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Träfflista för sökning "hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Maskinteknik) hsv:(Rymd och flygteknik) "

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  • Munjulury, Raghu Chaitanya, et al. (författare)
  • Knowledge-based future combat aircraft optimization
  • 2016
  • Ingår i: NFFP5/NFFP6. - Bonn : International Council of Aeronautical Sciences (ICAS). ; , s. 273-280
  • Konferensbidrag (refereegranskat)abstract
    • Future combat aircraft inherently conceal all the components internally essentially for stealth reasons. The geometry is optimized for subsonic and supersonic flight area distribution and the components and payload to be fitted inside the aircraft. The basic requirements to accomplish are fuel consumption, mission profile, and military performance. Analytical methods comprise of a quick aerodynamic and structural optimization. The result obtained is then compared with multi-fidelity aero-structural analysis
  • Shetty, Sandeep (författare)
  • Optimization of Vehicle Structures under Uncertainties
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Advancements in simulation tools and computer power have made it possible to incorporate simulation-based structural optimization in the automotive product development process. However, deterministic optimization without considering uncertainties such as variations in material properties, geometry or loading conditions might result in unreliable optimum designs. In this thesis, the capability of some established approaches to perform design optimization under uncertainties is assessed, and new improved methods are developed. In particular, vehicle structural problems which involve computationally expensive Finite Element (FE) simulations, are addressed.The first paper focuses on the evaluation of robustness, given some variation in input parameters, the capabilities of three well-known metamodels are evaluated. In the second paper, a comparative study of deterministic, reliability-based and robust design optimization approaches is performed. It is found that the overall accuracy of the single-stage (global) metamodels, which are used in the above study, is acceptable for deterministic optimization. However, the accuracy of performance variation prediction (local sensitivity) must be improved. In the third paper, a decoupled reliability-based design optimization (RBDO) approach is presented. In this approach, metamodels are employed for the deterministic optimization only while the uncertainty analysis is performed using FE simulations in order to ensure its accuracy.In the fifth paper, two new sequential sampling strategies are introduced that aim to improve the accuracy of the metamodels efficiently in critical regions. The capabilities of the methods presented are illustrated using analytical examples and a vehicle structural application.It is important to accurately represent physical variations in material properties since these might exert a major influence on the results. In previous work these variations have been treated in a simplified manner and the consequences of these simplifications have been poorly understood. In the fourth paper, the accuracy of several simple methods in representing the real material variation has been studied. It is shown that a scaling of the nominal stress-strain curve based on the Rm scatter is the best choice of the evaluated choices, when limited material data is available.In this thesis work, new pragmatic methods for non-deterministic optimization of large scale vehicle structural problems have been developed. The RBDO methods developed are shown to be flexible, more efficient and reasonably accurate, which enables their implementation in the current automotive product development process.
  • Saha, Ranjan, 1984-, et al. (författare)
  • Aerodynamic Implication of Endwall and Profile Film Cooling in a Transonic Annular Cascade
  • 2013
  • Ingår i: Sector Rig. - Busan, Korea.
  • Konferensbidrag (refereegranskat)abstract
    • An experimental study is performed to observe the aerodynamic implications of endwall and profile film cooling on flow structures and aerodynamic losses. The investigated vane is a geometrically similar transonic nozzle guide vane with engine-representative cooling geometry. Furthermore, a new formulation of the cooling aerodynamic loss equation is presented and compared with the conventional methods. Results from a 5-hole pneumatic probe show that the film coolant significantly alters the secondary flow structure. The effect of different assumptions for the loss calculation is shown to significantly change the measured loss.
  • Saha, Ranjan, 1984-, et al. (författare)
  • Suction and Pressure Side Film Cooling Influence on Vane Aero Performance in a Transonic Annular Cascade
  • 2013
  • Ingår i: Proceedings of the ASME Turbo Expo. - 9780791855225
  • Konferensbidrag (refereegranskat)abstract
    • An experimental study on a film cooled nozzle guide vane has been conducted in a transonic annular sector to observe the influence of suction and pressure side film cooling on aerodynamic performance. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at an exit reference Mach number of 0.89. The aerodynamic results using a five hole miniature probe are quantified and compared with the baseline case which is uncooled. Results lead to a conclusion that the aerodynamic loss is influenced substantially with the change of the cooling flow rate regardless the positions of the cooling rows. The aerodynamic loss is very sensitive to the blowing ratio and a value of blowing ratio higher than one leads to a considerable higher loss penalty. The suction side film cooling has larger influence on the aerodynamic loss compared to the pressure side film cooling. Pitch-averaged exit flow angles around midspan remain unaffected at moderate blowing ratio. The secondary loss decreases (greater decrease in the tip region compared to the hub region) with inserting cooling air for all cases compared to the uncooled case.
