The effect of small-amplitude time-dependent changes to the surface morphology of a sphere

Typical approaches to manipulation of flow separation employ passive means or active techniques such as blowing and suction or plasma acceleration. Here it is demonstrated that the flow can be significantly altered by making small changes to the shape of the surface. A proof of concept experiment is performed using a very simple time-dependent perturbation to the surface of a sphere: a roughness element of 1% of the sphere diameter is moved azimuthally around a sphere surface upstream of the uncontrolled laminar separation point, with a rotational frequency as large as the vortex shedding frequency. A key finding is that the non-dimensional time to observe a large effect on the lateral force due to the perturbation produced in the sphere boundary layers as the roughness moves along the surface is ˆt =tU_(∞)/D ≈4. This slow development allows the moving element to produce a tripped boundary layer over an extended region. It is shown that a lateral force can be produced that is as large as the drag. In addition, simultaneous particle image velocimetry and force measurements reveal that a pair of counter-rotating helical vortices are produced in the wake, which have a significant effect on the forces and greatly increase the Reynolds stresses in the wake. The relatively large perturbation to the flow-field produced by the small surface disturbance permits the construction of a phase-averaged, three-dimensional (two-velocity component) wake structure from measurements in the streamwise/radial plane. The vortical structure arising due to the roughness element has implications for flow over a sphere with a nominally smooth surface or distributed roughness. In addition, it is shown that oscillating the roughness element, or shaping its trajectory, can produce a mean lateral force

Interorganizational relationships : the transition of special education students to adult human services.

Theory and research regarding interorganizational relations (IOR) can be applied to many situations in the field of human service delivery. An example of IOR in public human services occurs in the transition of special needs students from special education programs to adult human services. In the Commonwealth of Massachusetts the transitional process is defined by legislation entitled Chapter 688. This research examines Chapter 688 from the conceptual framework of IOR theory. It examines some of the issues and problems involved in the implementation of IOR in the transition process. The organizational domain is delimited to include four key Chapter 688 organizations (agencies): public schools, rehabilitation commission, department of mental health, and department of mental retardation. Local (area) directors of each organization completed a survey questionnaire containing three parts; knowledge of Chapter 688, attitudes toward Chapter 688 and IOR, and the Klonglan Scale (a measure of intensity of IOR). Information on actual referral patterns and IOR in Chapter 688 was obtained through document analysis of Individual Transition Plans, ITP, and State data base files on Chapter 688 referrals. The results of the study indicated that the local area directors of the target agencies involved in the Chapter 688 interorganizational relationships, IOR, have a good working knowledge of the law. The area directors are of the opinion that the components of Chapter 688 implementation are satisfactory. They value IOR as a means of improving services, but need to develop a clearer idea of IOR. The area directors\u27 description of the intensity of IOR in the Klonglan Scale is not substantiated in terms of participation in ITP meetings and/or ITP services. Lastly, the local area directors identify the following barriers to interorganizational relationships: inadequate funding, lack of coordination of funding, lack of goal clarity and uniformity, and insufficient knowledge of, and trust in, other agencies

Using Graphic Elicitation to Explore Community College Transfer Student Identity, Development, and Engagement

The focus of this paper is to illustrate the use of graphic elicitation, in the form of a relational map, to explore community college transfer student (CCTS) identity, development, and engagement at four-year institutions. Using graphic elicitation illuminated aspects of CCTSs that they may not have been able to otherwise verbalize, and was used in combination with interview questions designed to capture participants\u27 development and engagement, investigating how they made meaning of their institutional experiences. A constructivist grounded theory approach was applied, given the lack of available literature pertaining to CCTSs in these areas. This paper draws upon and contributes to the current graphic elicitation literature and provides a detailed outline of the study’s research design and thorough justification of the use of a relational map. The interview questions and relational maps worked in tandem to uncover theoretical themes that contributed to findings. The study\u27s methodological approach, design using graphic elicitation, and limitations are discussed in addition to potential future research using graphic elicitation techniques

Approximation of the minimal robustly positively invariant set for discrete-time LTI systems with persistent state disturbances

Published versio

Editorial

Editorial for the 2nd CIRP Conference on Composite Material Parts Manufacturing, 10-11 October 2019, Advanced Manufacturing Research Centre, UK

An Integrated Telemetric Thermocouple Sensor for Process Monitoring of CFRP Milling Operations

