A survey on semisubmersible wind loads

The methods and assumptions of calculating wind drags and overturning moments on semisubmersible offshore drilling rigs are investigated. The empirical methods and the wind tunnel testing are compared.     

A comparative study of the design spectra defined by Eurocode 8, UBC, IBC and Turkish Earthquake Code on R/C sample buildings

Earthquake codes have been revised and updated depending on the improvements in the representation of ground motions, soils and structures. These revisions have been more frequently seen in recent years. One of the key changes in earthquake codes has been performed on the design spectra. In this paper, the design spectra recommended by Turkish Earthquake Code and three other well known codes (Uniform Building Code, Eurocode 8, and International Building Code) are considered for comparison. The main purpose of this study is to investigate the differences caused by the use of different codes in the dynamic analysis and seismic verification of given types of buildings located at code defined different sites. The differences in expressions and some important points for elastic and inelastic spectra defined by the codes are briefly illustrated in tables and figures. Periods, base shears, lateral displacements and interstory drifts for the analyzed buildings located at code defined ground type are comparatively presented.     

Parametrization of the precipitation in the Northern Hemisphere and its verification in Mexico

To improve results in monthly rainfall prediction, a parametrization of precipitation has been developed. The thermodynamic energy equation used in the Adem thermodynamic model (ATM) and the Clausius and Clapeyron equation, were used to obtain a linear parametrization of the precipitation anomalies as a function of the surface temperature and the 700 mb temperature anomalies. The observed rainfall in Mexico over 36 months, from January 1981 to December 1983, was compared with the results obtained of the heat released by condensation, which is proportional to precipitation, using our theoretical formula, and those obtained using a statistical formula, which was derived for the ATM using 12 years of hemispheric real data. The verification using our formula in Mexico, showed better results than the one using the statistical formula.     

Modelling the effect of an assumed cosmic ray-modulated global cloud cover on the terrestrial surface temperature

We have used the thermodynamic model of the climate to estimate the effect of variations in the oceanic cloud cover on the surface temperature of the Earth in the North Hemisphere (NH) during the period 1984–1990. We assume that the variations in the cloud cover are proportional to the variation of the cosmic ray flux measured during the same period. The results indicate that the effect in the temperature is slightly noticeable when we consider the surface hemispheric temperature on July 1987, finding an average temperature anomaly between −0.06°C and −0.14°C, along a latitudinal band between 20° and 40°. The surface temperature averaged globally in the NH presents a decrease of 0.01°C in average, which is almost the same for continents and oceans. However, these values are not significant when compared to the overall variability of the time series with and without forcing.     

Atomic oxygen distribution in the Venus mesosphere from observations of O2 infrared airglow by VIRTIS-Venus Express

This VIRTIS instrument on board Venus Express has collected spectrally resolved images of the Venus nightside limb that show the presence of the (0,0) band of the infrared atmospheric system of O₂ at 1.27 μm. The emission is produced by three-body recombination of oxygen atoms created by photodissociation of CO₂ on the dayside. It is consistently bright so that emission limb profiles can be extracted from the images. The vertical distribution of O₂() may be derived following Abel inversion of the radiance limb profiles. Assuming photochemical equilibrium, it is combined with the CO₂ vertical distribution to determine the atomic oxygen density. The uncertainties on the O density caused by the Abel inversion reach a few percent at the peak, increasing to about 50% near 120 km. We first analyze a case when the CO₂ density was derived from a stellar occultation observed with the SPICAV spectrometer simultaneously with an image of the O₂ limb airglow. In other cases, an average CO₂ profile deduced from a series of ultraviolet stellar occultations is used to derive the O profile, leading to uncertainties on the O density less than 30%. It is found that the maximum O density is generally located between 94 and 115 km with a mean value of 104 km. It ranges from less than 1×¹⁰¹¹ to about 5×¹⁰¹¹ cm⁻³ with a global mean of 2.2×¹⁰¹¹ cm⁻³. These values are in reasonable agreement with the VIRA midnight oxygen profile. The vertical O distribution is generally in good agreement with the oxygen profile calculated with a one-dimensional chemical-diffusive model. No statistical latitudinal dependence of the altitude of the oxygen peak is observed, but the maximum O density tends to decrease with increasing northern latitudes. The latitudinal distribution at a given time exhibits large variations in the O density profile and its vertical structure. The vertical oxygen distribution frequently shows multiple peaks possibly caused by waves or variations in the structure of turbulent transport. It is concluded that the O₂ infrared night airglow is a powerful tool to map the distribution of atomic oxygen in the mesosphere between 90 and 115 km and improve future Venus reference atmosphere models.     

