Combined preliminary–detailed design of wind turbines

Abstract. This paper is concerned with the holistic optimization of wind turbines. A multi-disciplinary optimization procedure is presented that marries the overall sizing of the machine in terms of rotor diameter and tower height (often termed "preliminary design") with the detailed sizing of its aerodynamic and structural components. The proposed combined preliminary–detailed approach sizes the overall machine while taking into full account the subtle and complicated couplings that arise due to the mutual effects of aerodynamic and structural choices. Since controls play a central role in dictating performance and loads, control laws are also updated accordingly during optimization. As part of the approach, rotor and tower are sized simultaneously, even in this case capturing the mutual effects of one component over the other due to the tip clearance constraint. The procedure, here driven by detailed models of the cost of energy, results in a complete aero-structural design of the machine, including its associated control laws. The proposed methods are tested on the redesign of two wind turbines, a 2.2 MW onshore machine and a large 10 MW offshore one. In both cases, the optimization leads to significant changes with respect to the initial baseline configurations, with noticeable reductions in the cost of energy. The novel procedures are also exercised on the design of low-induction rotors for both considered wind turbines, showing that they are typically not competitive with conventional high-efficiency rotors

Fatigue characterization of Poly Vinyl Chloride (PVC) foam core sandwich composite using the G-control method

This paper presents experimental results from cyclic crack propagation tests performed on sandwich specimens with glass/epoxy face sheets and Poly Vinyl Chloride (PVC) foam cores using the G-controlled cyclic energy release rate (ΔG) test procedure. The face material was tested in tension, compression and shear to determine in-plane and out-of-plane mechanical properties, such as Young’s modulus, Poisson’s ratio and shear modulus. These properties were then used in an analytical model of the mixed-mode bending sandwich specimen to calculate compliance and energy release rate. Finite element analysis was used to determine the mode-mixity of the crack loading. Experimental crack growth cyclic tests were carried out on pre-cracked mixed-mode bending sandwich specimens with H45, H100 and H160 PVC foam cores under two mode-mixities (mode I and mode II dominant). Post-mortem analysis was performed on tested specimens, highlighting the influence of mode mixity and foam density on the crack path. Crack propagation diagrams showing da/dN versus ΔG curves were obtained to establish the Paris-Erdogan relation for each material combination tested at the two mode-mixities. Results showed constant crack growth rates for all the materials tested and revealed the influence on mode-mixity on crack propagation speed and foam density (higher foam density, slower crack propagation). </jats:p

The moderating role of JIT links with suppliers on the relationship between lean manufacturing and operational performances

Abstract. Lean manufacturing impacts several operational performances. The usefulness of JIT links with suppliers is also well known. However, literature lacks strong empirical evidences to exhibit the relationship between lean manufacturing, operational performances and JIT linkages with suppliers. This paper aims to investigate this relationship. A questionnaire-based international survey was used to obtain the main purpose of the research. Data from a sample of 200 companies were analyzed using a multiple regression methodology. The analysis demonstrates that JIT linkages with suppliers positively moderate the impact of lean manufacturing on punctuality, while the moderating effect is absent when considering efficiency and throughput time performance

Measurement of the oil holdup for a two-phase oil-water flow through a sudden contraction in a horizontal pipe

Oil-water two-phase flow experiments were conducted in a horizontal duct made of Plexiglas to determine the holdup of oil by means of the quick closing valves technique, using mineral oil (viscosity: 0.838 Pa s at 20 °C; density: 890 kg m-3) and tap water. The duct presents a sudden contraction, with contraction ratio of 0.64. About 200 tests were performed by varying the flow rates of the phases. Flow patterns were investigated for both the up- and downstream pipe. Due to the relatively high value of the contraction ratio, it was not observed any relevant variation of the flow patterns across the sudden contraction. Data were then compared with predictions of a specific correlation for oil-water flow and some correlations for gas-water flow. A drift-flux model was also applied to determine the distribution parameter. The results agree quite well with flow pattern visualization

Towards a theory for lean implementation in supply networks

This paper aims to investigate the supply network (SN) characteristics affecting the extension of lean programmes to SN and the interactions between lean practices and these characteristics to understand how to create more favourable conditions for lean extension programmes. A multiple case study methodology is implemented to analyze different lean programmes in SNs and different contextual conditions in which they are implemented. Three different SNs have been analyzed to provide insights on the whole value stream of the Andalusian aeronautics SN. This study finds that there is a recursive influence between SN characteristics and lean practices, and explains how this interaction takes place. The choice of lean practices to adopt, their aim and implementation mode are influenced by the state of SN characteristics companies face at the beginning of the programme and the SN distance (i.e. number of SN echelons) between lean knowledge owners and recipients. This study explains also how lean practices can modify the state of SN characteristics and suggests managers a sequence of phases and sets of actions to use depending on the initial state of SN characteristics. \ua9 2016 Elsevier B.V. All rights reserved

