| 1. |
- Mao, Huina, et al.
(författare)
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Deployment of Bistable Self-Deployable Tape Spring Booms Using a Gravity Offloading System
- 2017
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Ingår i: Journal of Aerospace Engineering. - Journal of Aerospace Engineering. - 0893-1321 .- 1943-5525. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- Bistable tape springs are suitable as deployable structures thanks to their high packaging ratio, self-deployment ability, low cost, light weight, and stiffness. A deployable booms assembly composed of four 1-m long bistable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The aim of the present study was to investigate the deployment dynamics and reliability of the SEAM boom design after long-term stowage using onground experiments and simulations. A gravity offloading system (GOLS) was built and used for the onground deployment experiments. Two booms assemblies were produced and tested: a prototype and an engineering qualification model (EQM). The prototype assembly was deployed in a GOLS with small height, whereas the EQM was deployed in a GOLS with tall height to minimize the effects of the GOLS. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic relaxation, and other factors that act to decrease the deployment force. Experiments and simulations of the deployment dynamics indicate significant viscoelastic energy relaxation phenomena, which depend on the coiled radius and stowage time. In combination with friction effects, these viscoelastic effects decreased the deployment speed and the end-of-deployment shock vibrations.
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| 2. |
- Challamel, Noel, et al.
(författare)
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Boundary-Layer Effect in Composite Beams with Interlayer Slip
- 2011
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Ingår i: Journal of Aerospace Engineering. - 0893-1321 .- 1943-5525. ; 24:2, s. 199-209
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Tidskriftsartikel (refereegranskat)abstract
- An apparent analytical peculiarity or paradox in the bending behavior of elastic-composite beams with interlayer slip, sandwich beams, or other similar problems subjected to boundary moments exists. For a fully composite beam subjected to such end moments, the partial composite model will render a nonvanishing uniform value for the normal force in the individual subelement. This is from a formal mathematical point of view in apparent contradiction with the boundary conditions, in which the normal force in the individual subelement usually is assumed to vanish at the extremity of the beam. This mathematical paradox can be explained with the concept of boundary layer. The bending of the partially composite beam expressed in dimensionless form depends only on one structural parameter related to the stiffness of the connection between the two subelements. An asymptotic method is used to characterize the normal force and the bending moment in the individual subelement to this dimensionless connection parameter. The outer expansion that is valid away from the boundary and the inner expansion valid within the layer adjacent to the boundary (beam extremity) are analytically given. The inner and outer expansions are matched by using Prandtl's matching condition over a region located at the edge of the boundary layer. The thickness of the boundary layer is the inverse of the dimensionless connection parameter. Finite-element results confirm the analytical results and the sensitivity of the bending solution to the mesh density, especially in the edge zone with stress gradient. Finally, composite beams with interlayer slip can be treated in the same manner as nonlocal elastic beams. The fundamental differential equation appearing in the constitutive law associated with the partial-composite action in a nonlocal elasticity framework is discussed. Such an integral formulation of the constitutive equation encompassing the behavior of the whole of the beam allows the investigation of the mechanical problem with the boundary-element method.
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| 3. |
- Murali, Damu, et al.
(författare)
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Flow Over Flat and Curved Plates: A Flow Visualization Study
- 2022
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Ingår i: Journal of Aerospace Engineering. - : ASCE. - 0893-1321 .- 1943-5525. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- Visualization experiments are conducted in a water channel to investigate the wake vortex characteristics of a flat plate and convex and concave curved plates. Three parameters—vortex size (Sv��), vortex length (Lv��), and Strouhal number (St��)—are investigated in this study to deduce the effect of plate curvature and orientation. These parameters are estimated for both the upper and lower vortices by keeping the chord length (Lc��) fixed and changing the plate diameter (D). Various plate configurations are demonstrated by altering the Lc/D��/D ratio from 0 to 1; Lc/D=0��/D=0, 6/13, 3/4, and 1. The Reynolds number (Re) based on chord length remains unchanged at 5,878 throughout the analysis. For each case of the Lc/D��/D ratio, the angle of flow incidence of the plate (α�) is varied from 0° to 30° in steps of 5°. For the convex plate, the combined effect of curvature and orientation is found to enhance the vortex shedding frequency by 70.7%, whereas vortices shrink by 26.71%, and the vortex length is reduced by 25.38%. The manipulations achieved for concave plates reveal comparatively lesser enhancement in shedding frequency; however, concave surfaces are observed to be more suitable for stretching the vortices toward the downstream. The modifications thus achieved have significant practical relevance in various applications. A shedding mechanism that partially interrupts Gerrard’s mechanism is also found to operate with concave plate configurations.
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| 4. |
- Okda, Sherif, et al.
(författare)
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Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
- 2020
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Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
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Tidskriftsartikel (refereegranskat)abstract
- Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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| 5. |
- Wei, X. F., et al.
