Article
Materials Science, Multidisciplinary
D. Bernard, D. G. Hattingh, W. E. Goosen, M. N. James
Summary: The study found that both low speed and high speed friction stir welding of 5182-H111 aluminum alloy have excellent mechanical properties, although they derive from different thermomechanical mechanisms.
METALS AND MATERIALS INTERNATIONAL
(2021)
Article
Engineering, Aerospace
Kyungwon Oh, Seonghee Kho
Summary: The purpose of this paper is to analyze the structural stability of an underwater high-speed vehicle. The drag characteristics of a moving body in water at high speed were analyzed, and the non-conservative property was applied to perform stability analysis of the structure in a rocket propulsion environment. The fluid characteristics enabling high-speed maneuvering in an underwater environment were described, and the structural stability was analyzed by simplifying the modeling through increased drag. Additionally, an analysis of the forces generated by drag and axial load and their impact on structural stability was conducted by simplifying the structure attached to a specific location during supercavitation.
Article
Mechanics
George Khujadze, Dimitris Drikakis, Konstantinos Ritos, Ioannis W. Kokkinakis, S. Michael Spottswood
Summary: This paper presents a study of high speed boundary layers using the wavelet method. The analysis of direct numerical simulation data reveals that the coherent parts of the flow are close to the statistics of the total flow, while the incoherent parts show equidistributed energy. Furthermore, the study finds that the incoherent vorticity correlates with the near-wall pressure fluctuations, suggesting its importance in understanding compressible boundary layers.
Article
Mechanics
Manolia Andredaki, Anastasios Georgoulas, Nicolas Miche, Marco Marengo
Summary: In this study, an enhanced Volume of Fluid model is used for parametric numerical simulations to investigate breakup phenomena of accelerating, elongated vapor bubbles in circular mini-channels. The effect of fundamental controlling parameters on breakup characteristics is examined, leading to the identification of three prevailing regimes: full breakup, partial breakup, and no breakup. The results are consolidated into a well-defined flow map based on the We and Fr* numbers.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2021)
Article
Nanoscience & Nanotechnology
Mehmet Yasin Demirel, Ibrahim Karaagac
Summary: A low deformation rate is a disadvantage in the high-temperature superplastic forming process, and grain boundary sliding and creep mechanisms occur during deformation. The high-speed SPF method is being investigated to eliminate this disadvantage. In experimental studies, GBS deformation was observed at 870 degrees C, positively affecting formability with 1489% elongation at 870 degrees C and 701% at 910 degrees C. The effect of creep deformation was observed at 890 degrees C and 910 degrees C, leading to a decreasing trend in superplastic formability.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2023)
Article
Mechanics
Teng Zhou, Yuhan Lu, Zaijie Liu, Chao Yan
Summary: In the past decade, the suppression effect of streaks on the second mode has been studied through stability analysis. In this study, direct numerical simulations (DNS) were used to investigate direct nonlinear control in the complete laminar-to-turbulence transition scenario within a high Mach number supersonic boundary layer. The study aims to provide a comprehensive understanding of the mechanisms underlying the influence of streaks on high-speed boundary layer transition. The findings demonstrate the effective control effect of streaks generated by blowing and suction strips on laminar-to-turbulence transition via the second-mode oblique breakdown.
Article
Optics
Thomas Harder, Margherita Turconi, Remi Soulard, Walid Chaibi
Summary: In this paper, a novel strategy to control optomechanical parametric instability (PI) in gravitational wave (GW) detectors based on radiation pressure is proposed. The key element of this approach is the fast deflection of a high-power beam. A 2D deflection system based on a pair of acousto-optic modulators (AOMs) is built, which combines high rapidity and a large scan range. A Universal Software Radio Peripheral (USRP) combined with a high-performance personal computer (PC) is used as a fast frequency switching configurable AOM driver. A 2D beam steering system with flat efficiency over the whole scan range and a transition time of 50 ns between two arbitrary consecutive deflection positions for a beam power of 3.6 W is demonstrated.
