Beam diagnostics

Most beam measurements are based on the electro-magnetic interaction of fields induced by the beam with their environment. Beam current transformers as well as beam position monitors are based on this principle. The signals induced in the sensors must be amplified and shaped before they are converted into numerical values. These values are further treated numerically in order to extract meaningful machine parameter measurements. The lecture introduces the architecture of an instrument and shows where in the treatment chain digital signal analysis can be introduced. Then the use of digital signal processing is presented using tune measurements, orbit and trajectory measurements as well as beam loss detection and longitudinal phase space tomography as examples. The hardware as well as the treatment algorithms and their implementation on Digital Signal Processors (DSPs) or in Field Programmable Gate Arrays (FPGAs) are presented

Investigation of advanced counterrotation blade configuration concepts for high speed turboprop systems. Task 5: Unsteady counterrotation ducted propfan analysis

The primary objective of this study was the development of a time-marching three-dimensional Euler/Navier-Stokes aerodynamic analysis to predict steady and unsteady compressible transonic flows about ducted and unducted propfan propulsion systems employing multiple blade rows. The computer codes resulting from this study are referred to as ADPAC-AOAR\CR (Advanced Ducted Propfan Analysis Codes-Angle of Attack Coupled Row). This document is the final report describing the theoretical basis and analytical results from the ADPAC-AOACR codes developed under task 5 of NASA Contract NAS3-25270, Unsteady Counterrotating Ducted Propfan Analysis. The ADPAC-AOACR Program is based on a flexible multiple blocked grid discretization scheme permitting coupled 2-D/3-D mesh block solutions with application to a wide variety of geometries. For convenience, several standard mesh block structures are described for turbomachinery applications. Aerodynamic calculations are based on a four-stage Runge-Kutta time-marching finite volume solution technique with added numerical dissipation. Steady flow predictions are accelerated by a multigrid procedure. Numerical calculations are compared with experimental data for several test cases to demonstrate the utility of this approach for predicting the aerodynamics of modern turbomachinery configurations employing multiple blade rows

Modeling fan broadband noise from jet engines and rod-airfoil benchmark case for broadband noise prediction

This work has two primary parts: (1) an exhaustive literature review highlighting the need and the direction to study broadband noise generation from the fan stage of a modern high bypass ratio turbofan engine, and (2) a benchmark study of noise generation by the flow over a rod and an airfoil in tandem arrangement. The literature review highlights that not all the experimental data has been consistently explained with the theory and thus these gaps are required to be filled in to improve the fan noise prediction during the design phases. The benchmark case provides flow conditions where the upstream located circular rod sheds periodic vortices and creates turbulence which interacts with downstream located symmetric airfoil at zero angle of attack. This interaction produces noise which radiates to farfield. The periodic shedding and the resulting turbulence provides energy to the tonal and broadband components of the total noise. This test case is used to validate a new approach to predict noise in farfield which uses incompressible flow solver, pimpleFoam (part of OpenFOAM), along with Amiet\u27s theory

Atomic Scale Details of Defect-Boundary Interactions

The study is aimed to understand atomic scale details of defect-boundary interactions, which are critical to develop radiation tolerant fuel cladding materials for harsher neutron environments. By means of molecular dynamics simulations, we addressed the key questions of (1) how defects are trapped by a grain boundary, (2) how defect are annihilated at a grain boundary, and (3) what are upper limits of radiation tolerance of boundary-engineered metals. The modeling is performed by using large-scale atomic/molecular massively parallel simulator (LAMMPS) code and pure Fe is selected as the model material. For mechanism of defect tapping towards a grain boundary, we find that, instead of the general consensus that the trapping is caused by biased defect diffusions due to relatively lower defect formation energies at a grain boundary, long range defect migration is realized by creation of chain like defects. A chain is induced by the stress field around a defect, and is formed by pushing its immediate lattice atom neighbor into an interstitial site. This newly formed interstitial can induce formation of another vacancy-interstitial pair along the chain direction. The process is repeated or simultaneously occurs along the chain. Thus, a chain consists of alternately positioned interstitials and vacancies. The subsequent defect annihilation between neighboring defects on the chain leads to the defect transport. We identify three types of defect transport models which involve different chains. For mechanism of defect annihilation on a grain boundary, we find that both defect transport and interstitial-vacancy recombination are realized by formation of similar chain-like defects. The vacancy and interstitial along the chain correspond to the sites of their corresponding formation energy minima, thus the capability to form such chains is determined by the patterns of boundary defect formation energies. For a boundary of small misorientation angle, chain formation is allowed to occur in one direction only and all chains are parallel to each other. At large angles, however, chains are so close to each other that new allowable chain directions are created by linking patterns from different chains. This suggests that large angle boundaries are more efficient to move and recombine defects. The modeling further calculates the energy barriers for chain-mediated defect recombination under different boundary configurations. These findings lead to the conclusion that defect sink strengths of grain boundaries are determined by not only the efficiency to transport to boudnaries, but also the efficiency to recombine boundary defects. Otherwise, the difficulty to remove defects will quickly turn of the sink property. This is confirmed by comparing the width of defect denuded zone created around a boundary, in a cell randomly bombarded by Fe self-ions to different damage levels. A large angle boundary is more preferred to achieve maximum radiation tolerance

Accelerated Temporal Schemes for High-Order Unstructured Methods

The ability to discretize and solve time-dependent Ordinary Differential Equations (ODEs) and Partial Differential Equations (PDEs) remains of great importance to a variety of physical and engineering applications. Recent progress in supercomputing or high-performance computing has opened new opportunities for numerical simulation of the partial differential equations (PDEs) that appear in many transient physical phenomena, including the equations governing fluid flow. In addition, accurate and stable space-time discretization of the partial differential equations governing the dynamic behavior of complex physical phenomena, such as fluid flow, is still an outstanding challenge. Even though significant attention has been paid to high and low-order spatial schemes over the last several years, temporal schemes still rely on relatively inefficient approaches. Furthermore, academia and industry mostly rely on implicit time marching methods. These implicit schemes require significant memory once combined with high-order spatial discretizations. However, since the advent of high-performance general-purpose computing on GPUs (GPGPU), renewed interest has been focused on explicit methods. These explicit schemes are particularly appealing due to their low memory consumption and simplicity of implementation. This study proposes low and high-order optimal Runge-Kutta schemes for FR/DG high-order spatial discretizations with multi-dimensional element types. These optimal stability polynomials improve the stability of the numerical solution and speed up the simulation for high-order element types once compared to classical Runge-Kutta methods. We then develop third-order accurate Paired Explicit Runge-Kutta (P-ERK) schemes for locally stiff systems of equations. These third-order P-ERK schemes allow Runge-Kutta schemes with different numbers of active stages to be assigned based on local stiffness criteria, while seamlessly pairing at their interface. We then generate families of schemes optimized for the high-order flux reconstruction spatial discretization. Finally, We propose optimal explicit schemes for Ansys Fluent finite volume density-based solver, and we investigate the effect of updating and freezing reconstruction gradient in intermediate Runge-Kutta schemes. Moreover, we explore the impact of optimal schemes combined with the updated gradients in scale-resolving simulations with Fluent's finite volume solver. We then show that even though freezing the reconstruction gradients in intermediate Runge-Kutta stages can reduce computational cost per time step, it significantly increases the error and hampers stability by limiting the time-step size