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Evaluation of the Reliability of a System: Approach by Monte Carlo Simulation and Application

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Open Journal of Applied Sciences 2024年第3期14卷 721-739页

作者： Aslain Brisco Ngnassi Djami Jean Bosco Samon Boukar Ousman Ulrich Ngnassi Nguelcheu Wolfgang Nzié guy edgar ntamack Bienvenu Kenmeugne Department of Fundamental Sciences and Techniques of Engineer Chemical Engineering and Mineral Industries School University of Ngaoundere Ngaoundere Cameroon Department of Mechanical Engineering National School of Agro-Industrial Sciences University of Ngaoundere Ngaoundere Cameroon Department of Electrical Engineering Energy and Automation National School of Agro-Industrial Sciences University of Ngaoundere Ngaoundere Cameroon Department of Physics Faculty of Science University of Ngaoundere Ngaoundere Cameroon Department of Industrial and Mechanical Engineering National Advanced School of Engineering University of Yaounde I Yaounde Cameroon

The objective of this paper is to evaluate the reliability of a system in its different states (absence of failures, partial failure and total failure) and to propose actions to improve this reliability by an approach based on Monte Carlo simulation. It consists of a probabilistic evaluation based on Markov Chains. In order to achieve this goal, the functionalities of Markov Chains and Monte Carlo simulation steps are deployed. The application is made on a production system. .

关键词： Evaluation Reliability Monte Carlo Markov Chain

Thermal Properties of Earth Bricks Stabilised with Cement and Sawdust Residue Using the Asymmetrical Hot-Plane Method

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Open Journal of Applied Sciences 2023年第11期13卷 1910-1934页

作者： Gabin Alex Nouemssi guy edgar ntamack Martin Ndibi Mbozo’O Bonaventure Djeumako Ecole Nationale Supérieure des Sciences Agros Industrielles Laboratoire de Mécanique Matériaux et Photonique University of Ngaoundéré Ngaoundéré Cameroon Département de Physique/EGCIM Faculté des Sciences et Physique Université de Ngaoundéré Ngaoundéré Cameroon Ecole Nationale Supérieure des Sciences Agros Industrielles Département de Génie Mécanique et Productique University of Ngaoundéré Ngaoundéré Cameroon

This paper presents an experimental study of the characterisation of local materials used in the construction and thermal insulation of buildings. These materials are compressed earth bricks stabilised with cement and sawdust. The thermal conductivity, diffusivity, effusivity, and specific heat of earth-based materials containing cement or sawdust have been determined. The results show that the blocks with earth + sawdust are better thermal insulators than the blocks with simple earth. We observe an improvement in thermal efficiency depending on the presence of sawdust or cement stabilisers. For cement stabilisation, the thermal conductivity increases (λ: 1.04 to 1.36 W·m-1·K-1), the diffusivity increases (from 4.32 × 10-7 to 9.82 × 10-7 m2·s-1), and the effusivity decreases (1404 - 1096 J·m-2·K-1·s-1/2). For sawdust stabilisation, the thermal conductivity decreases (λ: 1.04 to 0.64 W·m-1·K-1), the diffusivity increases (from 4.32 × 10-7 to 5.9 × 10-7 m2·s-1), and the effusivity decreases (1404 - 906 J·m-2·K-1·s-1/2). Improving the structural and thermal efficiency of BTC via stabilisation with derived binders or cement is beneficial for the load-bearing capacity and thermal performance of buildings.

关键词： Clay Brick West Cameroon Thermal Conductivity Asymmetric Hot Surface Thermal Properties

Holes Effects in Plane Periodic Multilayered Viscoelastic Media

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Open Journal of Acoustics 2013年第3期3卷 80-87页

作者： Emmanuel Siryabe guy-edgar ntamack Pierre Maréchal Département de Physique Groupe de Mécanique et des Matériaux (GMM) Université de Ngaoundéré Ngaoundéré Cameroun Laboratoire Ondes et Milieux Complexes (LOMC) UMR 6294 CNRS Université du Havre Le Havre France

This work deals with the study of the reflection and transmission properties of plane periodic structures composed of N periods (1 ≤ N ≤ 3) in the MHz frequency range. The period consists of two bounded plates presenting a high acoustic impedance contrast one of which is in aluminum, the other is in polyethylene. The longitudinal and transversal attenuations are considered in polyethylene and neglected in aluminum. We take into account the case of emerging holes in the polyethylene layer. Simulations are based on the stiffness matrix method (SMM) developed by Rokhlin. When attenuation is considered in polyethylene, the reflection coefficients are different depending on the insonification side. The comparison of results without or with holes configurations are performed and showed that throughout holes allow the rapid observation of forbidden bands. The attenuation of the whole multilayer is also determined.

