Vibration Absorber

Nowadays, in every industrial field, one of the most important key item to be research is to eliminate or control of system's vibrations. In spite of this fact that the destructive and undesirable vibrations, will have a detrimental effect on the main system, it will also have negative impact on all machinery equipments in any complex. In this paper, we attempt to present a new design for Adaptive Tuned Dynamic Vibration Absorber (ATDVA), Based on Smart Slider-Crank Mechanism. This research will also investigate a practical scheme which is applied to reduce the excessive beam vibration to an acceptable range by adding an absorber to a vibratory resonant beam, especially as an alternative to active vibration control.

Single-axis shakers (mostly electrodynamic1) are widely employed for modal analysis, failure simulation and environmental testing in many research and design projects. In particular they are used for automotive and aerospace applications and (in combination with laser-vibrometers) for testing miniature high-technology MEMS sensors. A test engineer should have a good theoretical background to help prevent new designs from encountering long and costly feedbacks for design correction actions. Demonstration skills and teamwork with design and manufacturing engineers are also desirable. Many theoretical and experimental ‘details’ on shaker testing are not clearly covered, although they save time and assure high quality. This article presents helpful guidelines for sweep sine and random vibration testing, general relationships between natural and resonant frequencies and fatigue failure testing. Simple (but useful) equations are derived and applied to predict or interpret test parameters ...

Air pollution occurs when harmful substances are released into the earth's atmosphere. It can also harm other living organisms, such as animals and food crops, and damage the natural or built environment. Both human activities and natural processes can cause air pollution. Both biological and chemical methods are used to remove pollutants from the air. Algae and sodium hydroxide (NaOH) are used to reduce carbon dioxide (CO2), nitrogen dioxide (NO2) and sulphur dioxide (SO2) in the polluted air and produce oxygen. The equipment consists of a culture fluid containing algae and NaOH solution to capture 50 -60% of the carbon dioxide.

The problem of reducing the damage due to seismic loads in engineering structures by means of tuned mass dampers (TMDs) is addressed. Differently from previous studies focused on linear or geometrically nonlinear TMDs, the present work is concerned with a device that exhibits a hysteretic restoring force with pinching. A numerical TMD optimization is carried out so as to ensure optimal energy transfer from the main structure to the TMD for various seismic ground motion severities. The effectiveness of the vibration protection strategy is discussed for two different structural systems, i.e. a multi-story steel building with a purely elastoplastic behavior and a masonry building that exhibits stiffness and strength degradation. Numerical simulations demonstrate that the hysteretic TMD can achieve a meaningful average reduction of the root mean square (RMS) displacement of the steel structure between 40% (for 1% mass ratio) and 60% (for 5% mass ratio). Various seismic records related to soil types and seismic intensity levels different from those considered at the design stage, or unpredictable variations of the main system stiffness up to 10%, are shown to have rather limited influence on the TMD performance. It is shown that a classical linear TMD can attain a protection level comparable to that of the hysteretic TMD only at the expense of much higher mass ratios. Compared to the multi-story structure, the performance of the hysteretic TMD in a masonry building is still satisfactory although degraded, i.e. by about 15% in terms of RMS displacement. The performance is better than that of a classical linear absorber for very small mass ratios, especially for mid-or high-intensity seismic ground motions. The greater robustness of the hysteretic TMD performance for a wide range of seismic ground motions is due to its softening-type backbone, which can be optimized to accommodate the frequency changes that engineering structures typically undergo under seismic excitation. The role of the pinching in the performance of the hysteretic TMD is clarified.

The purpose of this paper is to present an efficient technique for the adjustment of the transmissibility of a SDOF system through the optimal selection of the damping ratio of the SDOF vibrating system. As an application a case of fraction transmissibility. Different objective function relationships are presented and the best one is assigned leading to the desired unit force transmissibility and a frequency spectrum of the system vibration amplitude ratio having a settling frequency ratio above 4.2. Five objective function expressions (ISE, IAE, ITAE, ITSE and ISTSE) are considered and their impact on the force transmissibility and other related parameters is investigated. Desired force transmissibility in the range 0.1 to 0.5 is considered. The force transmissibility of the vibrating system is adjusted around the mean value with standard deviation less than 0.085. System optimal damping ratio of the system is less than 1.3 depending on the desired force transmissibility and the objective function used. The optimum vibration amplitude ratio settles within a 0.05 band at an exciting frequency ratio greater than 4.2.

