Cristiano S. de Aguiar

Bio: Cristiano S. de Aguiar is an academic researcher from Federal University of Rio de Janeiro. The author has contributed to research in topics: Shear strength (soil) & Contact area. The author has an hindex of 3, co-authored 6 publications receiving 79 citations.

Undrained Load Capacity of Torpedo Anchors Embedded in Cohesive Soils

Abstract: This paper presents a numerical based study on the undrained load capacity of a typical torpedo anchor embedded in a purely cohesive isotropic soil using a three-dimensional nonlinear finite element model. In this model, the soil is simulated with solid elements capable of representing its nonlinear physical behavior and the large deformations involved. The torpedo anchor is also modeled with solid elements, and its geometry is represented in detail. Moreover, the anchor-soil interaction is addressed with contact finite elements that allow relative sliding with friction between the surfaces in contact. A number of analyses are conducted in order to understand the response of this type of anchor when different soil undrained shear strengths, load directions, and number and width of flukes are considered. The results obtained indicate two different failure mechanisms: The first one involves significant plastic deformation before collapse and, consequently, mobilizes a great amount of soil; the second is associated with the development of a limited shear zone near the edge of the anchor and mobilizes a small amount of soil. The total contact area of the anchor seems to be an important parameter in the determination of its load capacity, and, consequently, the increase in the undrained shear strength and the number of flukes and/or their width significantly increases the load capacity of the anchor.

Door crossing and state identification using robotic vision

Abstract: O presente relatorio tecnico trata de um dos projetos realizados no Laboratorio de Controle – CONTROLAB do Nucleo de Computacao Eletronica – NCE da Universidade Federal do Rio de Janeiro – UFRJ, nos anos de 2004 e 2005. Este projeto e voltado para a implementacao de um robo autonomo AGV (Autonomous Vehicle Guide) para navegar em ambientes internos, tais como hospitais, escritorios, residencias e etc. Especializado na area de visao computacional, O trabalho apresenta um novo algoritmo 3D para visao robotica, utilizado para identificacao automatica do estado de portas, sem quaisquer informacoes previas sobre o ambiente, tais como mapas, localizacao de obstaculos, iluminacao e etc. As proprias caracteristicas das portas que influenciariam na decisao do robo sobre a identificacao de seu estado, tambem nao ignoradas, tais como textura, cor, dimensoes. Publicado no 8th IFAC International Sysmposium on Robot Control (SYROCO 2006), o trabalho apresentou a aplicacao da Transformada de Hougth em imagens capturada pela visao robotica. As coordenadas de Hougth apresentavam entao a localizacao das arestas das portas e a analise de corelacao cruzada das quinas encontradas, nos davam a configuracao do estado da porta (aberta, fechada, entre-aberta). Com os resultados obtidos, a navegacao do robo autonomo se tornava mais segura, vez que os riscos de colisao eram minimizados. A navegacao utilizando visao 3D, com processamento em tempo real, tambem reduzia o risco de colisao com objetos dinamicamente posicionados no ambiente. Na primeira parte deste documento, apresentamos o artigo publicado em (SYROCO 2006). Na segunda parte, apresentamos alguns dos resultados experimentais obtidos durante a realizacao do projeto.

Undrained Load Capacity of Torpedo Anchors in Cohesive Soils

Abstract: This paper presents a numerical based study on the undrained load capacity of a typical torpedo anchor embedded in a purely cohesive isotropic soil using a three-dimensional nonlinear finite element (FE) model. In this model, the soil is simulated with solid elements capable of representing its nonlinear physical behavior as well as the large deformations involved. The torpedo anchor is also modeled with solid elements and its complex geometry is represented. Moreover, the anchor-soil interaction is addressed with contact finite elements that allow relative sliding with friction between the surfaces in contact. Various analyses are conducted in order to understand the response of this type of anchor when different soil undrained shear strengths, load directions as well as number and width of flukes are considered. The obtained results point to two different failure mechanisms: one that mobilizes a great amount of soil and is directly related to its lateral resistance; and a second one that mobilizes a small amount of soil and is related to the vertical resistance of the soil. Besides, the total contact area of the anchor seems to be an important parameter in the determination of its load capacity and, consequently, the increase of the undrained shear strength and the number of flukes and/or their width significantly increases the load capacity of the anchor.Copyright © 2009 by ASME

Numerical Simulation of Installed Torpedo Anchors Embedded in Cohesive Soil

Abstract: Torpedo anchors have proven to be one of the most important alternatives for mooring systems, especially in Brazilian offshore fields Their installation involves many hydrodynamic and soil-structure interaction aspects and, therefore, their vertical stability cannot be always assured This often results, after their installation, in an inclination between the anchor and a vertical axis called tilt angle The traditional approach to assess the holding capacity of torpedo anchors relies on the hypothesis that the relative angle between the load direction and the axis of the anchor may be used in conjunction with a finite element model in which a perfectly vertical anchor is considered In this work, this assumption is discussed A parametric study in which four different tilt angles are combined to various load inclinations was conducted The study relied on a previously proposed FE model The results obtained indicate that the use of the traditional approach is safe for relative angles higher than 40° and lower than 140° For other angles, the approach leads to values slightly higher than those predicted with the direct consideration of the tilt angleCopyright © 2011 by ASME