The social benefits of kaizen initiatives in healthcare: an empirical study

AbstractPurpose – This paper aims to identify the most influential determinants of employees’ problem-solving capabilities and attitude towards kaizen initiatives in healthcare and clarify how determinants are related with these two social outcomes. Design/methodology/approach – Drawing on the input-process-outcome framework applied to kaizen initiatives, we distinguished determinants into input and process factors, and developed hypotheses on the direct effect of input and process factors on social outcomes, and the indirect effect of input factors on social outcomes through process factors. The hypotheses were tested through multiple regressions using data from 105 kaizen initiatives in two hospitals.Findings – Among the 14 determinants investigated, goal clarity, team autonomy, management support, goal difficulty and affective commitment to change are the most influential determinants of kaizen capabilities and/or employees’ attitude. Additionally, we found that goal clarity, goal difficulty, team autonomy and management support influence social outcomes directly and/or indirectly through affective commitment to change, internal processes and/or action orientation. Practical implications – Results guide healthcare practitioners in understanding how to set-up focused actions levering on specific determinants to positively influence social outcomes.Originality – This study provides an original contribution to the literature on kaizen initiatives in healthcare by empirically testing a comprehensive model of the relationship between kaizen initiatives determinants and social outcomes. Unlike previous studies, mostly anecdotal and focused on one or few determinants, this research adopted a holistic view by investigating the effect of a wide set of determinants on social outcomes through a systematic and quantitative approach

Towards coordinated site monitoring and common strategies for mitigation of Radio Frequency Interference at the Italian radio telescopes

We present a project to implement a national common strategy for the mitigation of the steadily deteriorating Radio Frequency Interference (RFI) situation at the Italian radio telescopes. The project involves the Medicina, Noto, and Sardinia dish antennas and comprised the definition of a coordinated plan for site monitoring as well as the implementation of state-of-the-art hardware and software tools for RFI mitigation. Coordinated monitoring of frequency bands up to 40 GHz has been performed by means of continuous observations and dedicated measurement campaigns with fixed stations and mobile laboratories. Measurements were executed on the frequency bands allocated to the radio astronomy and space research service for shared or exclusive use and on the wider ones employed by the current and under-development receivers at the telescopes. Results of the monitoring campaigns provide a reference scenario useful to evaluate the evolution of the interference situation at the telescopes sites and a case series to test and improve the hardware and software tools we conceived to counteract radio frequency interference. We developed a multi-purpose digital backend for high spectral and time resolution observations over large bandwidths. Observational results demonstrate that the spectrometer robustness and sensitivity enable the efficient detection and analysis of interfering signals in radio astronomical data. A prototype off-line software tool for interference detection and flagging has been also implemented. This package is capable to handle the huge amount of data delivered by the most modern instrumentation on board of the Italian radio telecsopes, like dense focal plane arrays, and its modularity easen the integration of new algorithms and the re-usability in different contexts or telescopes.Comment: 39 pages, 10 Figures and 7 Tables. INAF Technical Report n. 149 (2022). http://hdl.handle.net/20.500.12386/3208

Wind turbine noise code benchmark: A comparison and verification exercise

In a number of institutions and companies, researchers and engineers are developing numerical models and frameworks that are used to predict the aerodynamic noise emissions from wind turbine rotors. The simulation codes range from empirically tuned engineering models to high-fidelity computational ones. Their common feature is the fact that they all specifically model the main aerodynamic noise mechanisms occurring at the rotating blades (namely, the turbulent boundary layer): trailing-edge and turbulent inflow noise. Nevertheless, different modelling techniques and implementations may generate different results, even when assessed on the same rotor design and operating conditions, whicmodels. Trailing-edge noise is put at the forefront of the present study, as it is recognized to be the main source of audible noise from modern wind turbines. The present benchmark aims at comparing the results from different modelling approaches and drawing some conclusions from these comparisons. This effort, denoted as Wind Turbine Noise Code benchmark, was initiated in 2019 as a joint activity between the IEA Wind Task 39 (Quiet Wind Turbine Technology) and Task 29 (Detailed Aerodynamics of Wind Turbines, now Task 47). In addition to the investigation of the noise emissions themselves, the rotor aerodynamic characteristics are investigated, as they are the source of the noise generation mechanisms discussed herein. A number of test cases are defined, and the aerodynamic and aeroacoustic predictions from the various models are compared. A fair agreement between the aerodynamic predictions is observed. There exist some discrepancies between the different noise prediction methods, but it is difficult to conclude if one methodology is better than another in order to design a wind turbine with noise as a constraint

The Nontradable Share Reform in the Chinese Stock Market

Nontradable shares (NTS) are an unparalleled feature of the ownership structure of Chinese listed companies and represented a major hurdle to domestic financial market development. After some failed attempts, in 2005 the Chinese authorities have launched a structural reform program aiming at eliminating NTS. In this paper, we evaluate the stock price effects of the actual implementation of this reform in 368 firms. The NTS reform generated a statistically significant 8 percent positive abnormal return over the event window, adjusting prices for the compensation requested by tradable shareholders. Results are consistent with the expectation of improved economic fundamentals such as better corporate governance and enhanced liquidity