scholarly journals Enhanced algorithms to ensure the success of rendezvous maneuvers using aerodynamic forces

2021 ◽  
Author(s):  
S. Bühler ◽  
C. Traub ◽  
S. Fasoulas ◽  
G. H. Herdrich
Keyword(s):  
State Of The Art ◽  
Initial Conditions ◽  
Formation Flight ◽  
Constant Density ◽  
Final Phase ◽  
Orbital Inclination ◽  
Control Phase ◽  
Motion Models ◽  
Density Assumption ◽  
Lift And Drag

AbstractA common practice in the field of differential lift and drag controlled satellite formation flight is to analytically design maneuver trajectories using linearized relative motion models and the constant density assumption. However, the state-of-the-art algorithms inevitably fail if the initial condition of the final control phase exceeds an orbit and spacecraft-dependent range, the so-called feasibility range. This article presents enhanced maneuver algorithms for the third (and final) control phase which ensure the overall maneuver success independent of the initial conditions. Thereby, all maneuvers which have previously been categorized as infeasible due to algorithm limitations are rendered feasible. An individual algorithm is presented for both possible control options of the final phase, namely differential lift or drag. In addition, a methodology to precisely determine the feasibility range without the need of computational expensive Monte Carlo simulations is presented. This allows fast and precise assessments of possible influences of boundary conditions, such as the orbital inclination or the maneuver altitude, on the feasibility range.

Interior heating and outgassing of Proxima Cen b: Identification of critical parameters

2021 ◽  
Author(s):  
Lena Noack ◽  
Kristina Kislyakova ◽  
Colin Johnstone ◽  
Manuel Güdel ◽  
Luca Fossati
Keyword(s):  
Magnetic Field ◽  
Induction Heating ◽  
Initial Conditions ◽  
Thermal Evolution ◽  
Rotation Period ◽  
Critical Parameters ◽  
Stellar Spectrum ◽  
Orbital Inclination ◽  
The Past ◽  
Tidal Heating

<p>Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.<br>We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.</p><p><br>To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. <br>We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. <br>We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.</p><p><br>Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.</p><p> </p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.53bcd48f2cff56572630161/sdaolpUECMynit/12UGE&app=m&a=0&c=314fe555893c77417d52bf9a6bd3825f&ct=x&pn=gnp.elif&d=1" alt="" width="307" height="339"> </p><p>Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.</p>

Validation of URANS Simulation of Truck Cooling Fan Performance

2014 ◽  
Author(s):  
Sassan Etemad ◽  
Peter Gullberg
Keyword(s):  
Test Data ◽  
Industrial Applications ◽  
Ideal Gas ◽  
Computational Time ◽  
Constant Density ◽  
Cfd Simulations ◽  
Simulation Accuracy ◽  
Cooling Fan ◽  
Density Assumption ◽  
Urans Cfd

The performance of an axial heavy duty truck cooling fan was investigated by measurements in a test rig and by CFD simulations. In order to account for the unsteadiness of the flow, URANS simulations were employed. Good agreement was achieved between the simulation and test data, in particular in the axial regime, despite the constant density assumption. To improve the simulation accuracy in the radial and transitional regime it is most likely insufficient to assume constant density. New simulations with ideal gas assumptions for these regimes are believed to give better agreement with the test data. The simulations show that URANS CFD can produce results very close to the ones obtained in the test facilities and thereby can be used for the industrial applications when flow unsteadiness has to be taken into account. The fact that it requires long computational time and is CPU-demanding can no longer be regarded as a major preventing factor for its application in the industry. In addition, it provides valuable information about the details of the flow which can contribute to the optimization of the geometry for improved efficiency and higher performance.

scholarly journals Ensemble flood forecasting considering dominant runoff processes: II. Benchmark against a state-of-the-art model-chain (Verzasca, Switzerland)

2018 ◽  
Author(s):  
Christoph Horat ◽  
Manuel Antonetti ◽  
Katharina Liechti ◽  
Pirmin Kaufmann ◽  
Massimiliano Zappa
Keyword(s):  
Real Time ◽  
State Of The Art ◽  
Initial Conditions ◽  
Current System ◽  
Weather Prediction ◽  
Swiss Alps ◽  
The Novel ◽  
Ungauged Catchments ◽  
Forecast Performance ◽  
Shallow Soils

Abstract. Model benchmarking is needed in order to establish how newly developed forecasting approaches perform against current state-of-the-art systems. In many cases, resources for re-forecasting long periods of time are limited and therefore, a period of parallel-operations is evaluated. For this study, the forecasting chain presented in the companion paper by Antonetti et al. (2018) has been set up for the Verzasca basins in the southern Swiss Alps. In this region, an operationally running system is available from previous studies on probabilistic flash flood (FF) forecasts. This current system relies on the calibrated semi-distributed hydrological model PREVAH. The new model RGM-PRO includes the concept of dominant runoff processes and requires a priori estimation of parameters but no direct discharge observations for calibration. This is a significant benefit to FF prediction in ungauged catchments. Both FF forecasting chains are forced by information from numerical weather prediction COSMO-1 and COSMO-E. Real-time rainfall is provided by the CombiPrecip product, which combines rain gauge and weather radar data. As RGM-PRO is an event-based model, initial conditions are not computed internally. Such initial conditions are obtained from operationally available gridded simulations of the PREVAH model. The current PREVAH-HRU setup uses rainfall data as obtained by interpolating real-time data of the station network maintained by MeteoSwiss. Initial conditions are tracked internally day-by-day. The PREVAH-HRU runs forced by COSMO-1 and COSMO-E during real-time operations in the period May to August 2016 have been compiled. Corresponding model runs using RGM-PRO have been computed a posteriori. Both sets of forecasts are evaluated against discharge observations using deterministic and probabilistic verification metrics. Results showed that the novel approach was able to compete with the operational benchmark prediction system and was consistently superior for high-flow situations. The new forecasting chains were able to react faster on precipitation in comparison with the benchmark forecasts. Confirming previous studies for all forecasting chains, a clear preference for using a meteorological ensemble as forcing data was found. In a synthesis of the two companion papers, more skill was found in the Verzasca basin than in the Emme catchment, suggesting a better forecast performance in strongly topography driven basins with shallow soils and weak dependence on initial conditions. The findings of the two studies suggest that the novel forecasting chains can compete with the traditional ones in operational setup without the need of long-term discharge measurements and extensive calibration. With the new runoff generation module, extension of FF prediction to ungauged catchments is possible, provided that spatially distributed information on dominant runoff processes is available.