(författare)
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Experimental Investigations of Screech Mitigation and Amplification by Beveled and Double-Beveled Nozzles
- 2022
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Ingår i: Journal of Aerospace Engineering. - : American Society of Civil Engineers (ASCE). - 0893-1321 .- 1943-5525. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study was conducted to investigate and compare the effects of beveled and double-beveled circular nozzles on supersonic jet screech at a nozzle pressure ratio of 5. In particular, near- and far-field microphone measurements and schlieren visualizations were utilized to look into selected acoustic and flow features associated with jet screech radiation. Results show that beveled nozzles eliminate jet screech by producing asymmetric shock structures and instability waves that are mismatched in phase and amplitude. In contrast, double-beveled nozzles produce symmetric shock structures and amplify screech intensity, even when jet mixing effects have been significantly enhanced. It is further observed that amplified jet screeches produced by double-beveled nozzles are highly unsteady and undergo nonperiodic and stochastic temporal variations. Last but not least, double-beveled nozzles also significantly impact screech peak noise locations and confer different changes along different measurement planes. The present study demonstrates that not all beveled-type nozzles are able to mitigate jet screech, with nonoptimal designs amplifying it instead.
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| 6. |
- Wärmefjord, Kristina, 1976, et al.
(författare)
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Form Division for Welded Aero Components in Platform-Based Development
- 2015
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Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 28:5
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Tidskriftsartikel (refereegranskat)abstract
- In aerospace engine industry, large casted components are, because of sustainability considerations, being replaced by smaller parts that are welded together. This reduces weight because some parts can be made of lighter material. It also opens up for use of platforms. The division of a large component into smaller parts is called form division. The form division affects the geometrical robustness in the weld splitlines between the parts and thereby the weldability. By optimizing the robustness in weld splitlines, conditions for welding can be improved. A greedy algorithm for weld splitline division is described and exemplified on aerospace case studies.
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| 7. |
- Xisto, Carlos, 1984, et al.
(författare)
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Parametric Analysis of a Large-scale Cycloidal Rotor in Hovering Conditions
- 2017
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Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 30:1, s. 04016066-04016066-14-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, four key design parameters of cycloidal rotors, namely the airfoil section; the number of blades; the chord-to-radius ratio; and the pitching axis location, are addressed. The four parameters, which have a strong effect on the rotor aerodynamic efficiency are analyzed with an analytical model and a numerical approach. The numerical method is based on a finite-volume discretization of two-dimensional Unsteady Reynolds Averaged Navier-Stokes equations on a multiple sliding mesh, are proposed and validated against experimental data. A parametric analysis is then carried out considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering conditions. Results demonstrate that the airfoil thickness significantly affects the rotor performance; such a result is partly in contrast with previous findings for small- and micro-scale configurations. Moreover, it will be shown that increasing the number of blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius will demonstrate that values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with micro-scale cyclogyros, the generated thrust increases as the pitching axis is located away from the leading edge, up to 35% of chord length. Further the shortcomings of using simplified analytical tools in the prediction of thrust and power in non-ideal flow conditions will be highlighted and discussed.
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| 8. |
- Benzerga, A. A., et al.
(författare)
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Computational methodology for modeling fracture in fiber-reinforced polymer composites
- 2009
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Ingår i: Journal of Aerospace Engineering. - 0893-1321 .- 1943-5525. ; 22:3, s. 296-303
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Tidskriftsartikel (refereegranskat)abstract
- A framework is presented for analyzing the inelastic behavior and fracture of polymer matrix composites. Physics-based viscoplastic constitutive equations are used and supplemented with a matrix cracking model and an energy-based debonding model. The capabilities of the framework are illustrated by finite-element solutions of boundary-value problems under plane strain conditions using the unit-cell concept. In the application, focus is centered on the effect of manufacturing induced voids on local modes of fracture under both tension and compression
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| 9. |
- Cella, U., et al.
(författare)
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Sensitivity to physical and numerical modeling in Navier-Stokes simulations
- 2000
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Ingår i: Journal of Aerospace Engineering. - 0893-1321 .- 1943-5525. ; 13:2, s. 47-51
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Tidskriftsartikel (refereegranskat)abstract
- Navier-Stokes Multiblock code solves the fully coupled system of equations simultaneously using a cell-centered finite-volume approach. This note assesses the sensitivity to some turbulence models and numerical schemes implemented in Navier-Stokes Multiblock when computing two test cases in standard mode, i.e., without tuning the code to these two cases. The cases are (1) subsonic flow around the MS(1)-0313 airfoil, and (2) transonic flow around the ONERA M6 wing, using various combinations of models (algebraic Baldwin-Lomax or Granville, one-equation Spalart-Allmaras, or the two-equation k - epsilon model of Chien) together with a numerical scheme of either the second-order central or third-order Roe upwind type.
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| 10. |
- Amadori, Kristian, et al.
(författare)
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Automated Design and Fabrication of Micro Air Vehicles
- 2011
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Ingår i: Journal of Aerospace Engineering. - : SAGE Journals online. - 0893-1321 .- 1943-5525. ; 226:10, s. 1271-1282
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for an automated design and fabrication of micro-air vehicles (MAVs) is presented. A design optimization framework has been developed that interfaces several software systems to generate MAVs to optimally fulfil specific mission requirements. By means of amulti-objective genetic algorithm, families of MAVs are tailored with respect to objectives such as weight and endurance. The framework takes into consideration the airframe and aerodynamic design as well as the selection and positioning of internal components. The selection of propulsion system components is made from a database of off-the-shelf components. In combination with a three-dimensional printer, physical prototypes can be quickly manufactured. A validation of the framework results from flight tests of a real MAV is also presented.
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