133 research outputs found
Overview of research activities during the secondment at the US Air Force Academy in Colorado Springs, October 2022 until July 2023
No full textThis report is dedicated to research activities conducted during the secondment at the US-Air Force Academy (USAFA) in Colorado Springs from end of October 2022 until end of July 2024. The content includes a brief description of the three published contributions to the AIAA Aviation Forum in San Diego, which took place in summer 2023. Also listed are the additional research that have arisen outside the common activities with the USAFA, namely bio-inspired Swarm Intelligence optimisation strategies and the treatment and implementation of the geometrically exact beam. Finally, there is a summary about the topics and an evaluation of the stay at the USAFA
Olfactory peptide production for gas phase biosensors
No full textAuthor Julian Widhalm, BScMasterarbeit Johannes Kepler Universität Linz 2025Arbeit gesperr
LINEAR FREQUENCY DOMAIN PREDICTIONS OF DYNAMIC DERIVATIVES FOR THE DLR F12 WIND TUNNEL MODEL
No full textStructural loads for full aircraft configurations can be represented by evaluating dynamic derivatives over a wide parameter space mainly including different mode shapes, an- gle of attack and Mach numbers. Traditionally, these values are determined by wind tunnel tests applying forced periodic motions to aircraft models. The ability of numerical simula- tions provide an excellent addendum to wind tunnel tests. Instead of time-accurate unsteady Reynolds-averaged Navier-Stokes (URANS) solvers which are recognized as extremely compu- tational expensive this paper considers a linearized frequency domain solver (LFD). With this approach the unsteady simulation reduces to a single steady state computation and a single linear simulation in the frequency domain. By the assumption of small perturbations and har- monic oscillations dynamic derivatives can be computed efficiently within a wide parameter space. In addition, the theoretical background for the LFD will be presented. Based on the linearization of the RANS equations and modeling of small perturbations with Fourier series a complex valued linear system has to be solved
Obese boys at increased risk for nonalcoholic liver disease: evaluation of 16 390 overweight or obese children and adolescents
No full textObjective: Comorbidities of childhood obesity challenge health-care systems in Europe. Further, there is a lack of population-specific prevalence data and diagnostic strategies available, especially for obesity-related disturbances of liver function. Therefore, the prevalence of elevated liver enzymes and their relationship to biological parameters were studied in a large pediatric obesity cohort. Methods: In 111 specialized pediatric obesity centers in Germany, Austria and Switzerland, 16 390 children and adolescents (age 12.4 +/- 2.6 years, 58% boys) were categorized as overweight (body mass index (BMI)>490th percentile) and obese (>97th percentile) and studied for related comorbidities, especially nonalcoholic fatty liver disease (NAFLD; as defined by aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) >50Ul(-1)). Data were collected using a standardized software program (APV) for longitudinal multicenter documentation. Pseudonymized data were transmitted for central statistical analysis. Results: In this pediatric cohort, 16% of the study population was overweight, 46% obese and 35% extremely obese (>99.5th percentile extreme obesity (Xob)). NAFLD was present in 11% of the study population, but predominantly in boys (boys vs girls; 14.4: 7.4%; P= 12 years; 8: 12%; P50Ul(-1) was significantly associated with fasting insulin and BMI-SDS. In multiple logistic regression models, Xob and male gender were strongly associated with NAFLD (odds ratio Xob vs normal weight=3.2; boys vs girls OR=2.3). Conclusion: In a large cohort of overweight and obese European children and adolescents, markers of nonalcoholic liver disease, especially ALT, are frequent and predicted by Xob and male gender. The results underline the epidemiological dimension of this obesity-related morbidity even in childhood. Therefore, at least ALT is recommended as a screening parameter in basic care. International Journal of Obesity (2010) 34, 1468-1474; doi:10.1038/ijo.2010.106; published online 8 June 201
Lagrangian Particle Tracking on Large Unstructured Three-Dimensional Meshes
No full textA prerequisite for the prediction of ice accretion on an aircraft flying
through clouds of supercooled liquid water is the accurate
determination of the water impingement rate on various components
of the aircraft. For this purpose, a droplet impingement module has been
developed using the datastructure of the unstructured Navier-Stokes
solver TAU. Since nowadays large computational grids are common
practice, an efficient algorithm for determination of the droplet
trajectories on such grids had to be implemented.
This paper describes the physics and details of the implemented
numerical algorithm. It summarizes lessons learned during
development. The paper concludes with the presentation of code
validation results and examples of applications
Efficient Computation of Dynamic Stability Data with a Linearized Frequency Domain Solver.
No full textDetermination of aeroelastic stability boundaries for full aircraft configu-
rations by solving the time-accurate unsteady Reynolds-averaged Navier-Stokes (RANS)
equations is recognized as extremely computationally expensive or impractical. This is due
to the wide range of
flight conditions, frequencies, and structural deformation mode shapes
that must be examined to ensure a configuration is free from
flutter. Nonetheless there
is an increasing demand within the aerospace industry for accurate
utter analysis in the
transonic regime, which can only be satisfied with the use of high-fidelity RANS codes.
