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Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2006,163(8):1699-1735
This is the first paper in a two-part series on the implementation of Godunov-type schemes on unstructured grids for atmospheric
flow simulations. Construction of a high-resolution flow solver for the scalar transport equation is described in detail.
Higher-order accuracy in space is achieved via a MUSCL-type gradient reconstruction after van Leer and the monotonicity of solution is enforced by slope limiters. Accuracy
in time is maintained by implementing a multi-stage explicit Runge-Kutta time-marching algorithm. The scheme is conservative
and exhibits minimal numerical dispersion and diffusion. Five different benchmark test cases are simulated for the validation
of the numerical scheme. 相似文献
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A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations
Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2007,164(1):217-244
In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique
approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the
numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These
finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus
avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical
quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured
adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate
Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved
via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for
maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion.
The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are
cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can
resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for
an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset
of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without
using explicit filtering for numerical stability. 相似文献
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This paper presents a probable isostatic model of the East Anatolian Region, which lies in a belt of significant plate movements.
Probable locations of the horizontal and vertical discontinuities in the crust structure were determined using the normalized
full gradient (NFG) method. For the purpose of explaining the mechanism that supports topography corresponding to the crust
thickness in the region, calculations of effective elastic thickness (T
e) were carried out initially by utilizing admittance and misfit functions. According to these results, the effective elastic
thickness value obtained was less than the crust thickness, even though the isostatic model does not conform with the Airy
model. Consequently, it was assumed that there could be problems beneath the crust. Hence, the NFG method was applied on
the Bouguer gravity data of the region in order to investigate probable discontinuities in the crust structure. According
to the NFG results, vertical structural transitions were observed at a depth ranging between 10 and 30 km, which begin immediately
north of the Bitlis Zagros Suture Zone (BZSZ) and continue in a northerly direction. The relationship between the effective
elastic thickness (T
e; 13 km in average as determined in the last stage), and the seismogenic zone in the region was investigated. If the T
e value happens to be less then the crustal thickness, then one can say that there are problems in the crustal structure of
the region similar to Eastern Anatolia. Indeed, when NFG results of the study area are examined, numerous vertical and horizontal
discontinuities in the crust can be observed. These discontinuities, which correspond to low Bouguer gravity anomalies and
shallow focal depth-earthquakes, are probably the source of the factors which rule the tectonic mechanism of the region. 相似文献
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Gksu Delta is an important wetland where the Gksu River reaches to sea in the eastern of the town Tasucu-Ice1. The delta is classified as a Wetland of International Impor-tance according to the Ramsar Convention on Wetlands of International Importance. The amount of fertilizers used in this area was 7200 tons in 2006. These pollutants affect the surface and groundwater quality negatively. The intensively used fertilizers and pesticides contain not only N- and P compounds but also some heavy metals. The contents of all pol-lutants in surface waters were determined for four different seasons between 2006 and 2008 and with these data a Geographic Information System (GIS) has been constructed by using Map Info. From the photometric heavy metal analysis, it is inferred that the excess concen-tration of Fe, Ni, Mn, Mo and Cu at some locations is the cause of undesirable quality for drinking purposes. The source of excess concentration of various heavy metals is the agri-cultural activities and fertilizers. It is determined that in all periods between 2006 and 2008 the heavy metals and other pollutants in the fertilizers and pesticides transported easily to river water with irrigation return flow. The organic pollutants, including COD, BOD, NH3 and NO3 followed the sharply increasing trends from Silifke city to Mediterranean Sea. The water quality of Gksu River is modeled and determined that the waste water discharge of 10,700 m3/day from Silifke city does not create a serious problem because of the high amount of flow rate of Gksu River. 相似文献
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Sedat İnan Kadriye Ertekin Cemil Seyis Şakir Şimşek Furkan Kulak Aynur Dikbaş Onur Tan Semih Ergintav Rahşan Çakmak Ahmet Yörük Muhiddin Çergel Hakan Yakan Hüseyin Karakuş Ruhi Saatçilar Zafer Akçiğ Yıldız İravul Bekir Tüzel 《Acta Geophysica》2010,58(5):767-813
Warm and hot spring water as well as soil gas radon release patterns have been monitored in the Aegean Extensional Province of Western Turkey, alongside regional seismic events, providing a multi-disciplinary approach. In the study period of 20 months, seven moderate earthquakes with M L between 4.0 and 4.7 occurred in this seismically very active region; two earthquakes with magnitude 5.0 also occurred near the study area. Seismic monitoring showed no foreshock activity. By contrast, hydro-geochemical anomalies were found prior to these seismic events, each lasting for weeks. The anomalies occurred foremost in conjunction with dip-slip events and seem to support the dilatancy and water diffusion hypothesis. Increased soil gas radon release was recorded before earthquakes associated with strike-slip faults, but no soil radon anomalies were seen before earthquakes associated with dip-slip faults. Geochemical anomalies were also noticeably absent at some springs throughout the postulated deformation zones of impending earthquakes. The reason for this discrepancy might be due to stress/strain anisotropies. 相似文献
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First insights into the demography of the rare gorgonian Spinimuricea klavereni in the Mediterranean Sea 
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下载免费PDF全文 We present the results of the first study to highlight the demography, morphometry and growth rates of Spinimuricea klavereni, a rare Mediterranean endemic gorgonian exceptionally common in shallow depths of the Northeast Marmara Sea. In the study area, this species forms vast populations on rocks, boulders and attached to pebbles/stones/shells on soft substrates between 20 and 45 m depth, with a total average density of 0.3 colonies·m?2 but comprising patches up to 3 colonies·m?2. Colonies, which are on average 42.9 (±20.1) cm in height, can reach up to 110 cm. Unlike other Mediterranean gorgonians, the colonies studied here showed fast growth rates that decreased with increasing colony height, between 1.5–11.1 and 4.96 ± 3.01 cm·year?1 on average. The low necrosis and high growth rates displayed by this species in the Northeast Marmara Sea confirm the previously hypothesized opportunistic behaviour of the species. The unique community consisting of S. klavereni and other rare gorgonian/soft corals has limited distribution in this area and should be considered to be a vulnerable marine ecosystem. Therefore we recommend that some conservation measures are taken, including the prohibition of all fisheries and anchoring over these assemblages. 相似文献
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Oya Ankaya Pamukçu Zafer Akçığ Şevket Demirbaş Ekrem Zor 《Pure and Applied Geophysics》2007,164(11):2345-2358
The tectonic regime of Eastern Anatolia is determined by the Arabia-Eurasia continent-continent collision. Several dynamic
models have been proposed to characterize the collision zone and its geodynamic structure. In this study, change in crustal
thickness has been investigated using gravity, magnetic and topographic data of the region. In the first stage, two-dimensional
low-pass filter and upward analytical continuation techniques were applied to the Bouguer gravity data of the region to investigate
the behavior of the regional gravity anomalies. Next the moving window power spectrum method was used, and changes in the
probable structural depths from 38 to 52 km were determined. The changes in crustal thickness where free air gravity and magnetic
data have inversely correlated and the type of the anomaly resources were investigated applying the Euler deconvolution method
to Bouguer gravity data. The obtained depth values are consistent with the results obtained using the power spectrum method.
It was determined that the types of anomaly resources are different in the west and east of the 40° E longitude. Finally,
using the obtained findings from this study and seismic velocity models proposed for this region by previous studies, a probable
two-dimensional crust model was constituted. 相似文献