  • Nilsson, Johan (författare)
  • Numerical methods for load and response prediction for use in acoustic fatigue
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Acoustic fatigue can occur in structural elements of an aircraft exposed to very high sound pressures. To deal with acoustic fatigue, mainly empirical methods have been applied and often late in the design phase. Current design guidelines have three main limitations. First, they do not say anything about the load intensities. The load levels can be determined either experimentally or numerically. Experimental testing tends to be expensive and time consuming. It is also desired to deal with acoustic fatigue early in the design phase. Therefore, it is desired to turn to numerical methods to determine the load levels. Second, the design guidelines assume that the spatial distribution of the load is uniform. In other words, the load is assumed to be perfectly in phase over the entire structural element. This assumption limits the accuracy of the response prediction and by extension the fatigue prediction. Third, the design guidelines are limited to a simple, single surface panel with linear response. In this thesis, both the load and response prediction are performed by numerical methods. The load is determined using Computational Fluid Dynamics (CFD). From the CFD simulations, both the load intensities and the spatial distributions are extracted. This solves the first and second mentioned limitations. The extracted load is used as force input to a Finite Element (FE) simulation of the exposed panel structure. Since complex structures and non-linearities can be handled using the FE-method, it avoids the third mentioned limitation. Two cases of separated flow are used as model problems for acoustic fatigue in this thesis. In both model problems, the simulations are compared to existing measurements. In Paper A, a ramped backward-facing step is used. The flow over the step induces a load on an aluminium sheet fitted downstream of the step. With the exception of the cut-off, or shedding mode, frequency being overpredicted, the spectral qualities of the load and the load intensities are well captured. The panel response prediction compares reasonably well with the existing measurements. In Paper B, a reduction in a range of low frequencies of the downstream load is observed when the ramped backward-facing step is lined with chevrons or serrations. The model problem used in Papers C-E is flow over an inclined fence at transonic Mach number and realistic Reynolds number for aircraft operation. A segment with cyclic boundary conditions of the flow setup is simulated in Paper C. This result in well predicted cross-spectra, but an energy concentration in the auto-spectra is not properly resolved. In Paper D, a full three-dimensional simulation of the entire setup is performed and it is concluded that the missing energy concentration in the auto-spectra is properly captured. In Paper E, the response of a realistic aircraft panel structure is simulated using FE random response analysis with the CFD-simulated load as input. The response is found to be sensitive to the cross-spectra of the input load. The strain predictions vary with strain gauge location. However, only one strain gauge is off by more than a factor of two, which appears to be the best one can hope for when using the design guidelines in favourable conditions and with a measured load. Therefore, the main conclusion of this thesis is that the method of using CFD to calculate the load which is to be used as input to an FE response simulation can produce useful results for acoustic fatigue.
  • Nilsson, Johan, et al. (författare)
  • Passive load control in backward-facing step flow by using chevrons
  • 2016
  • Ingår i: The International Conference on Jets, Wakes and Separated Flows (ICJWSF2015),Stockholm, Sweden,2015-06-16 - 2015-06-18. ; 185, s. 223-239
  • Konferensbidrag (refereegranskat)abstract
    • The ability of chevrons at the top edge of a backward-facing step to reduce downstream surface pressure fluctuations is investigated numerically. Three different chevron configurations are compared against a baseline case without chevrons. Low frequency reduction in the surface pressure fluctuations is observed for two of the configurations. The chevrons do not appear to have a significant effect on the flow as the mean reattachment length for all configurations is nearly constant and there is only a small increase in streamwise turbulence for one configuration with the other configurations unchanged.
  • Van der Kelen, Christophe, 1986-, et al. (författare)
  • Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Glass Wool
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • The air flow resistivity of nine adjacent glass wool samples is measured and estimated using a previously published method. The samples are extracted from a large slab of glass wool material. Identifying the full flow resistivity tensors for nine adjacent cubic glass wool samples allows for an estimation of the spatial distribution of normal and planar flow resistivity throughout the measured material. The average density of the samples tested is 27.8 kg/m3. The estimated flow resistivity tensors are validated by comparison to uni-directional measurements on cylindrical samples, extracted from the cubic glass wool samples tested. Furthermore, the uni-directional measurement method is studied, providing useful insights on the effect of sample thickness on the measured flow resistivity for an anisotropic material.
  • Van der Kelen, Christophe, 1986-, et al. (författare)
  • Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Melamine Foam
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • The flow resistivity tensor, which is the inverse of the viscous per- meability tensor, is one of the most important material properties for the acoustic performance of open cell foams used in acoustic treatments. Due to the manufacturing processes, these foams are most often geomet- rically anisotropic on a microscopic scale. For such a materials there is a need for improved characterisation methods, and this paper discusses the estimation of the flow resistivity tensor of Melamine samples using a methodology which is an improvement of a method previously published by Go ̈ransson et al. The validity of the new method is in addition ver- ified for a wider range of anisotropy. Measurements are performed on cubic Melamine samples, and the resulting 3D flow resistivity tensors are presented. The anisotropic flow resistivity tensors are validated by com- parison to measurements performed on uni-directional cylindrical samples extracted from the previously measured cubic samples. The results sug- gest that there is a relation between the direction of highest flow resistivity, and the rise direction of the material.
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