Selection of design and operational parameters in spindle-holder-tool assemblies for maximum chatter stability by using a new analytical model

In this paper, using the analytical model developed by the authors, the effects of certain system design and operational parameters on the tool point FRF, thus on the chatter stability are studied. Important conclusions are derived regarding the selection of the system parameters at the stage of machine tool design and during a practical application in order to increase chatter stability. It is demonstrated that the stability diagram for an application can be modified in a predictable manner in order to maximize the chatter-free material removal rate by selecting favorable system parameters using the analytical model developed. The predictions of the model, which are based on the methodology proposed in this study, are also experimentally verified

Analytical modeling of spindle-tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindleholdertool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modication methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is veried by comparing the natural frequencies of an example spindleholdertool assembly obtained from the model with those obtained from a nite element software

Effect analysis of bearing and interface dynamics on tool point FRF for chatter stability in machine tools by using a new analytical model for spindle-tool assemblies

Self-excited vibration of the tool, regenerative chatter, can be predicted and eliminated if the stability lobe diagram of the spindle–holder–tool assembly is known. Regardless of the approach being used, analytically or numerically, forming the stability lobe diagram of an assembly implies knowing the point frequency response function (FRF) in receptance form at the tool tip. In this paper, it is aimed to study the effects of spindle–holder and holder–tool interface dynamics, as well as the effects of individual bearings on the tool point FRF by using an analytical model recently developed by the authors for predicting the tool point FRF of spindle–holder–tool assemblies. It is observed that bearing dynamics control the rigid body modes of the assembly, whereas, spindle–holder interface dynamics mainly affects the first elastic mode, while holder–tool interface dynamics alters the second elastic mode. Individual bearing and interface translational stiffness and damping values control the natural frequency and the peak of their relevant modes, respectively. It is also observed that variations in the values of rotational contact parameters do not affect the resulting FRF considerably, from which it is concluded that rotational contact parameters of both interfaces are not as crucial as the translational ones and therefore average values can successfully be used to represent their effects. These observations are obtained for the bearing and interface parameters taken from recent literature, and will be valid for similar assemblies. Based on the effect analysis carried out, a systematic approach is suggested for identifying bearing and interface contact parameters from experimental measurements

Anne-Çocuk İlişkisinde Risk Faktörleri: Televizyona Maruz Kalma ve Anne-Çocuk Oyun Süresi

The objective of this study was to examine the associations of tv exposure, playtime with children and mother child relationship. Correlational research method was considered for this study. Sample size was 73 mothers whose children’s ages change between 50 and 74 months of age from the largest city İstanbul (33 boys and 40 girls). Turkish version of Child Parent Relationship Scale, family demographic characteristics form and a questionnaire (short answered questions about playtime and tv exposure hours) were used as data collection tools. Bivariate analyses using t tests, analysis of variance, and Pearson correlation coefficient were conducted. Multiple linear regression was run to examine associations between TV exposure, play time and mother child relationship. Mothers and children had a high level of positive relationship in the current study. Mothers’ education level, mothers’ age, parents’ work hours and children’s gender and order of birth which were assumed to have a link with mother child relationship didn’t make a significant difference on mother child relationship scores. The link was presented between tv exposure, playtime with children and mother child relationships via regression results. It was concluded that mothers who play with their children more were expected to have higher mother child relationship scores, after controlling for the household tv exposure. Household tv exposure had a significant negative weight, indicating that after accounting for playtime between mothers and children, participants who stated higher household tv exposure were expected to have lower mother child relationship scores.Bu araştırmanın amacı, televizyona maruz kalma süresi, anne-çocuk oyun süresi ve anne-çocuk ilişkisi arasındaki bağı ortaya koymaktır. Korelasyonel araştırma yöntemi kullanılarak gerçekleştirilen araştırmanın örneklemini İstanbul’da bir okul öncesi eğitimi kurumuna devam eden, yaşları 50-74 ay arasında değişen 73 okul öncesi dönemdeki çocuğun (33 erkek ve 40 kız) annesi oluşturmaktadır. Araştırmada anne-çocuk ilişkisini değerlendirmek için Çocuk Anababa İlişki Ölçeği ve aileye ilişkin demografik özellikleri elde etmek için kişisel bilgi formu kullanılmıştır. Verilerin analizinde t testi, varyans analizi ve Pearson korelasyon katsayısı kullanılmıştır. Televizyona maruz kalma süresi, anne-çocuk oyun süresi ile anne-çocuk ilişkisi arasındaki bağı incelemek üzere çoklu doğrusal regresyon analizi yapılmıştır. Araştırma sonucunda, örneklemi oluşturan anne ve çocuklar arasında olumlu bir ilişki olduğu belirlenmiştir. Anne-çocuk ilişkisi ile bağlantılı olduğu varsayılan annelerin öğrenim durumu, yaşı, anne baba çalışma saatleri ile çocukların cinsiyeti ve doğum sırası değişkenlerinin anne-çocuk ilişki puanları üzerinde anlamlı bir farklılık yaratmadığı belirlenmiştir. Çoklu regresyon analizi sonuçları televizyona maruz kalma süresi ve anne-çocuk oyun süresinin birlikte anne-çocuk ilişkisini anlamlı düzeyde yordadığını ortaya koymuştur. Buna göre; televizyona maruz kalma süresi kontrol altında tutulduğunda çocuklarıyla oyun oynayan annelerin daha güçlü bir anne- çocuk ilişkisi kuracağı, öte yandan annelerin çocuklarıyla oyun oynadıkları süre kontrol altında tutulduğunda evde televizyona maruz kalma süresi fazla olan ailelerde annelerin çocuklarıyla daha zayıf bir ilişki kuracağı beklenmektedir

