Local scour prediction around piers with complex geometry     

Ata Amini  Thamer Ahmed Mohammad 《Marine Georesources & Geotechnology》2017,35(6):857-864

A laboratory study of local scour at complex piers under steady clear-water conditions is presented. The term complex piers is used to define a bridge pier comprising of a column, pile cap, and pile group. Comprehensive data over the full range of possible pile cap elevations for complex piers with different geometries were obtained using five complex pier models, which were scaled down from existing bridges in Malaysia. The data are used to evaluate existing methodologies for characterizing the effective width of complex piers with varying pile cap location relative to the undisturbed streambed. The effect of pile cap location on scour depth is also addressed. To improve the predictions of local scour at complex piers, the new data and some previous data are used to propose a new method to predict local scour depth at complex piers.  相似文献   

Flare Index During the Rising Phase of Solar Cycle 23   总被引：1，自引：0，他引：1  

Ataç  Tamer  Özgüç  Atila 《Solar physics》2001,198(2):399-407

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Study of desaturation and resaturation in brittle rock with anisotropic damage   总被引：1，自引：0，他引：1  

J.F. Shao  N. Ata 《Engineering Geology》2005,81(3):341-352

This paper deals with numerical modelling of anisotropic damage induced by desaturation and resaturation processes in a brittle rock. This study is conducted in the framework of geological barrier safety analysis for deep disposal of nuclear waste. A non-linear poroelastic model coupled with anisotropic damage is proposed for constitutive modelling of unsaturated rock. A fully coupled FEM method is used for modelling of hydromechanical coupling problems. Instantaneous phase change without dissipation between water liquid phase and vapour is included. Parametric studies are performed to investigate influences of main factors involved in such processes. Rock damage induced by excavation, desaturation and resaturation is evaluated. Finally, we analyse the importance of taking into account the correlation between induced damage and rock permeability.  相似文献   

Locational analysis of slums and the effects of slum dweller’s activities on the social,economic and ecological facets of the city: insights from Kumasi in Ghana     

Takyi  Stephen Appiah  Amponsah  Owusu  Yeboah  Ata Senior  Mantey  Emmanuel 《GeoJournal》2021,86(6):2467-2481

GeoJournal - Slum development has become a major urban planning and management problem due to the challenges they pose to the larger urban environment. Activities of slum dwellers are...  相似文献   

The variability of foF2 in different phases of solar cycle 23   总被引：1，自引：0，他引：1  

Tamer Ataç  Atila Özgüç  Rıza Pektaş 《Journal of Atmospheric and Solar》2009,71(5):583-588

In this paper we examined the variations of the foF2 with solar activity for different local time and different seasons. Beside this we evaluated International Reference Ionosphere (IRI) models at different phases of solar cycle 23, different latitudes and different local time. We studied F2 layer critical frequency (foF2) of the ionosphere by using the flare index calculated by the Kandilli Observatory. For this purpose, we identified the months similar with high flare activity during the solar cycle 23. We chose 6 months which represented the different phases (ascending branch, maximum and descending branch) of the solar cycle. We also took into account the fact that these months were in different seasons. The hourly monthly means of observed foF2 data from four ionosonde stations for 6 months were calculated. On the other hand, the identical foF2 values of the same months were calculated for the year 1996, which is the minimum year of the previous solar activity cycle. We subtracted the foF2 values of 1996 from the values of the selected months of the last solar cycle to obtain the residuals, Δ(foF2). Then the magnitude of the residuals is compared through the cycle. We used IRI-2007 as well as IRI-2001 models to see the degree of deviation of the observed results from the predicted ones. We found that the predicted values of the ΔfoF2, which are calculated by the IRI-2007, fitted well with the observed Δ(foF2) and showed that the Δ(foF2) are dependent on the solar cycle variations in general.  相似文献   

The 2014 seismic hazard model of the Middle East: overview and results     

Karin Şeşetyan  Laurentiu Danciu  Mine B. Demircioğlu Tümsa  Domenico Giardini  Mustafa Erdik  Sinan Akkar  Levent Gülen  Mehdi Zare  Shota Adamia  Anooshiravan Ansari  Avetis Arakelyan  Ayşegül Askan  Mher Avanesyan  Hektor Babayan  Tamaz Chelidze  Raffi Durgaryan  Ata Elias  Hossein Hamzehloo  Khaled Hessami  Doğan Kalafat  Özkan Kale  Arkady Karakhanyan  Muhammad Asif Khan  Tahir Mammadli  Mahmood Al-Qaryouti  Mohammad Sayab  Nino Tsereteli  Murat Utkucu  Otar Varazanashvili  Muhammad Waseem  Hilal Yalçın  Mustafa Tolga Yılmaz 《Bulletin of Earthquake Engineering》2018,16(8):3535-3566