Geological Modeling of Gold Deposit Based on Grade Domaining Using Plurigaussian Simulation Technique

Mineral resource evaluation requires defining grade domains of an ore deposit. Common practice in mineral resource estimation consists of partitioning the ore body into several grade domains before the geostatistical modeling and estimation at unsampled locations. Many ore deposits are made up of different mineralogical ensembles such as oxide and sulfide zone: being able to model the spatial layout of the different grades is vital to good mine planning and management. This study addresses the application of the plurigaussian simulation to Sivas (Turkey) gold deposits for constructing grade domain models that reproduce the contacts between different grade domains in accordance with geologist’s interpretation. The method is based on the relationship between indicator variables from grade distributions on the Gaussian random functions chosen to represent them. Geological knowledge is incorporated into the model by the definition of the indicator variables, their truncation strategy, and the grade domain proportions. The advantages of the plurigaussian simulation are exhibited through the case study. The results indicated that the processes are seen to respect reproducing complex geometrical grades of an ore deposit by means of simulating several grade domains with different spatial structure and taking into account their global proportions. The proposed proportion model proves as simple to use in resource estimation, to account for spatial variations of the grade characteristics and their distribution across the studied area, and for the uncertainty in the grade domain proportions. The simulated models can also be incorporated into mine planning and scheduling.     

Investigation of dynamic response of masonry minaret structures

Almost all historical minarets in Turkey were constructed using cut stone, masonry blocks or combination of these two materials. The structural and geometrical properties of each masonry minaret, or slender tower structure, depend on many factors including the structural knowledge and applications at the time of construction, experience of the architect or engineer, seismicity of the region, and availability of construction materials in that area. Recent earthquakes in Turkey have shown that most masonry minarets in high seismic regions are vulnerable to structural damage and collapse. In this study, in order to investigate the dynamic behavior of historical unreinforced masonry minarets, three representative minarets with 20, 25, and 30 m height were modeled and analyzed using two ground motions recorded during the 1999 Kocaeli and Duzce, Turkey earthquakes. The modal analyses of the models have shown that the structural periods and the overall structural response are influenced by the minaret height and spectral characteristics of the input motion. The dynamic displacement and axial stress time histories are computed at the critical points on the minarets. During recent earthquakes, most minaret failures occurred above the base of the structure. Consistent with the observed response, the largest stresses were calculated at the same location.     

Strategies for Successful ANAMMOX Enrichment at Laboratory Scale

Studies on anaerobic ammonium oxidation (ANAMMOX) have been increasing due to its advantages over traditional nitrification–denitrification systems. However, long and difficult start‐up periods of ANAMMOX reactors may sometimes be frustrating for researchers dealing with them first time in the lab. Therefore, a guide for starting up ANAMMOX reactors will greatly help them and enhance the use of this technology. Three trials, each has three reactors, have been carried out to reach successful start up in this study. An expected ANAMMOX enrichment could not be achieved in the first and second trials. Under the light of the experiences gained from the unsuccessful ones, the third trial resulted in >95% ammonium removals within 20–50 days. It is possible to startup or to enrich ANAMMOX reactors within 50 days by presented strategy guide.