3,851 research outputs found
Research on the drag reduction performance induced by the counterflowing jet for waverider with variable blunt radii
Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST k–ω turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7–8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4–5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance
Influences of wind and rotating speed on the fluid-structure interaction vibration for the offshore wind turbine blade
For the 5MW offshore wind turbine blade, the control and discrete equations of the fluid domain and structural domain were established respectively, and the calculation formulas of blade loads and damping coefficient were given. Furthermore, the blade entity modeling was completed by using UG and ANSYS Workbench. Based on it, the numerical calculation of blade vibration characteristics under different wind and rotating speeds was carried out, and the reliability verification was conducted by the wind tunnel test. The results of calculation indicate that the numerical results of the first principal stresses at the blade surface along the span-wise direction are consistent with the results of wind tunnel test, which verifies the reliability of the theory and numerical models. Both the influences of the bidirectional fluid-structure interaction (BFSI) and the rotation effect on the characteristics of blade vibration should be underlined. The increase of wind or rotating speed results in the nonlinear increase of the maximum span-wise displacement of the blade and of the Mises-stresses. Under different wind or rotating speed, the blade’s maximum displacement occurs at its tip, its maximum Mises-stresses appear at the relative wingspan of 0.55, and the contribution of rotating speed and average wind speed to the displacement or Mises-stress along the span-wise direction is similar
How Committed Individuals Shape Social Dynamics: A Survey on Coordination Games and Social Dilemma Games
Committed individuals, who features steadfast dedication to advocating strong
beliefs, values, and preferences, have garnered much attention across
statistical physics, social science, and computer science. This survey delves
into the profound impact of committed individuals on social dynamics that
emerge from coordination games and social dilemma games. Through separate
examinations of their influence on coordination, including social conventions
and color coordination games, and social dilemma games, including one-shot
settings, repeated settings, and vaccination games, this survey reveals the
significant role committed individuals play in shaping social dynamics. Their
contributions range from accelerating or overturning social conventions to
addressing cooperation dilemmas and expediting solutions for color coordination
and vaccination issues. Furthermore, the survey outlines three promising
directions for future research: conducting human behavior experiments for
empirical validation, leveraging advanced large language models as proxies for
committed individuals in complex scenarios, and addressing potential negative
impacts of committed individuals
Stability and superconductivity of freestanding two-dimensional transition metal boridene: M4/3B2
The small atomic mass of boron indicates strong electron-phonon coupling, so
it may have a brilliant performance in superconductivity. Recently, a new 2D
boride sheet with ordered metal vacancies and surface terminals (Mo4/3B2-x) was
realized in experiments (Science 2021, 373, 801). Here, the 2D monolayer
freestanding Mo4/3B2is evidenced to be thermodynamically stable. Through
electronic structure, phonon spectrum and electron-phonon coupling, monolayer
Mo4/3B2 is found to be an intrinsic phonon-mediated superconductor. The
superconducting transition temperature (Tc) is determined to be 4.06 K by the
McMillian-Allen-Dynes formula. Remarkably, the Tc of monolayer Mo4/3B2 can be
increased to 6.78 K with an appropriate biaxial tensile strain (+5%). Moreover,
we predict that other transition metal replacing Mo atoms is also stable and
retaining the superconductivity. Such as monolayer W4/3B2 is also a
superconductor with the Tc of 2.37 K. Our research results enrich the database
of 2D monolayer superconductors and boron-related formed materials science
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