Effects of particle size of mono-disperse granular flows impacting a rigid barrier

Understanding the interaction between complex geophysical flows and barriers remains a critical challenge for protecting infrastructure in mountainous regions. The scientific challenge lies in understanding how grain stresses in complex geophysical flows become manifested in the dynamic response of a rigid barrier. A series of physical flume tests were conducted to investigate the influence of varying the particle diameter of mono-dispersed flows on the impact kinematics of a model rigid barrier. Particle sizes of 3, 10, 23 and 38 mm were investigated. Physical tests results were then used to calibrate a discrete element model for carrying out numerical back-analyses. Results reveal that aside from considering bulk characteristics of the flow, such as the average velocity and bulk density, the impact load strongly depends on the particle size. The particle size influences the degree of grain inertial stresses which become manifested as sharp impulses in the dynamic response of a rigid barrier. Impact models that only consider a single impulse using the equation of elastic collision warrant caution as a cluster of coarse grains induce numerous impulses that can exceed current design recommendations by several orders of magnitude. Although these impulses are transient, they may induce local strucutral damage. Furthermore, the equation of elastic collision should be adopted when the normalized particle size with the flow depth, δ/h, is larger than 0.9 for Froude numbers less than 3.5.     

Debris flow impact on flexible barrier: effects of debrisbarrier stiffness and flow aspect ratio

Conventionally, flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy. However, there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact. In this study, a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type, barrier stiffness, and flow aspect ratio(flow height to flow length) on the reaction force between the impacting medium and flexible barrier. Results show that, in contrast to flexible barriers for resisting rockfall, the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness. This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing, and only a small portion is forwarded to the barrier. Furthermore, a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder, and a flexible barrier. Under the circumstance of an extremely elongated debris flow event, i.e., low aspect ratio, the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.     

Seismic qualification of electrical equipment using a uniaxial test

The analytical development of a uniaxial test for the seismic qualification of electrical equipment is presented. This method comprises a single test using a uniaxial excitation having certain minimum intensity applied at the base of the test package in a predetermined optimal direction. It is anticipated that the proposed procedure would be more economical and less time consuming than, but functionally equivalent to, presently employed series of multiaxial tests. The test is shown to be superior to the symmetric tests. The determination of the minimum intensity of the optimal orientation of the base excitation requires a preliminary frequency response test which is a slightly more elaborate version of the sine sweep test presently employed to determine the resonance frequencies of the test package. A simulated test is presented to compare the proposed method with the uncorrelated triaxial test and the symmetric uniaxial test.     

Temperature dominance over human life

Summary Temperature bears an importance to man far beyond the mere matter of his hour-to-hour comfort. In some places it lays a heavy, stagnating hand over his life and holds him to a vegetative existence; in others, it generates an energy and progressiveness which drives him forward with irresistible impetus. Its effects begin even before he is conceived, for the metabolic vigor of parental germ cells at the time of their union exerts a potent influence over the entire course of the new life. Without favorable temperatures, neither individual nor nation can develop innate potentialities to the full.The human body is essentially a combustion machine that functions only as its cells release energy by burning the foodstuffs taken in. For every unit of combustion energy transformed into work-output by our bodies, three or four similar units must be dissipated as waste heat. Failure of such dissipation to keep pace with heat production in the body may mean heat stroke and death within a few hours. The waste heat of combustion thus becomes one of the body's most important excretory products.Following several weeks of difficulty in dissipation waste heat, physical and mental activity declines, and there is a drop in the combustion rate. A lowered total combustion rate means less energy for thought and action, as well as less waste heat to be dissipated. Physical and mental characteristics thus change, from the dynamic and pushing, to a more passive type; personal initiative gives way to a desire for security.That these are basic changes in the individual's metabolic make-up is evidenced by equally profound alterations in such body functions as growth, rate of development, resistance to infection, and thought capacity. When difficult heat loss induces a lowered combustion rate in the cells, growth slows down and may be completely halted, even though an ample food supply be available; onset of puberty and maturity is progressively delayed and ability to reproduce is reduced or completely obliterated, although matings go on freely; resistance to bacterial invasion is impaired, especially for those respiratory infections in which the white blood cells (phagocytes) provide the first and main line of the body's defense-system; and, finally, ability to solve problems is greatly impaired.Proper ease of body heat-loss means just the opposite—a fast growing, early maturing, highly fertile individual, with a keen mentality and good ability to fight infectious disease. These statements are by no means hypothetical but are based upon well authenticated statistical findings on man and on experimental animals under controlled conditions. They show up in the laboratory, under natural climatic differences, and during the wide seasonal swings in middle temperature latitudes.Climatic temperature differences, whether brought about by latitude or altitude, are potent factors in human life, and so also are the wide seasonal temperature swings of the earth's middle latitudes. The fortunate nations of the earth are those located where the body's waste heat can be lost readily.Man is in reality a pawn of the environmental forces encompassing him, being pushed forward to a vantage point at one time or held in lethargic bondage at another. Here is a challenge of the first magnitude—can human intelligence find an effective answer? If not an answer, then it should at least comprehend the forces at work and the major significance of their effects.

