FE - DCA | Dissertações de Mestrado e Teses de Doutoramento
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- Gestão Ótima do Fluxo de Tráfego Aéreo nas Zonas Terminais de Voo com Base em Redes DinâmicasPublication . Simão, Cátia Salomé Azevedo; Bousson, KouamanaO aumento da procura sentido no setor do transporte aéreo refletiu-se no aumento da densidade do fluxo de aeronaves principalmente nas zonas terminais, sendo estas áreas designadas em inglês por Terminal Maneuvering Area (TMA) e fundamentais para a correta realização das aterragens e das descolagens. Esta sobrecarga foi gerida por inúmeros(as) agentes que observaram, controlaram e tomaram as decisões adequadas em cada momento, aliando essas tarefas com o(a) correto(a) tratamento e análise dos dados obtidos através de inúmeras fontes relevantes e dos programas computacionais que têm sido criados, desenvolvidos e implementados nas últimas décadas. Tendo por base esta problemática, pretendeu-se com o presente trabalho de investigação analisar, de forma concreta e crítica, a complexidade da otimização da gestão da capacidade das TMAs e propor medidas corretivas, obtendo uma estimativa preditiva do nível de ocupação das mesmas, em um determinado momento futuro, evitando a ocorrência de congestionamentos. O desejo de garantir e até mesmo de aumentar os níveis da segurança operacional motivaram a constante procura por métodos e metodologias, aliados(as) a programas computacionais. Por esse motivo, a recolha obtida através da revisão bibliográfica permitiu enunciar, descrever e exemplificar as principais medidas utilizadas até aos dias de hoje para gerir o fluxo de tráfego aéreo. Foi possível, dessa forma, evidenciar aspetos que poderão ser analisados, de forma mais detalhada, em trabalhos futuros, proporcionando sugestões de melhoria que beneficiem todos(as) os(as) utilizadores(as) deste setor. Desta forma, e através da modelação realizada com o suporte e a aplicação de redes dinâmicas, foi possível detetar o padrão de funcionamento do fluxo de tráfego aéreo na TMA do Aeroporto Humberto Delgado e sugerir as medidas adequadas que permitirão melhorar a gestão diária do fluxo de tráfego aéreo e que auxiliarão na previsão do mesmo e do nível de ocupação da TMA em análise, com o intuito de implementar essas medidas de forma atempada e segura. A modelação do fluxo de tráfego aéreo efetuada através da aplicação da Teoria das Cadeias de Markov permitiu a criação de um algoritmo cujo principal objetivo incidiu na otimização e na gestão entre a capacidade da TMA e a procura de aeronaves em cada momento, tendo em conta os inúmeros recursos existentes e podendo o mesmo ser extrapolado para outras TMAs. A metodologia selecionada representa um processo de otimização pois tem a capacidade de, através de um procedimento matemático, definir uma solução ótima para a gestão do nível de ocupação da TMA em estudo, maximizando o fluxo de tráfego aéreo com o intuito de satisfazer a procura registada, mas salvaguardando o nível de segurança operacional pretendido a qualquer momento e, simultaneamente, minimizando os atrasos verificados nas operações de tráfego aéreo. Esta otimização é conseguida através da análise da dinâmica verificada no fluxo de tráfego aéreo registado e da identificação de padrões de procura, sendo possível, dessa forma, analisar a variação do congestionamento do fluxo de tráfego aéreo ao longo do tempo. Salienta-se que esta abordagem nunca foi implementada no contexto do presente trabalho de investigação, revelando o seu carácter de originalidade. Através dos modelos criados foi possível identificar o grau de saturação da TMA selecionada e a necessidade de adaptação de medidas e/ou políticas já instauradas, tendo em conta as limitações físicas existentes e que restringem o aumento da procura do fluxo de tráfego aéreo. Desta forma verificou-se o elevado grau de constrangimento vivenciado, durante os períodos analisados, tendo um impacto direto na segurança das operações de tráfego aéreo. Assim sendo, é notória a necessidade da implementação de medidas que consigam minimizar os períodos de saturação, podendo ser tomadas pelas companhias de transporte aéreo através, por exemplo, da disponibilização de diferentes horários de planeamentos de voos e/ou rotas de voo alternativas que, de alguma forma, evitem as situações de constrangimento ou, por outro lado, de medidas tomadas pelas infraestruturas aeroportuárias e pelos(as) agentes que colaboram com o intuito de minimizarem os atrasos verificados nos diferentes voos e, dessa forma, evitando a aglomeração de aeronaves nas TMAs, salvaguardando e garantindo margem para lidarem com situações de emergência e/ou inesperadas. Por fim, mas não menos importante, salienta-se a importante capacidade de previsão obtida a partir dos modelos criados, permitindo dessa forma, e através do conhecimento do comportamento presente de uma determinada rede dinâmica, antever o seu comportamento num momento futuro e auxiliar na otimização da gestão do fluxo de tráfego aéreo. Esta característica é fundamental e de extrema utilidade não só para o conhecimento dos(as) agentes como também para os(as) estudiosos(as) empenhados(as) no desenvolvimento de programas computacionais que pretendem ser instrumentos indispensáveis neste processo.
