Niall M. O’Dowd

Bio: Niall M. O’Dowd is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Pixel & Structured-light 3D scanner. The author has an hindex of 2, co-authored 5 publications receiving 6 citations. Previous affiliations of Niall M. O’Dowd include Los Alamos National Laboratory.

Effects of digital fringe projection operational parameters on detecting powder bed defects in additive manufacturing

Abstract: Additive manufacturing is a technology transforming traditional production timelines. Specifically, metal additive manufacturing (MAM) has been increasingly adopted by a variety of industries, not only to prototype, but also to fulfill full production scale applications with much lower lead times. Like any maturing manufacturing technology, developments in verifying and validating processes are necessary to support continuous growth. Due to the complex nature of MAM, part quality and repeatability remain integral challenges that inhibit further adoption of MAM for critical component production. In this study, we present data taken from a developing in-process monitoring system designed to measure and detect powder bed defects (PBDs) in powder bed fusion MAM systems using surface height maps created with structured light illumination. We showcase the feasibility of the monitoring technique for in-process implementation by detecting streak PBDs with varying severities (height, width) created in a lab environment. We present results of powder bed measurements for varying experimental parameters of the structured light system such as illumination angle, illumination pattern, and number of illuminations. We also present an expression used to determine experimental height noise based on input parameters for PBD detection based on the instrument transfer function of the structured light monitoring system for arbitrary pixel intensity noise contributions. With the results of PBD detection across across multiple experimental measurement parameters, we provide a best practices approach to in-process implementation of the monitoring system in powder bed fusion manufacturing.

Examination of single-substance multiphase material distribution in a cylindrical container using acoustic wavenumber spectroscopy

Abstract: This paper explores the use of a steady-state scanning laser Doppler vibrometer (LDV) system for the identification of transition areas between solid, liquid, and gaseous substances in an enclosed container. This technique images lateral surface velocity under the excitation of a single-frequency ultrasonic tone, produced by a piezoelectric actuator. Differences in measured spatial wavenumber at discrete measurement points of a surface scan can be used to detect the boundaries between solid, liquid and gaseous regions of material. We used the LDV system to compare the relative distributions of solid wax, liquid wax, and air in a cylindrical container based on local changes in wavenumber. Through the same methodology, we were able to distinguish the transition between solid and liquid epoxy in a container. Finally, by repeatedly scanning the container during a phase-changing reaction within the container, we established that the system can be used to monitor reactions as they progress.

Fringe projection profilometry system verification for 3D shape measurement using virtual space of game engine

Abstract: Fringe projection profilometry (FPP) is a technique used for obtaining the three-dimensional shape of an object in fields such as reverse engineering, cultural heritage, and computer vision. The FPP measurement accuracy significantly depends on the arrangement of the measurement system, measurement space conditions, equipment setting, and object characteristics. However, experimental verification of the measurement conditions is time-consuming and expensive. This study presents a simulator that can set a broader range of measurement conditions. This simulator was developed using Unity, which is an integrated development environment for video games. The proposed simulator can be configured with a graphical user interface for device placement and operation, and it can freely adjust the aperture, exposure time, and depth-of-field of the camera. The measurement simulation results for a CAD model obtained using the proposed simulator are presented. The results indicate that camera defocus or unfit exposure time causes phase measurement errors.

Supply Chain Management Optimization and Prediction Model Based on Projected Stochastic Gradient

Abstract: Supply chain management (SCM) is considered at the forefront of many organizations in the delivery of their products. Various optimization methods are applied in the SCM to improve the efficiency of the process. In this research, the projected stochastic gradient (PSG) method was proposed to increase the efficiency of the SCM analysis. The key objective of an efficient supply chain is to find the best flow patterns for the best products in order to select the suppliers to different customers. Hence, the focus of this research is on developing an efficient multi-echelon supply chain using factors such as cost, time, and risk. In the convex case, the proposed method has the advantage of a weakly convergent sequence of iterates to a point in the set of minimizers with probability one. The developed method achieves strong sequence convergence to the unique optimum, with probability one. The SCM dataset was utilized to assess the proposed method’s performance. The proposed PSG method has the advantage of considering the holding cost in the profit analysis of the company. The results of the developed PSG method are analyzed according to the product’s profit, stock, and demand. The proposed PSG method also provides the prediction of demand to increase profit.

Guided ultrasonic waves propagation imaging: a review

Abstract: This article presents a comprehensive review of the laser-based guided ultrasonic waves propagation imaging (G-UPI) system and respective signal/data processing methods related to the nondestructive testing and evaluation of thin-walled structures. The primary goal of this study is to review and recognize various processing methods, explain the working principles of the most influential methods, and highlight outstanding capabilities. In addition, the suitability of the methods for multiple types of damage and defect in various materials and structures are presented. At the same time, success stories of difficult-to-inspect cases are highlighted. Its secondary goal is to compare and discuss the merits and demerits of the laser-scanning part of the system for ultrasound generation and acquisition to provide a guideline for scanning scheme or hardware selection. Finally, the potential challenges and prospects of the G-UPI are discussed. It is expected that this review would serve as an entrance key for newcomers and a reference point for researchers to explore the opportunities for further improvement in the laser ultrasound-based evaluation of critical engineering structures.