V. Dedoussis

Architectural scale modelling using stereolithography

The purpose of this paper is to investigate the applicability and effectiveness of Stereolithography rapid prototyping to the field of scale modelling for architectural design evaluation and demonstration purposes. Two scale models concerning a modern renovated track and field sports facility and a reconstructed ancient stadium are examined. Both models were constructed by assembling together resin parts fabricated with Stereolithography instead of milling. Critical issues encountered during the building phase of the two models are addressed and presented in detail. Comments are made on the CAD requirements of the parts geometry, on the part building and the post‐processing phases as well as on the end achieved accuracy. Problems associated with the computational time, related to the 3‐D solid modelling, and with the physical properties of the parts, are also discussed. The present Stereolithography methodology is compared to conventional model building techniques by investigating efficiency and productivity factors, quality matters and time requirements.

Fabrication of graded structures by extrusion 3D Printing

3D Printing allows the cost-effective and fast fabrication of parts with intricate/complex external and internal structure through the controlled addition of thin layers of material. This way, heterogeneous structures, i.e. structures with non-uniform density, can be constructed. In the present paper a method for the production of gradient structures with extrusion-type 3D Printing is discussed. The method involves three main steps: defining the geometry and material distribution of each layer in the form of a grayscale image, generating a set of points distributed according to the gray tone of the image and constructing a continuous path through the points for guiding material deposition by the 3D printer. In order to better present and test the method, two test cases of gradient structures are examined.

Efficiency evaluation of natural gas power plants using Data Envelopment Analysis

The purpose of this paper is to evaluate the efficiency of a network of natural gas power plants using the Data Envelopment Analysis approach. The network is modeled as a linear system with multiple inputs and outputs. As inputs one could consider, for instance, the age of a plant, the total number of hours that a plant is in operation during each year, etc. As outputs the model considers the electrical energy delivered per year, the number of hours that the plant is not in operation, etc. The proposed approach does not only evaluate each plant relative to the other ones, but it also ‘produces’ policy making scenarios that would enable plant managers to improve the plants operational characteristics. Computational results based on real-world data are presented and discussed. Relationships between efficiency scores and various inputs/outputs are also investigated and some interesting trends are identified.

Evolutionary Computing and Genetic Algorithms: Paradigm Applications in 3D Printing Process Optimization

3D printing is a relatively new group of manufacturing technologies, methods and processes that produce parts through material addition. 3D printing technologies are mainly employed for the fabrication of prototypes and physical models during product design and development; however as they continuously improve in terms of accuracy and range of raw materials they are increasingly employed in the actual manufacturing process. This puts a new emphasis on the study of some of the process planning problems and issues that are related with the cost efficient use of 3D printing systems and the quality of their products. Among the most crucial process planning problems are: (i) the selection of fabrication orientation and parameters which is by definition a multi-criteria optimization problem in which the operator seeks to achieve the optimum trade-off between cost and quality, under given fabrication constraints and requirements, and (ii) the batch selection/planning or “packing” problem, at which the selection and placement of various different parts inside the machine workspace is considered. As such, the primary goal of the chapter is to present the effective utilization of Genetic Algorithms, which are a particular class of Evolutionary Computing, as a means of optimizing the 3D printing process planning.

3D biomedical implants fabricated using direct laser writing

We present our investigations into the design and fabrication of a complex shape, readily assembled micro check-valve using the two-photon polymerization technique and a hybrid material. A computational fluid dynamics study has been carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design and the capability of an internal moving component to perform its intended function.

Developing competitive products using Stereolithography Rapid Prototyping tools

The competition that manufacturing industries are facing in todays economic environment is tremendous. Nowadays international markets ask for better and cheaper products with a higher ‘innovative content’. In order to achieve these goals the manufacturing industry has to resort to computer aided-driven, practices and tools that shorten the overall product development cycle and increase the product innovation dynamic. Some of the most important such tools are those collectively known as Rapid Prototyping tools, which can build physical prototypes, production tools or even small batches of the actual product itself, within a few hours. The purpose of this paper is to present the most prominent and mature of the Rapid Prototyping technologies, namely Stereolithography, and investigate its role in the design and development process. The presentation is carried out by discussing specific successful test cases that concern the development of new plastic products and the improvement of ‘older’ versions of them.

Computer Tools for Modelling and Evaluating the Potential of Energy Storage Systems with Reference to the Greek Islands Case

In the effort to meet climate change targets the share of renewable energy in electricity market has to be increased. The augmented penetration of renewable sources in the electricity grids could be destabilizing and may create barriers to their future expansion. Energy storage technologies are being regarded as a potential solution to deal with the intermittent nature of renewable energy sources. Introduction of energy storage systems in a future Smart Grid is definitely a complex problem and requires the technological analysis of the energy system itself. The purpose of this paper is to present an up-to-date critical examination of the state of the art of different computer tools that can be used to analyse the integration of energy storage systems utilized in conjunction with distributed generation. Particular emphasis is given to the case of isolated Greek islands.

Effective nesting of Layer Manufacturing fabricated parts using a Genetic Algorithm and a bottom-left ray casting procedure

Two aspects have been identified to be the key elements to the effective utilization of Layer Manufacturing (LM) technologies, that is maximization of the build volume and part orientation. The present work examines the utilization of a Genetic Algorithm in conjunction with effective placement rules as a mean of optimizing the build volume of LM technologies. The optimization is achieved via the dense nesting of parts, to be fabricated, on the LM machine platform. The software tool developed tackles the 2D nesting problem associated with the parts projections on the machine platform. The effectiveness and reliability of the proposed methodology is demonstrated via a case study concerning representative “real-world” parts/objects with quite general free form geometry.

Determination of the Pareto-optimal build orientations in Stereolithography

The selection of build orientation for a given part is one of the most important tasks encountered in the process planning phase of Layer Manufacturing in general and Stereolithography in particular. The orientation selection is by definition a multi-criteria optimization problem in which the operator seeks to achieve the optimum trade-off between cost and quality depending on the given fabrication constraints and requirements. In the present work a solution approach that focuses on the determination of the set of Pareto-optimal orientations is examined. Pareto-optimal orientations could be considered as a set of good choices for the selection of the optimum orientation for both single part and multiple (batch) fabrication. For the construction of this set in a time-efficient manner a Genetic Algorithm is employed. In order to investigate the efficiency of the proposed approach a case study is examined and the corresponding results are presented.