V.S. Ozgur Kirca

Residual liquefaction of seabed under standing waves

AbstractThis paper presents the results of an experimental study of the seabed liquefaction beneath standing waves. Silt (with d50=0.070 mm) was used in the experiments. Two kinds of measurements were carried out: pore water pressure measurements and water surface elevation measurements. These measurements were synchronized with video recording of the liquefaction process from the side. The ranges of the various quantities in the experiments were wave height H=5.9–12.0 cm, wave period T=1.09 s, and water depth h=30 cm. The experiments show that the seabed liquefaction under standing waves, although qualitatively similar, show features different from that caused by progressive waves. The pore water pressure builds up (or accumulated) in the areas around the node and subsequently spreads out toward the antinodes. The experimental results imply that this transport is caused by a diffusion mechanism with a diffusion coefficient equal to the coefficient of consolidation. The experiments further show that the n...

Influence of Clay Content on Wave-Induced Liquefaction

AbstractThis paper presents the results of an experimental study of the influence of clay content (CC) on liquefaction of seabed beneath progressive waves. Experiments were, for the most part, conducted with silt and silt-clay mixtures; in supplementary tests, sand-clay mixtures were used. Two types of measurements were carried out: (1) pore-water pressure measurements across the soil depth and (2) water-surface elevation measurements. These measurements were synchronized with video recordings of the liquefaction process from the side. The ranges of the various quantities in the experiments were wave height H=7.6−18.3 cm, wave period T=1.6 s, and water depth h=55 cm. The experiments showed that the influence of CC on wave-induced liquefaction is very significant. Susceptibility of silt to liquefaction was increased with increasing CC up to CC≈30% (which is clay-specific), beyond which the mixture of silt and clay was not liquefied. Sand may become prone to liquefaction with the introduction of clay, contr...

Performance of an inclined thin plate in wave attenuation

ABSTRACT Açanal, L., Loukogeorgaki, E., Yagci, O., Kirca, V.S.O. and Akgül, A., 2013. Performance of an inclined thin plate in wave attenuation In practice, in some cases, tandemly applied pile-mounted horizontal or inclined thin plates emerge as functional coastal structures in terms of diminishing wave height in front of Rubble Mound Breakwaters (RMBs) and consequently, reduce the required armor unit size and RMBs overall weight. In this study, the hydrodynamic performance of an Inclined Thin Plate (ITP) under regular waves is experimentally investigated. The objective of the laboratory experiments is the assessment of the ITPs efficiency in terms of wave attenuation. Various inclination angles in combination with different submergence degree of the structure under various wave conditions are examined. Regarding the examined ITP configurations, three different inclination angles are considered, i.e. 5, 10, and 15 deg as well as a horizontal plate on the free surface. For the inclined configurations, ITP was placed in a manner such that 2/3 and 3/4 of its length was submerged. The findings revealed that the transmission coefficients can be reduced down to 0.2–0.3. The findings revealed that a tandemly applied ITP has great functionality in diminishing the wave height at the seaward side of a RMB. In this way, the overall weight of the RMB and the weight of the armor units of the RMB are markedly reduced, which is highly necessary in cases where the foundation stability is poor.

Fuzzy threshold for the initiation of sediment motion

Abstract The present paper considers the threshold for the initiation of sediment motion to be a fuzzy set by taking into account the uncertainty related to individual sediment positioning and turbulence intensity. Incipience of sediment motion across a stream-bed occurs gradually, and a fuzzy set facilitates the notation of partial sediment transport in the computations. For the derivation of this fuzzy threshold, the formula developed in Zanke, U.C.E. (2003), On the influence of turbulence on the initiation of sediment motion. Int. J. Sediment Res., 18(1), 17-31, for the computation of dimensionless critical shear stress is extended accordingly by using, instead of crisp values in order to describe the angle of grain contact and the turbulence intensity, fuzzy numbers. This can be achieved by exploiting the extension principle of fuzzy sets and logic. Hence, the proposed formula generates two three-dimensional surfaces by means of the extension principle of fuzzy sets, which define the lower and upper limits of the dimensionless critical shear stress membership function with respect to the shear Reynolds number and the relative roughness. The benefit of this approach, when compared to an approach that solely utilizes characteristic or average values, is that it can predict partial sediment transport of the most susceptible to movement particles, which is very common in gravel-bed streams even for bankfull flow conditions. In addition, a measure to compare the produced fuzzy dimensionless critical shear stress with the exerted dimensionless shear stress, is proposed, which is based on the concept of fuzzy subtraction and takes into account the whole shape of the membership function. To justify the proposed methodology, the produced results are compared with experimental data, and useful conclusions are drawn. Based on the fuzzy extension of the physically-based equation of Zanke, a fuzzy band is produced which includes almost all the used experimental data with a functional spread.

Monitoring Differential Urbanization to Integrate with Basin Management and a Basin Information System Modeling for Istanbul

This article intends to give the outline of a basin information system to be generated and managed in order to monitor the increase of urbanization and trend of pollution potential over seven major basins (watersheds) of Istanbul, Turkey. The data from basin monitoring studies of Istanbul Water and Wastewater Management Authority (Istanbul) was used to evaluate the differential settlement and construction. After the urbanization increase is evaluated by means of building/facility areas, the pollution trends are assessed for different time intervals in terms of five parameters by making certain unit load assumptions. The results indicate that residential settlement increased 0.124–0.003% during 29 months. Also in the same period, mean pollution potential of the basins is found to increase 8.747, 3.578, 5.970, 0.922, and 0.145 in terms of tons/day for Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), Suspended Solids (SS), Total Kjeldahl Nitrogen (TKN), and Total Phosphorus (TP), respectively, considering domestic wastewater and diffuse pollution loadings (from urban runoff and feedlots). These results state that monitoring of basins, especially those exposed to intense urbanization, must be conducted periodically and continuously by means of the basin information system as the first step to be able to control the pollution and to take measures against the threats that come with urbanization.