Cookies Policy
The website need some cookies and similar means to function. If you permit us, we will use those means to collect data on your visits for aggregated statistics to improve our service. Find out More
Accept Reject
  • Menu
Publications

2015

Trimming of 3D solid finite element meshes: sheet metal forming tests and applications

Authors
Barros, PD; Baptista, AJ; Alves, JL; Oliveira, MC; Rodrigues, DM; Menezes, LF;

Publication
ENGINEERING WITH COMPUTERS

Abstract
Over the last years, the numerical simulation of integrated processes has become the major challenge in virtual try-out of sheet metal components, including trimming operations that may occur between forming steps. Detailed simulation of trimming processes is a challenging task, particularly when integrated with other forming operations such as deep drawing or hemming. A simplified approach can be adopted in which elements outside the trim surface are deleted from the finite element (FE) model adjusting the remaining to the surface. Following this approach, the state variables are mapped from the old FE mesh to the new trimmed mesh to continue the simulation. This paper addresses this simplified approach to the trimming process exploring a previously presented algorithm (Finite Elem Anal Des 42: 1053-1060, Baptista et al. 2006), which allows the treatment of hexahedral finite element meshes. Particularly, it focuses on the performance evaluation of the implemented strategies for correcting the FE mesh to the trimming surface, including the treatment of pentahedral-shaped elements. Different correction and treatment strategies are evaluated on different types of meshes, based on numerical simulation results of simple mechanical tests: uniaxial tensile test and simple bending test. Finally, two practical applications are given where the local effect of the trimming algorithm is highlighted.

2015

Multi-objective decision-making framework for an electricity retailer in energy markets using lexicographic optimization and augmented epsilon-constraint

Authors
Nezhad, AE; Ahmadi, A; Javadi, MS; Janghorbani, M;

Publication
INTERNATIONAL TRANSACTIONS ON ELECTRICAL ENERGY SYSTEMS

Abstract
The objective of the retailer in medium-term planning is managing the portfolio of contracts from different sources as well as determining the optimal selling price offered to its customers. When supplying the electricity sold to the costumers, two main challenges are faced by retailers. The first problem occurs during the electricity procurement procedure. In this stage, the retailer must deal with the uncertainty due to the pool price that propels the retailers to move towards agreeing to forward contracts signed at higher average prices. Besides, when the retailer decides on selling the electricity, another problem is to face the uncertainty caused by the demand while taking into consideration the possibility of reducing its clients in the case of high selling price. In this regard, this paper proposes a stochastic multi-objective framework for the retailer with profit maximization and risk minimization as two objective functions. The risk, due to the market price uncertainty, is modeled, employing the expected downside risk. The problem is formulated as mixed-integer programming while the stochastic optimization problem is characterized using the roulette wheel mechanism and lattice Monte Carlo simulation. Furthermore, lexicographic optimization and augmented epsilon-constraint method are used to solve the proposed multi-objective problem, and the best compromise solution is determined employing a fuzzy satisfying method. The presented model has been implemented using a realistic case study to verify the effectiveness of the method used in this paper. © 2015 John Wiley & Sons, Ltd.

2015

Applications of Automata and Concurrency Theory in Networks (Invited Paper)

Authors
Silva, A;

Publication
26th International Conference on Concurrency Theory, CONCUR 2015, Madrid, Spain, September 1.4, 2015

Abstract

2015

A Mixed Reality Game using 3Pi Robots - "PiTanks"

Authors
Costa, H; Cebola, P; Cunha, T; Sousa, A;

Publication
2015 10TH IBERIAN CONFERENCE ON INFORMATION SYSTEMS AND TECHNOLOGIES (CISTI)

Abstract
In the growing field of Robotics, one of the many possible paths to explore is the social aspect that it can influence upon the present society. The combination of the goal-oriented development of robots with the interactivity used in games while employing mixed reality is a promising route to take in regard to designing user-friendly robots and improving problem solving featured in artificial intelligence software. In this paper, we present a competitive team-based game using Pololu's 3Pi robots moving in a projected map, capable of human interaction via game controllers. The game engine was developed utilizing the framework Qt Creator with C++ and OpenCV for the image processing tasks. The technical framework uses the ROS framework for communications that may be, in the future, used to connect different modules. Various parameters of the implementation are tested, such as position tracking errors.

2015

Simtwo as a simulation environment for flight robot dynamics evaluation

Authors
Amaral, G; Costa, P;

Publication
U.Porto Journal of Engineering

Abstract
Aerial Robots has become very popular in robotics groups. This ongoing interest is driven by a significant number of potential end-user applications where it is necessary to reduce human intervention. The validation of control/cooperation algorithms not always is an easy task and requires a large number of humans to keep tests safety. Is present in this paper the simulation of a quadrotor model in SimTwo simulation environment and evaluated the flight dynamic of the robot. To do that was developed a control layer responsible to the hovering maneuver and “go to” position function. The results prove that the objectives were achieved successfully and the simulation was validated. The navigation simulation is left as future work.

2015

Multicriteria Assessment of Crosswalk Location in Urban Roundabout Corridors

Authors
Fernandes, P; Fontes, T; Pereira, SR; Rouphail, NM; Coelho, MC;

Publication
TRANSPORTATION RESEARCH RECORD

Abstract
Midblock pedestrian crossing areas between closely spaced roundabouts can affect traffic operations and may result in a trade-off between capacity, environment, and safety benefits. Even though research has been conducted on the impacts of traffic performance on pedestrian crosswalks located at isolated roundabouts, few studies have focused on how pedestrian crosswalks between closely adjacent roundabouts affect traffic operations. A microsimulation approach was used to examine the integrated effect of a pedestrian crosswalk on traffic delay, carbon dioxide emissions, and relative speed between vehicles and pedestrians at different locations between closely spaced two-lane roundabouts. The main purpose of the study was to develop a simulation platform of traffic (VISSIM), emissions (vehicle-specific power), and safety (surrogate safety assessment model) to optimize such variables. The fast nondominated sorting genetic algorithm NSGA-II was mobilized to identify an optimized set of pedestrian crosswalk locations for the roundabout exit section along the midblock segment. One acceptable solution that provided a good balance between traffic performance, emissions, and pedestrian safety benefits was locating the crosswalks at 15, 20, and 30 m from the exit section. Even at low pedestrian demand, crosswalk effectiveness (as determined by capacity and environment) gradually decreased near the circulatory ring delimitation (<10 m). Findings suggest that crosswalks in the midblock segment (55 to 60 m from the exit section) also must be considered, especially under high traffic demand.

  • 2673
  • 4504