Structural Acoustic Design

1995 ◽  
Author(s):  
Jean Nicolas ◽  
Noureddine Atalla ◽  
Olivier Foin ◽  
Alain Berry
Keyword(s):  
Acoustic Radiation ◽  
Basic Structure ◽  
Wide Frequency Range ◽  
Design Stage ◽  
Constrained Layer Damping ◽  
Damping Force ◽  
Modal Shape ◽  
Acoustic Design ◽  
Aspect Ratios ◽  
Novel Approach

Abstract Nowadays, acoustic quietening of manufactured products is gaining importance. Due to cost, severe weight and operational constraints, classical noise control techniques, although still usable, are becoming less attractive. Nowadays, engineers follow essentially two major approaches (i) reduce noise by passive means, design modifications of structures and systems (ii) reduce noise by active sound and vibration control. This paper is devoted to the structural acoustic design approach for which there are either some simple rules of thumb either huge numerical codes. The main objective of this paper is to bridge the gap between these two extremes. For the vibration response, the approach is based on a variational method. The basic structure is a plate with several degrees of complexity: added local or distributed masses, added local or distributed stiffeners, added stiffeners, added damping and constrained layer damping, force and moment type of excitations. The general trend has been to model an equivalent plate with two objectives in mind: (i) numerical calculations may be performed on a P.C., (ii) results are as close as possible to the exact solution. For the acoustic radiation, a novel approach has been used based on Berry’s idea (Berry, 1994) to develop the Green function in terms of a Taylor expansion. Analytical impedance functions may then be calculated for various aspect ratios and then extracted directly from files which allow considerable atime gains over any other rigorous approaches. The A.D.N.R. (Acoustic Design Noise Reduction) code has been validated through several experimental steps and agreement is revealed to be quite good. Not only is A.D.N.R. precise, but it also covers a wide frequency range (low, medium and high frequencies) which is really an advantage. The output data are diversified and among them we may cite: modal shape, operating deflection shape, quadratic velocity, radiation factor and overall sound power. In practice, A.D.N.R. revealed itself to be a great tool at the pre-design stage, when clear and quick trends are needed.

scholarly journals A Comprehensive Study on the Optimal Design of Magnetorheological Dampers for Improved Damping Capacity and Dynamical Adjustability

Actuators ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 64
Author(s):  
Liankang Wei ◽  
Hongzhan Lv ◽  
Kehang Yang ◽  
Weiguang Ma ◽  
Junzheng Wang ◽  
...  
Keyword(s):  
Optimal Design ◽  
Optimization Methods ◽  
Design Stage ◽  
Damping Capacity ◽  
Damping Force ◽  
Simulation And Optimization ◽  
Damping Characteristics ◽  
Hysteretic Characteristics ◽  
Gap Width ◽  
Comprehensive Study

Purpose: We aim to provide a systematic methodology for the optimal design of MRD for improved damping capacity and dynamical adjustability in performing its damping function. Methods: A modified Bingham model is employed to model and simulate the MRD considering the MR fluid’s compressibility. The parameters that describe the structure of MRD and the property of the fluid are systematically examined for their contributions to the damping capacity and dynamically adjustability. A response surface method is employed to optimize the damping force and dynamically adjustable coefficient for a more practical setting related to the parameters. Results: The simulation system effectively shows the hysteretic characteristics of MRDs and shows our common sense understanding that the damping gap width and yoke diameter have significant effects on the damping characteristics of MRD. By taking a typical MRD device setup, optimal design shows an increase of the damping force by 33% and an increase of the dynamically adjustable coefficient by 17%. It is also shown that the methodology is applicable to other types of MDR devices. Conclusion: The compressibility of MR fluid is one of the main reasons for the hysteretic characteristics of MRD. The proposed simulation and optimization methods can effectively improve the MRD’s damping performance in the design stage.

