429 research outputs found
Chiral Current Algebras in Three--Dimensional Bf--Theory with Boundary
We consider the three--dimensional BF--model with planar boundary in the
axial gauge. We find two--dimensional conserved chiral currents living on the
boundary and satisfying Kac--Moody algebras.Comment: 18 page
Approximated models for aerodynamic coefficients estimation in a multidisciplinary design environment
In this paper variable fidelity analyses are investigated. Moreover different kind of approximations to be used in a wide multidisciplinary design environment for aircraft design are built. In order to obtain the surrogate models used in the main design process, a proper framework is built by different design of experiments techniques for process and variables management. Approximated models for the estimation of aerodynamic coefficients are evaluated on design spaces of different dimensions and considering different set of variables (i.e. geometric parameters and flight conditions). They are mainly based on the hybrid combination of Vortex Lattice Method (VLM) models
representing the basic low fidelity analysis) and 3D finite volume Computational Fluid Dynamics models (representing the basic high fidelity analysis). Different strategies for the evaluation of the surrogate model are considered and an original methodology for the model construction is here presented
Multidisciplinary Integrated Framework for the Optimal Design of a Jet Aircraft Wing
The preliminary design of a jet aircraft wing, through the use of an integrated multidisciplinary design environment, is presented in this paper. A framework for parametric studies of wing structures has been developed on the basis of a multilevel distributed analysis architecture with a "hybrid strategy" process that is able to perform deterministic optimizations and tradeoff studies simultaneously. The particular feature of the proposed multilevel optimization architecture is that it can use different set of variables, defined expressly for each level, in a multi-level scheme using "low fidelity" and "high fidelity" models, as well as surrogate models. The prototype of the design environment has been developed using both commercial codes and in-house tools and it can be implemented in a geographically distributed and heterogeneous IT contex
Application of dust removal technologies for future lunar exploration
American Association for Aerosol Research 28th Annual Conference, Minneapolis (MN), 26-30 October 2009, Abstract #144
Valley Singularities and Baryon Number Violation
We consider the valley--method computation of the inclusive cross section of
baryon number violating processes in the Standard Model. We show that any
physically correct model of the valley action should present a singularity in
the saddle point valley parameters as functions of the energy of the process.
This singularity prevents the saddle point configuration from collapsing into
the perturbative vacuum.Comment: 6 pages, LaTex, TPI-MINN-93/32-
Development of a Computational Fluid Dynamics Model for Ice Formation: Validation and Parameter Analysis
: In the history of civil aircraft transportation, ice formation has been identified as a key
factor in the safety of flight. Anti-icing and deicing systems have emerged through the years with the
aim to prevent or to eliminate ice formation on wing airfoils, control surfaces and probes. Modern
flying machines demand more efficiency in order to reduce the carbon footprint and increase the
sustainability of flight transport. In order to achieve this goal, the need to have an efficient aircraft
with an efficient and low power consuming system is fundamental. This paper proposes a new model
for ice accretion using computational fluid dynamics (CFD). This model permits the simulation of the
shape of the ice formed over a profile varying boundary condition (i.e., speed, liquid water content,
and so on). The proposed model also takes into account the amount of heat transferred between the
water and the surrounding environment and includes the effects of air turbulence on the ice formation
process. The CFD simulations have been validated with NASA experimental outcome and show good
agreement. The proposed model can be also used to investigate the effects of various parameters
such as air speed, liquid water content, and air temperature on the ice formation process. The results
evidence that the proposed model can accurately predict ice formation process and is suitable to
optimize the design of anti-icing or deicing systems for aircraft and helicopters. This approach is
not limited to aerospace but can also be exported to other applications such as transportation, wind
turbine, energy management, and infrastructure
Multifidelity modeling for the design of re-entry capsules
The design and optimization of space systems presents many challenges associated with the variety of physical domains involved and their coupling. A practical example is the case of satellites and space vehicles designed to re-enter the atmosphere upon completion of their mission [1]. For these systems, aerodynamics and thermodynamics phenomena are strongly coupled and relate to structural dynamics and vibrations, chemical non equilibrium phenomena that characterize the atmosphere, specific re-entry trajectory, and geometrical shape of the body. Blunt bodies are common geometric configurations used in planetary re-entry (e.g. Apollo Command Module, Mars Viking probe, etc.). These geometries permit to obtain high aerodynamic resistance to decelerate the vehicle from orbital speeds along with contained aerodynamic lift for trajectory control. The large radius-of-curvature of the bodies’ nose allows to reduce the heat flux determined by the high temperature effects behind the shock wave. The design and optimization of these bodies would largely benefit from accurate analyses of the re-entry flow field through high-fidelity representations of the aerodynamic and aerothermodynamic phenomena. However, those high-fidelity representations are usually in the form of computer models for the numerical solutions of PDEs (e.g. Navier-Stokes equations, heat equations, etc.) which require significant computational effort and are commonly excluded from preliminary multidisciplinary design and trade-off analysis.
