94,946 research outputs found
Structural Analysis of a Dragonfly Wing
No full textDragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in a lightweight structure with good aerodynamic performance. How insect wings carry aerodynamic and inertial loads, and how the resonant frequency of the flapping wings is tuned for carrying these loads, is however not fully understood. To study this we made a three-dimensional scan of a dragonfly (Sympetrum vulgatum) fore- and hindwing with a micro-CT scanner. The scans contain the complete venation pattern including thickness variations throughout both wings. We subsequently approximated the forewing architecture with an efficient three-dimensional beam and shell model. We then determined the wing’s natural vibration modes and the wing deformation resulting from analytical estimates of 8 load cases containing aerodynamic and inertial loads (using the finite element solver Abaqus). Based on our computations we find that the inertial loads are 1.5 to 3 times higher than aerodynamic pressure loads. We further find that wing deformation is smaller during the downstroke than during the upstroke, due to structural asymmetry. The natural vibration mode analysis revealed that the structural natural frequency of a dragonfly wing in vacuum is 154 Hz, which is approximately 4.8 times higher than the natural flapping frequency of dragonflies in hovering flight (32.3 Hz). This insight in the structural properties of dragonfly wings could inspire the design of more effective wings for insect-sized flapping micro air vehicles: The passive shape of aeroelastically tailored wings inspired by dragonflies can in principle be designed more precisely compared to sail like wings —which can make the dragonfly-like wings more aerodynamically effective
Optimal design of a flying-wing aircraft inner wing structure configuration
No full textFlying-wing aircraft are considered to have great advantages and potentials in
aerodynamic performance and weight saving. However, they also have many
challenges in design. One of the biggest challenges is the structural design of
the inner wing (fuselage). Unlike the conventional fuselage of a tube
configuration, the flying-wing aircraft inner wing cross section is limited to a
noncircular shape, which is not structurally efficient to resist the internal
pressure load. In order to solve this problem, a number of configurations have
been proposed by other designers such as Multi Bubble Fuselage (MBF),
Vaulted Ribbed Shell (VLRS), Flat Ribbed Shell (FRS), Vaulted Shell
Honeycomb Core (VLHC), Flat Sandwich Shell Honeycomb Core (FLHC), Y
Braced Box Fuselage and the modified fuselage designed with Y brace
replaced by vaulted shell configurations. However all these configurations still
inevitably have structural weight penalty compared with optimal tube fuselage
layout. This current study intends to focus on finding an optimal configuration
with minimum structural weight penalty for a flying-wing concept in a preliminary
design stage.
A new possible inner wing configuration, in terms of aerodynamic shape and
structural layout, was proposed by the author, and it might be referred as
‘Wave-Section Configuration’. The methodologies of how to obtain a structurally
efficient curvature of the shape, as well as how to conduct the initial sizing were
incorporated.
A theoretical analysis of load transmission indicated that the Wave-Section
Configuration is feasible, and this was further proved as being practical by FE
analysis. Moreover, initial FE analysis and comparison of the Wave-Section
Configuration with two other typical configurations, Multi Bubble Fuselage and
Conventional Wing, suggested that the Wave-Section Configuration is an
optimal design in terms of weight saving. However, due to limitations of the
author’s research area, influences on aerodynamic performances have not yet
been taken into account
Influence of wing kinematics on aerodynamic performance in hovering insect flight
No full textThe influence of different wing kinematic models on the aerodynamic performance of a hovering insect is investigated by means of two-dimensional time-dependent Navier–Stokes simulations. For this, simplified models are compared with averaged representations of the hovering fruit fly wing kinematics. With increasing complexity, a harmonic model, a Robofly model and two more-realistic fruit fly models are considered, all dynamically scaled at Re = 110. To facilitate the comparison, the parameters of the models were selected such that their mean quasi-steady lift coefficients were matched. Details of the vortex dynamics, as well as the resulting lift and drag forces, were studied. The simulation results reveal that the fruit fly wing kinematics result in forces that differ significantly from those resulting from the simplified wing kinematic models. In addition, light is shed on the effect of different characteristic features of the insect wing motion. The angle of attack variation used by fruit flies increases aerodynamic performance, whereas the deviation is probably used for levelling the forces over the cycle.Aerospace Design, Integration and OperationsAerospace Engineerin
Conceptual design and optimization methodology for box wing aircraft
No full textA conceptual design optimization methodology was developed for a medium range box
wing aircraft. A baseline conventional cantilever wing aircraft designed for the same mis-
sion and payload was also optimized alongside a baseline box wing aircraft. An empirical
formula for the mass estimation of the fore and aft wings of the box wing aircraft was
derived by relating conventional cantilever wings to box wing aircraft wings. The results
indicate that the fore and aft wings would use the same correction coe cient and that
the aft wing would be lighter than the fore wing on the medium range box wing aircraft
because of reduced sweep.