Mining discriminative patches for script identification in natural scene images

2021 ◽  
Vol 40 (1) ◽  
pp. 551-563
Author(s):  
Liqiong Lu ◽  
Dong Wu ◽  
Ziwei Tang ◽  
Yaohua Yi ◽  
Faliang Huang
Keyword(s):  
Neural Networks ◽  
Experimental Results ◽  
The Other ◽  
Natural Scene ◽  
Fixed Size ◽  
Script Identification ◽  
Aspect Ratios ◽  
Novel Approach ◽  
Public Datasets ◽  
Natural Scene Images

This paper focuses on script identification in natural scene images. Traditional CNNs (Convolution Neural Networks) cannot solve this problem perfectly for two reasons: one is the arbitrary aspect ratios of scene images which bring much difficulty to traditional CNNs with a fixed size image as the input. And the other is that some scripts with minor differences are easily confused because they share a subset of characters with the same shapes. We propose a novel approach combing Score CNN, Attention CNN and patches. Attention CNN is utilized to determine whether a patch is a discriminative patch and calculate the contribution weight of the discriminative patch to script identification of the whole image. Score CNN uses a discriminative patch as input and predict the score of each script type. Firstly patches with the same size are extracted from the scene images. Secondly these patches are used as inputs to Score CNN and Attention CNN to train two patch-level classifiers. Finally, the results of multiple discriminative patches extracted from the same image via the above two classifiers are fused to obtain the script type of this image. Using patches with the same size as inputs to CNN can avoid the problems caused by arbitrary aspect ratios of scene images. The trained classifiers can mine discriminative patches to accurately identify some confusing scripts. The experimental results show the good performance of our approach on four public datasets.

Active Control of Vibration and Noise Radiation from Fluid-Loaded Cylinder using Active Constrained Layer Damping

2002 ◽  
Vol 8 (6) ◽  
pp. 877-902 ◽  
Author(s):  
W. Laplante ◽  
T. Chen ◽  
A. Baz ◽  
W. Sheilds
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Acoustic Radiation ◽  
Sound Radiation ◽  
Element Model ◽  
Water Tank ◽  
Constrained Layer Damping ◽  
Active Constrained Layer Damping ◽  
Active Constrained Layer ◽  
Surrounding Fluid

Vibration and sound radiation from fluid-loaded cylindrical shells are controlled using patches of Active Constrained Layer Damping (ACLD). The performance and the enhanced damping characteristics via reduced vibrations and sound radiation in the surrounding fluid is demonstrated both theoretically and experimentally. A prime motivation for this work is the potential wide applications in submarines and torpedoes where acoustic stealth is critical to the effectiveness of missions. A finite element model is also developed to predict the vibration and the acoustic radiation in the surrounding fluid of the ACLD-treated cylinders. The developed model is used to study the effectiveness of the control and placement strategies of the ACLD in controlling the fluid-structure interactions. A water tank is constructed that incorporates test cylinders treated with two ACLD patches placed for targeting specific vibration modes. Using this arrangement, the effectiveness of different control strategies is studied when the submerged cylinders are subjected to internal excitation, and the radiated sound pressure level in the water is observed. Comparisons are made between the experimental results and the theoretical predictions to validate the finite element model.

scholarly journals Efficient Numerical Full-Polarized Facet-Based Model for EM Scattering from Rough Sea Surface within a Wide Frequency Range

2019 ◽  
Vol 11 (1) ◽  
pp. 75 ◽  
Author(s):  
Jinxing Li ◽  
Min Zhang ◽  
Ye Zhao ◽  
Wangqiang Jiang
Keyword(s):  
Cross Sections ◽  
High Efficiency ◽  
Wide Frequency Range ◽  
Sea Surface ◽  
Doppler Spectrum ◽  
Frequency Range ◽  
Em Scattering ◽  
Wind Speeds ◽  
Novel Approach ◽  
Rough Sea Surface

