scholarly journals Acoustic and Dynamic Response of Unbaffled Plates of Arbitrary Shape

2021 ◽  
Vol 11 (17) ◽  
pp. 8019
Author(s):  
Pablo García-Fogeda ◽  
Fernando de la Iglesia ◽  
Keyvan Salehi
Keyword(s):  
Arbitrary Shape ◽  
Plane Waves ◽  
Element Model ◽  
Pressure Jump ◽  
Rocket Launch ◽  
Solar Arrays ◽  
Aerospace Structure ◽  
Base Functions ◽  
Generalized Force ◽  
Comparison Of The Results

In this study, a method for determining the effects of fluids on the dynamic characteristics of an aerospace structure and the response of the structure when it is excited by the acoustical loads produced during a rocket launch, has been developed. Elevated acoustical loads are critical in the design of large lightweight structures, such as solar arrays and communication reflectors, because of the high acceleration levels. The acoustic field generated during rocket launch can be considered as a diffuse field composed of many uncorrelated incident plane waves traveling in different directions, which impinge on the structure. A boundary element method was used to calculate the pressure jump produced by an incoming plane wave on an unbaffled plate and the fluid–structure coupled loads generated through plate vibration. This method is based on Kirchhoff’s integral formulation of the Helmholtz equation for pressure fields. The generalized force matrix attributed to the fluid loads was then formulated, taking the modes of the plate in vacuum as base functions of the structural displacement. These modes are obtained using a finite-element model. An iteration procedure was developed to calculate the natural frequencies of the fully coupled fluid–plate system. Comparison of the results obtained using the proposed method with those of other theories and experimental data demonstrated its efficiency and accuracy. The proposed method is suitable for analyzing plates of arbitrary shape subjected to any boundary conditions in a diffuse field for low to medium values of the frequency excitation range.

scholarly journals Numerical investigation of the effects of unsupported railway sleepers on train-induced environmental vibrations

2017 ◽  
Vol 36 (2) ◽  
pp. 160-176 ◽  
Author(s):  
Seyed-Ali Mosayebi ◽  
Morteza Esmaeili ◽  
Jabbar-Ali Zakeri
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Two Dimensions ◽  
Railway Track ◽  
Sensitivity Analyses ◽  
Regression Equations ◽  
The Finite Element Method ◽  
Technical Literature ◽  
Support Force ◽  
Comparison Of The Results

Review of technical literature regarding to train-induced vibrations shows that the effects of unsupported railway sleepers on this issue have been less investigated. So, the present study was devoted to numerical investigations of the mentioned issue. In this regard, first the problem of longitudinal train–track dynamic interaction was simulated in two dimensions by using the finite element method and the developed model was validated through comparison of the results with those obtained by previous researchers. In the next stage, a series of sensitivity analyses were accomplished to account for the effects of value of gap beneath the unsupported sleeper(s) and the track support stiffness on increasing the sleeper displacement and track support force. Moreover, the raised sleeper support force was introduced as applied load to a two-dimensional plane strain finite element model of track in lateral section and consequently the train-induced vibrations were assessed. As a result, a series of regression equations were established between the peak particle velocity in the surrounding environment of railway track and the sleeper support stiffness for tracks without unsupported sleepers and with one and two unsupported sleepers.

A Quasi-Static Model for Studying Physical Interaction Between a Soft Robotic Digit and a Human Finger

2018 ◽  
Author(s):  
Mahdi Haghshenas-Jaryani ◽  
Muthu B. J. Wijesundara
Keyword(s):  
Human Performance ◽  
Theoretical Models ◽  
Element Model ◽  
Human Robot Interaction ◽  
Physical Interaction ◽  
Robotic Hand ◽  
Robot Interaction ◽  
Interaction Forces ◽  
Comparison Of The Results ◽  
Human Finger

This paper presents the development of a framework based on a quasi-statics concept for modeling and analyzing the physical human-robot interaction in soft robotic hand exoskeletons used for rehabilitation and human performance augmentation. This framework provides both forward and inverse quasi-static formulations for the interaction between a soft robotic digit and a human finger which can be used for the calculation of angular motions, interaction forces, actuation torques, and stiffness at human joints. This is achieved by decoupling the dynamics of the soft robotic digit and the human finger with similar interaction forces acting on both sides. The presented theoretical models were validated by a series of numerical simulations based on a finite element model which replicates similar human-robot interaction. The comparison of the results obtained for the angular motion, interaction forces, and the estimated stiffness at the joints indicates the accuracy and effectiveness of the quasi-static models for predicting the human-robot interaction.

