Highly Directional Acoustic Waves Generated by a Horned Parametric Acoustic Array Loudspeaker

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
L. H. Tong ◽  
S. K. Lai ◽  
J. W. Yan ◽  
C. Li
Keyword(s):  
Acoustic Waves ◽  
Sound Pressure ◽  
Low Frequencies ◽  
Equivalent Radius ◽  
Design And Optimization ◽  
Wide Range ◽  
Acoustic Array ◽  
Parametric Array ◽  
Overall Efficiency ◽  
Acoustic Horns

Acoustic horns can enhance the overall efficiency of loudspeakers to emanate highly directional acoustic waves. In this work, a theoretical model is developed to predict difference frequency acoustic fields generated by a parametric array loudspeaker (PAL) with a flared horn. Based on this model, analytical solutions are obtained for exponentially horned PALs. A numerical analysis on the performance of horned PALs subject to various horn parameters (i.e., horn length and flare constant) is implemented. To compare with nonhorned parametric acoustic array (PAA) devices, it is able to generate highly directional acoustic wave beams for a wide range of difference frequencies, in which the generated sound pressure levels at low frequencies can be significantly enhanced. In addition, the equivalent radius of a nonhorned emitter that matches the directivity achieved by a horned one is also quantitatively investigated. The present research will provide useful guidelines for the design and optimization of horned parametric array equipment.

scholarly journals Acoustic Structure Inverse Design and Optimization Using Deep Learning

2021 ◽  
Author(s):  
Xuecong Sun ◽  
Han Jia ◽  
Yuzhen Yang ◽  
Han Zhao ◽  
Yafeng Bi ◽  
...  
Keyword(s):  
Deep Learning ◽  
Acoustic Waves ◽  
Design Method ◽  
Helmholtz Resonator ◽  
Structure Design ◽  
Acoustic Structure ◽  
Design And Optimization ◽  
Wide Range ◽  
Potential Applications ◽  
Coupling Parameters

Abstract From ancient to modern times, acoustic structures have been used to control the propagation of acoustic waves. However, the design of acoustic structures has remained a time-consuming and computational resource-consuming iterative process. In recent years, deep learning has attracted unprecedented attention for its ability to tackle hard problems with large datasets, achieving state-of-the-art results in various tasks. In this work, an acoustic structure design method is proposed based on deep learning. Taking the design of multiorder Helmholtz resonator as an example, we experimentally demonstrate the effectiveness of the proposed method. Our method is not only able to give a very accurate prediction of the geometry of acoustic structures with multiple strong-coupling parameters, but also capable of improving the performance of evolutionary approaches in optimization for a desired property. Compared with the conventional numerical methods, our method is more efficient, universal and automatic, and it has a wide range of potential applications, such as speech enhancement, sound absorption and insulation.

Phase equilibria modeling of biorefinery-related systems: a systematic review

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Marcos L. Corazza ◽  
Julia Trancoso
Keyword(s):  
Phase Equilibria ◽  
Phase Behavior ◽  
Fossil Fuel ◽  
Process Conditions ◽  
Design And Optimization ◽  
Waste Reuse ◽  
Wide Range ◽  
Prisma Statement ◽  
Fuel Substitution ◽  
The Subject

Abstract The search for sustainable ideas has gained prominence in recent decades at all levels of society since it has become imperative an economic, social, and environmental development in an integrated manner. In this context, biorefineries are currently present as the technology that best covers all these parameters, as they add the benefits of waste reuse, energy cogeneration, and fossil fuel substitution. Thus, the study of the various applicable biological matrices and exploring the technical capabilities of these processes become highly attractive. Thermodynamic modeling acts in this scenario as a fundamental tool for phase behavior predictions in process modeling, design, and optimization. Thus, this work aimed to systematize, using the PRISMA statement for systematic reviews, the information published between 2010 and 2020 on phase equilibria modeling in systems related to biorefineries to organize what is already known about the subject. As a result, 236 papers were categorized in terms of the year, country, type of phase equilibria, and thermodynamic model used. Also, the phase behavior predictions of different thermodynamic models under the same process conditions were qualitatively compared, establishing PC-SAFT as the model that best represents the great diversity of interest systems for biorefineries in a wide range of conditions.