AbstractA wireless temperature measurement system was developed and integrated into a cutting tool holder via a thermocouple embedded within the cutting tool. The primary purpose of such an embedded thermal measurement sensor/system is for online process monitoring of machining processes within which thermal damage poses a significant threat both for the environment and productivity alike – as is the case with the machining of carbon fibre reinforced polymer (CFRP) components. A full system calibration was performed on the device. Response times were investigated and thermal errors, in the form of damping and lag, were identified. Experimental temperature results are presented which demonstrate the performance of the integrated wireless telemetry sensor during the edge trimming of CFRP composite materials. Thermocouple positioning relative to heat source effect was among the statistical factors investigated during machining experiments. Initial results into the thermal response of the sensor were obtained and a statistical package was used to determine the presence of significant main effects and interactions between a number of tested factors. The potential application of the embedded wireless temperature measurement sensor for online process monitoring in CFRP machining is demonstrated and recommendations are made for future advancements in such sensor technology

A Study on the Power Quality of DG Integrated Building Energy System in Virtual Environment

In this paper, the electrical energy demand of a typical residential building has been extracted from a Virtual Environment (VE) simulation. The extracted energy demand is generated by input load demand and hourly operating information. Based on the electrical energy demand for a typical day, a building integrated photovoltaic (PV) system is then simulated in MATLAB to extract the current/voltage disturbance information into the network. Outcome of this simulation shows the voltage/current waveform along with the disturbances at different locations in the building. The city of Dublin, Ireland has been chosen as a geographical location and VE-Pro software has been used to develop the virtual environment simulation for the building energy system. The simulation based on VE-Pro and MATLAB indicates the scope for possible placement of Custom Power Devices (CPDs) to improve the power quality of the DG integrated building energy system

Towards intelligent CFRP composite machining: surface analysis methods and statistical data analysis of machined fibre laminate surfaces

Many carbon fibre reinforced polymer composite parts need to be edged trimmed before use to ensure both geometry and mechanical performance of the part edge matches the design intent. Measurement and control of machining induced surface damage of composite material is key to ensuring the part retains its strength and fatigue properties. Typically, the overall surface roughness of the machined face is taken to be an indicator of the amount of damage to the surface, and it is important that the measurement and prediction of surface roughness is completed reliably. It is known that the surface damage is heavily dependent on the fibre orientation of the composite and cutting tool edge condition. This research has developed a new ply-by-ply surface roughness measurement methods using optical focus variation surface analysis and image segmentation for calculating areal surface roughness parameters of a machined carbon fibre composite laminate. Machining experiments have been completed using a polycrystalline diamond edge trimming tool at increasing levels of cutting edge radius. Optical surface measurement and µ-CT scanning have been used to assess machining induced surface and sub-surface defects on individual fibre orientations. Statistical analysis has been used to assess the significance of machining parameters on Sa (arithmetic mean height of area) and Sv (areal magnitude of maximum valley depth) areal roughness parameters, on both overall roughness and ply-by-ply fibre orientations. Empirical models have been developed to predict surface roughness parameters using statistical methods. It has been shown that cutting edge degradation, fibre orientation and feed rate will significantly affect the cutting mechanism, machining induced surface defects and surface roughness parameters

Chip formation in machining of unidirectional carbon fibre reinforced polymer laminates : FEM based assessment

Finite-element (FE) method offers a low cost virtual alternative to assist in optimisation of critical process parameters in machining of composites. This study is focussed on understanding the mechanics of chip formation in orthogonal cutting of unidirectional (UD) carbon-fibre-reinforced polymer (CFRP) laminates through development of FE models. Machining responses of UD CRFP laminates with fibre orientation of 45° (measured with respect to the cutting direction) are assessed. Modelling of material removal in the form of fragmented chips is considered. Damage initiation is determined using the Hashin stress criterion for the fibre component, while matrix failure predicted using Puck criteria. Subsequent damage evolution events are modelled using a strain-based softening approach to degrade relevant material properties linearly. Primary numerical results compared with experimental data revealed that developed FE models are able to predict global machining responses (i.e. cutting forces) and characterise various discrete damage modes associated with machining response of quasi-brittle CFRP laminates successfully. The models also provide a valuable insight into variation in chip morphology

Study of the machining induced damage in UD-CFRP laminates with various fibre orientations : FE assessment

Finite elements (FE) provide an excellent and low-cost approach in the assessment of composite machining induced damage. This article is focused on the evaluation of the damage underlying the machined surface through the development of a novel 3D FE model in composite machining. Sub-surface damage of UD-CFRP with fibre orientations from 0o to 90o is evaluated. An algorithm to assess composite damage evolution and chip formation is inserted via user-defined subroutine. Damage initiation is determined using Hashin’s failure criteria for fibre damage modes, while matrix damage modes are assessed via Puck’s failure criteria. Subsequent damage evolution is modelled using an energy-based linear damage degradation law. Numerical results reveal relevant advances in the prediction of the damage induced underlying the machined surface for fibre orientations from 60o to 90o obtained in previous investigations