CDRsp - Comunicações em conferências internacionais
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- Maximizing the placement of congruent polyhedrain a parallelepiped containerPublication . Gaspar, M. Belbut; Martins-Ferreira, N.Given multiple identical polyhedral objects and a parallelepiped container, how should one place the objects so that the largest number fits inside the container? This simple question is important in many applications, yet the answer is elusive. In fact, we know of no published solution for this very general formulation. Still, in many circumstances, further restrictions apply, resulting in a large number of variations requiring different algorithmic strategies. In this presentation we will further formalize the problem, present some of its many variations, and in particular one that applies to the stereolithographic rapid prototyping technology.
- Preface of the "Symposium on integrated computational tools for advanced manufacturing"Publication . Alves, NunoThe Symposium on Integrated Computational Tools for Advanced Manufacturing, held within 10th International Conference of Numerical Analysis and Applied Mathematics, Kos, Greece, from September 19 to 25, 2012, is a relevant forum for the scientific exchange of multidisciplinary issues related to integrated computational tools for advanced manufacturing. The symposium contains eight reviewed papers, covering important research topics, such as multidisciplinary optimization, numerical modelling, computer-aided design, computer-aided engineering and additive manufacturing technologies.
- Optimalmould-part I: Multi-objective optimization to moulds design for injection of polymersPublication . Ramos, Carina; Carreira, P.; Bártolo, Paulo; Alves, NunoThe problem of mould design optimisation for polymer injection is a key issue for both mouldmaking and polymer injection industries. Several computational tools have proposed to address this problem. However they do not cover all aspects related to both mould design and injection moulding process, usually requiring the geometrical configuration of the initial mould solution. This paper presents a novel multi-objective optimisation tool, integrating CAD and CAE tools to optimise mould design parameters and injection moulding process parameters. No initial geometric definition of the mould is required. An industrial case study was considered to validate the proposed approach and the performance of several optimisation algorithms evaluated.
- Thermo-kinetic curing model for stereolithographic applicationsPublication . Bártolo, PauloA thermal-kinetic model, using the finite element method to study, simulate and optimise stereolithography, is presented in this paper. The model, which is theoretically rigorous and practical in its implementation, describes both the heat transfer effects and the course of the chemical reaction. This model includes the effects of photo-initiator concentration, temperature and light intensity, predicting the diffusion-controlled effects that occur after vitrification, the phenomenon of unimolecular termination and the shrinkage effects. Light intensity values at the resin surface are defined by assuming an appropriated Gaussian intensity distribution. The Beer-Lambert law enables to describe the decrease in light intensity with depth. The non-linear variation of the glass transition temperature with fractional conversion can be determined and consequently the mechanical behaviour of the resin sample predicted.
- Optimalmould - part II: Global optimization of the injection moulding cycle timePublication . Ramos, Carina; Carreira, Pedro; Bartolo, Paulo; Alves, NunoThe time required to produce a plastic part is a key issue in injection moulding process as it strongly determine the cost per part. Several approaches have been proposed to address this problem. However they do not cover all aspects related to the complete cycle time of the injection moulding process, only focusing on steps such as filling time, cooling time and packing time. This paper presents a global optimisation strategy for the injection moulding cycle time, covering all time steps related to the injection moulding process, including a novel mathematical model to predict the ejection time. An industrial case study was considered to validate the proposed approach. The obtained results are very close to the experimental ones. © 2012 American Institute of Physics.
- Preface of the “2nd Symposium on Integrated Computational Tools for Advanced Manufacturing”Publication . Alves, Nuno; Pascoal-Faria, PaulaThe 2nd Symposium on Integrated Computational Tools for Advanced Manufacturing held within the 14th International Conference of Numerical Analysis and Applied Mathematics, in Rhodes, Greece, from September 19 to 25, 2016. This symposium is a relevant forum for the scientific exchange of multidisciplinary issues related to integrated computational tools for advanced manufacturing. It contains five reviewed papers, covering important research topics, such as numerical modelling using finite element method, computer-aided engineering, manufacturing technologies and optimization using evolutionary algorithms. Four papers related to numerical modelling using the finite element method were presented and covered four main areas: 1) structural optimization, 2) prediction of fruit damage, 3) computational fluid dynamics applied to helmet design, and 4) mould design and injection moulding process. The obtained results suggest a significant improvement regarding the state of the art. On the first one, an important research work was developed on numerical modelling of structural mechanical behaviour. Geometric and multimaterial parameters of wind towers were optimized. A mono and multimaterial combination using steel, concrete and polymer concreted was studied through static, modal and buckling analyses. The numerical model developed allows the optimization of wind towers design, reducing the structural mass and cost involved in the construction of this kind of structures. In the second one a nonlinear finite element model was developed to mimic accurately apple mechanical behavior whereas its nonlinear geometrical and material properties were considered. The numerical results obtained were compared with the experimental ones allowing the validation of the proposed numerical model. The third work used a computer fluid dynamics analysis to study drag force acting upon two helmets for wheelchair racers. Using this approach personalised 3D computer models of helmets were obtained, aiming to optimize athlete’s performance through the customization of 3D computer model of helmets. The forth is related to mould design and injection moulding process. In this work an integrated computer tool approach was developed taking into account the design, computer simulation and manufacturing processes. Biopolymer injection process was simulated predicting biopolymer injection parameters. In the fifth reviewed paper a novel global optimization framework using evolutionary algorithms is presented. The problematic of form follows energy was studied through this framework. Optimal 3D shape as a function of the solar energy location was calculated. This procedure adds value to the sustainable architectural building.
