Identification of a Significantly Non-Proportionally Damped Structure Using Force Appropriation

1995 ◽  
Author(s):  
P. S. Holmes ◽  
J. R. Wright ◽  
J. E. Cooper
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Normal Mode ◽  
Normal Modes ◽  
Dynamic Tests ◽  
High Quality ◽  
Element Analysis ◽  
Standard Curve ◽  
Complex Modes ◽  
Phase Resonance

Abstract Dynamic tests were carried out on an aluminium plate with significant non-proportional damping applied via two oil filled dampers. Normal mode force appropriation (phase resonance) methods were used to measure the undamped normal modes of the plate and the results compared with corresponding complex modes obtained using a standard curve fitting (phase separation) approach. It is demonstrated that, as long as suitable excitation positions are chosen, high quality undamped normal modes can be identified while the curve fitted modes are highly complex. A Finite Element analysis of the plate was used to show how the results of normal mode force appropriation are directly comparable, particularly when damping is non-proportional.

A vector finite-element analysis of complex modes in shielded microstrip lines

1993 ◽  
Vol 6 (16) ◽  
pp. 873-875 ◽  
Author(s):  
Md. Shah Alam ◽  
Koichi Hirayama ◽  
Yoshio Hayashi ◽  
Masanori Koshiba
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Element Analysis ◽  
Microstrip Lines ◽  
Complex Modes ◽  
Vector Finite Element

Complex Modal Analysis of a Nonmodally Damped Continuous Beam

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Xing Xing ◽  
Brian F. Feeny
Keyword(s):  
Finite Element ◽  
Eigenvalue Problem ◽  
Normal Modes ◽  
Damping Coefficient ◽  
Mode Analysis ◽  
Element Analysis ◽  
Assumed Mode Method ◽  
State Variable ◽  
Complex Modes ◽  
Assumed Mode

This work represents an investigation of the complex modes of continuous vibration systems with nonmodal damping. As an example, a cantilevered beam with damping at the free end is studied. Assumed modes are applied to discretize the eigenvalue problem in state-variable form and then to obtain estimates of the true complex normal modes and frequencies. The finite element method (FEM) is also used to get the mass, stiffness, and damping matrices and further to solve a state-variable eigenvalue problem. A comparison between the complex modes and eigenvalues obtained from the assumed-mode analysis and the finite element analysis shows that the methods produce consistent results. The convergence behavior when using different assumed mode functions is investigated. The assumed-mode method is then used to study the effects of the end-damping coefficient on the estimated normal modes and modal damping. Most modes remain underdamped regardless of the end-damping coefficient. There is an optimal end-damping coefficient for vibration decay, which correlates with the maximum modal nonsynchronicity.

Finite Element Analysis on Soft-Pad Grinding of Wire-Sawn Silicon Wafers

2002 ◽  
Author(s):  
X. J. Xin ◽  
Z. J. Pei ◽  
Wenjie Liu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Material Properties ◽  
Silicon Wafers ◽  
Semiconductor Material ◽  
Surface Grinding ◽  
High Quality ◽  
Element Analysis ◽  
Conventional Grinding

Silicon is the primary semiconductor material used to fabricate microchips. The quality of microchips depends directly on the quality of starting silicon wafers. A series of processes are required to manufacture high quality silicon wafers. Surface grinding is one of the processes used to flatten the wire-sawn wafers. A major issue in grinding of wire-sawn wafers is the reduction and elimination of wire-sawing induced waviness. Several approaches (namely, combination of grinding and lapping, reduced chuck vacuum, soft-pad, and wax mounting) have been proposed to address this issue. The results of finite element analysis modeling of these approaches have shown that soft-pad grinding is the most promising approach since it is very effective in reducing the waviness and very easy to be adopted to conventional grinding environment. This paper presents a study of finite element analysis on soft-pad grinding of wire-sawn silicon wafers, covering the mechanisms of waviness reduction and the effects of pad material properties.

scholarly journals Effect of Mesh Density on Finite Element Analysis Simulation of a Support Bracket

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Nicholas S Gukop ◽  
Peter M Kamtu ◽  
Bildad D Lengs ◽  
Alkali Babawuya ◽  
Adesanmi Adegoke
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Computation Time ◽  
Mesh Size ◽  
High Quality ◽  
Element Analysis ◽  
Fine Mesh ◽  
Finite Element Analysis Simulation ◽  
Mesh Analysis ◽  
Mesh Density

