Numerical study of ship motions and added resistance in regular incident waves of KVLCC2 model

Yavuz Hakan Ozdemir,Baris Barlas 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.2

In this study, the numerical investigation of ship motions and added resistance at constant forward velocity of KVLCC2 model is presented. Finite volume CFD code is used to calculate three dimensional, incompressible, unsteady RANS equations. Numerical computations show that reliable numerical results can be obtained in head waves. In the numerical analyses, body attached mesh method is used to simulate the ship motions. Free surface is simulated by using VOF method. The relationship between the turbulence viscosity and the velocities are obtained through the standard k ε turbulence model. The numerical results are examined in terms of ship resistance, ship motions and added resistance. The validation studies are carried out by comparing the present results obtained for the KVLCC2 hull from the literature. It is shown that, ship resistance, pitch and heave motions in regular head waves can be estimated accurately, although, added resistance can be predicted with some error.

Role of Reinforcement Materials on Mechanical and Tribological Properties of PTFE Composites

Yavuz Kaplan 한국고분자학회 2020 폴리머 Vol.44 No.4

The use of polytetrafluoroethylene (PTFE) in various industrial applications under extreme operating conditions makes it very important to determine the behavior of this material. The mechanical and wear properties of PTFE can be enhanced by adding filler materials. This study focused on both the mechanical and tribological properties of PTFE and its composites with a 25 wt% addition of carbon and glass fiber (GF). Glass transition temperature (Tg), hardness, tensile, and impact tests were carried out to determine the mechanical and physical properties of PTFE. In addition, abrasive wear tests were applied to obtain wear behavior. The tensile strength values of the pure and C/GF-filled PTFE were found as 28, 16.7, and 18.6MPa, respectively. Tensile tests clearly showed that the filler materials led to a reduction of the tensile strength and elongation at break of the PTFE. Impact energy values were similarly decreased by the addition of filler materials. However, the carbon and GF additions significantly increased the abrasive wear resistance and Tg of the PTFE. Consequently, carbon and GF-filled PTFE would be a suitable candidate for use in tribological applications.

The Relationship between Presbycusis and Mastoid Pneumatization

Yavuz Selim Pata,Yucel Akbas,Murat Unal,Meltem Nass Duce,Tugana Akbas,Deniz Micozkadioglu 연세대학교의과대학 2004 Yonsei medical journal Vol.45 No.1

Presbycusis is defined as the natural hearing loss accompanying aging, caused by degenerative changes in the inner ear. The etiology of presbycusis is uncertain. However, it would appear that a complex genetic cause is most likely. The determinants of mastoid size continue to be controversial. One of the pneumatization theories is the hereditary theory. In this study, the possible relationship between presbycusis and the extent of mastoid pneumatization was investigated. This study was carried out on 21 patients with presbycusis and 21 normal subjects of similar ages. The pneumatized volume was measured by computerized tomography. The temporal bone was scanned at 2mm thickness intervals. Exposure (kV 130, mA105). The scan plane was parallel to the orbitomeatal line and the CT images covered the entire mastoid region. The average mastoid pneumatization in presbycusis group was 6.08 ±2.52cm3 in the right ear and 6.19±2.93cm3 in the left ear. However, in the control group it was 4.69±3.17cm3 in the right ear (p=0.12) and 5.10±3.49cm3 in the left ear (p=0.28). No significant difference was found between the presbycusis patients and normal subjects in terms of the volume of mastoid pneumatization.

Reconstruction of the Orbit With a Temporalis Muscle Flap After Orbital Exenteration

Yavuz Uya,Tolgar Lütfi Kumral,Güven Yıldırım,Mustafa Kuzdere,Hamdi Arbağ,Chary Jorayev,Mehmet Vefa Kılıç,Said Serdar Gümrükçü 대한이비인후과학회 2015 Clinical and Experimental Otorhinolaryngology Vol.8 No.1

Objectives. This study presents the role of the temporalis muscle flap in primary reconstruction after orbital exenteration. Methods. A retrospective nonrandomized study of orbital exenterations performed between 1990 and 2010 for malignant tumors of the skin, paranasal sinus, and nasal cavity is presented. Results. The study included 13 patients (nine men, four women; age range, 30–82 years) with paranasal sinus, nasal cavity, or skin carcinomas. Primary reconstruction of the cavity was performed in all patients after orbital exenteration. No visible defects in the muscle flap donor site were present. Local recurrences were readily followed up with nasal endoscopy, whereas radiology helped to diagnose intracranial involvement in three patients. Two patients died of systemic metastases and five died for other reasonsConclusion. The temporalis muscle flap is readily used to close the defect after orbital exenteration, and does not prevent the detection of recurrence.

COEFFICIENT ESTIMATES FOR CERTAIN SUBCLASS FOR SPIRALLIKE FUNCTIONS DEFINED BY MEANS OF GENERALIZED ATTIYA-SRIVASTAVA OPERATOR

Yavuz, Tugba Korean Mathematical Society 2016 대한수학회논문집 Vol.31 No.4

In this article, we derive a sharp estimates for the Taylor-Maclaurin coefficients of functions in some certain subclasses of spirallike functions which are defined by generalized Srivastava-Attiya operator. Several corollaries and consequences of the main result are also considered.

