As in most applications of nanotechnology speed and precision are important requirements for getting good topographical maps of material surfaces using Scanning Tunneling Microscopes (STM) and Atomic Force Microscopes (AFM). Many STMs and AFMs use Piezoelectric tubes for scanning and positioning with nanometer resolution. In this work a piezoelectric tube of the type typically used in STMs and AFMs is considered. Scanning using this piezoelectric tube is hampered by the presence of a low- frequency resonance mode that is easily excited to produce unwanted vibrations. The presence of this low-frequency resonance mode restricts the scanning speed of the piezoelectric tube. Concept of a Positive Velocity and Position Feedback (PVPF) controller is introduced and a controller is designed to dampen the effect of the undesired first resonance mode. To achieve good precision, specific control signals are designed for the closed loop system to track a raster pattern. Experimental results revel a significant damping of the resonance mode of interest, and consequently, a good tracking performance.

The increasing industrialization and markets across the globe do result in noise pollution that affects humans. In order to reduce the sound pressure level (SPL) of disturbing noise active noise control (also known as noise cancellation, active noise reduction (ANR) or anti-noise) is a good option. Herewith unwanted noise from a primary sound source can be reduced significantly by anti-noise generated from a secondary source: At present commercial active noise reduction systems are using moving-coil loudspeakers as actuators. These actuators need a quite large built-in volume and they are not lightweight. Therefore the industrial application of ANR in vehicles is limited. To reduce these difficulties the use of flat loudspeakers made of electromagnetic films seems to be a promising approach. It is a precondition for the use of such new technologies within an ANR- system to have a basic understanding of the dynamic systems behaviour and the sound transmission behaviour of such a lightweight active component: This paper describes the investigation of a flat panel speaker which is based on electrostatic loudspeaker technology. First of all the passive transmission properties have been measured in a test bed. The passive acoustic insulation has been analyzed and weak spots in the frequency response were discovered. Afterwards the flat panel speaker has been used as actuator in an ANR-System to support insulation at those frequencies. An adaptive filter (FxLMS) was adjusted to the panel and the reduction capabilities of a single-output system have been determined.

This paper describes a multivariable controller design procedure that uses mixed-sensitivity H-infinity control theory. The design procedure is based on the assumption that structural noise can be modeled as entering a state-space system through a random input matrix. The design process starts with a full-order flexible state-space model that undergoes a frequency-weighted balanced truncation to obtain a reduced-order model with excellent low frequency matching. Weighting functions are then created to specify the desired frequency range for disturbance rejection and controller bandwidth. A structural noise input matrix is also designed to identify system modes where maximal damping is desired. An augmented plant is then assembled using the reduced-order model, weighting functions and structural noise input matrix to create a mixed-sensitivity configuration. A state-space controller is then realized using an H-infinity design algorithm. A two-input, three-output, doubly cantilevered beam system provides a design example. A 174th-order, discrete-time, state-space model of the cantilevered beam system was used to generate a reduced 40th- order model. A 55th-order Hinfinity controller was then designed with a controller bandwidth of approximately 300 Hz. This non-square modern controller uses feedback signals from two piezoelectric sensors, each collocated with one of two piezoelectric actuators, and one highly non-collocated accelerometer. The two piezoelectric actuators provide the control actuation. Frequency analysis and time-domain simulations are utilized to demonstrate the damping performance.

This paper presents a self-sensing method for semi-active vibration suppression that measures only the value of piezoelectric voltage. This self-sensing method is implemented with a Kalman filter with extended system equations, instead of the conventional bridge-circuit technique. The method has several advantages over the bridge-circuit self-sensing method, such as being applicable to MIMO systems. Experiments showed that our selfsensing system suppressed vibrations by combining the state-switching control and the synchronized-switching control. We confirmed that the self-sensing method is robust against model errors through the experiment with intentional frequency shift.