Earthquake is a phenomenon that has caused many financial damage and fatalities. Researchers have always tried to decrease the destructive effects of this phenomenon and have presented methods to control structure vulnerability during an earthquake. Passive energy dissipation (PED) devices are a group of structural protective systems which are widely accepted by the engineering community. The basic function of these devices when added to a structure is to absorb a portion of input energy due to earthquake or other dynamic excitations and, as a result, reducing energy dissipation demand on primary structural members. Tuned dampers are a group of passive control systems, which their applications in vibration control of 22-DOF buildings under seismic excitation are investigated with the Matlab/Simulink toolbox.

The use of centrifugal pendulum for dynamic vibration absorber design (CPVAs) is a proven method for reducing undesired torsional vibrations in rotating systems. These devices are in use for many years, most commonly in light aircraft engines, helicopter blade rotors etc. These devices have also been reported for reduction of rectilinear vibrations. Pendulum type dynamic vibration absorbers use impact forces for effective reduction of rectilinear vibrations describing modeling method and transient state analysis in view of spring impact absorbers, floating impact absorbers and pendulum impact absorbers. Bond graph technique for modeling of SDOF vibrating system excited by rotation unbalance at the sprung mass using a pendulum type dynamic vibration absorber is reported in the recent literature. This paper deals with the modeling and design procedure for a centrifugal pendulum type dynamic vibration absorber (CPVA) subjected to base excitation. This paper presents a detailed analysis...

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at take-off, climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal devi...

The dynamic response of suspension footbridges to pedestrian-induced excitations and its passive mitigation, via multiple tuned mass dampers (TMDs), are investigated. First, the nonlinear equations of motion are obtained assuming finite planar motions of the suspension bridge. A suitable approximate version of the equations of motion is shown to be in agreement with existing theories and its linearization is then employed in the structural dynamics analyses. A Galerkin discretization is exploited to calculate both the free and forced dynamic response towards the design of the vibration control system. First, the leading characteristics of the bridge dynamic response are outlined. Resonant vibrations induced by the passage of pedestrians are shown to be effectively reduced using viscoelastic TMDs. As the frequencies of the lowest two modes in suspension footbridges can be very close in the proximity of the crossover phenomenon, three different design scenarios are considered: below, ...

Dynamic vibration absorbers (DVAs) have received special attention in recent years due to their capability to reduce structural vibrations of a primary structure. In this work, a DVA of the Tuned Mass Damper type based on a Shape Memory Alloy (SMA) element with pseudoelastic behavior is considered. Owing to their rich thermomechanical response, SMAs can exhibit hysteresis loops with rather different features in terms of overall energy dissipation and of pseudoelastic stiffness. As a first step towards the comprehensive evaluation of the performances of such a device, the optimization of a TMD based on SMA devices with different features is studied. Numerical simulations show that the size and the shape of the pseudoelastic loops can influence in a significant way the performances of the DVA.

It is shown that a passive vibration absorber can completely quench the self-excited vibration only for certain parameter values, like the strength of instability in the primary system. The present paper numerically explores the performance of semi-active vibration absorber in controlling self-excited vibration. In the proposed semi-active scheme, the damping force of the absorber is switched between the maximum and the minimum values according to certain control logics. Four different control strategies are considered-these are on-off velocity-based groundhook control (VBG), on-off displacement-based groundhook control (DBG), continuous VBG and continuous DBG. Numerical simulations are performed in the MATLAB Simulink to explore the efficacy of the control strategies. It is shown that the on-off DBG control is superior to all other control strategies.

Air pollution occurs when harmful substances are released into the earth's atmosphere. It can also harm other living organisms, such as animals and food crops, and damage the natural or built environment. Both human activities and natural processes can cause air pollution. Both biological and chemical methods are used to remove pollutants from the air. Algae and sodium hydroxide (NaOH) are used to reduce carbon dioxide (CO2), nitrogen dioxide (NO2) and sulphur dioxide (SO2) in the polluted air and produce oxygen. The equipment consists of a culture fluid containing algae and NaOH solution to capture 50-60% of the carbon dioxide.

