Modal Loss Factor Predication in Flexible Mechanism Systems With Constrain Viscoelastic Layers

Dynamic responses of flexible linkage mechanisms with viscoelastic constrained layer damping treatment

The purpose of this study is to develop a design method of a flexible mechanical system using a hydrostatic skeleton driving mechanism. The system consists of two types of flexible bags in order to separate the roles into a structural part and an actuator part. One is a constant pressure bag as a structural part, and the other is a pressure tunable bag as an actuator part. There are remarkable advantages of using this system as listed below: i) Because of the flexibility, the system can be applied safely to various kinds of workspaces where living beings and mechanical systems work together. ii) Because of using two types of bags, driving efficiency of the system is higher than that of other flexible systems using only one type of bag. The theoretical design method of the system is required to realize these advantages. In order to realize the design method, it is important to calculate the structural strength of the structural part and driving force generated by the actuator part. In this paper, strength evaluation of the structural part is performed by nonlinear FEA. From the comparison between the analytical result and measurement results, deflection of the structural part is obtained. On the other hand, the driving force that is generated by the actuator part is also analyzed. Based on the analytical results, an empirical equation about the driving force is induced. The validity of the empirical equation is confirmed by the comparison between measurement values and the values of the empirical equation. These results will contribute to an optimum design of the proposed flexible mechanical system.

This paper presents a flexible mechanical system of the snake-like robot type. Our mechanical system is a hyper-redundant system consisting of 23 rigid solid-type elements (vertebra) actuated by means of 6 flexible wires. The developed constructive solution is intended to be a system with very high flexibility with applicability in various fields of activity in which exploration and operation in small or dangerous spaces is a priority. Also, due to the small size of the components, the geometry of the active surfaces, and the mode of operation, the proposed system can be a solution for medical applications such as Single Port Access (SPA) surgery. The virtual design is made using SOLIDWORKS software. The kinematic and dynamic simulation of the constructive solution is performed with the ADAMS software. The ADAMS-View module allows dynamic analysis on models that contain both rigid and deformable bodies, such as drive wires. Using dynamic simulation, depending on the mode of actuation (sequence and duration) of the elastic wires, the deformed shape as well as the working space of the flexible unit is obtained, which allows us to validate the constructive solution. Using rapid prototyping techniques based on the virtual prototype we will create a flexible mechanical system.

Dynamic recursive decoupling method for closed-loop flexible mechanical systems

Robust observer-based OMF vibration control of flexible linkage mechanisms using piezoelectric films

<abstract> <p>In this paper, in order to provides a powerful new tool for quantitative and qualitative analysis of dynamics properties in flexible mechanical multibody systems, the symmetry theory and numerical algorithms for preserving structure in modern analytical mechanics is introduced into flexible multibody dynamics. First, taking the hub-beam systems as an example, the original nonlinear partial differential-integral equations of the system dynamics model are discretized into the finite-dimensional Lagrange equations by using the assumed modal method. Second, the group analysis theory is introduced and the criterion equations and the corresponding conserved quantities of Noether symmetries are given according to the invariance principle, which provide an effective way for analytic integral theory of dynamic equations. Finally, a conserved quantity-preserving numerical algorithm is constructed by coordinates incremental discrete gradient, which makes full use of the invariance of conserved quantity to eliminate the error consumption for a long time. The simulation results show that the deeper mechanical laws and motion characteristics of flexible mechanical multibody systems dynamics can be obtained with the help of symmetries and conserved quantities, which can provide reference for more precise dynamic optimization design and advanced control of systems.</p> </abstract>

Modeling and vibration control of flexible mechanical systems for DEMO remote maintenance: Results from the FlexARM project

Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of the visco-elastic damping layer according to the plate response. With such active/passive control capabilities the energy dissipation mechanism of the visco-elastic layer is enhanced and its damping characteristics of the plate vibration is improved. A finite element model is developed to analyze the dynamics and control of flat plates which are partially treated with multi-patches of ACLD treatments. The model is validated experimentally using an aluminum plate which is 0.05 cm thick, 25.0 cm long, and 12.5 cm wide. The plate is treated with two ACLD patches. Each of which is made of SOUNDCOAT (Dyad 606) visco- elastic layer sandwiched between two layers of AMP/polyvinylidene fluoride (PVDF) piezo- electric films. The piezo-electric axes of the patches are set at zero degrees relative to the plate longitudinal axis to control the bending mode. The effect of the gain of a proportional control action on the system performance is presented. Comparisons between the theoretical predictions and the experimental results suggest the validity of the developed finite element model. Also, comparisons with the performance of conventional passive constrained layer damping clearly demonstrate the merits of the ACLD as an effective means for suppressing the vibration of flat plates.

<div class="htmlview paragraph">The present study is a continuation of the effort in the application of viscoelastic (VE) damping to large and flexible space systems design. In particular, this work extends the analytical passive damping predictions reported previously. The analytical study completed here relates the number of discrete joint VE dampers, in typical large and flexible space optical systems, to the overall damping of the structure. This data is crucial for the optimal blending of passive damping and active control technologies in space systems design.</div>

A methodology for the identification and robust digital control for very flexible mechanical systems is presented and applied to the control of a 360 degrees flexible robot arm. The importance of the identification in closed loop for improving the performances of the control system is emphasized.