In the design process of energy harvesting systems based on piezoelectric elements, achievable energy output is the most interesting factor. To estimate this amount a priori manufacturing of prototypes a mathematical model is very helpful. Within this contribution we will introduce a model based on electro-mechanical circuit theory. Its parameters are identified by measurements and the model is validated by comparison to experimental results. The model is designed to support the development-engineer in the dimensioning of energy harvesting units to specific application demands. Two main challenges in device design are investigated with the mathematical model: influence of the ambient excitation frequency, and influence of the load impedance. Typically, the equivalent model approach delivers models for piezoelectric elements that are driven in resonance by electrical excitation. In the case of energy harvesting the piezoelectric elements are excited mechanically and most often non-resonant. Thus, we first set up a mechanical equivalent model for base excited systems. In first approximation it represents an energy harvesting unit around one resonance frequency. The model is expandable for a wider frequency range using the superpositioning of multiple circuits. From the viewpoint of optimum energy transformation between mechanical and electrical energy it is favorable to drive piezoelectric elements at resonance or anti-resonance. Thus, an energy harvesting system should be tuned to the excitation frequency.

Over the past years, there has been growing interests in the field of power harvesting technologies for low-power electronic devices such as wireless sensor networks and biomedical sensor applications. Methodologies of using piezoelectricity to convert mechanical power to electric power with a cantilever beam excited by external environmental vibration were widely discussed and examined. Operating in resonant mode of the cantilever beam was found to be the most efficient power harvesting condition, but in most cases that the resonant frequencies of the cantilever beam are hardly matching with the frequency of external vibration sources. The mechanical resonant has relatively high Q factor, and thus the harvesting output will be significantly lower compared to the condition when resonant matching to external vibration frequency. A tunable resonant frequency power harvesting device in cantilever beam form which will shift its resonant frequency to match that of the external vibrations will be developed and verified in this paper. This system utilizes a variable capacitive load to shift the gain curve of the cantilever beam and a low power microcontroller will sampling the external frequency and adjust the capacitive load to match external vibration frequency in real-time. The underlying design thoughts, methods developed, and preliminary experimental results will be presented. Potential applications of this newly developed power harvesting to wireless sensor network will also be detailed.

Over the years, there has been a growing interest in the field of power harvesting technologies for low-power electronic devices, such as wireless sensor networks and biomedical sensor applications. Of all possible energy sources, the mechanical vibrations have been considered a potential choice for power harvesting in a wide variety of applications. This paper presents the development of a piezoelectric MEMS generator which has the ability to scavenge mechanical energy of ambient vibrations from their surroundings and transform it into electrical energy that can be used in energy storage applications. The piezoelectric MEMS generator comprises a beam structure based on the silicon wafer, and the digitate electrode placed in between the lead zirconate titanate (Pb(Zr,Ti) O₃, PZT) material and the beam structure, to transform mechanical strain energy into electrical charge with using the d₃₃ mode of PZT. An optional proof mass can be built at the tip of the beam, to adjust the structure resonant frequency of the piezoelectric MEMS generator, for most adaptable frequency matching to the ambient vibration of its surroundings. A theoretical model is also presented to investigate the relations between the charge generation ability and the design parameters of the piezoelectric MEMS generator. To improve the piezoelectric MEMS generator fabrication process, a self-made PZT deposition chamber which could deposit PZT thin film up to tens micron in minutes was used to deposit the piezoelectric layer on the beam structure of the piezoelectric MEMS generator.

Using piezoelectric elements to harvest energy from ambient vibration has been of great interest recently. Because the power harvested from the piezoelectric elements is relatively low, energy storage devices are needed to accumulate the energy for intermittent use. In this paper, we compare several energy storage devices including conventional capacitors, rechargeable batteries, and supercapacitors in piezoelectric energy harvesting. Their charge/discharge efficiency, adaptability, lifetime, and self-discharge are investigated and discussed. A quick test method is proposed to experimentally study the charge/discharge efficiency of the energy storage devices. The results show that the supercapacitors are suitable and more attractive than the rechargeable batteries as energy storage devices in piezoelectric energy harvesting for wireless sensor networks.

In this paper, a design methodology for an energy harvesting device will be investigated and results will be presented to validate the design. The energy harvesting device in the study is 31- unimorph piezoelectric cantilever beam which was used to convert small amplitude mechanical vibration from a specific machine application into an electrical energy source that could be used for electronic devices with low power requirements. The primary purpose of the design methodology is to illustrate a method to design a cantilever beam that is optimized for a particular application. The methodology will show how the vibration data (frequency and amplitude) from the machine was analyzed and then how this information was incorporated into the final design of the beam. From the given vibration data a range of frequencies where the energy harvesting device will generate the greatest amount of energy is determined. The device is then designed specifically targeting that frequency range. This approach is presented as part of a more general approach to designing energy harvesters for any application. Also, it will be shown how the thickness and type of materials used for each layer of cantilever beam were chosen, completely independent of the vibration data, without effecting the over all optimization process.

