Analytical and experimental investigation on vibrating rectangular plates with two opposite free edges and internal supports while the remaining are elastically restrained against rotation

This paper deals with the determination of an approximate fundamental frequency equation for a rectangular plate with two edges (y = 0, b) elastically restrained against rotation while the edges x=0, a are free but internal supports parallel to the free edges are present in the structural system. The algorithmic procedure can be easily implemented on a micro computer or even a hand, programmable calculator.Good engineering agreement with experimental results is shown to exist in the case of a plate with edges y=0,b rigidly clamped.     

Vibrations of a simply supported plate carrying an elastically mounted concentrated mass

A large number of papers and technical reports are available on the technically important problem of structural elements executing transverse vibrations and carrying concentrated masses. In general it is assumed that the attachment is perfectly rigid. On the other hand, a rather limited amount of published work is available when the mass is elastically connected to the structure. The system then exhibits a more complex behavior than in the case of rigid attachment. The present study deals with the solution of the title problem using the well-known normal mode, sinusoidal eigenfunction expansions.     

Resistance of Lophelia pertusa to coverage by sediment and petroleum drill cuttings

In laboratory experiments, the cold-water coral Lophelia pertusa was exposed to settling particles. The effects of reef sediment, petroleum drill cuttings and a mix of both, on the development of anoxia at the coral surface were studied using O₂, pH and H₂S microsensors and by assessing coral polyp mortality. Due to the branching morphology of L. pertusa and the release of coral mucus, accumulation rates of settling material on coral branches were low. Microsensors detected H₂S production in only a few samples, and sulfate reduction rates of natural reef sediment slurries were low (<0.3 nmol S cm⁻³ d⁻¹). While the exposure to sediment clearly reduced the coral’s accessibility to oxygen, L. pertusa tolerated both partial low-oxygen and anoxic conditions without any visible detrimental short-term effect, such as tissue damage or death. However, complete burial of coral branches for >24 h in reef sediment resulted in suffocation.     

Eddy covariance imaging of diffuse volcanic CO<Subscript>2</Subscript> emissions at Mammoth Mountain,CA, USA

Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO₂ fluxes and quantify CO₂ emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO₂ flux were made during September–October 2010 and ranged from 85 to 1,766 g m⁻² day⁻¹. Comparative maps of soil CO₂ flux were simulated and CO₂ emission rates estimated from three accumulation chamber (AC) CO₂ flux surveys. Least-squares inversion of measured eddy covariance CO₂ fluxes and corresponding modeled source weight functions recovered 58–77% of the CO₂ emission rates estimated based on simulated AC soil CO₂ fluxes. Spatial distributions of modeled surface CO₂ fluxes based on EC and AC observations showed moderate to good correspondence (R ² = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO₂ emissions over relatively large areas.     

Representing Grounding Line Dynamics in Numerical Ice Sheet Models: Recent Advances and Outlook

Recent satellite observations of the Antarctic and Greenland ice sheets show accelerated ice flow and associated ice sheet thinning along coastal outlet glaciers in contact with the ocean. Both processes are the result of grounding line retreat due to melting at the grounding line (the grounding line is the contact of the ice sheet with the ocean, where it starts to float and forms an ice shelf or ice tongue). Such rapid ice loss is not yet included in large-scale ice sheet models used for IPCC projections, as most of the complex processes are poorly understood. Here we report on the state-of-the art of grounding line migration in marine ice sheets and address different ways in which grounding line migration can be attributed and represented in ice sheet models. Using one-dimensional ice flow models of the ice sheet/ice shelf system we carried out a number of sensitivity experiments with different spatial resolutions and stress approximations. These are verified with semi-analytical steady state solutions. Results show that, in large-scale finite-difference models, grounding line migration is dependent on the numerical treatment (e.g. staggered/non-staggered grid) and the level of physics involved (e.g. shallow-ice/shallow-shelf approximation).     

Using Diurnal Temperature Signals to Infer Vertical Groundwater‐Surface Water Exchange

Heat is a powerful tracer to quantify fluid exchange between surface water and groundwater. Temperature time series can be used to estimate pore water fluid flux, and techniques can be employed to extend these estimates to produce detailed plan‐view flux maps. Key advantages of heat tracing include cost‐effective sensors and ease of data collection and interpretation, without the need for expensive and time‐consuming laboratory analyses or induced tracers. While the collection of temperature data in saturated sediments is relatively straightforward, several factors influence the reliability of flux estimates that are based on time series analysis (diurnal signals) of recorded temperatures. Sensor resolution and deployment are particularly important in obtaining robust flux estimates in upwelling conditions. Also, processing temperature time series data involves a sequence of complex steps, including filtering temperature signals, selection of appropriate thermal parameters, and selection of the optimal analytical solution for modeling. This review provides a synthesis of heat tracing using diurnal temperature oscillations, including details on optimal sensor selection and deployment, data processing, model parameterization, and an overview of computing tools available. Recent advances in diurnal temperature methods also provide the opportunity to determine local saturated thermal diffusivity, which can improve the accuracy of fluid flux modeling and sensor spacing, which is related to streambed scour and deposition. These parameters can also be used to determine the reliability of flux estimates from the use of heat as a tracer.     