Separation of active and passive components of short-range stiffness of muscle

1977 ◽  
Vol 232 (1) ◽  
pp. 45-49 ◽  
Author(s):  
D. L. Morgan
Keyword(s):  
Short Range ◽  
Muscle Tension ◽  
Isometric Tension ◽  
Incomplete Fusion ◽  
Low Frequencies ◽  
Passive Components ◽  
Stimulus Rate ◽  
Straight Line ◽  
Wide Range ◽  
Tendon Compliance

The short-range stiffness of smoothly but submaximally contracting isometric soleus muscles of anesthetised cats was measured by applying small fast stretches. The ratio of isometric tension to stiffness was plotted against tension over a wide range of muscle lengths and stimulus rates. The results fitted a straight line well, as predicted from crossbridge theory, showing the stiffness to be a function of tension only, independent of the combination of length and stimulus rate used to generate the tension. The major deviation from this line was attributed to incomplete fusion at low frequencies of stimulation. Values believed to be tendon compliance and crossbridge tension per unit of stiffness were found from the graph, and the tendon compliance correlated with the maximum muscle tension. Shortening the tendon by attaching nearer to the muscle changed the results in a manner consistent with the theory, provided that appropriate precautions were taken against slippage.

CFD Modeling of Transient Flow Phenomena in an Axial Flow VAD

2007 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Amy L. Throckmorton ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Blood Flow ◽  
Transient Flow ◽  
Axial Flow ◽  
The Body ◽  
Cfd Modeling ◽  
Ventricular Assist ◽  
Pump Design ◽  
Design And Optimization ◽  
Wide Range ◽  
Cfd Analyses

A ventricular assist device (VAD) effectively relieves the workload from a native heart, which has been weakened by disease, and increases blood flow supplied to the body to maintain normal physiologic function. The device must be able to operate over a wide range of conditions. Designed to operate at a single, best-efficiency operating point, it must frequently perform at off-design conditions due to a fluctuating flow rate demanded by the human body and a time varying flow within the pump, due to the beating of the native heart. The design and optimization of a blood pump is a challenging and complex process. Pump design equations are used to estimate the initial dimensions of the pump regions. Computational fluid dynamics (CFD) analyses are then performed to optimize the blood flow path according to specific design criteria under steady flow conditions [1].

scholarly journals Installation for measuring the dielectric anisotropy of liquid crystals at low frequencies by the bridge method with constant displacement

2021 ◽  
Vol 1198 (1) ◽  
pp. 012006
Author(s):  
S V Kalashnikov ◽  
N A Romanov ◽  
A V Nomoev
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Internal Resistance ◽  
Dielectric Anisotropy ◽  
Dielectric Parameters ◽  
Low Frequencies ◽  
Offset Voltage ◽  
Wide Range ◽  
Ac Current ◽  
Constant Displacement

Abstract Installation designed to measure the dielectric anisotropy in laboratory studies of liquid crystal polymer films is described. The installation operates on the principle of a balanced alternating current (AC) bridge, allowing the application of a direct external current (bias) to the liquid crystal cell. The internal resistance of the direct current (DC) source, which affects the equilibrium condition of the bridge, is compensated. The frequency of the AC current feeding the bridge and the offset voltage of the cell is regulated within a wide range, which makes it possible to study various functional dependences of the dielectric parameters of liquid crystals and their modifiers.Introduction

scholarly journals Palladium-Catalyzed [3+2] Cycloaddition via Two-Fold 1,3-C(sp3)−H Activation

2020 ◽  
Author(s):  
Hojoon Park ◽  
jin-quan yu
Keyword(s):  
Functional Groups ◽  
Sulfonic Acid ◽  
Cycloaddition Reaction ◽  
Wide Range ◽  
Leaving Group ◽  
Palladium Catalyzed ◽  
Directing Group ◽  
Overall Efficiency ◽  
Weak Coordination ◽  
Single Reaction