The aim of this paper, describing a semi-active Mass Damper system based on Magnetorheological (MR) Devices, is the evaluation of the effectiveness of a vibration control system based on semi-active dampers, applied to the case of a typical Italian historical construction subjected to seismic action. The reference model has been extracted from the structural scheme of a long-bay building and the control strategy takes into account a mass damper system. The MR damper design has been dealt with, by considering mechanical, hydraulic and electronic related aspects and problems. A specific logical scheme of the building integrated with the MR device has been analysed by means of the Simulink toolbox. By taking advantage of this model, the performance of the semi-active control system has been evaluated in comparison with the passive control strategy and with the structure without control.

This paper presents the results of vibration isolation analysis for the pump/motor component of hydraulic hybrid vehicles (HHVs). The HHVs are designed to combine gasoline/diesel engine and hydraulic power in order to improve the fuel efficiency and reduce the pollution. Electric hybrid technology is being applied to passenger cars with small and medium engines to improve the fuel economy. However, for heavy duty vehicles such as large SUVs, trucks, and buses, which require more power, the hydraulic hybridization is a more efficient choice. In function, the hydraulic hybrid subsystem improves the fuel efficiency of the vehicle by recovering some of the energy that is otherwise wasted in friction brakes. Since the operation of the main component of HHVs involves with rotating parts and moving fluid, noise and vibration are an issue that affects both passengers (ride comfort) as well as surrounding people (drive-by noise). This study looks into the possibility of reducing the transmitted noise and vibration from the hydraulic subsystem to the vehicle's chassis by using magnetorheological (MR) fluid mounts. To this end, the hydraulic subsystem is modeled as a six degree of freedom (6-DOF) rigid body. A 6-DOF isolation system, consisting of five mounts connected to the pump/motor at five different locations, is modeled and simulated. The mounts are designed by combining regular elastomer components with MR fluids. In the simulation, the real loading and working conditions of the hydraulic subsystem are considered and the effects of both shock and vibration are analyzed. The transmissibility of the isolation system is monitored in a wide range of frequencies. The geometry of the isolation system is considered in order to sustain the weight of the hydraulic system without affecting the design of the chassis and the effectiveness of the vibration isolating ability. The simulation results shows reduction in the transmitted vibration force for different working cycles of the regenerative system.

This paper presents some preliminary results concerning semi-active vibration isolation of a spacecraft during its launch using Magneto-Rheological (MR) dampers. In order to evaluate the isolation performance of such smart structures, a single degree of freedom isolation system was studied and the extension to a soft hexapod configuration is currently carried out. Semi-active isolation is known to offer appreciable improvement over passive isolation for tonal vibration. As regards broadband vibration, semi-active control leads to a conflict between the demand for damping, which induces less good isolation performance than for tonal vibration. This paper focuses on semi-active isolation of broadband vibration. In the single degree of freedom configuration, it is demonstrated experimentally that, for an example of broadband disturbance, band-passed white-noise, semi-active isolation using MR dampers performs better than passive isolation for various damping, when using a clipped-continuous skyhook control scheme. Then, a semi-active hexapod prototype using MR dampers is shown. The dynamic modelling of the hexapod as well as the investigated control strategy, a clipped-continuous version of the integral force feedback law are presented. Finally, some preliminary open-loop transmissibilities for a piston motion are measured.

The possibility of reducing offshore structural response under strong external excitations such as wind storm, sea ice and earthquake via control systems is attracting the interest of a large number of researchers. Up to now, lots of dampers have been installed on different offshore platforms. As one new kind of effective semi-active device, magnetorheological fluid (MRF) damper has been used in the field of mechanical equipment, automobile and civil buildings, however, the practical application for vibration control of offshore platform has not seen before. In this paper, 8 MRF dampers with maximum damping force of 100kN for vibration control of one offshore platform with total weight of 650t have been manufactured and tested. The general situation of MRF damper system and the offshore platform include manufacturing issues, powering, range of variability of the mechanical parameters and response time are introduced.

