 | Case Study: Platform Hydrodynamic Drag • Current Practice: – Use the drag coefficients from similar projects or an assembly of simple geometric shapes at early stages, and adapt them according to the project evolution; – The final coefficients are obtained experimentally at a more advanced design phase. • Objective: – A good estimate of hydrodynamic drag coefficients at early design stages.
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| | The present paper compares various numerical models which simulate the mechanical behaviour of the human lumbar intervertebral disc under static and time-varying uniaxial compressive loads, with the aid of the finite element method. Concerning the geometry and the mechanical properties of the disc, numerical values from the literature are adopted after suitable elaboration. All models consist of four distinct volumes, corresponding to the portions of the disc: The upper and lower endplates, the annulus and the nucleus. The differences between the models are focused to both the geometry of the various portions as well as to the mechanical behaviour of the material of each portion. The loads exerted simulate the typical daily activities of the human lumbar disc. The results of the analysis of all three models are in qualitative agreement with existing experimental data, with the most sophisticated one being closer to the reality.
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| | The object of the present work has been a preliminary design of the Helium cooling system for the capacitive tuning system of nuclear fusion reactor antennas. The use of Helium, instead of water, avoids the risk of serious problems if the cooling circuit would break, but the cooling process results to be less efficient. The finite element code ANSYS has been used to perform several analyses, because it takes into account different physical aspects of the problem. An electromagnetic High Frequency analysis has allowed calculating the surface current density distribution in the conductive materials of the system and the consequent power load deposition. Moreover, a coupled thermal and fluid dynamic analysis has allowed computing the heat transfer by conduction and convection trough the coolant and the tuning system components, and the consequent temperature distribution. Moreover, the pressure drop and velocity distribution of the fluid has been obtained.
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| | Finite element analysis usually neglects the contributions of wear and the changes in the surface due to wear. However, wear may be important in any structure subjected to repeated loadings and may be critical for certain tribological applications including the prediction of the sealing potential of surfaces. In this paper, a procedure is proposed whereby the effects of wear may be calculated and included in the overall analysis of the structure. The Archard equation is used as the basis for calculating wear strain which is used to modify the elastic strain in an element in an explicit manner. Extensions of the theory are also proposed and an example using explicit creep for the wear adjustments is included.
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| | A custom implicit creep routine was developed. The routine was based upon Norton's creep equation using Hoop Stress with an additional delay to the onset of creep. The delay, called an incubation time, was an exponential function of temperature and stress. The original implementation used Sz for 2D elements (182) and Sy for 3D element (85,186,187) but was extended to use Seqv. The procedure for compiling will be explained as well as other features including a verbose flag, a hoop vs. equivalent stress switch, and the use of state variables to track element status.
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| | The paper presents an investigation into how the introduction of internal cooling in rotomoulding influence the overall cooling rates. For the purpose of this investigation a simple cub mould is considered. The coupled fluid flow – heat transfer process, has been modelled by using ANSYS Flotran 2D. The mould motion was simulated, by implementing rotating boundary conditions. For the purpose of industrial design a comparative solution have been obtained, by using two moulds inside of the oven with the same dimensions and material characteristics. The first mould is with internal cooling device, while the second is without. From the results it is clear, that the internal cooling in rotomoulding can provide cooling rate inside of the mould, similar to the one outside or even better. This high cooling rate offers many practical advantages, including shortening the total production cycle by more than 40%. It also stabilise the plastic product and reduce the distortions during the rapid temperature change.
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| | The use of microjets has found application areas in the propulsion of target drones and missiles. These propulsion systems have their own challenging topics due to their small sizes and very high rotational speeds (in the order of 100000 rpm). The complete engine consists of the following main components: Inlet, Impeller, Diffuser, Combustion Chamber, Turbine and Nozzle. In this paper, the focus was given to present the methodologies used in the design of the impeller (radial compressor) only, which is one of the most critical components of an engine. The main function of an impeller is to efficiently compress the air coming from the inlet and to deliver it to the combustion chamber via a diffuser. The compressor pressure ratio is highly dependent on the impeller tip speed. Hence, high tip speeds are essential to obtain high pressure ratios. Therefore, in microjets, high rotational speeds are inevitable. This results in many challenges such as vibratory behavior, transonic flow, shock waves in diffusers and high stresses. Furthermore, tip clearance is one of the most important concerns affecting impeller performance. Special care must be taken to maintain tip clearance close to an optimum value under operating conditions.
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| | Hydro power industry uses hot forming processes of thick steel plates for the forming of components such as blades, crowns and bands of Francis runners. A reconfigurable discrete die could reduce the cost and the process time of the pressing of plates when compared to the current methods where a die is machined to the shape of the part. The proposed reconfigurable die is made of an array of pins with spherical tip. The height of each pin is adjustable and can be set to produce different parts in a Francis runner (crown sector, band sector or blade). That type of die can eliminate the need of machining a new surface for each new shape to press. In this paper finite element analysis is used to simulate the hot forming process of a part for a Francis runner with a reconfigurable discrete die. The goal of the analysis is to develop a representative model of the effect of tip radius of each pin, on the depth of the pin prints left on the part and on the required pressing force. The model must be valuable for parts of different thicknesses.
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| | Many engineering fields, including tribology and MEMS, seek to use or alter the behavior of the system at the surface or at the interface between surfaces. Thus, the topography of the surface is of great interest and must be included in finite element simulations. Four methods for generating normally distributed rough surfaces using APDL are proposed. The resulting geometry, meshes, and solutions are then compared to demonstrate the strengths and weaknesses of the various methods.
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