- Droplet Impact onto Heated Wetted Surfaces: A Fundamental StudyPublication . Rodrigues, Daniel de Almeida Vasconcelos ; Silva, André Resende Rodrigues daThe industrialisation and globalisation of the modern world severely increased the demand for energy production, primarily met by a dependence on fossil fuels. The projected exponential growth of the aviation sector will result in an increase in greenhouse gas and pollutant emissions. Due to this, researching sustainable and cleaner alternative fuels is crucial to neutralise the negative effects of conventional fuels. The physical and chemical processes occurring inside a combustion chamber include fluid dynamics, heat and mass transfer, combustion, among others. Specifically, the phenomena regarding the impact of droplets onto solid surfaces and liquid layers are often encountered in internal combustion engines, heat exchangers and spray cooling. Research on these applications focuses on understanding fluid flow and optimising heat and mass transfer mechanisms. Despite this, single droplets impacting onto liquid films are limited to isothermal conditions, as the influence of temperature on liquid films has been overlooked in the literature. Therefore, the primary objective of this work is researching the phenomena of droplet impact onto heated liquid films. An experimental facility was designed and adapted to account for isothermal and non-isothermal conditions. The key aspects of the experimental facility consist of high-speed imaging and heating systems. Prior to the impact phenomena, the liquid film characterisation is required in terms of temperature fields and evaporation rates. Subsequently, various outcomes from droplet impact are evaluated as a function of the liquid film temperature, including central jets, craters, splashing, and bubbling. Qualitative analysis is conducted on outcome development, while quantitative measurements focus on geometric parameters. Theoretical work is performed regarding the propagation of kinematic discontinuities in liquid layers and time scales for crater and central jet evolution, respectively. The experimental data provides a foundation for the implementation and validation of the numerical model. This model solves the incompressible Navier-Stokes equations coupled with the Volume of fluid (VOF) method under a 2D-axisymmetric assumption. The open-source Computational Fluid Dynamics (CFD) software Basilisk is adopted for the numerical simulations. Overall, the liquid film temperature and correspondent thermophysical properties play a major role in the impact dynamics. Higher values of the dimensionless temperature promote and increase the occurrence and number of secondary droplets, respectively. This is associated with lower values of viscosity and surface tension, contributing to higher Reynolds and Weber numbers. For the onset of boiling, the oscillations induced on the liquid film are not sufficient to affect the impact phenomena. The presence of vapour bubbles in the impact region decreases both the crown diameter and height, with its effect being more pronounced for the latter.
