In recent years, the desperate need for reliable clean and relatively small power demand has emerged for edge-of-grid or off-grid regions to keep pace with development demands. A salient technology that has gained much attention for this purpose is the Small Modular Reactors, i.e., SMRs. SMRs differ from conventional Nuclear Power Plants (NPPs) in many aspects, specifically the enclosing structure of the reactor. The burial depth of the SMR structure is expected to reach great depths. For example, the substructure depth reaches 30 m in the SMR design proposed by NuScale (NuScale Power, 2020). Consequently, seismic analysis of deeply embedded structures with a relatively small footprint has been identified as one of the challenges to the safe implementation of SMR technology (DIS-16-04, 2016). Such structures are expected to be more sensitive to surface wave propagation and the seismic interaction with nearby substructures and nonstructural elements such as pipelines. This dissertation develops analytical and numerical methods to analyze the seismic earth pressure exerted on the SMR substructure by considering the effects of seismic surface waves, structure-soil-structure interaction (SSSI), and the interaction with nearby pipelines. The three-dimensional wave propagation theory is employed in the analysis. Solutions for the earth pressure induced by Rayleigh waves are obtained for substructures deeply embedded into homogeneous or multilayered soil profiles. In addition, the effect of thin soil layer (stiff or soft) soils in a soil profile is investigated in the presence of Rayleigh waves. Furthermore, additional earth pressure due to SSSI is examined, and a simplified procedure is proposed based on the three-dimensional wave propagation theory and a guided flow chart to track seismic wave interference. The SSSI analysis yields solutions for the optimal distance between substructures corresponding to the minimum SSSI in new designs. The interaction between substructures and nearby pipelines is explored numerically using the Spectral Element Method. SPECFEM2D software is adopted to perform the analysis, where the three-dimensional wave propagation is successfully implemented. Based on the analysis for pipelines with different configurations, general conclusions are drawn regarding the additional earth pressure on substructures and pipelines based on a comprehensive parametric study of various parameters. In addition, this research also provides an approach to determine the backfill configuration and the selection of backfill materials, which could minimize the seismic amplitudes transmitted to substructures. / Thesis / Doctor of Philosophy (PhD) / Small Modular Reactors (SMRs) are the cornerstone of recent developments in the nuclear industry. However, the SMRs technology faces several safety-related challenges, which includes the earthquake hazards related to the large embedment depth of the enclosing structure. In particular, the major concerns are about the risks related to seismic surface waves as well as the seismic interaction between nearby structural and non-structural elements (e.g., pipelines). The thesis addressed these major concerns by developing analytical and numerical methods to complement the analysis for the integrity of SMRs with sufficient seismic resistance. The solutions are verified and benchmarked using data in the literature. Future researches are suggested to further improve seismic analysis of SMRs.

Unbounded domains often appear in engineering applications, such as acoustic or elastic wave radiation from a body immersed in an infinite medium. To simulate the unboundedness of the domain special boundary conditions have to be imposed: the Sommerfeld radiation condition. In the present work we focused on steady-state wave propagation. The objective of this research is to obtain accurate prediction of phenomena occurring in exterior acoustics and elastodynamics and ensure the quality of the solutions even for high wavenumbers. To achieve this aim, we develop higher-order domain-based schemes: Spectral Element Method (SEM) coupled to Dirichlet-to-Neumann (DtN ), Perfectly Matched Layer (PML) and Infinite Element (IEM) methods. Spectral elements combine the rapid convergence rates of spectral methods with the geometric flexibility of the classical finite element methods. The interpolation is based on Chebyshev and Legendre polynomials. This work presents an implementation of these techniques and their validation exploiting some benchmark problems. A detailed comparison between the DtN, PML and IEM is made in terms of accuracy and convergence, conditioning and computational cost.

The main purpose of this study is to develop a flow solver that employs triangular grids to solve two-dimensional, viscous, laminar, steady, incompressible flows. The flow solver is based on Least Squares Spectral Element Method (LSSEM). It has p-type adaptive mesh refinement/coarsening capability and supports p-type nonconforming element interfaces. To validate the developed flow solver several benchmark problems are studied and successful results are obtained. The performances of two different triangular nodal distributions, namely Lobatto distribution and Fekete distribution, are compared in terms of accuracy and implementation complexity. Accuracies provided by triangular and quadrilateral grids of equal computational size are compared. Adaptive mesh refinement studies are conducted using three different error indicators, including a novel one based on elemental mass loss. Effect of modifying the least-squares functional by multiplying the continuity equation by a weight factor is investigated in regards to mass conservation.

