Robert Nzengwa

• Phd in mathematics, ingenieur des ponts et chaussees
• Head of Department at University of Douala

L’objectif de cette étude est de stabiliser un sol avec la chaux et le ciment. Les essais ont été réalisés pour déterminer et identifier les caractéristiques physiques de ce sol. Les résultats obtenus de ces essais ont donné : pour la teneur en eau naturelle moyenne 14,62%, le poids spécifique 2,623T/m 3 , l’analyse granulométrique : 17.7% de s...

A shell is a three-dimensional medium that can be represented by the product of a surface and an interval whose dimension is relatively smaller than that of the surface. How to predict the three-dimensional behavior of a shell by the parameters of the surface is the objective of various models found in the literature. This chapter presents in the v...

This chapter covers the necessary basic knowledge of three-dimensional and two-dimensional curvilinear media. Tangent space, covariant derivation of tensors, strain tensor, tangent modulus tensor, curvature tensor, fundamental forms of a surface and curvilinear three-dimensional elasticity problems are briefly introduced. This knowledge is necessar...

Thin shell theory is the most widely used theory in engineering by practitioners. Various models derived from this theory are presented in their variational form. Membrane models, flexional models, mixed models are presented. Von Karman and Hubber equations on orthotropic plates are treated with application to some practical problems.

Numerical methods have proven to be the best tools for solving the complex equations in shell theories. Two new finite element methods based on the gradient recovery method and the strain deformation approach are presented. Their performance is compared with that of some well-known finite element methods on well-known benchmarks. They are found to...

Through-the-thickness transverse strain and transverse stresses are significant in thick shells. The model that accounts for their prediction is presented in static analysis and dynamic evolution in their variational forms. Additional new inertia terms are calculated.

Some specific models more or less heuristic and usually used to solve some non-familiar engineering problems are presented.

A parametric study on a discontinuous concrete slab pavement was carried out. The truck with axle and wheels type configuration was considered for different load positions on the slab pavement. The results show that the dual-wheels insulated axle produces the most detrimental damage indicators for the pavement surface tested. Based on the analysi...

The equilibrium of a structure is characterized by either Euler’s equations completed with boundary and some internal conditions, or by variational equations of a stationary point of the total potential energy defined in a set of admissible functions. Generally this set is defined as a reciprocal image of a constraint function defined between two B...

For the determination of global stability after long term advanced monitoring, artificial intelligence have been used for the data analysis of water level and displacements of Songloulou earth dam at Cameroon. Measurements of safety and reliability indicators follow changes set by piezometric and pendulums measurements. The results obtained from th...

This paper provides a thermodynamic and economic assessment of two-stage series organic Rankine cycle (TSORC) and regenerative TSORC (R-TSORC) for a solar project in hot, non-temperate climate. The objective thermodynamic parameters include the net power output (Pnet), the thermal efficiency (ηth) and exergy efficiency (ηex), while the objective ec...

Concrete shells are widespread in civil engineering constructions. Because of the moldability of concrete, special structures such as domes, bridge caissons, buried or raised reservoirs, and arch dams are built with concrete. In this study, we are particularly interested in the variation of the thickness and the resulting strains during a short-ter...

The article focuses on the influence of differential shrinkage linked by drying at the early-age displacements and strain distribution of a concrete ring specimen. Depending on the gradient of dimension changes through the thickness, tensile stress occurs near the exposed surface where drying is greater and thus results in strain gradients developm...

This paper deals with the comparative study of the reliability of some deterministic and stochastic interpolation methods for ground bearing mapping. Covering an area of 121,481.65 m², the site covered by this study is located in the locality of Olembé in the central region of Cameroon. The methodology consisted of collecting from the Ministry of H...

In this paper we present a 2D four-parameter model that accounts for the variation of transverse deformation through-the-thickness in thick linear elastic shells. is model is deduced directly from the 3D elasticity equations of the traction-displacement boundary value problem. Transverse shear strains and thickness variation are accountable through...

The Goswami combined power/cooling cycle is an appropriate way to convert energy efficiently. However, in the conventional Goswami cycle (CGC), the refrigeration is not available when the absorber temperature is high. In the present study, a mechanically driven compressor is used to compress the vapors leaving the turbine. This design creates a lin...

The target in this survey is to investigate deformations of laminates shells (DLS), due to asymmetric and axisymmetric loads, including several other loadings using N-T shell equations. We point out here, the contribution of the metric change in thickness for the analysis of static and linear behavior of laminated composite shells. To achieve this...

This paper presents a thermodynamic analysis of an organic Rankine cycle with a water-loop (ORC-WL) as an efficient means of heat regeneration and saving Water Consumption (WC). The ORC-WL was simulated with wet, dry and isentropic refrigerants such as R717, R600a and R1234yf, respectively, in order to compare its technical performance to the conve...

This paper proposes an alternative to the calculation of the liquid entropy of ammonia/NaSCN and ammonia LiNO3 solutions in the form of correlation equations with higher computation speed. These correlation equations were obtained by using both the least squares method for the modelling of the reference liquid entropy and a classical matrix compute...

In this paper, we used artificial intelligence for the analysis of water level and displacements data from the Songloulou earth dam of Cameroon. Measurements of safety and reliability indicators follow changes dictated by several reversible and irreversible phenomena like piezometric and pendulums measurements. The results obtained over many years...

