12 research outputs found
Generator Design for the Symphony Wave Power Device
No full textWave power is a large untapped source of renewable energy. There is a wide variety of wave energy converters and one of them is the Symphony Wave Power device. The aim of this thesis is to find the best generator design for the Symphony. There is some research available on generator designs for wave energy converters but the Symphony is a unique case, so a new research needed to be conducted. Several generator types can be used in the Symphony. Compared to an induction and switched reluctance generator, the iron-cored permanent magnet synchronous generator (PMSG) seems a good choice because it is efficient and reliable. A disadvantage, however, is that, in the case of the Symphony, the iron losses are relatively high at partial loads. An air-cored PMSG does not have this problem since it has no iron losses at all. A drawback of the air-cored PMSG is that it needs more permanent magnetic material, which is expensive. Finally, it was decided to test and compare the iron-cored radial flux PMSG and the air-cored axial flux PMSG on both performance and costs. For both generator types, an analytical model was built which puts out the efficiency and material cost. To find the best generator geometries for the case of the Symphony, an optimization procedure was created which minimizes both material costs and losses. It was found that an axial flux air-cored PMSG is both cheaper and more efficient than a radial flux iron-cored PMSG. The iron losses of an iron-cored generator are relatively high at partial loads while the Symphony operates at partial loads most of the time
Demonstration of degaussing by copper and HTS windings
No full textDue to their permeability, merchant and naval vessels distort Earth’s magnetic field which leaves a magnetic signature. These anomalies in the magnetic field may be detected by mines leaving the vessel exposed. To avoid detection by magnetic sensors, the vessels magnetic signature can be reduced in several ways. One of them is degaussing: a technique where a set of on-board coils produces a magnetic field to cancel the magnetic signature. Modelling studies have shown that the performance of a degaussing system can be improved by replacing the copper with high temperature superconductor (HTS) coils in terms of volume, weight and energy efficiency. This study aims to compare the degaussing functionality of copper and HTS windings. A table-top demonstration model is presented which is equipped with both copper and HTS degaussing coils. The demonstrator is prepared by removing the permanent magnetisation. The two degaussing topologies are compared in terms of functionality, efficiency, controllability and mutual inductances.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & StorageTransport Engineering and Logistic
Design of a Test Setup to Measure Magnetic Signature Reduction
No full textIn order to avoid detection by sea mines, the magnetic signature of merchant and naval vessels can be reduced by running a current through a set of on-board copper coils. This process is called degaussing. Studies have shown that the volume, weight and energy losses of a degaussing system can be reduced by replacing the copper coils with high temperature superconductive (HTS) coils. Moreover, since the technology and production of HTS has matured and the material is highly available, the use of HTS for degaussing coils is a serious option. As a preliminary study towards an HTS degaussing test setup, this paper presents the design of a table-top demonstration with copper degaussing coils. The goal of the demonstration is to measure the magnetic signature and the magnetic signature reduction of a cylindrical object. The design choices of the test setup and the measuring system are discussed. The magnetic signature of the table-top model is calculated as well as the optimal placement of the degaussing coils and the optimal degaussing currents. These results are compared with measurements of the magnetic flux density around the demonstrator.DC systems, Energy conversion & StorageTransport Engineering and Logistic
Participatory Design in Architecture: A toolkit to communicate needs between architects and users