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Zusammenfassung Die Temperatur besitzt eine Bedeutung für den Menschen, die weit über die Alltagsbedürfnisse des Wohlbefindens hinausgeht. In einzelnen Gebieten legt sie eine schwere, lähmende Hand auf das menschliche Leben und beschränkt es auf eine vegetative Existenz; in anderen dagegen erzeugt sie Energie und Arbeitsdrang. Ihre Auswirkung setzt schon vor der Konzeption ein, indem die Stoffwechselenergien der elterlichen Keimzellen im Augenblick ihrer Vereinigung einen mächtigen Einfluß auf den ganzen Verlauf des neuen Lebens ausüben. Ohne günstige Temperaturen kann weder das Individuum noch die Nation die angeborenen Fähigkeiten in vollem Umfang entwickeln.Der menschliche Körper stellt im Prinzip eineWärmemaschine dar, die nur soweit funktioniert, als ihre Zellen Energie durch Verbrennung der Nahrungsmittel freimachen. Für jede Einheit der Verbrennungsenergie, die durch unseren Körper in Arbeitsleistung verwandelt wird, müssen drei bis vier gleiche Einheiten als Wärmeverluste aufgebracht werden. Wenn diese Wärmeabgabe mit der Wärmeproduktion im Körper nicht im Gleichgewicht ist, kann dies innerhalb weniger Stunden zu Hitzschlag und zum Tode führen. Die Abgabe der Verbrennungswärme wird dadurch zu einem der wichtigsten Ausscheidungsprodukte des Körpers.Dauert die Erschwerung der Wärmeabgabe mehrere Wochen an, so geht die körperliche und geistige Aktivität zurück, wodurch auch die Verbrennungs-wärme abnimmt. Eine Reduktion der Gesamtverbrennungswärme bedeutet eine Verminderung der für Denken und Handeln disponibeln Energie wie auch eine Verkleinerung der Wärmeverluste. Physisches und psychisches Benehmen ändert sich von einem dynamischen zu einem mehr passiven Verhalten und die persönliche Initiative macht dem Sicherheitsbedürfnis Platz.Daß es sich dabei um grundlegende Veränderungen der individuellen Stoffwechselvorgänge handelt, geht aus den gleichermaßen tiefgreifenden Veränderungen verschiedener Körperfunktionen, wie Wachstum, Entwicklungsstand, Resistenz gegen Infektionen und Denkvermögen hervor. Wenn eine Erschwerung der Wärmeabgabe zu einer Reduktion der Verbrennungswärme in den Zellen führt, wird auch bei reichlicher Ernährung das Wachstum verlangsamt oder ganz unterbunden; der Beginn von Pubertät und Geschlechtsreife wird allmählich verzögert und die Fortpflanzungsfähigkeit wird trotz ungestörter Paarung vermindert oder gänzlich aufgehoben. Die Resistenz gegenüber Bakterien ist besonders für solche Infektionen der Atmungsorgane vermindert, bei denen die weißen Blutkörperchen (Phagozyten) die vorderste und wichtigste Abwehrlinie des Körpers bilden; und schließlich ist auch die Fähigkeit, geistige Probleme zu lösen, stark reduziert.Demgegenüber bedeutet Leichtigkeit der Wärmeabgabe des Körpers gerade das Gegenteil: schnelles Wachstum, frühe Reife, hohe Fruchtbarkeit, geistige Lebhaftigkeit und gute Abwehr gegen Infektionskrankheiten. Diese Feststellungen sind keineswegs etwa hypothetisch, sondern basieren auf statistischen Untersuchungen am Menschen oder an Versuchstieren unter genau kontrollierten Bedingungen; sie beruhen auf Laboratoriumsuntersuchungen unter normalen klimatischen Differenzen, aber auch auf den weiten Jahreszeitenschwankungen gemäßigter Breiten.Klimatische Temperaturdifferenzen, die durch Höhe oder geographische Breite hervorgerufen sind, bedeuten mächtige Faktoren im menschlichen Leben, und dasselbe gilt von den großen jahreszeitlichen Temperaturschwankungen der mittleren Breiten der Erde. Die begünstigten Völker der Erde wohnen in den Lagen, wo der Wärmeüberschuß des Körpers leicht abgegeben werden kann. Der Mensch ist in Wirklichkeit das Ergebnis seiner Umgebungskräfte; an einem Ort wird er dadurch vorwärts getrieben, am anderen in Gleichgültigkeit gehalten. Es erhebt sich hier die Frage, ob die menschliche Intelligenz einen wirksamen Ausweg aus diesem Dilemma findet oder ob es wenigstens gelingt, die hier wirksamen Kräfte und die Bedeutung ihrer Wirkungen zu verstehen.

