Aerospace Engineering

In the next decade or two, extremely accurate tests of general relativity under extreme conditions are expected from gravitational wave observations of binary black hole mergers with a wide range of mass ratios. In addition, major improvements are planned in both strong and weak equivalence principle tests; clock measurements based on the ACES program on the ISS; more accurate light-bending measurements; and other new types of tests. However, whether these tests are all consistent with general relativity or not, it still appears desirable to proceed with a much improved measurement of the Shapiro time delay. A suggested approach 1 is based on using a high-quality optical clock in a drag-free spacecraft near the sun-earth L1 point and a smaller drag-free transponder spacecraft in a two-year period solar orbit. Laser phase travel-time measurements would be made between the two spacecraft over a period of 10 or 20 days around the time when the line of sight passes through the Sun. The requirements on the optical clock stability and on the drag-free systems will be discussed. The accuracy achievable for the time-delay appears to be better than 1 part in 100 million.

NET, in collaboration with the Jet Propulsion Laboratories (JPL), the University of Colorado, Politecnico di Torino and Harvard Smithsonian Center for Astrophysics (SAO) is building a laser-cooled cesium (Cs) atomic clock for flight on the Intemational Space Station (ISS). The clock, named PARCS (Primary Atomic Reference Clock in Space) takes advantage of the microgravity environment of the ISS to achieve a high stability of ,.(e) 5 x 10-'4*-"2 and an ultimate accuracy of 5 x 1 O-", more than an order of magnitude better than terrestrial Cs fountains. Additionally, this accurate clock on the ISS will be used to perform a variety of tests of fundamental physics, such as relativity theory. Since the ISS orbit will cover a large portion of the earth, PARCS will serve as an internationally accessible primary standard thus improving comparisons between intemational standards laboratories. Here we describe the scientific objectives of the PARCS mission, present our design considerations and laboratory studies of prototypes of clock components, and evaluate the anticipated performance of PARCS such as systematic shifts and the ultimate accuracy of the device. * Contribution of the US Government. Not subject to US copyright.

This work is focused on the aerodynamic analysis of a small satellite provided with a deployable aerobrake. The satellite is intended to perform a completely aerodynamic de-orbiting maneuver from Low-Earth-Orbit. A brief discussion about the aerodynamic effects of the position of the aero-brake along the longitudinal axis of a simplified axisymmetric system is presented. Moreover, a more complex architecture, envisaging deployable solar panels for the enhancement of power generation along the orbital path, is proposed and analyzed. The present paper is aimed at the evaluation of the influence of such a configuration on the satellite aerodynamic parameters. Computations have been carried out by means of a Direct Simulation Monte Carlo (DSMC) code at altitude of 150 km, velocity of 7800 m/s and in the interval of angle of attack 0-180 deg with a spacing of 10 deg. The results verified that the deployable solar panels strongly influence Aerodynamics of the satellite. One of the most relevant aspects is the variation of the longitudinal stability equilibrium that becomes more stable. Furthermore, the deployable solar panels increase the aerodynamic drag when the aero-brake is closed, affecting the drag modulation capability.

HyPlane is the Italian aerospaceplane proposal targeting, at the same time, both the space tourism and point-to-point intercontinental hypersonic flights. Unlike other aerospaceplane projects, relying on boosters or mother airplanes that bring the vehicle to high altitude, HyPlane will take off and land horizontally from common runways. According to the current project, HyPlane will fly sub-orbital trajectories under high-supersonic/low-hypersonic continuum flow regimes. It can go beyond the von Karman line at 100 km altitude for a short time, then starting the descending leg of the trajectory. Its aerodynamic behavior up to 70 km have already been studied and the results published in previous works. In the present paper some aspects of the aerodynamic behavior of HyPlane have been analyzed at 80, 90 and 100 km. Computer tests, calculating the aerodynamic parameters, have been carried out by a Direct Simulation Monte Carlo code. The effects of the Knudsen, Mach and Reynolds numbers have been evaluated in clean configuration. The effects of the aerodynamic surfaces on the rolling, pitching and yawing moments, and therefore on the capability to control attitude, have been analyzed at 100 km altitude. The aerodynamic behavior has been compared also with that of another aerospaceplane at 100 km both in clean and flapped configuration.