scholarly journals On the exploitation of differential aerodynamic lift and drag as a means to control satellite formation flight

2019 ◽  
Vol 12 (1) ◽  
pp. 15-32 ◽  
Author(s):  
C. Traub ◽  
F. Romano ◽  
T. Binder ◽  
A. Boxberger ◽  
G. H. Herdrich ◽  
...  
Keyword(s):  
Formation Flight ◽  
Satellite Formation ◽  
Lift And Drag ◽  
Aerodynamic Lift ◽  
Satellite Formation Flight

Compressible Laminar Wake of a Thin Flat Plate

1970 ◽  
Vol 92 (3) ◽  
pp. 510-513 ◽  
Author(s):  
R. J. El Assar
Keyword(s):  
Flat Plate ◽  
Initial Conditions ◽  
Constant Density ◽  
Coordinate Plane ◽  
Edge Region ◽  
Boundary Layer Equations ◽  
Infinite Region ◽  
Laminar Wake ◽  
Finite Difference Solution ◽  
Von Mises

A finite difference solution is presented for the laminar, compressible wake behind a flat plate at zero angle of attack. The solution of the boundary layer equations is carried out in the von Mises coordinate plane. A coordinate transformation which maps the infinite region into a finite one is also introduced. The accuracy and range of validity of the asymptotic and preasymptotic theories of Goldstein and Tollmien for the incompressible wake are discussed. The effect of the Mach number and initial conditions on the evolution of the wake is investigated. The analysis is applicable outside a trailing edge region of O(LRc−3/4) and for a constant density-viscosity product and Prandtl number unity.

Fluid Dynamics of the Circular Porous Slider

1974 ◽  
Vol 41 (2) ◽  
pp. 343-347 ◽  
Author(s):  
Chang-Yi Wang
Keyword(s):  
Fluid Dynamics ◽  
Exact Solution ◽  
Stokes Equations ◽  
Approximate Solutions ◽  
Navier Stokes ◽  
Constant Density ◽  
Nonlinear Ordinary Differential Equations ◽  
Navier Stokes Equations ◽  
Lift And Drag ◽  
Gap Width

A fluid of constant density is forced through the porous bottom of a circular slider which is moving laterally on a flat plane. We assume the radius of the slider is much larger than the gap width between the slider and the plane. The Navier-Stokes equations reduce to a set of nonlinear ordinary differential equations. These equations are solved by three methods: series expansion for small crossflow Reynolds number R, matched asymptotic expansions for large R, and also exact numerical integration. The approximate solutions are compared with the numerical results, which is also an exact solution of the Navier-Stokes. Lift and drag are calculated. If everything else is held fixed, both lift and drag increase rapidly although at different rates, with decreasing gap width.

Numerical Analysis of the Trajectory of a Basketball Considering Lift and Drag

2015 ◽  
Vol 798 ◽  
pp. 493-499
Author(s):  
T.R Nikhilesh ◽  
Prahlad Kulkarni
Keyword(s):  
Differential Equation ◽  
Numerical Analysis ◽  
Numerical Methods ◽  
Initial Conditions ◽  
Equation Of Motion ◽  
Basketball Players ◽  
Magnus Effect ◽  
Lift And Drag

Basketball players are taught to release the ball with a backward spin. This causes a lift due to the Magnus effect. Added to this there is a drag on the ball which always acts opposite to the direction of motion. In this paper, the trajectory of a basketball considering the lift and drag is calculated using numerical methods and also the force required to shoot the ball with different initial conditions from a distance of 25 feet away from a basket which is at a height of 10 feet is analyzed. A differential equation of motion of the ball in air is framed which accounts for all the forces on the ball. It is solved by discretizing the equation and solved using a C++ code. The trajectory of the balls with different initial conditions is plotted and it is found that as the spin on the ball increases, the effort required to shoot decreases.

scholarly journals Chemodynamical Simulations of Dwarf Galaxy Evolution

2014 ◽  
Vol 2014 ◽  
pp. 1-30 ◽  
Author(s):  
Simone Recchi
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
State Of The Art ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
Mass Function ◽  
Initial Mass Function ◽  
Physical Processes ◽  
Modern Computer ◽  
Galactic Winds

In this review I give a summary of the state of the art for what concerns the chemo-dynamical numerical modelling of galaxies in general and of dwarf galaxies in particular. In particular, I focus my attention on (i) initial conditions, (ii) the equations to solve; (iii) the star formation process in galaxies, (iv) the initial mass function, (v) the chemical feedback, (vi) the mechanical feedback, (vii) the environmental effects. Moreover, some key results concerning the development of galactic winds in galaxies and the fate of heavy elements, freshly synthesised after an episode of star formation, have been reported. At the end of this review, I summarise the topics and physical processes, relevant to the evolution of galaxies, that in my opinion are not properly treated in modern computer simulations of galaxies and that deserve more attention in the future.

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