Development and validation of a numerical tool for structural analysis and design of inflatable structures

El tema de las estructuras neumáticas, en concreto los hangares hinchables, es un pequeño sector en el ámbito de la construcción que está en constante desarrollo y en el que existe un amplio margen de mejora, innovación e investigación que supone un reto en términos de cálculo y diseño. Por este motivo, existen varios estudios que intentan optimizar el análisis de esta tipología, que no cuenta con una norma específica. Entre los enfoques alternativos es posible encontrar estudios que van desde los modelos numéricos basados en normas de construcción hasta la mecánica de fluidos computacional. Sin embargo, en el primer caso no son suficientemente precisos o en el segundo el coste computacional los hace excesivos en el diseño práctico. Por este motivo, y con el fin de optimizar el análisis práctico con precisión y coste computacional razonable CIMNE está desarrollando actualmente el Túnel de Viento Virtual (VWT), una nueva solución que combina la aerodinámica de flujo potencial, la dinámica estructural FE explícita y el acoplamiento FSI escalonado. La tesis pretende realizar un estudio exhaustivo sobre el análisis estructural de hangares hinchables para optimizar su cálculo en base al nuevo código computacional. El estudio experimental se realiza mediante un análisis exhaustivo y la comparación de los resultados obtenidos con VWT y RAMseries, teniendo en cuenta como factor determinante la diferencia de aplicación de las cargas debidas al viento. La comparación se basa en la evaluación de las variables de estudio aerodinámico y estructural en función de condiciones como la dirección del viento, la velocidad del viento y una variación en la geometría de la estructura. Finalmente, se concluye que las capacidades de la herramienta computacional del Túnel de Viento Virtual (VWT) presentan resultados que pueden ser de óptima utilidad en la aplicación industrial al análisis y diseño estructural de estructuras hinchables.The subject of pneumatic structures, specifically inflatable hangars, is a small sector in the field of construction which is in constant development and where there is a wide margin for improvement, innovation, and research which is a challenge in terms of calculation and design. For this reason, there are several studies that attempt to optimize the analysis of this typology, which does not have a specific standard. Among the alternative approaches, it is possible to find studies ranging from numerical models based on building standards to computational fluid mechanics. However, in the first case, they are not sufficiently accurate, or in the latter, the computational cost makes them excessive in the practical design. For this reason, and in order to optimize the practical analysis with accuracy and reasonable computational cost, CIMNE is currently developing Virtual Wind Tunnel (VWT), a new solution combining potential flow aerodynamics, explicit FE structural dynamics, and staggered FSI coupling. The thesis aims to carry out an exhaustive study on the structural analysis of inflatable hangars in order to optimize their calculation based on the new computational code. The experimental study is carried out by means of exhaustive analysis and comparison of the results obtained with VWT and RAMseries, taking into account as a determining factor the difference in the application of the loads due to the wind. The comparison is based on the evaluation of the aerodynamic and structural study variables as a function of conditions such as wind direction, wind velocity, and a variation in the geometry of the structure. Finally, it is concluded that the capabilities of the Virtual Wind Tunnel (VWT) computational tool present results that can be of optimal utility in the industrial application to the analysis and structural design of inflatable structures

Interactive CFD simulations

This project is about the development of an implementable Interactive Computer Fluid Dynamics methodology -- The range of this work begins with an overview of the current status of computational fluid dynamics simulation software and methodologies, continues with an introduction to what interactive and interactivity mean, develops an all original interactive CFD methodology to follow for the solution of fluid scenarios and finally, the description of the implementation of an interactive solver for CFD using the earlier developed methodology -- The project was developed entirely at the EAFIT University’s Applied Mechanics Laboratory in Medellin and is part of a collaboration effort in companionship with the University of Aberta in Canada and Los Andes University in Bogota, Colombi

A Direct Comparison of Small Aircraft Dynamics between Wind Tunnel and Flight Tests

