a review of particle damping modeling and testing

Abstract This survey provides an overview of the different approaches seen in the literature concerning particle damping. The emphasis is on particle dampers used on beams vibrating at frequencies between 10 Hz and 1 kHz. Design examples, analytical formulations, numerical models, and experimental setups for such dampers are gathered. Modeling approaches are presented both for particle interaction and for systems equipped with particle dampers. The consequences of the nonlinear behavior of particle dampers are brought to attention. As such, the apparent contradictions of the conclusions and approaches presented in the literature are highlighted. A list of particle simulation software and their use in the literature is provided. Most importantly, a suggested approach to create a sound numerical simulation of a particle damper and the accompanying experimental tests is given. It consists of setting up a discrete element method simulation, calibrating it with literature data and a representative damper experiment, and testing it outside of the range of operation used for the tuning

A review of friction damping modeling and testing

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Weight Prediction of the Lifting System for an Unconventional Aircraft Configuration

In this paper a tool, previously developed and validated for the prediction of wing box structural weight in very early design stages, is improved to better match effects on panel sizing of stability constraints. It is applied to an unconventional configuration aircraft based on the Best Wing System concept, introduced by Ludwig Prandtl in 1924, to achieve minimum induced drag: such lifting system is composed of two swept wings (fore and aft) connected by vertical wings at their tips and two fins connecting the rear wing to the fuselage. The system is over-constrained to the fuselage and, thus, the structural design, as well as the static aeroelasticity and flutter characteristics, totally differs from a conventional aircraft. An optimization method finds out a suitable prediction of the structural weight by defining the wing span stiffness behavior compatible with a mix of global and local design constraints, but without any claim about a structural design. The link among stiffness properties and structural weight is made by means of simplified models of the box cross-sections, suitable also to supply responses for the approximated evaluation of local constraints

Transfer matrix representation for periodic planar media

Sound transmission through infinite planar media characterized by in-plane periodicity is faced by exploiting the free wave propagation on the related unit cells. An appropriate through-thickness transfer matrix, relating a proper set of variables describing the acoustic field at the two external surfaces of the medium, is derived by manipulating the dynamic stiffness matrix related to a finite element model of the unit cell. The adoption of finite element models avoids analytical modeling or the simplification on geometry or materials. The obtained matrix is then used in a transfer matrix method context, making it possible to combine the periodic medium with layers of different nature and to treat both hard-wall and semi-infinite fluid termination conditions. A finite sequence of identical sub-layers through the thickness of the medium can be handled within the transfer matrix method, significantly decreasing the computational burden. Transfer matrices obtained by means of the proposed method are compared with analytical or equivalent models, in terms of sound transmission through barriers of different nature

Analytically Driven Experimental Characterisation of Damping in Viscoelastic Materials

The damping assessment of highly dissipative materials is a challenging task that has been addressed by several researchers; in particular Oberst defined a standard method to address the issue. Experimental tests are often hindered by the poor mechanical properties of most viscoelastic materials; these characteristics make experimental activities using pure viscoelastic specimens prone to nonlinear phenomena. In this paper, a mixed predictive/experimental methodology is developed to determine the frequency behaviour of the complex modulus of such materials. The loss factor of hybrid sandwich specimens, composed of two aluminium layers separated by the damping material, is determined by experimental modal identification. Finite element models and a reversed application of the modal strain energy technique are then used to recover the searched storage modulus and loss factor curves of rubber. In particular, the experimental setup was studied by comparing the solutions adopted with the guidelines given in ASTM-E756-05. An exhaustive validation of the values obtained is then reported

Preliminary Sizing of the Wing-Box Structure by Multi-Level Approach

The paper describes a procedure, dedicated to the preliminary sizing of an aircraft wing-box, based on a two level decomposition and on two independent optimizations. An engineering approach is followed and the most suitable model is exploited at each level in order to generate information about the wing-box structure without the need of a previous knowledge, a very important feature in the case of unconventional structures. The first level uses a commercial structural multidisciplinary optimization code and a stick model of the wing primary structure to minimize the structural mass under global design constraints; a set of physical design variables are used referring to a schematic representation of the cross-section in terms of equivalent axial thickness supporting pure axial stress and the thickness of a box resisting to both axial and shear stresses. The second level, based on a genetic optimization, provides the minimum mass optimal design of the wing cross sections, in terms of local design variables, which safely support the internal loads supplied by the first level, under local constraints, e.g. panel buckling and stiffeners crippling, providing also a cross section stiffness in compliance with the first level. The reported example, concerning the B747-100 wing structure, shows the capability of the approach to predict the structural weight of the wing box, an information to be used mainly in an early stage of the aircraft design, and to suggest a set of cross sections design solutions all in compliance with both global and local requirements