- Development of high-performance epoxy- graphitic carbon nitride nanocompositesPublication . Moura, Liane Raquel Neves; Sadhu, Veera; Silva, Abílio Manuel Pereira da; Parente, João Miguel NunesThe introduction of nanofillers into epoxy resins is one of the numerous ways of reinforcing polymers. In accordance, this dissertation explores the synthesis, characterization, and performance optimization of epoxy-graphitic carbon nitride (GCN) nanocomposites, focusing on enhancing their mechanical and thermal properties. So, the research involves the preparation of epoxy-based nanocomposites through the incorporation of different concentrations of GCN nanoparticles into the epoxy resin, using common processing techniques, and subsequent analysis of their structural characteristics and properties. Besides that, this work aims to understand the influence of GCN loading and Polyhedral Oligomeric Silsesquioxane (POSS) particles on the nanocomposite's mechanical strength and thermal stability, aiming at aeronautical and aerospatial applications. The experimental results indicate that the most enhanced mechanical properties were observed for the nanocomposite reinforced with a concentration of 0.25 wt.% GCN. Consequently, this concentration was selected for the carbon fibre laminates, concluding that the addition of GCN resulted in an improvement of up to 81% in flexural strength (from 369.8 to 670 MPa) and up to 135% in flexural modulus (from 25.2 to 59.3 GPa), depending on the testing speeds. Increases of 25% in tensile strength (from 408.3 to 509.6 MPa) and 39% in elastic modulus (from 20.3 to 28.1 GPa) were also observed. As mentioned, the document also examines the influence of adding POSS particles to the carbon fibre laminates reinforced with GCN. Comparing the properties attained for the control sample with the ones obtained for the reinforced samples, it is possible to conclude that the incorporation of both nano reinforcements allows for improvements between up to 111% in flexural strength (from 369.8 to 781.2 MPa) and up to 117% in flexural modulus (from 25.2 to 54.7 GPa), for different testing speeds. In terms of tensile strength and elastic modulus, the increases were 30% (from 408.3 to 529.9 MPa) and 12% (from 20.3 to 22.7 GPa), respectively. The thermal properties of the laminates were also examined, through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found that the addition of nano reinforcements did not result in significant improvements in the glass transition and decomposition temperatures, although an improvement in the residual mass was observed in the laminates reinforced only with GCN. Finally, the hydrophobic properties of the two compositions and the control sample were evaluated, using water contact angle analysis (WCA). It was concluded that the presence of the reinforcements positively impacts these properties, with a more pronounced improvement in the sample reinforced only with GCN (from 73.6 to 82.5º).
- Experimental and Numerical Study of a Novel Airfoil Morphing Concept for UAV WingsPublication . Ukolov, Egor; Gamboa, Pedro VieiraThe conventional aircraft design process results in a compromise solution for its wings geometry that meets all design requirements and ensures satisfactory performance throughout its operational envelope. Consequently, the aircraft may operate under suboptimal performance conditions in various flight conditions. This dissertation presents a novel concept for executing wing morphing in its airfoil degree-of-freedom, which has the potential applications in small-to-medium size unmanned aerial vehicles, aimed at enhancing their flight performance across a broader range of flight conditions. A surrogate model is developed to evaluate the most significant design variables of the concept in relation to aerodynamic performance metrics – maximum lift coefficient, maximum lift-to-drag ratio, and the corresponding pitching moment coefficient. A prototype of the concept is implemented to demonstrate proof-of-concept and compare the experimental results of morphing actuation with those obtained numerically from a computational model. Case studies are conducted using the airfoils “NACA 2412”, “NACA 2415”, and “NACA 4418” to further investigate the potential benefits of morphing, alongside a comparison of the concept’s performance with conventional hinged surfaces. The results indicate that the concept is capable of enhancing lift-to-drag ratio across a considerable range of lift coefficients and reducing, in absolute value, the pitching moment coefficient. Furthermore, the concept allows for achieving a 12% higher maximum lift coefficient and an 88% higher maximum lift-to-drag ratio than that of a conventional hinged surface. The study concludes that the potential practical implementation of the concept can reduce take-off and landing distances, decrease the installed power requirements, extend range and endurance, and enable an aircraft to operate efficiently under varying weight conditions.
