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    Fluid selection for space thermal control systems
    ( 2014) Gerner, H.J. van ; Benthem, R.C. van ; Es, J. van ; Schwaller, D. ; Lapensée, S.
    The selection of a suitable fluid is one of the first and most important steps for the design of a thermal control system. For example, for a heat pipe it is important to use a fluid with a high surface tension and heat of evaporation, and a low viscosity. These characteristics can be combined in a ‘figure of Merit’. This figure of Merit is used to pre-select a number of fluids, after which these fluids are further investigated for material compatibility, safety, radiation hardness etc. This systematic approach results in the selection of the most favourable fluid for each application. In this paper, the fluid selections for heat pumps and pumped loops (both single- and two-phase) are discussed. It is explained for instance why CO2 is used in the thermal control system of AMS02 (which was launched with the space shuttle in May 2011 and subsequently mounted on the International Space Station). Also discussed is the selection of Galden HT80 for ESA’s single-phase Mechanically Pumped Fluid Loop (MPFL) and the selection of isopentane for an ESA Heat Pump application.
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    Crosstalk modelling of unshielded wire pairs
    (IEEE, 2014) Lansink Rotgerink, J.H.G.J. ; Schippers, H.
    Low-frequency analysis on multi-conductor transmission line equations results in closed-form leading order expressions for near-end crosstalk. Two wiring configurations are introduced for which leading order dependency on all model parameters can be derived. An interesting result is a 24 dB/octave decrease of crosstalk when distance is increased between two wire pairs, oriented parallel to an infinite, perfectly conducting ground plane.
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    A Heat Pump for Space Applications
    ( 2015) Gerner, H.J. van ; Donk, G. van ; Pauw, A. ; Es, J. van ; Lapensée, S.
    In commercial communication satellites, waste heat (5-10kW) has to be radiated into space by radiators. These radiators determine the size of the spacecraft, and a further increase in radiator size (and therefore spacecraft size) to increase the heat rejection capacity is not practical. A heat pump can be used to raise the radiator temperature above the temperature of the equipment, which results in a higher heat rejecting capacity without increasing the size of the radiators. A heat pump also provides the opportunity to use East/West radiators, which become almost as effective as North/South radiators when the temperature is elevated to 100°C. The heat pump works with the vapour compression cycle and requires a compressor. However, commercially available compressors have a high mass (40 kg for 10kW cooling capacity), cause excessive vibrations, and are intended for much lower temperatures (maximum 65°C) than what is required for the space heat pump application (100°C). Dedicated aerospace compressors have been developed with a lower mass (19 kg) and for higher temperatures, but these compressors have a lower efficiency. For this reason, an electrically-driven, high-speed (200,000 RPM), centrifugal compressor system has been developed in a project funded by the European Space Agency (ESA). This novel 3-stage compressor system has a mass of just 2 kg and a higher efficiency than existing aerospace compressors. The compressor system has been incorporated in a heat pump demonstrator, which uses isopentane (R601a) as refrigerant. Due to the exposure of isopentane to radiation in a space application, other substances will form. However, a literature study shows that the amounts of the formed substances are so small, that no significant influence on the performance of the heat pump is expected. Tests were carried out with the heat pump, and at the target setting (saturation temperature of 45°C at the evaporator, 100°C at the condenser, and a payload heat input of 5 kW), the measured COP is 2.3, which is higher than the original requirement of 2.
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    Generic prediction of crosstalk between shielded wires
    (IEEE, 2015) Lansink Rotgerink, J.H.G.J. ; Schippers, H.
    A closed-form expression for near-end crosstalk between an unshielded and a double shielded wire is derived. Analysis in the frequency domain of such crosstalk expressions leads to generic crosstalk predictions. These predictions contain regions of different frequency dependencies separated by transition frequencies.
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    Transient modelling of pumped two-phase cooling systems: Comparison between experiment and simulation
    (46th International Conference on Environmental Systems, 2016) Gerner, H.J. van ; Braaksma, N.
    Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature in a system, for example in the AMS02, which was launched with a space shuttle (in May 2011) and subsequently mounted on the International Space Station. However, a two-phase pumped cooling system can show complex transient behavior in response to heat load variations. For example, when the heat load is increased, a large volume of vapor is suddenly created, which results in a liquid flow into the accumulator and an increase in the pressure drop. This will result in variations in the temperature in the system, which are undesired. It is necessary to calculate these temperature variations before an application is being built. For this reason, a software tool for transient two-phase systems has been developed by NLR. This tool numerically solves the one-dimensional time-dependent compressible Navier-Stokes equations, and includes the thermal masses of all the components. The tool has been used for different projects, and the numerical results show an excellent agreement with experiments. In this paper, several pumped two-phase cooling systems are discussed, and a comparison between simulations and experiments is presented.
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    Crosstalk between wire pairs above a composite ground plane
    (IEEE, 2016) Lansink Rotgerink, J.H.G.J. ; Happ, F. ; Es, J.J.P. van
    Crosstalk between two wire pairs in three different configurations is compared to investigate the influence of replacing aluminium by carbon-fibre-reinforced plastic composite material in ground returns. Measurements and simulations show the same interesting effect involving a transition frequency at which the influence of the composite ground plane changes. For low frequencies it acts as a transparent layer on crosstalk behaviour, whereas for higher frequencies it can significantly decrease crosstalk levels. This phenomenon can be explained physically by investigating the skin effect of the composite ground plane. Reverse engineering can even lead to an estimation of the conductivity of the composite material when a crosstalk measurement is at hand.
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    Low-frequency closed-form expressions for crosstalk between twisted wire pairs
    (IEEE, 2016) Lansink Rotgerink, J.H.G.J. ; Verpoorte, J.
    Crosstalk between two twisted wire pairs of equal and unequal twist rate is analysed and compared. Low-frequency approximations to the Multi-conductor Transmission Line equations are used to derive closed-form expressions for near-end crosstalk. Such analysis on cable configurations with different twist scenarios gives insight into sensitivity on relevant twist parameters as well as dependencies of crosstalk on all other model parameters. Results show that crosstalk between twisted pairs of equal twist rate behaves similar to that between untwisted wire pairs. On the contrary, an ideal combination of twisted pairs, by for instance doubling the twist rate in one of the pairs, causes crosstalk to vanish up to linear order. The performed analysis and derived closed-form expressions agree to measured crosstalk results and can lead to good understanding of upper and lower boundaries for crosstalk in different cable configurations.
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    Modelling of effects of nose radomes on radar antenna performance
    (IEEE, 2016) Lansink Rotgerink, J.H.G.J. ; Ven, H. van der ; Voigt, T. ; Jehamy, E. ; Schick, M. ; Schippers, H.
    This paper describes two computational models for the assessment of effects of nose radomes on the performance of radar antennas. The first model is an improved Physical Optics approach that takes into account the wall thickness and multiple layers of the radome. The second model follows from the accelerated numerical solution of Electric Field and Magnetic Field Integral equations. The models are applied to predict the radiation patterns of a radar antenna behind a generic nose radome and behind a radome of a fighter aircraft. The applicability of the two models is discussed.
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    The Risk Observatory: Developing an Aviation Safety Information Sharing Platform in Europe
    (Macrothink Institute, 2016-12) Verstraeten, J. ; Baren, G.B. van ; Wever, R.
    In Europe the accident rate in commercial aviation has stagnated at around 40 accidents per ten million flights: forty times higher than Europe’s ambition. Currently safety management is done per organisation, focusing on an organisation’s own domain. European research institutions and the aviation sector have joined their expertise in the EU-funded Future Sky Safety Programme. One project within the programme aims to enable inter-organisation and inter-domain safety management. The four year project will deliver a tool, the Risk Observatory, which acquires safety data and translates it into actionable safety information. In the first year, more than 20 European stakeholder organisations have been consulted to express their needs for a Risk Observatory. The resulting requirements have been used to develop an early prototype: mock-ups of dashboards and a user interface. The Risk Observatory has four main elements. (1) Tracking of safety performance indicators distilled from input safety data. (2) Trend diagrams and visualisations of accident risk. Risk models will be developed to translate the input data into accident risk. The risk models also allow (3) assessment of the effects of mitigation measures. There is added value in sharing qualitative safety knowledge, such as identified hazards, therefore, (4) a searchable repository is included. The early prototype is successfully used to validate and further specify the requirements. The need for inter-organisation and inter-domain safety data dissemination was confirmed by the stakeholders. In the coming years the project will develop a fully functional prototype risk observatory, risk models and a business model.
