Analysis of Severe Accident in Complex System Reactor Using Moving Particle Semi-Implicit (MPS) Method

The very complex structure of nuclear reactors is one aspect of the cause of severe accidents in nuclear reactors. To prevent serious accidents, analysis is needed on the reactor design before the reactor is built. Reactor accident analysis can be done using the Moving Particle Semi-Implicit method. The Moving Particle Semi-Implicit method is excellent in simulating the movement of liquid fuel in a reactor because it can analyze the free surface flow of an incompressible liquid without using a mesh grid. Simulations were carried out using three types of fluids with different viscosities and densities such as water, oil, and wax. The simulation results show that the water takes the fastest time to drain all the particles and the oil takes the longest time. From the simulation results, it can be determined that the kinematic viscosity of a liquid affects its flow velocity.

Exploration of grid scheme for Frisch-grid ionization chamber

A new Frisch-grid ionization chamber has been built to explore the appropriate choice of Frisch-grid. Detailed studies of the relationship between grid geometries and detector performance have been performed with an $$^{241}$$ 241 Am source. This paper describes and compares the energy resolution of ionization chambers with parallel-wire and mesh grids of different grid parameters. Some specific recommendations for grid selection are provided based on the data currently available. To obtain optimal energy resolution, the operating voltage of the chamber must satisfy the condition of minimum electron collection on the grid with distinct geometries and parameters, respectively. Since there is no established theory applicable to both types of grids, we have devised a careful simulation procedure incorporating the COMSOL and Garfield++ codes to search for the conditions of the minimum electron collection on the grid. The simulation results fit the experimental data well, suggesting that this simulation method successfully predicts the suitable voltage setting when using a mesh grid or parallel wires grid as the shielding electrode.

Adhesive Boundary Element Method Using Virtual Crack Closure Technique

In this study, a new adhesive contact model is built upon a boundary element method (BEM) model developed by Pohrt and Popov (2015). The strain energy release rate (SERR) on the edge of the bonding interface is evaluated using Virtual Crack Closure Technique (VCCT) which is shown to have better accuracy and weaker mesh-size dependency than the closed-form SERR formula derived by Pohrt and Popov. A composite delamination criterion is proposed for crack nucleation and propagation. Numerical results predicted by the present model are in good agreement with the analytical solutions of two classic problems, namely, the axisymmetric parabolic contact and the sinusoidal waviness contact in the plane strain condition. The model of Pohrt and Popov can achieve a similar accuracy for the axisymmetric parabolic contact where the mesh grid is non-conforming to the crack front. Once the conforming mesh grid is used, the accuracy of their model is significantly deteriorated, especially at high work of adhesion and high mesh density. In both BEM models, however, the crack nucleation is found to be mesh-dependent which may be solved by introducing an upper limit for the tensile normal traction.

Rectangling irregular videos by optimal spatio-temporal warping

Image and video processing based on geometric principles typically changes the rectangular shape of video frames to an irregular shape. This paper presents a warping based approach for rectangling such irregular frame boundaries in space and time, i.e., making them rectangular again. To reduce geometric distortion in the rectangling process, we employ content-preserving deformation of a mesh grid with line structures as constraints to warp the frames. To conform to the original inter-frame motion, we keep feature trajectory distribution as constraints during motion compensation to ensure stability after warping the frames. Such spatially and temporally optimized warps enable the output of regular rectangular boundaries for the video frames with low geometric distortion and jitter. Our experiments demonstrate that our approach can generate plausible video rectangling results in a variety of applications.

Geomagnetic inverse modeling to estimate the volume of magnetization in areas with topographic variations

A three-dimensional geomagnetic modeling is proposed to obtain information about a magnetization over topographic area from magnetic total force from land data survey. The model is divided into three-dimensional mesh grid of rectangular prisms that cover a finite depth below topographic elevation. The model parameter is assigned to each prism describing magnetization. A set of linear equations was formulated in terms of volume magnetization for each prism. The inverse calculation is obtained using the solution of over-determined problems. In this inverse calculation over three-dimensional mesh grid, the weighted matrix will be used to determine distribution of volume magnetization in the subsurface and keep the zero value of volume magnetization above the surface. A computer program has been tested with artificial topographic data and applied to digital elevation model of Bandung. The result of the inversion shows the comparison between synthetic model and inverse model to provide several analysis of algorithm performance. The high magnetization value can be characterize using inverse model up to 77% of volume area with average success recovery of model parameter value up to 56%.

Numerical simulations of the agitation generated by coarse-grained bubbles moving at large Reynolds number

We present a numerical method for simulating the flow induced by bubbles rising at large Reynolds number. This method is useful to simulate configurations of large dimensions involving a great number of bubbles. The action that each bubble exerts on the liquid is modelled as a volume source of momentum distributed over a few mesh-grid elements. The flow in the vicinity of the bubbles is thus not finely resolved. The bubbles are treated as Lagrangian particles that move under the influence of the hydrodynamic force exerted by the liquid. The determination of this force on a given bubble requires knowledge of the liquid flow that is undisturbed by this bubble. A model is developed to accurately estimate this disturbance for large-Reynolds-number objects and get rid of any spurious self-induced effect. Thanks to that, a homogeneous swarm of rising bubbles is simulated. Comparisons with experiments show a good agreement with the flow scales larger than the bubbles, which turn out to be controlled by the interactions between bubble wakes and rather independent of unresolved smaller scales. This method can be used to study the coupling between bubble-induced agitation and large-scale motions, such as those produced in industrial bubble columns.

Adaptive spiral tool path generation for computer numerical control machining using point cloud

This paper reports a novel method to generate adaptive spiral tool path for the CNC machining of complex sculptured surface represented in the form of cloud of points without the need for surface fitting. The algorithm initially uses uniform 2 D circular mesh-grid to compute the cutter location (CL) points by applying the tool inverse offset method (IOM). These CL points are refined adaptively till the surface form errors converge below the prescribed tolerance limits in both circumferential and radial directions. They are further refined to eliminate the redundancy in machining and generate optimum region wise tool path to minimize the tool lifts. The NC part programs generated by our algorithm were widely tested for different case studies using the commercial CNC simulator as well as by the actual machining trial. Finally, a comparative study was done between our developed system and the commercial CAM software. The results showed that our system is more efficient and robust in terms of the obtained surface quality, productivity, and memory requirement.