No full textAs architects encounter challenges when comprehending and fulfilling the requirements of users and other stakeholders involved in thearchitectural design project, participatory design, which involves non-architects in the design process, is perceived as one of the solutions. It is a developing practice that can lead to greater engagement of non-architects in the architectural design process and create designs that meet the needs and values of all participants.Through field research, design, and iterations in workshops, a participatory design toolkit was proposed. It was designed for architects and users to communicate and accommodate personal, organizational, and spatial needs in the early phase of architectural design. The toolkit consists of three sessions supported by visual aids: the creation of common goals, unfolding spatial needs, and accommodating spatial needs. Communication starts with sharing personal and organizational values to formulate common goals, followed by exploration and identification on spatial needs of building users in relation to the common goals, and ends with collective visualization to accommodate needs with the architectural design.Overall, this project highlighted the importance of participatory design in the architectural design process and the challenges and successes that can be experienced when incorporating it into practice. It suggested that by involving non-architects in the design process, architects and users can communicate their knowledge, need, and value, leading to appropriate architectural designs that are functional, aesthetically pleasing, and meet the needs of all stakeholders.This project was organized with Kraaijvanger Architects, an architectural firm located in Rotterdam, the Netherlands.Strategic Product Desig
Converter Design for High Temperature Superconductive Degaussing Coils
No full textDetection of the magnetic signature of ships can be avoided by using a degaussing system; a set of on-board copper coils that compensates for the magnetic signature. High temperature superconductors (HTS) are currently investigated as a replacement for copper degaussing coils. By using HTS, we have to deal with higher currents and therefore with higher power supply losses. Also, large current leads are needed which introduces extra losses. This paper investigates different possible solutions to minimize these losses. Four H-bridge-based MOSFET topologies are presented that were designed to reduce the power supply and current lead losses. The first topology uses an H-bridge configuration so that the degaussing current can freewheel through the low-resistance MOSFETs. The second topology places the H-bridge inside the cryostat so that the current leads can be made smaller. The third topology includes a smoothing capacitor in the cryostat so that the current leads and input current are even smaller. The fourth topology uses a transformer so that the current leads can be eliminated. Measurements were done to determine the MOSFETs and capacitor performance in liquid nitrogen. The simulated losses of the four topologies are compared to determine the most energy-efficient option for supplying current to the HTS coils. It was found that by submerging multiple parallel MOSFETs in liquid nitrogen, the on-state resistance is decreased and the current supply can be made more efficient. Also, by placing a smoothing capacitor inside the cryostat, the current lead losses can be minimized significantly. The benefits of using a transformer do not outweigh the transformer losses.High Voltage Technology GroupDC systems, Energy conversion & StorageBUS/TNO STAF
Magnetic Signature Reduction by Converter Switching Frequency Modulation in Degaussing Systems
No full textShips can avoid to be detected by magnetic mines by reducing their magnetic signature with degaussing coils. Degaussing currents are provided by switched mode power supplies which impose a current ripple on top of the degaussing current. The ripple might be visible in the magnetic signature which would increase the detectability of the ship. A way to reduce the ripple in the magnetic field is to use a switching modulation scheme in the degaussing power supplies. In this paper, a magnetic model of a ship with degaussing coils is described. It is used to find the magnitude of the ripple in the magnetic signature. Also the effect of reducing the current ripple by frequency modulation is investigated. Several modulation schemes are modelled. It is found that the ripple in the magnetic signature is often, but not always, negligible due to attenuation by the ship’s hull. For low frequency switching applications, like high temperature superconductor degaussing systems, the ripple is visible in the magnetic signature. It is found that switching frequency modulation is a very effective technique to reduce the ripple of degaussing currents. Of the tested schemes, random lead lag and random switching frequency are the most effective.DC systems, Energy conversion & StorageTransport Engineering and Logistic
Modeling and Characterization of a ReBCO HTS Degaussing Demonstrator
