Showing papers on "Damper published in 2016"

A review of recent developments and technological advancements of variable-air-volume (VAV) air-conditioning systems

Abstract: This study reviewed VAV systems modeling and simulations, control strategies and optimization tools, the airflow characteristics of VAV systems, some common VAV systems׳ faults, detection and diagnosis, energy usage and analysis, and the current applications of variable air volume (VAV) air-conditioning systems. VAV system modeling is very complex as it involves complex structures and parameters a result of which has led to lack of models that combine both the AHU and building with all the required parameters. The most common controllers used in VAV systems are the PID controllers. We saw that supply air temperature and the flow rate of supply air are the best parameters that can be optimized in a VAV system as they greatly minimize energy consumption. Genetic algorithms have good robustness, and can be easily parallelized. However, they suffer from shortcomings such as slow convergence rates under some conditions, and have difficulty in adjustment of algorithms since there are no rules for determining the number of individuals in populations. FLCs boost of advantages such as less or minimum overshoot, oscillation and power consumption compared to conventional PID controllers, can be used in MIMO systems, and they do not require models as they can control non-linear processes. Airflow control in VAV systems can be achieved through controlling static pressure and position of the damper. Literature survey shows that balancing and distribution of airflow in VAV air-conditioning systems can be considered to be one of the main challenging areas of research concerning VAV system control. Most methods used today for detecting and diagnosing faults are hybrid. These are superior to the conventional methods of FDD. In conclusion, VAV air-conditioning systems are the most energy efficient systems in use today. Despite of their current strengths, VAV systems energy saving potential can still be improved.

An Efficient and Robust Hybrid Damper for $LCL$ - or $LLCL$ -Based Grid-Tied Inverter With Strong Grid-Side Harmonic Voltage Effect Rejection

Abstract: A high-order ( $LCL$ or $LLCL$ ) power filter with a small grid-side inductor is becoming more preferred for a grid-tied inverter due to less total inductance and reduced costs. In a microgrid, the background harmonic voltage (BHV) may distort the injected currents of the grid-tied inverters. In order to resist the effect of the BHV, a feedforward voltage compensator and a proportional resonant regulator with harmonic compensation are often adopted. However, they still have their own limitations, particularly when there are higher order BHVs at the point of common coupling and when the equivalent grid impedance widely varies due to the different numbers of grid-tied inverters in parallel. Thus, an extra damper should be inserted to keep the system stable. In this paper, the control bandwidth limitation of a multiloop control active damping (AD) method is analyzed and illustrated by the capacitor-current-feedback AD. Based on this, a single-loop current control with a hybrid damper is proposed for a single-phase $LCL$ - or $LLCL$ -filter-based grid-tied inverter. A step-by-step design of the controller method is also introduced in detail. Experiments on a 2-kW prototype fully demonstrate the strong robustness of the stability and the high harmonic rejection ability of the inverter using the proposed control method.

Experimental investigations of building structure with a superelastic shape memory alloy friction damper subject to seismic loads

Abstract: With the goal to assess its effectiveness in structural vibration suppression under strong seismic excitations, this paper experimentally investigates shaking table tests of a new superelastic shape memory alloy friction damper (SSMAFD). The damper consists of pre-tensioned superelastic shape memory alloy (SMA) wires and friction devices. The main function of SMA wires is to provide re-centering capacity, while the integrated friction devices provide the most energy dissipation. With the inherent damping property, the superelastic SMA wires also provide energy dissipation. In the shaking table tests, a scaled-down building structure were used as the subject for vibration control and several representative seismic signals as well as white noise motions were used as the inputs. Comparative studies of dynamic behaviors, i.e. story displacements, interstory drifts and story accelerations, of the structural model with and without SSMAFD under seismic loading were performed. The experimental results demonstrated that the SSMAFD was effective in suppressing the dynamic response of the building structure subjected to strong earthquakes by dissipating a large portion of the energy. In addition, with the re-centering capacity of the proposed damper, the structure was able to undergo strong earthquakes without remarkable residual drift under different seismic loads.

Design and Evaluation of Tuned Inerter-Based Dampers for the Seismic Control of MDOF Structures

Abstract: The tuned viscous mass damper (TVMD) and tuned inerter damper (TID) are tuned inerter-based dampers (TIBDs) that can utilize amplified apparent mass and tuning effects. This study investiga...

Experimental and Theoretical Study of Viscoelastic Dampers with Different Matrix Rubbers

Abstract: Viscoelastic (VE) dampers are one of the most popular structural control devices, and serious efforts have been undertaken to develop their availability in civil engineering. However, the performance of VE dampers is dependent on the energy dissipation properties of VE materials. In this study, several kinds of VE materials based on different matrix rubbers were developed, and tests on VE dampers based on nitrile butadiene rubber (NBR) matrix and silicone rubber (SR) matrix were carried out. The results indicate that NBR matrix VE dampers have a high energy dissipation capacity, whereas SR matrix VE dampers have stable performance under different working conditions. To clarify the mechanical properties of VE dampers based on NBR and SR matrices, the equivalent higher-order fractional derivative model, which takes into account the effects of temperature and frequency simultaneously, is proposed. The numerical results using this model are in accord with experimental results.