A full-polarized facet based scattering model (FPFSM) for investigating the electromagnetic (EM) scattering by two-dimensional electrically large sea surfaces with high efficiency at high microwave bands is proposed. For this method, the scattering field over a large sea facet in a diffuse scattering region is numerically deduced according to the Bragg scattering mechanism. In regard to near specular directions, a novel approach is proposed to calculate the scattered field from a sea surface based on the second order small slope approximation (SSA-II), which saves computer memory considerably and is able to analyze the EM scattering by electrically large sea surfaces. The feasibility of this method in evaluating the radar returns from the sea surface is proved by comparing the normalized radar cross sections (NRCS) and the Doppler spectrum with the SSA-II. Then NRCS results in monostatic and bistatic configurations under different polarization states, scattering angles and wind speeds are analyzed as well as the Doppler spectrum at Ka-band. Numerical results show that the FPFSM is a reliable and efficient method to analyze the full-polarized scattering characteristics from electrically large sea surface within a wide frequency range.

The Effect of Aspect Ratio on Wall Pressure Fluctuations at a Wing-Plate Junction

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
M. Awasthi ◽  
J. Rowlands ◽  
D. J. Moreau ◽  
C. J. Doolan
Keyword(s):  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Wide Frequency Range ◽  
Wall Pressure ◽  
Frequency Range ◽  
Three Dimensional Flow ◽  
Wall Pressure Fluctuations ◽  
Aspect Ratios

Abstract Measurements of the wall pressure fluctuations near a wing-plate junction were made for wings with three different aspect ratios (AR) of 0.2, 0.5, and 1.0 at several angles of attack. The chord-based Reynolds number for each wing was 274,000. The results show that the wall pressure fluctuations are a function of wing AR for cases where AR≤ 1.0. For each wing, the pressure fluctuations are highest upstream of the wing leading-edge due to three-dimensional flow separation; wings with AR = 1.0 and 0.5 show comparable levels, while those with AR = 0.2 show lower fluctuation levels over a wide frequency range. Downstream of the leading-edge, the pressure fluctuations decay rapidly on both sides of the wing until the maximum thickness location after which little variation is observed. The pressure fluctuations downstream of the leading-edge on the suction-side were observed to be comparable for AR = 0.2 and 0.5, while those for AR = 1.0 were higher in magnitude. On the pressure-side, the pressure fluctuations near the leading-edge are a weak function of AR; however, those further downstream remain independent of AR. The pressure fluctuations aft of the wing on the suction-side are more coherent for lower ARs and show higher convection velocity, possibly due to an interaction between the tip and the junction flows for lower ARs.

FIV Characteristics of U-Tubes Due to Relocation of the Tube Support Plate

2005 ◽  
Author(s):  
Ki-Wahn Ryu ◽  
Hyung-Jin Kim ◽  
Chi-Yong Park
Keyword(s):  
Aspect Ratio ◽  
Steam Generator ◽  
Mode Shapes ◽  
Design Stage ◽  
Parameter Study ◽  
Stability Ratio ◽  
Integrity Assessment ◽  
Support Plate ◽  
Aspect Ratios ◽  
The Stability

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the PIAT (Program for Integrity Assessment of Steam Generator Tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-vibration bars such as vertical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.

scholarly journals A Terahertz (THz) Single-Polarization-Single-Mode (SPSM) Photonic Crystal Fiber (PCF)

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2442 ◽  
Author(s):  
Tianyu Yang ◽  
Can Ding ◽  
Richard W. Ziolkowski ◽  
Y. Jay Guo
Keyword(s):  
Photonic Crystal ◽  
Photonic Crystal Fiber ◽  
Single Mode ◽  
Propagation Distance ◽  
Wide Frequency Range ◽  
Crystal Fiber ◽  
Novel Approach ◽  
Gain Material ◽  
Single Polarization ◽  
Different Diameters

