Magnetic Resonance Imaging Clinics of North America, 2015
Vascular rings and pulmonary artery slings present with symptoms of tracheal and esophageal compr... more Vascular rings and pulmonary artery slings present with symptoms of tracheal and esophageal compression during infancy and childhood. Double aortic arch and right aortic arch with aberrant left subclavian artery and left patent ductus arteriosus (PDA) are the 2 most common types of vascular ring. Atretic segments cannot be directly visualized on MR imaging, but their presence can be inferred from other indirect imaging signs. MR imaging/magnetic resonance angiography (MRA) can diagnose these vascular anomalies and evaluate the airway and esophagus without the use of ionizing radiation.
Proceedings of the 19th International Meshing Roundtable, 2010
Solid modeling engines are capable of faceting CAD models but may facet each face independent of ... more Solid modeling engines are capable of faceting CAD models but may facet each face independent of adjacent faces. Regions of the resulting model have gaps between faces of their boundaries. An algorithm is described to seal faceted CAD models such that the boundary of neighboring faces has the same discretization along their shared edges. The algorithm works by sealing skin edges of geometric face faceting to geometric model edge facets, using vertex-vertex and vertex-edge contraction. Ten intricate CAD models of moderate to high complexity are tested with a range of facet tolerances. The algorithm succeeds in creating watertight models in most cases, with failures only at extreme values of facet tolerance and/or in the presence of geometric features which are outside the normal features encountered in most models.
In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homoge... more In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homogeneous, linearly elastic material. The material exhibits either isotropic or transverse isotropic symmetry. When the problem is formulated in material coordinates, the balance of mass equation is satisfied automatically. Also, the material is assumed to be kept at constant temperature, so the only relevant
There is a long literature studying the criticality of space reactors immersed in water/sand afte... more There is a long literature studying the criticality of space reactors immersed in water/sand after a launch accident; however most of these studies evaluate nominal or uniformly compacted system configurations. There is less research on the reactivity consequences of impact, which can cause large structural deformation of reactor components that can result in changes in the reactivity of the system. Predicting these changes is an important component of launch safety analysis. This paper describes new features added to the DAG-MCNP5 neutronics code that allow the criticality analysis of deformed geometries. A CAD-based solid model of the reactor geometry is used to generate an initial mesh for a structural mechanics impact calculation using the PRONTO3D/PRESTO continuum mechanics codes. Boundary conditions and material specifications for the reactivity analysis are attached to the solid model that is then associated with the initial mesh representation. This geometry is then updated with the deformed finite element mesh to perturb node coordinates. DAG-MCNP5 was extended to accommodate two consequences of the large structural deformations: dead elements representing fracture, and small overlaps between adjacent volumes. The dead elements are removed during geometry initialization and adjustments are made to conseve mass. More challenging, small overlaps where adjacent mesh elements contact cause the geometric queries to become unreliable. A new point membership test was developed that is tolerant of self-intersecting volumes, and the particle tracking algorithm was adjusted to enable transport through small overlaps. These new features enable DAG-MCNP5 to perform particle transport and criticality eigenvalue calculations on both deformed mesh geometry and CAD geometry with small geometric defects. Detailed impact simulations were performed on an 85-pin space reactor model. Iin the most realistic model that included NaK coolant and water in the impact simulation, the eigenvalue was determined to increase 2.7% due to impact.
This paper describes techniques for determining impact deformation and the subsequent reactivity ... more This paper describes techniques for determining impact deformation and the subsequent reactivity change for a space reactor impacting the ground following a potential launch accident or for large fuel bundles in a shipping container following an accident. This technique could be used to determine the margin of subcriticality for such potential accidents. Specifically, the approach couples a finite element continuum mechanics model (Pronto3D or Presto) with a neutronics code (MCNP). DAGMC, developed at the University of Wisconsin-Madison, is used to enable MCNP geometric queries to be performed using Pronto3D output. This paper summarizes what has been done historically for reactor launch analysis, describes the impact criticality analysis methodology, and presents preliminary results using representative reactor designs.
