Method for calculating the critical heat flux at pool boiling on structured surfaces

A method of the critical heat flux enhancements at pool boiling using rough structures of various regular and irregular geometries is investigated. The experimental data are compared, and the critical heat flux is calculated since the V. V. Yagov model, which considers the additional inflow of liquid into the evaporation zone due to the action of capillary forces in the porous space. Based on the comparison of experimental and calculated data, it is concluded that the model is not universal for all microstructured surfaces. Recommendations for the calculation are given.

Modeling And Simulation of The Advanced Structured Surfaces Machined By Specially Patterned Grinding Wheels Via The Structuring Grinding Process

In this work, the ability to reshape the grinding wheels with special patterns to produce advanced structured surfaces with several geometries is studied. Firstly, a mathematical model is built for the process relating geometries of the grinding wheel, geometries of wheel patterns, the produced structured surface with the grinding operating parameters. Then, different regular and irregular geometries are designed to be patterned over the wheel surface. Afterward, a simulation method to express the patterned wheels and the structured surface at different working conditions is developed. The effects of the pattern geometries on the obtained structured surfaces are investigated.

COMPACT: Concurrent or Ordered Matrix-Based Packing Arrangement Computation Technique

Despite their versatility in treating irregular geometries, the raster methods have received limited attention in solving packing problems involving rotatable objects. In addition, raster approximation allows the use of unique performance metrics and indirect consideration of constraints, which have not been exploited in the literature. This study presents the Concurrent or Ordered Matrix-based Packing Arrangement Computation Technique (COMPACT). The method allows the objects to be rotated by arbitrary angles, unlike the right-angled rotation restrictions imposed in many existing packing optimization studies based on raster methods. The raster approximations are obtained through loop-free operations that improve efficiency. Additionally, a novel performance metric is introduced, which favors efficient filling of the available space by maximizing the overall contact within the domain. Moreover, the objective functions are exploited to discard the overlap and overflow constraints and enable the use of unconstrained optimization methods. The results of the case studies demonstrate the effectiveness of the proposed technique.

On the adaptive spectral approximation of functions using redundant sets and frames

The approximation of smooth functions with a spectral basis typically leads to rapidly decaying coefficients, where the rate of decay depends on the smoothness of the function and vice versa. The optimal number of degrees of freedom in the approximation can be determined with relative ease by truncating the coefficients once a threshold is reached. Recent approximation schemes based on redundant sets and frames extend the applicability of spectral approximations to functions defined on irregular geometries and to certain nonsmooth functions. However, due to their inherent redundancy, the expansion coefficients in frame approximations do not necessarily decay even for very smooth functions. In this paper, we highlight this lack of equivalence between smoothness and coefficient decay, and we explore approaches to determine an optimal number of degrees of freedom for such redundant approximations.

A 3-D FINITE ELEMENT FEW-GROUP DIFFUSION CODE AND ITS APPLICATION TO GENERATION IV REACTOR CONCEPTS

In this paper, a recently developed 3-d few-group finite element-based diffusion code is de-scribed. Its geometrical flexibility allows future modeling of complex and irregular geometries of (very) small and medium size reactor concepts –(v)SMRs –being in the spotlight for energy provision in remote residential and industrial regions or for space applications, and also liquid metal cooled Generation IV reactors where thermally induced core deformation results in localized assembly lattice distortions which cannot be treated by traditional 3-d neutron kinetics codes devoted to the regular lattices of LWR and Generation IV systems. The description of the implemented FEM solution method is followed by first applications to a prismatic (or block type) high-temperature reactor MHTGR-350MW within an OECD/NEA benchmark activity and to the sodium cooled fast reactor concept ASTRID within the past EU project ESNII+. Finally, an outlook to planned further code development activities is given.

Steerable differential beamformers with planar microphone arrays

Humanoid robots require to use microphone arrays to acquire speech signals from the human communication partner while suppressing noise, reverberation, and interferences. Unlike many other applications, microphone arrays in humanoid robots have to face the restrictions in size and geometry. To address these challenges, this paper presents an approach to differential beamforming with arbitrary planar array geometries. The major contributions of this work are as follows: (1) a method is presented to design differential beamformers, which works for regular geometries such as linear, circular, and concentric circular ones, as well as irregular geometries, as long as the sensors’ positions are given or can be measured; (2) fundamental requirements for the design of different orders of linear differential microphone arrays (DMAs), partially steerable DMAs, fully steerable DMAs, and robust DMAs are discussed; (3) the validity and limitations of the Jacobi-Anger expansion approximation is analyzed, where we discuss how to achieve an optimal approximation by properly choosing the reference point; and (4) we show how to design an Nth-order DMA with 2N microphones using the Jacobi-Anger expansion.