1,356,673 research outputs found
Ultra-fast escape of a deformable jet-propelled body
No full textIn this work a cephalopod-like deformable body that fills an internal cavity with fluid and expels it to propel an escape manoeuvre, while undergoing a drastic external shape change through shrinking, is shown to employ viscous as well as mainly inviscid hydrodynamic mechanisms to power an impressively fast start. First, we show that recovery of added-mass energy enables a shrinking rocket in a dense inviscid flow to achieve greater escape speed than an identical rocket in a vacuum. Next, we extend the shrinking body results of Weymouth & Triantafyllou (J. Fluid Mech., vol. 702, 2012, pp. 470–487) to three-dimensional bodies and show that three hydrodynamic mechanisms must be combined to achieve rapid escape performance in a viscous fluid: added-mass energy recovery; flow separation elimination; and an optimized energy storage and recovery. In particular, we show that the mechanism of separation elimination achieved through rapid body shrinking, coordinated with the mechanism of recovering the initially imparted added-mass energy, is critical to achieving a high escape speed. Hence a flexible, collapsing body can be vastly superior to a rigid-shell jet-propelled body
Vortex-induced vibrations of a long flexible cylinder in shear flow
No full textWe investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.United States. Office of Naval Research (Grant N00014-07-1-0135)United States. Office of Naval Research (Grant N00014-07-1-0446)BP (Firm) (MIT Major Projects Research Program
Real time estimation of the heaving and pitching motions of a ship using a Kalman filter
No full text"May 1982" "Reprinted from Proc. OCEANS' 81, Boston, Mass., September 1981."Bibliography: leaf 1094."Grant NGL-22-009-124"Michael Triantafyllou, Michael Athans
Erratum: Corrigendum to “Esophageal remnant cancer 35 years after acidic caustic injury: A case report” (International Journal of Surgery Case Reports (2016) 25 (215–217) (S2210261216302358) (10.1016/j.ijscr.2016.06.051))
No full textThe authors regret to change the first name of the second author; more specifically we would like to change the first name “Stamatina” to “Tania”—the family name (“Triantafyllou”) remains as it is. On behalf of all the authors, I assure that we are in agreement with this change. The authors would like to apologise for any inconvenience caused. © 2016 The Author(s
Global vorticity shedding for a shrinking cylinder
No full textWe study numerically the viscous flow around a steadily moving two-dimensional cylinder undergoing a rapid reduction in its diameter as a model problem for force production through shape change which is encountered in the locomotion of certain animals. We consider first the case of a rapidly collapsing circular cylinder in steady translation, starting from an original diameter and reaching a final, smaller diameter under prescribed kinematics. We show that the difference in added mass energy is recovered by the body, and the boundary layer vorticity is reduced through annihilation with opposite-sign vorticity generated during the reduction phase. Next we consider a steadily moving circular cylinder which undergoes rapid but orderly melting, resulting in the same reduction of its diameter but which exhibits radically different flow patterns compared to the collapsing cylinder. The original vorticity in the boundary layer is shed instantaneously and globally in the fluid at the start of the melting phase, and then rapidly rolls up to form a pair of strong vortices, which contain the energy difference between the original and final cylinder states. The formation of the vortices in the melting cylinder takes less than a third of the time required by a rigid translating cylinder to form such vortices
Spatial layout of retail waste logistics – the case for localised treatment
No full textIn recent years, the spatial layout of waste logistics in the retail sector has presented significant changes, as a result of legislative mandates and environmental concerns raised by the increased use of packaging and hazardous materials by retailers. The enactment of new legislation has affected producers and distributors by placing them responsible for the collection, treatment and recovery of hazardous waste. This has had direct impacts on the type, number and location of treatment/disposal facilities and the design, planning and management of the associated logistics networks.This project investigates current trends in waste supply-chain configurations, using a substantial database of logistics operations compiled from 92 businesses in a shopping centre. The aim is to develop an origin-destination inventory in order to quantify the considerable transport and environmental footprint currently associated with retail waste logistics. Through selected case studies, this paper investigates the scope for coordinated collection strategies across supply-chains potentially using either local treatment facilities or an under-examination sub-urban consolidation centre intended to accommodate deliveries destined for the businesses in the shopping centr
Neutrophil to Lymphocyte Ratio in Oropharyngeal Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis
No full textThis study was supported by grants from the Plan Nacional de I+D+I 2013–2016 (ISCIII (PI19/00560 to J.P.R.), CIBERONC (CB16/12/00390 to J.P.R.), Ayudas a Grupos PCTI Principado de Asturias (IDI/2021/000079 to J.P.R.), and the FEDER Funding Program from the European Union.Rodrigo J.P., Sánchez-Canteli M., Triantafyllou A., de Bree R., Mäkitie A.A., Franchi A., Hellquist H., Saba N.F., Stenman G., Takes R.P., Valero C., Zidar N., Ferlito A
Developing business establishment surveys to understand reverse logistics processes within a multi-retailer shopping environment
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