Passive Absorber Research Articles

A novel nonlinear variable damping device and its application for the systems with uncertain parameters

This paper deals with the performance of a novel nonlinear viscous dashpot with variable damping. The new proposed dashpot can be utilized in devices for instance dynamic vibration absorbers (DVAs). When the vibration absorber is tuned to the bridge's fundamental frequency, it represents a robust effect in controlling the vibrations of the bridge; however, a DVA is very sensitive to frequency detuning. The proposed nonlinear dashpot can be applied in a passive vibration absorber and upgrades it to a nonlinear variable damping one. Since the parameter of such DVA can be adjusted, it is the so-called nonlinear adjustable DVA. The mentioned dashpot, provides a quadratic nonlinearity for the damping element. The proposed dashpot in this study possesses a simple mechanism, which can handle large range of flow rates of fluid, smoothly without turbulence, in the oil channel. To investigate the effectiveness of an adjustable vibration absorber, a semi-active DVA with variable damping, and stiffness elements is applied on a footbridge; where, the footbridge is experienced variations of the fundamental frequency over time, and is subjected to a walking pedestrian. For the case study in the present study, a vibration reduction of 31% in comparison with the attached traditional passive DVA with constant parameters was achieved. The results show that, by using the proposed nonlinear dashpot, presented in this study, into an attached DVA, the footbridge will experience about 10% more deflection reduction concerning a classical linear DVA.

Implementation of fuzzy logic control on a new low cost semi-active vehicle shock absorber

This work implements a fuzzy logic control (FLC) on a proposed new low-cost semi-active shock absorber to improve vehicle ride comfort. The ordinary passive shock absorber is replaced with a new apparatus consisting of a conventional hydraulic cylinder with a proportional throttle valve placed outside the cylinder between its ports. FLC is used to adjust the damping coefficient by regulating the valve opening region. The fuzzy logic controller is configured using acceleration driven damping (ADD) methodology. Inputs are the accelerations of the sprung and the un-sprung masses, while the opening region of the valve is the output of the controller. Simscape/Matlab is used to build the model of the suggested semi-active shock absorber. The magneto-rheological (MR) suspension system and the suggested semi-active shock absorber with artificial neural network (ANN) controller are provided for comparison purposes. The findings demonstrated superior performance for the suggested shock absorber controlled by FLC relative to other controllers and to the ordinary damper as well, with one fourth of the cost of the magneto-rheological (MR) damper.

Mode-locked ytterbium-doped fiber laser with zinc phthalocyanine thin film saturable absorber

A stable mode-locked laser was demonstrated using a newly developed zinc phthalocyanine (ZnPc) thin film as passive saturable absorber (SA) in ytterbium-doped fiber laser (YDFL). The ZnPc thin film was obtained using a casting method and then inserted between the two fiber ferrules of a YDFL ring cavity to generate mode-locked pulses. The resulting pulsed laser operated at a wavelength of 1034.5 nm having a repetition rate of 3.3 MHz. At pump power of 277 mW, the maximum output power and pulse energy are achieved at 4.92 mW and 1.36 nJ, respectively. ZnPc has a high chemical and photochemical stability, and its significance for use as a potential SA in a mode-locked laser is reported in this work.Graphical

Numerical Experiments on the Optimum Design and Location of a Passive Vibration Absorber Applied to Multi Degrees of Freedom System Under Base Excitation

Numerical experiments are used to investigate the optimal design parameters and the location of a passive vibration absorber and its application to reduce resonant vibration amplitudes of a base excited, discrete, Multi Degrees of Freedom (MDOF) vertical system. Attaching a passive vibration absorber (simple undamped resonator) to the system’s end mass (top mass) is preferable when dealing with the vibrations of multi degrees freedom systems. As the absorber is moved closer to the primary system's farthest end, the amplitude reduction results get better. The numerical analysis is less sensitive to slight variations in mass ratio than minor variations in the absorber’s natural frequency, according to perturbation analysis on a two degree of freedom system. Introducing damping to the used passive vibration absorber has no discernible effect on the absorber’s effectiveness.