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    Transient Modelling of Pumped Two-Phase Cooling Systems: Comparison between experiment and simulation with R134a
    ( 2017) Gerner, H.J. van ; Bolder, R. ; Es, J. van
    Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature in a system, for example in the AMS02, which was launched with a space shuttle (in May 2011) and subsequently mounted on the International Space Station. However, a two-phase pumped cooling system can show complex transient behavior in response to heat load variations. For example, when the heat load is increased, a large volume of vapor is suddenly created, which results in a liquid flow into the accumulator and an increase in the pressure drop. This will result in variations in the temperature in the system, which are undesired. It is necessary to calculate these temperature variations before an application is being built. For this reason, a software tool for transient two-phase systems has been developed by NLR. This tool numerically solves the one-dimensional time-dependent compressible Navier-Stokes equations, and includes the thermal inertia of all the components. In this paper, the numerical results from the model are compared to experimental results obtained with the NLR two-phase test facility with R134a as refrigerant.
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    Braking Capabilities on Flooded Runways: Flight Test Results Obtained with a Business Jet
    (AIAA, 2017) Es, G.W.H. van
    Statistics show that the likelihood of a runway excursion during takeoff or landing is much higher on flooded runways than on dry runways. Extreme loss of tyre braking can occur during rejected takeoffs and landings on flooded runways. As a result the stopping distance increases significantly and could exceed the available runway length. Most research in the past has focused on the braking capabilities of aircraft on wet runways instead of flooded runways. Most of the knowledge of aircraft braking performance on flooded runways was gained with older aircraft designs. This knowledge is still used to determine the takeoff and landing performance of today’s modern aircraft. During the development of the European Action Plan for the Prevention of Runway Excursions it was recognised that current aircraft designs may act differently when braking on water flooded runways from aircraft tested earlier, due to new tyres and anti-skid system designs. Also the water depths during these earlier tests were often just above the wet-flooded runway threshold. Flight tests with more modern aircraft designs were therefore scheduled as part of a research project under EU’s Horizon 2020 Research and Innovation Programme. This paper summarises the flight tests conducted with a Cessna Citation II aircraft on a flooded runway. Unbraked and braked tests were conducted in a specially constructed water pond at different ground speeds. Numerous parameters were recorded during each test run including accelerations, speeds, engine performance, etc. From the test data, effective braking friction for different grounds speeds were derived, contamination drag levels were established, and insight into the hydroplaning characteristics under unbraked and braked conditions were obtained.
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    Multi-conductor transmission line modelling of transfer impedance measurement methods
    (IEEE, 2017) Lansink Rotgerink, J.H.G.J. ; Verpoorte, J. ; Schippers, H.
    Electromagnetic shielding is of high importance to avoid coupling between cables or pick-up of external fields. The use of metal braids around cables improves its protection. Shielding effectiveness of these braids is characterized by the transfer impedance of infinitesimally short braids. In practice, the transfer impedance is measured along a braid of finite length by either a line injection or a triaxial method. Analytical models for the calculation of transfer impedance do not include the finite length and terminations of the measurement setup. Mismatches in the terminations cause resonances starting from frequencies where the length of the transmission line becomes significant in terms of wavelengths. This paper presents a multi-conductor transmission line model for line injection and triaxial methods, which takes into account the finite length and the terminations of the measurement setup. By the application of this model a clear difference is observed between resonance effects caused by mismatches of terminations and by differences in propagation speeds inside and outside of the coax under test.
