Biomimetic mechanism for micro aircraft

A biomimetic pitching and flapping mechanism including a support member, at least two blade joints for holding blades and operatively connected to the support member. An outer shaft member is concentric with the support member, and an inner shaft member is concentric with the outer shaft member. The mechanism allows the blades of a small-scale rotor to be actuated in the flap and pitch degrees of freedom. The pitching and the flapping are completely independent from and uncoupled to each other. As such, the rotor can independently flap, or independently pitch, or flap and pitch simultaneously with different amplitudes and/or frequencies. The mechanism can also be used in a non-rotary wing configuration, such as an ornithopter, in which case the rotational degree of freedom would be suppressed

Revisiting the dynamics of catastrophic late Pleistocene glacial-lake drainage, Altai Mountains, central Asia

In this work, we present a whole system model of megafloods from catastrophic ice-dam failure in the late Pleistocene that comprises the study of the dynamics of the glacial lake, the propagation of the flood wave downstream of the dam, and an approximation to the ice breach process. The ice-dam incision rate was simply considered an unknown constant, which was varied systematically to best fit the maximum altitude of the simulated water surface and the paleostage indicators in the downstream valley during the transient megaflood. Hence, the hydrograph resulting from the breach of the ice dam was not prescribed but was an output of the paleohydraulic reconstruction. By considering two possible configurations of the breach in the ice dam, i.e. full or partial removal of the ice, we constrained the incision rate in the narrow range of 28 − 42 m ⋅ h−1. Two connected glacial lakes, Kuray and Chuja, released 95% of the stored water volume (i.e., 564 km3) in 33.8 hours. A peak discharge of 10.5 M m3 ⋅ s−1 was required to form numerous giant bars and run-up deposits in the Chuja and Katun valleys. The peak streamflow occurred after 11 h when 45% of the available lake volume had been evacuated from the Kuray and Chuja basins. Further verification of the reconstructed megaflood was achieved by studying the computed hydraulic conditions during the lake draining that justify the existence and orientation of several fields of subaqueous gravel-dunes in the glacial lake. Complex spatiotemporal patterns during the recession stage of the flood built most of the fields of bedforms. In terms of nondimensional parameters, the Froude and Shields numbers that formed the dune fields were similar to those observed in large sandy rivers, but the flow was undoubtedly unsteady and two-dimensional. We conclude by noting that the extensions of the simulated area cannot be cropped or analysed by independent parts in order to predict the formation of the most relevant geological records due to the unsteady, two-dimensional nature of the flow motion and the development of backwater effects in the drainage network. Lastly, the paleohydrological reconstruction of a megaflood has helped not only to infer the dynamics of the event but also to retrodict the mean parameters of the ice-dam failure mechanism.This work was supported by the Spanish Ministry of Science, Innovation and Universities (MICINN/FEDER, UE) under Grant SEDRETOCGL2015-70736-R. P.R.J. was supported by the European Social Fund and the University of Jaén

Paz, complejidad e ingeniería

Paz, complejidad e ingenierí

Paz, complejidad e ingeniería

Peace, complexity and engineeringPaz, complejidad e ingenierí

Identifying head accumulation due to transient wave superposition in pipelines

Fluctuations in pressures are part of the normal behavior of water distribution systems. The common perception is that transient events dissipate quickly in a network without significant consequences; however, under certain circumstances, the superposition of waves from a transient event can magnify the pressure response, effectively accumulating head in a pipeline. This paper studies this accumulation phenomenon in a single pipeline from a theoretical point of view, with supporting numerical simulation and laboratory validation. Transient wave propagation analysis shows that after the generation of a transient event, multiple wave reflections induce an increase in the head. A cycle of accumulation is defined and the potential maximum number of cycles is studied for a pipeline connected to a long, large impedance pipe section. The analysis is then extended to a system connected to a shorter large impedance pipe section where the maximum head accumulation is not reached. Expressions to calculate the potential maximum head accumulation in pipeline systems are proposed and numerically validated. A general classification for the head accumulation is presented to specify how severe a head accumulation event may be. Experimental validation of the phenomenon has been conducted, showing that under a proposed configuration, the head in the pipeline increases significantly after the first small head rise due to a valve closure. A comparison between the maximum measured head in the laboratory and the theoretical expected maximum head has been undertaken. More realistic configurations that could result in the same phenomenon are briefly discussed.Jessica Bohorquez, Martin F. Lambert, and Angus R. Simpso