Hence we are motivated to seek a more efficient numerical method. By assuming that
perturbations to the
ow are small and harmonic, we can derive an efficient alternative
method by linearization of the RANS equations, a linearized frequency domain (LFD)
solver. With this approach the unsteady simulation reduces to a single non-linear steady
computation followed by a single linear simulation in the frequency-domain. This method
is not new, but has principally been applied to turbomachinery so far. The contribution
of this paper twofold: firstly to show that LFD is sufficiently accurate and reliable for
applications to aeroelastic problems that occur in external aerodynamics, and secondly to
demonstrate the speed-up that can be expected over full unsteady computations. Viscous
transonic analysis is carried out on complex geometries in three-dimensions. The results
show good agreement with full unsteady simulation and experiment, and a reduction in
computational costs up to one order of magnitude is demonstrated
Lagrangian Trajectory Simulation of Rotating Regular Shaped Ice Particles
No full textThis paper focuses on the numerical simulation of the motion
of regular shaped ice particles under the forces and
torques generated by aerodynamic loading. Ice particles
can occur during landing and take-off of aircraft at ground
level up to the lower bound of the stratosphere at cruising
altitude. It may be expected that the particle Reynolds
number is high because the flow around the aircraft is in
certain regions characterized by strong acceleration and
deceleration of the flow. In combination with this flow pattern,
the rotation of particles becomes important. Applicable
translational and rotational equations of motion combined
with a drag correlation taking into account rotation
will be derived for a Lagrangian type particle tracking. Orientation
is described with quaternions to prevent the singularities
associated with the description by Euler angles.
The influence of regular shaped particles on collection efficiencies
is investigated. Test cases are the flow past a
cylinder, a NACA0012 airfoil and a NHLP L1/T2 three element
airfoil. Due to the increased computational effort
compared to the purely translational approach, observed
trajectory simulation times are reported
Numerical investigation of a cooling stack based on dynamic simulations
No full textEs wurde ein Kühlkamin untersucht, welcher die entstehenden Gase eines LD-Konverters beim Frischen des Stahles abkühlt. Das Abzukühlende Gasgemisch besteht hauptsächlich aus Kohlenmonoxid. Da es sich um ein dynamisches System handelt ist die Lösung nur mit Hilfe von Simulationsprogrammen möglich. Für diese Aufgabe wurden die Simulations Softwaren Power Plant Simulator & Designer KED und APROS benutzt.A cooling stack was investigated, which cools the produced gases from a LD-converter by the refining of the steel. The cooled gas mixture consists mainly of carbon monoxide. Since this is a dynamic system, the solution is only with simulation programs possible. For this task, the simulation softwares Power Plant Simulator & Designer KED and APROS were used.<br /
Linear frequency domain and harmonic balance predictions of dynamic derivatives
No full textDynamic derivatives are used to represent the influence of the aircraft rates on the aerodynamic forces and moments needed for flight dynamics studies. These values have traditionally been estimated by processing measurements made from periodic forced motions applied to wind tunnel models. The use of Computational Fluid Dynamics has potential to supplement this approach. This paper considers the problem of the fast computation of forced periodic motions using the Euler equations. Three methods are evaluated. The first is computation in the time domain, and this provides the benchmark solution in the sense that the time accurate solution is obtained. Two acceleration techniques in the frequency domain are compared. The first uses an harmonic solution of the linearised problem referred to as the linear frequency domain approach). The second uses the Harmonic Balance method, which approximates the nonlinear problem using a number of Fourier modes. These approaches are compared in the sense of their ability to predict dynamic derivatives and their computational cost. The standard NACA aerofoil CT cases, the SDM fighter model geometry and the DLR F12 passenger jet wind tunnel model are used as test cases. Compared to time accurate simulations an order of magnitude reduction in CPU costs is achieved for flows with a narrow frequency spectrum and moderate amplitudes, as the solution does not evolve through transients to reach periodicity
Flight Dynamic Stability Prediction with a Linear Frequency Domain Method
No full textEach slight perturbation to a trimmed aircraft state causes additional aerodynamic loads on the aircraft, which is quantified with stability derivatives of forces and moments for a motion. Small disturbance approaches based on Navier-Stokes equations have become a solution to combine efficiency and accuracy for predicting stability derivatives. This approach leads to the presented linear frequency domain method, which is capable to resolve the first harmonic stability derivatives for the complete flight envelope of a transport aircraft. Its implementation involves the exact evaluation of the flux Jacobian including the turbulence model for reflecting the flow physics as well as the grid-node and grid-node velocity Jacobian. With forced rigid body motions, the proof for the good predictive accuracy of stability derivatives in comparison with fully time-accurate unsteady simulations is examined for various test cases. The importance for efficiently evaluating stability derivatives is demonstrated by a flight dynamics stability computation for an aircraft in subsonic and transonic flow. Flight dynamic stability prediction becomes feasible in practice with the derived frequency domain method. It achieves a speed-up of about two orders of magnitude in comparison with time-accurate unsteady simulations
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