Littérature scientifique sur le sujet « Numerical anlysis »

The sharp 90°corner of bow found on American Tarawa class general amphibious assault ship LHA-1 will produce large separated region in the airwake over the ship, and the turbulence in the separation region seriously affects the operation safety of the helicopter. In order to reduce the separation in bow region of the LHA-1, and optimize the helicopter operating environment, the numerical simulation method is used to study the influence of the bow flap on the airwake of LHA-1. The study results show that: the ANSYS k-ε two equation model based on the hybrid grid can be used to predict the steady-state characteristics of the ship airwake; the bow flap can improve the flow field downwind of the flap installation position, and the impact range can cover two spots; in headwind, the optimal installation angle of the bow flap is 15°~25°. The research results of this paper can provide modification and improvement reference for the amphibious assault ship in-service and under construction, so as to achieve the purpose of optimizing the ship airwake, thereby improving the safety of helicopter landing process and extending the service life.

The paper presents the process of optimisation of geometry of connecting rod used in the automotive industry. This connecting rod is used in a sports car with a high power engine, where high torque values can damage individual components. Three numerical, geometric models of 40HNMA structural steel connecting rods were made for optimisation. Statistical analysis of strength properties using the finite element method was carried out, and results for the models were compared. The simulation and calculations were performed in SolidWorks.

Reinforced concrete core walls with good anti-side rigidity and spatial rigidity is used widely in high-rise buildings. Elasto-plastic static analysis of core walls are be realized by the program CANNY based on the theory of fiber model. Compared with the tests, Results from the simulation anlysis match well with those from the tests. The influence of axial compression ratio and height-width ratio on the bearing capacity and deformation of core walls are analyzed systemically. It is shown that the fiber model is available and successful for the numerical simulation of core walls. The axial compression ratio has distinct affect on the elastic and inelastic behavior of RC core walls. The ratio of height to width not only has effect on the bearing capacity and deformation performance, but also changes the failure mode of RC core walls. The numerical results confirmed the accuracy of this analysis procedure in representing the nonlinear behavior of core walls.

Three-vertical-line-element model and uniaxial spring model were adopted to simulate walls and beams. Based on the existing experiment data, numerical simulation is used to analysis the nonlinear behavior of reinforced concrete core walls. The analysis also considered the influence of relevant parameters on the elasto-plastic in core walls structure. Results from the simulation anlysis match well with those from the tests. It is shown that the higher axial compression ratio enhance the bearing capacity; the ratio of height to width has effect on the bearing capacity, deformation performance and the failure mode; the decrease of span-depth ratio of coupling beam reduce ductility and deformation ability of the core walls; the imposed horizontal angle has important effect on the overall space behavior of reinforced concrete core wall.

It was more convenient to describe track irregularity by the spatial frequency.The conventional frequency-domain transfer function can not effectively solve the vibration equation when anlysis of the vibration response to structure of vehicle-track dynamic coupling system, the time domain numerical integration must be used to solve it.The trigonometric series superposition method can be used to convert track irregularity spectrum into time domain frequency power spectral density function, and then turn the simulated irregularity samples into spectral density by the Inverse Fast Fourier Transform (IFFT), which compared with the theoretical spectral density to test the reliability of the sample. The results show that the simulated sample have the same characteristics with the given power spectral density function, which demonstrate the high reliability of this sample and it can be used as the external excitation of the locomotive vehicle system.

We describe the application of the rotated staggered‐grid (RSG) finite‐difference technique to the wave equations for anisotropic and viscoelastic media. The RSG uses rotated finite‐difference operators, leading to a distribution of modeling parameters in an elementary cell where all components of one physical property are located only at one single position. This can be advantageous for modeling wave propagation in anisotropic media or complex media, including high‐contrast discontinuities, because no averaging of elastic moduli is needed. The RSG can be applied both to displacement‐stress and to velocity‐stress finite‐difference (FD) schemes, whereby the latter are commonly used to model viscoelastic wave propagation. With a von Neumann‐style anlysis, we estimate the dispersion error of the RSG scheme in general anisotropic media. In three different simulation examples, all based on previously published problems, we demonstrate the application and the accuracy of the proposed numerical approach.

