Pasternak Zeminine Yaslanan Ve Kısmen Akışkan İle Temas Eden Mindlin Plağının Dinamik Davranışı

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2013Bu çalışmada Pasternak zeminine oturan ve aynı zamanda durağan bir akışkan alanıyla kısmen temas eden Mindlin plaklarının dinamik davranışı incelenmiştir. Gâteaux türevinden yararlanılarak plak-zemin etkileşimi karışık sonlu eleman yöntemi ile ele alınmış, yayılı kütle matrisinde plak dönel eylemsizlikleri de gözetilmiştir. Akışkan-yapı etkileşimi içinse sınır eleman yönteminden yararlanılmıştır. Uygulanan kabuller, plak-zemin sisteminin akışkanla temas sırasında kendi doğal modlarında titreştiği ve her bir elastik moda karşılık plak ıslak yüzeyi üzerinde bir basınç dağılımının oluştuğu şeklindedir. Akışkan serbest yüzey etkileri sonsuz-frekans kabulü altında ihmal edilmiştir. Ortaya çıkan etkileşim kuvvetleri akışkan eylemsizlik etkisini temsil eden genelleştirilmiş ek su kütlesi formundadır. Sunulan çözüm yaklaşımı örneklerle test edilmiş, zemin varlığının ve akışkan etkileşiminin Mindlin plağının dinamik davranışına olan etkileri parametrik olarak ayrıca incelenmiştir.This study is concerned with the dynamic response of Mindlin plates resting on an Pasternak foundation and simultaneously interacting partially with a quiescent fluid field. Plate-foundation interaction is simulated in the framework of a mixed finite element by employing the Gâteaux differential. Consistent mass matrix formulation is used by considering the rotary inertia. Fluid-structure interaction analysis is carried out by the boundary element method. It is assumed that the plate – elastic foundation system vibrates in its in vacuo eigenmodes when it is in contact with fluid, and that each mode gives rise to a corresponding surface pressure distribution on the wetted surface of the structure. The fluid free-surface effects are neglected by imposing the high-frequency limit condition. The fluid-structure interaction forces are calculated in terms of the generalized hydrodynamic added mass coefficients that represent the inertial effect of the fluid. The methodology is verified, and the influence of foundation and fluid interaction on the dynamic behavior of the Mindlin plate is studied through parametric investigations

A boundary element method for dynamic analysis of elastic structures subjected to uniform axial flow