The Earthquake Model of Middle East (EMME) Project aimed to develop regional scale seismic hazard and risk models uniformly throughout a region extending from the Eastern Mediterranean in the west to the Himalayas in the east and from the Gulf of Oman in the south to the Greater Caucasus in the North; a region which has been continuously devastated by large earthquakes throughout the history. The 2014 Seismic Hazard Model of Middle East (EMME-SHM14) was developed with the contribution of several institutions from ten countries. The present paper summarizes the efforts towards building a homogeneous seismic hazard model of the region and highlights some of the main results of this model. An important aim of the project was to transparently communicate the data and methods used and to obtain reproducible results. By doing so, the use of the model and results will be accessible by a wide community, further support the mitigation of seismic risks in the region and facilitate future improvements to the seismic hazard model. To this end all data, results and methods used are made available through the web-portal of the European Facilities for Earthquake Hazard and Risk (www.efehr.org).  相似文献   

3D numerical simulation of flow field around twin piles     

Ata Amini  Akram Asadi Parto 《Acta Geophysica》2017,65(6):1243-1251

In this study to identify the flow pattern and local scour mechanism around pile groups, the flow field was simulated using FLOW-3D software. A pair of pile on a flat-bed channel with side by side and tandem arrangements was investigated. To establish Navier–Stokes equations, the RNGk-ε turbulence model was used and the results were verified using experimental data. In case of FLOW-3D capability, it was found that the software was able to properly simulate the expected interaction between the pile groups. The results of flow field simulation showed that Reynolds number and the pile spacing are the most influential variables in forming vortices. The flow around tandem pile and the downward flow around wake vortices were more intense and complicate in comparison with side by side arrangements and single pile.  相似文献   

Geohazards analysis of Pisa tunnel in a fractured incompetent rocks in Zagros Mountains, Iran     

Hojjat Ollah Safari  Saeid Pirasteh  Biswajeet Pradhan  Hossein Amid 《Arabian Journal of Geosciences》2013,6(4):1101-1112

The Pisa 2 tunnel with 740 m in length and 20° N trend is located along the Kazerun fault zone in Simply Folded Belt of Zagros, Iran. This tunnel has been excavated in the fractured incompetent marl layers with high expansive pressure of up to 2 kg/cm². In this study, the geological hazards along the tunnel have been recognized and categorized. This study revealed that, in the long-term usage of the tunnel, the lining did not endure against the loading and the secondary leakages. It is mainly attributed due to the non-efficiencies of drainage and isolation systems in the tunnel site. Therefore, it caused asphalt damage, drainage damage, and wall distortion. FLAC^3D software has been used in this research. We conducted various analyses for pre-excavation stress states, syn-excavation, and post-excavation strain states. The results showed no indication of instability and critical deformations during the excavation time. It also revealed that due to the non-efficiencies of drainage and isolation systems against secondary leakages and consequently marl expansion, the volumetric and shear strains (i.e., expansions and displacements) have exceeded from the critical states of strain along the tunnel. For various remedy purpose, this paper attempted several measures that can be taken in order to modify the drainage and isolation systems along the tunnel area. The reconstruction of drainage systems with suitable reinforced concrete and adequate slope has been proposed. The width of channel and isolation of backside of lining and implementation of multi-order outlets (i.e., backside of lining) for draining of groundwater into where the main drainage systems are located in the tunnel gallery were suggested.  相似文献   

The 73-day periodicity of the flare index during the current solar cycle 22     

Atila Özgüç  Tamer Ataç 《Solar physics》1994,150(1-2):339-346

The flare index of the current solar cycle 22 is analysed to detect periodicities. Power spectral analysis of the time series of solar flare index data reveals a periodicity around 73 and 53 days. We find that a periodicity of 73 days was in operation from November 1988 to the end of December 1991. We also find that when the 73-day periodicity or the 154-day periodicity is in operation the flare index is well correlated with the relative sunspot numbers.  相似文献   

A multi‐temporal analysis of AMSR‐E data for flood and discharge monitoring during the 2008 flood in Iowa     

Marouane Temimi  Teodosio Lacava  Tarendra Lakhankar  Valerio Tramutoli  Hosni Ghedira  Riadh Ata  Reza Khanbilvardi 《水文研究》2011,25(16):2623-2634

The objective of this work is to demonstrate the potential of using passive microwave data to monitor flood and discharge conditions and to infer watershed hydraulic and hydrologic parameters. The case study is the major flood in Iowa in summer 2008. A new Polarisation Ratio Variation Index (PRVI) was developed based on a multi‐temporal analysis of 37 GHz satellite imagery from the Advanced Microwave Scanning Radiometer (AMSR‐E) to calculate and detect anomalies in soil moisture and/or inundated areas. The Robust Satellite Technique (RST) which is a change detection approach based on the analysis of historical satellite records was adopted. A rating curve has been developed to assess the relationship between PRVI values and discharge observations downstream. A time‐lag term has been introduced and adjusted to account for the changing delay between PRVI and streamflow. Moreover, the Kalman filter has been used to update the rating curve parameters in near real time. The temporal variability of the b exponent in the rating curve formula shows that it converges toward a constant value. A consistent 21‐day time lag, very close to an estimate of the time of concentration, was obtained. The agreement between observed discharge downstream and estimated discharge with and without parameters adjustment was 65 and 95%, respectively. This demonstrates the interesting role that passive microwave can play in monitoring flooding and wetness conditions and estimating key hydrologic parameters. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献