An experimental study of vibration control of wind-excited high-rise buildings using particle tuned mass dampers

Abstract: A particle tuned mass damper (PTMD) system is the combination of a traditional tuned mass damper (TMD) and a particle damper (PD). This paper presents the results of an experimental and analytical study of the damping performance of a PTMD attached to the top of a benchmark model under wind load excitation. The length ratio of the test model is 1:200. The vibration reduction laws of the system were explored by changing some system parameters (including the particle material, total auxiliary mass ratio, the mass ratio between container and particles, the suspending length, and wind velocity). An appropriate 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 method, reasonably accurate estimates of the dynamic response of a primary system under wind load excitation can be obtained. The experimental and simulation results show the robustness of the new damper and indicate that the damping performance can be improved by controlling the particle density, increasing the amount of particles, and aggravating the impact of particles etc.

A Seat Suspension with a Rotary Magnetorheological Damper for Heavy Duty Vehicles

Abstract: This paper presents the development of an innovative seat suspension working with a rotary magnetorheological (MR) fluid damper. Compared with a conventional linear MR damper, the well-designed rotary MR damper possesses several advantages such as usage reduction of magnetorheological fluid, low sealing requirements and lower costs. This research starts with the introduction of the seat suspension structure and the damper design, followed by the property test of the seat suspension using an MTS machine. The field-dependent property, amplitude-dependent performance, and the frequency-dependent performance of the new seat suspension are measured and evaluated. This research puts emphasis on the evaluation of the vibration reduction capability of the rotary MR damper by using both simulation and experimental methods. Fuzzy logic is chosen to control the rotary MR damper in real time and two different input signals are considered as vibration excitations. The experimental results show that the rotary MR damper under fuzzy logic control is effective in reducing the vibrations.

Vibration Control of a Pipeline Structure Using Pounding Tuned Mass Damper

Abstract: Pipeline structures are often very flexible and susceptible to vibrations induced by many sources, such as vortex, external flow, and internal fluid flow. The pounding tuned mass damper (PTMD) is one device that may be employed to absorb and dissipate these undesired vibrations. The PTMD is a combination of the tuned mass damper and the impact damper. It utilizes the tuned mass to absorb kinetic energy and dissipates the absorbed energy through collisions. To examine the vibration control effectiveness of the PTMD, both numerical analysis and experimental study were performed. In the numerical analysis, a pounding force model was established based on the Hertz contact element. The motion equation of a pipeline structure incorporated with a PTMD was derived. Free vibration analysis and forced vibration analysis were performed. In the experimental study, an M-shaped pipeline was fabricated and installed with the PTMD. Due to safety issues the pipe was kept empty during the experiments. A free vibrat...

Dynamic behavior of stay cables with passive negative stiffness dampers

Abstract: This paper systematically investigates the dynamic behavior of stay cables with passive negative stiffness dampers (NSD) installed close to the cable end. A passive NSD is modeled as a combination of a negative stiffness spring and a viscous damper. Through both analytical and numerical approaches, parametric analysis of negative stiffness and viscous damping are conducted to systematically evaluate the vibration control performance of passive NSD on stay cables. Since negative stiffness is an unstable element, the boundary of passive negative stiffness for stay cables to maintain stability is also derived. Results reveal that the asymptotic approach is only applicable to passive dampers with positive or moderate negative stiffness, and loses its accuracy when a passive NSD possesses significant negative stiffness. It has been found that the performance of passive NSD can be much better than those of conventional viscous dampers. The superior control performance of passive NSD in cable vibration mitigation is validated through numerical simulations of a full-scale stay cable.

Design and control of a prosthetic leg for above-knee amputees operated in semi-active and active modes

Abstract: This paper proposes a new prosthesis operated in two different modes; the semi-active and active modes. The semi-active mode is achieved from a flow mode magneto-rheological (MR) damper, while the active mode is obtained from an electronically commutated (EC) motor. The knee joint part of the above knee prosthesis is equipped with the MR damper and EC motor. The MR damper generates reaction force by controlling the field-dependent yield stress of the MR fluid, while the EC motor actively controls the knee joint angle during gait cycle. In this work, the MR damper is designed as a two-end type flow mode mechanism without air chamber for compact size. On other hand, in order to predict desired knee joint angle to be controlled by EC motor, a polynomial prediction function using a statistical method is used. A nonlinear proportional-derivative controller integrated with the computed torque method is then designed and applied to both MR damper and EC motor to control the knee joint angle. It is demonstrated that the desired knee joint angle is well achieved in different walking velocities on the ground ground.