As part of the methodology, a computational study was performed to analyze di erent
wing/tip n xities using a statically loaded idealized box wing con guration. The analy-
ses determined the best joint xity by comparing the stress distributions in nite element
torsion box models in addition to aerodynamic requirements. The analyses indicates that
the rigid joint is the most suitable.
Studies were also performed to investigate the structural implications of changing only
the tip n inclinations on the box wing aircraft. Tip n inclination refers to the angle the
tip n makes to the vertical body axis of the aircraft. No signi cant variations in wing
structural design drivers as a function of tip n inclination were observed.
Stochastic and deterministic optimization routines were performed on the baseline box
wing aircraft using the methodology developed where the variables were wing area, av-
erage thickness to chord ratio and sweep angle. The conventional aircraft design showed
similar performance and characteristics to the equivalent in-service aircraft thereby pro-
viding some validation to the methodology and the results for the box wing aircraft.
Longitudinal stability investigations showed that the extra fuel capacity of the box wing in
the ns could be used to reduce trim drag. The short period oscillation of the conventional
cantilever wing aircraft was found to be satisfactory but the box wing aircraft was found
to be unacceptable hence requiring stability augmentation systems. The eld and
ight
performance of the box wing showed to be better than the conventional cantilever wing
aircraft. Overall, the economic advantages of the box wing aircraft over the conventional
cantilever wing aircraft improve with increase in fuel price making the box wing a worthy
replacement for the conventional cantilever wing aircraft
Analysis of composite wing structures with a morphing leading edge
No full textOne of the main challenges for the civil aviation industry is the reduction of its environmental impact. Over the past years, improvements in performance efficiency have been achieved by simplifying the design of the structural components and using composite materials to reduce the overall weight. These approaches however, are not sufficient to meet the current demanding requirements set for a „greener‟ aircraft.
Significant changes in drag reduction and fuel consumption can be obtained by using new technologies, such as smart morphing structures. These concepts will in fact help flow laminarisation, which will increase the lift to drag ratio. Furthermore, the capability to adapt the wing shape will enable to optimise the aerodynamic performance not only for a single flight condition but during the entire mission. This will significantly improve the aircraft efficiency.
The current research work has been carried out as part of the European Commission founded Seventh Framework Program called „Smart High Lift Device for the Next Generation Wing‟ (SADE), which main aim is to develop and study morphing high lift devices. The author‟s investigation focused on developing a design concept for the actuation mechanism of a morphing leading edge device. A detailed structural analysis has been carried out in order to demonstrate its feasibility.In the first phase of the research the attention was directed on the preliminary design and analysis of the composite wing box. The parameters of the key structural components, such as skin, spars, ribs and stringers were set to satisfy the static stress and buckling requirements. Moreover, numerical and experimental studies were conducted to analyse the static failure and buckling behaviour of two typical composite wing structural components: a spar section and a web and base joint assembly.
