scholarly journals A Four-Parameter Iwan Model for Lap-Type Joints

2005 ◽  
Vol 72 (5) ◽  
pp. 752-760 ◽  
Author(s):  
Daniel J. Segalman
Keyword(s):  
Energy Dissipation ◽  
Structural Dynamics ◽  
Degrees Of Freedom ◽  
Joint Stiffness ◽  
Constitutive Models ◽  
Practical Method ◽  
Dynamics Analysis ◽  
Structural Dynamic ◽  
Length Scales ◽  
Experimental Values

The constitutive behavior of mechanical joints is largely responsible for the energy dissipation and vibration damping in built-up structures. For reasons arising from the dramatically different length scales associated with those dissipative mechanisms and the length scales characteristic of the overall structure, this physics cannot be captured through direct numerical simulation (DNS) of the contact mechanics within a structural dynamics analysis. The difficulties of DNS manifest themselves either in terms of Courant times that are orders of magnitude smaller than that necessary for structural dynamics analysis or as intractable conditioning problems. The only practical method for accommodating the nonlinear nature of joint mechanisms within structural dynamic analysis is through constitutive models employing degrees of freedom natural to the scale of structural dynamics. In this way, development of constitutive models for joint response is a prerequisite for a predictive structural dynamics capability. A four-parameter model, built on a framework developed by Iwan, is used to reproduce the qualitative and quantitative properties of lap-type joints. In the development presented here, the parameters are deduced by matching joint stiffness under low load, the force necessary to initiate macroslip, and experimental values of energy dissipation in harmonic loading. All the necessary experiments can be performed on real hardware or virtually via fine-resolution, nonlinear quasistatic finite elements. The resulting constitutive model can then be used to predict the force/displacement results from arbitrary load histories.

Analysis of the Damping of Beams With Discontinuous Viscoelastic Damping Layer Using Integral Finite Elements

Volume 2 ◽  
2004 ◽  
Author(s):  
T. Liang ◽  
Qian Chen ◽  
S. Olutunde Oyadiji ◽  
Andrew Leung
Keyword(s):  
Finite Elements ◽  
Structural Dynamics ◽  
Degrees Of Freedom ◽  
Dynamic Properties ◽  
Viscoelastic Damping ◽  
Fe Model ◽  
Dynamics Analysis ◽  
Viscoelastic Composite ◽  
Constraint Damping ◽  
Damping Treatments

The damping performance of discontinuous constrained viscoelastic damping layer using Integral Finite Elements (IFE) are investigated in this paper. The IFE involves the dynamic analysis of Elastic-Viscoelastic Composite (EVC) structures with frequency-dependant material properties. EVC structures, which incorporate constrained viscoelastic damping treatment, are modelled using IFE’s and conventional FE’s together to deal with the discontinuous treatment of the constraint damping layers. This approach dramatically reduces the number of degrees of freedom of the FE model compared with conventional FE models. By using specialised algorithms developed for EVC structural dynamics analysis, IFE makes the estimation of the dynamic properties of the EVC structures an easy task similar to the structural dynamics analysis using conventional finite element method. Using an IFE model and the special algorithms, the damping performance of various designs of viscoelastic damping treatments are investigated at extremely low computational costs compared with the use of current commercial FE software packages. A guideline is introduced based on the results of the damping performance analysis for the structural design of viscoelastic damping treatments.

Modular Distributed Models of Structural Dynamics

2004 ◽  
Author(s):  
Drew Reichenbach ◽  
Clark J. Radcliffe ◽  
Jon Sticklen
Keyword(s):  
Structural Dynamics ◽  
Degrees Of Freedom ◽  
Structural Model ◽  
Integrated Design ◽  
Model Systems ◽  
Structural Dynamic ◽  
Distributed Modeling ◽  
Communications Network ◽  
Component Models ◽  
Distributed Assembly

Approaches to engineering design and manufacturing such as integrated design and manufacture and just in time fabrication depend on interaction with and among component supply companies that most often use very diverse technologies. Modular Distributed Modeling (MDM) is a distributed, component-based, agent methodology that is realized following a strong black box approach to modeling. An individual Design Agent (DA) is a virtual product capable of encapsulating both descriptive and model based information about the product it represents. Hierarchically recursive agents for sub-systems and/or components are linked via a communications network to form larger integrated model systems. A two dimensional bridge system structural model is used as an example to illustrate the distributed assembly of structural models from components registered as DA’s on a communications network. Modular Distributed Modeling of system dynamics performs dynamic analysis. This paper presents the methodology required to assemble dynamic structural deflection models provided by internet agents representing structural components. The methodology discussed assembles these component models into the structural dynamic model of an assembly. Using MDM method, models of complex assemblies can be built and distributed while hiding the topology and characteristics of their structural subassemblies. The automated, modular, assembly of structural dynamics models will be derived for discrete, multi-degree-of-freedom structural connections. Discrete connections are important to the assembly of components such as truss and shaft structures where the relationship between component displacements involve discrete, matching, degrees of freedom on components to be assembled. Specific examples of discrete assembly of truss bridge component models will be presented. Specific examples for distributed assembly of component models will be presented. Internet connection permitting, real-time, automated assembly of models and deflection analysis will be performed.