Locking Zipper-Coupled Origami Tubes for Deployable Energy Absorption

Abstract Energy absorption devices are widely used to mitigate damage from collisions and impact loads. Due to the inherent uncertainty of possible impact characteristics, passive energy absorbers with fixed mechanical properties are not capable of serving in versatile application scenarios. Here, we explore a deployable design concept where origami tubes can extend, lock, and are intended to absorb energy through crushing (buckling and plasticity). This system concept is unique because origami deployment can increase the crushing distance between two impacting bodies and can tune the energy absorption characteristics. We show that the stiffness, peak crushing force, and total energy absorption of the origami tubes all increase with the deployed state. We present numerical and experimental studies that investigate these tunable behaviors under both static and dynamic scenarios. The energy-absorbing performance of the deployed origami tubes is slightly better than conventional prismatic tubes in terms of total absorbed energy and peak force. When the origami tubes are only partially deployed, they exhibit a nearly elastic collapse behavior; however, when they are locked in a more deployed configuration, they can experience non-recoverable crushing with higher energy absorption. Parametric studies reveal that the geometric design of the tube can control the nonlinear relationship between energy absorption and deployment. A physical model shows the potential of the self-locking after deployment. This concept for deployable energy-absorbing origami tubes can enable future protective systems with on-demand properties for different impact scenarios.

Robotically assisted active vibration control in milling: A feasibility study

The role of robots has been increasing in machining applications, with new concepts such as robotic-assisted machining where a robot supports the workpiece while it is machined by a machine tool. This method improves chatter stability to a certain extent. However, forced vibrations or unstable vibrations such as chatter can still be a limiting factor for the productivity and quality of the machining process. In this paper, the robotically assisted milling approach is extended to consider an actively controlled robot arm, to suppress the chatter vibrations for milling operation. To assess the feasibility of the method, a proof-mass actuator is assembled on a beam structure that is representative of the robot system. The beam structure is designed to exhibit two degrees of freedom in its structural dynamics, thereby emulating the robots’ dynamic response. The effect of active control is evaluated. Frequency domain results show that the actively controlled robot arm increases the chatter stability and critical limiting depth of cut. A range of active control methods are evaluated, namely direct velocity feedback (DVF), virtual passive absorber (VPA), proportional integrated derivative (PID), linear quadratic regulator (LQR), H infinity (H∞) and μ synthesis control. To validate the simulated frequency response function (FRF) results, several experimental tests are carried out for each control method. Furthermore, a time domain model is used to validate the stability lobe diagrams by detecting the chatter boundaries with/without actuator force saturation. It is shown that the critical limiting depth of cut can be increased by a factor of 2.6, compared to the scenario where the robot has no active control applied.

Rainbow reflection and broadband energy absorption of water waves by graded arrays of vertical barriers

The rainbow reflection effect describes the broadband spatial separation of wave spectral components caused by a spatially graded array of resonators. Although mainly studied in optics and acoustics, this phenomenon has recently been demonstrated both theoretically and experimentally for water waves travelling through an array of vertical cylinders. The scattering of two-dimensional linear water waves by an array of vertical, surface-piercing barriers is considered here, in which both the submergence and spacing between the barriers are spatially graded. The rainbow reflection effect arises naturally as wave energy temporarily becomes amplified at different locations depending on frequency. Band diagram calculations are used to demonstrate that this is a consequence of the wave gradually slowing down throughout the array. The wave/barriers scattering problem is then augmented by positioning heave-restricted, rectangular floating bodies equipped with a linear damping mechanism between each adjacent pair of barriers. A solution to the resulting boundary value problem is obtained using an integral equation/Galerkin method. Using constrained optimisation, passive rainbow absorbers are designed that achieve near-perfect absorption (i) over a discrete set of frequencies and (ii) over an octave. This suggests potential applications of rainbow absorbers in the design of smart coastal technologies.

Modeling parallel arranged transparent micro-perforated panels to enhance low-mid frequency sound absorption

Passive absorbers such as fibrous or porous materials are indispensable for high-frequency damping noises; still, problems are increasingly found at low frequencies. Resonant structures, such as membranes, Helmholtz resonators, and micro-perforated panels (MPPs), are usually used for treating the latter issues. These reactive structures are mass-spring systems with damping to absorb the system's resonant frequency, offering only narrowband absorption. For the sake of broadening the absorption bandwidth, a series of structures based on MPP networks in series and parallel have been explored to introduce multiple resonances. The current study examines the computational modeling of four parallel arranged transparent MPPs with different hole sizes, perforations, and back cavities. A prototype of this absorber is machined by laser and CNC techniques and tested in an impedance tube. The experimental data obtained from using the transfer function are in good agreement with the absorption performance calculated by the electro-acoustic equivalent circuit model (ECM). Results show a wider half absorption bandwidth of the overall system for more than 3 octaves (from 160 Hz to 1120 Hz). The initial findings enhance the possibility of designing single-layer absorbers that are wideband, tunable, and free from porous/fibrous materials.

