National Technical University of Athens

About: National Technical University of Athens is a education organization based out in Athens, Attiki, Greece. It is known for research contribution in the topics: Large Hadron Collider & Nonlinear system. The organization has 13445 authors who have published 31259 publications receiving 723504 citations. The organization is also known as: Athens Polytechnic & NTUA.

Predicting surface roughness in machining: a review

Abstract: The general manufacturing problem can be described as the achievement of a predefined product quality with given equipment, cost and time constraints. Unfortunately, for some quality characteristics of a product such as surface roughness it is hard to ensure that these requirements will be met. This paper aims at presenting the various methodologies and practices that are being employed for the prediction of surface roughness. The resulting benefits allow for the manufacturing process to become more productive and competitive and at the same time to reduce any re-processing of the machined workpiece so as to satisfy the technical specifications. Each approach with its advantages and disadvantages is outlined and the present and future trends are discussed. The approaches are classified into those based on machining theory, experimental investigation, designed experiments and artificial intelligence (AI).

The Method of Proper Orthogonal Decomposition for Dynamical Characterization and Order Reduction of Mechanical Systems: An Overview

Abstract: Modal analysis is used extensively for understanding the dynamic behavior of structures. However, a major concern for structural dynamicists is that its validity is limited to linear structures. New developments have been proposed in order to examine nonlinear systems, among which the theory based on nonlinear normal modes is indubitably the most appealing. In this paper, a different approach is adopted, and proper orthogonal decomposition is considered. The modes extracted from the decomposition may serve two purposes, namely order reduction by projecting high-dimensional data into a lower-dimensional space and feature extraction by revealing relevant but unexpected structure hidden in the data. The utility of the method for dynamic characterization and order reduction of linear and nonlinear mechanical systems is demonstrated in this study.

An Equation of State for Associating Fluids

Abstract: An equation of state (EoS) suitable for describing associating fluids is presented. The equation combines the simplicity of a cubic equation of state (the Soave−Redlich−Kwong), which is used for the physical part and the theoretical background of the perturbation theory employed for the chemical (or association) part. The resulting EoS (Cubic Plus Association) is not cubic with respect to volume and contains five pure compound parameters which are determined using vapor pressures and saturated liquid densities. Excellent correlations of both vapor pressures and saturated liquid volumes are obtained for primary-alcohols (from methanol up to 1-tridecanol), phenol, tert-butyl alcohol, triethylene glycol, and water. Moreover, excellent prediction of saturated liquid volumes may be obtained from parameters which have been estimated by regressing only vapor pressures. Finally, we suggest a method for reducing the number of adjustable parameters for alcohols to three while maintaining the good correlation of vap...