The dynamic coupling of mechanical vibratory systems results in the oscillatory interaction between the bodies of the system as a whole, for a certain selection of some parameters the phenomenon of vibration absorption occurs, in this phenomenon the main system transfers its mechanical energy to the absorber, resulting in a minimum amplitude of movement of the primary system and the absorber develops a certain amplitude. In this work it is proposed to design a vibration absorber for a primary system that in turn is affected by the motion in the base, which produces vibrations, the motion in the base includes elastic and viscous actions. It has been possible to determine a set of parameters that allow the absorption of vibrations, likewise, the parameters determined not only allow the absorption, but also establish a transfer of the effect of the damping present in the base to the absorber.

In this work the impact vibration absorber of pendulum type is examined. It consists of pendulum with motion limiting stops attached to the vibrating system. Pendulum vibration absorbers are widely used in practice. The influence of pendulum parameters on the possibility of suppression of vibrations of the basic system under harmonic excitation is discussed in this study.

An adaptive tuned vibration absorber (ATVA) with a smart variable stiffness element is capable of retuning itself in response to a time-varying excitation frequency, enabling effective vibration control over a range of frequencies. This paper discusses novel methods of achieving variable stiffness in an ATVA by changing shape, as inspired by biological paradigms. It is shown that considerable variation in the tuned frequency can be achieved by actuating a shape change, provided that this is within the limits of the actuator. A feasible design for such an ATVA is one in which the device offers low resistance to the required shape change actuation while not being restricted to low values of the effective stiffness of the vibration absorber. Three such original designs are identified: (i) A pinned–pinned arch beam with fixed profile of slight curvature and variable preload through an adjustable natural curvature; (ii) a vibration absorber with a stiffness element formed from parallel c...

Air pollution occurs when harmful substances are released into the earth's atmosphere. It can also harm other living organisms, such as animals and food crops, and damage the natural or built environment. Both human activities and natural processes can cause air pollution. Both biological and chemical methods are used to remove pollutants from the air. Algae and sodium hydroxide (NaOH) are used to reduce carbon dioxide (CO2), nitrogen dioxide (NO2) and sulphur dioxide (SO2) in the polluted air and produce oxygen. The equipment consists of a culture fluid containing algae and NaOH solution to capture 50-60% of the carbon dioxide.

A numerical simulation to calculate the dynamic response of a beam attached with beam vibration absorber through a viscoelastic layer subjected to a moving load is presented in this paper. The mathematical model is formulated by using Euler-Bernoulli theory to calculate the vertical response of the system. The effect of the inertia of the moving load is included in the model to study its effect on the beam response at the mid span. The viscoelastic layer is introduced as uniformly distributed stiffness and damping and the concept of mixed damping ratio is implemented which allows the system to be modeled for different rigidity ratio. The response is calculated using time integration method for different moving mass inertia, rigidity ratio of the beams and the stiffness and damping of the visco-elastic layer. The effect is investigated for different values of mass and speed of the moving load.

This paper presents a design of vibration absorber using spring and rubber for armored vehicle 5.56 mm caliber rifle. Such a rifle is used in a Remote-Controlled Weapon System (RCWS) or a turret where it is fixed using a two degree of freedom pan-tilt mechanism. A half car lumped mass dynamic model of armored vehicles was derived. Numerical simulation was conducted using fourth order Runge Kutta method. Various types of vibration absorbers using spring and rubber with different configurations are installed in the elevation element. Vibration effects on horizontal direction, vertical direction and angular deviation of the elevation element was investigated. Three modes of fire were applied i.e. single fire, semi-automatic fire and automatic fire. From simulation results, it was concluded that the parallel configuration of damping rubber type 3, which has stiffness of 980,356.04 (N/m 2) and damping coefficient of 107.37 (N.s/m), and Carbon steel spring whose stiffness coefficient is 5.547 x 10 6 (N/m 2) provides the best vibration absorption.

