Noise control devices such as panels and barriers, when of high efficiency, generally are of difficult acquisition due to high costs turning in many cases their use impracticable, mainly for limited budget small-sized companies. There is a huge requirement for new acoustic materials that have satisfactory performance, not only under acoustic aspect but also other relevant ones and are of low cost. Vegetable fibers are an alternative solution when used as panels since they promise satisfactory acoustic absorption, according to previous researches, exist in abundance, and derive from renewable sources. This paper, therefore, reports on the development of panels made from vegetable fibers (coconut, palm, sisal, and açaí), assesses their applicability by various experimental (flammability, odor, fungal growth, and ageing) tests, and characterize them acoustically in terms of their sound absorption coefficients on a scale model reverberant chamber. Acoustic results point out that the aforementioned fiber panels play pretty well the role of a noise control device since they have compatible, and in some cases, higher performance when compared to commercially available conventional materials.
The new Brazilian building performance standard is a landmark in terms of housing regulation in Brazil. Nevertheless, due to the standard recent release, it becomes essential to make its requirements compatible with users' needs. This work has the objective to evaluate the acoustic performance requirements of buildings based on the users' perceptions of acoustic comfort. In order to do this, field tests were performed and surveys were applied to the users. The results demonstrate that the requirements defined by the Brazilian norm are unsuitable to meet the users' necessities. The correlation analysed shows a clear perception of the habitants in relation to the transmitted noise through the slabs and walls. These unsatisfactory results concern the acoustic performance of impact noise between slabs, as well as internal and external walls, showing that construction companies must implement new solutions that can provide greater acoustic performance to achieve acoustic comfort to the users.
In the Amazon, river navigation is very important due to the length of navigable rivers and the lack of alternative road networks. Boats usually operate in unfavorable conditions, since there is no hydrodynamic relation among propellers, geometry, and the dimensions of the boat hull. Currently, there is no methodology for propeller hydrodynamic optimization with low computational cost and easy implementation in the region. The aim of this work was to develop a mathematical approach for marine propeller design applied to boats typically found on Amazon rivers. We developed an optimized formulation for the chord and pitch angle distributions, taking into account the classical model of Glauert. A theoretical analysis for the thrust and torque relationships on an annular control volume was performed. The mathematical model used was based on the Blade Element Momentum Theory (BEMT). We concluded that the new methodology proposed in this work demonstrates a good physical behavior when compared with the theory of Glauert and the experimental data of the Wageningen B3-50 propeller. KEYWORDS: Optimization, BEMT model, theory of Glauert, Wageningen B3-50. Contribuição ao projeto hidrodinâmico de propulsores marítimos voltados as pequenas embarcações da região Amazônica RESUMONa Amazônia, a navegação é muito importante devido a extensão de rios navegáveis e a falta de redes rodoviárias alternativas. As embarcações geralmente trabalham em condições desfavoráveis, uma vez que não há relação entre a hidrodinâmica dos hélices, geometria e as dimensões do casco da embarcação. Atualmente, não há metodologia para otimização hidrodinâmica com baixo custo computacional e fácil implementação na região. O objetivo deste trabalho foi o desenvolvimento de uma abordagem matemática voltada para o projeto de propulsores marítimos aplicados as embarcações tipicamente encontradas nos rios da Amazônia. Nós desenvolvemos uma formulação otimizada para o cálculo das distribuições de corda e ângulo de torção, considerando o modelo clássico de Glauert. Uma análise teórica para as relações de empuxo e torque em um volume de controle anular foi realizado. O modelo matemático utilizado foi baseado na teoria do momento do elemento de pá (BEMT). Concluímos que a nova metodologia, proposta neste trabalho, demonstra bom comportamento físico quando comparado com a teoria de Glauert e os dados experimentais do propulsor Wageningen B3-50. PALAVRAS-CHAVE: Otimização, modelo BEMT, Teoria de Glauert, Wageningen B3-50. Contribution to the marine propeller hydrodynamic design for small boats in the Amazon region ACTA AMAZONICA small dimensions requiring small propellers. Eighty interviews in total were performed, including fifty-four with users and twenty-six with producers. Most of the foundry workshops in the towns were visited. The document contemplated information on the boats' specifications (average speed, length of the waterline, number of passengers and crew members, quantity of cargo), the marine motor (brand, model, nominal power, rpm), and th...
Nomenclature loaded distance between the inner and outer raceway A j groove curvature centre, mm radial component of , mm Ar j A j axial component of , mm Aa j A j B total curvature factor, dimensionless Bd unloaded distance between the inner and outer raceway groove curvature centre, mm c speed of sound, m/s C damping matrix, Ns/m d rolling element diameter, mm F load vector, N force on the spring which represents the gear meshF m stiffness, N mass moment of inertia with respect to direction i, kg m 2 Im i k wave number, m -1 gear mesh stiffness, N/m k g stiffness constant elements of the bearing stiffness k ij matrix, N/m K stiffness matrix, N/m load-deflection constant, N/m K cd gear mesh coupling stiffness matrix, N/m K e bearing stiffness matrix, N/m K m finite element matrix, N/m n K Mi gear mass, kg m i M mass matrix, kg resultant moment in the i direction, Nm M i p pressure, N/m 2 q displacement vector, m velocity vector, m/s . q acceleration vector, m/s 2 .. q r curvature radius of the internal ring (for ball roller) or primitive radius (for cylindrical roller), m curvature radius of the external ring of the ball bearing, m r e curvature radius of the internal ring of the ball bearing, m r i radial gap, m r L base circle radius of the i-th gear, m R bi driven gear pitch radius, m R bc driver gear pitch radius, m R bp resultant force in the i direction, N R i X main axis in the x-direction Y main axis in the y-direction Z main axis in the z-direction, or number of rolling elements Greek Symbols angular displacement in the i-direction, degrees i contact angle without load, degrees 0 resultant elastic deformation of the j-th ball or roller j element, mm axial displacement of the j-th roller element, mm a j translational displacement in the i-direction, mm i resultant elastic deformation of the j-th ball element, mm E radial displacement of the j-th roller element, mm r j resultant elastic deformation of the j-th roller ele-R ment, mmIn this article, a global vibro-acoustic method to model gearboxes, which is based on the finite element and boundary element methods, is presented. The final aim of the method is to investigate the vibration and noise transmitted to the gearbox structure casing, which originate from the excitation caused by the gear train, in order to predict the vibro-acoustic parameters. Thus, the mathematical formulae that allow the determination of generalised stiffness matrices are presented in terms of the bearing and gear elements. A numerical model of the geared axle system that allows the estimation of the bearing reactions due to the gear forces transmitted is developed. This model takes into account the influence of modifying the gears teeth profile. The finite elements and boundary meshes were devised and generated in order to represent the gearbox. These meshes were used for the estimation of the acoustic parameters and for vibro-acoustic predictions. † Member of the International Institute of Acoustics and Vibration (IIAV) (pp 61-72)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.