Mechanics of tidally driven fractures in Europa's ice shell     

Sunwoong Lee  Nicholas C. Makris 《Icarus》2005,177(2):367-379

A fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden. It is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on Europa. Such penetration is found to be very unlikely in the absence of an ocean. A cycloidal crack would then form as a sequence of near instantaneous discrete failures, each extending roughly the brittle layer thickness in range, linked with a much lower apparent propagation speed set by the moving tidal stress field. The implications of this porous ice fracture model for ice-penetrating radar scattering loss and seismic activity are quantified.  相似文献   

Crustal and upper mantle structure in the Ryukyu Island Arc deduced from deep seismic sounding   总被引：4，自引：0，他引：4  

T. Iwasaki  N. Hirata  T. Kanazawa  J. Melles  K. Suyehiro  T. Urabe  L. Möller  J. Makris  H. Shimamura 《Geophysical Journal International》1990,102(3):631-651

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Stochastic tracking of mesoscale convective systems: evaluation in the West African Sahel     

Alexandros Makris  Clémentine Prieur  Théo Vischel  Guillaume Quantin  Thierry Lebel  Rémy Roca 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(2):681-691

In this work we apply a recently proposed Bayesian multiple target tracking model to mesoscale convective systems tracking. This stochastic model follows the multiple hypothesis tracking paradigm and can handle a varying number of targets while detecting the target birth, death, split, and merge events. The model is tested experimentally with real MCS targets detected from meteosat IR data over the Sahelian region. The performance of the stochastic tracking is evaluated by comparing it qualitatively and quantitatively with well established deterministic methods.  相似文献   

Dimensional analysis of the earthquake‐induced pounding between adjacent structures     

Elias Dimitrakopoulos  Nicos Makris  Andreas J. Kappos 《地震工程与结构动力学》2009,38(7):867-886

In this paper the dynamic response of two and three pounding oscillators subjected to pulse‐type excitations is revisited with dimensional analysis. Using Buckingham's Π‐theorem the number of variables that govern the response of the system is reduced by three. When the response is presented in the dimensionless Π‐terms remarkable order emerges. It is shown that regardless of the acceleration level and duration of the pulse all response spectra become self‐similar and follow a single master curve. This is true despite the realization of finite duration contacts with increasing durations as the excitation level increases. All physically realizable contacts (impacts, continuous contacts, and detachments) are captured via a linear complementarity approach. The study confirms the existence of three spectral regions. The response of the most flexible among the two oscillators amplifies in the low range of the frequency spectrum (flexible structures); whereas, the response of the most stiff among the two oscillators amplifies at the upper range of the frequency spectrum (stiff structures). Most importantly, the study shows that pounding structures such as colliding buildings or interacting bridge segments may be most vulnerable for excitations with frequencies very different from their natural eigenfrequencies. Finally, by applying the concept of intermediate asymptotics, the study unveils that the dimensionless response of two pounding oscillators follows a scaling law with respect to the mass ratio, or in mathematical terms, that the response exhibits an incomplete self‐similarity or self‐similarity of the second kind with respect to the mass ratio. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The eigenvalues of isolated bridges with transverse restraints at the end abutments     

Nicos Makris  Dimitra Angelopoulou 《地震工程与结构动力学》2010,39(8):869-886

This paper examines the eigenvalues of multi‐span seismically isolated bridges in which the transverse displacement of the deck at the end abutments is restricted. With this constraint the deck is fully isolated along the longitudinal direction, whereas along the transverse direction the deck is a simple‐supported beam at the end abutments which enjoys concentrated restoring forces from the isolation bearings at the center piers. For moderate long bridges, the first natural period of the bridge is the first longitudinal period, while the first transverse period is the second period, given that the flexural rigidity of the deck along the transverse direction shortens the isolation period offered by the bearings in that direction. This paper shows that for isolated bridges longer than a certain critical length, the first transverse period becomes longer than the first longitudinal period despite the presence of the flexural rigidity of the deck. This critical length depends on whether the bridge is isolated on elastomeric bearings or on spherical sliding bearings. This result is also predicted with established commercially available numerical codes only when several additional nodes are added along the beam elements which are modeling the deck in‐between the bridge piers. On the other hand, this result cannot be captured with the limiting idealization of a beam on continuous distributed springs (beam on Wrinkler foundation)—a finding that has practical significance in design and system identification studies. Finally, the paper shows that the normalized transverse eigenperiods of any finite‐span deck are self‐similar solutions that can be represented by a single master curve and are independent of the longitudinal isolation period or on whether the deck is supported on elastomeric or spherical sliding bearings. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

A study on the effects of the foundation compliance on the response of yielding structures using dimensional analysis     

Dimitris Pitilakis  Nicos Makris 《Bulletin of Earthquake Engineering》2010,8(6):1497-1514

The effects of the foundation compliance on the dynamic response of yielding systems are evaluated using rigorous dimensional analysis. To this end, a soil-foundation-structure system is subjected to strong ground motion and its seismic response is determined in terms of dimensionless parameters. The seismic demand of the system is calculated as a function of meaningful engineering parameters, such as the yielding acceleration and yielding displacement of the structure, the system mass and damping, as well as the dynamic characteristics of the foundation. It is proved that the seismic demand is strongly dependent on the foundation to excitation pulse predominant frequency ratio. For large values of yielding acceleration, the demand depends strongly on the yielding displacement and the mass. Moreover, there is a strength range where an increase in strength results in an increase in displacements—a counter intuitive situation. The larger the yielding displacement, the larger the seismic demand. Furthermore, the larger the foundation soil mass, the larger the seismic demand. Finally, an application of the procedure on an actual structure proves that soil-foundation-structure interaction (SFSI) is not always beneficial for the structure.  相似文献   