Human health is constantly threatened by the appearance and resurgence of several diseases, as shown by recent epidemics. COVID-19 was one of the epidemics that left its mark on the world in terms of economic and human damages. In the search for solution to this pandemic, the scientific community is involved in all its diversity. Mathematicians are taking part in the fight through mathematical modeling in various approaches. Ordinary derivative compartmental modeling approache is one of the techniques widely used in epidemiological modeling. This paper presents a mathematical contribution to fight against COVID-19 using a compartmental SQEICRS model. This model takes into account five stages. In particular, the role of chronic diseases on the dynamique of COVID-19, is focused. A mathematical analysis of the model has been carried out, and shows that the model is well-posed in the biological and mathematical sense. Aspects such as existence, equilibrium points and their stability, the basic reproduction number R0and sensitivity anlysis have been discussed. Sensitivity analysis allowed us to identify the parameters which contribute to the spread of the disease, including the chronicity rate due to chronic diseases. The direction of disease propagation was also determined according to <I>R</I><sub>0</sub>. Finally, the numerical results with Matlab are in conformity with theoretical results.

In the milling process of thin wall workpiece, the more cutter flutes, the high metal remove ratio can be gotten. Milling forces with two-futes and four-flutes milling cutter were anlysised and compared using finite element method. The possibility and advantage of machining thin wall workpiece with four flutes milling cutter was introduced. The four flutes cutter can improve the metal remove ratio, and cutting force is more uniform in general.