- Localização de novas infraestruturas aeroportuárias de aviação civilPublication . Fonseca, Afonso Miguel Alves Pereira Ferreira da; Silva, Jorge Miguel dos Reis; Bernardi, Carlos Alejandro DiEsta dissertação aborda um dos temas mais delicados na aviação civil portuguesa dos últimos 50 anos, a localização de novas infraestruturas aeroportuárias de aviação civil. Desenvolveu-se através do suporte teórico providenciado pelas referências bibliográficas uma metodologia preliminar para a decisão de localização de novas infraestruturas aeroportuárias de aviação civil. A presente metodologia preliminar poderá ser aplicada a qualquer projeto de infraestrutura aeroportuária ou aeródromo aquando da discussão e debate da sua localização espacial. Procedeu-se, posteriormente, a validação e otimização da metodologia preliminar apresentada através do caso de estudo relativo à localização do novo aeroporto de lisboa (NAL). Utilizou-se a ferramenta Google Earth Pro para avaliar a localização espacial das alternativas possíveis a “receber” o aeroporto, facilitando assim a aplicação dos diversos pontos da metodologia. Após a aplicação da metodologia preliminar, obteve-se uma ponderação para cada fator crítico de decisão para cada alternativa e gerou-se, a partir daí, uma ordem hierárquica da melhor para a pior alternativa com base num modelo matemático: Simple Additive Weighting (SAW). Em jeito de conclusão, avaliou-se os resultados obtidos e ponderou-se sobre alterações futuras para otimização e aumento da abrangência da metodologia preliminar proposta nesta dissertação, de forma a torná-la numa ferramenta de análise mais complexa e pormenorizada. Este trabalho contribuiu para realizar uma reflexão sobre as possibilidades de localização do novo aeroporto de lisboa (NAL), mostrando que as principais alternativas em destaque noutros estudos e na comunicação social são as que apresentam melhor ponderação, e também que o design e aplicação de metodologias preliminares genéricas (e de simples perceção) pode ter eficácia satisfatória em casos concretos.
- Numerical Analysis of a Centrifugal Pump in OpenFOAMPublication . Gouveia, Pedro Miguel da Silva; Silva, André Resende Rodrigues da; Magalhães, Leandro Barbosa; Moreira, HorácioThis dissertation investigates the development and validation of a numerical model for the analysis of centrifugal pumps using the OpenFOAM v11 software. The primary focus was on simulating pumps operating with constant fluid density and minimal temperature variation. The model was validated against experimental data from the literature, using the Navier-Stokes equations with RANS approximation and the k - e turbulence model. Numerical results for global parameters, such as total head and power, showed an agreement with errors of 4.30% and 4.37% compared to experimental data, respectively, and the best efficiency point was predicted with a 3.73% deviation. Additionally, the performance of a pump developed by Omnidea, Lda. was initially intended to be analyzed. However, these simulations were discarded due to lack of computational resources and insufficient time to implement the necessary cavitation and multiphase flow models. The absence of these models made it impossible to accurately represent regions where the pressure drops below the fluid’s vapor pressure, a critical factor in cryogenic applications. Therefore, it was concluded that the numerical model used is suitable for simple flow conditions but requires improvements to be applied in more complex simulations. The results suggest that, while the method is efficient for pump analysis in non-cavitating conditions, future studies should incorporate more advanced cavitation and two-phase flow models to enable more accurate analysis in high-performance systems.
- Filtragem de Kalman Neuronal para Aplicações AeroespaciaisPublication . Silva, Felippe Ferreira da; Bousson, KouamanaA estimação em tempo real é um dos tópicos mais importantes na engenharia, principalmente em sistemas não-lineares, presentes em praticamente todas as aplicações aeroespaciais. Na indústria aeroespacial, há cada vez mais a tendência de utilizar instrumentos, sensores e métodos de estimação que sejam precisos, leves e com baixos custos computacional e financeiro. O termo filtragem ou estimação é utilizado para o conjunto de técnicas e algoritmo que permitem obter uma redução de ruídos ou erros de medição além de estimar estados não mensuráveis diretamente. A grande dificuldade encontra-se justamente na complexidade dos sistemas observados, que podem apresentar dinâmica altamente não-linear, além de ruídos e baixa disponibilidade de dados, o que torna a seleção do método de filtragem um fator muito importante para que haja o máximo de redução do erro de estimação. Um dos métodos mais importantes desenvolvidos foi o filtro de Kalman linear, considerado filtro ótimo para sistemas lineares. Mas, visto que a maioria dos sistemas reais envolve dinâmica não-linear, outros métodos foram desenvolvidos com vista a superar este impasse. Métodos como o famoso filtro de Kalman Estendido (EKF – Extended Kalman Filter), o filtro de Kalman Unscented (UKF – Unscented Kalman Filter) e o filtro de Kalman Pseudolinear (PSELIKA – Pseudo Linear Kalman Filter) foram algumas das soluções implementadas que tiveram sucesso em aplicações reais, apresentando vantagens e limitações