91 research outputs found
On the Possibility of Intensity Based Registration for Metric Resolution SAR and Optical Imagery
No full textMultimodal image registration is a key to many remote sensing tasks like fusion, change detection, GIS overlay operations, 3D visualization etc. With advancements in research, intensity based similarity metrics namely mutual information (MI) and cluster reward algorithm (CRA) have been utilized for intricate multimodal registration problem. The computation of these metrics involves estimating the joint histogram directly from image intensity values, which might have been generated from different sensor geometries and/or modalities (e.g. SAR and optical). Modern day satellites like TerraSAR-X and IKONOS provide high resolution images generating enormous data volume along with very different image radiometric properties (especially in urban areas) not observed ever before. Thus, performance evaluation of intensity based registration techniques for metric resolution imagery becomes an interesting case study. In this paper, we analyze the performance of similarity metrics namely, mutual information and cluster reward algorithm for metric resolution images acquired over both plain and urban/semi-urban areas. Techniques for handling the generated enormous data volume and influence of really different sensor geometries over images especially acquired over urban areas have also been proposed and rightfully analyzed. Our findings from three carefully selected datasets indicate that the intensity based techniques can still be utilized for high resolution imagery but certain adaptations (like compression and segmentation) become useful for meaningful registration results
Numerical Investigations of the Effects of Sidewall Compression and Relaminarization in 3D Scramjet Inlet
No full textThis paper presents the numerical simulations and performance analysis of a 3D scramjet inlet with focus on the effects of sidewall compression and relaminarization. A well-validated �finite volume flow solver was used to simulate a scramjet inlet with a double ramp configuration for outer compression and varying degrees of sidewall compression. The computed wall pressure and heat transfer in the symmetry plane are in close agreement with the measurements and numerical results indicate that sidewall compression alters the inlet performance significantly. The effects of relaminarization over the expansion corner prior to the interior part of the inlet is isolated and studied in both experiment and simulation
Effects of Sidewall Compression and Relaminarization in a Scramjet Inlet
No full textThis paper presents the numerical simulations and the performance analysis of a scramjet inlet as part of a combined experimental and numerical study. A well-validated finite volume flow solver was used to simulate a scramjet inlet with a double ramp configuration for outer compression, including varying degrees of sidewall compression. The computed wall pressure and heat transfer in the symmetry plane are in close agreement with the measurements, and the numerical results indicate that the weak sidewall compression alters the inlet performance significantly. The effects of partial relaminarization over the expansion corner, before the interior part of the inlet, is isolated and investigated in both the experiment and simulation. It is shown that relaminarization of a boundary layer is predicted accurately using the current numerical methods. This work represents a contribution to the understanding of the effects of sidewall compression and relaminarization in designing a scramjet inlet
Wärmebelastung der Brennkammer eines Staustrahltriebwerks mit Überschallverbrennung
No full textThe aim of the dissertation project is the numerical simulation of the flow in a scramjet combustion chamber with diabatic walls. In order to analyze the aerothermal load on the structure and to determine the energy loss of the flow, an integrated fluid-thermal-structural analysis is performed. Of special interest is the mutual influence of flow and temperature boundary layer as well as the aerodynamic heating rate. For modeling the energy boundary condition at the wall, a coupled analysis of the heat transfer within the multi-layer wall material is conducted. Within the fluid, the unsteady compressible conservation equations are solved using a Galerkin finite-element method on adaptive hybrid grids. In addition to the flexible unstructured triangular elements, semi-structured quadrilaterals are employed to better resolve the viscous layers near solid walls. Due to the fact that a nonreactive one-component fluid is considered, the heat addition due to the combustion process is modeled by a heat source distribution according to a one-dimensional combustion model. An algebraic as well as a low Reynoldsnumber q-omega turbulence model are applied to account for the influence of turbulence on the heat transfer. The same finite-element method is applied to the conservatively coupled solution of the structural conservation equation. Measurements obtained by the experimental combustion chamber of the German-Russian Hypersonic Technology Program are used to validate the computations
Parameter Study for Scramjet Intake Concerning Wall Temperatures and Turbulence Modeling
No full textNumerical Investigation of Wall Temperature and Entropy Layer Effects on Double Wedge Shock / Boundary Layer Interactions
No full textA combined experimental as well as computational analysis of hypersonic flows over heated ramp and wedge configurations has been initiated. This paper presents an overview of the ongoing work on the numerical simulation using two different, well validated Reynolds averaged Navier–Stokes solvers with a variety of turbulence models. Different surface temperatures are specified to investigate the impact on the shock / boundary layer interaction and on the size of the separation. To analyze the effect of an entropy layer behind a blunt leading edge on the structure of the boundary layer as well as on the development of the inviscid flow field, flows over double wedge configurations with different nose radii are computed and compared to the experimental result
Assessment of aerodynamic roughness parameters of turbulent boundary layers over barnacle-covered surfaces
No full textFull-scale drag penalty predictions of flows over rough walls require surface roughness characterisation from laboratory experiments or numerical simulations. In either approach, it is necessary to determine the so-called equivalent sand-grain roughness height (ks ). There are several steps involved in determining this aerodynamic roughness lengthscale, but its procedure typically includes a combination of measurement of wall-shear stress (τw ) using direct or indirect methods as well as analysis of velocity profiles. Indirect methods usually rely on assumptions made about flow and its scaling including the validity of universal outer-layer similarity. However, the implications of the underlying assumptions involved in full-scale drag prediction are unclear. In this work, we carry out wind tunnel measurements over a realistic rough surface (from a fouled ship-hull) to evaluate the impact of different methods with an emphasis on using the outer-layer similarity hypothesis for full-scale drag predictions. Wall-shear stress is measured using an in-house floating-element drag balance (DB), and velocity profiles are obtained using particle image velocimetry (PIV), allowing the evaluation of ks , and the associated wake parameters through several methods. The aerodynamic roughness parameters hence obtained are used for full-scale drag penalty calculations. It is observed that the predicted drag penalty can vary by over 15 % among the different methods highlighting the care that should be taken when employing such methods.Fluid Mechanic
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