In recent years, the need to expand the land area for infrastructure development, such as roads and streets near residential buildings, in urban areas in Vietnam has become more widespread. Such tendency leads to narrowing of the space available for further development thus the ground condition around existing buildings often need improvement. The foundations of existing buildings can no longer bear additional stresses. In such cases the foundation and the ground conditions need engineering solutions to provide geotechnical safety. The present paper presnts a numerical anlyses of soil nailing, to enhance the stability of the foundation of an existing building constructed on firm clay soil. The finite element method was empolyed to compute the stability of the foundation with/without incorporating soil nail reinforcements. Additionally, the analyses concern also the retaining wall construction to assure long-term performance of proposed scenarios. The numerical computation results indicate that the stability of the foundation improved by soil nailing was not enough to meet the ultimate limit state. The combination of a retaining wall supported by soil nails increased the factor of safety to a value considered sufficient. The settlements, as well as the horizontal displacements analyses proved the correctness of proposed solutions.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2017.
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A análise e desenvolvimento de perfis aerodinâmicos para operação em baixas velocidades têm ganhado importância recentemente devido à crescente utilização de VANTs (Veículos Aéreos Não Tripulados) e turbinas eólicas. Nessas aplicações, o número de Reynolds característico para o escoamento sobre a asa pode ser inferior a 3·105 e o escoamento pode sofrer separação na região laminar da camada limite, formando o que se conhece por bolhas de separação laminar. O principal objetivo deste trabalho é avaliar o comportamento das bolhas de separação laminar em um perfil aerodinâmico de alta sustentação por meio de simulações numéricas suportadas por medições em túnel de vento. Inicialmente, apresenta-se uma comparação entre os resultados previstos por quatro modelos de turbulência, sendo dois para escoamentos totalmente turbulentos (Spalart-Allmaras e SST k-?), e dois para escoamentos de transição (?-Re? e k-kL-?), usando o software FLUENT. Os modelos foram aplicados a um perfil Eppler 387, que foi escolhido por apresentar dados experimentais disponíveis e medidos em diferentes laboratórios, e a um perfil Selig 1223, por ser um perfil de alta sustentação e utilizado em aeronaves de baixa velocidade. Os resultados indicaram que, embora seja possível prever a evolução do coeficiente de sustentação para baixos ângulos de ataque usando qualquer um dos modelos, apenas os modelos de transição foram capazes de prever o surgimento da bolha de separação laminar, resultando em grandes diferenças no coeficiente de sustentação próximo ao ângulo de estol. Essas diferenças se tornaram particularmente relevantes para o perfil Selig 1223, que apresentou um ganho na sustentação máxima de 20 % movendo do Reynolds de 1·105 para 2·105. Em relação ao coeficiente de arrasto, os modelos de transição apresentaram uma diferença média de 10 % em relação às referências, enquanto que nos outros, essa diferença chegou a 40 % em alguns ângulos. Na sequência do trabalho, fabricou-se um perfil Selig 1223 instrumentado com tomadas de pressão em sua superfície, para medição do coeficiente de pressão ao longo de sua corda. Para visualizar o local da bolha de separação laminar, foi utilizado um óleo pigmentado. Os resultados mostraram boa concordância na previsão do coeficiente de pressão utilizando os modelos de transição e a observação com filme de óleo comprovou a posição e extensão da bolha de separação. Concluiu-se que a separação do escoamento na camada limite laminar foi a principal causa de estol no número de Reynolds de 1·105. Finalmente, estudou-se a possibilidade de eliminação da separação em regime laminar através da adição de um tubo de carbono à frente do bordo de ataque. Experimentalmente, verificou-se que, com a aplicação dessa técnica, o ângulo de estol em número de Reynolds de 1·105 aumentou de 10° para 20°. A técnica da visualização com óleo mostrou que a bolha é eliminada com o emprego do gerador de turbulência. Os modelos de transição forneceram boa comparação com as medições, sendo recomendado o seu uso nessas aplicações.
Abstract : The development and analysis of airfoils for low-speed operations have recently become important because of their vast use in UAVs (Unmanned Aerial Vehicle) and wind turbines. In these applications, the characteristic Reynolds number for the flow over the wing may be as low as 3·105 and separation may occur in the laminar region of the boundary layer, forming the so-called laminar separation bubbles (LSB). The main objective of this work is to evaluate the behavior of the LSBs in a high lifting airfoil by means of numerical simulations supported by measurements in wind tunnel. Primarily, a comparison of four turbulence models is given: two for fully-turbulent flows (Spalart-Allmaras e SST k-?), and two for transitional flows (?-Re? e k-kL-?), using FLUENT software. The models were initially used in an Eppler 387 airfoil, which was chosen due to the availability of experimental data obtained in different laboratories, and then in a Selig 1223, because it is a high lifting airfoil and used in low-speed aircrafts. Results indicated that, although it is possible to predict the development of the lift coefficient for low angles of attack using anyone of the models, only the transition-sensitive models were capable of predicting the LSBs, which resulted in large differences of the lift coefficient close to the region of stall. These differences became relevant for the S1223 airfoil, which presented a maximum lift coefficient difference of 20 % when comparing the Reynolds number cases of 1·105 and 2·105. Regarding drag coefficient in comparison to the references, transition-sensitive models showed an average difference of 10 %. Fully-turbulent models achieved maximum difference of 40 %. Following the work, a Selig 1223 wing was manufactured with pressure tapping holes on the surface to measure the pressure coefficient over it chord. In order to visualize the location of the laminar separation bubble, a pigmented oil was used. Results reported good agreement in predicting the pressure coefficient using the transition-sensitive models and the observations with oil film proved the position and extension of the LSBs. It was concluded that the separation in the laminar boundary layer was the main cause of stall in the Reynolds number of 1·105. Finally, it was considered the possibility of suppressing the laminar separation by installing a carbon fiber tube in front of the leading edge. Experimentally, it was verified that this technique provided an increase in the angle of stall from 10° to 20° at a Reynold number of 1·105. The oil visualization technique showed that the bubble is suppressed with the use of the turbulence generator. Altogether, transition-sensitive models provided results in better agreement with the experimental data. Their use is recommended in these applications.