Modeling and control performance of a negative stiffness damper for suppressing stay cable vibrations

Abstract: Summary A negative stiffness damper (NSD) is proposed, and its performance on suppressing stay cable vibrations is investigated by numerical simulations and experimental tests. First, the NSD consists of two pressed springs and an oil damper. The two pressed springs are attached perpendicularly to the piston rod of the oil damper in symmetrical configuration. Mechanical model of this damper is derived according to the geometrical configuration and validated experimentally. Considering the simplified model of single-mode vibration of a cable, the cable frequency with the NSD is investigated theoretically by average method, and the lower limit on the pressed degree of two springs is proposed. Numerical examples of cable with NSD and oil damper under sinusoidal excitations are conducted. The NSD shows the superior reduction performance of both amplitudes in time history and peak values of frequency response. A series of single-mode and multi-mode cable vibration control experiments are carried out to evaluate mitigation performance achieved by the NSD. The results indicate that this NSD can provide larger additional modal damping ratio to the cable regardless of single-mode and multiple-mode vibration. Thus, this NSD achieves further reduction of the cable than the oil damper through negative stiffness behavior, instead of complex active or semi-active devices with real-time feedback. Copyright © 2015 John Wiley & Sons, Ltd.

Large-Signal Stability Analysis of DC Power System With Shunt Active Damper

Abstract: This paper proposes a large-signal stabilization method for the dc power system with a constant power load (CPL), which is detrimental to system stability due to its negative incremental resistance (NIR). The proposed method utilizes a shunt active damper at the point of common coupling of the dc bus and controls it as a parallel set of a virtual capacitor, virtual inductor, and resistor. The Takagi–Sugeno fuzzy model is employed with the Lyapunov stability theorem to verify the asymptotic stability of the system and to estimate the region of asymptotic stability. Improvements on the dc-bus voltage stability are evaluated based on dc-bus voltage deviation or dc-bus capacitance reduction. The performance of the proposed shunt active damper is verified by simulation and experimental results.

Strength prediction of rotary brace damper using MLR and MARS

Abstract: This study predicts the strength of rotary brace damper by analyzing a new set of probabilistic models using the usual method of multiple linear regressions (MLR) and advanced machine-learning methods of multivariate adaptive regression splines (MARS), Rotary brace damper can be easily assembled with high energy-dissipation capability. To investigate the behavior of this damper in structures, a steel frame is modeled with this device subjected to monotonic and cyclic loading. Several response parameters are considered, and the performance of damper in reducing each response is evaluated. MLR and MARS methods were used to predict the strength of this damper. Displacement was determined to be the most effective parameter of damper strength, whereas the thickness did not exhibit any effect. Adding thickness parameter as inputs to MARS and MLR models did not increase the accuracies of the models in predicting the strength of this damper. The MARS model with a root mean square error (RMSE) of 0.127 and mean absolute error (MAE) of 0.090 performed better than the MLR model with an RMSE of 0.221 and MAE of 0.181.

Collapse risk and residual drift performance of steel buildings using post-tensioned MRFs and viscous dampers in near-fault regions

Abstract: The potential of post-tensioned self-centering moment-resisting frames (SC-MRFs) and viscous dampers to reduce the collapse risk and improve the residual drift performance of steel buildings in near-fault regions is evaluated. For this purpose, a prototype steel building is designed using different seismic-resistant frames, i.e.: moment-resisting frames (MRFs); MRFs with viscous dampers; SC-MRFs; and SC-MRFs with viscous dampers. The frames are modeled in OpenSees where material and geometrical nonlinearities are taken into account as well as stiffness and strength deterioration. A database of 91 near-fault, pulse-like ground motions with varying pulse periods is used to conduct incremental dynamic analysis (IDA), in which each ground motion is scaled until collapse occurs. The probability of collapse and the probability of exceeding different residual story drift threshold values are calculated as a function of the ground motion intensity and the period of the velocity pulse. The results of IDA are then combined with probabilistic seismic hazard analysis models that account for near-fault directivity to assess and compare the collapse risk and the residual drift performance of the frames. The paper highlights the benefit of combining the post-tensioning and supplemental viscous damping technologies in the near-source. In particular, the SC-MRF with viscous dampers is found to achieve significant reductions in collapse risk and probability of exceedance of residual story drift threshold values compared to the MRF.

