Search results for "Propeller"
showing 10 items of 38 documents
On the maximum efficiency of the propeller mass-ejection mechanism
2007
Aims. We derive simple estimates of the maximum efficiency with which matter can be ejected by the propeller mechanism in disk-fed, rotating magnetic neutron stars. Some binary evolution scenarios envisage that this mechanism is responsible for expelling to infinity the mass inflowing at a low rate from the companion star, therefore limiting the total amount of mass that can be accreted by the neutron star. Methods. We demonstrate that, for typical neutron star parameters, a maximum of ��_{pro} < 5.7 (P_{-3})^{1/3} times more matter than accreted can be expelled through the propeller mechanism at the expenses of the neutron star rotational energy (P_{-3} is the NS spin period in unit of …
Design of a Close Power Loop Test Bench for Contra-Rotating Propellers
2020
The aim of the research is to develop an azimuthing contra-rotating propeller for commercial applications with a power of 2000 kW. The thruster system is designed especially to be installed on high speed crafts (HSCs) for passenger transport with a cruising speed of about 35–40 knots. The topic is very useful because the azimuth thruster solutions currently do not find commercial applications in naval units for passenger transport. The latter are heavy, not very efficient from a hydrodynamic point of view and suitable for maximum cruising speed of about 18–20 knots. The study is interesting because among the advantages that these solutions provide are the possibility of transmitting very hi…
Mathematical background of the Riga dynamo experiment
2013
The Riga dynamo experiment is a laboratory model of the natural process that is responsible for all environmental magnetic-fields which are generated without human interference. This applies to the field of the Earth, the Sun, stars, and even galaxies which are produced by intense motions of large volumes of good electro-conducting fluids. For our experiment, we use molten sodium – the best liquid electro-conductor available in the laboratory. Approximately 2 m3 of molten sodium are filled into a prolonged cylinder, at the top of which rotates a propeller powered by 200 kW from two motors. The cylinder is divided by thin coaxial inner walls into three parts: in the inner tube the propeller …
Extensible Wind Towers
2014
The diffusion of wind energy generators is restricted by their strong landscape impact. The PERIMA project is about the development of an extensible wind tower able to support a wind machine for several hundred kW at its optimal working height, up to more than 50 m. The wind tower has a telescopic structure, made by several tubes located inside each other with their axis in vertical direction. The lifting force is given by a jack-up system confined inside a shaft, drilled below the ground level. In the retracted tower configuration, at rest, tower tubes are hidden in the foundation of the telescopic structure, located below the ground surface, and the wind machine is the only emerging part …
Propeller Flaps: A Review of Indications, Technique, and Results
2014
In the last years, propeller flaps have become an appealing option for coverage of a large range of defects. Besides having a more reliable vascular pedicle than traditional flap, propeller flaps allow for great freedom in design and for wide mobilization that extend the possibility of reconstructing difficult wounds with local tissues and minimal donor-site morbidity. They also allow one-stage reconstruction of defects that usually require multiple procedures. Harvesting of a propeller flap requires accurate patient selection, preoperative planning, and dissection technique. Complication rate can be kept low, provided that potential problems are prevented, promptly recognized, and adequate…
Computational Fluid Dynamics Simulation for Propeller
2017
A Reynolds-Averaged Navier-Stokes (RANS) method has been employed in conjunction with an overlapping moving grid approach to provide accurate resolution of a five-blade propeller flows under both the design and offdesign conditions. It is well known that some off-design propeller flow phenomena are dominated by viscous effects and cannot be accurately predicted by the potential flow methods. To properly account for viscous effects, it is necessary to employ accurate and robust numerical methods which can provide detailed resolution of the propeller boundary layer, turbulent wake, leading edge separation,and unsteady ring vortices induced by propeller operations under off-design conditions. …
Performance analysis of photovoltaic powered dc motor &#x2014; Propeller system
2015
The application of autonomous directly photovoltaic (PV) powered electro-mechanical has received increasing attention for different applications (e.g. PV water pumping, PV powered cooling of arid climate greenhouses, solar vehicles etc). The PV array output is a nonlinear and time-dependent power supply that varies with solar intensity and cell temperature, so the performance characteristics of the directly PV-powered DC motor — propeller system are very different than when powered by a constant DC voltage. The focus of this work is to do performance analysis of directly PV-powered DC motor — propeller system. Through performance evaluation, it has been observed that power transfer matching…
Novel fasciocutaneous flaps for the reconstruction of complicated lower extremity wounds
2009
Summary: Reconstruction of the leg is particularly challenging especially when the defect involves its lower third. The options for lower leg reconstruction are very few because of the lack of local soft tissue available for transfer. Novel fasciocutaneous flaps nourished by perforator vessels have been developed and are increasingly used as a valuable local alternative to the local flaps, with their high complication rates, and to the microsurgical flaps, with their more difficult and specialized technique. They provide local tissue, replacing like with like, but they harvest it from a distant, undamaged, region of the leg, which means healthy and well-vascularized tissue. They do not need…
Axial propeller flaps: A proposal for update of the "Tokyo consensus on propeller flaps".
2017
LETTER TO EDITOR
Complications and Solutions in Propeller Flap Surgery
2020
AbstractPropeller perforator flaps (PPFs) have long been proven as valid reconstructive tools for a wide range of soft tissue defects in different body regions. During the last decade, despite their numerous advantages, many authors have thoroughly analyzed outcomes of these flaps, sometimes discouraging their use mainly because of a high failure rate. Accurate patient selection, adequate preoperative planning, and an appropriate dissection technique seem to potentially improve outcomes. Our study provides a review of the relevant literature related to PPF complications and of our experience, describing reasons for failure, measures for preventing them, and approaches for a prompt evaluatio…