Akışkan taşıyan ya da eksenel bir akım içine daldırılmış elastik yapıların dinamik analizi için, lineer bir hidroelastik çözüm metodu sunulmuştur. Modal analiz tekniklerinden hareketle geliştirilen metod, bağımsız iki analize dayanmaktadır: (i) yapısal sönüm ve dış kuvvetlerin yokluğunda elastik yapının dinamik karakteristiklerinin belirlenmesi ve (ii) yapının akışkanla temastayken doğal modlarında hareket ettiği ve her bir modal formun, yapı ıslak yüzeyi üzerinde karşılık gelen bir basınç dağılımına neden olduğu varsayımları altında akışkan probleminin çözülerek, etkileşim kuvvetlerinin hesaplanması. Akışkan-yapı sisteminin davranışı, hidrodinamik kuvvetlerin, yapısal sönüm ve var olan diğer dış yüklerle birlikte genelleştirilmiş hareket denklemine etkitilmesiyle belirlenmektedir. Çözümün ilk aşaması ANSYS sonlu eleman yazılımıyla, ikinci aşama ise yapının elastik hareketlerinin akışkan ortamında neden olduğu pertürbasyonları tanımlayan potansiyel problemin, akışkan-yapı arayüzü üzerinde bir sınır integral denklemine dönüştürülmesiyle, sayısal olarak gerçekleştirilmektedir. Analizler sırasında, elastik yapının göreceli olarak yüksek frekanslarda titreştiği kabul edilerek, serbest yüzey dalgası etkileri ihmal edilmiş, ortaya çıkan serbest yüzey şartı ise imaj metodu kullanılarak doğrudan sağlanmıştır. Genelleştirilmiş eksu kütlesi, hidrodinamik sönüm ve hidrodinamik rijitlik formunda elde edilen etkileşim kuvvetleri, akışkan ortamının elastik yapı üzerindeki sırasıyla ve  Coriolis ve santrifüj etkilerini temsil etmektedir. Uçları basit bağlı silindirik bir kabuk üzerinde yapılan analizler, sunulan metodun güvenilirliğini ve etkinliğini ortaya koymaktadır.Anahtar Kelimeler: Dinamik akışkan-yapı etkileşimi, hidroelastisite, dinamik stabilite, eksenel akım etkisindeki elastik sistemler, sınır eleman metodu. The dynamic interaction between an elastic structure and a flowing fluid medium is an important aspect in the design of various engineering applications, such as flexible pipe lines conveying fluid, heat exchanger tubes in axial flow, inflatable dams in the presence of flowing water, etc. In all of these systems, fluid affects the dynamical behavior of the structure strongly and in the extreme case may cause instability. A general 3-D hydroelastic method is presented for linear dynamic analysis of structures subjected to uniform axial flow. The developed numerical approach is based on the fundamental principles of linear hydroelasticity theory, where a weak coupling methodology is preferred and co-use of finite element and boundary integral equation methods for elastic and fluid domains, respectively. By assuming that the structure does not deform the fluid, but only affects it through its elastic vibrations, the interested problem may also be taken as free or self-induced vibrations of elastic structures under the influence of hydrodynamic loads. The proposed numerical procedure is founded on two separate analysis: (i) evaluation of dynamic characteristics (natural frequencies and corresponding principal mode shapes) in the absence of any external excitation and structural damping (vacuum analysis), and (ii) by assuming that the elastic structure preserves its in-vacuo mode shapes when in contact with fluid, and that each mode shape gives rise to a corresponding surface pressure distribution on the wet part of the structure, solution of the fluid problem and calculation of the generalized fluid-structure interaction forces (wet analysis). In the former stage, a standard finite element software (ANSYS) is adopted and in the latter one, the fluid problem is converted to a boundary integral equation over fluid-structure interface and solved numerically. In this investigation, it is assumed that the fluid is ideal (inviscid and incompressible) and its motion is irrotational. It is also assumed that the elastic structure vibrates at relatively high frequencies so that the effect of surface waves can be neglected. The resulting free surface condition is satisfied implicitly by using method of images. During the analysis, the interaction problem is considered in two separate parts: (i) the vibration of the elastic structure in a quiescent fluid and (ii) the disturbance in the main axial flow due to the oscillation of the elastic structure. Using the Bernoulli's equation, the dynamic fluid pressure on the elastic structure is expressed in terms of potential function, and interaction forces are calculated from the pressure distribution over the wetted surface of the structure, as generalized added mass, hydrodynamic damping and hydrodynamic stiffness coefficients, due to the inertia, Coriolis and centrifugal effects of fluid, respectively. By merging the generalized structural matrices (mass and stiffness) with the hydrodynamic matrices, an eigenvalue problem is obtained for the elastic structure immersed in or containing flowing fluid, from which the wet dynamic characteristics of the system is obtained. In order to demonstrate the applicability of the proposed method, a circular cylindrical shell, simply supported at both ends is studied. The cylindrical shell is considered, separately, with rigid and flexible extensions at its ends. A cylindrical shell with rigid extensions corresponds to a finite length, flexible cylindrical shell connected to infinitely long rigid cylindrical baffles, of the same diameter as the shell at both ends and the cylindrical shell with flexible extensions coincides with one that is infinitely long and periodically supported. To assess the influence of flowing fluid on the dynamic behavior of the shell structure, the non-dimensional eigenfrequencies are presented as a function of the non-dimensional flow velocity. The imaginary parts of the eigenfrequencies decrease with increasing fluid velocity, and they reach zero values at certain axial fluid velocities, which correspond to points of static divergence. Due to the gyroscopic conservative nature related with Coriolis forces, the cylindrical shell may regain stability with increasing flow velocity and even for further velocities coupled mode flutter may also occur. But both of these are post-divergence behavior of the shell, involving large deformations and so cannot be decided by a linear theory. In general, a very good comparison is obtained between the calculations of the present study and results found in the literature.Keywords: Dynamic fluid-structure interaction, hydroelasticity, dynamic stability, elastic systems subjected to axial flow, boundary element method

A Boundary Element Method for Dynamic Analysis of Elastic Structures Subjected to Axial Flow

Abstract A boundary element method is presented to investigate the dynamic behavior of elastic structures partially or completely in contact with uniform axial flow. In the analysis of the linear fluid-structure interaction problem, it is assumed that the fluid is ideal and its motion is irrotational. Furthermore, the elastic structure is assumed to vibrate in relatively high-frequencies, so the infinite frequency limit condition is imposed for fluid free surface, which is satisfied implicitly by using method of images. When in contact with the flowing fluid, the structure is assumed to vibrate in its in vacuo eigen-modes that are obtained by using a finite element software. The wetted surface of the structure is idealized by using appropriate hydrodynamic panels and a boundary element method is formulated for velocity potential function, which is taken as linearly varying over the panels. Using the Bernoulli's equation, the dynamic fluid pressure on the elastic structure is expressed in terms of potential function, and the fluid-structure interaction forces are calculated as generalized added mass, hydrodynamic damping and hydrodynamic stiffness coefficients, due to the inertia, Coriolis and centrifugal effects of fluid, respectively. Solution of the eigenvalue problem associated with the generalized equation of motion gives the dynamic characteristics of the structure in contact with fluid. As an application of the method, the dynamics of a simply supported cylindrical shell subjected to internal flow is studied. The predictions compare quite well with the previous results in the literature