Investigation on the effect of mesh density on the analysis of simple support bracket was conducted using Finite element analysis simulation. Multiple analyses were carried out with mesh refinement from coarse mesh of 3.5 mm to a high-quality fine mesh with element size of 0.35 mm under 15 kN loading. Controlled mesh analysis was also conducted for the same loading. At the mesh size of 0.35 mm, it has a maximum stress value of 42.7 MPa. As the element size was reduced, it was observed that below 1.5 mm (higher mesh density) there was no significant increase in the peak stress value; the stress at this level increased by 0.028 % only. Further decreased of mesh size shows insignificant effect on the stresses and displacements for the high-quality fine mesh analysis. The application of High-quality mesh control analysis showed a significant reduction in the computation time by more than 90%. Regardless of the reduction in computation time, the controlled mesh analysis achieved more than 99% accuracy as compared to high-quality fine mesh analysis. Keywords— Computation time, Finite Element Analysis, Mesh density, Support Bracket.

scholarly journals Long, elliptically bent, active X-ray mirrors with slope errors <200 nrad

2017 ◽  
Vol 24 (3) ◽  
pp. 615-621 ◽  
Author(s):  
Ioana T. Nistea ◽  
Simon G. Alcock ◽  
Paw Kristiansen ◽  
Adam Young
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Free Electron Laser ◽  
State Of The Art ◽  
Optical Metrology ◽  
Optical Surface ◽  
High Quality ◽  
Element Analysis ◽  
Bending Performance ◽  
X Ray

Actively bent X-ray mirrors are important components of many synchrotron and X-ray free-electron laser beamlines. A high-quality optical surface and good bending performance are essential to ensure that the X-ray beam is accurately focused. Two elliptically bent X-ray mirror systems from FMB Oxford were characterized in the optical metrology laboratory at Diamond Light Source. A comparison of Diamond-NOM slope profilometry and finite-element analysis is presented to investigate how the 900 mm-long mirrors sag under gravity, and how this deformation can be adequately compensated using a single, spring-loaded compensator. It is shown that two independent mechanical actuators can accurately bend the trapezoidal substrates to a range of elliptical profiles. State-of-the-art residual slope errors of <200 nrad r.m.s. are achieved over the entire elliptical bending range. High levels of bending repeatability (ΔR/R = 0.085% and 0.156% r.m.s. for the two bending directions) and stability over 24 h (ΔR/R = 0.07% r.m.s.) provide reliable beamline performance.

Evaluation of Hexahedral Mesh Quality for Finite Element Method in Electromagnetics

2010 ◽  
Vol 670 ◽  
pp. 318-324 ◽  
Author(s):  
Y. Motooka ◽  
So Noguchi ◽  
H. Igarashi
Keyword(s):  
Finite Element Method ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Computation Time ◽  
Poor Quality ◽  
Mesh Quality ◽  
Hexahedral Mesh ◽  
High Quality ◽  
Element Analysis ◽  
Mesh Generator

We have previously proposed an automatic hexahedral mesh generator. It is necessary to understand about the quality and characteristic of the generated mesh to perform hexahedral edge finite element analysis in electromagnetic. Therefore, we have compared high-quality meshes with poor-quality meshes, and investigated about the factors that affect the accuracy and the computation time. In addition, we investigated about the effect of the templates used in the proposed method. We will conclusively apply the result to improving the automatic hexahedral mesh generator.

Experimental Investigation and Finite Element Analysis of Dynamic Behavior and Damage of Glass/Epoxy Tubular Structures

2011 ◽  
Vol 471-472 ◽  
pp. 951-956
Author(s):  
Mostapha Tarfaoui ◽  
Papa Birame Gning
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Thick Filament ◽  
Tubular Structures ◽  
Dynamic Tests ◽  
Element Analysis ◽  
Damage Prediction ◽  
Damage Initiation ◽  
Filament Wound ◽  
Order Of Magnitude

This paper presents finite element analysis (FEA) of static and dynamic tests of thick filament wound glass/epoxy tubes. The first part involves the validation of elastic properties and identification of damage initiation and its development in dynamic tests. The results of FEA of the dynamic tests without damage appeared satisfactory. An impact model, including material property degradation, is used for damage prediction. The simulated damage is compared with that obtained experimentally. The sizes of projected and cumulated surfaces are of the same order of magnitude as in the experimental measurements.

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