Influence of the nonlinear behavior of viscous dampers on the seismic demand hazard of building frames

Abstract: Summary This paper analyzes the influence of damper properties on the probabilistic seismic performance of building frames equipped with viscous dampers. In particular, a probabilistic methodology is employed to evaluate the influence of the damper nonlinearity, measured by the damper exponent, on the performance of structural and nonstructural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. The performance variations due to changes in the damper nonlinearity level are evaluated and highlighted by considering two realistic design scenarios and by comparing the results of a set of cases involving dampers with different exponents designed to provide the same deterministic performance. By this way, it is possible to evaluate the influence of the nonlinear response and of its dispersion on the demand hazard. It is shown that the damper nonlinearity level strongly affects the seismic performance and different trends are observed for the demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas accounting for the damping nonlinearity level. Copyright © 2015 John Wiley & Sons, Ltd.

Numerical and experimental study of comb-teeth metallic yielding dampers

Abstract: In this paper, a new type of metallic yielding damper called comb-teeth damper, CTD, is introduced. CTD is made of steel plates and includes a number of teeth that dissipate energy through in-plane flexural yielding. An optimum geometry of teeth is suggested, which assures uniform distribution of stress along them and prevents strain localization. Finite element modeling is used to verify the design of proposed damper and to study nonlinear behavior of the damper subjected to monotonic as well as cyclic loading. Three full scale specimens have also been made and tested under cyclic loading. In order to restrict out-ofplane buckling of damper teeth, a special clamp has been designed. A numerical study has elaborated the effects of these clamps in comparison to increasing the thickness of individual tooth. The tested samples have tolerated considerable cumulative displacement in their hysteresis cycles without any significant loss of strength.

Simultaneous optimization of force and placement of friction dampers under seismic loading

Abstract: It is known that the use of passive energy-dissipation devices, such as friction dampers, reduces considerably the dynamic response of a structure subjected to earthquake ground motions. Nevertheless, the parameters of each damper and the best placement of these devices remain difficult to determine. Some articles on optimum design of tuned mass dampers and viscous dampers have been published; however, there is a lack of studies on optimization of friction dampers. The main contribution of this article is to propose a methodology to simultaneously optimize the location of friction dampers and their friction forces in structures subjected to seismic loading, to achieve a desired level of reduction in the response. For this purpose, the recently developed backtracking search optimization algorithm (BSA) is employed, which can deal with optimization problems involving mixed discrete and continuous variables. For illustration purposes, two different structures are presented. The first is a six-storey shear bu...

Experimental study on using electromagnetic devices on bridge stay cables for simultaneous energy harvesting and vibration damping

Abstract: Flexible bridge stay cables are often vulnerable to problematic vibrations under dynamic excitations. However, from an energy perspective, such excessive vibrations denote a green and sustainable energy source to some electronic devices (such as semi-active dampers or wireless sensors) installed on the same cables. This paper presents an experimental study on a novel dual-function system called electromagnetic damper cum energy harvester (EMDEH). The proposed EMDEH, consisting of an electromagnetic device connected to an energy-harvesting circuit (EHC), simultaneously harvests cable vibration energy and provides sufficient damping to the cables. A fixed-duty-cycle buck–boost converter is employed as the EHC, which emulates a resistive load and provides approximately optimal damping and optimal energy harvesting efficiency when operating in discontinuous conduction mode. A 5.85 m long scaled stay cable installed with a prototype EMDEH is tested in the laboratory under a series of harmonic and random excitations. The EMDEH can achieve a control performance comparable to passive viscous dampers. An average electrical power of 31.6 and 21.51 mW is harvested under harmonic and random vibrations, respectively, corresponding to the efficiency of 16.9% and 13.8%, respectively. Moreover, this experimental study proves that optimal damping and energy harvesting can be achieved simultaneously, which answers a pending question regarding such a dual-objective optimization problem. Self-powered semi-active control systems or wireless sensor networks may be developed for bridge stay cables in the future based on the proposed concept in this study.

Active Damping of LLCL -Filter Resonance Based on LC -Trap Voltage or Current Feedback

Abstract: LLCL -filter is an emerging fourth-order filter proposed after the third-order LCL -filter. It uses smaller passive components than the LCL -filter, but is still burdened by resonance complications when used with a grid converter. An LLCL -filtered converter must, hence, be passively or actively damped. Active damping is presently more efficient, and can easily be realized by feeding back a state variable. For the LCL -filter, the variable is usually its middle capacitor current. However, with computational delays considered, a simple proportional damper cannot be used with the capacitor current. Instead, a high-pass damper must be used, which as commonly known, may cause undesired noise complications depending on operating conditions. In this paper, the same capacitor current damper has been investigated for the LLCL -filter with its limitations clarified. Both cases of with and without delays have been considered. The investigation has also been extended to consider the LC -trap voltage feedback, which based on the formulated transfer functions and experimental results, permits a simple proportional damper to be used. Lesser noise complications and faster dynamic can then be achieved. Circuit equivalences for the presented dampers have also been derived, from which quick damping insights can be easily drawn. These equivalences are, therefore, helpful tools to the practicing engineers.