Die Dissertation behandelt methodische und algorithmische Aspekte der Spektralelementemethode zur räumlichen Diskretisierung partieller Differentialgleichungen. Die Weiterentwicklung einer symmetriebasierten Faktorisierung ermöglicht effiziente Operatoren für Tetraederelemente. Auf Grundlage einer umfassenden Leistungsanalyse werden Engpässe in der Implementierung der Operatoren identifiziert und durch algorithmische Modifikationen der Methode eliminiert.

Submitted by Sanderson Manoel Da Conceição (enders83@yahoo.com.br) on 2018-08-24T00:09:53Z No. of bitstreams: 1 TeseDR_Sanderson.pdf: 5806318 bytes, checksum: 51410134afd7ae86d0783074d6012e88 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-08-24T17:09:49Z (GMT) No. of bitstreams: 1 conceicao_sm_dr_ilha.pdf: 5957405 bytes, checksum: 16cab2d9c84f81cd3cd4ff0b9fa36219 (MD5) / Made available in DSpace on 2018-08-24T17:09:49Z (GMT). No. of bitstreams: 1 conceicao_sm_dr_ilha.pdf: 5957405 bytes, checksum: 16cab2d9c84f81cd3cd4ff0b9fa36219 (MD5) Previous issue date: 2016-12-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A ideia central deste trabalho é utilizar o método dos Elementos Espectrais (SEM, do inglês Spectral Element Method) para aplicações de controle ativo de vibrações e monitoramento da integridade estrutural (SHM, do inglês Structural Health Monitoring). Diversos trabalhos têm abordado estes tópicos de forma independente. No entanto, para aplicações reais de engenharia, utilizar os mesmos atuadores, sensores e sistemas de aquisição de dados para controle e monitoramento pode reduzir investimentos e simplificar processos. Por esta motivação, este trabalho apresenta um estudo de modelos espectrais para estruturas do tipo viga considerando aplicações de controle de vibrações e monitoramento da integridade estrutural. Na modelagem são considerados os modelos de vigas de Euler-Bernoulli e Timoshenko, além de transdutores piezelétricos acoplados. A técnica de controle clássico PID (Proporcional, Integral, Derivativo) é explorada e uma nova modelagem é proposta para se considerar técnicas modernas de controle por realimentação de estados na formulação espectral. Em particular, discute-se o controlador LQR (do inglês, Linear Quadratic Regulator), no entanto, a metodologia permite se considerar outras técnicas de controle por realimentação baseada na representação no espaço de estados. Também, especificamente para monitoramento estrutural, no presente trabalho de tese apresenta-se uma discussão sobre índices de detecção de danos. Índices de detecção calculados a partir de sinais experimentais têm sido amplamente utilizados em trabalhos da literatura de SHM. No entanto, pouco tem sido esclarecido sobre seus comportamentos em função das características estruturais e dos danos. Neste sentido, o presente trabalho apresenta uma discussão do comportamento de índices baseados na norma H2, norma H∞ e no CCDM (Correlation coefficient deviation metric), para duas faixas de frequência, em função da severidade do dano e quantidade de amortecimento no sistema. Os resultados obtidos indicam que a formulação por Elementos Espectrais é adequada para viabilizar os projetos simultâneos de um controlador de vibrações e um sistema de monitoramento estrutural utilizando os mesmos equipamentos e simplificando análises ao se utilizar um único modelo dinâmico do sistema. / The main idea of this thesis is to use the Spectral Element Method (SEM), in applications of Active Vibration Control (AVC) and Structural Health Monitoring (SHM). These two topics have been approached in several works, but in an independent way. However, for real engineering applications, to use the same actuators, sensors and data acquisition systems to active control and structural monitoring can reduce the costs and simplify processes. For this reason, this thesis presents a study of spectral models for beam-like structures considering applications of vibration control and structural health monitoring. The Euler-Bernoulli and Timoshenko beam theories are used in the spectral modelling and the piezelectric transducers bonded in the structures are also considered. A classical control technique, PID (Proportional, Integral, Derivative) is explored and a new modelling approach to consider modern control methods of state feedback is proposed in spectral formulation. In particular, the Linear Quadratic Regulator (LQR) is discussed, however, this methodology allows for any other state feedback control techniques based in state space representation. Also, specifically for structural monitoring, is presented a discussion about damage detection indices. Detection indices computed from experimental data have been widely used in SHM studies. However, little has been clarified about their behaviours due to structural characteristics and damages. In this context, this work presents a discussion of the behaviour of indices based in the H2 norm, H∞ norm and CCDM (Correlation coefficient deviation metric), for two frequency ranges, depending on the severity of damage and amount of damping in the system. The obtained results indicate that the spectral element formulation is suited to enable the simultaneous design of a vibration controller and a structural monitoring system using the same data acquisition systems and simplifying analysis when using just one dynamic model of the system.