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    Stopping performance flight test on a flooded runway
    (Society of Experimental Test Pilots, 2017-07) Tump, R.S. ; Mulder, T.J.
    One of the identified solutions for runway excursions is the research into the “Impact of fluid contaminants of varying depth on aircraft stopping performance”. For this, NLR has carried out water-pond flight testing with the NLR/TUD Cessna Citation research aircraft to assess braking performance of modern aircraft and tyres on water covered runways. Airbus Military performed the same test using an A400M. Both tests took place using the water-pond facility of NLR. Aircraft operating on runways that are contaminated by standing water or slush (> 3 mm, up to the AFM limit) are significantly affected in take-off and landing performance. Most data available today is bases on test carried out in the 60s and 70s of the last century. Improved aircraft braking systems and tires were only tested at small scale in recent years.
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    NLR’s experience with flight testing on wet and flooded runways
    (Society of Flight Test Engineers, 2017-09) Es, G.W.H. van ; Koks, P.
    Braking performance of aircraft is affected whenever a runway is wet or flooded. Aircraft manufacturers do wet runway braking tests during the certification of a civil transport aircraft. These are normally limited to tests on smooth runways. Additional tests are sometimes conducted on wet grooved or porous friction course runways when the manufacturer seeks for additional stopping performance credit for such runways. Braking tests on flooded runways are not conducted during certification. In the past such tests have been conducted in research programmes on runway friction. The Netherlands Aerospace Centre NLR has conducted braking tests on a highly textured runway under wet and flooded conditions. The wet runway tests were conducted to demonstrate an equivalent performance of the test surface with grooved and porous friction course runways under wet conditions. The flooded tests were conducted as part of an European Research project on the prevention of runway excursions. All tests were conducted in the autumn of 2016 at a former Air Force base in the Netherlands (Twente Airport). This paper discusses in detail the preparation, logistics, and execution of the flight tests conducted with NLR’s Cessna Citation test aircraft. The use of large water trucks to wet the runway and the construction of a water pond to conduct the flooded runway tests is discussed in detail. Difficulties encounter during the preparation and execution of the flight tests are briefed and finally lessons learned are shared with the reader.
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    Testing of high heat flux 3D printed aluminium evaporators
    ( 2018) Gerner, H.J. van ; Smit, M. de ; Helvoort, D. van ; Es, J. van
    The amount of waste heat that is generated in electronic components in aerospace application is increasing because of higher electrical power demands. As a result, conventional cooling methods are not able to maintain the electronic component below its maximum temperature. For this reason, a two-phase Mechanically Pumped Fluid Loop is being developed for high-power electronic components in a commercial aerospace application. These electronic components generate a heat load of 722 W on a 3.8 cm x 3.8 cm surface, resulting in a heat flux of 50 W/cm2. Tests with 8 different evaporator samples were carried out to determine the heat transfer coefficients and pressure drop and to select the optimal evaporator sample that is further developed in the detail design phase of the project. The tests show that the 3D printed aluminium evaporators are able to keep the heat source well below its maximum temperature.
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    A clustered and surrogate-based MDA use case for MDO scenarios in AGILE project
    (AIAA, 2018) Lefebre, T. ; Bartoli, N. ; Dubreuil, S. ; Panzeri, M. ; Lombardi, R. ; Lammen, W.F. ; Mengmeng, Z. ; Gent, I. van ; Ciampa, P.D.
