conditions. Simulation analyses are also carried out using a simple structure model with the SHD model. It is shown that this SHD model can be used to precisely evaluate the control effect of the semi-active damper system and is useful in practical SHD design under the applied conditions. Copyright © 2000 John Wiley & Sons, Ltd.

Forced vibration test of a building with semi-active damper system

The authors developed a semi-active hydraulic damper (SHD) and installed it in an actual building in 1998. This was the first application of a semi-active structural control system that can control a building's response in a large earthquake by continuously changing the device's damping coefficient. A forced vibration test was carried out by an exciter with a maximum force of 100 kN to investigate the building's vibration characteristics and to determine the system's performance. As a result, the primary resonance frequency and the damping ratio of a building that the SHDs were not jointed to, decreased as the exciting force increased due to the influence of non-linear members such as PC curtain walls. The equivalent damping ratio was estimated by approximating the resonance curves using the steady-state response of the SDOF bilinear hysteretic system. After the eight SHDs were jointed to the building, the system's performance was identified by a response control test for steady-state vibration. The elements that composed the semi-active damper system demonstrated the specified performance and the whole system operated well. Copyright © 2000 John Wiley & Sons, Ltd.

Actual seismic response controlled building with semi‐active damper system

This paper presents the first application of a semi-active damper system to an actual building. The Semi-active Hydraulic Damper (SHD) can produce a maximum damping force of 1000 kN with an electric power of 70 W. It is compact, so a large number of them can be installed in a single building. It is thus possible to control the building's response during a severe earthquake, because a large control force is obtained in comparison with a conventional active control system. This paper outlines the building, the control system configuration, the SHD, the control method using a Linear Quadratic Regulator, the response analysis results of the controlled building, and the dynamic loading test results of the actual SHD. The simulation analysis shows that damage to buildings can be prevented in a severe earthquake by SHD control. The dynamic loading test results of the SHD are reported, which show that the specified design values were obtained in the basic characteristic test. The control performance test using simulated response time histories, also shows that the damping force agrees well with the command. Finally, it is confirmed that the semi-active damper system applied to an actual building effectively controls its response in severe earthquakes. Copyright © 1999 John Wiley & Sons Ltd.