Orientador: Vicente Lopes Junior / Resumo: A ideia central deste trabalho é utilizar o método dos Elementos Espectrais (SEM, do inglês Spectral Element Method) para aplicações de controle ativo de vibrações e monitoramento da integridade estrutural (SHM, do inglês Structural Health Monitoring). Diversos trabalhos têm abordado estes tópicos de forma independente. No entanto, para aplicações reais de engenharia, utilizar os mesmos atuadores, sensores e sistemas de aquisição de dados para controle e monitoramento pode reduzir investimentos e simplificar processos. Por esta motivação, este trabalho apresenta um estudo de modelos espectrais para estruturas do tipo viga considerando aplicações de controle de vibrações e monitoramento da integridade estrutural. Na modelagem são considerados os modelos de vigas de Euler-Bernoulli e Timoshenko, além de transdutores piezelétricos acoplados. A técnica de controle clássico PID (Proporcional, Integral, Derivativo) é explorada e uma nova modelagem é proposta para se considerar técnicas modernas de controle por realimentação de estados na formulação espectral. Em particular, discute-se o controlador LQR (do inglês, Linear Quadratic Regulator), no entanto, a metodologia permite se considerar outras técnicas de controle por realimentação baseada na representação no espaço de estados. Também, especificamente para monitoramento estrutural, no presente trabalho de tese apresenta-se uma discussão sobre índices de detecção de danos. Índices de detecção calculados a partir de sinais experimen... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The main idea of this thesis is to use the Spectral Element Method (SEM), in applications of Active Vibration Control (AVC) and Structural Health Monitoring (SHM). These two topics have been approached in several works, but in an independent way. However, for real engineering applications, to use the same actuators, sensors and data acquisition systems to active control and structural monitoring can reduce the costs and simplify processes. For this reason, this thesis presents a study of spectral models for beam-like structures considering applications of vibration control and structural health monitoring. The Euler-Bernoulli and Timoshenko beam theories are used in the spectral modelling and the piezelectric transducers bonded in the structures are also considered. A classical control technique, PID (Proportional, Integral, Derivative) is explored and a new modelling approach to consider modern control methods of state feedback is proposed in spectral formulation. In particular, the Linear Quadratic Regulator (LQR) is discussed, however, this methodology allows for any other state feedback control techniques based in state space representation. Also, specifically for structural monitoring, is presented a discussion about damage detection indices. Detection indices computed from experimental data have been widely used in SHM studies. However, little has been clarified about their behaviours due to structural characteristics and damages. In this context, this work presents a d... (Complete abstract click electronic access below) / Doutor

Ce travail de thèse présente une contribution à l'analyse des effets dynamiques des interactions sol-structure sur le mouvement sismique du sol et des bâtiments. Il repose essentiellement sur une approche numérique qui utilise la méthode des éléments spectraux et une représentation simplifiée des bâtiments par des modèles « par blocs » dont la réponse est ajustée par comparaison à plusieurs jeux de données expérimentales. L'objectif principal est de définir un cadre permettant une modélisation réaliste des effets macroscopiques d'interactions sol-structure et structure-sol-structure dans le calcul du mouvement du sol et des bâtiments. Après une présentation du cadre théorique de l'interaction sol-structure et des principales méthodes utilisées pour sa modélisation, divers exemples, comprenant le site Euroseistest / Volvi (Grèce), les tours de l'Ile Verte à Grenoble et Anchorage (Alaska), sont étudiés en détail pour identifier les difficultés de modélisation et proposer une procédure d'ajustement des paramètres des modèles par blocs au comportement réel des structures. Cela inclue une discussion sur les caractéristiques dynamiques les plus importantes à reproduire (fréquence de résonance, amortissement et mouvement de bascule) et sur la façon d'adapter les propriétés fictives des modèles par blocs afin de reproduire le comportement dynamique de structures dont les propriétés mécaniques varient fortement sur des échelles spatiales beaucoup plus faibles. Une attention particulière est consacrée à la modélisation par blocs de bâtiments ayant des propriétés dynamiques non-isotropes et des réponses mêlant flexion et cisaillement (de type « poutre de Timoshenko ») via l'introduction de propriétés hétérogènes au sein des éléments spectraux, et sans modification de la section géométrique globale. Ce travail comprend également une comparaison détaillée des différences entre modèles 2D et 3D et une discussion de leur origine physique : pour des bâtiments ayant des rapports d'aspect (longueur sur largeur) inférieurs à 6, les modèles 2D sont non-conservatifs, dans le sens où ils surestiment de façon significative l'amortissement et le mouvement de bascule. Cette thèse comprend également une grande partie sur les effets de l'interaction de structure à structure au travers du sol. De nombreuses situations sont étudiées, depuis le cas de 2 bâtiments à 2D ou 3D jusqu'au cas de zones densément urbanisées en 3D, avec divers types d'excitations (« pull-out », source superficielle ou profonde). Les effets de la distance inter-bâtiments sont étudiés dans diverses gammes de fréquence. La tendance générale obtenue est une diminution du mouvement du sol et des bâtiments autour de la fréquence de résonance fondamentale et une augmentation autour de la fréquence du premier harmonique. Des effets significatifs de réduction de la sollicitation sismique apparente sont obtenus en raison de l'effet de bouclier joué par les bâtiments vis à vis des ondes de surface. / This work is a contribution to investigations on the effects of dynamic soil-structure interaction on the seismic motion of both ground surface and buildings. It is based mainly on a numerical approach using the spectral element method and a simplified representation of buildings with "block models", calibrated however on a comparison with various sets of instrumental data. One of the main goals is to set the frame for a relevant macroscopic modeling of SSI and SSSI effects on ground and structural dynamic response. After a presentation of the background theoretical framework of soil-structure interaction and the main modeling approaches, various examples from Euroseistest / Volvi (Greece), Grenoble Ile Verte towers (France) and Anchorage (Alaska) are investigated in detail to identify the main modeling issues and to propose a procedure to best tune the model and its parameters to the actual behavior. It includes a discussion on the main relevant macroscopic dynamic characteristics to fit (frequency, damping and rocking ratio), and on the way to use "block models", i.e., models consisting of blocks full of fictitious material, to satisfactorily reproduce the macroscopic response of actual buildings having highly variable slenderness ratios, with frames or shear walls. A special attention is devoted to the "block-modeling" of buildings with non-symmetrical dynamic properties and Timoshenko beam like behavior, through the introduction of material heterogeneities within the spectral elements of block models, while keeping unchanged the geometrical cross-section. It also includes a thorough comparison on the major differences between 2D and 3D models and their physical origins: for long buildings with aspect ratios (length over width ratio) lower than 6, 2D models are shown un-conservative, as they tend to significantly overestimate the damping and rocking ratios. This work also includes a large part on the effects of Structure-to-Structure interaction through the soil. Various cases are considered, from the 2 building case in 2D and 3D geometries to an idealized, densely urbanized 3D area, with various types of excitations (pull-out, surface or deep source). Effects of inter-building distance and frequencies are investigated. The general trend is a reduction of the ground and building motion around the fundamental frequency, with however opposite effects for the first higher mode. The reduction effects are found of particular importance because of the shielding effects of building clusters for surface waves.