Incorporation of clay in polymers is known to improve mechanical properties such as tensile modulus and tensile strength, but to generally decrease elongation at break and toughness. However, recent studies reported an increase in elongation at break for linear low density polyethylene based nanocomposites. In this work, the tensile properties of clay micro-and nanocomposites based on high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) of similar molecular weights were evaluated. LLDPE micro-and nanocomposites exhibited an extraordinary enhancement in toughness compared to LDPE or HDPE microcomposites. Based on electron microscopy and on acoustic emission and volume strain measurements during tensile testing, micro-mechanisms of deformation in polyethylene/clay micro-and nanocomposites were proposed.

The effect of the return from the platform on which a cross-eye jammer is mounted is significant in many practical cross-eye jamming scenarios. However, all published analyses of skin-return affected cross-eye jamming have significant limitations. These limitations are addressed by deriving equations for the distribution of the cross-eye gain in the presence of skin return. The value of these results is demonstrated by using them to gain insight into how skin return affects cross-eye jamming. Index Terms-Cross-eye jamming, electronic warfare (EW), electronic countermeasures (ECM), radar countermeasures, and monopulse radar.

The simultaneous use of multiple retrodirective cross-eye jammers is analysed for both the case where the jammer loops point in different directions and when they point in the same direction. In both cases, the use of multiple cross-eye jammer loops is shown to lead to significantly increased angular errors in the threat radar under certain conditions. Alternatively, the sum-channel return can be increased to reduce the jammer-to-signal ratio (JSR) requirements for each jammer loop.

It is desirable to limit the apparent target to one side of a retrodirective cross-eye jammer despite the variation caused by platform skin return. The relationship between the jammer parameters and the jammer-to-signal ratio (JSR) to ensure that this occurs is investigated. When this relationship is not satisfied, the proportion of the apparent targets generated on the opposite side of the jammer is determined.

The matching required between the two directions through a retrodirective cross-eye jammer is considered using both the traditional phase-front analysis and an extended analysis. The design parameters to achieve a specified tracking error are derived and an optimal design is proposed. The results for the extended analysis show that the tolerances required to induce large angular errors in a monopulse radar are not as strict as the traditional analysis suggests.

The RadioAstron mission has obtained a series of detailed multi-frequency images of the brightest blazars of the radio sky concentrated in three key science programs. We present here results of the program on powerful jets in blazars. In the first two years of the mission, observations of compact relativistic jets in 0836+710, 3C 345, 3C 273, and 4C +69.21 were made at kk 18, 6, and 1.3 cm. The resulting images have revealed compact emitting regions with brightness temperature in excess of 10 13 K and a complex jet structure that can be explained by plasma instability developing in a relativistic outflow. We present here some highlights of these space-VLBI observations, designed to resolve the innermost regions in these powerful targets and address some of the still unanswered questions on their physical nature.

We present the first results on the analysis of the structures observed in the jet of the quasar 0836+710. We obtain the ridge lines of the jet at different epochs and several frequencies. We interpret the oscillatory structures obtained as waves that can be attached to the growth of instabilities. We explain how to derive information on the nature and origin of these structures by fitting together the ridge lines at different epochs and frequencies. Finally we show the predictive power of this approach: by generating an artificial wave and applying the corresponding relativistic and projection effects we show that apparent changes in the jet direction in the inner regions of jets can be attached to the transversal motion of structures.

In this paper we report measurements of mean and fluctuating axial velocities, measured using a laser Doppler anemometer, for a 0.125% solution of a polyacrylamide, Separan AP 273 E, in fully-developed pipe flow. Although the results cover the laminar, transitional and fully turbulent regime, particular attention is placed on the transition regime, where, as has been observed previously, the mean velocity profiles exhibit a stable, and repeatable, asymmetry. Radial distributions of axial velocity at three axial locations, and for various azimuthal angles, highlight the three dimensional nature of this asymmetry.

A known difficulty with using the Clauser chart method to determine the friction velocity in wall bounded flows is that it assumes, a priori, a logarithmic law for the mean velocity profile. Using both experimental and DNS data in the literature, this note explicitly shows how friction velocities obtained using the Clauser chart method can potentially mask subtle Reynolds-number-dependent behavior.

Carbon fiber reinforced plastics (CFRP) are more and more used in aerospace applications because of their potential to considerably reduce the weight. Using CFRP, however, the problem occurs that at painted parts the paint thickness has to be measured non-destructively. Traditional procedures using eddy current or ultrasound come to their limits because the substrate is only medium conducting and furthermore anisotropic. These substrate properties reduce the reliability of traditional non-destructive paint thickness measurements considerably. In 2007 we have presented a new procedure to measure paint thickness on CFRP in a laboratory environment. This procedure was based on microwave technology. The present paper describes the development of an instrument which allows the paint thickness measurement also mobile in an industrial environment. Basically it makes use of the above mentioned microwave procedure. The instrument that was presented in 2007 already showed the measurement resu...