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Résumé La température a pour l'homme une importance qui dépasse largement ses besoins journaliers de bien-être. Dans certaines régions elle exerce une action paralysante sur la vie humaine en la réduisant à une existence végétative; dans d'autres au contraire elle suscite l'énergie et le goût au travail. Son action commence déjà avant la conception puisque l'énergie métabolique des cellules germinales des parents au moment de leur réunion exerce une grande influence sur toute l'évolution de la vie de l'être nouveau. Faute de vivre dans des conditions favorables de température, les individus pas plus que les nations ne peuvent développer complètement leurs aptitudes naturelles.L'organisme humain représente en principe une machine thermique qui ne peut fonctionner que dans la mesure où ses cellules libèrent de l'énergie par combustion des aliments. Pour chaque unité d'énergie de combustion transformée par notre corps en travail, trois ou quatre unités égales disparaissent sous forme de perte calorique. Si cette perte et la production de chaleur du corps ne sont pas en équilibre, cet état peut conduire en quelques heures au coup de chaleur et à la mort. La mise en liberté de la chaleur de combustion est de ce fait un des plus importants phénomènes de sécrétion de l'organisme.Lorsque les conditions extérieures gênent le refroidissement normal pendant des semaines, l'activité corporelle et mentale recule et par suite la chaleur de combustion diminue, ce qui a pour effet de réduire l'énergie disponible pour la pensée et l'action ainsi que les pertes de chaleur. L'attitude physique et psychique d'active devient passive et l'initiative personnelle fait place au besoin de sécurité.Le fait que différentes fonctions physiologiques telles que la croissance, la maturité, la résistance aux infections et la capacité de penser subissent de profondes modifications prouve qu'il s'agit de changements fondamentaux du metabolisme individuel. Lorsque la perte insuffisante de chaleur provoque une réduction de la chaleur de combustion dans les cellules de l'organisme, la croissance s'en trouve ralentie même si l'alimentation est abondante; le début de la puberté et de la maturité sexuelle est peu à peu retardé et la capacité de reproduction se trouve diminuée ou même complètement annihilée malgré l'appariement normal. La résistance à l'infection bactérienne diminue, surtout dans les cas d'infection des voies respiratoires pour lesquels les phagocytes forment la plus importante ligne de défense. Enfin la capacité de résoudre des problèmes d'ordre intellectuel est fortement réduite.Par contre la facilité pour le corps humain de perdre facilement sa chaleur a un effet contraire: croissance rapide, maturité précoce, fécondité élevée, vivacité intellectuelle et bonne défense contre les maladies infectieuses. Ces considérations ne sont pas du tout hypothétiques, mais se fondent sur des recherches statistiques portant sur l'homme ou sur des animaux placés dans des conditions parfaitement contrôlées; elles reposent sur des recherches faites en laboratoire reproduisant les différences climatiques normales ou en observant l'effet des grandes variations saisonnières des latitudes moyennes.Les différences climatiques de température résultant des écarts d'altitude ou de latitude sont donc des facteurs agissant puissamment sur la vie humaine; il en est de même des grandes variations thermiques saisonnières des latitudes moyennes. Les peuples privilégiés de la terre habitent les régions où l'organisme perd facilement son excès de chaleur. L'homme est en réalité la résultante des forces de son milieu; à un endroit celles-ci stimulent son énergie, tandis qu'à un autre elles le maintiennent dans l'apathie. On peut se demander si l'intelligence humaine trouve une issue à ce dilemme ou si elle réussit au moins à comprendre les forces agissantes et la signification de leurs effets.

