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@article{di2019seismic,
  title = {Seismic fragility analysis of a coupled tank-piping system with surrogate modelling and synthetic ground motions},
  author = {di Filippo, Rocco and Abbiati, Giuseppe and Sayginer, Osman and Bursi, Oreste S},
  year = {2019},
  doi = {10.1115/pvp2019-93685}
}

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@conference{collab3b,
  title = {İnce Film Optik Filtreler İçin Otomatize Tasarim Sistemi (in Turkish)},
  author = {Z. Arslanturk and A. Sezgin and O. Sayginer},
  year = {2019},
  journal = {21st National Photonics Workshop (Fotonik ’19),},
  url = {https://collab.sayginer.com/ifofo/abstract-poster-presented-in-fotonik-19-workshop-in-turkish/}
}

Abstract

1-D multilayer dielectric films consisting of seven pairs of SiO2 and TiO2 alternating layers are deposited on a SiO2 substrate using the radio frequency sputtering technique. The thicknesses of the film layers are chosen to reflect the visible radiation around 650 nm. An elastic microcavity layer made of Polydimethylsiloxane was sandwiched between two Bragg reflectors. A fabrication process was then developed for elastic microcavity in order to tailor the thickness, establish the surface planarity and to increase reproducibility of the samples. Optical transmittance of the single Bragg reflector and the microcavity were both simulated and measured. A comparison between measurement data and Transfer Matrix Method calculations shows a favourable correlation. Furthermore, in order to assess the suitability of the microcavity as a force sensor, transmittance measurements were carried out as a function of the applied forces. The change in the elastic microcavity thickness due to applied forces resulted in cavity resonance peak shifts proportional to the applied forces.

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@article{sayginer2019b,
  title = {Fabrication, modelling and assessment of hybrid 1-D elastic Fabry Perot microcavity for mechanical sensing applications},
  author = {Osman Sayginer and Alessandro Chiasera and Lidia Zur and Stefano Varas and Lam Thi Ngoc Tran and Cristina Armellini and Maurizio Ferrari and Oreste S Bursi},
  year = {2019},
  journal = {Ceramics International},
  doi = {10.1016/j.ceramint.2019.01.083},
  issn = {0272-8842}
}

Abstract

Seismic risk evaluation of coupled systems of industrial plants often needs the implementation of complex finite element models to consider their multicomponent nature. These models typically rely on significant computational resources. Moreover, the relationships between seismic action, system response and relevant damage levels are often characterized by a high level of nonlinearity, thus requiring a solid background of experimental data. Furthermore, fragility analyses depend on the adoption of a significant number of seismic waveforms generally not available when the analysis is site-specific. To propose a methodology able to manage these issues, we present a possible approach for a seismic reliability analysis of a coupled tank-piping system. The novelty of this approach lies in the adoption of artificial accelerograms, FE models and experimental hybrid simulations to evaluate a surrogate meta-model of our system. First, to obtain the necessary input for a stochastic ground motion model able to generate synthetic ground motions, a disaggregation analysis of the seismic hazard is performed. Hereafter, we reduce the space of parameters of the stochastic ground motion model by means of a global sensitivity analysis upon the seismic response of our system. Hence, we generate a large set of synthetic ground motions and select, among them, a few signals for experimental hybrid simulations. In detail, the hybrid simulator is composed by a numerical substructure to predict the sliding response of a steel tank, and a physical substructure made of a realistic piping network. Furthermore, we use these experimental results to calibrate a refined ANSYS FEM. More precisely, we focus on tensile hoop strains in elbow pipes as a leading cause for leakage, monitoring them with strain gauges. Thus, we present the procedure to evaluate a numerical Kriging meta-model of the coupled system based on both experimental and finite element model results. This model will be adopted in a future development to carry out a seismic fragility analysis.

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@proceedings{101115pvp2019-93685,
  title = {Numerical Surrogate Model of a Coupled Tank-Piping System for Seismic Fragility Analysis With Synthetic Ground Motions},
  author = {Rocco di Filippo and Giuseppe Abbiati and Osman Sayginer and Patrick Covi and Oreste S Bursi and Fabrizio Paolacci},
  year = {2019},
  doi = {10.1115/PVP2019-93685}
}