Magnetic Resonance Imaging Clinics of North America, 2015
Vascular rings and pulmonary artery slings present with symptoms of tracheal and esophageal compr... more Vascular rings and pulmonary artery slings present with symptoms of tracheal and esophageal compression during infancy and childhood. Double aortic arch and right aortic arch with aberrant left subclavian artery and left patent ductus arteriosus (PDA) are the 2 most common types of vascular ring. Atretic segments cannot be directly visualized on MR imaging, but their presence can be inferred from other indirect imaging signs. MR imaging/magnetic resonance angiography (MRA) can diagnose these vascular anomalies and evaluate the airway and esophagus without the use of ionizing radiation.
Proceedings of the 19th International Meshing Roundtable, 2010
Solid modeling engines are capable of faceting CAD models but may facet each face independent of ... more Solid modeling engines are capable of faceting CAD models but may facet each face independent of adjacent faces. Regions of the resulting model have gaps between faces of their boundaries. An algorithm is described to seal faceted CAD models such that the boundary of neighboring faces has the same discretization along their shared edges. The algorithm works by sealing skin edges of geometric face faceting to geometric model edge facets, using vertex-vertex and vertex-edge contraction. Ten intricate CAD models of moderate to high complexity are tested with a range of facet tolerances. The algorithm succeeds in creating watertight models in most cases, with failures only at extreme values of facet tolerance and/or in the presence of geometric features which are outside the normal features encountered in most models.
In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homoge... more In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homogeneous, linearly elastic material. The material exhibits either isotropic or transverse isotropic symmetry. When the problem is formulated in material coordinates, the balance of mass equation is satisfied automatically. Also, the material is assumed to be kept at constant temperature, so the only relevant
There is a long literature studying the criticality of space reactors immersed in water/sand afte... more There is a long literature studying the criticality of space reactors immersed in water/sand after a launch accident; however most of these studies evaluate nominal or uniformly compacted system configurations. There is less research on the reactivity consequences of impact, which can cause large structural deformation of reactor components that can result in changes in the reactivity of the system. Predicting these changes is an important component of launch safety analysis. This paper describes new features added to the DAG-MCNP5 neutronics code that allow the criticality analysis of deformed geometries. A CAD-based solid model of the reactor geometry is used to generate an initial mesh for a structural mechanics impact calculation using the PRONTO3D/PRESTO continuum mechanics codes. Boundary conditions and material specifications for the reactivity analysis are attached to the solid model that is then associated with the initial mesh representation. This geometry is then updated with the deformed finite element mesh to perturb node coordinates. DAG-MCNP5 was extended to accommodate two consequences of the large structural deformations: dead elements representing fracture, and small overlaps between adjacent volumes. The dead elements are removed during geometry initialization and adjustments are made to conseve mass. More challenging, small overlaps where adjacent mesh elements contact cause the geometric queries to become unreliable. A new point membership test was developed that is tolerant of self-intersecting volumes, and the particle tracking algorithm was adjusted to enable transport through small overlaps. These new features enable DAG-MCNP5 to perform particle transport and criticality eigenvalue calculations on both deformed mesh geometry and CAD geometry with small geometric defects. Detailed impact simulations were performed on an 85-pin space reactor model. Iin the most realistic model that included NaK coolant and water in the impact simulation, the eigenvalue was determined to increase 2.7% due to impact.
This paper describes techniques for determining impact deformation and the subsequent reactivity ... more This paper describes techniques for determining impact deformation and the subsequent reactivity change for a space reactor impacting the ground following a potential launch accident or for large fuel bundles in a shipping container following an accident. This technique could be used to determine the margin of subcriticality for such potential accidents. Specifically, the approach couples a finite element continuum mechanics model (Pronto3D or Presto) with a neutronics code (MCNP). DAGMC, developed at the University of Wisconsin-Madison, is used to enable MCNP geometric queries to be performed using Pronto3D output. This paper summarizes what has been done historically for reactor launch analysis, describes the impact criticality analysis methodology, and presents preliminary results using representative reactor designs.
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