In the second stage of the research, a design for the morphing leading edge actuation mechanism was developed. The actuation system was designed in such a way that the target shape was reached with minimum actuation force demand. A geometrical nonlinear FE analysis was conducted to simulate the leading edge morphing deflection and ensure that structural strength requirements were satisfied. Furthermore, the behaviour of the skin integrated with the internal actuation mechanism was modelled under the aerodynamic pressure, at different flight conditions and gust loads, in order to prove that the proposed actuation system can compete with the conventional rigid rib.
This study demonstrated that a feasible morphing leading edge design for a next generation large aircraft wing can be achieved. Developing the readiness of this technology will have a significant impact on aircraft efficiency and considerable contribution towards a more environmental friendly aviation
Optimal design of an aeroelastic wing structure with seamless control surfaces
No full textThis article presents an investigation into the concept and optimal design of a lightweight seamless aeroelastic wing (SAW) structure for small air vehicles. Attention has been first focused on the design of a hingeless flexible trailing edge (TE) control surface. Two innovative design features have been created in the SAW TE section: an open sliding TE and a curved beam and disc actuation mechanism. This type of actuated TE section allows for the SAW having a camber change in a desirable shape and minimum control power demand. This design concept has been simulated numerically and demonstrated by a test model. For a small air vehicle of large sweep back wing, it is noted that significant structural weight saving can be achieved. However, further weight saving is mainly restricted by the aeroelastic stability and minimum number of carbon/epoxy plies in a symmetric layup rather than the structural strength. Therefore, subsequent effort was made to optimize the primary wing box structure. The results show that an initial structural weight can be reduced significantly under the strength criterion. The resulting reduction of the wing box stiffness and aeroelastic stability and control effectiveness can be improved by applying the aeroelastic tailoring. Because of the large swept angle and resulting lightweight and highly flexible SAW, geometrical non-linearity and large bending-torsion aeroelastic coupling have been considered in the analysis
Optimization of a Composite Wing Subject to Multi Constraints
No full textIn this thesis, an investigation has been carried out into a minimum weight optimization analysis of a composite wing with multi design constraints under both static and dynamic loadings. The study includes the influence of a morphing leading edge on the wing stiffness and gust load reduction by employing a passive gust alleviation device at the wing tip.
The design process started from a generic study of optimal structure against buckling for three typical types of reinforced skin panel structures including stiffener panel, sandwich and grid panel. The optimal design in terms of buckling performance and structural efficiency were compared. The study then focused on the optimal design of stiffened skin panels for a particular wing. Parametric studies on optimal design for isotropic stiffened panels were carried out in which practical design constraints were introduced. The optimal design method was further extended to composite stiffened skin panels. Optimal designs were obtained within a compression distributed load range from 500 N/mm to 5250 N/mm and a symmetric balanced layup with 0˚, 90˚, and ±45˚ plies. Based on the study, the modelling and optimal design method for composite stiffened panels was applied to a composite wing box for its upper surface panel design. The initial composite wing box was designed to achieve a minimum weight. Gradient based optimization method was applied in the analysis with practical design constraints. The results indicate that the effect of leading edge morphing on the overall wing structural stiffness is negligible. It has been shown that the weight of the upper surface of the wing box structure can be reduced by 19.8% from its initial design.
Optimal design of a passive gust alleviation device (PGAD) mounted at the wing tip was then investigated. Based on the dynamic analysis of the 3D wing FE model in different flight and payload cases, a method and program was developed to create a dynamically equivalent beam model. Gust response of the optimized wing model was computed for a wide range of frequencies in accordance with the CS-25. Next, a parametric study of the key design variables of the PGAD was carried out to determine the optimal design parameters for minimum gust loading. The results have shown that the gust response can be reduced by 15% by using a 1m long PGAD for a conventional aircraft wing and yet reduce 50% tip displacement with 37.2% bending moment at wing root for a flying wing concept aircraft wing with 1.6m long PGAD mounted at the wing tip.
