Shock and Vibration - Volume 18, issue 4

Authors: Guo, Yanfeng | Xu, Wencai | Fu, Yungang | Wang, Hongtao

Article Type: Research Article

Abstract: X-PLY corrugated paperboard is a new-type corrugated paperboard with three layers of orthotropic corrugated sandwiches structure, and may be employed to protect products from shock or vibration damage during distribution. This article deals with the characterization of properties of X-PLY corrugated paperboard relevant to its application for protective packaging in distribution, such as dynamic cushioning curves, vibration transmissibility and frequency curves. The main feature of article is the evaluation on the dynamic …shock cushioning characteristics and vibration transmissibility of X-PLY corrugated paperboards by a series of experimental studies on the drop shock tester and vibration tester, the establishment of experimental formulas of dynamic cushioning curves, and the analysis of peak frequencies, vibration transmissibility and damping ratios. By using the fitting polynomial of curve and method of the least mean square, the experimental formulas and characteristic coefficients of dynamic cushioning curves have been obtained. From the vibration tests with slow sine sweep, the peak frequencies and vibration transmissibility are measured and used to estimate the damping ratios. These works provide basic data and curves relevant to its application for protective packaging in distribution. Show more

Keywords: X-PLY corrugated paperboard, dynamic shock cushioning characteristics, vibration transmissibility

DOI: 10.3233/SAV-2010-0559

Citation: Shock and Vibration, vol. 18, no. 4, pp. 525-535, 2011

Authors: Giunta, G. | Carrera, E. | Belouettar, S.

Article Type: Research Article

Abstract: The free vibration analysis of composite thin and relatively thick plates accounting for uncertainty is addressed in this work. Classical and refined two-dimensional models derived via Carrera's Unified Formulation (CUF) are considered. Material properties and geometrical parameters are supposed to be random. The fundamental frequency related to the first bending eigenmode is stochastically described in terms of the mean value, the standard deviation, the related confidence intervals and the cumulative distribution function. The …Monte Carlo Method is employed to account for uncertainty. Cross-ply, simply supported, orthotropic plates are accounted for. Symmetric and anti-symmetric lay-ups are investigated. Displacements based and mixed two-dimensional theories are adopted. Equivalent single layer and layer wise approaches are considered. A Navier type solution is assumed. The conducted analyses have shown that for the considered cases, the fundamental natural frequency is not very sensitive to the uncertainty in the material parameters, while uncertainty in the geometrical parameters should be accounted for. In the case of thin plates, all the considered models yield statistically matching results. For relatively thick plates, the difference in the mean value of the natural frequency is due to the different number of degrees of freedom in the model. Show more

Keywords: Free vibration, uncertainty, Monte Carlo Method, refined two-dimensional models, composite plates

DOI: 10.3233/SAV-2010-0560

Citation: Shock and Vibration, vol. 18, no. 4, pp. 537-554, 2011

Authors: Yardimoglu, Bulent | Aydin, Levent

Article Type: Research Article

Abstract: Longitudinal natural vibration frequencies of rods (or bars) with variable cross-sections are obtained from the exact solutions of differential equation of motion based on transformation method. For the rods having cross-section variations as power of the sinusoidal functions of ax+b, the differential equation is reduced to associated Legendre equation by using the appropriate transformations. Frequency equations of rods with certain cross-section area variations are found from the general solution of this equation …for different boundary conditions. The present solutions are benchmarked by the solutions available in the literature for the special case of present cross-sectional variations. Moreover, the effects of cross-sectional area variations of rods on natural characteristics are studied with numerical examples. Show more

Keywords: Exact solution, longitudinal vibration, variable cross-section

DOI: 10.3233/SAV-2010-0561

Citation: Shock and Vibration, vol. 18, no. 4, pp. 555-562, 2011

Authors: Živanović, Stana | Pavić, Aleksandar

Article Type: Research Article

Abstract: Due to their slenderness, many modern footbridges may vibrate significantly under pedestrian traffic. Consequently, the vibration serviceability of these structures under human-induced dynamic loading is becoming their governing design criterion. Many current vibration serviceability design guidelines, concerned with prediction of the vibration in the vertical direction, estimate a single response level that corresponds to an "average" person crossing the bridge with the step frequency that matches a footbridge natural frequency. However, different …pedestrians have different dynamic excitation potential, and therefore could generate significantly different vibration response of the bridge structure. This paper aims to quantify this potential by estimating the range of structural vibrations (in the vertical direction) that could be induced by different individuals and the probability of occurrence of any particular vibration level. This is done by introducing the inter- and intra-subject variability in the walking force modelling. The former term refers to inability of a pedestrian to induce an exactly the same force with each step while the latter refers to different forces (in terms of their magnitude, frequency and crossing speed) induced by different people. Both types of variability are modelled using the appropriate probability density functions. The probability distributions were then implemented into a framework procedure for vibration response prediction under a single person excitation. Instead of a single response value obtained using currently available design guidelines, this new framework yields a range of possible acceleration responses induced by different people and a distribution function for these responses. The acceleration ranges estimated are then compared with experimental data from two real-life footbridges. The substantial differences in the dynamic response induced by different people are obtained in both the numerical and the experimental results presented. These results therefore confirm huge variability in different people's dynamic potential to excite the structure. The proposed approach for quantifying this variability could be used as a sound basis for development of new probability-based vibration serviceability assessment procedures for pedestrian bridges. Show more

Keywords: Footbridge, vibration serviceability, probabilistic model, walking, dynamic excitation potential, variability

DOI: 10.3233/SAV-2010-0562

Citation: Shock and Vibration, vol. 18, no. 4, pp. 563-577, 2011

Authors: Rodriguez-Nikl, T. | Hegemier, G.A. | Seible, F.

