Dynamic Modeling and Environmental Analysis of Hydrokinetic Energy Extraction

The world is facing an imminent energy supply crisis. Our well-being is linked to the energy supply, and energy is in high demand in both the developed and the developing world. In order to sustain our energy supply, it is necessary to advance renewable technologies. Despite this urgency, however, it is paramount to consider the larger environmental effects associated with using renewable resources.Hydropower, in the past, has been seen as a viable resource to examine, given that its basics of mechanical to electrical energy conversion seem to have little effect on the environment. Discrete analysis of dams and in-stream diversion set-ups has shown otherwise, though. Modifications to river flows and changes in temperature (from increased and decreased flows) cause adverse effects to fish and other marine life because of changes in their adaptive habitat.Recent research has focused on kinetic energy extraction in river flows, which may prove to be more sustainable, as this type of extraction does not involve a large reservoir or large flow modification. The field of hydrokinetic energy extraction is immature; little is known about the devices' performance in the river environment, and their risk of impingement, fouling, and suspension of sediments. Governing principles of hydrokinetic energy extraction are presented, along with a two-dimensional computational fluid dynamics (CFD) model of the system. Power extraction methods are compared, and verification and validation of the CFD model through mesh sensitivity and experimental data are presented. A 0.0506 average mesh skew and 0.2m/s velocity convergence was obtained within the mesh sensitivity analysis. In comparing particle image velocimetry (PIV) data with the CFD model, a 0.0155m offset and 20\% error were present. However, including a volume of fluid (VOF) model within the CFD model produced a 5\% error improvement and gave a 0.0124m offset. These are improvements over the current state of the art, where visual comparisons are common. Three-dimensional CFD models of a submerged water wheel, Savonius turbine, squirrel cage Darrieus turbine, and Gorlov Darrieus turbine are also presented; however, they are non-VOF CFD models.Using the results of the CFD models, preliminary predictions could be made of the environmental impact of hydrokinetic turbines with respect to fish swimming patterns. Additionally, a life cycle assessment (LCA) was conducted for hydrokinetic energy extraction (HEE), which gives insight into the total system environmental impact. HEE has been seen as a potentially ``benign' form of renewable hydropower. This work provides a benchmark for initial measurement of HEE environmental impacts, since negative outcomes have been present with previously-assumed benign renewable hydropower. A Gorlov system was used to represent a HEE system. LCA was utilized to compare the environmental impacts of HEE with small hydropotential (HPP) power, coal, natural gas and nuclear power. Environmental Protection Agency (EPA) criteria air emissions were quantified and compared over the life cycle of the systems. Life cycle air emissions were used in combination with the TRACI impact assessment tool to compare the systems. The Gorlov system was found to have the lowest life cycle impact with a system lifetime comparison, and compared closely with small HPP.Finally, various issues connected to the implementation of hydrokinetic power generation were discussed. Policy development and sediment movement were investigated in more detail. Additionally, two applications of this technology were explored: in-situ river health monitoring and remote energy generation

Delayed colorectal cancer care during covid-19 pandemic (decor-19). Global perspective from an international survey

Background The widespread nature of coronavirus disease 2019 (COVID-19) has been unprecedented. We sought to analyze its global impact with a survey on colorectal cancer (CRC) care during the pandemic. Methods The impact of COVID-19 on preoperative assessment, elective surgery, and postoperative management of CRC patients was explored by a 35-item survey, which was distributed worldwide to members of surgical societies with an interest in CRC care. Respondents were divided into two comparator groups: 1) ‘delay’ group: CRC care affected by the pandemic; 2) ‘no delay’ group: unaltered CRC practice. Results A total of 1,051 respondents from 84 countries completed the survey. No substantial differences in demographics were found between the ‘delay’ (745, 70.9%) and ‘no delay’ (306, 29.1%) groups. Suspension of multidisciplinary team meetings, staff members quarantined or relocated to COVID-19 units, units fully dedicated to COVID-19 care, personal protective equipment not readily available were factors significantly associated to delays in endoscopy, radiology, surgery, histopathology and prolonged chemoradiation therapy-to-surgery intervals. In the ‘delay’ group, 48.9% of respondents reported a change in the initial surgical plan and 26.3% reported a shift from elective to urgent operations. Recovery of CRC care was associated with the status of the outbreak. Practicing in COVID-free units, no change in operative slots and staff members not relocated to COVID-19 units were statistically associated with unaltered CRC care in the ‘no delay’ group, while the geographical distribution was not. Conclusions Global changes in diagnostic and therapeutic CRC practices were evident. Changes were associated with differences in health-care delivery systems, hospital’s preparedness, resources availability, and local COVID-19 prevalence rather than geographical factors. Strategic planning is required to optimize CRC care