Solid Earth-atmosphere interactions and possibly solid Earth-seafloor interactions prior to major earthquakes are the subject of this study. Using data from Moderate Resolution Imaging Spectroradiometer (MODIS) onboard National Aeronautical Space Agency (NASA) Terra and Aqua satellites, we have begun to analyze infrared (IR) emissivity, land surface temperature (LST) and sea surface temperature (SST) data. Specifically, we look for correlations between solid Earth processes and atmosphere/ocean dynamics prior to strong earthquakes, selecting examples from 2001 and 2000. We find evidence for such correlations, specifically for a thermal anomaly LST pattern that is apparently related to pre-seismic activity. A new mechanism has recently been proposed based on positive hole-type charge carriers in rocks, which become activated when rocks are subjected to high levels of stress prior [J. Geodyn. 33 (2002) 545-572]. The appearance of these electronic charge carriers within a finite rock volume leads to enhanced IR emission from the rock surface in the 8-12 lm region.

This paper first discusses the nature of the space which people in small urban areas use for recurrent activities. It is postulated that most work on the individual's activity space is founded on a classical geometric conception of place. An alternative cognitive definition is proposed. Places which are used for such purposes as shopping or recreation are described by learned bundles of meanings (constructs) given a transportation system permitting movement within space. Recent modifications of Kelly's personal construct theory are used to demonstrate the cognitive definition of place, with data from a sample of 31 university students. It is suggested that elicited transportation-related constructs of places can be utilized to develop improved models of behavior within urban activity spaces.

In this paper we report a 3U CubeSat named CUAVA-1 designed by the ARC Training Centre for CubeSats, UAVs, and Their Applications (CUAVA). CUAVA, funded by the Australian Research Council, aims to train students, develop new instruments and technology to solve crucial problems, and help develop a world-class Australian industry in CubeSats, UAVs, and related products. The CUAVA-1 project is the Centre’s first CubeSat mission, following on from the 2 Australian satellites INSPIRE-2 and UNSW-EC0 CubeSats that launched in 2017. The mission is designed to serve as a precursor for a series of Earth observations missions and to demonstrate new technologies developed by our partners. We also intend to use the satellite to provide students hands-on experiences and to gain experience for our engineering, science and industry teams for future, more complex, missions.

Virtual Cathode lifetimes and floating potential measurements in a Polywell T M fusion device MATTHEW CARR, JOE KHACHAN, School of Physics, University of Sydney -The Polywell T M is a spherically convergent ion focus concept first developed by R Bussard in the 1980s as a possible device for controlled thermonuclear fusion. The device aims to magnetically confine electrons with a quasi-spherical-cusp magnetic field, forming a deep potential well in the centre of the device, which can attract and maintain a high density of local energetic ions passing through the potential well. Careful design of the magnetic field and coil formers might help to substantially reduce the former/grid collision losses that plague other IEC devices. Floating potential measurements in the core of a Polywell have shown that a virtual cathode is established, with floating potentials of up to -250V obtained for milliseconds. The lifetime of the virtual cathode was determined only by the shape and duration of the magnetic coil current. This implies that currents of increasing duration will increase the lifetime of the virtual cathode. Further measurements reveal that virtual cathode formation could only be established within a narrow magnitude range of coil currents. We find that the floating potential increases with decreasing gas pressure.

In this work the authors investigate how target sputtering, dose retention, and damage formation is generated in thin-body semiconductors by means of energetic ion impacts. The problems associated with ion implanting or plasma doping Si thin-bodies are well documented, however it is not clear how changing the target material to other semiconductors currently being considering for multi-gate field-effect transistor devices will counteract or enhance these effects. By means of Binary Collision Approximation based modeling with The Stopping and Range of Matter (SRIM) software, we explore the consequences of different target atomic density, lattice density, surface binding energies, and lattice binding energies on target sputtering, dose retention, and damage formation.