particulares. Para o filtro EKF, a sua principal limitação é o seu comportamento errático e possivelmente divergente em sistemas altamente não-lineares, ou com estimações iniciais imprecisas. Já para o UKF, a dimensão do estado pode aumentar significativamente a complexidade temporal do algoritmo, o que pode torná-la uma solução inviável para tempo real. O filtro PSELIKA apresenta limitação parecida onde a complexidade das operações efetuadas é a principal causa do custo computacional elevado. Destes métodos, o PSELIKA chama atenção pelo facto de ser aplicável em praticamente qualquer sistema não-linear, dentro das condições necessárias, mas sendo possível utilizar os métodos de filtragem linear ao modelar a dinâmica do sistema numa estrutura pseudolinear. A limitação é dada pela necessidade de resolver a equação Algébrica de Riccati associada e realizar inversões matriciais para o cálculo da matriz de ganho do sistema, necessitando bastantes recursos computacionais. Assim, com o objetivo de reduzir o custo computacional e melhorar o desempenho, as redes neuronais têm sido integradas aos métodos de filtragem. Estas são ferramentas extraordinárias que atuam como funções não-lineares capazes de obter conhecimento experimental, e neste caso, podem atuar para prever os cálculos efetuados durante o método de filtragem PSELIKA. De forma a reduzir a principal limitação do método de estimação PSELIKA, aproveitando do facto de apresentar uma estrutura pseudo-linear, esta dissertação propôs a integração de uma rede neuronal do tipo Perceptron de Múltiplas Camadas (MLP- Multilayer Perceptron) ao algoritmo PSELIKA, tendo como principal objetivo a redução do custo computacional original, implementando, por fim, um algoritmo denominado PSELIKAMLP. Com vista a validar a utilização do algoritmo, nesta dissertação são abordados dois casos de estudo: a estimação da taxa angular e atitude de um veículo aeroespacial, além da estimação da órbita de um satélite artificial. Nestes, são comparados a exatidão, complexidade temporal e espacial entre o algoritmo implementado, o filtro EKF e o filtro PSELIKA. Os resultados demonstram que o algoritmo implementado foi capaz de reduzir significativamente o tempo computacional do método PSELIKA, sem um grande detrimento da exatidão da estimação, mas apresentando complexidade espacial superior. Assim, é uma possível aplicação para a redução do custo computacional servindo de complemento para o algoritmo original.
- Improvement of Compliance Monitoring System in an EASA AOC and Part-CAMO organisationPublication . Leite, Maria Beatriz de Sousa; Saúde, José Manuel Mota Lourenço da; Moreira, Carla RibeiroFor as long as the aviation industry has been developed, and during all its evolution and improvement, there have been multiple factors to be considered in order to improve and maximise its coordination and conformity with the necessary norms implied. As a result of the advancement of the aviation sector, there was a notorious increase of pressure in order to guarantee its safety, efficiency, accountability and compliance with the rules dictated by civil aviation authorities. Consequently, aviation organisations may ensure their operations fulfil the strictest regulatory and safety requirements. The term compliance in the aviation sector is a reference to an operator’s capability to meet the requirements specified by the own company and responsible authorities. The compliance management system in an aviation organisation may cover all different areas, from flight operations to crew training to aircraft maintenance and continued airworthiness. Consequently, a cohesive interaction between safety and compliance in the aviation industry is fundamental in order to assert operational integrity and present safety to both clients and flight crew. Aviation organisations which hold an AOC (Air Operator Certificate) are authorized to perform commercial air transport operations and must conform with severe regulations set forth by international and regional aviation authorities, for example the European Union Aviation Safety Agency (EASA). These regulation frameworks mandate that AOC holders implement dynamic management systems that ensure continuous adherence to safety and operational standards. In this sense, the increasing complexity of compliance requirements mandates a structured and effective approach to regulatory oversight. The presented paper will address and answer these compliance challenges in PHS Aviation - an AOC holder operator and Part Camo organisation - through the development and implementation of Compliance Checklists (see Annex B, Annex C and Annex D). The integration of these checklists in the company was a result of a study and gap analysis of the operator’s Compliance Monitoring System. The company and civil aviation authorities have established regulatory requirements and standards that must be met by all activities related to aircraft maintenance and operation. These requirements must be systematically verified and continuously monitored. The role and significance of compliance monitoring in an aviation company, a division of CAMO, will be examined in detail in this project. The result of this study aims to improve auditing processes, enhance regulatory adherence and ultimately contribute to the safety and reliability of all PHS Aviation’s departments and operations.