La modélisation numérique de la propagation des ondes sismiques fait partie des études principales sur le calcul du mouvement sismique basées sur de différents schèmes numériques. La prise en compte du comportement nonlinéaire du sol est consideré désormais très important afin de pouvoir calculer la réponse du milieu cohéremment aux observations sous les sollications sismiques très fortes. En plus, le paramètre de pression interstitielle, qui pourrait emmener le sol aux phénomènes de liquéfaction, devient très important pour les sols saturés. Dans cette étude, dans un premier temps, la propagation des ondes sismiques est modelisée sur une composante (1C) dans les milieux linéaires et nonlinéaires en utilisant la méthode numérique des éléments spéctraux. Les rhéologies viscoélastique et nonlinéaire sont implementées par le méthode de technique des variables de mémoire et le modèle élastoplastique d’Iwan, respectivement. Ensuite, le modèle 1D - trois composantes (3C) est développé et une comparaison préalable sur l’effet de la considération des approches 1C et 3C est faite. L’effet de pression interstitielle est implementé dans le code 1D-3C et le site américain Wildlife Refuge Liquefaction Array (WRLA), qui a été frappé par le séisme de Superstition Hills en 1987 est étudié. Le changement de la réponse du sol sous les différents hypothèses de rhéologie du sol et de mouvement d’entrée est étudié. Le mouvement calculé est noté d’être amplifié pour les basses fréquences et atténué pour les hautes fréquences en raison de l’excès de pression interstitielle dans les sols liquéfiables. Par ailleurs, le sol devient plus nonlinéaire sous le chargement triaxial dans l’approche 3C et plus dilatant dû à la nonlinéarite élevée. En dépit de la similitude entre les accélérations et les vitesses en surface des approches 1C et 3C, une importante différence dans le déplacement en surface entre les deux approches est notée. Les analyses sont répétées pour deux sites japonais Kushiro Port et Onahama Port, qui ont été influencés par le séisme de Kushiro-Oki en 1993 et le séisme de la côte Pacifique de Tohoku en 2011, respectivement. Il a été montré que les changements apportés par la nonlinéarite ne sont pas identiques dans toute la gamme de fréquence concernée et l’influence du comportement des sols non-cohésives sur la propagation des ondes sismiques dépend fortement des propriétés du modèle et des conditions de chargement. Dernièrement, le code SEM est avancé en 2D en considerant les mêmes modèles implementés en 1D-3C pour la nonlinéarite du sol et les effets de pression interstitielle. Le code SEM 2D est mis en application dans un modèle de bassin sédimentaire dont la géometrie est assymmétrique et le profile du sol est composé des couches possédant différentes propriétés nonlinéaires. Le modèle est étudié par les analyses totale et effective pour les propagation des ondes P-SV et SH. La differentiation du mouvement calculé en surface est très importante sous les chargements avec les signaux d’entrée synthétique et réel. L’analyse effective résulte en plus de déformations dans les couches superficielles par rapport à l’analyse totale.De plus, la durée de propagation des ondes augmente à l’intérieur du bassin et les reflections aux frontières de bassin-rocher entraînent plus de nonlinéarite dans les coins du bassin. Cette thèse révèle la possibilité de la modélisation du comportement nonlinéaire du sol en prenant en compte l’effet de pression interstitielle dans les études de la propagation des ondes sismiques en couplant les modèles différents avec la méthode des éléments spéctreaux. Ces analyses contribuent à l’identification et la compréhension des phénomènes majeures qui se déroulent dans les couches superficielles en respectant les conditions locales et les mouvements d’entrées, ce quirend ce travail très important pour les études spécifiques de sites / Numerical modeling of seismic wave propagation has been a major topic on ground motion studies using a number of different numerical integration schemes. The consideration of soil nonlinearity holds an important place in order to achieve simulations consistent with real observations for strong seismic shaking. Additionally, in the presence of strong ground motion in saturated soils, pore pressure becomes an important parameter to take into account for related phenomena such as flow liquefaction and cyclic mobility. In this study, first, one component (1C) - seismic wave propagation is modeled in linear and nonlinear media in 1D based on the spectral element numerical method. Viscoelastic and nonlinear soil rheologies are implemented by use of the memory variables technique and Iwan’s elastoplastic model, respectively. Then, the same study is extended to a 1D - three component (3C) model and a preliminary comparison on the effect of using 1C and 3C approaches is made. Then, the influence of excess pore pressure development is included in the 1D-3C model and the developped numerical model is applied to realistic case on the site of Wildlife Refuge Liquefaction Array (USA) which is affected by the 1987 Superstition Hills event. The ground motion modification for different assumptions of the soil rheology in the media and different input motions is studied. The calculated motion is found to be amplified on low frequency and damped in high frequency range due to excess pore pressure development. Furthermore, the soil is found to be more nonlinear under triaxial loading in 3C approach and more dilative due to higher nonlinearity. Despite the similitude in surface acceleration and velocity results, significant differences in surface displacement results of 1C and 3C approaches are remarked. Similar analyses are performed on two Japanese sites Kushiro Port and Onahama Port, which are influenced by the 1993 Kushiro-Oki