A parametric study on the effect of post-tensioning in bridge pier foundations

Bu çalışmada, iki açıklıklı bir köprünün orta ayak temelinde ardgerme etkisi sonlu elemanlar analizleri ile araştırılmıştır. Bu amaçla, daha once inşa edilmiş olan gerçek bir köprünün temeli seçilmiş ve bu temel 3 farklı halat tipi ve 3 farklı halat aralığı için olmak üzere toplam 9 farklı ardgerme opsiyonu ile analiz edilmiştir. Sonuçlar enine ve boyuna toplam 6 kesitte; maksimumve minimum temel basınçları, temel basınç dağılımları; temele gelen eğilme momentleri ve moment dağılımları açısından incelenmiştir. Analiz sonuçlarına gore ardgerme uygulanmadığı durumlarda temellerde kolon altına denk gelen bölgede temel basınçları ciddi şekilde yoğunlaşmaktadır. Ardgerme uygulanan analizlerin çoğunda ardgermesiz duruma gore çok daha düzgün yayılı bir basınç dağılımı elde edilirken, temel uç basınçlarında bir miktar artış görülmüştür. Bu etkinin, toplam düşey yükün değişmemesi ancak temelin deformasyon profilinin iyileştirilmesi sebebiyle oluştuğu sonucuna varılmıştır. Temel basınçlarına benzer şekilde moment dağılımlarının da, analiz edilen bir çok durum için ardgerme uygulanması halinde ardgermesiz duruma gore çok daha düzenli olduğu görülmüştür. Ancak halat sayısı ve halat aralıklarında belirli bir optimum noktadan sonra moment yönlerinin değiştiği görülmüştür. Bu durum dikkatli olunmazsa tasarımda olumsuz etkiler yaratabilecektir. Temelde ardgerme uygulanması ile görülen bir diğer avantaj da, tüm temelin basınç altında çalışmasıdır. Bu durumun temelin uzun dönemdeki çatlama ve korozyon problemlerine olumlu yönde katkı yapacağı değerlendirilmiştir

Risk assessment of atmospheric emissions using machine learning

Supervised and unsupervised machine learning algorithms are used to perform statistical and logical analysis of several transport and dispersion model runs which simulate emissions from a fixed source under different atmospheric conditions. <br><br> First, a clustering algorithm is used to automatically group the results of different transport and dispersion simulations according to specific cloud characteristics. Then, a symbolic classification algorithm is employed to find complex non-linear relationships between the meteorological input conditions and each cluster of clouds. The patterns discovered are provided in the form of probabilistic measures of contamination, thus suitable for result interpretation and dissemination. <br><br> The learned patterns can be used for quick assessment of the areas at risk and of the fate of potentially hazardous contaminants released in the atmosphere

Role of Anomalous Warm Gulf Waters in the Intensification of Hurricane Katrina

The year 2005 experienced several strong hurricanes intensifying in the Gulf of Mexico before making landfall that severely damaged the Gulf States, especially Hurricane Katrina. Remarkable similarities between sea surface temperature anomaly (SSTA) and major hurricane (categories 3 and higher) activity over the Gulf are identified. However, the intensification of individual hurricanes may not necessarily be temporally and spatially coincident with the distribution of warm waters or high sea surface temperature (SST). High SST values are found in advance of significant intensification of Hurricane Katrina. We emphasize that high SSTA which occurred at the right time and right place was conducive to the hurricane intensification. In particular, high SSTA in the northeastern quadrant of the storm track induced significant increases in surface latent heat fluxes (LHF) contributing to the rapid intensification of Katrina. We also compared and verified model simulations with buoy observations

Numerical Simulations of the Impacts of the Saharan Air Layer on Atlantic Tropical Cyclone Development

In this study, the role of the Saharan air layer (SAL) is investigated in the development and intensification of tropical cyclones (TCs) via modifying environmental stability and moisture, using multisensor satellite data, long-term TC track and intensity records, dust data, and numerical simulations with a state-of-the-art Weather Research and Forecasting model (WRF). The long-term relationship between dust and Atlantic TC activity shows that dust aerosols are negatively associated with hurricane activity in the Atlantic basin, especially with the major hurricanes in the western Atlantic region. Numerical simulations with the WRF for specific cases during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) experiment show that, when vertical temperature and humidity profiles from the Atmospheric Infrared Sounder (AIRS) were assimilated into the model, detailed features of the warm and dry SAL, including the entrainment of dry air wrapping around the developing vortex, are well simulated. Active tropical disturbances are found along the southern edge of the SAL. The simulations show an example where the dry and warm air of the SAL intruded into the core of a developing cyclone, suppressing convection and causing a spin down of the vortical circulation. The cyclone eventually weakened. To separate the contributions from the warm temperature and dry air associated with the SAL, two additional simulations were performed, one assimilating only AIRS temperature information (AIRST) and one assimilating only AIRS humidity information (AIRSH) while keeping all other conditions the same. The AIRST experiments show almost the same simulations as the full AIRS assimilation experiments, whereas the AIRSH is close to the non-AIRS simulation. This is likely due to the thermal structure of the SAL leading to low-level temperature inversion and increased stability and vertical wind shear. These analyses suggest that dry air entrainment and the enhanced vertical wind shear may play the direct roles in leading to the TC suppression. On the other hand, the warm SAL temperature may play the indirect effects by enhancing vertical wind shear; increasing evaporative cooling; and initiating mesoscale downdrafts, which bring dry air from the upper troposphere to the lower levels

A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations

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

Protocol: A systematic review and meta-analysis of the role of fetal and infantile environmental exposure in etiopathogenesis of infantile hypertrophic pyloric stenosis

Infantile hypertrophic pyloric stenosis (IHPS) is one of the hallmark pediatric surgical diseases. However, its etiology remains incompletely understood. By systematically reviewing the literature, we aim to clarify the effect of the effect of occupational and environmental factors and role of nitric oxide (NO) metabolism in the etiopathogenesis of IHPS. The systematic review is drafted with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement (PRISMA) and the Meta-analysis of Observational Studies in Epidemiology (MOOSE). Systematic literature search will be performed for the period 2000 (Jan) to 2020 (Dec) in the databases: MEDLINE, EMBASE, PubMed. The systematic search will cover the literature in English and Turkish language and will be limited to studies on human subjects. Four investigators will independently search the databases (MEDLINE, EMBASE, PubMed) according to the defined search strategy. The full-text of the selected articles will be screened independently by four reviewers, against the inclusion criteria. Descriptive data will be extracted from each study regarding: study details, methods, participants, outcomes and calculations of association for potential further statistical analysis. If meta-analysis could not be undertaken, systematic approach to analyzing the findings of included multiple studies will be described. Heterogeneity will be assessed by quantifying the inconsistency across studies using I2 statistic. Statistical analysis will be performed using Comprehensive Meta-Analysis Version 3.0 software. The p values lower than 0.05 will be considered statistically significant for all analyses