No full textThe magnetic modelling and experimental validation of a superconducting degaussing system for maritime vessels is discussed. Degaussing coils compensate for the distortion in the earths' magnetic field by the magnetized steel hull of a ship, thus rendering it 'invisible' for magnetic field sensors. Whereas typical power requirements with copper coils are of the order of 100 kW, a ReBCO HTS degaussing system in principle allows to reduce this by an order of magnitude. In order to validate such efficiency estimates and to demonstrate the required hardware, a table-top test setup was realized with magnetic ship steel. The vessel-imitating cylindrical demonstrator is equipped with six degaussing coils, grouped in three sets that act in two different directions, with each set consisting of one copper and one ReBCO coil, the latter one equipped with a sub-cooled forced-flow liquid nitrogen system. Static magnetic field measurements are reported and compared to both analytical and numeric finite element models. The results illustrate how even relatively simple analytical models can be used as a powerful tool to extrapolate design parameters and thus to predict the power requirements of large-scale degaussing systems.DC systems, Energy conversion & Storag
Effect of colchicine on perioperative atrial fibrillation and myocardial injury after non-cardiac surgery in patients undergoing major thoracic surgery (COP-AF): an international randomised trial
No full textBackground: Higher levels of inflammatory biomarkers are associated with an increased risk of perioperative atrial fibrillation and myocardial injury after non-cardiac surgery (MINS). Colchicine is an anti-inflammatory drug that might reduce the incidence of these complications. Methods: COP-AF was a randomised trial conducted at 45 sites in 11 countries. Patients aged 55 years or older and undergoing major non-cardiac thoracic surgery were randomly assigned (1:1) to receive oral colchicine 0·5 mg twice daily or matching placebo, starting within 4 h before surgery and continuing for 10 days. Randomisation was done with use of a computerised, web-based system, and was stratified by centre. Health-care providers, patients, data collectors, and adjudicators were masked to treatment assignment. The coprimary outcomes were clinically important perioperative atrial fibrillation and MINS during 14 days of follow-up. The main safety outcomes were a composite of sepsis or infection, and non-infectious diarrhoea. The intention-to-treat principle was used for all analyses. This trial is registered with ClinicalTrials.gov, NCT03310125. Findings: Between Feb 14, 2018, and June 27, 2023, we enrolled 3209 patients (mean age 68 years [SD 7], 1656 [51·6%] male). Clinically important atrial fibrillation occurred in 103 (6·4%) of 1608 patients assigned to colchicine, and 120 (7·5%) of 1601 patients assigned to placebo (hazard ratio [HR] 0·85, 95% CI 0·65 to 1·10; absolute risk reduction [ARR] 1·1%, 95% CI –0·7 to 2·8; p=0·22). MINS occurred in 295 (18·3%) patients assigned to colchicine and 325 (20·3%) patients assigned to placebo (HR 0·89, 0·76 to 1·05; ARR 2·0%, –0·8 to 4·7; p=0·16). The composite outcome of sepsis or infection occurred in 103 (6·4%) patients in the colchicine group and 83 (5·2%) patients in the placebo group (HR 1·24, 0·93–1·66). Non-infectious diarrhoea was more common in the colchicine group (134 [8·3%] events) than the placebo group (38 [2·4%]; HR 3·64, 2·54–5·22). Interpretation: In patients undergoing major non-cardiac thoracic surgery, administration of colchicine did not significantly reduce the incidence of clinically important atrial fibrillation or MINS but increased the risk of mostly benign non-infectious diarrhoea. Funding: Canadian Institutes of Health Research, Accelerating Clinical Trials Consortium, Innovation Fund of the Alternative Funding Plan for the Academic Health Sciences Centres of Ontario, Population Health Research Institute, Hamilton Health Sciences, Division of Cardiology at McMaster University, Canada; Hanela Foundation, Switzerland; and General Research Fund, Research Grants Council, Hong Kong
Accelerated surgery versus standard care in hip fracture (HIP ATTACK) : an international, randomised, controlled trial