<div>Cycloaddition reactions provide an expeditious route to construct ring systems in a highly convergent and stereoselective manner. For a typical cycloaddition reaction to occur, however, the installation of multiple reactive functional groups (π-bonds, leaving group, etc.) are required within the substrates, compromising the overall efficiency or scope of the cycloaddition reaction. Here, we report a palladium-catalyzed [3+2] reaction that utilizes C(sp<sup>3</sup>)–H activation to generate the three-carbon unit for formal cycloaddition with maleimides. We implemented a strategy where the initial C(sp<sup>3</sup>)–H activation/olefin insertion would trigger a relayed, second remote C(sp<sup>3</sup>)–H activation to complete a formal [3+2] cycloaddition. The diastereoselectivity profile of this reaction resembles that of a typical pericyclic cycloaddition reaction in that the relationships between multiple stereocenters are exquisitely controlled in a single reaction. The key to success was the use of weakly coordinating amides as the directing group, as undesired Heck or alkylation pathways were preferred with other types of directing groups. The use of the pyridine-3-sulfonic acid ligands is critical to enable C(sp<sup>3</sup>)–H activation directed by this weak coordination. The method is compatible with a wide range of amide substrates, including lactams, which lead to novel spiro-bicyclic products. The [3+2] product is also shown to undergo a reductive desymmetrization process to access chiral cyclopentane bearing multiple stereocenters with excellent enantioselectivity.</div>

scholarly journals Prediction of noise from wind turbines: theoretical and experimental study

2018 ◽  
pp. 34-41 ◽  
Author(s):  
Carlos Alberto Echeverri-Londoño ◽  
Alice Elizabeth González Fernández
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Sound Pressure ◽  
Prediction Method ◽  
Wide Band ◽  
Propagation Models ◽  
Low Frequencies ◽  
High Frequencies ◽  
Wind Speeds ◽  
Sound Pressure Levels

Several noise propagation models used to calculate the noise produced by wind turbines have been reported. However, these models do not accurately predict sound pressure levels. Most of them have been developed to estimate the noise produced by industries, in which wind speeds are less than 5 m/s, and conditions favor its spread. To date, very few models can be applied to evaluate the propagation of sound from wind turbines and most of these yield inaccurate results. This study presents a comparison between noise levels that were estimated using the prediction method established in ISO 9613 Part 2 and measured levels of noise from wind turbines that are part of a wind farm currently in operation. Differences of up to 56.5 dBZ, with a median of 29.6 dBZ, were found between the estimated sound pressure levels and measured levels. The residual sound pressure levels given by standard ISO 9613 Part 2 for the wind turbines is larger for high frequencies than those for low frequencies. When the wide band equivalent continuous sound pressure level is expressed in dBA, the residual varies between −4.4 dBA and 37.7 dBA, with a median of 20.5 dBA.

The reflexion of a spherical acoustic pulse by an absorbent infinite plane and related problems

1952 ◽  
Vol 215 (1121) ◽  
pp. 233-254 ◽  
Keyword(s):  
Acoustic Waves ◽  
Acoustic Pulse ◽  
Practical Interest ◽  
Exact Result ◽  
Integral Solution ◽  
Blast Waves ◽  
Angle Of Incidence ◽  
Infinite Plane ◽  
Formal Integral ◽  
Wide Range

A formal integral solution is given for the problem of the reflexion of a spherical acoustic pulse by an infinite plane interface having an impedance of arbitrary dependence on frequency and angle of incidence. In many cases of practical interest the impedance may be assumed to be independent of angle of incidence, and under this assumption the integral solution is relatively easy to evaluate. A simple exact expression for the reflected pulse, in closed form, is obtained when the wall impedance is purely resistive (i.e. independent of frequency). This solution is a special case of a general type of solution of the wave equation when it is reduced to a rotationally symmetric Laplace’s equation in the ‘spherical polar’ co-ordinates [√{( ct / r ) 2 - sin 2 θ}, ( ct cos θ/ r )/ √{( ct / r ) 2 - sin 2 θ}]. To illustrate the relatively wide range of validity of the assumption of an impedance independent of angle of incidence, when applied to real materials, this exact result is compared with an approximate solution for the case where the interface separates two homogeneous isotropic lossless materials. The formal integral solution is evaluated approximately for wall impedances of the following types: (i) resistance and mass, (ii) resistance and stiffness, (iii) resistance, mass and stiffness. The solutions are compared with corresponding solutions for plane incident waves, and the behaviour of the scattered wave, distinguishing between the spherical and the plane wave, is discussed. Possible applications of the results for acoustic waves to problems in the reflexion of blast waves and of transient radiation by an electric dipole are indicated briefly.