The miniaturization of embedded electronics and sensors driven by the rapid development of mobile devices has enabled powerful avionics systems for very small aircraft. This enables a potential step forward in accurate flight data gathering for vehicles weighing 5 kg or less. Being able to flight test a small platform like this also allows the comparison of the results with reference data from ground testing in a standard sized wind tunnel of an identical airframe. With this process, the following questions can be answered: Firstly, would such a system then be able to collect accurate flight data for system identification (ID)? Is it possible at all to fly a small, remotely piloted aircraft precisely enough to record the required data, given its sensitivity to atmospheric turbulence, airframe noise, limitations of the remote piloting and so on? And secondly, if accurate data has been obtained, how well do the two experiments match? The small scale might potentially result in previously unknown or at least insignificant physical phenomena, which need to be taken into account when flight testing such a small platform. The changes in the inertial properties of the platform due to the added mass effect is one of these phenomena, which can typically be ignored for full scale aircraft. However, this has proven to be critically important for the successful analysis and comparison of the flight- and wind tunnel data obtained throughout this project. The avionics suite designed for this research was developed in house, since the weight restrictions of the small platform excluded any commercially available flight data recording packages. The suite features an lightweight airdata probe, control surface feedback sensors, a custom designed GPS receiver and many other advanced components previously not possible at this scale. A commercial reference INS was used to benchmark the system. The UAVmainframe also provides basic flight control functionality to aid the pilot in obtaining the required trim conditions and turbulence mitigation. Extensive data compatibility analysis and calibrations were performed on the recorded data using an Extended Kalman Filter (EKF) and various other methods to ensure the best possible data quality. The inertial properties of the test aircraft were determined by swing tests. The significance of the added mass contributions was discovered during these tests, which added up to 25% onto the `true' airframe inertial properties. In an effort to estimate these added mass terms, it has been found that the methods presented in literature to determine the corrections for full scale aircraft do not give the correct results for the small scale aircraft under consideration. Swing tests of a flat plate model of the test aircraft also did not capture the magnitude of the phenomenon correctly, which led to swing tests with a geometrically similar 3-d object of known inertial properties to successfully estimate the added mass corrections. Static derivatives were obtained from conventional wind tunnel testing, in conjunction with a high fidelity three dimensional inviscid solution using the PanAir code. A dynamic test rig was used in the wind tunnel to determine the dynamic derivatives. It allowed the instrumented airframe to rotate freely on a three axis gimbal, essentially 'fly' in the tunnel. The aerodynamic derivatives from these 3 DoF tests were estimated by performing system ID on the recorded data, where the model structures were modified for the reduced set of motion variables. Extensive flight testing was performed at the university's flight test centre. These tests showed the difficulty of testing such a small and light airframe due to wind and airframe noise, as well as the limitations due to lack of feedback received by the remote pilot. The pilot was aided by the flight control system to achieve a good trim condition, and pre-recorded input sequences, similar to the dynamic wind tunnel tests, were used to excite the longitudinal and lateral dynamics of the aircraft. One particular finding during the test campaign was that there is no such thing as totally calm conditions for this scale of airframe. Other findings include a high correlation between the pitch damping term and the pitching moment due to elevator, making it impossible to determine both at the same time, and that in flight the inertial properties of the test aircraft change to the values that include the added mass components, as compared to the dynamic wind tunnel tests, where the `true' inertias are used. By including these findings in the data processing, close agreement between flight and ground test data has been achieved

The effects of wind shear on convective boundary layer entrainment.

24 large eddy simulations (LES) were conducted for CBLs growing under varying conditions of surface buoyancy flux, free atmospheric stratification, and wind shear. With the intent of elucidating the effects of surface layer shear versus shear at the CBL top, the simulations were divided into three categories: a free atmosphere with no mean wind (NS), an atmosphere with a height-constant geostrophic wind of 20 m/s (GC), and a case with strong shear in the geostrophic wind (GS). The entrainment predictions of LES were then compared with predictions from two 1.5-order, e-l turbulence models based on the Reynolds-Averaged Navier-Stokes (RANS) and with two bulk models based on integral budgets of CBL buoyancy, momentum, and turbulence kinetic energy (TKE): the zero order model (ZOM) and the first order model (FOM).In the LES cases, the sheared CBLs grew fastest, relative to the shear-free CBLs when the surface buoyancy flux was weak and the atmospheric stratification was moderate or weak. From the simulations, there are two fundamental findings. The first is that the entrainment zone shear is much more important than the surface shear in enhancing CBL entrainment. The other is the discovery of a layer of constant Ri that forms within the entrainment zone when the relative effects of shear stand out strongly enough.Tests of RANS-based e-l closures against the LES data show that the e-l closures exaggerate the differences between the entrainment rates of shear-free CBLs and sheared CBLs. The entrainment rate predicted by e-l closures for sheared CBLs is too large, regardless of whether the modeled entrainment zone TKE is larger or smaller than that in LES. It is possible that the formulation of the master length scale l for CBL turbulence needs to be reduced when shear is a significant source of TKE.The current study examines the dynamics of entrainment and the evolution of the dry atmospheric convective boundary layer (CBL) when wind shear is present and seeks to make comprehensive tests of existing hypotheses regarding the effects of wind shear on entrainment and the parameterizations that have been developed from them.The comparisons between LES and the lidar data for the May 22, 2002 sheared CBL case show that CBL depth comparisons can be made relatively easily when a suitable atmospheric sampling strategy is used. However, the observed CBL growth rates differed considerably from LES, underscoring the fact that atmospheric processes not simulated in LES have a significant influence on the CBL depth. Despite these problems, the conclusions based on the simulation results need to be tested more fully against atmospheric data.The tests of the ZOM parameterizations using LES data highlighted their mathematical deficiencies, which caused them to fail when shear was strong. When the full FOM equations were integrated using an entrainment zone depth limited by a critical Richardson number (Ri), they were able to model some of the sheared CBL cases in which ZOM fails. Based on the FOM and LES results and the results of testing other parameterizations, any Ri-limited entrainment equation would seem to be most suited to model the dynamics of entrainment in sheared CBLs. Despite its shortcomings, the ZOM places the shear-free CBLs in a common framework from which they can be easily compared to sheared CBLs

