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Öğe 2-D and 3-D finite element analyses for the settlement due to soft ground tunnelling(Elsevier Ltd, 2006) Karakus M.; Fowell R.J.The objective of this paper is to describe and evaluate two-dimensional and three-dimensional Finite Element analyses for New Austrian Tunnelling Method (NATM) in soft ground. Firstly, 2-D plane strain FE analyses were conducted to predict ground response to NATM tunnelling. In order to take account the deformations prior to lining installation Hypothetical Modulus of Elasticity (HME) soft lining approach were adopted. The best 2-D model whose predictions were in a great agreement with the field measurements was found to be sequential excavation model (SEM), which follows closely the construction sequences used in the field. Secondly, three-dimensional FEM analysis has been carried out to predict transverse and longitudinal settlement profiles. Results from the analyses compared with each other as well as field measurements recorded during construction of Heathrow Express Trial tunnel in London clay.Öğe Assessing deformability of siltstone under compressive loading by ultrasonic wave propagation(2011) Karakus M.; Tutmez B.Determination of stress-strain behaviour of rocks plays a crucial role in understanding the response of rocks during loading. However, it is a tedious, expensive and a time-consuming process to obtain such characteristics both in the laboratory and in situ. On the other hand, non-destructive testing methods such as ultrasonic velocities can produce a reliable and fast solution to indentify state of strain and stress in rocks. The present paper aims to provide insight into the relations amongst ultrasonic wave velocities, amplitudes and deformability properties of porous siltstone under compressive loading. For this purpose, pulse (v P) and shear wave velocities (v S) along with amplitudes (AP - AS), and applied loads with resultant strain were measured simultaneously so that response of siltstone to compression can be evaluated. In addition, initial v P and v S were recorded at the beginning of each test to calculate dynamic elastic properties of the specimens. This provided a comparison between static and dynamic elasticity properties of siltstone. Crack damage associated with the onset of dilation was also investigated. The results showed that there is a non-linear logarithmic relation between velocities and stress-strain level for siltstones.Öğe Particle Swarm Optimization-Enhanced Virtual Multicast Trees Embedding in SDNs(Institute of Electrical and Electronics Engineers Inc., 2023) Guler E.; Ayaz F.; Karakus M.; Hanbay D.The truly innovative network virtualization technology allows for multi-tenancy, enabling different Virtual Network (VN) requests to share the same physical network. This is achievable because network services are no longer bound to the architecture of the lessor hardware. Virtual Network Embedding (VNE) is a multi-dimensional NP-Hard problem that maps VN entities such as virtual nodes and virtual links onto a shared Substrate Network (SN) while assuring the requested network resources (e.g., bandwidth, computing power, etc.). This research explores how to efficiently map VNs with one-to-many (multicast) interactions, in the form of Virtual Multicast Trees (VMTs), onto an SN in contrast to the VNE problem where one-to-one (unicast) communication is at focus. Thus, we propose a Virtual Multicast Tree Embedding (VMTE) enhanced by Particle Swarm Optimization framework, VMTE-PSO, to put VMTs on a shared SN. The VMTE-PSO aims to minimize the amount of network resource consumption (i.e., bandwidth) in the SN while simultaneously satisfying the computing demand of virtual nodes and minimizing the redundant substrate link usage. Extensive simulations reveal our algorithm outperforms the dynamic node ranking and traditional greedy-based VMTE approaches with respect to bandwidth consumption and redundant multicast transmission on NSFNET and USNET network topologies. © 2023 IEEE.Öğe Ultrasonic evaluation of igneous and metamorphic rocks under compressive loading(Grup Matbaacilik, 2009) Karakus M.; Tütmez B.; Kaleci D.This research aims to assess deformability characteristics of extrusive volcanic and metamorphic rocks under compressive loading using ultrasonic wave propagation technique. An experimental methodology developed in house was used to measure applied load, resultant strain, P and S wave velocities along with maximum amplitudes simultaneously. Wave velocities were measured perpendicular to the compressional axis using pairs of receivers' lead-zirconate piezoceramic transducers (PZT) which are specifically designed for use in geological testing. PUNDIT instrument was used to generate low frequency ultrasonic pulses. According to the results, a non-linear relationship between velocities and stress level that rock specimens have undergone were found. Increase in velocities is closely related to closure of void spaces in the specimens. Rate of velocity increments was also found to be greatest at the early stress level. As a result, ultrasonic velocities can be used to detect high stress concentrations and to monitor stress level in the underground structures.