Design of geosynthetic reinforcements for platforms subjected to localized sinkholes

2008 ◽  
Vol 45 (2) ◽  
pp. 196-209 ◽  
Author(s):  
Pascal Villard ◽  
Laurent Briançon
Keyword(s):  
Analytical Method ◽  
Design Method ◽  
Element Model ◽  
Full Scale ◽  
Geosynthetic Reinforcement ◽  
New Developments ◽  
Full Scale Experiment ◽  
Current Design ◽  
Scale Experiment ◽  
Comparison Of The Results

Construction of road and railway platforms in areas subject to localized sinkholes requires the use of specific reinforcements, for example, geosynthetics. The current design method for these structures is based on the assumption that there is no displacement of the geosynthetic in the anchorage areas on either side of the cavity. A new analytical method is proposed that takes into account the displacements and deformation of the geosynthetic reinforcement in the anchorage areas and the increase in stress at the edge of the cavity. To validate this new analytical method, a full-scale experiment was carried out; the use of optical fibre sensors integrated into the geosynthetic sheet made it possible to accurately measure the strain of the geosynthetic reinforcement. Comparison of the results obtained by this new analytical method with measurements of a full-scale experiment and the results of a finite element model confirmed the relevance of these new developments.

FINITE‐ELEMENT COMPUTATION OF SEISMIC ANOMALIES FOR BODIES OF ARBITRARY SHAPE

Geophysics ◽  
1976 ◽  
Vol 41 (1) ◽  
pp. 145-150 ◽  
Author(s):  
Bruce A. Bolt ◽  
Warwick D. Smith
Keyword(s):  
Finite Element ◽  
Arbitrary Shape ◽  
Plane Waves ◽  
Surface Profile ◽  
Massive Sulfide ◽  
Spectral Ratios ◽  
Element Analysis ◽  
S Waves ◽  
Ore Bodies ◽  
Upward Moving

A method which uses observed frequency spectral ratios of seismic plane waves for exploration of ore bodies is now available. The new method is based on the numerical solution of the response of a two‐dimensional shallow structural anomaly to an upward‐moving seismic wave from a distant earthquake or explosion. Finite‐element analysis is used for both P- and S-waves. Solutions to the direct problem for bodies of arbitrary shape have not previously been available. Results in the time and frequency domains are discussed here for a salt ridge and for a massive sulfide body. For the inverse problem, interpretation using contours of spectral ratios along a surface profile is suggested.

Effect of Reeling on Pipeline Structural Performance

2016 ◽  
Author(s):  
Yafei Liu ◽  
Stelios Kyriakides
Keyword(s):  
Kinematic Hardening ◽  
Element Model ◽  
External Pressure ◽  
Structural Performance ◽  
Loading History ◽  
Cross Sectional ◽  
Collapse Pressure ◽  
Comparison Of The Results ◽  
Tension Loading ◽  
D Model

The winding and unwinding of a pipeline in the reeling installation process involves repeated excursions into the plastic range of the material, which induce ovality and changes to the mechanical properties. We present two modeling schemes for simulating reeling/unreeling capable of capturing these changes and can be used to assess their impact on the structural performance of the pipeline in deeper waters. In the first model, the complete 3-D reeling process is simulated through a finite element model that includes proper treatment of contact and nonlinear kinematic hardening for plasticity. The second model includes the pipe geometric cross sectional nonlinearities, contact, and nonlinear kinematic hardening, but variations along the length of the line are neglected. Instead, an axially uniform curvature/tension loading history is applied that corresponds to that experienced by a point of the line during the process. The two models are used to simulate a set of experiments in which tubes were wound and unwound on a model reel at different values of tension. Both models are shown to reproduce the induced ovality and elongation very well. Several of the reeled tubes were subsequently tested under external pressure demonstrating the effect of the reeling cycle on structural performance. The two models are shown to also reproduce the decrease in collapse pressure as a function of the applied back tension. Comparison of the results of such simulations highlight when a fully 3-D model is required and when the simpler 2-D model is adequate for evaluating the structural performance of a reeled pipe.

Solar Array Mounting Effects on Flutter Characteristics of Solar-Powered UAV

2014 ◽  
Vol 940 ◽  
pp. 410-414
Author(s):  
Wei Wang ◽  
Zhou Zhou ◽  
Xiao Ping Zhu
Keyword(s):  
Element Model ◽  
Solar Array ◽  
Structural Flexibility ◽  
Lattice Method ◽  
Flutter Speed ◽  
Solar Arrays ◽  
Aerodynamic Model ◽  
Structural Surface ◽  
Doublet Lattice Method ◽  
Solar Powered

Solar powered UAV has the characteristics of high aspect ratio, low structural surface density, high structural flexibility and low flutter speed. Different solar array mountings will affect the flutter characteristics of the structure. The mechanical properties of solar arrays packaged and unpackaged are measured in this paper and the solar powered UAV structural finite element model based on Patran/Nastran was also established in the paper. Two solar array mounting ways are researched: embedded solar arrays and patching solar arrays. To investigate the flutter characteristics under the two solar array mounting ways, the Doublet lattice method (DLM) aerodynamic model is used to model the unsteady aerodynamic loads. Finally, flutter speed of the structure was determined by using the P-K method and the analysis result indicate that patching solar arrays is more conductive to improve the flutter characteristics of the structure.

