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   

Turbulence in vegetated flows: Volume-average analysis and modelling aspects     

Dimitris Souliotis  Panagiotis Prinos 《Acta Geophysica》2008,56(3):894-917

Two approaches for the modelling of turbulence in vegetated flows have been developed in the past. The “microscopic” approach which is straightforward but limited to simple cases and the “macroscopic” approach which is based on Volume Average Theory (VAT). In this study, aspects of Volume-Average (VA) analysis and modelling are investigated for turbulent vegetated flow using computed three-dimensional results from the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations around a representative vegetal element. In particular (a) the VA transport equations for k and ε, based on VAT, are properly derived, (b) the Boussinesq hypothesis for the VA quantities, employed in 〈k〉-〈ε〉 turbulence models is tested, and (c) the values of the coefficients used in such turbulence models are assessed in comparison with those used in the classical turbulence models.  相似文献   

Topological statistics and the liquid-mirror telescope galaxy redshift project     

Dimitris Mitsouras  Robert Brandenberger  Paul Hickson 《Monthly notices of the Royal Astronomical Society》1999,305(1):19-27

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Microseismicity and focal mechanisms at the western termination of the North Anatolian Fault and their implications for continental tectonics   总被引：4，自引：0，他引：4  

Denis Hatzfeld  Maria Ziazia  Despina Kementzetzidou  Panayotis Hatzidimitriou  Dimitris Panagiotopoulos  Kostas Makropoulos  Panayotis Papadimitriou  & Anne Deschamps 《Geophysical Journal International》1999,137(3):891-908

For seven weeks, a temporary network of 68 seismological stations was operated in Central Greece, in the region of Thessaly and Evia, located at the western termination of the North Anatolian Fault system. We recorded 510 earthquakes and computed 80 focal mechanisms. Seismic activity is associated with the NE–SW dextral North Aegean Fault, or with very young E–W-striking normal faults that are located around the Gulf of Volos and the Gulf of Lamia. The important NW–SE-striking faults bounding the Pilion, or the basins of Larissa and Karditsa, are not seismically active, suggesting that it is easier to break continental crust, creating new faults perpendicular to the principal stresses, than to reactivate faults that strike obliquely to the principal stress axes  相似文献   

Study of the air-earth electrical current density in Athens     

Dimitris A. Retalis 《Pure and Applied Geophysics》1991,136(2-3):217-233

In the present study, we examine the daily and annual variation of the air-earth current density in Athens for all weather as well as for fair weather for a 16-year period 1965–1980.The daily variation of the air-earth current density has a definite bimodal form while the annual variation has no definitive form but simply reaches its larger values during the summer months. There has also been a Fourier analysis of the daily variation.Furthermore, and for a 3-year period 1968–70, we present the mean daily and annual variation of the electric field, air-earth current density and total conductivity of the air. Based on these parameters we have estimated the conduction and the convection current and we have correlated them to the total (measured) current. In addition, we have estimated the values of the parameter, in order to test the fulfillment of Ohm's law in atmosphere.  相似文献   

Surface tension effects on energy dissipation by small scale,experimental breaking waves     

Dimitris Stagonas  David Warbrick  Gerald Muller  Davide Magagna 《Coastal Engineering》2011

Much of the existing knowledge about breaking waves comes from physical model experiments scaled using Froude's law. A widely held assumption is that surface tension effects are not significant at typical laboratory scales and specifically for waves longer than 2 m. Since, however, smaller wavelengths are not untypical in small to medium scale laboratory facilities, a consideration of surface tension effects is indeed important. Although some emphasis has been given in the past, little is known regarding the importance of surface tension following impingement of the breaking-wave crest and especially on the overall energy dissipation by laboratory breaking waves.  相似文献   

Meta-analysis of electron cyclotron resonance absorption features detected in high-mass X-ray binaries     

Dimitris M.Christodoulou  Silas G.T.Laycock  Demosthenes Kazanas 《天文和天体物理学研究(英文版)》2019,(10)

Using recent compilations of detailed X-ray observations and spectral models of exceptional quality, we record the electron cyclotron resonance absorption(ECRA) features that have been detected in 45 pulsating high-mass X-ray binaries(HMXBs) and ultraluminous X-ray(ULX) sources harboring neutron stars, although seven of these detections are still questionable and another 21 are single and/or not independently confirmed. From the comprehensive catalogs of Jaisawal Naik and Staubert et al.and from several additional recent observations, we produce two lists of HMXB ECRA sources: a list of 17 sources in which multiple ECRA lines or single very low-energy lines are seen, in which we can reasonably assume that the lowest energy reveals the fundamental cyclotron level for each source; and a"contaminated" list of 38 sources including the 21 detections of single ECRA lines that may(not) be higherlevel harmonics. Both lists confirm a previous result that we have obtained independently by modeling the propeller lines of Magellanic HMXB pulsars: the surface dipolar magnetic fields B*of HMXB neutron stars are segregated around five distinct values with B*= 0.28 ± 0.08, 0.55 ± 0.11, 1.3 ± 0.37, 3.0 ± 0.68 and 7.9 ± 3.1, in units of TG. However, an explanation of this phenomenon is currently lacking. We have found no correlation between these B*values and the corresponding observed spin periods, spin period derivatives, orbital periods, maximum X-ray luminosities, neutron star masses or companion star masses.  相似文献   

A striking confluence between theory and observations of high-mass X-ray binary pulsars     

Dimitris M.Christodoulou  Silas G.T.Laycock  Demosthenes Kazanas 《天文和天体物理学研究(英文版)》2018,(10)

We analyze the most powerful X-ray outbursts from neutron stars in eleven Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray sources. Most of the outbursts rise to L_(max) which is about the level of the Eddington luminosity, while the remaining more powerful outbursts also appear to recognize that limit when their emissions are assumed to be anisotropic and beamed toward our direction. We use the measurements of pulsar spin periods P_S and their derivatives P_S to calculate the X-ray luminosities L_p in their faintest accreting("propeller-line") states. In five cases with unknown P_S, we use the lowest observed X-ray luminosities, which only adds to the heterogeneity of the sample. Then we calculate the ratios L_p/L_(max) and we obtain an outstanding confluence of theory and observations from which we conclude that work done on both fronts is accurate and the results are trustworthy: sources known to reside on the lowest Magellanic propeller line are all located on/near that line, whereas other sources jump higher and reach higher-lying propeller lines. These jumps can be interpreted in only one way, higher-lying pulsars have stronger surface magnetic fields in agreement with previous empirical results in whichP_S and L_p values were not used.  相似文献   

Epistemic uncertainty assessment using Incremental Dynamic Analysis and Neural Networks     

Dimitris G. Giovanis  Michalis Fragiadakis  Vissarion Papadopoulos 《Bulletin of Earthquake Engineering》2016,14(2):529-547

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The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation     

Dimitris Stamatellos  Anthony P. Whitworth 《Monthly notices of the Royal Astronomical Society》2009,392(1):413-427

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