A CLASS OF □-RECURRENT ALMOST COSYMPLECTIC SPACE

( Yavuz Selim Balkan ),( Siraj Uddin ),( Ali H. Alkhaldi ) 호남수학회 2018 호남수학학술지 Vol.40 No.2

In this paper, we study '-recurrent almost cosymplectic (k, μ)-space and prove that it is an □-Einstein manifold with constant coefficients. Next, we show that a three-dimensional lo-cally □-recurrent almost cosymplectic (k, μ)-space is the space of constant curvature.

Transient response of functionally graded non-uniform cylindrical helical rods

Yavuz C. Cuma,Faruk Firat Calim 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.4

This paper have the objective of investigating forced vibration behaviour of axially functionally graded cylindrical helices with variable cross-section. An algorithm is developed in order to solve corresponding problems. The ordinary differential equations governing the dynamic behaviour of cylindrical helices are determined in Laplace domain by using Timoshenko beam theory. Then transfer matrix method is implemented for the solution, including shear and axial deformation effects. Obtained results are transferred to time domain using Durbin’s modified numerical inverse algorithm for Laplace transform. A benchmark problem has been solved to check the accuracy of developed algorithm then a parametric study is conducted considering the effects of material gradient index ( ), section variation parameter ( ) and number of active turns ( ). Results are compared with solutions attained from ANSYS for verification

Effects of Material Properties on Seismic Vulnerability Assessment of Unreinforced Masonry Buildings

Yavuz Yardim,Enea Mustafaraj,Erion Luga 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.5

This study investigates the seismic performance of existing unreinforced masonry buildings considering the effects of different material properties selected from design codes’ assumptions and experimental values. For this purpose, work was conducted to analyze a selection of existing buildings in Albania designed with typical methodologies of the past structural design codes. Experimental investigations were carried out on bricks and mortars extracted from the selected buildings, as well as a series of regular and irregular sized mortar specimens prepared in the laboratory for comparative evaluation purpose. In addition, diagonal compression tests were performed on two full-size (1.2 m × 1.2 m) masonry walls built in the laboratory, which were prepared based on the existing building’s construction method and material properties. Selected typical URM buildings were analyzed with commercial program CDSWin using different masonry mechanical characteristics that were obtained from experimental work in this study. The equivalent frame method (EFM) was used for the modeling of the buildings and pushover analysis was performed to obtain their seismic capacity. To evaluate the seismic response of each case, a comparison was established between the drift ratio and maximum base shear. As a result, using the code assumptions for the mechanical properties of masonry, overly conservative results were obtained. To understand better and clarify how stresses are being distributed in the walls, it is essential to perform experimental investigations to acquire the representative masonry characteristics such that a reliable structure assessment and retrofitting could be implemented.

Performance Analysis on Solar Concentrating Thermoelectric Generator Coupled with Heat Sink

Yavuz Köysal 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.2

The usage of thermoelectric generators (TEGs) is rapidly increasing where the waste heat exists. Today, many experiments are being conducted to investigate solar energy systems with waste heat. This work focuses on the performance of an individual TEG via a spot Fresnel lens. Therefore, an experimental system was constructed so that the TEG module could show high performance under the concentrated solar radiation. For this aim, the system was adapted to one-axis sun tracking system for receiving maximum solar irradiation. It was observed that the obtained experimental values of the parameters such as open circuit voltage, hot side temperature and cold side temperature of the TEG module are consistent with the collected solar values. The experimental data was collected at GPS coordinates of 41°14′N and 36°26′E (Samsun, Turkey) on 8th of September, 2017. The maximum open circuit voltage value was obtained as 0.822 V.

Effect of Probiotics on the Treatment of Children with Atopic Dermatitis

( Yavuz Yesilova ),( Omer Calka ),( Necmettin Akdeniz ),( Mustafa Berktas ) 대한피부과학회 2012 Annals of Dermatology Vol.24 No.2

Background: Atopic dermatitis, a chronic recurrent disease, is frequently encountered in clinical practice. In the last 30 years, the prevalence of atopic dermatitis has rapidly increased due to industrialization. Therefore, there have been attempts in recent years to find new ways of treating and preventing atopic dermatitis. Objective: In this double-blind, randomized, placebo-controlled study, a combination of Bifidobacterium bifidum, Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus salivarius strains were evaluated in the treatment of atopic dermatitis in pediatric patients. Methods: Forty pediatric patients (23 males and 17 females) aged 1∼13 years were enrolled. One eligible individual who was approached declined to participate. The probiotic group was administered a probiotic complex containing B. bifidum, L. acidophilus, L. casei, and L. salivarius for 8 weeks. The placebo group, on the other hand, was administered skim milk powder and dextrose. All of the parameters including serum cytokines, eosinophil cationic protein), SCORing Atopic Dermatitis (SCORAD) index, and total serum immunoglobulin E (IgE) were measured in both the probiotic group and the placebo group at the end of 8 weeks. Results: Probiotic intervention in pediatric atopic dermatitis patients effectively reduced the SCORAD index and serum cytokines interleukin (IL)-5, IL-6, interferon (IFN)-γ, and total serum IgE levels, but did not reduce levels of serum cytokines IL-2, IL-4, IL-10, ECP, or tumor necrosis factor-α (TNF-α) compared to the placebo group. Conclusion: Our study found probiotics to be effective in reducing atopic dermatitis patients` SCORAD index, serum IL-5, IL-6, IFN-γ, and total serum IgE levels but not effective in reducing serum IL-2, IL-4, IL-10, ECP, or TNF-α levels. (Ann Dermatol 24(2) 189∼193, 2012)