Nonlinear Dynamics Characteristic of Rotor-Bearing System by a Finite Element Model

2009 ◽  
Author(s):  
Chaofeng Li ◽  
Zhaohui Ren ◽  
Xiaopeng Li ◽  
Bangchun Wen
Keyword(s):  
Nonlinear Dynamic ◽  
Discrete Model ◽  
Element Model ◽  
Dynamic Responses ◽  
Runge Kutta Method ◽  
Significant Difference ◽  
Rotor Bearing ◽  
Comparison Of The Results ◽  
Bearing System ◽  
The Continuum

The nonlinear dynamic behavior of a rotor-bearing system is analyzed with its continuum model based on the analysis of the discrete model, with considering some other important influencing factors besides the nonlinear factors of the bearing, such as, the effect of inertia distribution and shear, transverse-torsion, structural geometric parameters of the system, which make the description of the system more embodiment and avoid the casualness of selection of system parameters. The dynamic responses of the continuum system and discrete system in the same unbalance condition are approached by the Runge-Kutta method and Newmark-β method. With the comparison of the results, significant difference about the dynamic characteristics is found with the addition of the considered factors. It is suggested that the substitution of discrete model by the continuum ones can get more accurate and abundant results. Furthermore, these results can provide more accurate verification and reference for the experiment and nonlinear dynamic design of the more complicated rotor system.

Using Plane Waves as Base Functions for Solving Time Harmonic Equations with the Ultra Weak Variational Formulation

2003 ◽  
Vol 11 (02) ◽  
pp. 227-238 ◽  
Author(s):  
Olivier Cessenat ◽  
Bruno Després
Keyword(s):  
Domain Decomposition ◽  
Variational Formulation ◽  
Degrees Of Freedom ◽  
Wave Equations ◽  
Plane Waves ◽  
Interface Problem ◽  
Weak Formulation ◽  
Time Harmonic ◽  
Base Functions ◽  
New Formulation

This article deals with the use of the Ultra Weak Variational Formulation to solve Helmholtz equation and time harmonic Maxwell equations. The method, issued from domain decomposition techniques, lies in partitioning the domain into subdomains with the use of adapted interface conditions. Going further than in domain decomposition, we make so that the problem degenerates into an interface problem only. The new formulation is equivalent to the weak formulation. The discretization process is a Galerkin one. A possible advantage of the UWVF applied to wave equations is that we use the physical approach that consists in approximating the solution with plane waves. The formulation allows to use a very large mesh as compared to the frequency, on the contrary to the Finite Element Method when applied to time harmonic equations. Furthermore, the convergence analysis shows the method is a high order one: the order evolves as the square root of the number of degrees of freedom.

Semianalytical Method for the SIF Calculation for a Crack of Arbitrary Shape in Infinite Body

2014 ◽  
Author(s):  
Anatolii Batura ◽  
Igor Orynyak ◽  
Andrii Oryniak
Keyword(s):  
Arbitrary Shape ◽  
Shape Function ◽  
Crack Problem ◽  
Elliptic Crack ◽  
Infinite Body ◽  
Analytical Technique ◽  
Base Functions ◽  
Semianalytical Method ◽  
Crack Faces ◽  
Flat Crack

The exact analytical approach for stress intensity factor calculation for an arbitrary shape mode I crack loaded by the polynomial stresses is proposed. The approach is based on the calculation of the crack faces displacement at given loading. The displacement field is presented as a shape function multiplied by an adjustment polynomial. At that the key problem is the solution of well-known inverse task: obtaining the stresses field at the crack faces on the base of a given displacements field. Multiply solution of such task for a whole set of certain displacements base functions (e.g., for the single terms of the adjustment polynomial) allows to get analytical expression which connects stresses and displacements fields. The original semi-analytical technique for integration with subsequent differentiation of well-known singular integral equation of the flat crack problem is developed. The excellent accuracy of the method is confirmed for an elliptic crack as well as for a rectangular one in the infinite 3D body. New results are given for an inner semi-elliptic crack in the infinite body which surfaces are loaded by polynomial stresses up to the 6th order. The importance of choosing the appropriate shape function is demonstrated.

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