A simple and practical hybrid vibration absorber (HVA) is proposed for global vibration control of flexible structures under random stationary excitations. The HVA, regulated by a pole placement controller, uses a linear translational feedback signal to synthesize active moment via a moment actuator. It is shown, analytically and experimentally, capable of damping vibration in the entire primary structure. While the passive tuned mass damper (TMD) can suppress tonal vibration in the primary structure at the vicinity of the coupling point, it enhances vibration at other locations and other frequencies. The presented HVA, in contrast, can provide more than 48% extra broadband attenuation on vibrations at multiple points when compared with the passive TMD in experimental verification on a beam structure. Up to 85% extra broadband attenuation can be observed at the coupling point. The proposed HVA is a simple and economic alternative for engineers to retrofit the conventional TMD to a higher performance HVA for damping vibrations at multiple locations of the primary structure.

In this article, the H ∞ optimization design of a hybrid vibration absorber (HVA), including both passive and active elements, for the minimization of the resonant vibration amplitude of a single degree-of-freedom (SDOF) vibrating structure is derived by using the fixed-points theory. The optimum tuning parameters are the feedback gain, the tuning frequency, damping and mass ratios of the absorber. The effects of these parameters on the vibration reduction of the primary structure are revealed based on the analytical model. Design parameters of both passive and active elements of the HVA are optimized for the minimization of the resonant vibration amplitude of the primary system. One of the inherent limitations of the traditional passive vibration absorber is that its vibration absorption is low if the mass ratio between the absorber mass and the mass of the primary structure is low. The proposed HVA overcomes this limitation and provides very good vibration reduction performance even at a low mass ratio. The proposed optimized HVA is compared to a recently published HVA designed for similar propose and it shows that the present design requires less energy for the active element of the HVA than the compared design.

In this study, we consider the numerical solution of the Helmholtz equation, arising from numerous physical phenomena and engineering applications including energy systems. We make use of a Padé Approximation method for the solution of the Helmholtz equation. Firstly, Helmholtz partial differential equation had been converted to power series by two-dimensional differential transformation, then the numerical solution of the equation was put into Padé series form for accelerating convergence and decreasing computational time. Hereby, we obtained numerical solution of Helmholtz type partial differential equation.

A design method is proposed to suppress stationary random vibration in flexible structures using a hybrid vibration absorber (HVA). While the traditional vibration absorber can damp down the vibration mainly at the pre-tuned mode of the primary structure, active damping is generated by the proposed HVA to damp down all resonant modes of interest of the vibrating structure and the spatial average mean square motion of the vibrating structure can be minimized. Only one absorber and one feedback signal are required to achieve global vibration suppression of a flexible structure under stationary random excitation. A special pole-placement controller is designed such that all vibration modes of the flexible structures become critically damped. It is proved analytically that the proposed HVA damps the vibration of the entire structure instead of just the attachment point of the absorber. The proposed optimized HVA is tested on a beam structure and it shows a superior performance on global suppression of broadband vibration in comparison to other published designs of passive and hybrid vibration absorbers.

Vibration dynamic absorber is in use to reduce machinery vibrations. This paper presents a novel idea for using the mass-spring absorber as an energy harvester. The aim is to tune the absorber to cancel the machine vibration and produce maximum vibration of the absorber mass to act as an energy harvester. The main vibrating system is damped and assumed as a SDOF. A new frequency is defined called harvesting frequency at which the amplitude of the absorber mass vibration is maximum. It is shown that his frequency is dependent only on the mass ratio of the absorber and independent of the main system damping ratio. The optimal operation of the proposed system is investigated for damping ratio between 0.1 and 0.4 and mass ratio between 0.05 and 4.5. The absorber succeeds to eliminate completely the main system vibrations at a tuning condition and provides high vibration amplitude at the absorber mass at the new defined harvesting frequency..

The aim of the paper is to develop a new nonlinear tuned vibration absorber (NLTVA) capable of mitigating the vibrations of nonlinear systems which are known to exhibit frequency-energy-dependent oscillations. A nonlinear generalization of Den Hartog's equal-peak method is proposed to ensure equal peaks in the nonlinear frequency response for a large range of forcing amplitudes. An analytical tuning procedure is developed and provides the load-deflection characteristic of the NLTVA. Based on this prescribed relation, the NLTVA design is performed by two different approaches, namely thanks to (i) analytical formulas of uniform cantilever and doubly-clamped beams and (ii) numerical shape optimization of beams with varying width and thickness. A primary system composed of a cantilever beam with a geometrically nonlinear component at its free end serves to illustrate the proposed methodology. this paper, a nonlinear tuned vibration absorber (NLTVA) is introduced to mitigate a specific nonlinear resonance of the main structure in wide ranges of motion amplitudes. The basic idea develops from Den Hartog's method, which is extended to ensure equal peaks in the nonlinear frequency response. The linear parameters of the NLTVA are selected according to Asami's solution [5], and the absorber's nonlinear load-deflection characteristic is tailored according to the nonlinear restoring force of the host structure. Experimental structure c Modal model c NLTVA analytic tuning c Load-deflection function © d d Continuous beams (analytic design) Discretised beams (shape optimisation)

