Paulo Coelho

Path-following control of mobile robots in presence of uncertainties

This paper presents, in detail, the implementation of a new control strategy, Kalman-based active observer controller (AOB), for the path following of wheeled mobile robots (WMRs) subject to nonholonomic constraints. This control strategy presents some particularities as being used in discrete mode, and being robust against uncertainties and disturbances such as the ones due to the use of the input-output feedback-linearization method in discrete mode, while it was developed to be used in continuous mode. The performance of the proposed control algorithm is verified via computer simulation, and is compared with other control strategies, such as pole placement controller (PPC) and PPC with a Kalman filter observer (CKF).

Lie algebra application to mobile robot control: a tutorial

Lie algebra is an area of mathematics that is largely used by electrical engineer students, mainly at post-graduation level in the control area. The purpose of this paper is to illustrate the use of Lie algebra to control nonlinear systems, essentially in the framework of mobile robot control. The study of path following control of a mobile robot using an input-output feedback linearization controller is performed. The effectiveness of the nonlinear controller is illustrated with simulation examples.

Behavior of an Atypical Embankment on Soft Soil: Field Observations and Numerical Simulation

This paper compares the behavior of an embankment with nonsymmetric geometry built on soft soil with that predicted numerically using four elastoplastic soil models. Two of these models are based on isotropic conditions (Modified Cam-Clay on its own or in association with Von Mises) and two other are derived from anisotropic conditions (Melanie on its own or conjugated with Mohr Coulomb). The performance of the models, whose parameters are derived from experimental data, is checked against triaxial tests results. For the embankment, the measured and computed displacements and excess pore pressure are compared, with the isotropic models performing best. The maximum horizontal displacements versus settlements, the change in excess pore pressure versus vertical stress, the extent of the yield domain and the contours of the effective vertical and horizontal stress increments are also examined. The numerical results are explained based on the characteristics of the numerical models, namely the size and shape of the yield surface. The embankment, despite its nonsymmetric geometry, exhibits some similarities with typical behavior.

Solving High-Speed Rail Planning with the Simulated Annealing Algorithm

High-speed rail (HSR) networks require large investments, and the performance of the infrastructure is affected by varying local environments, while subject to tight layout restrictions. This paper presents a fully integrated three-dimensional model to optimize the HSR alignment at a planning scale, which sets boundaries for the final project design. The model considers mandatory and desirable specifics for the locations to link and the geometry in both the plan view and the longitudinal profile. It also allows one to define prohibited and restricted land-use areas. A computational tool has been developed that takes into account the problem specifics using a simulated annealing algorithm to optimize the problem solution. The capabilities of the model and the tool are demonstrated with the application to an intentionally simple and synthetic case study, considering construction costs and problem constraints, for which sound results are obtained. Both the model and the tool can be expanded to incorporate additional complexity, establishing the basis for real applications and for further integration of geotechnical and hydrological risk factors that affect the HSR performance.

Application of the Simulated Annealing Algorithm for Transport Infrastructure Planning

Decisions in planning for transport infrastructure are the result of complex technical, political, and societal concerns. Its context of limited public funding and large costs require that decision making is soundly supported. When addressing real-world problems, however, it is extremely difficult to ascertain the system configuration yielding the most value. Different alternatives exist that trade-off interrelated factors governing the value of the configurations. Metaheuristics can be of assistance when solving such real-world problems. This chapter presents an application of the simulated annealing algorithm to solve an integrated approach to high-speed rail planning. The algorithm capabilities in addressing the intricacies imposed by large and complex problems are discussed.

Decision Support Systems for Real-World High-Speed Rail Planning

AbstractThe selection of the macrolocation of new high-speed rail (HSR) systems during the planning stage affects the associated infrastructure costs. The process is influenced by the complex interaction between the HSR alignment, the technical solutions, and the characteristics of the deployment site, subject to layout restrictions. Decision support systems for the optimization of the HSR alignment are developed for addressing the requirements of large and complex real projects. The formulation includes costs, geometric constraints, connection requirements, and consideration of natural barriers such as protected land use and bodies of water, ubiquitous in real projects. The simulated annealing algorithm is implemented to address challenges of real problems and solve the optimization model. The approach is applied to a Portuguese HSR case. The solution obtained optimizes its alignment by minimizing the construction costs, consistent with existing projects worldwide, and complying with location, geometry, ...

Critical State-Based Interpretation of the Monotonic Behavior of Hostun Sand

AbstractA series of bender element tests and drained and undrained monotonic triaxial compression and extension tests were performed on air-pluviated samples of Hostun sand. Samples were prepared t...

Centrifuge Modeling of Liquefaction Effects on Shallow Foundations

Earthquake-induced liquefaction is a major concern for structures built on saturated cohesionless soils in seismically active regions, as it often causes failure of critical structures such as bridges and quay walls, which severely restricts post-earthquake emergency response and economic recovery. The destructive consequences of this phenomenon have remarkably increased since it was firstly identified in US and Japan in 1964. This paper describes an investigation on the performance of shallow foundations susceptible to seismic liquefaction, considering the particular vulnerability that this type of foundation has shown in the field during past earthquakes. The research program included three dynamic centrifuge experiments, conducted at the Schofield Centre, University of Cambridge, UK, as part of a SERIES’ TNA Use Agreement focusing on the magnitude of liquefaction effects on shallow foundations, under different conditions, including interaction effects between adjacent structures, and on the assessment of the performance of innovative mitigation techniques, particularly narrow densified zones combined with selectively positioned high-capacity vertical drains.

Solid Pseudopapillary Tumor of the Pancreas in a Child: Imaging Findings with Diffusion-Weighted MR Imaging

CONTEXT Solid pseudopapillary tumor of the pancreas is a rare tumor more common in young girls and rare in males. CASE REPORT We present a case of a solid pseudopapillary tumor of the pancreas in a 13-year-old boy, with typical imaging features. CONCLUSIONS Our case report specifically illustrates the potential of diffusion-weighted imaging findings on solid pseudopapillary tumor in pediatric patients.

Planning for Natural Hazards: Robust Approach for High-Speed Rail Infrastructure

AbstractHigh-speed rail (HSR) infrastructure is often built in areas prone to multiple hazards. In the planning stage, large areas and substantially different configurations can be considered, but ...