This work presents an experimental study to examine the flow properties of magneto-rheological fluids (MR) fluids in channel flow. The channel walls are non-ferrous porous surfaces impregnated with a MR fluid. The porous walls are impregnated with no flow through the porous media. Different porosity sizes and two different impregnation techniques are studied. The pressure drop and flow rate data are obtained for each porosity and impregnation technique. It is demonstrated that under an applied magnetic field, the impregnated porous wall surface increases the pressure drop significantly, when compared to a smooth surfaces with no porosities. The pressure drop can be increased by 65% without changing the channel size and MR fluid's properties.

Thin film Nitinol is evaluated for a new damping solution to microscale damping. In this study, thin film Nitinol was mechanically tested under steady and cyclic tensile loads in a DMA Q800 load frame to determine stiffness and hysteric losses (tan δ = 0.17). A method of determining the damping properties of a multilayered laminate was derived and evaluated using measured and predicted values of Nitinol film damping. Hysteretic loss of tan δ = 0.76 was predicted for a tensile/compressive loading of a film indicative of loading in a MEMS structure. Damping in a silicon/Nitinol laminate using the tensile/compressive loading film damping prediction was calculated to be tan δ = 0.127.

In this paper, the effect of air viscous damping in the out-of-plane motion of vibrating microbeams is modeled analytically and compared with experimental results. This analysis results in a closed-form expression that can be used to accurately predict the dynamic response of microbeams used in MEMS devices such as vibration and pressure sensors, microswitches, and micromechanical resonators. First, the squeeze-film damping for a solid and straight vibrating cantilever beam, caused by the force in the narrow gap, is analyzed using the well-known Reynolds' equation under the conditions of small amplitude oscillations in an incompressible isothermal squeeze-film. The expression is then modified to include the effects of the initial curled-shape of the microbeams due to fabrication and inherent film stress gradients. Next, the airflow damping, caused by the air surrounding the cantilever beam, is determined by solving the modified form of the Navier-Stokes equation using the bead model, which is based on the oscillation of a string of spheres (beads). The closed-form solution is compared against experimental data gathered during the dynamic characterization of micro cantilever beams with different widths and air gaps. By comparing the measured results to those generated by analytical models, we demonstrate that the damping coefficient match to within 10%.

Conventionally, the viscoelastic cores of Constrained Layer Damping (CLD) treatments are made of materials that have uniform shear modulus. Under such conditions, it is well-recognized that these treatments are only effective near their edges where the shear strains attain their highest values. In order to enhance the damping characteristics of the CLD treatments, we propose to manufacture the cores from Functionally Graded ViscoElastic Materials (FGVEM) that have optimally selected gradient of the shear modulus over the length of the treatments. With such optimized distribution of the shear modulus, the shear strain can be enhanced, and the energy dissipation can be maximized. The theory governing the vibration of beams treated with CLD, that has functionally graded viscoelastic cores, is presented using the finite element method (FEM). The predictions of the FEM are validated experimentally for plain beams, beams treated conventional CLD, and beams with CLD/FGVEM of different configurations. The obtained results indicate a close agreement between theory and experiments. Furthermore, the obtained results demonstrate the effectiveness of the new class of CLD with functionally graded cores in enhancing the energy dissipation over the conventional CLD over a broad frequency band. Extension of the proposed one-dimensional beam/CLD/FGVEM system to more complex structures is a natural extension to the present study.

Floor damping is an essential parameter in the evaluation of the dynamic performance of a floor as the amount of floor damping has a significant impact on floor vibration levels. This paper explores the not well understood relationship between floor damping and seated crowds of people. The paper contributes to the understanding by presenting results of controlled experimental investigations that involved crowds of people sitting on a vibrating test floor. In tests, floor damping and floor frequency are identified for various sizes of the crowd. This in itself throws some light on the not well understood relationship, but it is further investigated whether modelling the human crowd as a single-degree-of-freedom spring-mass-damper system attached to the vibrating floor can explain the recorded floor frequency and damping. Thus, a crowd-floor interaction model describes the combined crowd-floor system, and results show that this model is capable of explaining the overall tendency in recorded floor damping and frequency, and the calibration of the interaction model gives some indications of the frequency and damping of the spring- mass-damper system representing the crowd. The paper describes the tests and the methods used to evaluate the appropriateness of modelling a crowd as a spring-massdamper system. Some implications of the observed crowd-floor interaction are discussed in light of the results.

