scholarly journals Acoustics of the banjo: theoretical and numerical modelling

Acta Acustica ◽  
2021 ◽  
Vol 5 ◽  
pp. 16
Author(s):  
Jim Woodhouse ◽  
David Politzer ◽  
Hossein Mansour
Keyword(s):  
Numerical Modelling ◽  
Critical Frequency ◽  
Sound Radiation ◽  
Dynamical Behaviour ◽  
The Other ◽  
Amplitude Envelope ◽  
Distinctive Pattern ◽  
Local Effects ◽  
Modal Density ◽  
Strong Contrast

A previous paper [Woodhouse et al., Acta Acustica 5, 15 (2021) https://doi.org/10.1051/aacus/2021009] showed acoustical measurements of an American 5-string banjo alongside similar measurements on a guitar, revealing a strong contrast in bridge admittance. Theoretical and numerical modelling is now presented to probe the physics behind this contrast. Without the bridge and strings, the banjo membrane has a rising trend of admittance associated with its modal density, and it has a distinctive pattern of sound radiation because an ideal membrane has no critical frequency. When the bridge and strings are added to the banjo, three formants shape the amplitude envelope of the admittance. One is associated with local effects of mass and stiffness near the bridge, and is sensitive to bridge mass and the break angle of the strings over the bridge. The other two formants are associated with dynamical behaviour of the bridge, analogous to the “bridge hill” in the violin.

Influence of Internal Structures of High Modal Density on Shell’s Radiation

1997 ◽  
Author(s):  
Lionel Oddo ◽  
Bernard Laulagnet ◽  
Jean-louis Guyader
Keyword(s):  
Cylindrical Shell ◽  
Sound Radiation ◽  
Numerical Results ◽  
Structural Damping ◽  
Radiation Spectra ◽  
Modal Density ◽  
Internal Structures ◽  
High Modal Density

Abstract The aim of this paper is to study the sound radiation by a cylindrical shell internally coupled with mechanical structures of high modal density. The model is based on a mobility technique. The numerical results show a smoothing of the cylinder’s velocity and radiation spectra associated with an increase of the apparent damping. The use of the S.E.A. method allows us to calculate an additional structural damping of the shell, equivalent to the effect of the internal structures.

A Numerical Approach for Simulation of Rock Fracturing in Engineering Blasting

2012 ◽  
pp. 203-224
Author(s):  
Mani Ram Saharan ◽  
Hani Mitri
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Numerical Modelling ◽  
Knowledge Base ◽  
Plane Stress ◽  
Numerical Approach ◽  
The Other ◽  
Brittle Rock ◽  
Rock Fracturing ◽  
Element Elimination

An approach for simulation of rock fracturing as a result of engineering blasting is presented in this paper. The approach uses element elimination technique within the framework of finite element method to capture the physics of engineering blasting. The approach does not require pre-placement of fracture paths which is the severe drawback of the other existing methodologies and approaches. Results of plane stress modelling for isotropic brittle rock behaviour are presented in this paper and these results are in good agreement with the existing knowledge base. The authors also review the existing approaches of numerical modelling to compare the efficacy of the element elimination technique. It is anticipated that the further developments with this approach can prove to be good experimental tool to improve engineering blasting operations.

scholarly journals µ-Synthesis Control of Flexible Modes of AMB Rotor

2009 ◽  
Author(s):  
Arkadiusz Mystkowski
Keyword(s):  
Critical Frequency ◽  
Closed Loop ◽  
Dynamical Behaviour ◽  
Mode Analysis ◽  
Effective Control ◽  
Stable Operation ◽  
Value Analysis ◽  
Wide Range ◽  
Speed Up ◽  
Problem Stability

In the paper the optimal robust vibrations control of flexible rotor supported in active magnetic bearings (AMBs) is presented. The purpose of the research is to stabilize the rotate rotor and effective control of rotor vibrations. The noncollocation effect which produce no interlaced of zeros and poles of AMBs system problem stability is investigated. The frequency mode analysis of collocation and noncollocation cases is presented. The μ-Synthesis Control is applied to stabilize the rigid and flexible critical frequency modes of the rotor AMBs. The singular value analysis is used to obtain the robust performances of closed-loop system. The dynamical behaviour of AMBs system in wide range of rotation speed (up 21000 rpm) is investigated. The goal of this paper is also the experimental evaluation of the robust performance. The stable operation, good stiffness of the rotor and robust performances of the closed-loop AMBs systems is reached. Finally, the success of the robust control is demonstrated through results of computer simulations and experimental results.