Pavement sections constructed over expansive soil deposits often exhibit excessive distresses due to volume changes in the underlying soil strata. Differential movements within these deposits resulting from fluctuations in the moisture content manifest themselves in the form of localized heaves on the pavement surface. A pavement section near the western border of Idaho has experienced recurrent damage due to volume changes in the underlying expansive soil layer; traditional treatment methods such as lime stabilization and moisture barrier installation have provided partial relief over the years. A recently concluded forensic research study at Boise State University investigated the causes for failure of earlier treatment methods. This study involved extensive laboratory characterization of expansive soil samples collected from underneath this pavement section to identify location of the problematic soil strata, and to propose suitable rehabilitation measures. Laboratory characterization included tests such as moisture content, Atterberg limits and One-Dimensional swell test to determine the potential vertical rise (PVR) and establish approximate active zone. Laboratory test results indicated that the most expansive soil deposits were at a depth of at least 1.83 m from the pavement surface. PVR values calculated closely matched with the surface profile trends observed in the field. In addition, the soluble sulfate tests performed on various soil samples indicated that sulfate heaving could be a problem for calcium-based stabilizer. Based on the findings, the research team proposed that the pavement section be reinforced using a flexible mechanical system that dissipates the swell pressures originating from the underlying clay layers.

It has been understood by architects and engineers that office buildings with easily re-configurable space and flexible mechanical and electrical systems are able to provide comfort that increases worker productivity while using less energy. Raised floors are an example of how fresh air, thermal conditioning, lighting needs, and network access can be delivered in a flexible manner that is not ''embedded'' within the structure. What are not yet documented is how well these systems perform and how much energy they can save. This area is being investigated in phased projects of the 21st Century Research Program of the Air-conditioning and Refrigeration Technology Institute. For the initial project, research teams at the Center for Building Performance and Diagnostics, Pittsburgh, Pennsylvania, and Oak Ridge National Laboratory, Oak Ridge, Tennessee, documented the diversity, performance, and incidence of flexible and adaptive HVAC systems. Information was gathered worldwide from journal and conference articles, case studies, manufactured products and assemblies, and interviews with design professionals. Their report thoroughly describes the variety of system types along with the various design alternatives observed for plenums, diffusers, individual control, and system integration. Many of the systems are illustrated in the report and the authors provide quantitative and qualitative comparisons. Among conclusions regarding key design issues, and barriers to widespread adoption, the authors state that flexible and adaptive HVAC systems, such as underfloor air, perform as well if not better than ceiling-based systems. Leading engineers have become active proponents after their first experience, which is resulting in these flexible and adaptive HVAC systems approaching 10 percent of the new construction market. To encourage adoption of this technology that improves thermal comfort and indoor air quality, follow-on work is required to further document performance. Architects, professional engineers, and commercial real estate developers will benefit from the availability of information that quantifies energy savings, first cost construction differences, and additional operating costs created when office space must be reconfigured to accommodate new tenants.

In vibration analysis of sandwich beam/plates, it is often assumed that there is shear deformation only, without extension or compression in the viscoelastic layer. Certainly, this assumption may have limitations, for example, with increase of the core thickness or frequency range of vibration. The purpose of this paper is to consider the normal, as well as shear strain of the core material for modal parameter estimation of the sandwich plates and to investigate how much error will be caused by neglecting the extension or compression in the core material. Natural frequencies and modal loss factors are estimated for a simply supported square plate by taking the normal as well as shear deformation into account for dynamic modeling. Nondimensional characteristic equations are formulated and solved numerically for various ratios of the base layer thickness to plate length, core layer thickness to base layer, constraining layer thickness to base layer, and shear modulus of core material to elastic modulus of base layer. The effects of the various parameters on the modal properties are shown to be intercorrelated to each other and hence difficult to summarize in one phrase. Normal deformation of the core material plays an important role when the thickness ratio of constraining layer to base layer is 0.5 and its Poisson’s ratio is smaller than 0.49, and hence need to be included in the dynamic modeling especially for estimation of modal damping when one of the following conditions are met; 1) the ratio of base layer thickness to plate length is greater than 0.02, 2) the thickness ratio of core layer to base layer is greater than 0.01, 3) the wavelength of a mode is less than one third of the plate length, 4) the ratio of shear modulus of core material to elastic modulus of base material is less than 10−5.

The optimal design and operation of flexible energy polygeneration systems using coal and biomass to coproduce power, liquid fuels, and chemicals are investigated. This problem is formulated as a multiperiod optimization problem, which is a potentially large‐scale nonconvex mixed‐integer nonlinear program (MINLP) and cannot be solved to global optimality by state‐of‐the‐art global optimization solvers, such as BARON, within a reasonable time. A duality‐based decomposition method, which can exploit the special structure of this problem, is applied. In this work, the decomposition method is enhanced by the introduction of additional dual information for faster convergence. The enhanced decomposition algorithm (EDA) guarantees to find an ε‐optimal solution in a finite time. The case study results show that the EDA achieves much faster convergence than both BARON and the original decomposition algorithm, and it solved the large‐scale nonconvex MINLPs to ε‐optimality in practical times. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3080–3095, 2012

A phenomenological model of active constrained layers