Today's aerospace assembly is a huge manual task according to strictly controlled instructions, where different operators are responsible for different areas. This harmonizes with the overall lean approach, but the assembly is very time-consuming and some tasks are not ergonomically friendly, such as assembly tasks inside a wing box. Here, it could be possible to increase automation with the aim to facilitate a shorter assembly time and ergonomically improved workplace. This paper will present different assembly cell concepts utilizing different safety strategies to achieve human-robot cooperation in an aerospace industry assembly line. These concepts will be discussed in relation to a case in the aerospace industry. The paper concludes with suggestions for three conceptual human-robot cooperation layouts. These are based on previous research in the areas of safety and human-robot cooperation, in combination with observations from an aerospace assembly line.

We formulate and solve data-driven aerodynamic shape design problems with distributionally robust optimization (DRO) approaches. Building on the findings of the work [13], we study the connections between a class of DRO and the Taguchi method in the context of robust design optimization. Our preliminary computational experiments on aerodynamic shape optimization in transonic turbulent flow show promising design results.

Triton is one of the most peculiar satellites of the Solar System, for several reasons. First of all, for its retrograde orbit that makes of Triton a plausibly captured satellite. Moreover, Triton is synchronously rotating, so we can speak of leading and trailing sides. The analysis of the Voyager images showed remarkable differences between the two hemispheres, being the leading side much more cratered that the trailing one. The origin of this huge asymmetry is still not clearly understood. We think that some hints can arise from a spectral investigation of Triton's two faces. To this end, we obtained new observations of Triton with the ESO New Technology Telescope (La Silla, Chile) in October 2002. We discuss here the spectra and the differences between the two faces, and the implications of these findings for a better understanding of the surface composition of Triton.

This paper aims to give a brief description of the Wide Angle Camera (WAC), built by the Centro Servizi e Attività Spaziali (CISAS) of the University of Padova for the ESA ROSETTA Mission to comet 46P/Wirtanen and asteroids 4979 Otawara and 140 Siwa. The WAC is part of the OSIRIS imaging system, which comprises also a Narrow Angle Camera (NAC) built by the Laboratoire d'Astrophysique Spatiale (LAS) of Marseille. CISAS had also the responsibility to build the shutter and the front cover mechanism for the NAC. The flight model of the WAC was delivered in December 2001, and has been already integrated on ROSETTA.

This study systematically investigates the effect of Shear Thickening Fluid (STF) treatment on the high strain rate properties of UHMWPE (Ultra High Molecular Weight Poly Ethylene) composites. Spherical nanosilica particles of size 100 nm were used for the synthesis of STF. The high strain rate impact studies were accomplished on in-house designed and fabricated Split Hopkinson Pressure Bar (SHPB) experimental set-up. Ò was used as the ballistic composite. Both STF-treated as well as neat Gold Shield Ò specimens were subjected to high strain rate impact testing. From the experimental results and Fractography studies it was revealed that STF treatment enhanced the ballistic resistance of Gold Shield Ò composite material. In the SHPB experiments, the improved ballistic performance of STFtreated Gold Shield Ò specimens was manifested in terms of higher peak stress, specimen strain rates and impact toughness.

I would like to thank and express my gratitude to Assistant Professor Funda Tõhmõnlõoğlu for her supervision and guidance during my studies. I am also grateful to Professor Devrim Balköse, and Professor Semra Ülkü for their valuable comments and suggestions. Special thanks to Research Specialist Filiz Özmõhçõ for her contributions to my thesis. I also would like to thank Research Specialist Özlem Çağlar for the FTIR analyses, Research Specialist Nesrin Gafaroğullarõ for the ICP analyses, Research Assistant Mert Sudağõdan, and the Biotechnology and Bioengineering Department for the microbiological tests, Petkim Petrochemicals Company, Feridun Şenol, and Research Assistant Dildare Metin, for performing the mechanical tests. I am also indebted to the laboratory technicians for their helps in the laboratory work. Special thanks to my roommates, Research Assistants: Ayben Top, Dildare Metin, and Semih Elbir for their friendships, understandings, and supports. Finally I would like to than...

Biophysical properties of agricultural materials are important in designing of processing machines. In this study, some physical properties of tomato ( Solanum lycopersicum ) fruits were determined and their mutual relationships were studied. Dimensions (major diameter, minor diameter, and length), mass, volume, fresh and dry matter weight, as well as rupture point under uniaxial loading were measured. Other properties; including Poisson's ratio, modulus of elasticity, energy for rupture, density, arithmetic mean diameter, geometric mean diameter, diameter of equivalent volume sphere, and sphericity were calculated accordingly. Statistical analysis of the data indicated significant correlations between the rupture force and fresh weight, volume, dry weight, major diameter, minor diameter, arithmetic mean diameter, geometric mean diameter, and diameter of equivalent volume sphere. Fruit volume has significant correlations with fresh weight and average diameter. Correlations betwe...