Fast acceleration algorithm based on DFT expansion for the iterative MoM analysis of electromagnetic radiation/scattering from two-dimensional large phased arrays

An acceleration algorithm based on Discrete Fourier Transform (DFT) is developed to reduce the computational complexity and memory storages of iterative methods of moment (IMoM) solution to O(Ntot), where Ntot is the total number of elements in the array. As such, numerical results for free-standing dipoles obtained using IMoM-DFT approach are presented and compared with the conventional MoM solution

Efficient analysis of large phased arrays using iterative MoM with DFT-based acceleration algorithm

A discrete Fourier transform (DFT)-based iterative method of moments (IMoM) algorithm is developed to provide an O(Ntot) computational complexity and memory storages for the efficient analysis of electromagnetic radiation/scattering from large phased arrays. Here, Ntot is the total number of unknowns. Numerical results for both printed and free-standing dipole arrays are presented to validate the algorithm's efficiency and accuracy

Extension of forward backward method with DFT based acceleration algorithm for the efficient analysis of large periodic arrays with arbitrary boundaries

An extension of Forward-Backward (FB) with Discrete Fourier Transform (DFT) based acceleration approach is presented. This is given to provide a relatively efficient analysis of EM radiation/scattering from an electrically large, planar, periodic, finite arrays with arbitrary boundaries, such as arrays with circular or elliptical boundaries. It is shown that only very few significant DFT terms are sufficient to provide accurate results

Analytical modeling of spindle-tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindle-holder-tool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modification methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is verified by comparing the natural frequencies of an example spindle-holder-tool assembly obtained from the model with those obtained from a finite element software

Extension of forward-backward method with DFT-based acceleration algorithm for the efficient analysis of large periodic arrays with arbitrary boundaries

An extension of the discrete Fourier transform (DFT)-based forward-backward algorithm is developed using the virtual-element approach to provide a fast and accurate analysis of electromagnetic radiation/scattering from electrically large, planar, periodic, finite (phased) arrays with arbitrary boundaries. Both the computational complexity and storage requirements of this approach are O(Ntot) (Ntot is the total number of unknowns). The numerical results for both printed and freestanding dipole arrays with circular and/or elliptical boundaries are presented to validate the efficiency and accuracy of this approach. © 2005 Wiley Periodicals, Inc

The Role of Oxygen Free Radicals in Acute Renal Failure Complicating Obstructive Jaundice: An Experimental Study

Oxydant injury is considered to be an important mechanism in the pathophysiology of acute renal failure. It has been thought that decrease in extracellular and intracellular fluid and endotoxemia seen in obstructive jaundice may cause an increase in production of oxygen free radicals and impairment in antioxydant defense mechanism. This study is designed to investigate the possible role of oxydant injury in renal failure seen in jaundiced patients. In this study, 28 rats were divided into four groups: Control(C) (N=7); Renal ischemia (RI) (N=7); Obstructive jaundice+renal ischemia (OJ+RI) (N=7); Obstructive jaundice (OJ) (N=7). All groups were compared with each other according to renal failure findings and enzyme activities, such as Xanthine oxidase (XOD), Superoxide Dismutase (SOD) and Catalase in renal cortex and Glutathione Peroxidase (GSH-Px), in blood at 3rd day after ischemia and reperfusion. Renal failure findings monitored by blood urea and creatinine levels, seemed more evident in OJ+RI than RI group (p <0.05). When compared with RI, in OJ+RI group, increase in XOD activity at 3rd day was statistically significant [0.259 ±0.01 U/g (tissue) and 0.362±0.03 U/g (tissue) respectively] (p <0.05). SOD and GSH-Px activities of each ischemic group at 3rd day were decreased compared to non-ischemic groups. This fall was significant (p <0.05). But there was no statistical difference between jaundiced and non-jaundiced groups. Alterations in catalase activities also had no statistical significance