This paper presents a novel approach to attain a single-polarization-single-mode (SPSM) photonic crystal fiber (PCF) in the terahertz (THz) regime. An initial circular hole PCF design is modified by introducing asymmetry in the first ring of six air holes in the cladding, i.e., epsilon-near-zero (ENZ) material is introduced into only four of those air holes and the other two remain air-filled but have different diameters. The resulting fundamental X-polarized (XP) and Y-polarized (YP) modes have distinctly different electric field distributions. The asymmetry is arranged so that the YP mode has a much larger amount of the field distributed in the ENZ material than the XP mode. Since the ENZ material is very lossy, the YP mode suffers a much higher loss than the XP mode. Consequently, after a short propagation distance, the loss difference (LD) between the XP and YP modes will be large enough that only the XP mode still realistically exists in the PCF. To further enhance the outcome, gain material is introduced into the core area to increase the LDs between the wanted XP mode and any unwanted higher order (HO) modes, as well as to compensate for the XP mode loss without affecting the LD between the XP and YP modes. The optimized PCF exhibits LDs between the desired XP mode and all other modes greater than 8.0 dB/cm across a wide frequency range of 0.312 THz. Consequently, the reported PCF only needs a length of 2.5 cm to attain an SPSM result, with the unwanted modes being more than 20 dB smaller than the wanted mode over the entire operational band.

Dynamic Positioning: Early Design, Capability and Offsets—A Novel Approach

2011 ◽  
Author(s):  
R. van ’t Veer ◽  
M. Gachet
Keyword(s):  
Dynamic Environment ◽  
Low Frequency ◽  
Numerical Approach ◽  
Time Variable ◽  
Design Stage ◽  
Dynamic Positioning ◽  
Novel Approach ◽  
Wave Drift Forces ◽  
Variable Wind ◽  
Drift Forces

Many vessels use a Dynamic Positioning (DP) system that automatically controls vessel position and heading with its own propulsion system. The limiting environment in which a vessel can maintain heading and position under DP operation is typically shown in a capability plot. Capability is usually evaluated assuming constant environmental forces — the static DP approach. In this paper we discuss the methodology of how such a capability assessment can be made early in the vessel design stage. The insights obtained in the heading and position variability over time, and the effects of the environmental forces varying with time can be assessed through model tests and time domain simulations: the dynamic DP approach. This implies that the DP system characteristics are modeled. In a numerical approach, the time variable wind load and low-frequency drift forces are included in the assessment. This paper presents a novel approach on how static DP capability calculations can be corrected to account for the time variable wind and wave drift forces. This leads to a DP capability plot that provides a more realistic insight in the actual DP capability of the vessel in the dynamic environment.

Topology Optimization in Support of Spaceborne Device Based on Variable Density Method

2013 ◽  
Vol 568 ◽  
pp. 109-113
Author(s):  
Bing Hui Wu ◽  
Bao Jun Pang ◽  
Zong Quan Deng
Keyword(s):  
Topology Optimization ◽  
Base Plate ◽  
Basic Structure ◽  
Variable Density ◽  
Design Stage ◽  
Finite Model ◽  
Thin Wall ◽  
Density Method ◽  
Before And After ◽  
Optimization Function

Support is not load bearing components, but also carrier of other component. To reduce the valid load, mass of the support should be low down under the condition of enough stiffness and strength. Topology optimization is employed here to solve the problem. The finite model must be built up according to the basic structure of analysis object in topology optimization. The supports are typical box-style part with thin-wall. Thus, solid model is adopted in ANSYS, and the element shell93 is employed here. Definition of optimization function based on linear-static analysis was employed here. Take maximum flexibility as the constrain conditions of the structure. And the optimality criterion (OC) method was adapted to the problem due to it is suitable for the problem which target is volume. Define the base plate, face and back of the support as the topology area separately. Main part of support is optimization with the variable density method. The results before and after the optimization are compared. When the topology form is unknown, the best topology relation of the structure in the initiate design stage of the whole product has very important meanings.

Sign in / Sign up

Export Citation Format

Share Document