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at takeoff , climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal device capable to be tuned at two different frequencies in order to optimize the fuselage noise reduction at two different flight regimes (100% and 86%), has been designed and numerically verified. The functional effectiveness of the bi-frequential tuned device has been analysed by finite elements simulations on a linear beam, representative of the turboprop fuselage frame. The outcomes achieved within this activity encourage the advancement of this research sector, as a support to the needs of the turboprop aeronautical industry. According to the long experience gained by the research group, the proposed multifunctional concept can be a valid technology solution ready to be manufactured as well as validated in flight.

In this article a new bidirectional tuned liquid column damper (BTLCD) is proposed for controlling the seismic response of structures. The device acts as two independent and orthogonal tuned liquid column dampers (TLCDs), but due to its configuration it requires less liquid than two equivalent independent TLCDs. The equations of motion of the system formed by the BTLCD and the primary structure to be controlled, are obtained by means of Lagrangian dynamics explicity considering the non symetrical action of the damping forces. First, the primary structure was assumed to have two degrees of freedom (DOFs). Assuming that the system is excited by a base acceleration that can be considered to be a white noise random process, the optimum design parameters of the device were obtained to minimize the response of the primary structure. The optimum design parameters are presented as expressions covering a wide range of possible configurations for the device in a controlled structure. The use of a BTLCD to control the seismic response of several DOF structures was also studied, showing that if the structural response occurs mainly in two perpendicular modes, then the optimum design parameters for two DOF structures can be used. Finally, experimental analysis of the BTLCD for controlling the seismic response of 3-story structure scale model are developed in order to verify the effectiveness and accuracy of the equations and design procedures proposed herein.

The study has proposed a newly tuned vibration absorber (TVA) based on one degree-of-freedom (1DOF) of translational motion. The absorber mass takes the shape of a tank filled with fluid. The device has been attached to the fluid circulating system, which plays the role of changing the absorber mass. It fills the tank or drains it depending on the data received from the frequency force sensor. The type of TVA used is similar to simple damped TVA. A MATLAB software has been applied, and a numerical procedure was used to test the TVA and compare the performance with the other TVAs. The method is simple to carry out the performance of the TVA as it is adequate for real-life problems.

A passive tuned mass friction damper (P-TMFD) has a pre-determined and fixed slip force at which it can reduces the response of the structure effectively. At any value other than the predetermined slip force, it losses its effectiveness and simply behaves as a normal bracing system. Also, P-TMFD changes its state between stick and slip mode many times during a seismic or harmonic excitation which results in high frequency response of the system and reduces its efficiency. To overcome the disadvantage of P-TMFD, a semi-active tuned mass friction damper (SA-TMFD) is proposed. The control algorithm proposed by Lu (2004) which is known as Predictive control law, is used. The SA-TMFD produces continuous and smooth slip force and eliminates the high frequency response of the structure which usually occurs in case of PTMFD. The governing differential equations of motion of the SDOF system with SA-TMFD are solved numerically using state-space method. To investigate the effectiveness of SA-T...

Most of seismic design codes of buildings, in spite of collapse prevention, allow implicitly some unacceptable consequences, such as massive required reconstruction works, in large populated cities located near active faults. One preventing idea in this regard is ‘Deliberate Directing of Damage’, which means guiding the damage to some pre-decided parts of the structural system, so that other parts do not experience any major plastic deformation. This idea has been employed here for design of repairable regular steel multistory buildings, by using a 4-cell configuration structure with inclined columns around the central main vertical column of each cell at its base level. The inclined columns, with their bases shifted toward the central column, which cause the building to move basically in rocking mode, are equipped with Double-ADAS (DADAS) devices, and are connected to some strong girders at the first floor of the building. These girders help the upper floors to remain elastic, whil...