In recent years, increasing research efforts have been devoted to the development of new controllable dampers, in the aim of mitigating vibration of mechanical equipment, automobile, civil construction and so on. Most of the new controllable dampers are made with special performance of smart materials, such as MR/ER fluid, piezoelectric ceramic and shape memory alloy. Although has similar smart performance such as rapid response time, low power requirement and large driving force with those smart materials, magnetostrictive material, especially magnetostrictive composite material is only got attention by a few researchers. In this paper, by analysis character of magnetosrtrictive effect, the possible applications of magnetosrtrictive composite material in area of vibration control are discussed; several new dampers, made with magnetosrtrictive composite material, such as smart friction or viscous dampers are presented.

Damping treatments with stand-off layer (SOL) have been widely accepted as an attractive alternative to conventional constrained layer damping (CLD) treatments. Such an acceptance stems from the fact that the SOL, which is simply a slotted spacer layer sandwiched between the viscoelastic layer and the base structure, acts as a strain magnifier that considerably amplifies the shear strain and hence the energy dissipation characteristics of the viscoelastic layer. Accordingly, more effective vibration suppression can be achieved by using SOL as compared to employing CLD. In this paper, a comprehensive finite element model of the stand-off layer constrained damping treatment is developed. The model accounts for the geometrical and physical parameters of the slotted SOL, the viscoelastic, layer the constraining layer, and the base structure. The predictions of the model are validated against the predictions of a distributed transfer function model and a model built using a commercial finite element code (ANSYS). Furthermore, the theoretical predictions are validated experimentally for passive SOL treatments of different configurations. The obtained results indicate a close agreement between theory and experiments. Furthermore, the obtained results demonstrate the effectiveness of the CLD with SOL in enhancing the energy dissipation as compared to the conventional CLD. Extension of the proposed one-dimensional CLD with SOL to more complex structures is a natural extension to the present study.

Granular damping is a technique of achieving high structural damping with granules embedded within or attached to the vibrating structure. The discrete element method (DEM), which is based on the direct dynamic analysis of all granules using Newton's equations, can accurately predict the granular damping behavior. However, the numerical implementation of such approach is complicated and the key issue is the time-consuming granule contact detection in DEM. In this research, a new computational scheme is presented for granular damping analysis using DEM. Instead of using the straightforward search over all granular pairs, the link cell (LC) method is used to find the candidate pairs for possible contacts, which performs contact check of a granule only with the neighbor granules. To further reduce the number of candidate pairs, a Verlet table is incorporated with the LC method which lists all granular pairs whose distances are less than a threshold distance d_t. The Verlet table for candidate pairs can be updated in an adaptive manner, corresponding to the dynamic states of the vibrating system. Collectively, these improvements can increase the computational efficiency of DEM by multiple times as compared to the state-of-the-art.

A novel set of auxetic (negative Poisson's ratio) open cell polyurethane foam has been developed and tested under dynamic loading conditions to assess the viscoelastic response under white noise random excitation and compressive cycling. Foam pads normalized to standard ISO 13753 have been tested at room temperature and frequency bandwidth 10-500 Hz to assess transmissibility characteristics for possible antivibration glove applications. The results show that the ISO 13753 normalized transmissibility for these foams falls below 0.6 above 100 Hz, with lower peak maximum stresses under indentation compared to conventional open cell solids. These results suggest possible use of the auxetic foam for pads or linens against "white fingers" vibration applications. Further tests have been conducted on cyclic compressive loading up to 3 Hz and loading ratios of 0.95 for loading histories up to 100000 cycles. The damping capacity of the auxetic foams showed and increase by a factor 10 compared to the conventional foams used to manufacture the negative Poisson's ratio ones, and stiffness degradation stabilized after few tens on cycles.

Space and weapon delivery systems contain guidance components and payload that need to be protected from the extremely harsh acoustic excitation present during launch operations. The above example represents just one application where high-damping viscoelastic materials are used in the design of shock and vibration isolation components. The shock transients generally encountered are characterized by a broad frequency spectrum. Widely available finite element codes do not offer the proper tools to model the frequency- dependent mechanical properties of viscoelastic materials over the frequency domain of interest. An added difficulty is the large Poissson's ratio exhibited by some of these materials, which indicates that previously developed displacement-based finite element formulations should be complemented with mixed pressure-displacement finite element formulations. A pure displacement-based finite element generally predicts the displacements well, if the mesh used is fine enough, but the same thing may not be said about the values of the predicted stresses. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency-dependence of material properties within a time-domain finite element framework and using a mixed displacement-pressure finite element formulation. Finite elements based on this new formulation are developed.