No full textBackground: Observational studies have suggested that accelerated surgery is associated with improved outcomes in patients with a hip fracture. The HIP ATTACK trial assessed whether accelerated surgery could reduce mortality and major complications. Methods: HIP ATTACK was an international, randomised, controlled trial done at 69 hospitals in 17 countries. Patients with a hip fracture that required surgery and were aged 45 years or older were eligible. Research personnel randomly assigned patients (1:1) through a central computerised randomisation system using randomly varying block sizes to either accelerated surgery (goal of surgery within 6 h of diagnosis) or standard care. The coprimary outcomes were mortality and a composite of major complications (ie, mortality and non-fatal myocardial infarction, stroke, venous thromboembolism, sepsis, pneumonia, life-threatening bleeding, and major bleeding) at 90 days after randomisation. Patients, health-care providers, and study staff were aware of treatment assignment, but outcome adjudicators were masked to treatment allocation. Patients were analysed according to the intention-to-treat principle. This study is registered at ClinicalTrials.gov (NCT02027896). Findings: Between March 14, 2014, and May 24, 2019, 27 701 patients were screened, of whom 7780 were eligible. 2970 of these were enrolled and randomly assigned to receive accelerated surgery (n=1487) or standard care (n=1483). The median time from hip fracture diagnosis to surgery was 6 h (IQR 4–9) in the accelerated-surgery group and 24 h (10–42) in the standard-care group (p<0·0001). 140 (9%) patients assigned to accelerated surgery and 154 (10%) assigned to standard care died, with a hazard ratio (HR) of 0·91 (95% CI 0·72 to 1·14) and absolute risk reduction (ARR) of 1% (−1 to 3; p=0·40). Major complications occurred in 321 (22%) patients assigned to accelerated surgery and 331 (22%) assigned to standard care, with an HR of 0·97 (0·83 to 1·13) and an ARR of 1% (−2 to 4; p=0·71). Interpretation: Among patients with a hip fracture, accelerated surgery did not significantly lower the risk of mortality or a composite of major complications compared with standard care. Funding: Canadian Institutes of Health Research
Effect of colchicine on perioperative atrial fibrillation and myocardial injury after non-cardiac surgery in patients undergoing major thoracic surgery (COP-AF): an international randomised trial
No full textBackground: Higher levels of inflammatory biomarkers are associated with an increased risk of perioperative atrial fibrillation and myocardial injury after non-cardiac surgery (MINS). Colchicine is an anti-inflammatory drug that might reduce the incidence of these complications. Methods: COP-AF was a randomised trial conducted at 45 sites in 11 countries. Patients aged 55 years or older and undergoing major non-cardiac thoracic surgery were randomly assigned (1:1) to receive oral colchicine 0·5 mg twice daily or matching placebo, starting within 4 h before surgery and continuing for 10 days. Randomisation was done with use of a computerised, web-based system, and was stratified by centre. Health-care providers, patients, data collectors, and adjudicators were masked to treatment assignment. The coprimary outcomes were clinically important perioperative atrial fibrillation and MINS during 14 days of follow-up. The main safety outcomes were a composite of sepsis or infection, and non-infectious diarrhoea. The intention-to-treat principle was used for all analyses. This trial is registered with ClinicalTrials.gov, NCT03310125. Findings: Between Feb 14, 2018, and June 27, 2023, we enrolled 3209 patients (mean age 68 years [SD 7], 1656 [51·6%] male). Clinically important atrial fibrillation occurred in 103 (6·4%) of 1608 patients assigned to colchicine, and 120 (7·5%) of 1601 patients assigned to placebo (hazard ratio [HR] 0·85, 95% CI 0·65 to 1·10; absolute risk reduction [ARR] 1·1%, 95% CI –0·7 to 2·8; p=0·22). MINS occurred in 295 (18·3%) patients assigned to colchicine and 325 (20·3%) patients assigned to placebo (HR 0·89, 0·76 to 1·05; ARR 2·0%, –0·8 to 4·7; p=0·16). The composite outcome of sepsis or infection occurred in 103 (6·4%) patients in the colchicine group and 83 (5·2%) patients in the placebo group (HR 1·24, 0·93–1·66). Non-infectious diarrhoea was more common in the colchicine group (134 [8·3%] events) than the placebo group (38 [2·4%]; HR 3·64, 2·54–5·22). Interpretation: In patients undergoing major non-cardiac thoracic surgery, administration of colchicine did not significantly reduce the incidence of clinically important atrial fibrillation or MINS but increased the risk of mostly benign non-infectious diarrhoea. Funding: Canadian Institutes of Health Research, Accelerating Clinical Trials Consortium, Innovation Fund of the Alternative Funding Plan for the Academic Health Sciences Centres of Ontario, Population Health Research Institute, Hamilton Health Sciences, Division of Cardiology at McMaster University, Canada; Hanela Foundation, Switzerland; and General Research Fund, Research Grants Council, Hong Kong