The detection of astrophysical very high energy (VHE) neutrinos in the range of TeV-PeV energies by the IceCube observatory has opened a new season in high energy astrophysics. Energies PeV imply that the neutrinos are originated from sources where cosmic rays (CRs) can be accelerated up to 10 17 eV. Recently, we have shown that the observed TeV gamma-rays from radio-galaxies may have a hadronic origin in their nuclear region and in such a case this could lead to neutrino production. In this paper we show that relativistic protons accelerated by magnetic reconnection in the core region of these sources may produce VHE neutrinos via the decay of charged pions produced by photo-meson process. We have also calculated the diuse ux of VHE neutrinos and found that it can be associated to the IceCube data.

Knowledge of the surface properties of small asteroids is important for relating astronomical observations of these objects to geologic ‘ground truth’, for understanding their relationships to meteorites, and for designing technologies and techniques for future robotic and human exploration, resource utilization, and impact hazard mitigation. Unfortunately, many of the interesting physical processes governing the microgravity geology of these small bodies are partially or completely masked in the 1-g environment in which we usually work and develop our ‘intuitive’ sense of how geologic processes work. Our Box-of Rocks Experiment II (BORE II) continues our ‘hands-on’ exploration of the processes in a relevant microgravity environment. Since nearly all asteroid regoliths are expected to have a substantial ferromagnetic component, magnetic sampling/grappling thus offers a novel mission concept and/or instrumentation architecture for future development. BORE II will be effectively a ref...

This paper proposes a spatial point process model on a linear network to analyse cruise passengers’ stop activities. It identifies and models tourists’ stop intensity at the destination as a function of their main determinants. For this purpose, we consider data collected on cruise passengers through the integration of traditional questionnaire-based survey methods and GPS tracking data in two cities, namely Palermo (Italy) and Dubrovnik (Croatia). Firstly, the density-based spatial clustering of applications with noise algorithm is applied to identify stop locations from GPS tracking data. The influence of individual-related variables and itinerary-related characteristics is considered within a framework of a Gibbs point process model. The proposed model describes spatial stop intensity at the destination, accounting for the geometry of the underlying road network, individual-related variables, contextual-level information, and the spatial interaction amongst stop points. The analy...

The mechanical performances and viscoelastic behaviour of starch-grafted-polypropylene/kenaf fibres composites were investigated on composites prepared by melt compounding and compression molding. In particular, the effects of various amounts (10, 20 and 30 wt.%) of kenaf fibres having two different initial aspect ratios (L/D = 30 and 160) were analyzed. The processing-induced variation of fibre length was quantified by optical microscopy observations. Young modulus, stress at break, impact resistance and hardness values of starch-grafted-polypropylenes were remarkably improved by kenaf fibres. Moreover, creep tests have shown a noticeable enhancement of the creep stability of composites with fibres loading.

The mechanical performances and viscoelastic behaviour of starch-grafted-polypropylene/kenaf fibres composites were investigated on composites prepared by melt compounding and compression molding. In particular, the effects of various amounts (10, 20 and 30 wt.%) of kenaf fibres having two different initial aspect ratios (L/D = 30 and 160) were analyzed. The processing-induced variation of fibre length was quantified by optical microscopy observations. Young modulus, stress at break, impact resistance and hardness values of starch-grafted-polypropylenes were remarkably improved by kenaf fibres. Moreover, creep tests have shown a noticeable enhancement of the creep stability of composites with fibres loading.