Design and Simulation of a Passive Absorber to Reduce Measured Postural Tremor Signal.

Tremor is a semirhythmic oscillatory movement of a body part caused by alternating simultaneous contractions of an antagonistic muscle group. Medical and surgical treatments used to reduce the symptoms of involuntary tremor can cause negative side effects. This study examined the ability of passive vibration absorbers in reducing the amplitude of postural tremor (PT). Inertial measurement unit (IMU) was used to record PT signals at the forearm and hand of a patient. IMU signal was used to excite an upper limb modeled to represent the flexion-extension vibrational motion at the joints. Equations of motion were solved numerically to obtain a response that fits the measured tremor signal. Passive tuned mass damper (TMD) was modeled as a cantilever beam and a screw placed along its length, at a position reflecting its operational frequency. Natural frequency of the TMD was derived for different mass positions and validated numerically and experimentally. Modal damping ratio of the TMD, for each mass position, was also estimated. Mass position and damping coefficient of the TMD were optimized depending on the minimization in the power spectral density (PSD) of angular displacement amplitude at the wrist joint. Optimized three-TMD system of 28.64 g total effective mass with the estimated modal damping ratio reduced 83.1% of the PSD of the angular displacement amplitude. This study showed the performance ability of a lightweight passive absorber in controlling the involuntary tremor of a system excited by the measured tremor signal of a patient.

Frequency independent, remotely reconfigurable passive coherent perfect absorber using conventional inkjet-printing technology

This work presents a systematic theoretical analysis and experimental validation of a novel coherent absorber which is printed through conventional inkjet-printing technology. The new absorber consists of a single resistively loaded sheet printed on a conventional plastic sheet, resulting a low complexity and passive design. The low-cost and easily fabricated absorber is frequency independent, polarization insensitive, wide-angle and we demonstrate its absorbance reconfigurability using a remote illumination as a control signal. Theoretical, numerical and experimental results are in good agreement. Specifically, experimental results shown that near perfect absorption (i.e., 100%) can be achieved using a printed sheet of thickness lambda /215.

Artificial neural networks controller of active suspension for ambulance based on ISO standards

The level of vibration to which a patient is subjected in an ambulance is often too high. Ambulance personnel should take steps to reduce these vibrations. To avoid slowdowns and other barriers that create high vibration peaks, the speed is reduced or the ambulance deviates from the quicker or shorter path. This work implements Artificial Neural Network (ANN) control over five low-cost active shock absorbers proposed to decreasing the impact of vibration on a patient’s body during an ambulance ride. For this, the passive shock absorber is replaced by a new actuator consisting of a conventional hydraulic cylinder with a proportional butterfly valve placed outside the cylinder between its orifices. The ANN is used to adjust the damping coefficient. The ANN controller inputs are the accelerations of the sprung and unsprung masses, and the output is the valve opening area. Two forces may be exerted by this active suspension system: one is used to compensate for the mass of the stretcher, the patient and the medical equipment if present and a second is used to actively isolate the patient from the vibrations of the ambulance. The performance of the active suspension ambulance is contrasted to that of a traditional ambulance, in which the stretcher is rigidly linked to the ambulance body. When compared to alternative controllers, the findings showed that the proposed register controlled by ANN performed better. The simulations demonstrate that the active system may minimize the vibrations of the patient’s mass and the stretcher by more than 70% for random abnormalities in the road that meet the ISO2631-5 and ISO 8608 standards.

Upper limb involuntary tremor reduction using cantilever beam TMDs

Tuned mass dampers (TMDs) are proposed as a solution to reduce the involuntary tremor at the upper limb of a patient with postural tremor. The upper limb is modeled as a three-degrees-of-freedom rotating system in the vertical plane, with a flexion-extension motion at the joints. The measured extensor carpi radialis signal of a patient is used to excite the dynamic model. We propose a numerical methodology to optimize the parameters of the TMDs in the frequency domain combined with the response in the time domain. The objective function for the optimization of the dynamic problem is the maximum angular displacement of the wrist joint. The optimal stiffness and damping of the TMDs are obtained by satisfying the minimization of the selected objective function. The considered passive absorber is a cantilever beam–like TMD, whose length, beam cross-sectional diameter, and mass position reflect its stiffness for a chosen additional mass. A parametric study of the TMD is conducted to evaluate the effect of the TMD position along the hand segment, the number of TMDs, and the total mass of TMDs. The sensitivity of the TMD to a decrease of its modal damping ratio is studied to meet the range of stainless steel. TMDs are manufactured using stainless steel beams of the same length (9.1 cm) and cross-sectional diameter (0.79 mm), for which the mass (14.13 g) position is adjusted to match the optimal frequency. Three TMDs holding a mass of 14.13 g each cause 89% reduction in the wrist joint angular displacement.