     

Marine radar ocean wave retrieval’s dependency on range and azimuth

The strength of the surface wave signal in marine X-band radar (MR) images strongly depends on range and azimuth (i.e., the angle between antenna look and peak wave direction). Traditionally, MR wave analysis is carried out in a set of rectangular windows covering the radar field of view (FOV). The FOV is typically partially obstructed, e.g., due to the coastline or ship superstructures. Especially for ships that are subject to regular course changes, this results in an increased variability or error associated with wave parameters. Using MR measurements from R/P FLIP, acquired off California during the 2010 US Office of Naval Research (ONR) high resolution air–sea interaction (Hi-Res) experiment, this study quantifies the dependency of the radar-based 2D wave spectrum and parameters on range and azimuth. With the help of reference data from a nearby Datawell Waverider buoy, we propose empirical methods to remove the dependency and we illustrate their efficacy.     

Turbulent Airflow and Wave-Induced Stress Over the Ocean

We examine the structure of turbulent airflow over ocean waves. Based on an analysis of wind and wave observations derived from a moored and floating Air–Sea Interaction Spar buoy during the Shoaling Waves Experiment field campaign, we show that the cospectra of momentum flux for wind–sea conditions follow established universal scaling laws. Under swell-dominant conditions, the wave boundary layer is extended and the universal cospectral scaling breaks down, as demonstrated previously. On the other hand, the use of peak wave frequency to reproduce the universal cospectra successfully explains the structure of the turbulent flow field. We quantify the wave-coherent component of the airflow and this clarifies how ocean waves affect momentum transfer through the wave boundary layer. In fact, the estimated wave-induced stresses for swell-dominant conditions explain the anomalous cospectral shapes observed near the peak wave frequency.     

Dynamic response of flexible rockfall barriers under different loading geometries

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.     

A whistler study of plasmapause motion in the vicinity of sanae,Antarctica

For 4 months of synoptic records whistlers have been analyzed in two groups, high latitude (HL) whistlers with f_n?8 kHz and low latitude (LL) whistlers with f_n?8 kHz. A decrease in percentage occurrence of HL whistlers with increasing K_p is interpreted as being due to equatorwards movement of the plasmapause in the vicinity of SANAE, Antarctica (L=4). The diurnal variation in HL and LL whistler occurrence reveals an average behaviour of the plasmapause, namely, an equatorwards movement beginning at around 2000 LT followed by a return movement from 0400 LT to 0800 LT.     

Performance of ethylene-vinyl acetate foam as cushioning material for rigid debris-resisting barriers

This paper reports an investigation on the performance of ethylene-vinyl acetate (EVA) foam when used as a cushion layer for rigid barriers used to resist debris flow. Large-scale pendulum impact tests were conducted to study the effects of layer thickness on cushion performance under six successive impacts. Results show that for the first impact at 70 kJ, the peak contact force with the EVA foam thickness of 500 mm is about twice larger compared to that of 1000 mm. Results also reveal that the cushion mechanism of elastic collapse of cell walls in the EVA foam results in peak contact forces and maximum transmitted loads that are up to 30 and 50% lower compared to gabions for the first impact at 70 kJ, respectively. The elastic behavior of EVA foam provides consistent cushioning efficiency. Furthermore, EVA foam is found to be susceptible to degradation by ultraviolet light so that a suitable coating layer is required for outdoor use. Polyurea was identified as a suitable coating material and a small-scale coating trial was performed to confirm this. Findings presented in this paper will have direct implications on the future design of cushion layers for rigid barriers used to intercept debris flows.