The leakage flow in low-speed fans provided with rotating shroud has been surveyed by means of two-dimensional LDV and PIV. Measurements have been taken upstream of the rotor and in the gap area at different operating conditions. The flow contains both periodic and non-periodic large-scale flow structures, which are responsible for the noise generation. The former structures have been extracted by means of the ensemble average technique, and, in order to study the latter ones, the non-periodic part of the instantaneous velocity field has been analysed by means of the proper orthogonal decomposition technique. In the present fan, the leakage flow consists in a jet which leaves the gap in the diagonal direction. Depending on rotational speed and blade loading, the jet may form a recirculation bubble anchored to the rotor ring or it may turn radially, forming a large recirculating flow zone. Large-scale, periodic vortical structures leaving the gap are convected by the leakage flow, either wrapping around the recirculation bubble or flowing radially outwards with a spiral pattern. In the former case, such structures, though weakened, likely reach the rotor, while, in the latter case, they have not been found at the rotor entrance. Hence, a different degree of mixing takes place which is consistent with the extension of the blade part where the leakage flow is reingested. This is consistent with the differences in acoustic measurements. The POD technique has shown that, at high loading, large-scale non-periodic vortical structures convect towards the rotor inlet. They are weaker though comparable to the periodic ones released from the gap; at low rotational speed they are stronger than at high rotational speed. Non-periodic flow structures may be present in the flow leaving the gap also, but it has not been possible to identify them clearly. Likely, non-periodic flow structures are originated by the ripping of the periodic ones. A possible explanation for the noise generation in fans with rotating shroud is that the periodic pressure field anchored to the rotor results in the release of periodic flow structures from the gap. Then, such structures may reach the rotor or rip during convection, likely resulting in non-periodic ones which are ingested by the rotor. In both cases, the interaction with the rotor blades likely results in noise generation. The degree of prerotation of the leakage flow is consistent with the frequency shift of the narrowband humps observed in the sound pressure spectra.

In the present study, the effect of hinge position (H) has been numerically investigated to find the appropriate position for improving the aerodynamic performance of the NACA 0012 flapped airfoil. In addition, perpendicular and tangential suctions have been applied to control the flow separation and enhance the aerodynamic performance over the NACA 0012 flapped airfoil at each different hinge positions. The simulations were carried out at a Reynolds number of 5 × 10 5 (Ma = 0.021) based on two-dimensional incompressible unsteady Reynolds-averaged Navier-Stokes calculations to determine the adequate hinge position. The turbulence was modeled using the shear stress transport k-ω turbulence model. The effect of perpendicular suction (θ jet = -90°) and tangential suction (θ jet = -30°) was computationally studied over NACA 0012 flapped airfoil for five different hinge positions (H = 0.7c, 0.75c, 0.8c, 0.85c and 0.9c) and a flap deflection (δ f ) of 15°. Based on the results, the hinge position significantly affects the aerodynamic performance of the airfoil. The lift coefficient increased clearly as the hinge position moved to the trailing edge of the airfoil. Using perpendicular suction caused to increase the lift coefficient and decrease the drag coefficient. Consequently, the maximum value of the lift-to-drag ratio (C L /C D ) for perpendicular and tangential suctions was achieved about 35.8% and 25.1% higher than that of the case without suction at an angle of attack of 12° and H = 0.9c. Also, the effect of perpendicular suction was more considerable compared to the tangential suction. This caused a reduction in the size of the recirculation zone from 0.5 to 0.09 of the airfoil chord length and also transferred it from 1.13 to 1.18 of the airfoil chord length.

The direct simulation Monte-Carlo (DSMC) method was applied to the analysis of low-density plumes exhausting from a small Mach 2.5 nozzle into vacuum and finite ambient pressures. Three different plume regimes were considered: 1) the underexpanded jet flow achieved when expanding into vacuum, 2) the ideal expanded jet flow achieved when the nozzle exit flow pressure is equal to the ambient pressure and 3) the overexpanded jet flow achieved when the ambient pressure exceeds the nozzle exit flow pressure. The numerical simulations indicates that the idealand over-expanded jet can be treated with continuum methods, whereas for the highly underexpanded jet an approach based on kinetic theory is required.

The past decade has seen a qualitative advancement of our understanding of physical phenomena involved in flow separation in supersonic nozzles; in particular, the problem of side loads due to asymmetrical pressure loads, which constitutes a major restraint in the design of nozzles for satellite launchers. The development in this field is to a large extent motivated by the demand for high-performance nozzles in rocket engineering. The present paper begins with an introduction to the physical background of shock-boundary-layer interactions in basic 2D configurations, and then proceeds to internal axisymmetric nozzle flow. Special attention is given to past and recent efforts in modeling and prediction, turning physical insight into applied engineering tools. Finally, an overview is given on different technical solutions to the problem if separation and side loads, discussed in the context of rocket technology.