Last ice-dammed lake in the Kuray basin, Russian Altai: New results from multidisciplinary research

Results from geomorphological, sedimentological and geochronological analyses, together with micropaleontological and mineralogical characteristics of lacustrine deposits in five locations within the Kuray intermountain depression, southeast Altai, mountains of south Siberia, support the thesis of repeated formations of ice-dammed lakes during MIS-2 and their draining by high energy floods. Our data suggest that the timing of one of the last cataclysmic draining events in the area can be estimated by an Optically-Stimulated Luminescence (OSL) age of 19.0 ± 1.1 ka for a sandy layer at the top of the diluvial (i.e. large flood) deposit, revealed in a sedimentary sequence of the 1570 m a.s.l. strandline – one of the lowest preserved strandlines in the western part of the basin. New OSL and radiocarbon ages, augmenting previously published dates, indicate that the last lake to occupy the Kuray depression occurred around 19–16 ka with a depth of at least 170 m in the central part of the basin and to a depth of no less than 220 m near the glacier dam. Lacustrine deposits are represented by two horizons of sandy clays separated by interlayers of mixed-size sands. The mineralogical data, supported by analysis of sedimentological and micropaleontological records, indicate accumulation of a lower lacustrine horizon in a deeper reservoir. Finding of Leucocythere sp.1, Leucocythere sp.2, and Leucocythere dorsotuberosa ostracod species in lacustrine deposits characterizes these reservoirs as periglacial freshwater cold and deep lakes. The presence of well-crystallized mica and chlorite in lacustrine silts and clays from the lower lacustrine horizon indicates cold, dry conditions at the time of their formation, as well as a predominance of physical weathering of rocks within the denudation area. After an abrupt dropping of the lake level around 16 ka, determined from OSL dating, the lake never recovered its former depth. The available radiocarbon ages for organic material in subaerial deposits within the study area and the new OSL ages suggest that the last ice-dammed lake in the Kuray basin was drained between ~16.7 and 9.9 ka. The presence of this lake might explain the absence of late Paleolithic surface finds within the basin that remained generally unsuitable for human habitation until its final drying. The last outburst flood passed along the Chuya and Katun river valleys, which had been already carved by older cataclysmic floods, but did not significantly affect the topography downstream of the Kuray-Chuya intermountain depressions. We numerically simulated the draining of a palaeolake in the Kuray basin with the water level 1650 m a.s.l. (maximal depth about 220 m near the dam) with different scenarios of breaching the ice dam. In contrast to a relatively gradual breach of the ice dam due to thermal erosion, an instantaneous dam break due to structural failure can cause an outburst flood with a peak discharge of around 2 × 106 m3 s−1. The high speeds of the water flow, 1.9–5.6 m s−1, with the maximum Froude numbers of 0.06–0.22, and peak Shields values of 0.03–0.25 indicate competence to mobilize gravel. Generally, the simulated flow remained subcritical, suggesting that bedforms developed under supercritical flows, such as antidunes, could not have developed, although the development of dunes cannot be precluded. Our data also contribute to the issue of correlating the low lake strandlines in the Kuray basin with the landforms associated with cataclysmic outburst floods.The study was supported by State Assignment of IGM SB RAS and partly funded by Russian Foundation for Basic Researches (grant 18-05-00998). We also benefited from the funds of the projects EX-AQUA (1623P) “Palaeohydrological Extreme Events - evidence and archives”, sustained by INQUA TERPRO. The flood modelling contribution by Bohorquez was supported by the Spanish Ministry of Science, Innovation and Universities (MICINN/FEDER, UE) under Grant SEDRETO CGL2015-70736-R

A Universal Model of Global Civil Unrest

Civil unrest is a powerful form of collective human dynamics, which has led to major transitions of societies in modern history. The study of collective human dynamics, including collective aggression, has been the focus of much discussion in the context of modeling and identification of universal patterns of behavior. In contrast, the possibility that civil unrest activities, across countries and over long time periods, are governed by universal mechanisms has not been explored. Here, we analyze records of civil unrest of 170 countries during the period 1919-2008. We demonstrate that the distributions of the number of unrest events per year are robustly reproduced by a nonlinear, spatially extended dynamical model, which reflects the spread of civil disorder between geographic regions connected through social and communication networks. The results also expose the similarity between global social instability and the dynamics of natural hazards and epidemics.Comment: 8 pages, 3 figure