This paper considers the analysis of structures with nonlocal damping, where the reaction force at any point is obtained as a weighted average of state variables over a spatial domain. The model yields an integro-differential equation, and obtaining closed form solutions is only possible for a limited range of boundary conditions by the transfer function method. Approximate solutions using the Galerkin method for beams are presented for typical spatial kernel functions, for a nonlocal viscoelastic foundation model. This requires the approximation of the displacement to be defined over the whole domain. To treat more complicated problems with variable damping parameters, non-uniform section properties, intermediate supports or arbitrary boundary conditions, a finite element method for beams is developed. However, in nonlocal damping models, nodes remote from the element do have an effect on the energy expressions, and hence the damping matrix is no longer block diagonal. The expressions for these direct and cross damping matrices are obtained for separable spatial kernel functions. The approach is demonstrated on a range of examples.

This work investigates numerically and experimentally the nonlinear vibration of a Shape Memory Alloy (SMA)passive damping vibration device, where the main elements are pseudoelastic SMA wires. At first, a one-degree of freedom SMA oscillator, composed of a mass balanced by two pseudoelastic SMA wires, where the configuration was based on the SMA passive damping vibration device, was considered. A thermomechanical constitutive model, based on the thermodynamic framework proposed by Boyd and Lagoudas, was used to predict the constitutive behavior of the SMA wires. The mechanical model was supplemented by simple heat transfer analysis, so that temperature variations caused by martensitic phase transformation and the effect of different frequency responses could be investigated. Numerical simulations of transmissibility curves and temperature variations of SMA oscillator are correlated with experimental results obtained from vibration sine sweep tests.

In this paper, based on a general formulation for linear complex systems, an in situ frequency-domain model identification method is introduced. In this technique, frequency response function (FRF) models of the subsystems are extracted without the need for disassembling the system. The FRF-based substructuring (FBS) synthesis and standard NVH testing are used to obtain FRF models of the overall system model. The model is linked to an optimization routine to predict the optimum set of vibration isolation devices for a desired objective function. Three automotive applications of this method are presented: engine mount optimization, body mount optimization, and engine rigid body inertia identification.

Recently, there exists an abundance of research on the semi-active suspension system. The skyhook control is commonly known to control semi-active suspension system because it has practicality. In this paper, the fuzzy logic control based on heuristic knowledge is combined with the skyhook control. And it simulated in a quarter car model. The acceleration value of the sprung mass was reflected in fuzzy inference to reduce the vertical acceleration RMS value of the sprung mass. Then scale factors and membership functions that determine performance efficiency of fuzzy skyhook controller are tuned by a genetic algorithm known as a kind of optimization method.

This paper presents an analysis on the structural damping characteristics of polymeric composites containing dilute, randomly oriented nanoropes. The SWNT (single-wall nanotube) rope is modeled as a closed-packed lattice consisting of seven nanotubes in hexagonal array. The resin is described as a viscoelastic material using two models: Maxwell model and three-element standard solid model. The composite is modeled as a three-phase system consisting of a resin, a resin sheath acting as a shear transfer zone, and SWNT ropes. The "stick-slip" mechanism is proposed to describe the load transfer behavior between a nanorope and a sheath and between individual SWNTs. The analytical results indicate that the loss factor of the composite is sensitive to stress magnitude. It is illustrated that the "stick-slip" friction is the main contribution for the total loss factor of CNT-based composites even with a small amount of nanotubes/ropes.

Several recent studies have shown that interfacial slip at the nanotube-matrix interfaces in carbon nanotube polymer composites can give rise to significant dissipation of energy causing the material structural damping to increase. This effect can be used to efficiently inject damping into composite and heterogeneous structures. However if the interfacial slip of nanotube additives can be prevented, then significant enhancement in stiffness and strength is possible. To inhibit interfacial slippage of nanotubes we established covalent bonds at the nanotube-matrix interfaces by using an epoxidation procedure. The resultant nano-composites are shown to be resistant to interfacial slip and exhibited a higher storage modulus and a lower loss modulus compared to the baseline composite (without nanotube epoxidation). These results indicate that functionalizing nanotubes to establish direct covalent linkages is an effective way to engineer structural components with enhanced mechanical properties.