The increasing demand for higher performance in rocket launchers promotes the development of nozzles with higher performance, which is basically achieved by increasing the expansion ratio. However, this may lead to flow separation and ensuing unstationary, asymmetric forces, so-called side-loads, which may present life-limiting constraints on both the nozzle itself and other engine components. Substantial gains can be made in the engine performance if this problem can be overcome, and hence different methods of separation control have been suggested, however none has so far been implemented in full scale, due to the uncertainties involved in modelling and predicting the flow phenomena involved. The present thesis presents a comprehensive, up-to-date review of supersonic flow separation and side-loads in internal nozzle flows with ensuing side-loads. In addition to results available in the literature, it also contains previously unpublished material based on this author's work, whose main contributions are (i) discovery the role of transition between different separation patterns for side-load generation, (ii) experimental verification of side-loads due to aeroelastic effects and (iii) contributions to the analysis and scaling of side-loads. A physical description of turbulent shock wave boundary layer interactions is given, based on theoretical concepts, computational results and experimental observation. This is followed by an in-depth discussion of different approaches for predicting the phenomena. This includes methods for predicting shock-induced separation, models for predicting side-load levels and aeroelastic coupling effects. Examples are presented to illustrate the status of various methods, and their advantages and shortcomings are discussed. The third part of the thesis focuses on how to design sub-scale models that are able to capture the relevant physics of the full-scale rocket engine nozzle. Scaling laws like those presented in here are indispensable for extracting side-load correlations from sub-scale tests and applying them to full-scale nozzles. The present work was performed at VAC's Space Propulsion Division within the framework of European space cooperation.

This study explores the hydrodynamic and aerodynamic performance of a submarine and an airfoil under various angles of attack (AoA) using advanced computational fluid dynamics (CFD) simulations. The incompressible Reynolds Averaged Navier-Stokes (RANS) equations were solved using ANSYS, leveraging its segregated flow solver and adjoint optimization capabilities to automate the creation and meshing of computational domains. By analyzing velocity and pressure distributions across coarse and fine mesh resolutions, the research highlights the superior accuracy of fine meshes in capturing complex flow phenomena, such as flow separation, wake behavior, and velocity gradients. Submarine simulations with control surfaces revealed distinct symmetries and nearly zero maneuvering coefficients for specific configurations, filling gaps in the existing literature on fully appended geometries. Optimization efforts led to an enhanced design with improved aerodynamic efficiency, achieving reduced drag and stabilized flow, as validated by consistent performance at AoAs of 0°, 20°, and 80°. This work demonstrates the importance of fine mesh resolution, automated workflows, and adjoint solvers in accelerating the iterative design process and optimizing marine and aerodynamic structures for real-world applications. These findings highlight the significant influence of high attack angles on the submarine's vertical plane flow. Such insights offer a mechanical foundation for analyzing nonlinear motion phenomena during submarine surfacing. .

In metal/insulator/semiconductor structures, capacitance–voltage characteristics and capacitance or voltage transients can be measured in different conditions, which are described and implemented. Each method contains information about charges which are accommodated, captured, or emitted by energy levels or bands at interface and inside the oxide. Pulsed capacitance measurements and differential isothermal procedures are analyzed and performed. Calibration of the energy scale from the interface potential as a function of the applied voltage and extraction of the interface state spectra and characteristic response times independently are possible with the help of signal processing by Fourier transform of transients at one or few selected temperatures. Different trap filling conditions may help to discriminate between interface and oxide states. These methods are applied to Al/SrTiO3/Si capacitors as an example.

A three-dimensional thermal simulation investigation for the thermal management of GaN-on-SiC monolithic microwave integrated circuits (MMICs) of consisting multi-fingers (HEMTs) is presented. The purpose of this work is to demonstrate the utility and efficiency of the three-dimensional Transmission Line Matrix method (3D-TLM) in a thermal analysis of high power AlGaN/GaN heterostructures single gate and multi-fingers HEMT SSPA (solid state power amplifiers). The self-heating effects induce thermal cross-talk between individual fingers in multi-finger AlGaN/GaN that affect device performance and reliability. Gate-finger temperature differences only arise after a transient state, due to the beginning of thermal crosstalk which is attributed to the finite rate of heat diffusion between gate fingers. The TLM method accounts for the real geometrical structure and the non-linear thermal conductivities of GaN and SiC in order to improve the realistic calculations accuracy heat dissipation and thermal behavior of the device. In addition, two types of heat sources located on the top of GaN layer are considered in thermal simulations: Nano-scale hotspot as a pulsed wave heat source under gate and micro-scale hotspot as a continuous wave heat source, between gate and drain. Heat diffusion however, occurs not only between individual gate fingers (inter-finger) in a multi-finger HEMT, but also within each gate finger (intra-finger). To compare results, a Micro-Raman Spectroscopy experience is conducted to obtain a detailed and accurate temperature distribution. Good agreement between the microscopic spectral measurement and TLM simulation results is observed by accepting an error less than 2.2% relative to a maximum temperature. Results show that the 3D-TLM method is suitable for understanding heat management in particular for microwave devices AlGaN/GaN HEMTs SSPA amplifier. TLM method helps to select and locates the expected hot spots and to highlight the need of thermal study pre-design in order to minimize the system-level thermal dissipation and lead therefore to higher reliability.