Response analysis of rigid structures rocking on viscoelastic foundation     

Alessandro Palmeri  Nicos Makris 《地震工程与结构动力学》2008,37(7):1039-1063

In this paper the rocking response of slender/rigid structures stepping on a viscoelastic foundation is revisited. The study examines in depth the motion of the system with a non‐linear analysis that complements the linear analysis presented in the past by other investigators. The non‐linear formulation combines the fully non‐linear equations of motion together with the impulse‐momentum equations during impacts. The study shows that the response of the rocking block depends on the size, shape and slenderness of the block, the stiffness and damping of the foundation and the energy loss during impact. The effect of the stiffness and damping of the foundation system along with the influence of the coefficient of restitution during impact is presented in rocking spectra in which the peak values of the response are compared with those of the rigid block rocking on a monolithic base. Various trends of the response are identified. For instance, less slender and smaller blocks have a tendency to separate easier, whereas the smaller the angle of slenderness, the less sensitive the response to the flexibility, damping and coefficient of restitution of the foundation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The existence of ‘complete similarities’ in the response of seismic isolated structures subjected to pulse‐like ground motions and their implications in analysis     

Nicos Makris  Michalis F. Vassiliou 《地震工程与结构动力学》2011,40(10):1103-1121

In this paper the seismic response of isolated structures supported on bearings with bilinear and trilinear behavior is revisited with dimensional analysis in an effort to better understand the relative significance of the various parameters that control the mechanical behavior of isolation systems. An isolation system that consists of lead rubber bearings or of single concave spherical sliding bearings exhibits bilinear behavior; whereas, when a double concave configuration is used the behavior is trilinear. For the case of bilinear behavior it is well known that the value of the normalized yield displacement is immaterial to the response of the isolated superstructure—or, in mathematical terms, that the response of the bilinear oscillator exhibits complete similarity in the dimensionless yield displacement. Similarly, for the case of trilinear behavior the paper shows that the presence of the intermediate slope is immaterial to the peak response of most isolated structures—a finding that shows the response of the trilinear oscillator exhibits a complete similarity in the difference between the coefficients of friction along the two sliding surfaces as well as in the ratio of the intermediate to the final slope. This finding implies that even when the coefficients of friction of the two sliding surfaces are different, the response of isolated structures for most practical configurations can be computed with confidence by replacing the double concave spherical bearings with single concave spherical bearings with an effective radius of curvature and an effective coefficient of friction. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Delineation of fluvial sediment architecture of subalpine riverine systems using noninvasive hydrogeophysical methods   总被引：2，自引：2，他引：0  

Daniel Altdorff  Jannis Epting  Jan van der Kruk  Peter Dietrich  Peter Huggenberger 《Environmental Earth Sciences》2013,69(2):633-644

River management and restoration measures are of increasing importance for integrated water resources management (IWRM) as well as for ecosystem services. However, often river management mainly considers engineering and construction aspects only and the hydrogeological settings as the properties and functions of ancient fluvial systems are neglected which often do not lead to the desired outcome. Knowledge of the distribution of sediment units could contribute to a more efficient restoration. In this study, we present two noninvasive approaches for delineation of fluvial sediment architecture that can form a basis for the restoration, particularly in areas where site disturbance is not permitted. We investigate the floodplain of a heavily modified low-mountain river in Switzerland using different hydrogeophysical methods. In the first approach, we use data from electromagnetic induction (EMI) with four different integral depths (0.75–6 m) and gamma-spectrometry as well as the elevation data as input for a K-means cluster algorithm. The generated cluster map of the surface combines the main characteristics from multilayered input data and delineates areas of varying soil properties. The resulting map provides an indication of areas with different sedimentary units. In the second approach, we develop a new iterative method for the generation of a geological structure model (GSM) by means of various EMI forward models. We vary the geological input parameters based on the measured data until the predicted EMI maps match the measured EMI values. Subsequently, we use the best matched input data for the GSM generation. The derived GSM provides a 3D delineation of possible ancient stream courses. A comparison with an independent ground penetrating radar (GPR) profile confirmed the delineations on the cluster map as well as the vertical changes of the GSM qualitatively. Thus, each of the approaches had the capacity for detecting sedimentary units with distinct hydraulic properties as an indication of former stream courses. The developed methodology presents a promising tool for the characterization of test sites with no additional subsurface information.  相似文献   

Climate change effects on the marine characteristics of the Aegean and Ionian Seas     

Christos Makris  Panagiota Galiatsatou  Konstantia Tolika  Christina Anagnostopoulou  Katerina Kombiadou  Panayotis Prinos  Kondylia Velikou  Zacharias Kapelonis  Elina Tragou  Yannis Androulidakis  Gerasimos Athanassoulis  Christos Vagenas  Ioannis Tegoulias  Vassilis Baltikas  Yannis Krestenitis  Theodoros Gerostathis  Kostantinos Belibassakis  Eugen Rusu 《Ocean Dynamics》2016,66(12):1603-1635

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