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@conference{sayginer2018,
  title = {Er3+ 1-D photonic band gap structure for photonic band edge assisted spontaneous emission enhancement},
  author = {Osman Sayginer and Cesare Meroni and Alessandro Chiasera and Francesco Scotognella and Anna Lukowiak and Giorgio Speranza and Stefano Varas and Lidia Zur and Giancarlo C. Righini and Roberta Ramponi and Oreste Bursi and Maurizio Ferrari},
  year = {2018},
  doi = {10.1016/j.optmat.2018.04.034},
  issn = {0925-3467},
  url = {http://d-photon.fbk.eu/home}
}

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@conference{sayginer2017b,
  title = {Fabrication of functionally graded ceramic- polymer dielectrics via freeze casting for RF applications},
  author = {Osman Sayginer and Gullu Kiziltas},
  year = {2017},
  journal = {Materials and Packaging},
  issn = {0272-9172},
  url = {http://2017apsursi.org/Papers/ViewPapers.asp?PaperNum=2593}
}

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@conference{sayginer2017a,
  title = {Integrated topology optimization of volumetric antenna substrates and conductor surfaces for broadband microstrip patch antennas},
  author = {Osman Sayginer and Gullu Kiziltas},
  year = {2017},
  journal = {Metamaterial Based Designs},
  url = {http://2017apsursi.org/Papers/ViewPapers.asp?PaperNum=1925}
}

Abstract

In parallel to current important developments in electronics and communication technologies, needs on wireless systems have become more popular yet stringent. In order to meet that demand, development of novel technologies and materials has become crucial. Patch antennas are widely used in the radio frequency (RF) industry. This is due to their simple shape, easy and low cost manufacturing capability and their suitability for conformal applications. However, most of current patch antenna designs rely on efforts puts towards their geometrical parameters with limited available dielectric materials in the market. This thesis mainly focuses on the topology optimization of polymer- ceramic composite substrates. These substrates allow for spatial dielectric permittivity variation via their functionally graded multilayer configuration with the objective to achieve minimization of reflected power at desired frequency values. Towards this goal in the proposed optimization study, Comsol Multiphysics 5.2 software was integrated with Matlab 2014b software and genetic algorithm was used as the optimization solver. In addition to the design study, in the second part of the thesis, a cooling system which allows for the adjustment of temperature values between 0℃ and -100℃ was designed to control the substrate properties of functionally graded materials (FGM) of ceramicpolymer antenna substrates, similar to those designed in the first part of the thesis. These substrates were produced via a novel manufacturing method based on freeze casting process. A new test platform was developed in order to investigate the effect of cooling rate and temperature on microporosity and permittivity of these substrate materials.

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@mastersthesis{sayginer2016,
  title = {Topology optimization and cooling system design for functionally graded patch antenna substrates},
  author = {Osman Sayginer},
  year = {2016},
  url = {http://research.sabanciuniv.edu/34797/}
}

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@conference{sayginer2013,
  title = {Resonance frequency analysis of MEMS based on piezoelectric microcantilever beam for vibration energy harvesting applications},
  author = {Osman Sayginer and Ugur Akyol},
  year = {2014}
}

Abstract

Titanium-based and cobalt-chrome alloys have been widely used in orthopaedic applications as these materials can significantly enhance the quality of human life as implant materials. The longevity of these materials is highly influenced by their mechanical properties. In some devices cobalt chrome components articulate with titanium alloy counter faces (e.g. in the taper connections of stems and femoral heads in modern modular designs) and damage has been reported of the harder cobalt chrome by the softer titanium alloy component. This study attempts to understand why this might occur by investigating bulk and surface mechanical properties (such as hardness and Young's modulus) of a number of hip implants and test samples using a Hysitron Triboindenter. AFM images were also obtained to determine the contact area and hence, pile-up correction factors.

The results were compared for samples before being used in the body, to account for surface mechanical response due to implant manufacture, and after, to account for the materials response to long-term cyclic loads. To assess the effects of oxidation, the alloys were treated electrochemically with Sodium-Chloride (NaCl) solution at body temperature. It was found that titanium oxidised preferentially compared with cobalt-chrome alloys. Furthermore, the oxidised titanium showed significantly higher hardness values therefore damaging the un-oxidised cobalt-chrome material. The implications for device design and manufacture are discussed.

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@article{moharrami2013does,
  title = {Why does titanium alloy wear cobalt chrome alloy despite lower bulk hardness: A nanoindentation study?},
  author = {N Moharrami and DJ Langton and O Sayginer and SJ Bull},
  year = {2013},
  journal = {Thin Solid Films},
  doi = {10.1016/j.tsf.2013.06.020},
  issn = {0040-6090}
}