Reframing the selection of hydraulic turbines integrating analytical hierarchy process (AHP) and fuzzy VIKOR multi-criteria methods

Before selecting a proper hydraulic turbine for power generation, conflicting factors frequently emerge from the wide range of available technology alternatives. The preliminary selection of hydraulic turbines (PSHT) has been usually carried out by overlooking and/or overshadowing downstream and upstream processes. The development of a new conceptual framework that allows for including more parameters into the decision-making process at company levels is still required to avoid the danger of engaging in a one-dimensional approach, which would not only result in a reduced and simplistic vision of the choice but would also overlook the trade-offs between individual aspects and the possible unintended side-effects. This paper aims to provide empirical evidence for the PSHT by proposing a well-thought-out framework based on a mixed methodology approach (analytical hierarchy process (AHP) and fuzzy-VIKOR multi-criteria methods) and focused on small hydropower projects. A total of 16 criteria are proposed and divided into 4 main categories—(i) turbine performance, (ii) turbine and generator costs, (iii) other equipment costs, and (iv) civil costs. Findings reported here reveal a specific alignment between investors’ preferences and experts’ judgments with real market practices. The 16 proposed criteria can be further considered to support the decision-making process for PSHT in different head and flow conditions.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020

Determinação da difusividade térmica de sólidos através do método do problema inverso

Thermal diffusivity of materials is a necessary data for solving problems in different areas, such as food, construction, mechanics, among others. There are different methods of obtaining this data, chosen according to the type of physical system, practicality, accuracy and costeffectiveness. The present work aims to determine the thermal diffusivity of metal samples using the Inverse Problem Method (IP). The Direct Problem (DP) of conduction heat transfer in a bar, with first kind boundary conditions, was numerically solved using the Finite Differences Method. Discretisations of the space and time variables were implemented with the Explicit, Implicit and Crank-Nicolson schemes in order to evaluate their computational performances, aiming at their use in the IP. This was implemented with the Network Search Method, using experimental time temperature data, obtained through an Electronic Data Acquisition System (EDAS). The experiments were performed at the Laboratory of Mathematical Education of UFFS / Chapecó (MEL) and the computer programs were elaborated in Scilab language. The thermal diffusivity of the researched metal was 4,110−6 2/ obtained by IP and is in the same order of magnitude of steels available in the literature. Such approximation does not confirm the accuracy of the method used, since the steels referred to in the literature probably do not have the same composition as the samples analyzed. However, it can be said that IP is a method: practical because it involves simple and fast experiments; cost-effective because it provides a result in the same order of magnitude as literature data and demands only low-cost electronic materials and the computational execution of a mathematical model.A difusividade térmica de materiais é um dado necessário para a solução de problemas de diferentes áreas, tais como a de alimentos, construção civil, mecânica, entre outras. Existem diferentes métodos de obtenção desse dado, escolhidos em função do tipo de sistema físico, praticidade, precisão e custo-benefício. O presente trabalho tem como objetivo determinar a difusividade térmica de amostras de metal, utilizando o Método do Problema Inverso (PI). O Problema Direto (PD) de transferência de calor por condução em uma barra, com condições de contorno de primeira espécie, foi resolvido numericamente utilizando do Método das Diferenças Finitas. Foram implementadas discretizações das variáveis espaço e tempo com os esquemas Explícito, Implícito e o Crank-Nicolson com o objetivo de avaliar seus desempenhos computacionais, visando sua utilização no PI. Esse, foi implementado com o Método de Procura em Rede, utilizando dados experimentais de temperatura por tempo, obtidos através um Sistema de Aquisição Eletrônica de Dados (SAED). Os experimentos foram realizados no Laboratório de Educação Matemática da UFFS/Chapecó (LEM) e os programas computacionais foram elaborados em linguagem Scilab. A difusividade térmica do metal pesquisado foi de 4,110−6 m2/s obtida pelo PI e encontra-se na mesma ordem de grandeza de aços disponíveis na literatura. Tal aproximação não atesta a precisão do método utilizado, visto que os aços referidos na literatura, provavelmente, não tem a mesma composição das amostras analisadas. Porém, podese afirmar que o PI é um método: prático, porque envolve experimentos simples e rápidos; eficiente custo-benefício, porque fornece um resultado na mesma ordem de grandeza dos dados da literatura e demanda apenas de materiais eletrônicos de baixo custo e da execução computacional de um modelo matemático