Log-Compound-Poisson Distribution Model of Intermittency in Turbulence

1998 ◽  
Vol 53 (10-11) ◽  
pp. 828-832
Author(s):  
Feng Quing-Zeng
Keyword(s):  
Energy Dissipation ◽  
Poisson Distribution ◽  
Turbulent Energy ◽  
Compound Poisson Distribution ◽  
Distribution Model ◽  
Velocity Difference ◽  
Scaling Exponents ◽  
Compound Poisson ◽  
Developed Turbulence ◽  
Experimental Values

Abstract The log-compound-Poisson distribution for the breakdown coefficients of turbulent energy dissipation is proposed, and the scaling exponents for the velocity difference moments in fully developed turbulence are obtained, which agree well with experimental values up to measurable orders. The under-lying physics of this model is directly related to the burst phenomenon in turbulence, and a detailed discussion is given in the last section.

Stress-Strain Relations and Vibrations of a Granular Medium

1957 ◽  
Vol 24 (4) ◽  
pp. 585-593
Author(s):  
J. Duffy ◽  
R. D. Mindlin
Keyword(s):  
Energy Dissipation ◽  
Contact Forces ◽  
Face Centered Cubic ◽  
Stress Strain ◽  
Differential Stress ◽  
Elastic Bodies ◽  
Strain Relation ◽  
Stress Strain Relation ◽  
Face Centered ◽  
Experimental Values

Abstract A differential stress-strain relation is derived for a medium composed of a face-centered cubic array of elastic spheres in contact. The stress-strain relation is based on the theory of elastic bodies in contact, and includes the effects of both normal and tangential components of contact forces. A description is given of an experiment performed as a test of the contact theories and the differential stress-strain relation derived from them. The experiment consists of a determination of wave velocities and the accompanying rates of energy dissipation in granular bars composed of face-centered cubic arrays of spheres. Experimental results indicate a close agreement between the theoretical and experimental values of wave velocity. However, as in previous experiments with single contacts, the rate of energy dissipation is found to be proportional to the square of the maximum tangential contact force rather than to the cube, as predicted by the theory for small amplitudes.

Structural Dynamics Analysis of “Shenguang-III” Target System

2007 ◽  
pp. 281-281
Author(s):  
Shaorong Yu ◽  
Jun Wang ◽  
Xueqian Chen ◽  
Shifu Xiao ◽  
Bing Xu ◽  
...  
Keyword(s):  
Structural Dynamics ◽  
Target System ◽  
Dynamics Analysis

scholarly journals Full-Span Flying Wing Wind Tunnel Test: A Body Freedom Flutter Study

Fluids ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 34
Author(s):  
Pengtao Shi ◽  
Jihai Liu ◽  
Yingsong Gu ◽  
Zhichun Yang ◽  
Pier Marzocca
Keyword(s):  
Wind Tunnel ◽  
Theoretical Analysis ◽  
Mass Balance ◽  
Degrees Of Freedom ◽  
Wind Tunnel Test ◽  
Suspension System ◽  
The Body ◽  
Structural Dynamic ◽  
Flutter Speed ◽  
Theoretical Results

Aiming at the experimental test of the body freedom flutter for modern high aspect ratio flexible flying wing, this paper conducts a body freedom flutter wind tunnel test on a full-span flying wing flutter model. The research content is summarized as follows: (1) The full-span finite element model and aeroelastic model of an unmanned aerial vehicle for body freedom flutter wind tunnel test are established, and the structural dynamics and flutter characteristics of this vehicle are obtained through theoretical analysis. (2) Based on the preliminary theoretical analysis results, the design and manufacturing of this vehicle are completed, and the structural dynamic characteristics of the vehicle are identified through ground vibration test. Finally, the theoretical analysis model is updated and the corresponding flutter characteristics are obtained. (3) A novel quasi-free flying suspension system capable of releasing pitch, plunge and yaw degrees of freedom is designed and implemented in the wind tunnel flutter test. The influence of the nose mass balance on the flutter results is explored. The study shows that: (1) The test vehicle can exhibit body freedom flutter at low airspeeds, and the obtained flutter speed and damping characteristics are favorable for conducting the body freedom flutter wind tunnel test. (2) The designed suspension system can effectively release the degrees of freedom of pitch, plunge, and yaw. The flutter speed measured in the wind tunnel test is 9.72 m/s, and the flutter frequency is 2.18 Hz, which agree well with the theoretical results (with flutter speed of 9.49 m/s and flutter frequency of 2.03 Hz). (3) With the increasing of the mass balance at the nose, critical speed of body freedom flutter rises up and the flutter frequency gradually decreases, which also agree well with corresponding theoretical results.

Electron Incoherent Scattering from Nanometer-Sized Charge Ordering in Colossal Magnetoresistive La2/3ca1/3mnO3

2001 ◽  
Vol 7 (S2) ◽  
pp. 434-435
Author(s):  
J. M. Zuo
Keyword(s):  
Phase Separation ◽  
Electron Diffraction ◽  
Degrees Of Freedom ◽  
Complex Oxides ◽  
Charge Ordering ◽  
Phase Separations ◽  
Length Scales ◽  
Colossal Magnetoresistive ◽  
Electronic Phase Separation ◽  
Electronic Phase

Electronic phase separation is known to occur in complex oxides ranging from high-Tc superconductors to colossal magnetoresisitive (CMR) manganites. Accumulating experimental evidences show regions of temperature dependent conducting and insulating regions, whose exact origin is unknown. Theoretically, it is has been shown that these systems are unstable from the strong interplay between the lattice, charge and spin degrees of freedom.The key to understand the electronic phase separation in complex oxides is the structure. Electron diffraction is the only probe that covers the length scales from angstroms to microns. Characterization at these length scales is critical (electronic phase separations are typically about nanometers in sizes). Traditionally, electron diffraction has been played important roles in discovering the new types of phase separations, but has contributed little to the quantitative understanding. The reason is the strong interaction of electrons with matter, which gives both strong inelastic background and multiple scattering.

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