- Ask not what additive manufacturing can do for youPublication . Gibson, I.The paraphrase of John F Kennedy’s famous words is for 2 purposes. Firstly it is to acknowledge that there are some people who have considered that it is a major part of their life’s work to promote Additive Manufacturing (AM) technology as primarily a selfless act. AM comprises an outstanding range of technology that should be brought to public attention as a true revolution in how we design and manufacture products. The second purpose is to show that technology development is only one part of this promotion process and that there are other ways in which we can get involved. This paper describes the author’s journey over the (approximately) 20 years since he was introduced to what was then called Rapid Prototyping (RP). It is not a catalogue of research and development projects but rather a list of activities that he has been involved in to help promote and support AM technology over these years. It will describe the conferences, activities, associations and publications that have been created to allow academics and professionals to describe and discuss their work amongst themselves and to the larger society.
- MICRO MOLD COOLING OPTIMIZATION USING A CONSTRUCTAL APPROACHPublication . Clemente, Miguel R.; Panão, Miguel R. OliveiraMold cooling is one of the most important phases in the molding cycle, comprising more than half of the total cycle time. This affects the final quality of the part and the production rate of the mold. Therefore, the design of a mold cooling channel system is essential to improve its thermal management and achieve a better control over the cycle time. The hardening of small thin wall plastic parts with complex geometries is one of the most challenging problems in the plastics injection industry, since we need to ensure quality, distortion free plastic parts. The solution lies in optimizing the cooling system, particularly the case of mold inserts with unconventional geometries compatible with the geometry of the part. Using the constructal principle, we develop a channel configuration as an umbrella for cooling a mold insert volume. This configuration includes a central channel transporting the coolant until the tip of the mold insert where a certain number of divergent channels depart performing the fluid flow return. A relation for the svelteness allows determining the channels sizes to ensure negligible local head losses, depending on the angle and number of divergent channels. Svelteness orientates the evolution of the flow towards smaller secondary channels returning the flow with higher divergent angles.
- Biomechanics modeling for functional analysis: Sheep modelPublication . Silva, Rui; Amado, Sandra; João, Filipa; Morouço, Pedro; Pascoal-Faria, Paula; Alves, Nuno; Veloso, AntónioThe aim of the present manuscript was to provide information on the suitability of using ovine as models for conducting in vivo bone tissue engineering studies, regarding the biomechanical considerations. Despite the need of knowledge of the animal model used for bone tissue research a good planning and study design is equal important. The purpose of this review is to contribute to extrapolation of reliable data for those who pretend to use the ovine model in tissue engineering and regenerative medicine.
- Cyclic plastic behaviour of 7075 aluminium alloyPublication . Nogueira, F.; Cunha, J.; Mateus, A.; Malça, C.; Costa, J. D.; Branco, R.This paper aims at studying the cyclic plastic behaviour of the 7075-T651 aluminium alloy under fully-reversed strain-controlled conditions. Tests are conducted under strain-control mode, at room temperature, in a conventional servo-hydraulic machine, from smooth samples, using the single step method, with strain amplitudes (∆ε/2) in the range ±0.5 to ±2.75%. This material has exhibited a mixed behaviour, i.e. cyclic strain-hardens at higher strain amplitudes (∆ε/2/>1.1%) and cyclic strain-softens at lower strain amplitudes (∆ε/2<1.1%). A linear relationship between the degree of cyclic strain-hardening and the strain amplitude has been established for higher strain amplitudes. Fatigue-ductility and fatigue-strength properties agree with those found in the open literature for the same loading conditions.
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