Directional sound processing and interaural sound transmission in a small and a large grasshopper

1995 ◽  
Vol 198 (9) ◽  
pp. 1817-1827 ◽  
Author(s):  
A Michelsen ◽  
K Rohrseitz
Keyword(s):  
Outer Surface ◽  
Sound Pressure ◽  
Schistocerca Gregaria ◽  
Sound Transmission ◽  
Directional Hearing ◽  
Sound Processing ◽  
Low Frequencies ◽  
High Frequencies ◽  
Physical Mechanisms ◽  
Chorthippus Biguttulus

Physical mechanisms involved in directional hearing are investigated in two species of short-horned grasshoppers that differ in body length by a factor of 3&shy;4. The directional cues (the effects of the direction of sound incidence on the amplitude and phase angle of the sounds at the ears) are more pronounced in the larger animal, but the scaling is not simple. At high frequencies (10&shy;20 kHz), the sound pressures at the ears of the larger species (Schistocerca gregaria) differ sufficiently to provide a useful directionality. In contrast, at low frequencies (3&shy;5 kHz), the ears must be acoustically coupled and work as pressure difference receivers. At 3&shy;5 kHz, the interaural sound transmission is approximately 0.5 (that is, when a tympanum is driven by a sound pressure of unit amplitude at its outer surface, the tympanum of the opposite ear receives a sound pressure with an amplitude of 0.5 through the interaural pathway). The interaural transmission decreases with frequency, and above 10 kHz it is only 0.1&shy;0.2. It still has a significant effect on the directionality, however, because the directional cues are large. In the smaller species (Chorthippus biguttulus), the interaural sound transmission is also around 0.5 at 5 kHz, but the directionality is poor. The reason for this is not the modest directional cues, but rather the fact that the transmitted sound is not sufficiently delayed for the ear to exploit the directional cues. Above 7 kHz, the transmission increases to approximately 0.8 and the transmission delay increases; this allows the ear to become more directional, despite the still modest directional cues.

Model-Based Design and Optimization of Passive Shoulder Exoskeletons

2021 ◽  
Author(s):  
Ali Nasr ◽  
Spencer Ferguson ◽  
John McPhee
Keyword(s):  
Elevation Angle ◽  
Differential Algebraic Equations ◽  
Joint Torque ◽  
Algebraic Equations ◽  
Joint Torques ◽  
Design And Optimization ◽  
Passive Mechanism ◽  
Wide Range ◽  
Passive Exoskeleton ◽  
Selection Of

Abstract To physically assist workers in reducing musculoskeletal strain or to develop motor skills for patients with neuromuscular disabilities, recent research has focused on Exoskeletons (Exos). Designing active Exos is challenging due to the complex human geometric structure, the human-Exoskeleton wrench interaction, the kinematic constraints, and the selection of power source characteristics. Because of the portable advantages of passive Exos, designing a passive shoulder mechanism has been studied here. The study concentrates on modeling a 3D multibody upper-limb human-Exoskeleton, developing a procedure of analyzing optimal assistive torque profiles, and optimizing the passive mechanism features for desired tasks. The optimization objective is minimizing the human joint torques. For simulating the complex closed-loop multibody dynamics, differential-algebraic equations (DAE)s of motion have been generated and solved. Three different tasks have been considered, which are common in industrial environments: object manipulation, over-head work, and static pointing. The resulting assistive Exoskeleton’s elevation joint torque profile could decrease the specific task’s human shoulder torque. Since the passive mechanism produces a specific torque for a given elevation angle, the Exoskeleton is not versatile or optimal for different dynamic tasks. We concluded that designing a passive Exoskeleton for a wide range of dynamic applications is impossible. We hypothesize that augmenting an actuator to the mechanism can provide the necessary adjustment torque and versatility for multiple tasks.

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