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  • 1.
    Eller, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Jansson, Natascha
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Efficient Laplace-Domain Aerodynamics for Load Analyses2013Conference paper (Refereed)
    Abstract [en]

    An existing finite-element solver for steady, non-linear subsonic flow is extended in order to treat unsteady potential flow problems in the Laplace domain. The numerical formulation makes use of unstructured meshes including explicitly modelled, triangulated wake surfaces. Meshes can contain both linear and quadratic volume and surface elements, thus allowing to favor either very fast solution times or high spatial resolution. Aeroelastic problems are dealt with by modelling moving or deforming bodies by means of transpiration boundary conditions. Deformations of the aerodynamic mesh are computed either by projection of aerodynamic mesh nodes onto the finite elements of a structural shell model, or by radial basis function interpolation suitable for beam-type structural models. In addition to simple validation cases, an application of the solver for the evaluation of gust loads on a commuter aircraft is presented. In order to evaluate the use of the method in the context of a relevant, industrial-scale load analysis, typical geometrical and structural models for a twin-turboprop aircraft in the 15t-class (e.g. Saab 340, CN-235, Dash 8, Do 328) are employed.

  • 2.
    Jansson, Natascha
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Analysis of Dynamic Flight Loads2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the determination of loads on an aircraft struc- ture during flight. The focus is on flight conditions where the loads are significantly time-dependent. Analysis of flight loads is primarily motivated to ensure that structural failure is avoided. The ability to ac- curately determine the resulting structural loads which can occur during operation allows for a reduction of the safety margins in the structural design. Consequently it is then possible to decrease the aircraft struc- tural weight. The demand for safe and fuel efficient aircraft creates a desire for efficient and accurate methods for determining the structural loads.

    The first paper of this thesis discusses the use of control laws for robust atmospheric turbulence load alleviation in the time domain. A numerical aircraft model including structural elasticity and unsteady aerodynamic effects is used. A limited set of longitudinal flight mechanic degrees of freedom are considered and two methods for structural load analysis are compared for evaluation of the wing root bending moment.

    In the second paper a method to perform time domain simulation of both motion of center of gravity and elastic deformation is described. The intention with the development of this simulation method is to enable efficient analysis of dynamic flight loads.

    A third study is finally included, where steady and unsteady pressure measurements have been carried out during wind tunnel testing. The motivation for performing these experiments is that knowledge about the aerodynamic force distribution which affect an aircraft structure is needed to correctly determine the structural loads.

  • 3.
    Jansson, Natascha
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Time-domain simulation for flight loads analysis2012Report (Other academic)
    Abstract [en]

    A method for performing flight simulations considering both the motion of the center of gravity and the elastic deformation of the aircraft structure is developed. The time history of the included states is intended to be used for analysis of structural loads. The utilized time-integration scheme, the evaluation of ex- ternal forces and the solution of the equations of motion for the included states are presented. The effect of including elastic ef- fects and quasi-steady aerodynamic modeling is investigated for a simple longitudinal maneuver with a generic commuter aircraft.

  • 4.
    Jansson, Natascha
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Eller, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Robust Turbulence Load Alleviation2011In: IFASD 2011: International Forum on Aeroelasticity and Structural Dynamics, 2011Conference paper (Other academic)
    Abstract [en]

    Using a comparatively detailed aeroelastic model for a generic commuter aircraft, a turbulence load alleviation system is designed with the objective of reducing structural fatigue. An H-optimal controller for the nominal model is found to be highly sensitive to small disturbances in the control system dynamics, so that a slightly perturbed closed-loop model is destabilized. Robust control methods are exploited to construct an alternative controller which improves robustness to disturbances at a small cost in nominal performance. Finally, fatigue loads experienced by the (open-loop and controlled) model are evaluated by means of two different load reconstruction methods, showing that the simpler modal displacement approach may introduce significant errors in wing bending moments.

  • 5.
    Jansson, Natascha
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Stenfelt, Gloria
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Steady and unsteady pressure measurements on a swept-wing aircraft2011Report (Other academic)
  • 6.
    Jansson, Natascha
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Stenfelt, Gloria
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Steady and unsteady pressure measurements on a swept-wing aircraft2014In: Aeronautical Journal, ISSN 0001-9240, Vol. 118, no 1200, p. 109-122Article in journal (Refereed)
    Abstract [en]

    Steady and unsteady pressure measurements are conducted for a tailless aircraft model. The main aim with the presented experimental work is to investigate the difficulties and possibilities involved in using an available pressure sensing system for accurate unsteady pressure measurement. The experimental procedure which is utilised for unsteady pressure measurements is described in detail. In particular, the importance of synchronised timing is recognised. For a harmonically varying pressure a small time delay in the measurement chain can result in a significant phase shift. Also, difficulties and uncertainties that are still present are pointed out. The results from these experiments are compared to numerical results based on unsteady potential flow theory. In general, the experimental and computational results show similar trends. Especially good agreement is found for the steady pressure measurements. For the unsteady pressure measurements a possible Reynolds number dependency is found for the considered test conditions.

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