Cette thèse porte sur le développement et l'analyse de méthodes numériques performantes pour l'approximation des solutions d'équations cinétiques collisionnelles éventuellement non linéaires. Ces équations apparaissent dans divers domaines tels que la physique, notamment dans l'étude des semi-conducteurs et de la dynamique des gaz. Elles apparaissent aussi en biologie dans la modélisation du mouvement de cellules dans un tissu. Ces modèles présentent un aspect multi-échelle. D'une part, on a une description mésoscopique (ou cinétique) qui donne l'évolution de la fonction de distribution des particules, molécules ou cellules. D'autre part, par un processus de moyennisation, on obtient l'échelle dite macroscopique (ou fluide) qui permet de suivre l'évolution de grandeurs physiques observables : les moments de la fonction de distribution. Ces derniers correspondent notamment à la densité, la vitesse moyenne et la température des particules considérées. Nous présentons dans ce manuscrit différentes façons de tirer partie de la dynamique fluide afin de construire et étudier des méthodes numériques efficaces pour l'échelle cinétique.Dans la première partie, nous explorons des méthodes de discrétisation visant à préserver la structure des équations continues. Nous commençons par introduire un schéma volumes finis implicite en temps pour un modèle cinétique de réaction non linéaire. Nous étudions le comportement en temps long de la solution discrète par une méthode d'hypocoercivité. Ensuite, nous examinons une méthode spectrale, basée sur des polynômes orthogonaux généraux, capable de préserver les moments de la solution, tout en assurant de bonnes propriétés de convergence.La seconde partie est consacrée à la conception de méthodes numériques visant à réduire le coût des simulations cinétiques. Pour ce faire, nous étudions deux approches exploitant l'évolution des moments de l'inconnue. La première, une méthode dite hybride cinétique/fluide, consiste à adopter dynamiquement et localement en espace une description fluide moins coûteuse du système au lieu de la description cinétique plus onéreuse. La seconde approche repose également sur l'utilisation d'un modèle fluide, mais cette fois-ci pour accélérer les itérations temporelles de la méthode. Nous proposons ici un prototype de méthode pararéelle multi-échelle, utilisant un modèle fluide comme solveur grossier et un modèle cinétique comme solveur fin
This thesis focuses on the development and analysis of efficient numerical methods for approximating solutions of potentially nonlinear kinetic collisional equations. These equations arise in various fields such as physics, notably in the study of semiconductors and gas dynamics. They also appear in biology in modeling the movement of cells within tissue. These models exhibit a multiscale aspect where there is, on one hand, a mesoscopic (or kinetic) description that gives the evolution of the distribution function of particles, molecules, or cells. On the other hand, through a process of averaging, we obtain the so-called macroscopic (or fluid) scale which allows to track the evolution of observable physical quantities: the moments of the distribution function. These moments correspond to the density, average velocity, and temperature of the considered particles. Throughout this manuscript, we present various ways to take advantage of fluid dynamics to construct and study efficient numerical methods for the kinetic scale.In the first part, we explore discretization methods aiming to preserve the structure of continuous equations. We begin by introducing an implicit finite volume scheme for a nonlinear reaction kinetic model. We study the long-time behavior of the discrete solution using hypocoercivity methods. Then, we examine a spectral method, based on general orthogonal polynomials, capable of preserving the moments of the solution while ensuring good convergence properties.The second part is dedicated to the design of numerical methods aiming to reduce the cost of kinetic simulations. To do this, we study two approaches exploiting the evolution of the unknown's moments. The first, a hybrid kinetic/fluid method, involves adopting dynamically and locally in position a less costly fluid description of the system instead of the more expensive kinetic one. The second approach also relies on the use of a fluid model, but this time to accelerate the temporal iterations of the method. Here, we propose a prototype of a multiscale parareal method, using a fluid model as a coarse solver and a kinetic model as a fine solver

A major challenge during the design process of a modern low aspect ratio high speed axial compressor is to find rotor blade geometries that meet both, aerodynamic and mechanical requirements. This paper deals with the mechanical design of a transonic compressor blade. In order to meet the mechanical requirements in a short development time, new methods were used: A numerical optimization tool and an optical blade vibration measurement method: The numerical resonance tuning took advantage of a semi-automatic optimization technique, based on a Finite Element vibration anlysis tool. The intention was to find a geometry which has no critical resonances (with fundamental engine orders) within the operation range. To verify the calculated blade natural frequencies and eigen-values standard shaker tests using a laser holography system were carried out. Blades under g-load in the running compressor were investigated with an in-house developed vibration measurement system. This system is able to measure frequencies and amplitudes of the rotor blade vibrations without blade instrumentation but small optical probes, mounted in the compressor casing. The measured resonance points are in good agreement with the predictions. All amplitudes are far below the blade fatigue limits.

The paper presents not a nonlinear static research but dynamic anlysis for an electrically actuated piezoelectric laminated micro-beam. On the basis of the Euler-Bernoulli hypothesis, and the responses under electric force [a purely direct current and a combined current composed of a direct current and an alternating current] are investigated, respectively. By using the Taylor series expansion, a set of governing equations of nonlinear integro-differential type is derived. Then using the Galerkin method and the fourth-order Runge-Kutta method, an analytical is presented. Numerical examples show, when a purely DC is applied, there exist an instantaneous pull-in voltage, under the combined current, not only the direct current voltage and the amplitude of the alternating current voltage can make the piezoelastic laminated microbeam collapse, but also the different voltage parameter of it can affect the pull-in phenomenon.