The Multiobjective Optimization of a Prismatic Drive

The multiobjective optimization of Slide-o-Cam is reported in this paper. Slide-o-Cam is a cam mechanism with multiple rollers mounted on a common translating follower. This transmission provides pure-rolling motion, thereby reducing the friction of rack-and-pinions and linear drives. A Pareto frontier is obtained by means of multiobjective optimization. This optimization is based on three objective functions: (i) the pressure angle, which is a suitable performance index for the transmission because it determines the amount of force transmitted to the load vs. that transmitted to the machine frame; (ii) the Hertz pressure used to evaluate the stresses produced on the contact surface between cam and roller; and (iii) the size of the mechanism, characterized by the number of cams and their width

Simulation of fully resolved finite-size particles in a turbulent flow

In this study we are interested on the statistics of finite sized particles. A sustained homogeneous isotropic turbulence with particles is numerically simulated in order to obtain those statistics

Stencil and kernel optimisation for mesh-free very high-order generalised finite difference method

Generalised Finite Difference Methods and similar mesh-free methods (Point set method, Multipoint method) are based on three main ingredients: a stencil around the reference node, a polynomial reconstruction and a weighted functional to provide the relation sbetween the derivatives at the reference node and the nodes of the stencil.Very few studies were dedicated to the optimal choice of the stencil together with the other parameters that could reduce the global conditioning of the system and bring more stability and better accuracy. We propose a detailed construction of the very high-order polynomial representation and define a functional that assesses the quality of the reconstruction. We propose and implement several techniques of optimisation and demonstrate the advantages in terms of accuracy and stability.J. Figueiredo acknowledges the financial support by FEDER – Fundo Europeu de Desenvolvimento Regional, through COMPETE 2020 – Programa Operational Fatores de Competitividade through FCT – Fundação para a Ciência e a Tecnologia, project N° UID/FIS/04650/2019. S. Clain the financial support by FEDER – Fundo Europeu de Desenvolvimento Regional , through COMPETE 2020 – Programa Operational Fatores de Competitividade through FCT – Fundação para a Ciência e a Tecnologia, project N° UIDB/00324/2020

Second-order finite volume mood method for the shallow water with dry/wet interface

The shallow water system is a fundamental work-piece for tsunami or flooding simulations. One of the major difficulties is the correct location of the dry/wet interface to evaluate accurate approximations of the velocity and kinetic energy. On the other hand, the MOOD method has been recently proposed to provide more efficient schemes in the framework of the Euler system. We propose to compare two second-order methods, namely the MUSCL and the MOOD techniques, and draw comparisons on accuracy shock capturing and dry/wet interface.This research was financed by FEDER Funds through Programa Operational Fatores de Competitividade — COMPETE and by Portuguese Funds FCT — Fundaçãoo para a Ciência e a Tecnologia, within the Projects PEst-C/MAT/UI0013/2014, PTDC/MAT/121185/2010 and FCT-ANR/MAT-NAN/0122/2012

Kinetostatic design of an innovative Schoenflies-motion generator

International audienceIn this paper, a novel parallel robot is introduced. The robot, a Schoenflies-Motion Generator (SMG), is capable of a special class of motions, namely, those produced with serial robots termed SCARA, an acronym for Selective-Compliance Assembly Robot Arm. These motions involve three independent translations and one rotation about an axis of fixed direction. Such motions are known to form a subgroup of the displacement group of rigid-body motions, termed the Schoenflies subgroup. The SMG is composed of two identical four-degree-of-freedom serial chains in a parallel array, sharing one common base and one common moving platform. The proximal module of each chain is active and has two controlled axes, the motors being installed on the fixed base. The links can thus be made light, thereby allowing for higher operational speeds. The distal module, in turn, is passive and follows the motions of its active counterpart, the whole mechanism giving, as a result, a four-degree-of-freedom motion to its end-platform

A Formulation of Complexity-Based Rules for the Preliminary Design Stage of Robotic Architectures

International audienceIn this paper we propose a formulation capable of measuring the complexity of robotic architectures at the conceptual-design stage. The motivation lies in providing a tool to the robot designer when selecting the best alternative among various candidates generated at the early stages of the design process, when a parametric design is not yet available. While the performance evaluation of a robot includes many criteria, we focus on: the kinetostatic, the elastostatic and the elastodynamic performances; workspace volume; actuation complexity and the life-cycle cost. Within the realm of conceptual design, characterized by the absence of a mathematical model, it is not possible to optimize the performance at hand using classical mathematical programming methods. In this paper, a set of rules derived from robotics knowledge is outlined. These rules are then used to formulate a complexity measure used to filter-out less promising architectures at the conceptual stage. The complete formulation is applied to the development of a six-degree-of-freedom robot with low topological complexity, high performance and low actuation-system complexity. A complexity-comparison between the proposed architecture, the DIESTRO and the PUMA robots, is also provided

The Isoconditioning Loci of Planar Three-DOF Parallel Manipulators

The subject of this paper is a special class of parallel manipulators. First, we analyze a family of three-degree-of-freedom manipulators. Two Jacobian matrices appear in the kinematic relations between the joint-rate and the Cartesian-velocity vectors, which are called the "inverse kinematics" and the "direct kinematics" matrices. The singular configurations of these matrices are studied. The isotropic configurations are then studied based on the characteristic length of this manipulator. The isoconditioning loci of all Jacobian matrices are computed to define a global performance index to compare the different working modes

An overview on the multidimensional optimal order detection method

Finite volume method is the usual framework to deal with numerical approximations for hyperbolic systems such as Shallow-Water or Euler equations due to its natural built-in conservation property. Since the first-order method produces too much numerical diffusion, popular second-order techniques, based on the MUSCL methodology, have been widely developed in the ’80s to provide both accurate solutions and robust schemes, avoiding non-physical oscillations in the vicinity of the discontinuities. Although second-order schemes are accurate enough for the major industrial applications, they still generate too much numerical diffusion for particular situations (acoustic, aeronautic, long time simulation for Tsunami) and very high-order methods i.e. larger than third-order, are required to provide an excellent approximation for local smooth solution as well as an efficient control on the spurious oscillations deriving from the Gibbs’ phenomenon. During the ’90s and up to nowadays, two main techniques have been developed to tackle the accuracy issue. The ENO/WENO which can cast in the finite volume context mainly concerns structured grids since the unstructured case turns to be very complex with a huge computational cost. The Discontinuous Galerkin method handles very well accurate approximations but the computational cost and implementation effort are also very high. In 2010 was published a seminal paper that proposed a radically different method. The philosophy consists to use an a posteriori approach to prevent from creating oscillations whereas the traditional methods employ an a priori method which dramatically cuts the accuracy order. In this document, I shall briefly present the MOOD method, show its main advantages and give an overview of the current applications.This research was financed by FEDER Funds through Programa Operational Fatores de Competitividade — COMPETE and by Portuguese Funds FCT — Fundação para a Ciência e a Tecnologia, within the Projects PEst-C/MAT/UI0013/2014, PTDC/MAT/121185/2010 and FCT-ANR/MAT-NAN/0122/2012