关键词： Periodic Structures Holes Porosity Phononic Crystal Forbidden Bands Transmission Reflection Attenuation

On the Simulation of the Influence of Defects on Immersed Plane Periodic Multilayer Viscoelastic Media

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Open Journal of Acoustics 2021年第2期11卷 17-30页

作者： Massaï Hatoumva Emmanuel Siryabe Pierre Marechal guy edgar ntamack Gambo Betchewe Faculté des Sciences Département de Physique Université de Maroua Maroua Cameroon Safran Helicopter Engines Groupe Evaluation Non Destructive Bordes France Laboratoire Ondes et Milieux Complexes (LOMC) UMR 6294 CNRS Université du Havre Le Havre France Groupe de Mécanique Matériaux et Acoustique P.B: 454 Département de Physique Faculté des Sciences Université de Ngaoundéré Ngaoundéré Cameroon

This work deals with the study of a plane periodic multilayer structure in which the elementary stack consists of two plates in contact: one in aluminum (AL) and the other one in polyethylene (PE). These isotropic materials, present a high acoustic impedance contrast. The attenuation of the longitudinal and transverse waves is taken into account in the polyethylene but neglected in the aluminum plate. The effect of different defects is analyzed. Firstly, we focus on the effect of the presence of grease inclusion in the polyethylene plate (considering the two plates of the elementary stack in perfect contact). Secondly, the effect of disbond simulated by the insertion of a thin Teflon layer between the interfaces of the two layers constituting the elementary stack of the multilayer structure is investigated. Finally, the effect of the stacking sequences of the multilayer is analyzed. In order to obtain the effective acoustic parameters of polyethylene layer, allowing to evaluate the reflection and transmission coefficients using the stiffness matrix method developed by Rokhlin et al., four homogenization models are analyzed, then the best one to our configuration is chosen. The comparison of the simulation results is carried out.

关键词： Reflection Coefficients Transmission Coefficients Defects Multilayer Peri-odic Structure

High Temperature Effect on Absorption Coefficient of M-MPPs and Sandwich Structures Coupled with MPPs

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Open Journal of Acoustics 2020年第1期10卷 1-18页

作者： Daliwa Joseph Bainamndi Emmanuel Siryabe Serge Yamigno Doka guy edgar ntamack Groupe de Mé canique des Mat&#233 riaux et Acoustique (GMMA) Universit&#233 de Ngaoundé ré Ngaound&#233 ré Cameroun Safran Helicopter Engines Groupe Evaluation Non Destructive Bordes France

This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.

关键词： Absorption Coefficient Finite Element Model Microperforated Plates Poroelastic Core Sandwich Structures

Thermal Characteristics of Earth Blocks Stabilized by Rice Husks

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Open Journal of Applied Sciences 2023年第10期13卷 1796-1819页

作者： Mbairangone Samson ntamack guy edgar Bianzeube Tikri Tsopmo Fabien Akana Ouanmini Bobet Civil Engineering Laboratory National High School of Public Works of N’Djamena N’Djamena Chad Laboratory of Mechanical Engineering and Materials Mongo Polytechnic University Mongo Chad Group of Mechanics Materials and Acoustics (GMMA) Department of Physics Faculty of Science University of N’Gaoundéré N’Gaoundéré Cameroon Department of Industrial and Mechanical Engineering National High Polytechnic School of Yaoundé (ENSPY) Yaoundé Cameroon Department of Chemistry Higher Normal School of Bongor Bongor Chad

The objective of this study is to determine the thermal characteristics of bricks produced from clay soils in Chad using the asymmetric plane method. Indeed, in Sahelian countries like Chad, temperature variations are excessive. The study of the thermal behavior of a recyclable local material with low environmental impact could not only improve thermal comfort in homes, but also help mitigate the effects of climate change. It is in this context that this study is envisaged. Before carrying out these measurements, we first produced different formulations of soil blocks 0%, 1% 1.5%, 2% and 2.5% by mass of rice husks (1.25 mm sieve refusal). Brick specimens of dimensions 10 cm × 10 cm × 1 cm were developed at 0 day, 7 days and 14 days of maturation of the formulated pastes. After, those bricks were submitted after drying to the measurements of various thermal parameters: in particular the conductivity, the effusivity, the volumetric capacity and the diffusivity. The obtained results show that the addition of rice husks to clay soils improves conductivity by 13% to 49%, effusivity by 19% to 24%, volumetric capacity by 23% to 27%, and diffusivity by 47% to 58% for the Moundou soils, depending on the maturation period. For the N’Djamena soil, these thermal characteristics are improved from 11% to 38%, from 11% to 13%, from 40% to 47% and from 39% to 40% respectively.

关键词： Thermal Conductivity Bricks Mixtures Fiber Reinforced Material Thermal Confort