Patterns in the Timing of Corporate Event Waves

2010 ◽  
Vol 46 (1) ◽  
pp. 209-246 ◽  
Author(s):  
P. Raghavendra Rau ◽  
Aris Stouraitis
Keyword(s):  
Initial Public Offering ◽  
The Other ◽  
Stock Repurchases ◽  
Distinctive Pattern ◽  
Seasoned Equity Offering ◽  
Data Set ◽  
Equity Issues ◽  
Comprehensive Data ◽  
Different Types ◽  
Public Offering

AbstractCorporate events happen in waves. In this paper, we examine the timing patterns of 5 different types of corporate event waves (new stock and seasoned equity issues, stock- and cash-financed acquisitions, and stock repurchases) using a comprehensive data set of more than 151,000 corporate transactions over the 25-year period from 1980 to 2004. We document a distinctive pattern, previously not found in the literature, in the way stock-related waves form. Corporate waves seem to start with new issue waves (seasoned equity offering preceding initial public offering waves), followed by stock-financed merger waves, followed in turn by repurchase waves. Our results hold over separate decades and across industries. Our results seem consistent with both the neoclassical efficiency hypothesis and the misvaluation hypothesis, and there are distinct periods when one or the other appears dominant.

scholarly journals The Cosmological Decrease of Galactic Density and the Induced Retarded Gravity Effect on Rotation Curves

2021 ◽  
Author(s):  
Asher Yahalom
Keyword(s):  
Dark Matter ◽  
Galactic Center ◽  
Temporal Change ◽  
The Other ◽  
Local Effects ◽  
Physical Systems ◽  
Cosmic Expansion ◽  
The Galaxy ◽  
Action At A Distance ◽  
Retardation Effects

Galaxies are huge physical systems having dimensions of many tens of thousands of light years. Thus any change at the galactic center will be noticed at the rim only tens of thousands of years later. Those retardation effects seems to be neglected in present day galactic modelling used to calculate rotational velocities of matter in the rims of the galaxy and surrounding gas. The significant differences between the predictions of Newtonian instantaneous action at a distance and observed velocities are usually explained by either assuming dark matter or by modifying the laws of gravity (MOND). In this paper we will show that taking general relativity seriously without neglecting retardation effects one can explain the radial velocities of galactic matter without postulating dark matter. However, this will rely on a temporal change of galactic mass. We will compare two different mechanisms of density change, one is local, that is accretion of matter from the intergalactic medium. The other is global, that is the cosmological decrease of density due to the cosmic expansion. It will be shown that local effects are much more important in this respect.

scholarly journals Development of a hybrid SmEdA/SEA model for predicting the power exchanged between low and high modal density subsystems

2021 ◽  
Vol 263 (3) ◽  
pp. 3824-3832
Author(s):  
Guang Zhu ◽  
Laurent Maxit ◽  
Nicolas Totaro ◽  
Alain Le Bot
Keyword(s):  
Power Flow ◽  
The Other ◽  
Mode Shapes ◽  
Distribution Analysis ◽  
Coupled Subsystems ◽  
Modal Density ◽  
Spectrum Density ◽  
Energy Equipartition ◽  
Cavity System ◽  
High Modal Density

Statistical modal Energy distribution Analysis (SmEdA) was developed from classical Statistical Energy Analysis (SEA). It allows computing power flow between coupled subsystems from the deterministic modes of uncoupled subsystems without assuming the SEA modal energy equipartition. SmEdA is well adapted in mid-frequency when the subsystems have not a very high modal density. However, for some systems e.g. the plate-cavity system, one subsystem can exhibit a low modal density while the other one a high one. The goal of the paper is then to propose an extension of SmEdA formulation that allows describing one subsystem by its deterministic modes, and the other one as a diffuse field statistically supposing modal energy equipartition. The uncertain subsystem is then characterized by sets of natural frequencies and mode shapes constructed based on Gaussian Orthogonal Ensemble matrix and the cross-spectrum density of a diffuse field, respectively. This formulation permits not only the computation of mean noise response but also the variance generated by the uncertainties and furthermore without bringing in much computation. It is demonstrated that the obtained analytical results from the proposed hybrid SmEdA/SEA are consistent with numerical results computed by FEM with an appropriate degree of uncertainty.

