Location effects on bend-twist coupling modes characteristic of the laminate plates

In this paper, the effects of coupling location on the properties of bending-twist modes are proposed. The static test and modal analysis of the composite plates are investigated. Initial coupling effects are first obtained from the static test of the plates. The frequencies, nodal lines, and the mode shapes are then studied experimentally and numerically. A new method is proposed to quantitatively describe the bending-twist coupling performance of laminates using modal assurance criterion. The results show that the coupling location in the middle coupled plates show good coupling effects at lower order vibrations. These results also show that the effect of coupling stiffness. The conclusions can be considered as a reference to analyze the coupling phenomenon of large composite wind turbine blades.

Frequency Response Evaluation of Guitar Bodies with Different Bracing Systems

Wood is a natural composite, having a porous structure, with a complex elastic symmetry specific to orthotropic solid, influenced by three mutually perpendicular planes of elastic symmetry. The classical guitar is obtained from different wooden species, each of them having their own elastic properties and, as a whole, forming a lignocellulosic composite structure. Generally, some constructive parts of the classical guitar body are based on symmetry, starting from the structural features of wooden plates, which are symmetrically cut, and some patterns of the stiffening bars. The other elements, such as the strings system, are not symmetric. This study aims to evaluate the frequency responses of the guitar body as a symmetrical mechanical system from constructive points of view. Because theoretical results (analytic and numeric) regarding the symmetrical systems cannot be applied to quasi-symmetric systems, the dynamic response was analyzed from experiments performed on four types of classical guitar body (without neck), different from each other by the pattern of stiffening bars placed inside of the top plate. The experiments were performed using a Brüel&Kjær mini-shaker to excite the structure, and the signal was captured with accelerometers. The symmetric behavior of coupled plates from the guitar body was noticed in the case of an applied dynamic force of 110 Hz and 440 Hz, but in the case of 146 Hz, 588 Hz, 720 Hz, quasi skew symmetrical modes were recorded.

Free Vibration Analysis of Moderately Thick Coupled Plates with Elastic Boundary Conditions and Point Supports

Plates are applied to a wide array of structural applications of varying complexity. Each application requires rigorous analysis to determine the viability of the proposed model. One such application involves modeling a larger structure as a collection of smaller flat plates connected at the plate boundaries. Previous research into these types of structures has led to varying levels of accuracy. It has been dependent on the applications and assumptions involved. To improve the accuracy of these types of structures in a more general context, we propose expanding on current models of coupled plates by modeling the plates using Mindlin plate theory. We analyze the vibration of the improved model with general elastic boundary conditions, point supports and coupling conditions using the Fourier series method and finite element software. When the Fourier series method is applied directly, continuity issues arise at the plate coupling boundaries. To resolve these issues, the Fourier series solution of the vibration displacements is amended to include auxiliary functions. This improved coupled plate model is analyzed and numerically simulated for a variety of elastic boundary conditions and coupling conditions. The numerical results are produced using the Fourier series method and a finite element solution to demonstrate the validity of the improved coupled plate model.

Vibration Analysis and Energy Transmission of Finite Coupled Mindlin Plates

Power flow analysis of finite coupled Mindlin plates and energy transmission through the structure are investigated by employing the method of reverberation-ray matrix (MRRM). The rectangular Mindlin plates are connected at an arbitrary angle. Both in-plane and out-of-plane waves propagation solutions are considered by establishing the dual local coordinates in each plate. The boundary conditions at the plate edges, continuous conditions at the driving force locations, and coupling conditions at the line junction between several rectangular plates are established and solved simultaneously. Then the flexural and in-plane vibrations of the finite coupled Mindlin plate are obtained by using the MRRM, which are verified by comparing the results obtained with those by the finite element method (FEM). The vibration behaviors of coupled plates such as L-shaped structure, T-shaped structure and box-shaped structure are calculated and verified.

Coupling strength assumption in statistical energy analysis

This paper is a discussion of the hypothesis of weak coupling in statistical energy analysis (SEA). The examples of coupled oscillators and statistical ensembles of coupled plates excited by broadband random forces are discussed. In each case, a reference calculation is compared with the SEA calculation. First, it is shown that the main SEA relation, the coupling power proportionality, is always valid for two oscillators irrespective of the coupling strength. But the case of three subsystems, consisting of oscillators or ensembles of plates, indicates that the coupling power proportionality fails when the coupling is strong. Strong coupling leads to non-zero indirect coupling loss factors and, sometimes, even to a reversal of the energy flow direction from low to high vibrational temperature.