Investigation of Fibrous Materials for Low Frequency and High-Frequency Passive Noise Reduction using Transfer Matrix Method

The concern about the adverse effects of noise pollution is enhancing day by day due to fast industrialization. Hence a wide variety of active and passive noise controllers made of natural and synthetic materials are widely used for various types of inevitable noise reduction. The different types of passive noise controllers fabricated using various techniques vary in their microstructure and surface morphology. In turn, they cause a difference in the noise-controlling mechanisms happening inside it, leading to its unique acoustic absorption characteristics. This article uses five different fibers of different fiber diameters to fabricate passive acoustic absorbers of different textures. The frequency response of their acoustic absorption coefficient is tested with the help of impedance tube apparatus using the transfer matrix method. Acoustic properties of coir fiber, basalt fiber, glass fiber, graphene fiber, and carbon fiber are investigated and compared. The present investigation focused on the influence of fiber diameter, the porosity, and the difference in the texture of these passive absorbers on the acoustic characteristics, frequency response of acoustic absorption coefficient, and the frequency corresponding to maximum absorption. The investigation also focuses on fabricating the passive absorbers for low-frequency noise reduction where only the active absorbers are available.

Crushing behavior of aluminum alloy hexagonal ring for varying interior angle

This paper investigates the effect of changing the interior angle of a hexagonal passive energy absorber. 5052 aluminum alloy hexagonal rings with various interior angles were designed, fabricated, and tested under an in-plane quasi-static compression test to study the effect of the angle on the crushing behavior and the energy absorption capability. The results showed that the rings with angles 40° and 45° achieved a stable crushing behavior with about 100% crushing force efficiency and low initial peak force. Thus, hexagonal rings with these angles have a high potential to be used in the vehicle's crumple zones to absorb energy during collisions. However, the bigger interior angles required a much higher initial peak force to initiate the crushing, which indicates that these structures are best suited in applications where high load carrying capacity is needed.

An optimal control method for time-delay feedback control of 1/4 vehicle active suspension under random excitation

Time-delay feedback control can effectively broaden the damping frequency band and improve the damping efficiency. However, the existing time-delay feedback control strategy has no obvious effect on multi-frequency random excitation vibration reduction control. That is, when the frequency of external excitation is more complicated, there is no better way to obtain the best time-delay feedback control parameters. To overcome this issue, this paper is the first work of proposing an optimal calculation method that introduces stochastic excitation into the process of solving the delay feedback control parameters. It is a time-delay control parameter with a better damping effect for random excitation. In this paper, a 2 DOF one-quarter vehicle suspension model with time-delay is studied. First, the stability interval of time-delay feedback control parameters is solved by using the Lyapunov stability theory. Second, the optimal control parameters of the time-delay feedback control under random excitation are solved by particle swarm optimization (PSO). Finally, the simulation models of a one-quarter vehicle suspension simulation model are established. Random excitation and harmonic excitation are used as inputs. The response of the vehicle body under the frequency domain damping control method and the proposed control method is compared and simulated. To make the control precision higher and the solution speed faster, this paper simulates the model by using the precise integration method of transient history. The simulation results show that the acceleration of the vehicle body in the proposed control method is 13.05% less than the passive vibration absorber under random excitation. Compared with the time-delay feedback control optimized by frequency response function, the damping effect is 12.99%. The results show that the vibration displacement, vibration velocity, and vibration acceleration of the vehicle body are better than the frequency domain function optimization method, whether it is harmonic excitation or random excitation. The ride comfort of the vehicle is improved obviously. It provides a valuable tool for time-delay vibration reduction control under random excitation.

Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) spin-coated onto polyvinyl alcohol film as saturable absorber for generating Q-switched laser at 1.5 µm region

In this article, we proposed and demonstrated a Q-switched laser operating at a 1.5 µm region utilizing Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) spin-coated onto polyvinyl alcohol (PVA) thin film as a passive saturable absorber (SA). A stable Q-switched pulse train was successfully obtained to operate at 1563.3 nm with a 3-dB bandwidth of 1.24 nm while the highest pulse rate and the minimum pulse duration were recorded at 85.91 kHz, and 1.97 µs, respectively. The maximum average output power and pulse energy were measured to be 13.36 mW and 155.51 nJ respectively, with the highest peak power of 78.93 mW. The spin-coated PEDOT: PSS/PVA SA showed no deterioration sign even when the laser cavity was pumped at 225 mW power. This is the first time that PEDOT: PSS/PVA has been used as a SA to produce a stable Q-switched laser in 1.55 µm.