    In this paper methodological investigations regarding an innovative Multidisciplinary Design and Optimization (MDO) approach for conceptual aircraft design are presented. These research activities are part of the ongoing EU-funded research project AGILE. The next generation of aircraft MDO processes is developed in AGILE, which targets significant reductions in aircraft development cost and time to market, leading to cheaper and greener aircraft solutions. The paper introduces the AGILE project structure and recalls the achievements of the first year of activities where a reference distributed MDO system has been formulated, deployed and applied to the design and optimization of a reference conventional aircraft configuration. Then, investigations conducted in the second year are presented, all aiming at making the complex optimization workflows easier to handle, characterized by a high degree of discipline interdependencies, multi-level processes and multi-partner collaborative engineering activities. The paper focuses on an innovative approach in which knowledge-based engineering and collaborative engineering techniques are used to handle a complex aircraft design workflow. Surrogate models replacing clusters of analysis disciplines have been developed and applied to make workflow execution more efficient. The paper details the different steps of the developed approach to set up and operate this test case, involving a team of aircraft design and surrogate modelling specialists, and taking advantage of the AGILE MDO framework. To validate the approach, different executable workflows were generated automatically and used to efficiently compare different MDO formulations. The use of surrogate models for clusters of design competences have been proved to be efficient approach not only to decrease the computational time but also to benchmark different MDO formulations on a complex optimization problem.
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    Water-filled heat pipes for CubeSat thermal control
    (IOP Publishing, 2018) Gerner, H.J. van ; Brouwer, H. ; Groot, Z. de ; Guo, J.
    Currently, the amount of electrical power that is available for CubeSat's is very small and for this reason, simple thermal conductance through the frame of the CubeSat is sufficient for most CubeSat missions. However, deployable solar panels have been developed recently and peak powers up to 40W can now be generated. This higher generated electrical power results in more waste heat and potentially too high temperatures inside the CubeSat. For this reason, the use of water-filled heat pipes is studied, since these are cheap, widely commercially available, and can be bent in the desired shape. Both the condenser and evaporator thermal resistance and the total heat transfer capacity of these heat pipes have been measured for a wide range of temperatures with a unique automated setup that uses Peltier elements to control the temperature. Furthermore, the heat pipes have been subjected to multiple freeze/thaw cycles and start-ups from a frozen state. After these successful tests, a heat pipe was integrated in a CubeSat and tests were carried out in several orientations. The tests show that commercially available water-filled heat pipes are suitable for CubeSat thermal control.
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    A Crosstalk Sensitivity Analysis on Bundles of Twisted Wire Pairs
    (IEEE, 2018) Lansink Rotgerink, J.H.G.J. ; Leferink, F.
    Uncertainties in the geometry of complex cable bundles highly complicate crosstalk predictions. A change in for instance the position or the twist rate of individual cables in a bundle might have an impact on crosstalk levels. Application of sensitivity analyses can indicate which model parameters are most sensitive, and in which cabling configurations. In this paper, the efficient Stochastic Reduced Order Models (SROM) method is used to perform such a sensitivity analysis. It is applied to two cable bundles with two and seven twisted wire pairs, respectively. Monte Carlo simulations are performed to determine the accuracy of the SROM method. The sensitivity of parameters like inter-pair and intra-pair separation distance and the twist rate is determined in two different cases. Moreover, the effects of bundle twist and cable meandering to parameter sensitivities is investigated.
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    Advanced models for the transfer impedance of metal braids in cable harnesses
    (IEEE, 2018) Verpoorte, J. ; Schippers, H. ; Lansink Rotgerink, J.H.G.J.
    Since the development of the model for transfer impedance of metal braids by E.F. Vance, a large number of authors have tried to improve this model in order to make it more accurate and more reliable. The improvements were based on a more accurate physical or electromagnetic description, or on empirical data of a large number of transfer impedance measurements. This paper provides an overview of the specific models for diffusion, hole inductance and braid inductance. In addition to the general overview, a preferred combination of models for the calculation of transfer impedance is presented.
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    EMC aspects of compact wiring for future aircraft
    (IEEE, 2018) Lansink Rotgerink, J.H.G.J. ; Schippers, H. ; Verpoorte, J. ; Nuyten, K.
    The installation of wiring in future aircraft will become a big challenge. Available space for wiring will decrease, while the amount of wiring will increase, since more and more aircraft systems will be electronically driven instead of hydraulically. It is proposed to make wiring systems more compact. The aim of this paper is to investigate EMC aspects of this compact wiring by simulations and measurements in a representative part of a smart wing of a future aircraft.