One-Stage Combined Thoracic Ancient Schwannomas Total Removal and Coronary Artery Bypass

Ancient schwannoma is a rare variant of neural tumors though rarely seen in the thorax. The combination with coronary artery diseases is also rare. Here we describe a 66 year-old male who had undergone one-stage combined surgery for thoracic ancient schwannomas removal and coronary artery disease. The masses were, respectively, 13 cm in the middle mediastinum and 5 cm in diameter originating from the intercostal nerve. The tumors were successfully removed using sternotomy, and then a coronary artery bypass grafting was performed. Here we discuss this rare tumor in relation to the relevant literature

A comparison of dexmedetomidine, moxonidine and alpha-methyldopa effects on acute, lethal cocaine toxicity

Background: The treatment of cocaine toxicity is an important subject for emergency physicians. We investigated the effects of dexmedetomidine, moxonidine and alpha-methyldopa on acute cocaine toxicity in mice. Objectives: The aim of this study was to evaluate the effects of dexmedetomidine, moxonidine and alpha-methyldopa in a mouse model of acute cocaine toxicity. Materials and Methods: We performed an experiment consisting of four groups (n = 25 each). The first group received normal saline solution, the second group received 40 μg/kg of dexmedetomidine, the third group received 0.1 mg/kg of moxonidine and the fourth group received 200 mg/kg of alpha-methyldopa, all of which were intraperitoneally administered 10 minutes before cocaine hydrochloride (105 mg/kg). All animals were observed for seizures (popcorn jumping, tonic-clonic activity, or a loss of the righting reflex) and lethality over the 30 minutes following cocaine treatment. Results: The ratio of animals with convulsions was lower in all treated groups when compared to the control (P 0.05). In addition, the time to lethality was also longer in the same group (P < 0.001). Conclusions: The present study provides the first experimental evidence in support of dexmedetomidine treatment for cocaine-induced seizures. Premedication with dexmedetomidine reduces seizure activity in a mouse model of acute cocaine toxicity. In addition, while dexmedetomidine may be effective, moxonidine and alpha-methyldopa did not effectively prevent cocaine-induced lethality. © 2015, Iranian Red Crescent Medical Journal

The Prevalence of Risky Behaviors Related to Violence in High School Students in a Southern City, Turkey

Injuries are the leading cause of mortality and morbidity in adolescents and can be grouped as unintentional (such as motor vehicle crashes and fires) and intentional (violence and suicide). The aim of this study was to find the prevalence of high risk behaviors related to violence in high school students. The population comprised 2,480 randomly selected students from 10 schools among 46,271 students from 72 high schools in 1999–2000 in Adana and 2,352 (94.8%) were reached. They completed a Youth Risk Behavior Survey Questionnaire (YRBSQ). The mean age was 16.5 ± 1 (14–21) years. 275 (11.7%) students stated that they carried a knife or a sharp weapon during the last 30 days, 151 (6.4%) carried a gun, 710 (30.2%) participated in a physical fight, 68 (2.9%) were threatened or injured by a weapon, 73 (3.1%) could not attend school because of threats from other students, 96 (4.1%) were forced into sexual intercourse. Male students were significantly more likely than female students to report all types of high risk behaviors except forced sexual intercourse. The rate of risky behaviors increased with higher grade. Violence towards and by adolescents is a severe problem. Families, teachers, and health care professionals should be aware of risk factors and be active in prevention of high risk behaviors in youth

Depressive symptomatology among university students in Denizli, Turkey: Prevalence and sociodemographic correlates