An effective resonant wave absorber for long regular water waves

A new type of resonant wave absorber is proposed to absorb long regular waves more effectively in physical wave flume based on the mechanism of gap resonance. The wave absorber is designed by placing a fixed box in front of the end of a physical wave flume, thereby forming a gap between the box and the end wall. To achieve optimal performance, both resonant and damping conditions for the wave absorber should be matched. The resonant condition requires that the resonant period of the fluid confined in the wave absorber closely mirrors the incident wave period, and the damping condition requires the introduction of appropriate damping into the absorber. The experimental results show that the present short-length resonant wave absorber performs well within a wide range of wave period T ∈ [1.37 s, 3.63 s], which is difficult to be achieved with traditional passive wave absorbers. The reflection coefficient Cr, ratio of wave heights of reflected to incident, remained smaller than 0.1 for the present wave absorber when encountering long waves with 7.04 m in experiments with a typical water depth h = 0.4 m. The working principle of resonant wave absorber is further clarified by revealing the wave components outside the wave absorber.

Parameters optimization and performance evaluation for the novel tuned inertial damper

This paper presents a double-flywheels architecture for a novel tuned inertial damper with grounded stiffness device acts as a passive vibration absorber. An undamped primary structure model with a single degree of freedom controlled by the proposed tuned inertial damper is developed and used to derive the equations of motion of the coupled system. The optimum frequency ratio and the optimum damping ratio are found based on the fixed points theory under harmonic force-excited primary structure. Then, the optimum grounded stiffness ratio is deduced. According to the change on the system parameters, there are three cases for the optimum grounded stiffness ratio, i.e., negative, zero and positive. It is found that from these three cases, the proposed tuned inertial damper with positive grounded stiffness device has the best control performance. When compared with some existing dynamic vibration absorbers, the proposed model in this paper in three cases presented the best control performance, featured by the broadest suppression bandwidth and the minimal vibration amplitude of vibration reduction effect under harmonic and random excitation.

Effects of bi-stable grounded nonlinear energy sink on energy dissipation of the system

In this paper, one of the most efficient passive absorbers, called nonlinear energy sink (NES), is analytically studied. A two-degree-of-freedom system is considered which consists of a linear oscillator (LO) with a base excitation and an NES, called grounded NES (GNES), which is connected to the ground with a nonlinear spring. In this study, we proposed a new arrangement of potential elements in GNES and studied invariant manifolds of the system, as well as the energy absorption performance of the NES. The system is considered in the vicinity of 1:1 resonance to investigate the strongly modulated response (SMR). To this end, after obtaining the equations of motion, the Manevitch complex variable and multiple scale method are applied to solve the equations, analytically. Then, the slow invariant manifold (SIM) is obtained. Also, the energy dissipation ratio of the NES and the percentage of the instantaneous total energy stored in the NES are calculated via the time-amplitude diagram. The results show that when the nonlinear effect decreases, the occurrence of energy pumping is less probable. Also, when the excitation amplitude decreases, the percentage of the instantaneous total energy stored in the NES increases as well as the amount of energy dissipation.

Design and Experimental Implementation of a Passive Dynamic Vibration Absorber to Attenuate Broadband Vibration

The challenge of designing an effective vibration absorber for any mechanical or mechatronic system is formidable. A good vibration absorber must provide broadband vibration reduction yet still keep in lightweight and size to minimize space requirements and maximize equipment accessibility. Broadband vibration is usually attenuated by using an active or semi-active vibration absorber. However, these methods are relatively costly and complicated compared with a passive vibration absorber. Moreover, passive vibration absorber often limited to narrowband frequency reduction since, in the past, it is usually tuned to the targeted frequency or optimum damping and optimum tuning ratio. This paper demonstrated that a passive vibration absorber could be implemented to reduce the broadband vibration of a system, considering the effect of the parameter of passive vibration absorber, the location attachment of the absorber, and the targeted mode shape. The result shows that a properly tuned passive vibration absorber can reduce the root mean square amplitude vibration by 60.91%, covering the first four vibration modes (0 to 300Hz).