Research Reports: 1997 NASA/ASEE Summer Faculty Fellowship Program

For the 33rd consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The program was conducted by the University of Alabama in Huntsville and MSFC during the period June 2, 1997 through August 8, 1997. Operated under the auspices of the American Society for Engineering Education, the MSFC program was sponsored by the Higher Education Branch, Education Division, NASA Headquarters, Washington, D.C. The basic objectives of the program, which are in the 34th year of operation nationally, are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA centers. The Faculty Fellows spent 10 weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague. This document is a compilation of Fellows' reports on their research during the summer of 1997. The University of Alabama in Huntsville presents the Co-Directors' report on the administrative operations of the program. Further information can be obtained by contacting any of the editors

Numerical and experimental optimisation of a high performance heat exchanger.

The aim of this research is to numerically and experimentally scrutinise the thermal performance of a typical heat exchanger fitted in a domestic condensing boiler. The optimisation process considered the pins' geometry (circular pins and elliptical pins), pins' spacing, pitch distance, the pressure drop across the heat chamber and the occurrence of thermal hot spots. The first part of the study focused on the effect of altering the circular pins spacing and pins pitch distance of the heat exchanger. Computational Fluid Dynamics (CFD) is used to scrutinise the thermal performance and the air flow properties of each model by changing these two parameters. In total, 13 circular pin models were investigated. Numerical modelling was used to analyse the performance of each model in three-dimensional computational domain. For comparison, all models shared similar boundary conditions and maintained the same pin height of 35 mm and pin diameter of 8 mm. The results showed that at a given flow rate, the total heat transfer rate is more sensitive to a change in the pins spacing than a change of the pins pitch. The results also showed that an optimum spacing of circular pins can increase the heat transfer rate by up to 10%.The second part of the study, focused on investigating the thermal performance of elliptical pins. Four elliptical pin setups were created to study the thermal performance and the air flow properties. In comparison with circular pins, the simulation results showed that the optimum use of eccentricity of elliptical pins could increase the total energy transfer by up to 23% and reduce the pressure drop by 55%. To validate the acquired CFD results, a Thermal Wind Tunnel (TWT) was designed, built and commissioned. The experimental results showed that the numerical simulation under predicted the circular pin models' core temperatures, but over predicted the elliptical models core temperatures. This effect is due to the default values of the standard k - E transport equations model used in the numerical study. Both numerical and experimental results showed that the elliptical models performed better compared to its circular pins counter parts.The study also showed that heat exchanger optimisation can be carried out within a fixed physical geometry with the effective use of CFD

Hands-on science. Rethinking STEAM education in times of uncertainty

After over two years of major constraints imposed by the COVID pandemic, the education world is still trying to find ways to adapt in order to keep providing, in an effective way, its crucial contribution to the world’ development our societies need and expect

Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems

The electrical power system is undergoing a revolution enabled by advances in telecommunications, computer hardware and software, measurement, metering systems, IoT, and power electronics. Furthermore, the increasing integration of intermittent renewable energy sources, energy storage devices, and electric vehicles and the drive for energy efficiency have pushed power systems to modernise and adopt new technologies. The resulting smart grid is characterised, in part, by a bi-directional flow of energy and information. The evolution of the power grid, as well as its interconnection with energy storage systems and renewable energy sources, has created new opportunities for optimising not only their techno-economic aspects at the planning stages but also their control and operation. However, new challenges emerge in the optimization of these systems due to their complexity and nonlinear dynamic behaviour as well as the uncertainties involved.This volume is a selection of 20 papers carefully made by the editors from the MDPI topic “Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems”, which was closed in April 2022. The selected papers address the above challenges and exemplify the significant benefits that optimisation and nonlinear control techniques can bring to modern power and energy systems

Wind Power

This book is the result of inspirations and contributions from many researchers of different fields. A wide verity of research results are merged together to make this book useful for students and researchers who will take contribution for further development of the existing technology. I hope you will enjoy the book, so that my effort to bringing it together for you will be successful. In my capacity, as the Editor of this book, I would like to thanks and appreciate the chapter authors, who ensured the quality of the material as well as submitting their best works. Most of the results presented in to the book have already been published on international journals and appreciated in many international conferences