Systemic and local effects of endotoxin on canine gracilis muscle vascular conductance

1990 ◽  
Vol 258 (5) ◽  
pp. H1498-H1506
Author(s):  
R. F. Bond ◽  
C. G. Scott ◽  
L. H. Krech ◽  
C. H. Bond
Keyword(s):  
Vascular Tone ◽  
Gracilis Muscle ◽  
The Other ◽  
Constant Flow ◽  
Vascular Conductance ◽  
Local Effects ◽  
Peripheral Vasculature ◽  
Systemic Endotoxemia ◽  
Dependent Mechanism

To define the site and mechanism of action that endotoxin has on the peripheral vasculature, an in situ constant-flow double-canine gracilis muscle (GM) preparation was utilized. During systemic endotoxemia, one GM was innervated and the other was denervated during a 30-min intravenous infusion of 2 mg/kg endotoxin. Significantly increased vascular conductance (URP) in the denervated GM (106 +/- 26%) occurred compared with the innervated GM (50 +/- 7%), which suggests that decompensation is not totally dependent on neural depression. During local endotoxemia, with both GMs either intact or denervated, one GM was infused intra-arterially for 30 min with a dose of endotoxin calculated to provide a blood concentration similar to that achieved during systemic endotoxemia, whereas the other GM was infused with the vehicle. The URPs did not change significantly in either the saline or endotoxin GMs. Therefore, endotoxin does not act directly on peripheral vasculature or totally through depression of the autonomic nervous system. It apparently interacts with a systemically dependent mechanism to release a vasodepressor substance that is transported to the peripheral vasculature causing relaxation of vascular tone.

scholarly journals Improved Sound Radiation of Flat Panel Loudspeakers Using the Local Air Spring Effect

2020 ◽  
Vol 10 (24) ◽  
pp. 8926
Author(s):  
Benjamin Zenker ◽  
Robert Schurmann ◽  
Sebastian Merchel ◽  
M. Ercan Altinsoy
Keyword(s):  
Frequency Response ◽  
Low Frequency ◽  
Sound Radiation ◽  
Air Spring ◽  
Flat Panel ◽  
Modal Density ◽  
Alternative Approach ◽  
Additional Mode ◽  
Modal Behavior ◽  
Density Results

The low-frequency performance of exciter-driven flat-panel loudspeakers is technically challenging. The lower modal density results in high deviations in the frequency response, and dips of more than 20 dB are possible. This paper presents an alternative approach for optimizing the modal behavior through the additional air spring effect of an irregular shaped enclosure. The additional mode-dependent air compliance suppresses the panel’s anti-phase components, which minimizes dips in the frequency response and improves the response without adding mass to the system. The approach is analyzed with the measured and simulated results of a prototype. Furthermore, additional enclosure changes were made to visualize the influence of the air spring improved system.

A Numerical Approach for Simulation of Rock Fracturing in Engineering Blasting

2010 ◽  
Vol 1 (2) ◽  
pp. 38-58
Author(s):  
Mani Ram Saharan ◽  
Hani S. Mitri
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Numerical Modelling ◽  
Plane Stress ◽  
Numerical Approach ◽  
The Other ◽  
Rock Fracturing ◽  
Experimental Tool ◽  
Element Elimination ◽  
Good Agreement

An approach for simulation of rock fracturing as a result of engineering blasting is presented in this paper. The approach uses element elimination technique within the framework of finite element method to capture the physics of engineering blasting. The approach does not require pre-placement of fracture paths which is the severe drawback of the other existing methodologies and approaches. Results of plane stress modelling for isotropic brittle rock behaviour are presented in this paper and these results are in good agreement with the existing knowledge base. The authors also review the existing approaches of numerical modelling to compare the efficacy of the element elimination technique. It is anticipated that the further developments with this approach can prove to be good experimental tool to improve engineering blasting operations.

In Situ-Tests and Advanced Numerical Modelling for Masonry Arches Retrofitted with Steel Reinforced Grout

2017 ◽  
Vol 747 ◽  
pp. 242-249 ◽  
Author(s):  
Elisa Bertolesi ◽  
Francesca Giulia Carozzi ◽  
Gabriele Milani ◽  
Carlo Poggi
Keyword(s):  
Numerical Modelling ◽  
Numerical Technique ◽  
Experimental Results ◽  
The Other ◽  
Global Behavior ◽  
Vertical Load ◽  
Masonry Arches ◽  
Lime Mortar ◽  
Single Leaf

The paper presents the results of a series of In Situ tests carried out on two masonry arches, one unreinforced and the other reinforced with SRG (Steel Reinforced Grout). An advanced numerical modelling based on a heterogeneous discretization is also reported. The arches have a span equal to 3.30 m and height 0.83 m, and are built with common Italian bricks with dimensions 250x120x55 mm3 and 10 mm thick mortar joints. The arches are built regularly spacing out two bricks laid edge on (thickness of the arch 12 cm) with two bricks (one over the other) disposed in single leaf. One of the two arches is tested unreinforced, whereas the second is reinforced with an SRG constituted by an inox grid embedded into a layer of lime mortar. For all samples, an eccentric vertical load placed at 1⁄4 of the span is increased up to failure. An advanced numerical technique is adopted to reproduce experimental results, namely a heterogeneous micro-modelling where bricks, mortar and strengthening are meshed separately. The numerical outcomes are comparatively assessed with respect to the experimental global behavior and crack patterns obtained at the end of the tests.

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