This work addresses the integration of high-fidelity computer-based simulations for the multidisciplinary design of space systems conceived for controlled re-entry in the atmosphere. In particular, we discuss the use of multifidelity methods to obtain efficient aerothermodynamic models of the re-entering vehicles. Multifidelity approaches allow to accelerate the exploration and evaluation of design alternatives through the use of different representations of a physical system/process, each characterized by a different level of fidelity and associated computational expense [2, 3]. By efficiently combining less-expensive information from low-fidelity models with a principled selection of few expensive simulations, multifidelity methods allow to incorporate high-fidelity costly information for multidisciplinary design analysis and optimization [4–7]. This presentation proposes a multifidelity Bayesian optimization framework leveraging surrogate models in the form of gaussian processes, which are progressively updated through acquisition functions based on expected improvement. We introduce a novel formulation of the multifideltiy expected improvement including both data-driven and physics-informed utility functions, specifically implemented for the case of the design optimization of an Orion-like atmospheric re-entry vehicle. The results show that the proposed formulation gives better optimization results (lower minimum) than single fidelity Bayesian optimization based on low-fidelity simulations only. The outcome suggests that the multifidelity expected improvement algorithm effectively enriches the information content with the high-fidelity data. Moreover, the computational cost associated with 100 iterations of our multifidelity strategy is sensitively lower than the computational burden of 6 iterations of a single fidelity framework invoking the high-fidelity model.
References
[1] Gallais, P., Atmospheric re-entry vehicle mechanics, Springer Science and Business Media, 2007.
[2] Peherstorfer, B., Willcox, K., and Gunzburger, M., “Survey of Multifidelity Methods in Uncertainty Propagation, Inference, and Optimization,” SIAM Review, Vol. 60, 2018, pp. 550–591.
[3] Fernandez-Godino, G., Park, C., Kim, N., and Haftka, R., “Issues in Deciding Whether to Use Multifidelity Surrogates,” AIAA Journal, 2019, p. 16.
[4] Mainini, L., and Maggiore, P., “A Multifidelity Approach to Aerodynamic Analysis in an Integrated Design Environment,” AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, AIAA, 2012.
[5] Goertz, S., Zimmermann, R., and Han, Z. H., “Variable-fidelity and reduced-order models for aero data for loads predictions,” Computational Flight Testing, 2013, pp. 99–112.
[6] Meliani, M., Bartoli, N., Lefebvre, T., Bouhlel, M.A., J., Martins, and Morlier, J., “Multi-fidelity efficient global optimization: Methodology and application to airfoil shape design,” AIAA Aviation 2019 Forum, AIAA, 2019.
[7] Beran, P., Bryson, D., Thelen, A., Diez, M., and Serani, A., “Comparison of Multi-Fidelity Approaches for Military Vehicle Design,” AIAA Aviation 2020 Forum, AIAA, 2020
Additive Manufacturing Technologies and Applications
The present Special Issue proposes articles in the area of Additive Manufacturing with particular attention to the different employed technologies and the several possible applications. The main investigated technologies are the Selective Laser Sintering (SLS) and the Fused Deposition Modelling (FDM). These methodologies, combined with the Computer Aided Design (CAD), provide important advantages. Numerical, analytical and experimental knowledge and models are proposed to exploit the potential advantages given by 3D printing for the production of modern systems and structures in aerospace, mechanical, civil and biomedical engineering fields. The 11 selected papers propose different additive manufacturing methodologies and related applications and studies
Multifidelity domain-aware learning for the design of re-entry vehicles
The multidisciplinary design optimization (MDO) of re-entry vehicles presents many challenges associated with the plurality
of the domains that characterize the design problem and the multi-physics interactions. Aerodynamic and thermodynamic
phenomena are strongly coupled and relate to the heat loads that affect the vehicle along the re-entry trajectory, which drive
the design of the thermal protection system (TPS). The preliminary design and optimization of re-entry vehicles would benefit
from accurate high-fidelity aerothermodynamic analysis, which are usually expensive computational fluid dynamic simulations.
We propose an original formulation for multifidelity active learning that considers both the information extracted from
data and domain-specific knowledge. Our scheme is developed for the design of re-entry vehicles and is demonstrated for
the case of an Orion-like capsule entering the Earth atmosphere. The design process aims to minimize the mass of propellant
burned during the entry maneuver, the mass of the TPS, and the temperature experienced by the TPS along the re-entry.
The results demonstrate that our multifidelity strategy allows to achieve a sensitive improvement of the design solution with
respect to the baseline. In particular, the outcomes of our method are superior to the design obtained through a single-fidelity
framework, as a result of the principled selection of a limited number of high-fidelity evaluations
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