Article Type: Research Article

Abstract: The blast simulator at the University of California, San Diego is a unique tool for conducting full-scale testing of blast effects on structures without the use of explosive materials. This blast simulator uses high speed hydraulic actuators to launch specially designed modules toward the specimen, thereby imparting impulse in a blast-like manner. This method of testing offers numerous advantages over field tests with actual explosives, including cost, turn-around time, repeatability, and a clear view of the …progression of damage in the specimen. The viability of this method is established by comparing results obtained in the blast simulator with results obtained with actual explosives. The process by which the impulse is imparted to the specimen is then described by a detailed model based on the equivalent single degree of freedom method. Impulse calculated by the model is found to be in good agreement with the experimentally recorded values. Calculated impulse is found to be relatively insensitive to assumptions made about the specimen's resistance function (often not well known before a test) implying that the model can be used with confidence in designing an experimental study. Show more

Keywords: Blast simulator, blast hardening, blast mitigation, infrastructure protection, single degree of freedom method

DOI: 10.3233/SAV-2010-0563

Citation: Shock and Vibration, vol. 18, no. 4, pp. 579-592, 2011

Authors: Pennacchi, Paolo | Vania, Andrea

Article Type: Research Article

Abstract: Instability phenomena in steam turbines may happen as a consequence of certain characteristics of the steam flow as well as of the mechanical and geometrical properties of the seals. This phenomenon can be modeled and the raise of the steam flow and pressure causes the increase of the cross coupled coefficients used to model the seal stiffness. As a consequence, the eigenvalues and eigenmodes of the mathematical model of the machine change. The real part of …the eigenvalue associated with the first flexural normal mode of the turbine shaft may become positive causing the conditions for unstable vibrations. The original contribution of the paper is the application of a model-based analysis of the dynamic behavior of a large power unit, affected by steam-whirl instability phenomena. The model proposed by the authors allows studying successfully the experimental case. The threshold level of the steam flow that causes instability conditions is analyzed and used to define the stability margin of the power unit. Show more

Keywords: Rotordynamics, steam-whirl, steam-whip, instability, model based analysis

DOI: 10.3233/SAV-2010-0575

Citation: Shock and Vibration, vol. 18, no. 4, pp. 593-612, 2011

Authors: Mahfoud, Jarir | Skladanek, Yan | Der Hagopian, Johan

Article Type: Research Article

Abstract: The performances for controlling a rotating machine by using either an Electromagnetic Actuator or a Piezoelectric Actuator are compared in this work. The aim is to establish selection criteria based on environmental impact. Life Cycle Analysis shows that the operating stage has a considerable impact. In this study, only the operating stage is considered. The energy consumed by the actuators seems to be the appropriate indicator for the same "mechanical" performances. Numerical studies are carried out …in order to quantify the energy consumed in each case. Modal control strategy with a fuzzy controller is used. The controller inputs are displacements and velocities. The system studied is modeled by using finite element method and the electrical circuit of each actuator is modeled by using basic electricity and electromagnetism theories. Several configurations are assessed and defined by using the chosen Functional Unit. The results obtained show that both controllers are efficient and enable recommendations for optimal control procedures design for the energy consumed. Show more

Keywords: Control, rotordynamics, life cycle analysis, energy consumption

DOI: 10.3233/SAV-2010-0576

Citation: Shock and Vibration, vol. 18, no. 4, pp. 613-625, 2011

Authors: Bashmal, S. | Bhat, R. | Rakheja, S.

Article Type: Research Article

Abstract: In-plane free vibrations of an elastic and isotropic annular disk with elastic constraints at the inner and outer boundaries, which are applied either along the entire periphery of the disk or at a point are investigated. The boundary characteristic orthogonal polynomials are employed in the Rayleigh-Ritz method to obtain the frequency parameters and the associated mode shapes. Boundary characteristic orthogonal polynomials are generated for the free boundary conditions of the disk while artificial springs are used …to account for different boundary conditions. The frequency parameters for different boundary conditions of the outer edge are evaluated and compared with those available in the published studies and computed from a finite element model. The computed mode shapes are presented for a disk clamped at the inner edge and point supported at the outer edge to illustrate the free in-plane vibration behavior of the disk. Results show that addition of point clamped support causes some of the higher modes to split into two different frequencies with different mode shapes. Show more

Keywords: Rayleigh-Ritz method, in-plane free vibration, natural frequencies, boundary characteristic orthogonal polynomials

DOI: 10.3233/SAV-2010-0578

Citation: Shock and Vibration, vol. 18, no. 4, pp. 627-640, 2011