and the 2011 off the Pacific coast of Tohoku earthquakes, respectively. It has been shown that the nonlinearity-related changes are not homogeneous all over the concerned frequency band and the influence of cohesionless soil behavior on wave propagation is highly dependent on model properties and loadingconditions. Lastly, the 2D SEM code is developped by taking into account soil nonlinearity and pore pressure effects similary to 1D-3C SEM code. The developped 2D SEM code is applied to a 2D sedimentary basin site where the basin geometry is asymmetrical and soil profile consists of layers with different nonlinearity properties. Total and effective stress analyses are performed on the 2D basin for P-SV and SH zave propagation models. The calculated surface motion is shown to differ significantly under synthetic and realistic input motion loading conditions and the resultant deformation in superficial layers is found to be very high in effective stress analysis compared to total stress analysis. Also, wave propagation takes longer time inside basin media and the reflections on bedrock-basin boundaries lead the soil in basin edges to higher nonlinearity. This study shows the possibility of modeling nonlinear soil behavior including pore pressure effects in seismic wave propagation studies by coupling different models with spectral element method. These analyses help identifying and understanding dominant phenomena occurring in superficial layers, depending on local conditions and input motions. This is of great importance for site-specific studies

La ecuación de la difusión neutrónica describe la población de neutrones de un reactor nuclear. Este trabajo trata con este modelo para reactores nucleares con geometría hexagonal. En primer lugar se estudia la ecuación de la difusión neutrónica. Este es un problema diferencial de valores propios, llamado problema de los modos Lambda. Para resolver el problema de los modos Lambda se han comparado diferentes métodos en geometrías unidimensionales, resultando como el mejor el método de elementos espectrales. Usando este método discretizamos los operadores en geometrías bidimensiones y tridimensionales, resolviendo el problema algebraica de valores propios resultante con el método de Arnoldi. La distribución de neutrones estado estacionario se utiliza como condición inicial para la integración de la ecuación de la difusión neutrónica dependiente del tiempo. Se utiliza un método de Euler implícito para integrar en el tiempo. Cuando un nodo está parcialmente insertado aparece un comportamiento no físico de la solución, el efecto ``rod cusping'', que se corrige mediante la ponderación de las secciones eficaces con el flujo del paso de tiempo anterior. Cuando la solución de los sistemas algebraicos que surgen en el método hacia atrás, un método de Krylov se utiliza para resolver los sistemas resultantes, y diferentes estrategias de precondicionamiento se evalúan se. La primera consiste en el uso de la estructura de bloque obtenido por los grupos de energía para resolver el sistema por bloques, y diferentes técnicas de aceleración para el esquema iterativo de bloques y un precondicionador utilizando esta estructura de bloque se proponen. Además se estudia un precondicionador espectral, que hace uso de la información en un subespacio de Krylov para precondicionar el siguiente sistema. También se proponen métodos exponenciales de segundo y cuarto orden integrar la ecuación de difusión neutrónica dependiente del tiempo, donde la exponencial de la matriz del sistema tiene qu / González Pintor, S. (2012). Approximation of the Neutron Diffusion Equation on Hexagonal Geometries [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17829 / Palancia

The purpose of a multi-element high lift device is to increase lift dramatically while controlling the stall limit. The fluid flow over a multi-element high lift device has been explored widely both experimentally and numerically at high Reynolds numbers (O(10^6 )). The numerical simulations use turbulence models and hence details of the flow are not yet available. Low Reynolds number (O(10^4 )) flows over high lift devices have not been explored until recently. These lower Reynolds number flows have applications in the development of small aerial vehicles. The present work discusses both two-dimensional and three-dimensional direct numer- ical simulations of fluid flow over a 30P30N three-element high lift system using a high-order spectral element method code, Nek5000, that solves the incompressible Navier-Stokes equations. The intricate geometry of the multi-element device poses a challenge for the high-order spectral element method. We study the complex flow physics in the slat cove region and the wake/shear layer interaction over a 30P30N three-element high lift device. The targeted cases are at Reynolds num- bers based on stowed chord lengths (Rec ) of 8.32 × 10^3 , 1.27 × 10^4 , and 1.83 × 10^4 at angle of attack of 4. A critical interval for Rec has previously been found between 1.27 × 10^4 and 1.38 × 10^4 in experiments. This divides the flow into two types: when Rec is below the critical interval, no roll-up is observed in the slat cove and Görtler vortices dominate the slat wake; however when the Rec is above the critical interval, a roll-up is observed in the slat cove and co-existence of streamwise and spanwise vortices is confirmed in the slat wake. We confirm the presence of the critical interval from the simulations performed at three values of Rec . Lift and drag analysis is provided along with pressure coefficient plots for each element of the multi-element airfoil. Different vortical structures are also identified in the transition of flow from two dimensions to three dimensions. The relevant validation is performed with the available experimental data.