In this work the impact vibration absorber of pendulum type is examined. It consists of pendulum with motion limiting stops attached to the vibrating system. Pendulum vibration absorbers are widely used in practice. The influence of pendulum parameters on the possibility of suppression of vibrations of the basic system under harmonic excitation is discussed in this study.

Door closing mechanisms are used in all building venues using air conditioning systems to reduce thermal losses. One of the closing mechanisms is the torsional type. The visco-elastic characteristics of the closing mechanism may exhibit certain sort of nonlinearities from its linear characteristics. The dynamics of the door with nonlinear characteristic with positive and negative deviation from the linear characteristics of the door closing mechanism are studied. The system dynamics are defined by a nonlinear ordinary second-order differential equation which is solved using Runge-Kutta 4 technique through the MATLAB environment. Two types of nonlinearity are considered depending on the deviation from the linear characteristics of the closing mechanism. One type reveals dynamic behaviour similar to that of overdamped linear dynamic system while the other type reveals dynamic behaviour similar to that of underdamped linear dynamic system. The second type has large effect on the door d...

Experimental procedures for the research of vibrations in automatic weapons mounted on combat vehicles is introduced. Experiment preparation procedures, experience and examples of evaluation of measured results in direct fire from a tracked combat vehicle are explained on BMP-2 IFV example. The result is the movements of the turret and the hull of a combat vehicle in single shot firing, and short and long burst firing. In addition to time domain analysis, methods of correlation and spectral analysis are used. Live firing experiments are complemented by laboratory experiments and are used to determine model parameters for calculations such as stiffness and damping in the suspensions of the hull, elevation parts, clearance in the elevating gear, and the natural vibration frequency of the hull and elevation parts.

Tuned Liquid Column Damper (TLCD) has become an alternative solution for reducing low frequency vibration response of machines and structures. This is not surprisingly that the damper has simply structure and low maintenance cost. The main disadvantage of using TLCD is the complexity in controlling TLCD damping factor experimentally. Theoretically, damping factor can be controlled by adjusting the orifice dimension. However, this method is time consuming and not appropriate conducted in the real application. A more simply method for adjusting TLCD damping factor is by varying the fluid viscosity. This research is aimed to evaluate the effect of fluid viscosity to the damper performance. Two DOF shear structure with TLCD is used as the experimental model. Several TLCD fluids with different viscosity are evaluated. Evaluation of TLCD damping factor due to variation of the fluid viscosity is conducted by comparing the Frequency Response Function (FRF) obtained from the experimental data.

Vibration dynamic absorber is in use to reduce machinery vibrations. This paper presents a novel idea for using the mass-spring absorber as an energy harvester. The aim is to tune the absorber to cancel the machine vibration and produce maximum vibration of the absorber mass to act as an energy harvester. The main vibrating system is damped and assumed as a SDOF. A new frequency is defined called harvesting frequency at which the amplitude of the absorber mass vibration is maximum. It is shown that his frequency is dependent only on the mass ratio of the absorber and independent of the main system damping ratio. The optimal operation of the proposed system is investigated for damping ratio between 0.1 and 0.4 and mass ratio between 0.05 and 4.5. The absorber succeeds to eliminate completely the main system vibrations at a tuning condition and provides high vibration amplitude at the absorber mass at the new defined harvesting frequency..

Door closing mechanisms are used in all building venues using air conditioning systems to reduce thermal losses. One of the closing mechanisms is the torsional type. The visco-elastic characteristics of the closing mechanism may exhibit certain sort of nonlinearities from its linear characteristics. The dynamics of the door with nonlinear characteristic with positive and negative deviation from the linear characteristics of the door closing mechanism are studied. The system dynamics are defined by a nonlinear ordinary second-order differential equation which is solved using Runge-Kutta 4 technique through the MATLAB environment. Two types of nonlinearity are considered depending on the deviation from the linear characteristics of the closing mechanism. One type reveals dynamic behaviour similar to that of overdamped linear dynamic system while the other type reveals dynamic behaviour similar to that of underdamped linear dynamic system. The second type has large effect on the door dynamics where the maximum deviation in the door dynamic response may exceed 700 % from the linear characteristics of the door.

