skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Static and Dynamic Nonlinear In-plane Effect in the Response of a Cantilevered Plate with Tip Mass Load: Theory and Experiment
In this paper two nonlinear effects are investigated. One is the effect of the static stiffness nonlinearity in changing the linear dynamic natural frequency and the other is the combination of nonlinear stiffness and nonlinear inertia effects in changing the nonlinear dynamic transient response due to a change in the initial release state of the system. A theoretical model has been developed for a cantilevered thin plate with a range of length to width ratio using beam theory and considering both stiffness and inertial nonlinearities in the model. Lagrange’s equation was used to deduce nonlinear inertia and stiffness matrices for a modal representation. Some insights into how these nonlinear components influence the beam response are presented. Measurements with both a hammer test and also a release test of cantilevered thin plates were done using different configurations and tip mass values. Results from static and dynamic analysis using the linear and the nonlinear theoretical model show good agreement between theory and experiment for natural frequencies and the amplitude displacements versus time.  more » « less
Award ID(s):
1907500
PAR ID:
10347597
Author(s) / Creator(s):
Date Published:
Journal Name:
journal of applied mechanics
ISSN:
2423-6705
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    Recent equations of motion for the large deflections of a cantilevered elastic beam are analyzed. In the traditional theory of beam (and plate) large deflections, nonlinear restoring forces are due to the effect of stretching on bending; for an inextensible cantilever, the enforcement of arc-length preservation leads to quasilinear stiffness effects and inertial effects that are both nonlinear and nonlocal. For this model, smooth solutions are constructed via a spectral Galerkin approach. Additional compactness is needed to pass to the limit, and this is obtained through a complex procession of higher energy estimates. Uniqueness is obtained through a non-trivial decomposition of the nonlinearity. The confounding effects of nonlinear inertia are overcome via the addition of structural (Kelvin–Voigt) damping to the equations of motion. Local well-posedness of smooth solutions is shown first in the absence of nonlinear inertial effects, and then shown with these inertial effects present, taking into account structural damping. With damping in force, global-in-time, strong well-posedness result is obtained by achieving exponential decay for small data. 
    more » « less
  2. The dynamic stability of a cantilevered beam actuated by a nonconservative follower force has previously been studied for its interesting dynamical properties and its applications to engineering designs such as thrusters. However, most of the literature considers a linear model. A modest number of papers consider a nonlinear model. Here, a system of nonlinear equations is derived from a new energy approach for an inextensible cantilevered beam with a follower force acting upon it. The equations are solved in time, and the agreement is shown with published results for the critical force including the effects of damping (as determined by a linear model). This model readily allows the determination of both in-plane and out-of-plane deflections as well as the constraint force. With this novel transparency into the system dynamics, the nonlinear postcritical limit cycle oscillations (LCO) are studied including a concentration on the force which enforces the inextensibility constraint. 
    more » « less
  3. This work investigates the steady-state nonlinear dynamics of a large-deformation flexible beam model under oscillatory flow. A flexible beam dynamics model combined with hydrodynamic loading is employed using large deformation beam theory. The equations of motion discretised using the high-order finite element method (FEM) are solved in the time domain using the efficient Galerkin averaging-incremental harmonic balance (EGA-IHB) method. The arc-length continuation method and Hsu’s method trace stable and unstable solutions. The numerical results are in accordance with the physical experimental results and reveal multiple resonance phenomena. Low-order resonances exhibit hardening due to geometric nonlinearity, while higher-order resonances transition from softening to hardening influenced by inertia and geometric nonlinearity. A strong coupling between tensile and bending deformation is observed. The axial deformation is dominated by inertia, while bending resonance is influenced by an interplay between inertia, structure stiffness, and fluid drag. Finally, the effects of two dimensionless parameters, Keulegan and Carpenter number (KC) and Cauchy number (Ca), on the response of the flexible beam are discussed. 
    more » « less
  4. null (Ed.)
    Nonlinear systems leveraging the effects of negative stiffness can exhibit beneficial qualities for passive seismic mitigation in structures. Such systems can be achieved by placing nonlinear devices displaying negative stiffness in parallel with linear positive stiffness systems such as a structure or spring. This thesis presents research into two such systems: (i) a device which causes apparent weakening in a structure subjected to horizontal ground motions and (ii) an isolation system to protect building contents from vertical seismic effects. Apparent weakening is the softening of a structure’s apparent stiffness by adding negative stiffness to the overall system via negative stiffness devices. Apparent weakening is an elastic effect that has the benefit of reducing the peak accelerations and base shears induced in a structure due to a seismic event without reducing the main structural strength. The smooth negative stiffness device (SNSD) presented in this thesis consists of cables, pulleys, and extension springs. A nonlinear mathematical model of the load-deflection behavior of the SNSD was developed and used to determine the optimal geometry for such a device. A prototype device was designed and fabricated for installation in a bench-scale experimental structure, which was characterized through static and dynamic tests. A numerical study was also conducted on two other SNSD configurations designed to achieve different load-deflection relations for use in an inelastic model building subject to a suite of historic and synthetic ground motions. In both the experimental prototype and the numerical study, the SNSDs successfully produced apparent weakening, effectively reducing accelerations and base shears of the structures. The buckled-strut vertical isolation system (BSVIS) presented in this thesis combines the non-linear behavior of a laterally-loaded buckled strut with a linear spring. The lateral load-deflection relation for a buckled strut, which is nonlinear and displays negative stiffness, was investigated for various conditions to two- and three-term approximations of the deflected shape of a strut. This relation and the linear positive effect of a spring were superimposed to give the load-deflection relation of a BSVIS. An experimental prototype was fabricated and subjected to static tests. These tests confirmed the validity of the model and the effectiveness of adding a spring in parallel with a buckled strut to achieve isolation-level stiffness. Based on the theoretical and experimental findings, a design guide is proposed for the engineering of a BSVIS to protect a payload from vertical seismic content. 
    more » « less
  5. A recent large deflection cantilever model is considered. The principal nonlinear effects come through the beam’s  inextensibility —local arc length preservation—rather than traditional extensible effects attributed to fully restricted boundary conditions. Enforcing inextensibility leads to:  nonlinear stiff- ness  terms, which appear as quasilinear and semilinear effects, as well as  nonlinear inertia  effects, appearing as nonlocal terms that make the beam implicit in the acceleration.In this paper we discuss the derivation of the equations of motion via Hamilton’s principle with a Lagrange multiplier to enforce the  effective inextensibility constraint . We then provide the functional framework for weak and strong solutions before presenting novel results on the existence and uniqueness of strong solutions. A distinguishing feature is that the two types of nonlinear terms prevent independent challenges: the quasilinear nature of the stiffness forces higher topologies for solutions, while the nonlocal inertia requires the consideration of Kelvin-Voigt type damping to close estimates. Finally, a modal approach is used to produce mathematically-oriented numerical simulations that provide insight to the features and limitations of the inextensible model. 
    more » « less