Plakların Sayısal Bir Yöntemle Elasto-plastik Dinamik Analizi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada amaç, dört kenarı ankastre dikdörtgen ince plakların elastik ve elasto-plastik dinamik deplasmanlarının, değişik yükler altında Newmark Doğrusal İvme Metodu ile hesaplamaktır. İlk olarak, dikdörtgen plakların genel hareket denklemi Kirchhoff Plak Teorisi uygulanarak elde edildi ve plakın özdeğerleri ve özvektörleri sonlu farklar metodu kullanılarak hesaplandı. Daha sonra, plakın rijitlik matrisi ve kütle matrisi direkt rijitlik metoduyla oluşturuldu. Sonuçta, plakın rijitlik matrisi, kütle matrisi ve yük vektöründen oluşan sistemin hareket denklemi Newmark doğrusal ivme metodu ile çözüldü.The aim of this study is to examine the elastic and elasto-plastic deflections of rectangular thin plates with clambed supported under various dynamic loads by Newmark’s linear acceleration method. Firstly, the general equation of motion of the rectangular plate has been derived by applying Kirchhoff’s Plate Theory and the eigenvalues and eigenvectors of the plate with clambed supported have been obtained using the finite difference method. Then the stiffness matrix and mass matrix of the plate was constructed by the direct stiffness method. Finally, the equation of motion of the system which consists of the stiffness matrix, the mass matrix, and the load vector has been solved using the Newmark’s linear acceleration method

A finite strain theory of elastoplasticity and its application to wave propagation

Bibliography: pages 154-164.A constitutive theory of finite strain plasticity is developed by using the methods of convex analysis. The theory abstracts and extends the classical assumptions of a convex region of admissible stresses, and the normality law. The overall effects of plastic behaviour are contained in the theory through the presence of one or more internal variables. The thermodynamic restrictions of the second law together with the use of results of convex analysis lead in a natural way to the evolution equation or flow law. Non-smooth yield surfaces are included in the theory; nevertheless, the form of this theory makes a study of propagation of singular surfaces awkward. With a view to carrying out such a study, an alternative means of treating non-smooth convex yield surfaces is developed. This alternative theory is essentially a synthesis of the theory of Sewell, and that presented earlier in the thesis. The theory of singular surfaces is reviewed in the context of finite strain elastoplasticity, and necessary conditions for the propagation of acceleration waves are derived. A comparison of elastic and plastic wave speeds is made, and inequalities similar to those of Mandel for the small-strain case are derived. The propagation conditions for principal waves in both longitudinal and transverse directions, and the corresponding wave speeds, are found and compared for solids obeying a neo-Hookean elastic law, and with either the von Mises or Tresca yield criteria

A full Eulerian finite difference approach for solving fluid-structure coupling problems

A new simulation method for solving fluid-structure coupling problems has been developed. All the basic equations are numerically solved on a fixed Cartesian grid using a finite difference scheme. A volume-of-fluid formulation (Hirt and Nichols (1981, J. Comput. Phys., 39, 201)), which has been widely used for multiphase flow simulations, is applied to describing the multi-component geometry. The temporal change in the solid deformation is described in the Eulerian frame by updating a left Cauchy-Green deformation tensor, which is used to express constitutive equations for nonlinear Mooney-Rivlin materials. In this paper, various verifications and validations of the present full Eulerian method, which solves the fluid and solid motions on a fixed grid, are demonstrated, and the numerical accuracy involved in the fluid-structure coupling problems is examined.Comment: 38 pages, 27 figures, accepted for publication in J. Comput. Phy

Termoelastik Kısıtlı Cisimlerde Zayıf Şok Dalgası Yayılması Ve Kayma Bandı Oluşumu

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Belli bir doğrultudaki uzamazlık kısıtlaması altındaki termoelastik cisim için zayıf şok dalgası hızları elde edilmiştir. Bunun için birinci mertebe tekillik yüzeyi olan zayıf şok dalgası eşiği üzerindeki sıçramalar Taylor serisi açılımı yapılarak hesaplanmıştır. Bünye denklemleri serbest ve kısıtlı kısımların toplamları olarak yazılmıştır. Hiperelastik malzeme modeli olarak sıcaklık terimlerinin bulunduğu geliştirilmiş St.Venant – Kirchhoff modeli seçilmiştir. Son kısımda incelenen örnek problemde tek eksenli çekme altında, yatay ile 45º açı yapan liflerle donatılmış sıkıştırılabilir termoelastik cisim için zayıf şok dalgası yayılma hızları, bunların sıcaklık ve uzama değerleri ile değişimleri ve kayma bandı oluşturacak kritik uzama değerleri sunulmaktadır.Weak shock wave propagation speeds are determined in an inextensible thermoelastic solid. Jumps across the shock wave front are obtained by using Taylor’s series expansion. The constitutive equations are written as the summation of unconstrained and constrained parts. For the hyperelastic material, the modified St Venant-Kirchhoff material model is considered. Weak shock wave propagation speed variation versus temperature and stretches, and critical stretches corresponding to shear band formation are obtained for a thermoelastic solid reinforced with inextensible fibers

Propagation of acceleration waves in the viscoelastic Johnson-Segalman fluids

The propagation conditions of acceleration waves are investigated for a viscoelastic fluid using the Johnson-Segalman viscoelastic model. Explicit expressions are obtained for the wave speeds adopting the theory of singular surfaces. The simple shearing motion, uniaxial, biaxial extension and uniform dilation are considered as the initial states of deformation. The variations of the speeds with the propagation direction, stretch ratio and material parameters are presented. © 2009 Elsevier Ltd. All rights reserved

Burnout Syndrome During Residency

OBJECTIVE: The aim of this study is identified the degree of Burnout Syndrome (BOS) and find out its correlation with years of recidency and sociodemograpfic chareacteristics, training, sleeping habits, such as smoking and alcohol consumption. METHODS: After approval from the Hospital Ethics Committee and obtaining informed consent, First, second, third, fourth and fifth year of recidency staff (n=127) working in our hospital were involved in this study. The standardized Maslach Burnout Inventory (MBI) was used in this study. RESULTS: Fifty six male (44.1%) and seventy one female (55.9%) residents were enroled in this study (Coranbach Alfa(α)=0.873). 57% of the first year residents smokes cigaret and 54% of them use alcohol. 2% of them gets one day off after hospital night shift, 61% of them suffers from disturbed sleep. 60% of them had been stated that they willingly selected their profession. 61% of them prefers talking to friends and 32% of them prefers shopping to overcome stress. There were statistical difference acording to years of recidency in MBI, Emotional Burnout (EB) and desensitisation scale (DS) points. EB scale points of the second year of residency group was statisticaly higher than fourth year of residency group. DS points of second year of residency group was also statisticaly higher than the third and fourth year of residency group. There was no statistical difference between any groups in Personal Success. CONCLUSION: BOS is a frequent problem during residency in anaesthesia. Appropriate definition and awareness are the first important steps to prevent this syndrome. Further administrative approaches should be evaluated with regard to their effects