- Low Speed Airfoil Optimization for Improved Multi-Point Performance of ACC AircraftPublication . Pangas, Guilherme Filipe da Silva; Gamboa, Pedro VieiraThe advancement of computational capabilities has allowed for more efficient analysis and iteration of airfoil designs. Consequently, it has become possible to expand the design space and explore new geometries and configurations. However, the current state does not allow for a press-and-run optimization. The new capabilities have simply carried over the trial-and-error approach, previously used for the geometry, to the formulation of the optimization problem. The goal of this work is to study the formulation of an optimization problem and propose a new methodology that better portrays the aircraft’s requirements for airfoil performance. The new objective, based on the Aircargo Challenge 2022, is implemented by modifying an existing tool. This software has implemented a constraint multi-point optimization to improve the aircraft’s airfoil performance. The optimization is based on the free-gradient technique called Particle Swarm Optimization (PSO), using B-spline parametrization and a coupled viscous/inviscid interaction method. The new objective function, added to this program, estimates the performance of the aircraft developed for the competition, such as lift-off weight, the climb speed, and the maximum cruise and turn velocity. The estimations are done using a method that extrapolates the characteristics of the airfoil, analyzed through a sequence of operating points, into the aircraft’s performance. A penalty is then added to the score if any of the restrictions imposed are not met, and the sum is used as the objective function value. The dissertation includes two case studies. First, the PSO optimizer is evaluated through the effect of some of its settings on design space exploration and the resulting airfoil. The study concluded that the exhaustive option obtains the best and most consistent results among the settings studied. These results also provide an estimation of the airfoil and the score variance across different optimizations. Furthermore, in terms of the objective function, this case also reveals the tendency to increase the payload carried in order to obtain a higher flight score in the competition. In the second case study, the behavior of the new objective function under different initial conditions is analyzed. This investigation revealed the same trends in terms of scoring and validated/refuted some of the ACC2022 team’s decisions.
- Propulsive Enhancement and Dynamic Stall Mitigation in Flapping AirfoilsPublication . Camacho, Emanuel António Rodrigues; Silva, André Resende Rodrigues da; Marques, Flávio DonizettiThe study of oscillating airfoils is the centerpiece for the biomimetization of flight, exploring newer energy-extracting devices, and improving rotor blade design. Typically, these are affected by highly nonlinear aerodynamic effects, which in most cases, still require substantial research regarding the aerodynamics and parameters that govern these systems. The present investigation looks into some of these topics by scrutinizing two primary fronts: the propulsive enhancement and the dynamic stall mitigation of flapping airfoils. After a comprehensive review of past investigations, the current work proposes a newer airfoil, the NACA0012-IK30 airfoil, that introduces the concept of dynamic curvature. This bioinspired concept is applied to the conventional NACA0012, producing an innovative geometry by dividing the airfoil into two parts, where we can deflect the leading edge independently from the rest of the airfoil. This newer design went through parametrical and optimal analysis by employing a diverse set of experimental and numerical methodologies, divided into two domains: lower Reynolds number, where the propulsive capabilities are studied, and higher Reynolds number, where dynamic stall mitigation is explored. At the lower spectrum of the Reynolds number, results show that the activation of the leading edge offered by the IK30 mechanism demonstrated the ability to improve considerably the propulsive power and efficiency. When comparing the proposed geometry with standard flapping, it is clear that the suggested design can provide optimal thrust with near-optimal propulsive efficiency, something unachievable in traditional flapping. Results obtained at the higher range of the Reynolds number, where the IK30 mechanism functions with dynamic stall mitigation purposes, show the adequacy of the proposed geometry under different plunging and pitching conditions. When correctly deflecting the leading edge, the aerodynamic stall experienced both in static and dynamic conditions can be mitigated or even eradicated, leading to significant drag reductions and modest lift enhancements. While the present study yielded encouraging results, the IK30 mechanism and the broad concept of dynamic curvature need to be the focus of further research. Using newer technologies, for instance, continuous camber morphing, coupled with ingenious kinematics, will allow us to explore newer pathways to extend our knowledge and exploit the aerodynamics of unsteady airfoils.