Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 5 Articles
An over-the-wing-nacelle-mount airplane configuration is known to prevent the noise propagation from jet engines toward\r\nground. However, the configuration is assumed to have low aerodynamic efficiency due to the aerodynamic interference effect\r\nbetween a wing and a nacelle. In this paper, aerodynamic design optimization is conducted to improve aerodynamic efficiency\r\nto be equivalent to conventional under-the-wing-nacelle-mount configuration. The nacelle and wing geometry are modified to\r\nachieve high lift-to-drag ratio, and the optimal geometry is compared with a conventional configuration. Pylon shape is also\r\nmodified to reduce aerodynamic interference effect. The final wing-fuselage-nacelle model is compared with the DLR F6 model to\r\ndiscuss the potential of Over-the-Wing-Nacelle-Mount geometry for an environmental-friendly future aircraft....
We propose to model ice shedding trajectories by an innovative paradigm that is based on cartesian grids, penalization and level\r\nsets. The use of cartesian grids bypasses the meshing issue, and penalization is an efficient alternative to explicitly impose boundary\r\nconditions so that the body-fitted meshes can be avoided, making multifluid/multiphysics flows easy to set up and simulate. Level\r\nsets describe the geometry in a nonparametric way so that geometrical and topological changes due to physics and in particular\r\nshed ice pieces are straight forward to follow. The model results are verified against the case of a free falling sphere. The capabilities\r\nof the proposed model are demonstrated on ice trajectories calculations for flow around iced cylinder and airfoil....
This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread\r\nconcept ââ?¬Å?vortex breakdownââ?¬Â is found theoretically impossible and never happened in practice. The ring-like vortex is found the\r\nonly formexisting inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counterrotating\r\nprimary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex\r\ntube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to\r\nlink two ?-vortex legs. The bridge finally develops as a new ring. This process keeps going on to formamultiple ring structure. The\r\nU-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex,\r\nserves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary\r\nlayer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive\r\nspikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive\r\nspike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated....
This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion\r\nmodel (DiSSEL). In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water.\r\nDuring the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge,\r\nsway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage,\r\nrespectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions\r\nand their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering,\r\na universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces\r\nand moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an\r\nExperimentalHull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL\r\nand experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder,\r\nwhich is included using a flow acceleration factor....
Cerebral aneurysms are local expansions of blood vessel walls in the brain blood system. The rupture of an aneurysm is a very\r\nsevere event associated with a high rate of mortality.When cerebral aneurysms are detected, clinicians need to decide if operation\r\nis required. The risk of aneurysm rupture is then compared to the risks associated with the medical intervention. In the present\r\npaper, a probabilistic framework for a mechanically based rupture risk assessment of cerebral aneurysms is proposed. The method\r\nis based on the assumption that the strength of aneurysmal tissues can be described by a statistical distribution. A structural\r\nanalysis of the aneurysm in question is performed, and the maximum stress experienced by the aneurysm is compared to the\r\nstrength distribution. The proposed model was compared with clinical results for ruptured aneurysms in terms of rupture density\r\nand accumulated rupture risk as a function of aneurysm size. The model was able to reproduce the clinical results well. The\r\nproposed framework may potentially be used under in vivo conditions to predict the risk of rupture for diagnosed aneurysms....
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