Aim: To determine overall and subgroup prevalence of depressive symptomatology among university students in Denizli, Turkey during the 1999-2000 academic year, and to investigate whether sociodemographic factors were associated with depressive symptoms in university students. Methods: A stratified probability sample of 504 Turkish university students (296 male, 208 female) was used in a cross-sectional study. Data were obtained by self-administered questionnaire, including questions on sociodemographic characteristics and problem areas. The revised Beck Depression Inventory (BDI) was used to determine depressive symptoms of the participants. BDI scores 17 or higher were categorized as depressive for logistic regression analysis. Student t-test and linear regression were used for continuous data analysis. Results: Out of all participants, 26.2% had a BDI score 17 or higher. The prevalence of depressive symptoms increased to 32.1% among older students, 34.7% among students with low socioeconomic status, 31.2% among seniors, and 62.9% among students with poor school performance. The odds ratio of depressive symptoms was 1.84 (95% confidence interval [CI], 1.03-3.28) in students with low socioeconomic status and 7.34 (95% CI, 3.36-16.1) in students with poor school performance in the multivariate logistic model. The participants identified several problem areas: lack of social activities and shortage of facilities on the campus (69.0%), poor quality of the educational system (54.8%), economic problems (49.3%), disappointment with the university (43.2%), and friendship problems (25.9%). Conclusions: Considering the high frequency of depressive symptoms among Turkish university students, a student counseling service offering mental health assistance is necessary. This service should especially find the way to reach out to poor students and students with poor school performance

Effects of moderate smoking on the central visual field

Purpose: To investigate whether moderate cigarette smoking has any effects on the central visual field. Methods: This study included 30 healthy, moderate cigarette smokers (10-20 cigarettes per day for at least the past 5 years) and 22 healthy non-smokers. After two training test sessions, all individuals underwent computerized visual field examinations (Humphrey 30-2 Full Threshold Test) with both white-on-white (W-W) perimetry and blue-on-yellow (B-Y) perimetry. One eye of each subject with reliable visual field test results was evaluated. The foveal threshold, mean deviation (MD), pattern standard deviation (PSD), short-term fluctuation (SF), corrected pattern standard deviation (CPSD), glaucoma hemifield test (GHT) and number of significantly depressed points deviating at p 0.55). The number of depressed points deviating at p 0.05). The number of significantly depressed points deviating at p 0.05). No significant difference in GHT was determined with either perimetry for the smokers compared with the non-smokers (p > 0.05). Conclusion: This study suggests that moderate cigarette smoking is associated with both diffuse and localized reductions in retinal sensitivity with W-W perimetry. Only reduction in the foveal threshold was observed with B-Y perimetry, with no hints of diffuse and localized reductions

Frequency of skeletal chest injuries associated with cardiopulmonary resuscitation: forensic autopsy

BACKGROUND: Fractured ribs and sternum are frequent complications of thoracic compression during CPR (cardiopulmonary resuscitation) in adults. This study was conducted to determine the incidence of rib and sternal fractures after conventional closed-chest compression in the treatment of cardiac arrest. METHODS: We reviewed the forensic autopsy findings of 231 deaths referred to the Pamukkale University Department of Forensic Medicine over a 12-month period, 2004-2005. CPR-related chest injuries comprising rib and sternum fractures, ecchymosis and subcostal hemorrhage were compared retrospectively in 104 patients. RESULTS: Ninety-one (87.5%) of the 104 patients were adults, and 13 patients (12.5%) were children. The mean (SD) age in the pediatric group (5F/8M) was 5.48 (±5.96) and in the adult group (18F/73M) was 44.88 (±18.31). Forty-four (42.3%) of the 104 patients died of traumatic cause and 60 (57.7%) of non-traumatic cause. Ecchymosis was present in 26 (28.8%) patients, subcostal hemorrhage in 16 (17.6%) patients and fractures (sternal and costal) in 12 (13.2%) patients in adults. There were no significant differences between groups according to age, sex and traumatic-nontraumatic cause in terms of skeletal chest injuries associated with CPR in adult patients (p>0.05). CONCLUSION: This study shows a low incidence of rib and sternal fracture after closed-chest compression in the treatment of cardiac arrest in forensic autopsy cases

Suicidal Thought and Behavior in High School Students in Adana, Turkey

Fifty years ago adolescents mostly died of natural causes, whereas they now die from more preventable causes. Part of this change has been a worldwide rise in adolescent suicide rates in both developed and developing countries. Suicides are probably under reported due to cultural and religious stigma attached to self-destruction. Objectives of this study were to collect data about suicidal thoughts, plans and attempts and related sociodemographic details in high school students. The population comprised 2,480 randomly selected students among 46,271 students from 72 high schools in 1999–2000 in Adana and 2,352 (94.8%) students from 10 schools were reached and given a questionnaire modified using Youth Risk Behavior Survey Questionnaire (YRBSQ). x2 and Kolmogorov-Smirnov tests were used. Mean age was 16.5 ±1 (14–21) year, 1,187 (50.5%) students reported severe desperation, 526 students (22.4%) had suicidal thoughts, 332 (14.1%) planned committing suicide, 145 (6.2%) attempted suicide. The occurrence rate of desperation, suicidal thoughts, plans, attempts and the mean number of attempts were significantly higher in females than males. Adolescent suicide is a tragedy affecting individual, family, peers, and community. Families, teachers, and physicians should be aware of risk factors for suicide