This work is focused on the development of a chassis for a compact modular vehicle (called the MN). This is to provide a solution other than the use of motorcycles (popular means of transport in sub Saharan African countries paradoxically highly dangerous), and other tricycles (greedy in space and uncomfortable). This tubular chassis comprises thre...

Maintaining the quality of breathing air in urban and industrial areas is one of the biggest challenges faced by humanity in the modern era. Diesel engines, as one of the main providers of energy supply for modern equipment and transport, are also unfortunately contributing highly to the deterioration of air quality. A recent research path on the l...

Maintainingthequalityofbreathingairinurbanandindustrialareasisoneofthebiggestchallengesfacedbyhumanityinthe duetoitsinjectionandatomizationproperties;mostoftherecentresearchfocusedonimprovingbiodieselfuelqualityby unfortunatelycontributinghighlytothedeteriorationofairquality.Arecentresearchpathonthelimitationofdieselengine betweenB100propertiesands...

We present a simple methodology to design curved shell finite elements based on Nzengwa-Tagne's shell equations. The element has three degrees of freedom at each node. The displacements field of the element satisfies the exact requirement of rigid body modes in a 'shifted-Lagrange' polynomial basis. The element is based on independent strain assump...

This work presents the results of a study on evaluation of primary and secondary school buildings in the city of Bafoussam, Cameroon. The methods used in the collection of data included the administration of questionnaires to the various managers of public primary and secondary schools in the three districts of Bafoussam (Bafoussam I, Bafoussam II...

This paper reports the findings of a survey on assessment of degradations/defects and maintenance of administrative primary and secondary school buildings of the city of Bafoussam, Cameroon. Data were collected with the use of structured questionnaires as shown in appendix II administered on various managers of public primary and secondary schools...

Despite the presence of raw materials (limestone and clay) deposits for Portland cement production, the major part of cement sold in Cameroon is from crushed imported clinker. This contributes to high cost of this material and reduction of local employment. In this study and based on existing data, a multi-criteria analysis tool was developed and a...

The pollution of diesel engines is a problem that can be addressed by the use of alternative fuels. We propose two numerical predictions for the combustion of dual fuel and bio diesel in diesel engines. The predictions are based on zero-Dimensional modelling. The results obtained give good predictability and can be used for parametric study of the...

This author purposed a new family of nite element for spherical thick shells with governing equations based on the Nzengwa-Tagne's model proposed in 1999. The model referred to here after as N-T model contains the classical Kirchho-Love (K-L) kinematic with additional terms related to the third fundamental form. Strain energy contains also the chan...

The gradient Polynomial Preserving Recovery (PPR) method is used to validate a linear elastic thick shell model proposed in 1999 by [25] with the ratio χ = h r in which h is half of the thickness and r the absolute value of the smallest curvature radius, a shell is said to be thin if this ratio (the caracteristic parameter) is less than 0.1. In thi...

Thermal annealing (TA) is a well-know method, consisting in heating material, to enhance some of its properties. With Nanomaterials, particularly carbon nanomaterials, TA allows differentiating them and becomes one off characterization techniques. Carbon Nanostructures (CNTs) was synthesized using PE HF CCVD (Plasma Enhanced Hot Filament Catalytica...

To meet more stringent norms and standards concerning engine performances and emissions, engine manufacturers need to develop new technologies enhancing the nonpolluting properties of the fuels. In that sense, the testing and development of alternative fuels such as biodiesel are of great importance. Fuel testing is nowadays a matter of experimenta...

We have developed a curved finite element for a cylindrical thick shell based on the thick shell equations established in 1999 by Nzengwa and Tagne (N-T). The displacement field of the shell is interpolated from nodal displacements only and strains assumption. Numerical results on a cylindrical thin shell are compared with those of other well-known...

The design and monitoring of modern diesel engines running on alternative fuels require reliable models that can validly substitute experimental tests and predict their operating characteristics under different load conditions. Although there exists a multitude of models for diesel engines, 0D phenomenological models present the advantages of givin...

The present work presents the comparative simulation of a diesel engine fuelled on diesel fuel and biodiesel fuel. Two models, based on tabulated chemistry, were implemented for the simulation purpose and results were compared with experimental data obtained from a single cylinder diesel engine. The first model is a single zone model based on the K...

Diesel engines have proven over the years important in terms of efficiency and fuel consumption to power generation ratio. Many research works show the potential of biodiesel as a substitute for conventional gasoil. Mainly, previous and recent researches have focused on experimental investigation of diesel engine performance fuelled by biodiesel. R...

In this paper, a two-dimensional model for linear elastic thick shells is deduced from the three-dimensional problem of a shell thickness 2ε, ε > 0. From different scalings on the tangent and normal components of the displacement uε as widely used in recent works, the limit displacement appears to be Kirchhoff–Love displacement of a different type....

We solve a fixed point problem by proving that the solution is the value at the point 1 of the solution of an appropriate ordinary differential equation. This approach is applied in nonlinear elasticity to the pure traction boundary-value problem with live load. An incremental method is then used in approximating the solution. The number of success...

On applique les methodes incrementales pour approcher les equations d'equilibre des corps elastiques non lineaires incompressibles, soumis a des forces mortes ou a des forces vives, avec des conditions aux limites de deplacement pur ou de traction pure. On etablit la convergence de ces methodes