Dynamic modeling of complex structures in a broad frequency range.

2009 ◽  
Vol 125 (4) ◽  
pp. 2693-2693
Author(s):  
Hongan Xu ◽  
Wen L. Li
Keyword(s):  
Dynamic Modeling ◽  
Complex Structures ◽  
Frequency Range ◽  
Broad Frequency Range

Design of a Variable Thickness Plate to Focus Bending Waves

2012 ◽  
Author(s):  
Noah H. Schiller ◽  
Sz-Chin Steven Lin ◽  
Randolph H. Cabell ◽  
Tony Jun Huang
Keyword(s):  
Numerical Simulations ◽  
Thin Plate ◽  
Traveling Waves ◽  
Variable Thickness ◽  
Focal Point ◽  
Frequency Range ◽  
Additional Energy ◽  
Broad Frequency Range ◽  
Bending Waves ◽  
Energy Dissipated

This paper describes the design of a thin plate whose thickness is tailored in order to focus bending waves to a desired location on the plate. Focusing is achieved by smoothly varying the thickness of the plate to create a type of lens, which focuses structure-borne energy. Damping treatment can then be positioned at the focal point to efficiently dissipate energy with a minimum amount of treatment. Numerical simulations of both bounded and unbounded plates show that the design is effective over a broad frequency range, focusing traveling waves to the same region of the plate regardless of frequency. This paper also quantifies the additional energy dissipated by local damping treatment installed on a variable thickness plate relative to a uniform plate.

SIMP for Complex Structures

2016 ◽  
Vol 846 ◽  
pp. 535-540
Author(s):  
David J. Munk ◽  
David W. Boyd ◽  
Gareth A. Vio
Keyword(s):  
Natural Frequencies ◽  
Dynamic Loads ◽  
Topology Optimisation ◽  
Complex Structures ◽  
Structural Failure ◽  
Frequency Range ◽  
Aerodynamic Loading ◽  
Frequency Excitation ◽  
Wing Structure ◽  
Lifting Surfaces

Designing structures with frequency constraints is an important task in aerospace engineering. Aerodynamic loading, gust loading, and engine vibrations all impart dynamic loads upon an airframe. To avoid structural resonance and excessive vibration, the natural frequencies of the structure must be shifted away from the frequency range of any dynamic loads. Care must also be taken to ensure that the modal frequencies of a structure do not coalesce, which can lead to dramatic structural failure. So far in industry, no aircraft lifting surfaces are designed from the ground up with frequency optimisation as the primary goal. This paper will explore computational methods for achieving this task.This paper will present a topology optimisation algorithm employing the Solid Isotropic Microstructure with Penalisation (SIMP) method for the design of an optimal aircraft wing structure for rejection of frequency excitation.

Reduction of Vibrations in Complex Structures With Viscoelastic Neutralizers: A Generalized Approach

1995 ◽  
Author(s):  
J. J. de Espíndola ◽  
C. A. Bavastri
Keyword(s):  
General Procedure ◽  
Linear Optimization ◽  
Sound Radiation ◽  
Complex Structures ◽  
Frequency Range ◽  
Optimization Scheme ◽  
Modal Theory ◽  
Equivalent Quantity ◽  
Invariant Structures ◽  
Time Invariant

Abstract A general procedure for the optimization of the parameters of dynamic neutralizes is presented. It can be applied to the minimization of the vibration response and sound radiation of linear strutures subjected to excitations in a specified frequency range. Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espíndola and Silva (1992), are applied to a non-linear optimization scheme. The proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the struture complexity and the degree of discretization adopted. In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods.

Reduction of Vibrations in Complex Structures With Viscoelastic Neutralizers: A Generalized Approach and a Physical Realization

1997 ◽  
Author(s):  
J. J. de Espíndola ◽  
C. A. Bavastri
Keyword(s):  
General Procedure ◽  
Linear Optimization ◽  
Complex Structures ◽  
Frequency Range ◽  
Optimization Scheme ◽  
Modal Theory ◽  
Equivalent Quantity ◽  
Invariant Structures ◽  
Structure Complexity ◽  
Time Invariant

Abstract A general procedure for the optimization of the parameters of dynamic neutralizers is reviewed. It can be applied to the minimization of the vibration response and sound radiation of linear structures subjected to excitations in a specified frequency range. Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espíndola and Silva (1992), as applied to a non-linear optimization scheme, are also reviewed for clarity. That proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the structure complexity and the degree of discretization adopted. In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods. Experimental results are compared with numerical ones.

scholarly journals An Analysis of the Elements of an all Sky Survey

1985 ◽  
Vol 112 ◽  
pp. 405-410
Author(s):  
Edward T. Olsen ◽  
Anatoly Lokshin ◽  
Samuel Gulkis
Keyword(s):  
Observation Time ◽  
Frequency Resolution ◽  
Frequency Range ◽  
Broad Frequency Range ◽  
Sky Survey ◽  
Microwave Signals ◽  
Celestial Sphere

One component of the NASA search for microwave signals of extraterrestrial intelligent origin will be an all sky survey at a significantly low limiting flux over a broad frequency range. We are currently designing an overall strategy which will permit this survey to be: (1) carried out using existing antennas in less than 3 years of observation time, (2) uniform in sensitivity (within 0.5 db) over the celestial sphere for any given frequency, and (3) complete to 6×10−23 W/m2 or better over the frequency range 1.2GHz⩽ν⩽10GHz with a frequency resolution of 32 Hz.

scholarly journals Pre-selection of the candidate fields for deep imaging of the epoch of reionization with SKA1-low

2020 ◽  
Vol 499 (3) ◽  
pp. 3434-3444
Author(s):  
Qian Zheng ◽  
Xiang-Ping Wu ◽  
Quan Guo ◽  
Melanie Johnston-Hollitt ◽  
Huanyuan Shan ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Low Frequency ◽  
Far Field ◽  
Frequency Range ◽  
High Quality ◽  
Average Surface ◽  
Square Kilometre Array ◽  
Broad Frequency Range ◽  
Deep Imaging ◽  
Selection Of

ABSTRACT The Square Kilometre Array (SKA) will be the first low-frequency instrument with the capability to directly image the structures of the epoch of reionization (EoR). Indeed, deep imaging of the EoR over five targeted fields of 20 sq deg each has been selected as the highest priority science objective for SKA1. Aiming at preparing for this highly challenging observation, we perform an extensive pre-selection of the ‘quietest’ and ‘cleanest’ candidate fields in the southern sky to be suited for deep imaging of the EoR using existing catalogues and observations over a broad frequency range. The candidate fields should meet a number of strict criteria to avoid contaminations from foreground structures and sources. The candidate fields should also exhibit both the lowest average surface brightness and smallest variance to ensure uniformity and high-quality deep imaging over the fields. Our selection eventually yields a sample of 7 ‘ideal’ fields of 20 sq deg in the southern sky that could be targeted for deep imaging of the EoR. Finally, these selected fields are convolved with the synthesized beam of SKA1-low stations to ensure that the effect of sidelobes from the far-field bright sources is also weak.

Determination of dynamic properties of elastomers over broad frequency range

1983 ◽  
Vol 23 (2) ◽  
pp. 158-164 ◽  
Author(s):  
G. M. Smith ◽  
R. L. Bierman ◽  
S. J. Zitek
Keyword(s):  
Dynamic Properties ◽  
Frequency Range ◽  
Broad Frequency Range
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