A vibration exciter is a machine which produces mechanical vibratory motion to which the test object is subjected. This article presents design, construction, performance and testing of mechanical vibrations exciter, which have unbalanced mass to generate uniaxial vibrations. The exciter is designed to produce a given range of harmonic or time dependent excitation force and displacement through a given range of frequencies. The mechanical vibration exciter produces vibrations due to centrifugal force of rotating eccentric mass. The vibrations produced lie in the low frequency range. The construction of working device and its important parts are described here. The most important part of exciter is unbalanced mass attached with rotating disc of motor. Exciter has unbalanced mass at one end of disc, base frame, top plate as platform, springs and motor. This exciter is used for testing of welded parts, consolidation of concrete, concrete filling in mould. The obtained experimental results are in line with theoretical results.

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at takeoff , climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal device capable to be tuned at two different frequencies in order to optimize the fuselage noise reduction at two different flight regimes (100% and 86%), has been designed and numerically verified. The functional effectiveness of the bi-frequential tuned device has been analysed by finite elements simulations on a linear beam, representative of the turboprop fuselage frame. The outcomes achieved within this activity encourage the advancement of this research sector, as a support to the needs of the turboprop aeronautical industry. According to the long experience gained by the research group, the proposed multifunctional concept can be a valid technology solution ready to be manufactured as well as validated in flight.

Iran are investigated during this study. The main focus of this study is on passive control techniques used in private typical buildings with relatively low seismic performance, which are quite common in Iran. This study also includes a brief outline of different passive dampers and vibration absorbers. According to the technical and economical issues, it is shown that tuned liquid column-gas damper, TLCGD, is one of the best options for enhancing the seismic behavior of typical buildings in the country. A simple yet accurate procedure is proposed to estimate equivalent damping ratio corresponding to the TLCGD. Finally, through a numerical assessment, effect of TLCGD is investigated. Based on the obtained results, TLCGD can reduce rout mean square (RMS) response of buildings, but its capability in reducing the maximum response depends on the excitation itself. TLCGD was shown an efficient scheme for enhancement of seismic capacity of both new and under-operation existing buildings.

Upgrading structural damping in civil engineering prone by Tuned Liquid Column Damper (TLCD) has been investigated during last decades extensively and control vibrations of some buildings and bridges with such dampers have been studied under wind or earthquake loadings as well. In this paper, the idea of adding gas spring effect in TLCD to increase the range of the frequency is expanded to arch dams in order to upgrade the structural damping. This improvement is extremely needed for the retrofit of existing ancient dams that are not verified with the criteria of modern seismic civil engineering codes. The structural continuum of concrete dam body is idealized and discretized as an assemblage of finite elements. The dynamic analysis of a seismically activated dam with TLCGD is studied and the coupled modal equations considering one isolated structural mode is derived By transferring into state space and following the optimization procedure, the optimal parameters of TLCGD are defined. The results show a proper decrease in displacements under the earthquake excitations.

The study has proposed a newly tuned vibration absorber (TVA) based on one degree-of-freedom (1DOF) of translational motion. The absorber mass takes the shape of a tank filled with fluid. The device has been attached to the fluid circulating system, which plays the role of changing the absorber mass. It fills the tank or drains it depending on the data received from the frequency force sensor. The type of TVA used is similar to simple damped TVA. A MATLAB software has been applied, and a numerical procedure was used to test the TVA and compare the performance with the other TVAs. The method is simple to carry out the performance of the TVA as it is adequate for real-life problems.

In this paper, the application of tuned mass damper in improving the response of structures is considered. At first, three frames of 3, 9 and 20 stories are evaluated in which time history analysis is done according to El-Straw earthquake. The maximum reduction of among the three mentioned frames belongs to a 20-stories structure in which the rate of story displacement reduction is between 25 to 45%, and this indicates that by increasing the height of the structure, the performance of tuned mass damper improved. In the second part, the effect of semi-active tuned mass damper is studied on a 10-stories frame. Studies showed that using a tuned mass damper system with viscous damper with controller force decreases the average of maximum displacement of roof story down to 39.9 % and this amount of reduction is 22.8% for semi-active tuned mass damper. Finally, the performance of tuned Single and multiple mass Damper is evaluated on a 20-stories frame, and the results show that single and multiple dampers decrease structures 'responses and the performance of tuned multiple dampers depends on the mass and frequency ratio and also concluded that the performance of tuned multiple mass dampers is reduced by transition to middle of the structure stories.

