| 1. |
- Da Ronch, A., et al.
(författare)
-
A framework for constrained control allocation using CFD-based tabular data
- 2011
-
Ingår i: AIAA Aerosp. Sci. Meet. Incl. New Horiz. Forum Aerosp. Expos.. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781600869501
-
Konferensbidrag (refereegranskat)abstract
- This paper describes a framework for control allocation problem using Computational Fluid Dynamics (CFD) aerodata, which is represented by a multidimensional array of dimensionless coefficients of aerodynamic forces and moments, stored as a function of the state vector and control-surface deflections. The challenges addressed are, first, the control surface treatment for the automated generation of aerodata using CFD and, second, sampling and data fusion to allow the timely calculation of large data tables. In this framework, the generation of aerodynamic tables is described based on an efficient sampling/data fusion approach. Also, the treatment of aerodynamics of control surfaces is being addressed for three flow solvers: TORNADO, a vortex-lattice method, and two CFD codes, EDGE from the Swedis Defence Agency and PMB from the University of Liverpool. In TORNADO, the vortex points located at the trailing edge of the flaps are rotated around the hinge line to simulate the deflected surfaces. The transpiration boundary conditions approach is used for modeling moving flaps in EDGE, whereas, the surface deflection is achieved using mode shapes in PMB. The test cases used to illustrate the approaches is the Ranger 2000 fighter trainer and a reduced geometry description of Boeing 747-100. Data tables are then generated for the state vector and multiple control surface deflections. The look-up table aerodata are then used to resolve the control allocation problem under the constraint that each surface has an upper and lower limit of deflection angle.
|
|
| 2. |
- Da Ronch, A., et al.
(författare)
-
Benchmarking ceasiom software to predict flight control and flying qualities of the B-747
- 2010
-
Ingår i: 27th Congress of the International Council of the Aeronautical Sciences 2010, ICAS 2010. - 9781617820496 ; , s. 2906-2912
-
Konferensbidrag (refereegranskat)abstract
- CEASIOM, the Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods, is a framework that integrates discipline-specific tools for conceptual design. At this early stage of the design it is very useful to be able to predict the flying and handling qualities of the aircraft. In order to do this for the configuration being studied, the aerodynamic database needs to be computed and coupled to the stability and control tools to carry out the analysis. This paper describes how the adaptivefidelity CFD module of CEASIOM computes the aerodynamic database of an aircraft configuration, and how that data is analyzed by the FCSDT module to determine the flying qualities and the control laws of the aircraft. The paper compares the predicted flying qualities with the flight-test data of the Boeing B747 aircraft in order to verify the goodness of the overall approach.
|
|
| 3. |
|
|
| 4. |
- Dia, B. M., et al.
(författare)
-
Boundary feedback control of 2-D shallow water equations
- 2013
-
Ingår i: International Journal of Dynamics and Control. - : Springer. - 2195-268X .- 2195-2698. ; 1:1, s. 41-53
-
Tidskriftsartikel (refereegranskat)abstract
- Local explicit feedback boundary conditions are given for the stabilization in L2-norm of the 2-D shallow water model. The proposed method is based on symmetrization of the flux matrices of the linearized model and analysis of the Riemann invariants. The non-conservative 2-D shallow water equations are linearized around the target steady state sub-critical flow. The established feedback control laws guarantee a decay of the energy of the perturbation model. We present numerical simulations to demonstrate how the proposed controller works for the linearized as well as nonlinear shallow water problem.
|
|
| 5. |
- Dia, Ben Mansour, et al.
(författare)
-
Stabilizing local boundary conditions for two-dimensional shallow water equations
- 2018
-
Ingår i: Advances in Mechanical Engineering. - : Sage Publications. - 1687-8132 .- 1687-8140. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a sub-critical two-dimensional shallow water flow regulation. From the energy estimate of a set of one-dimensional boundary stabilization problems, we obtain a set of polynomial equations with respect to the boundary values as a requirement for the energy decrease. Using the Riemann invariant analysis, we build stabilizing local boundary conditions that guarantee the stability of the hydrodynamical state around a given steady state. Numerical results for the controller applied to the nonlinear problem demonstrate the performance of the method.
|
|
| 6. |
- Eliasson, Peter, et al.