Shaking‐table tests of flat‐bottom circular silos containing grain‐like material

According to Eurocode 8, the seismic design of flat‐bottom circular silos containing grain‐like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents. Copyright © 2015 John Wiley & Sons, Ltd.     

Deformability characteristics of brazilian laterites

This paper summarizes the resilient and permanent deformation characteristics of laterite gravels, determined by cyclic loading in triaxial tests of compacted specimens. A study of laterite pavements was carried out on eight paved road sections in the state of Mato Grosso. Also reported is the influence of fine sand admixture, specimen size and soaking in two laterite samples from Roraima and Rondônia in the North of Brazil. The experimental relationships of resilient moduli against applied stresses are interpreted empirically for models what may be incorporated in a structural analysis of full depth of laterite pavement.     

Roughness control on hydraulic conductivity in fractured rocks

The influence of joint roughness on the typologies of fluid flow inside fractures is well known and, thanks to experiences in the field of hydraulics, it has been studied from both a physical and mathematical point of view. Nevertheless, the formulations adopted by traditional hydraulic models are hardly applicable in the geological field, because of the difficulty encountered in the roughness parameter estimation. Normally this parameter can be estimated using the joint roughness coefficient (JRC), which considers both the asperity height and its regularity and directional trend. The main advantage in using the JRC arises from the fact that it can easily be obtained from geological-technical surveys and from comparison with the standard Barton profiles. Some relationships have been built up that allow for the estimation of the hydraulic conductivity tensor (an essential parameter for understanding water flow in fractured rock masses), not only as a function of traditional parameters like aperture, spacing, dip and dip direction, etc., but also of joint roughness, precisely expressed in terms of the roughness coefficient. These relationships have been studied initially from a theoretical point of view and then practically, through laboratory investigations.

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Resumen  Se conoce muy bien la influencia de la rugosidad de las grietas en las tipologías del flujo de fluidos a lo interior de las fracturas y gracias a las experiencias en el campo de hidráulica ha sido posible estudiarla desde puntos de vista matemáticos y físicos. Sin embargo, las formulaciones adoptadas por los modelos hidráulicos tradicionales tienen poca aplicabilidad en el campo geológico debido a la dificultad relacionada con la estimación del parámetro de rugosidad. Normalmente este parámetro puede estimarse usando el coeficiente de rugosidad de grieta (JRC) el cual considera tanto la altura de la aspereza como su regularidad y tendencia direccional. La principal ventaja de utilizar el JRC se deriva del hecho que puede obtenerse fácilmente de levantamientos técnico-geológicos y de la comparación con los perfiles Standard Barton. Se han construido algunas relaciones que permiten la estimación del tensor de conductividad hidráulica (un parámetro esencial para el entendimiento del flujo de agua en masas de roca fracturadas), no solo en función de parámetros tradicionales como apertura, espaciado, buzamiento y dirección de buzamiento, etc., sino también en función de la rugosidad de la grieta estimada con precisión en términos del coeficiente de rugosidad. Estas relaciones se han estudiado inicialmente desde un punto de vista teórico y luego de modo práctico a través de investigaciones de laboratorio.

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Résumé  L’influence de la rugosité des joints sur les types d’écoulement de fluide dans les fractures est bien connue et a été étudiée aussi bien du point de vue physique que mathématique grace à des expériences menées dans le domaine de l’hydraulique. Cependant les formulations adoptées dans les modèles hydrauliques traditionnels sont difficilement applicables dans le domaine de la géologie à cause de la difficulté rencontrée pour estimer la rugosité. Ce paramètre peut normalement être apprécié grace au coefficient de rugosité du joint (JRC), lequel prend en compte à la fois la hauteur de l’aspérité ainsi que sa régularité et sa direction. Le principal avantage dans l’utilisation du JRC réside dans le fait qu’il peut facilement être obtenu à partir d’études techniques-géologiques et par comparaison avec la classification de Barton. Des relations qui permettent une estimation du tenseur de conductivité hydraulique (un paramètre essentiel pour comprendre l’écoulement de l’eau dans les masses rocheuses fracturées) ont été élaborées, pas seulement en fonction de paramètres traditionnels tels que l’ouverture, l’espacement, l’inclinaison et la direction d’inclinaison, etc , mais aussi en prenant en compte la rugosité des joints à travers le coefficient de rugosité. Ces relations ont initialement été étudiées d’un point de vue théorique puis expérimentalement à travers des recherches en laboratoire.

     

Correction to: Cultural heritage and earthquakes: bridging the gap between geophysics,archaeoseismology and engineering

Journal of Seismology -