This paper analyzes the application of semi-active variable damping TMD (SAVDTMD) with piezoelectric friction dampers as an alternative to existing methods to control floor vibrations, especially walking-induced vibrations. The use of a MDOF floor model in the analysis provides some insight on the effect of modes not targeted in the design of the controller. An optimal semi-active control law originally developed for vehicle suspension control was incorporated into the analytical models. Two floor system examples, typical of those that would have a floor vibration problem, are evaluated and shown to be controlled successfully by the SAVDTMD at both the targeted and untargeted modes. Problems of spillover of the control force to untargeted modes was analyzed and determined to be stabilizing.

Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control or Helmholtz resonator. In this paper, an electrical impedance is connected to the terminals of an acoustic loudspeaker, the mechanical dynamics, and hence acoustic response can be made to emulate a sealed acoustic resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is simply the parallel connection of a capacitor and resistor. Experimental application to a closed acoustic duct results in 14 dB pressure attenuation of a single acoustic mode.

The suppression of vibrations of a structure is commonly considered a necessary measure for the extension of its lifetime, when high amplitude vibrations are observed. As an alternative to the introduction of discrete damping devices, the modification of the stiffness of a beam is proposed as a means to suppress vibrations due to resonance, thank to the ability to reject mechanical energy input at specific frequencies. Previous work has outlined the principle and the potential advantages of such an approach based on the behavior of a small scale system. In order to confirm the feasibility of the approach on macro-scale systems, such as a light weight pedestrian bridge, experiments for the tuning of a 2.5 m long glass fiber reinforced polymer I-beam were performed. The results of the experiments show that it is possible to modify the bending stiffness of structural elements that can be used for real life engineering applications. Measurements show that it is possible to shift the resonance peak of a beam while maintaining a reasonably good q-factor in the transfer function, thus indicating that the change in behavior happens in connection with an increased stiffness rather than with the introduction of substantial damping. Based on the presented feasibility study, the development of an adaptive bridge deck will be considered.

It has pointed out that uplifting response can reduce seismic force of buildings. In this paper, to understand this phenomenon from the point of view of modal analysis, vibration characteristics and dynamic behavior of multiple story buildings allowed to uplift are investigated. Analytical models are simplified 2-dimensional multiple story buildings with vertical springs at the bottom, where uplifting is allowed. Models are assumed to be elastic and have no damping. At first, eigenvalue analysis is carried out to clarify the vibration characteristics, that is, natural period and participation vector. Eigenvalue problem is solved utilizing reduced formula for tridiagonal matrix. Next, dynamic behavior is investigated to clarify the effects of higher modes on responses, distribution of shear force along the height and the amount of energy which can be stored as potential energy of self-weight. Dynamic behavior is initiated by means of just adding a certain level of initial horizontal velocities to the model at rest. The distribution of initial velocities along the height is proportional to the 1st mode shape of fixed base model. Analysis is carried out between the initiation of uplift and landing, that is, half cycle of uplifting behavior. From the results of some examples, it is concluded that higher modes have much effect on story shear force responses and distribution of shear force along the height differs from that of ordinary fixed base model.

To reduce seismic responses of steel building structures, we are now developing the base plate yielding system (BPY system). This system has base plates yielding in the uplift direction at each column base. When the base plates yield, the structure can cause rocking. As some researches have pointed out, rocking effects can reduce seismic damage of buildings under some conditions. In this paper, to improve the seismic performance of the BPY system, conventional or adaptive viscous dampers are attached at each column base besides yielding base plates. Using the adaptive dampers, we can change the damping coefficient according to a sign of vertical velocity at each uplifting part. When a building starts uplifting, and when the sign of vertical velocity is plus, we should set moderate damping coefficient to the damping devices so that they do not restrain a building from uplifting. When the building is landing, and when the sign of the vertical velocity is minus, we can set larger damping coefficient to them so that they can dissipate seismic energy as much as possible. To examine the effect of these additional dampers, numerical tests are carried out. A building structure is replaced by a one-mass system with a footing beam. The height and width of the one-mass system are 30 m and 8 m respectively. The 1995 Kobe NS and an artificial ground motion are used for seismic analyses. It is concluded that the seismic responses of the BPY system can be reduced using the adaptive dampers effectively.