(författare)
-
IMPROVING STALL CHARACTERISTICS OF UCAV WING WITH VORTEX GENERATORS
- 2022
-
Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. - : International Council of the Aeronautical Sciences. ; , s. 2990-2998
-
Konferensbidrag (refereegranskat)abstract
- Recent Unmanned Combat Air Vehicle (UCAV) configurations have not-so-slender wings with moderate leading-edge sweepangles of 45◦ to 60◦. Planforms vary from pure delta to diamond and even lambda more or less blended wing bodies with a relatively small thickness ratio at the inner wing/fuselage region. The performance and low-observable signature considerations require a compromise between a small radar cross-section and lifting surface shapes for long range and sufficient agility. The airflow is governed largely by the progression of vortices shed from the wing leading edge which interact and produce non-linear aerodynamics. Like early swept wing fighters like the Saab 32 the UCAV may exhibit undesirable flying characteristics over part of the envelope with tip stall and pitch-up. Such problems were mitigated by vortex control "devices" like leading edge fences and notches which violate the low observable requirement. The AVT-181 SACCON is a well studied case. We attempt to improve its stalling characteristics by mimicking the leading edge fence action by a configuration of very small vortex generators and study their effect by CFD.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Gustavsson, Katarina, et al.
(författare)
-
Numerical 2D models of consolidation of dense flocculated suspensions
- 2001
-
Ingår i: Journal of Engineering Mathematics. - 0022-0833 .- 1573-2703. ; 41:2-3, s. 189-201
-
Tidskriftsartikel (refereegranskat)abstract
- A mathematical 2D model for a consolidation process of a highly concentrated, flocculated suspension is developed. The suspension is treated as a mixture of a fluid and solid particles by an Eulerian two-phase fluid model. The suspension is characterized by constitutive relations correlating the stresses, interaction forces, and inter-particle forces to concentration and velocity gradients. This results in three empirical material functions: a permeability, a non-Newtonian viscosity and a non-reversible particle interaction pressure. Parameters in the models are fitted to experimental data. A simulation program using finite difference methods both in time and space is applied to one and two dimensional test cases. The effect of different viscosity models as well as the effect of shear on consolidation rate is studied. The results show that a shear thinning viscosity model yields a higher consolidation rate compared to a model that only depends on the volume fraction. It is also concluded that the size of the viscosity influences the time scale of the process and that the expected effect of shear on the process is not weil reproduced with any of the models.
|
|
| 10. |
- Litvinenko, A., et al.
(författare)
-
Computation of electromagnetic fields scattered from objects with uncertain shapes using multilevel monte carlo method
- 2019
-
Ingår i: IEEE Journal on Multiscale and Multiphysics Computational Techniques. - : Institute of Electrical and Electronics Engineers Inc.. - 2379-8793. ; 4, s. 51-64
-
Tidskriftsartikel (refereegranskat)abstract
- Computational tools for characterizing electromagnetic scattering from objects with uncertain shapes are needed in various applications ranging from remote sensing at microwave frequencies to Raman spectroscopy at optical frequencies. Often, such computational tools use the Monte Carlo (MC) method to sample a parametric space describing geometric uncertainties. For each sample, which corresponds to a realization of the geometry, a deterministic electromagnetic solver computes the scattered fields. However, for an accurate statistical characterization, the number of MC samples has to be large. In this paper, to address this challenge, the continuation multilevel Monte Carlo (CMLMC) method is used together with a surface integral equation solver. The CMLMC method optimally balances statistical errors due to sampling of the parametric space, and numerical errors due to the discretization of the geometry using a hierarchy of discretizations, from coarse to fine. The number of realizations of finer discretizations can be kept low, with most samples computed on coarser discretizations to minimize computational cost. Consequently, the total execution time is significantly reduced, in comparison to the standard MC scheme.
|
|