Article
Mechanics
Kaiwen Chen, Duo Xu, Baofang Song
Summary: In this study, we investigated the propagation of turbulent fronts in pipe flow at high Reynolds numbers by conducting direct numerical simulation. By using a combination of a moving frame of reference and an artificial damping technique, we were able to isolate the fronts in short periodic pipes and explore the bulk Reynolds number up to Re = 10(5). Our analysis revealed that the speed of the downstream front increases monotonically as the Reynolds number increases, whereas the speed of the upstream front agrees with previous studies. Based on our observations of the front dynamics, we proposed that both front speeds would continue to follow their respective monotonic trends as the Reynolds number increases further.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Reza Jahanbakhshi, Tamer A. Zaki
Summary: The influence of surface roughness on the transition to turbulence in a Mach 4.5 boundary layer is investigated through direct numerical simulations. It is found that the shape and location of the localized roughness have a significant impact on the amplification of second-mode instabilities, and optimizing the roughness parameters can delay the transition to turbulence.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Mohan Ananth, Mario F. Trujillo
Summary: This study investigates the instability of high-speed liquid sheets injected into a quiescent gas environment using mean flow spatial linear stability and two-dimensional volume-of-fluid simulations. The gas shear layer thickness is found to play a significant role in the instability, affecting the growth of sinuous and varicose modes differently.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Optics
Zhiyuan Gao, Kangda Hao, Lianyong Xu, Yongdian Han, Lei Zhao, Hongyang Jing
Summary: Plate inclination was used to prevent undercut defect in high-speed MAG welding. The behavior of the molten pool and droplets was observed, and the undercut defect was analyzed. Results showed that the droplets moved in the opposite direction to the welding and fell into the tail of the gouging region at an inclination angle below 10 degrees, while they moved along the welding direction and fell out of the gouging region at an angle above 30 degrees. Plate inclination at an angle of 30 degrees effectively inhibited undercut defect due to the flow of the molten metal.
OPTICS AND LASER TECHNOLOGY
(2023)
Article
Engineering, Multidisciplinary
Weicheng Huang, Longhui Qin, Qiang Chen
Summary: A method based on discrete differential geometry is proposed to study the natural frequencies of elastic rods and gridshells in their post-buckling configurations. A numerical approach is used to characterize the linear vibration near the post-buckling equilibria, and a parameter sweep is performed to quantify the vibration frequency of pre-buckled gridshells. The study finds that the natural frequency of pre-deformed rods and gridshells decreases linearly with the enlargement of compressive distance, while the vibration frequency almost linearly rises with the number of rods in a gridshell.
APPLIED MATHEMATICAL MODELLING
(2022)
Article
Engineering, Ocean
Luyao Wang, Shijie Qin, Hezhen Fang, Dazhuan Wu, Bin Huang, Rui Wu
Summary: This study reveals that the cavity formed by artificial ventilation can significantly inhibit the porpoising instability of planing vessel at high speeds. The increase in longitudinal stability after the formation of the cavity is believed to be directly related to the increase in volume of displacement led by the cavity, which strengthens the impact of hydrostatic lift in the vertical force balance.
APPLIED OCEAN RESEARCH
(2021)
Article
Metallurgy & Metallurgical Engineering
Liu Shao-hui, Jiang Li-zhong, Zhou Wang-bao, Feng Yu-lin
Summary: Based on Hamilton's principle, the differential equations for free vibration of track-bridge systems with mortar gap are derived. A method for calculating the natural frequencies of track-bridge systems is proposed. The study analyzes the influence of the flexural stiffness of the track-bridge system, the vertical and longitudinal stiffness of the mortar layer, gap position, and gap length on the natural frequencies. The results show that the flexural stiffness of the bridge layer has the greatest impact on the system's natural frequencies, while the longitudinal stiffness of the mortar layer and gap position have minimal effect. The gap length significantly affects the 4th-5th order natural frequencies of the track-bridge system.
JOURNAL OF CENTRAL SOUTH UNIVERSITY
(2022)
Article
Biochemistry & Molecular Biology
Nhung Pham, Zhenxin Yan, Yang Yu, Mosammat Faria Afreen, Anna Malkova, James E. Haber, Grzegorz Ira
Summary: The research demonstrates that mutagenic break-induced replication (BIR) is suppressed at two-ended DNA double-strand breaks (DSBs) by proteins coordinating the usage of two ends of a DSB. Key proteins involved in this suppression include ssDNA annealing proteins Rad52 and Rad59, D-loop unwinding helicase Mph1, and the Mre11-Rad50-Xrs2 complex promoting synchronous resection of DSB ends. Sir2 also plays a role in silencing heterochromatic repair templates to prevent BIR.