Comparison Between Finite Element Model and an Artificial Neural Networks Procedure for Riser Analysis

Abstract: As exploitation activities moves into fields located in deep water, the industry has been addressing studies aiming at concepts of offshore systems that reduce the influence of environmental loads on risers. The Buoy Support Riser (BSR) system is one of these new proposed concepts. The BSR is composed by a subsurface tethered buoy, where flexible jumpers connect the Floating Production Unit (FPU) to the BSR and Steel Catenary Risers (SCRs). Due to its complexity and non-linearity, this offshore system requires a highly refined finite element model for dynamic analysis, which demands a high computational cost. In order to increase feasibility of the analysis it is proposed a low computational cost methodology based on Artificial Neural Networks (ANN). This work aims to develop a program to train an ANN to predict the jumpers’ dynamic tension from FPU motions without running the finite element model for every time step. In this way, the purpose is to find results as reliable as those achieved in a dynamic analysis with a finite element model. Statistical parameters will be used for this comparison.Copyright © 2015 by ASME

Semantic 3D Object Maps for Everyday Manipulation in Human Living Environments

Abstract: Environment models serve as important resources for an autonomous robot by providing it with the necessary task-relevant information about its habitat. Their use enables robots to perform their tasks more reliably, flexibly, and efficiently. As autonomous robotic platforms get more sophisticated manipulation capabilities, they also need more expressive and comprehensive environment models: for manipulation purposes their models have to include the objects present in the world, together with their position, form, and other aspects, as well as an interpretation of these objects with respect to the robot tasks. The dissertation presented in this article (Rusu, PhD thesis, 2009) proposes Semantic 3D Object Models as a novel representation of the robot’s operating environment that satisfies these requirements and shows how these models can be automatically acquired from dense 3D range data.

Autonomous door opening and plugging in with a personal robot

Abstract: We describe an autonomous robotic system capable of navigating through an office environment, opening doors along the way, and plugging itself into electrical outlets to recharge as needed. We demonstrate through extensive experimentation that our robot executes these tasks reliably, without requiring any modification to the environment. We present robust detection algorithms for doors, door handles, and electrical plugs and sockets, combining vision and laser sensors. We show how to overcome the unavoidable shortcoming of perception by integrating compliant control into manipulation motions. We present a visual-differencing approach to high-precision plug-insertion that avoids the need for high-precision hand-eye calibration.

Recent advances in offshore geotechnics for deep water oil and gas developments

Abstract: The paper presents an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water. Typically the seabed in deep water comprises soft, lightly overconsolidated, fine grained sediments, which must support a variety of infrastructure placed on the seabed or anchored to it. A particular challenge is often the mobility of the infrastructure either during installation or during operation, and the consequent disturbance and healing of the seabed soil, leading to changes in seabed topography and strength. Novel aspects of geotechnical engineering for offshore facilities in these conditions are reviewed, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seabed; and submarine slides and their impact on infrastructure. Example results from sophisticated physical and numerical modelling are presented.

Planning for autonomous door opening with a mobile manipulator

Abstract: Computing a motion that enables a mobile manipulator to open a door is challenging because it requires tight coordination between the motions of the arm and the base. Hard-coding the motion, on the other hand, is infeasible since doors vary widely in their sizes and types, some doors are opened by pulling and others by pushing, and indoor spaces often contain obstacles that limit the freedom of the mobile manipulator and the degree to which the doors open up. In this paper, we show how to overcome the high-dimensionality of the planning problem by identifying a graph-based representation that is small enough for efficient planning yet rich enough to contain feasible motions that open doors. The use of graph search-based motion planning enables us to handle consistently the wide variance of conditions under which doors need to be open. We demonstrate our approach on the PR2 robot - a mobile manipulator with an omnidirectional base and a 7 degree of freedom arm. The robot was successful in opening a variety of doors both by pulling and pushing.

Laser-based perception for door and handle identification

Abstract: In this paper, we present a laser-based approach for door and handle identification. The approach builds on a 3D perception pipeline to annotate doors and their handles solely from sensed laser data, without any a priori model learning. In particular, we segment the parts of interest using robust geometric estimators and statistical methods applied on geometric and intensity distribution variations in the scan. We present experimental results on a mobile manipulation platform (PR2) intended for indoor manipulation tasks. We validate the approach by generating trajectories that position the robot end-effector in front of door handles and grasp the handle. The robustness of our approach is demonstrated by real world experiments conducted on a large set of doors.