The aim of this project is to how to reduce vibration through dual cantilever mass mechanism which is call adaptive vibration absorber that is different than the tune vibration absorber. Design incorporates the use of two concentrated masses cantilevered from two rods. The adaptive solution is achieved by moving the two masses along the length of the rod, producing a changing natural frequency for the absorber device. To do so we applied this system to frequency range of 30 to 80 Hz .For our design we take concentrated masses of 1.2 kg. When we change length from 81.5mm to 210 mm. So, our frequency range will be in range of 80 to 30 Hz (natural frequency).We would design the absorber for the setup having maximum acceleration at 50 Hz frequency and observe the amount of vibrations absorbed by it.

The aim of this project is to how to reduce vibration through dual cantilever mass mechanism which is call adaptive vibration absorber that is different than the tune vibration absorber. Design incorporates the use of two concentrated masses cantilevered from two rods. The adaptive solution is achieved by moving the two masses along the length of the rod, producing a changing natural frequency for the absorber device. To do so we applied this system to frequency range of 30 to 80 Hz .For our design we take concentrated masses of 1.2 kg. When we change length from 81.5mm to 210 mm. So, our frequency range will be in range of 80 to 30 Hz (natural frequency).We would design the absorber for the setup having maximum acceleration at 50 Hz frequency and observe the amount of vibrations absorbed by it.

In this paper we focused on the comparative study of three very popular and most recently developed nature inspired evolutionary algorithms namely Biogeography based optimization algorithm (BBO), Flower pollination algorithm (FPA) and Artificial bee colony optimization algorithm (ABC) for developing a model of 6 layers thin broadband (0.2-20GHz) microwave absorber. The model is optimized for oblique wide angle of incidence (45 0 , 60 0) taking both TE and TM polarization of the electromagnetic wave under consideration. The primary goal of our design is to minimizing the overall reflection coefficient of the absorber and its total thickness by selecting the proper layer of materials from a predefined database of existing materials. 8 different models are presented and synthesize considering both these design consideration simultaneously and for only overall reflection coefficient of the absorber while total thickness is not taken into consideration during optimization for each cases. The optimum values of all the significant parameters of the multilayer absorber for different models have been compared and tabulated using BBO, FPA and ABC algorithms which established the superiority of our proposed design.

In this article, the performance of a two degree-of-freedom dynamic vibration absorber (DVA) with very large or very small moment of inertia is studied. Although it has been shown previously that an optimally tuned DVA with a negligibly small moment of inertia marginally outperforms the optimally tuned DVA with a very large moment of inertia, the physical reasons for this have not been made clear. Using a simplified model of the stiffness elements of the DVA, it is shown that the two sets of parallel combinations of stiffness and damping elements of the DVA with negligibly small moments of inertia effectively act in series, rather than in parallel as in the other case. Furthermore, it is shown that the stiffness and damping elements can be represented as a single stiffness and a single damping element whose properties are frequency dependent. This frequency dependency means that there is additional freedom in choosing the optimum stiffness and damping of the DVA, which results in better performance.

This paper presents the vibration attenuation performance of a double-cantilever dynamic vibration absorber (DCDVA) attached to a simply-supported beam in two different orientations using theoretical and experimental methods. The results showed that the longitudinal configuration of the DCDVA yield better vibration attenuation by absorbing 80% more vibration than the transverse configuration. For the experimental results, the orientation of the DCDVA has very little effect on the resonant frequencies of the combined DCDVA and simply-supported beam system, however the damping of the second resonant frequency is higher for the transverse configuration. The lumped-mass model characterized the frequency response functions of the DCDVA oriented in the transverse direction only, the model could not reproduce the experimental response for the longitudinal orientation of the DCDVA.

A physical model used to demonstrate the use of a passive dynamic vibration absorber (DVA) to cancel out resonance of a classic mass spring damper system was developed for this project. It incorporates an eccentric mass as a rotational unbalance to generate movement with two degrees of freedom (DOF). The excitation frequency can be manually controlled to demonstrate discussed phenomena of a two mass system.