The results of the investigation contribute to knowledge in the following aspects. It provides an evaluation of the structural efficiency of three typical types of stiffened panels against buckling prevention. The research also provided an optimal design method for composite stringer stiffened panels by combining theoretical and practical design constraints. It made possible for the first-time a numerical evaluation of the novel PGAD as applied to a large aircraft
Formation of the leading-edge vortex and spanwise flow on an insect-like flapping-wing throughout a flapping half cycle
No full textThis paper presents an experimental investigation of the evolution of the leading-edge vortex and spanwise flow generated by an insect-like flapping-wing at a Reynolds number relevant to flapping-wing micro air vehicles (FMAVs) (Re = ~15,000). Experiments were accomplished with a first-of-its-kind flapping-wing apparatus. Dense pseudo-volumetric particle image velocimetry (PIV) measurements from 18% - 117% span were taken at twelve azimuthal positions throughout a flapping half cycle. Results revealed the formation of a primary leading-edge vortex (LEV) which saw an increase in size and spanwise flow (towards the tip) through its core as the wing swept from rest to the mid-stroke position where signs of vortex breakdown were observed. Beyond mid-stroke, spanwise flow decreased and the tip vortex grew in size and exhibited a reversal in its axial direction. At the end of the flapping half cycle, the primary LEV was still present over the wing surface, suggesting that the LEV remains attached to the wing throughout the entire flapping half cycle
Does Parental Unemployment Cause Right-Wing Extremism?
No full textRecent years have witnessed a rise in right-wing extremism among German youth and young adults. This paper investigates the extent to which the experience of parental unemployment during childhood affects young people's far right-wing attitudes and xenophobia. Estimates from three German data sets show a positive relationship between growing up with unemployed parents and right-wing extremism, with xenophobia in particular. This paper uses stark differences in unemployment levels between East and West Germany, both before and after reunification, to investigate a causal relationship. Instrumental variables estimates suggest strong and significant effects of parental unemployment on right-wing extremism. Various panel estimates also point to a positive relationship. The results are consistent with classical theories of economic interest and voting behaviour which predict that persons who develop feelings of economic insecurity are more susceptible to right-wing extremism and anti-foreign sentiments.Right-wing extremism, unemployment, instrumental variables estimations, panel estimators, intergenerational links
Optimal design of a composite active aeroelastic wing
No full textThe primary aim of this research was to design a Seamless Aeroelastic Wing (SAW) structure applicable to a lightweight Unmanned Aerial Vehicle (UAV). Therefore the study focused on optimal design of a SAW structure by utilising the maximum aeroelastic beneficial effect. Although similar to the Active Aeroelastic Wing (AAW) and relevant to the Flapless Air Vehicle Integrated Industrial Research (FLAVIIR), the major difference from them is that a SAW will function as an integrated one piece lifting and control surface. It is designed to produce a desirable wing camber for control by deflecting a hinge-less flexible trailing edge (TE) part instead of a traditional control surface.
Attention was firstly paid on the design of a hinge-less flexible trailing edge control surface and the actuation mechanism applicable for a light-weight aircraft (UAV). The proposed mechanism in the SAW TE section has two innovative design features: an open sliding TE and a curved beam and disc actuation mechanism. This type of actuated TE section allows for the SAW having a smooth camber change in a desirable shape with minimum control power demand. This design concept has been simulated numerically and its feasibility has been demonstrated by a test model.
The wing structure for a small scale UAV is likely to be over designed in terms of strength, stiffness and weight due to manufacturing constraints. For the optimal wing design, the investigation was conducted in two stages. In the first stage, effort was made to design and model an optimised composite wing box for a minimum weight and maximum flutter speed. Both analytical and numerical methods were used for structural stress, vibration and aeroelastic analyses. In the second stage, the study focused on integrating the TE actuation mechanism with the optimised wing box for detailed understanding of the structure. A finite element analysis was conducted to simulate the SAW TE to ensure that structural strength requirements were satisfied. Furthermore, a study was carried out on the structural dynamic behaviour of the SAW TE section under the aerodynamic pressure to demonstrate its dynamic stability. Hence, the outcome of this research shows that a feasible SAW design for a UAV can be achieved
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