Capturing the surface mechanics of musculoskeletal extremities would enhance the realism of life-like mechanics imposed on the limbs within surgical simulations haptics. Other fields that rely on surface manipulation, such as garment or prosthetic design, would also benefit from characterization of tissue surface mechanics. Eight homogeneous tissue models were developed for the upper and lower legs and arms of two donors. Ultrasound indentation data was used to drive an inverse finite element analysis for individualized determination of region-specific material coefficients for the lumped tissue. A novel calibration strategy was implemented by using a ratio based adjustment of tissue properties from linear regression of model predicted and experimental responses. This strategy reduced requirement of simulations to an average of under four iterations. These free and open-source specimen-specific models can serve as templates for simulations focused on mechanical manipulations of limb surfaces.
Oil filled transformer explosions and their prevention is a complex industrial issue. Experimental tests showed that when an electrical fault occurs in a transformer, it generates dynamic pressure waves that propagate in the oil. Reflections of these waves on the walls build up high static pressure which transformer tanks cannot withstand. The tank’s ability to withstand this pressure is thus one of the key parameters of transformer explosion prevention, and a numerical tool was developed to simulate the phenomena highlighted during the tests, especially the pressure wave propagation. The present paper’s aim is thus to complete this numerical tool so that the mechanical behavior of the tank can be accurately studied. The hydrodynamic numerical tool was subsequently coupled with a dynamic structure analysis package: the open source software Code_ASTER. A weak coupling strategy was first developed by applying the simulated pressures to the structure geometry in order to evaluate stresses and deformations. This strategy has evolved with the development of a strong coupling strategy which required establishing a moving mesh technique for the hydrodynamic code to accept displacement data from the structure code and complete the exchange between hydrodynamic and structure codes. First encouraging results are shown.
Within the highly competitive electricity market, companies often reduce costs by using aging equipment and by overloading their transformers. These conditions substantially increase the risk of transformer explosions. These incidents are caused by electrical arcs occurring within oil filled transformers. The arc, within milliseconds, vaporizes the surrounding oil and the generated gas is pressurized because the liquid inertia prevents its expansion. The pressure difference between the gas bubble and the surrounding liquid oil generates a dynamic pressure peak, which interacts with the transformer. The reflections generate pressure waves that lead to transformer rupture since transformers are not designed to withstand these pressures. This results in dangerous explosions, expensive damages and possible environmental pollution. Despite all these risks, and contrary to usual pressure vessels, no specific standard has been set to protect sealed transformer tanks subjected to large dynamic overpressures. In order to study transformer rupture and its prevention, experiments have been performed on transformers. However, safely carrying out live tests is difficult and expensive. In order to limit the costs, to reduce the risks and to gain insight on these phenomena numerical simulation tools are necessary. First a computational fluid dynamics solver was developed; it is based on an unsteady compressible two-phase flow model, the equations parameterizing the system are solved using a 3D finite volume method. Previous papers showed the ability of the hydrodynamic tool to study in detail (1) dynamic pressure wave propagation inside transformer oil that leads to transformer rupture and (2) depressurization induced by efficient protection means. Later, the hydrodynamic numerical tool has been one-way coupled with Code_ASTER, a dynamic structural analysis package, to create a fluid structure interaction (FSI). Preliminary results were shown and this strategy has been applied to the study of more complex electrical equipment. The present paper’s goal is to illustrate the development and application of a two-way coupling for the aforementioned fluid structure interaction strategy. The methodology for the enhanced coupling is explained and the simulation results about the structural behavior caused by these dynamic pressures are presented.
Scientists plan projects this year to help a rugged, troubled region of central Asia retune traditional timekeeping methods based on environmental cues in the face of climate change.
Electrical arcing can occur within the oil-filled tanks of transformers and On Load Tap Changers (OLTCs) when the oil dielectric properties are reduced. The electrical arc then, within milliseconds, vaporizes a portion of the oil, creating a highly pressurized gas bubble. The rapid pressure rise inside the generated bubble creates a dynamic pressure peak which then propagates and interacts with the tank structure. The wave reflections on the walls generate secondary pressure waves that raise the static pressure inside the tank. This static pressure increase leads to tank rupture since tanks are not designed as pressure vessels and therefore cannot withstand such levels of static pressure. This results in explosions, fire, expensive damages and possible environmental pollution. Despite all these risks, conventional protections are not effective to avoid explosion and contrarily to usual pressure vessels, no specific standard has been set to protect sealed tanks subjected to large dynamic overpressures. In order to study transformer and OLTC explosions and their prevention, experiments were performed on large scale transformers. Nevertheless, live tests require specific laboratory equipment and they are thus expensive and can be dangerous. In order to limit the costs, to reduce risks and to get a deep insight on the physical phenomena, numerical simulation tools are necessary. The development of such tools was presented at previous ASME Conferences. The present paper’s goal is to illustrate the use of this tool by an investigation of an arcing event in an OLTC. This arcing was simulated in the OLTC in both the unprotected case and also when the OLTC has been protected using a fast depressurization method. The stress and strain results are then used to determine how effectively the depressurization relieved pressures in the tank.
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