Mosquitoes have slimmer wings, higher flapping frequencies, and much lower amplitudes than most other insects. These unique features signify special aerodynamic mechanisms. Besides the leading-edge vortex, which is one of the most common mechanisms of flapping-wing flight, mosquitoes have two distinctive mechanisms: trailing-edge vortex and rotational drag. In this study, the three-dimensional flow field around a hovering mosquito is simulated by using the immersed boundary method. The numerical results agree well with previous experimental data. Mechanisms unique to mosquitoes are identified from the instantaneous pressure and vorticity fields. The flow domains, containing several vortical structures produced by the flapping wings, are divided into different regions for quantitatively analyzing the contribution of vortical structures to the lift. Advection of the trailing-edge vortex and production of the leading-edge vortex each contribute peaks in lift. Passive deformation of the...

This paper presents the mission analysis, requirements, system design, system level test results, as well as mass and power budgets of a 1-unit CubeSat ESTCube-1 built to perform the first in-orbit demonstration of electric solar wind sail (E-sail) technology. The E-sail is a propellantless propulsion system concept that uses thin charged electrostatic tethers for turning the momentum flux of a natural plasma stream, such as the solar wind, into spacecraft propulsion. ESTCube-1 will deploy and charge a 10 m long tether and measure changes in the satellite spin rate. These changes result from the Coulomb drag interaction with the ionospheric plasma that is moving with respect to the satellite due to the orbital motion of the satellite. The following subsystems have been developed to perform and to support the E-sail experiment: a tether deployment subsystem based on a piezoelectric motor; an attitude determination and control subsystem to provide the centrifugal force for tether deployment, which uses electromagnetic coils to spin up the satellite to one revolution per second with controlled spin axis alignment; an imaging subsystem to verify tether deployment, which is based on a 640 × 480 pixel resolution digital image sensor; an electron gun to keep the tether at a high positive potential; a high voltage source to charge the tether; a command and data handling subsystem; and an electrical power subsystem with high levels of redundancy and fault tolerance to mitigate the risk of mission failure.

Solidification processing followed by hot coextrusion was used to fabricate a bimetal magnesium/aluminum macrocomposite containing millimeter-scale Al core reinforcement. Microstructural characterization revealed limited interfacial interdiffusion of both metals into each other. Compressive testing revealed that the presence of Al core does not affect 0.2%YS, marginally decreases ultimate compressive strength (UCS), and significantly increases failure strain (115%) and work of fracture (55%) of Mg. The effect of the presence of mm-scale Al core on the compressive properties of the bimetal macrocomposite is investigated in this article.

New bimetal AZ31-CNT/AA5052 macrocomposite comprising: (a) carbon nanotube (CNT) reinforced magnesium alloy AZ31 shell and (b) aluminium alloy AA5052 millimeter-scale core reinforcement was fabricated using solidification processing followed by hot coextrusion. Microstructural characterisation revealed more rounded intermetallic particle of decreased size, reasonable CNT distribution, and dominant (1 0 À1 1) texture in the longitudinal and transverse directions in the AZ31-CNT nanocomposite shell. Interdiffusion of Mg and Al across the core-shell macrointerface into each other was also significant. Compared to monolithic AZ31, the AZ31-CNT shell had significantly higher hardness (+30%). In tension, the presence of CNT (in the AZ31 shell) and AA5052 core significantly increased stiffness (+39%), ultimate strength (+13%), failure strain (+17%) and work of fracture (+27%) of AZ31, while yield strength (À2%) was marginally decreased. In compression, the presence of CNT (in the AZ31 shell) and AA5052 core significantly increased yield strength (+35%), failure strain (+42%) and work of fracture (+70%) of AZ31, while ultimate strength (+1%) was marginally increased. The effect of joint presence of: (a) CNT (in the AZ31 shell) and (b) AA5052 millimeter-scale core on tensile and compressive properties of AZ31 is investigated in this paper.