Tuncay Karaçay

An experimental investigation on the effect of powder mixed dielectric on machining performance in electric discharge machining

Abstract In this study, the variations of machining performance outputs, namely workpiece surface roughness, surface profile power spectral density, workpiece removal rate, electrode wear rate, relative wear, workpiece surface hardness, and workpiece surface microstructure were experimentally investigated with the varying machining parameters for metal powder mixed dielectric liquid in electrical discharge machining (EDM). The machining tests were conducted by using a prismatic steel workpiece and copper electrodes with graphite and boric acid powders (H3BO3) mixed kerosene dielectric at different powder concentrations and pulse time settings. The experiments have shown that the type and concentration of the powders mixed into the dielectric and the pulse time were effective on machining performance outputs in EDM.

Vibrations of a grinding spindle supported by angular contact ball bearings

In the current paper, the radial, axial, rocking, and yawing vibrations of a rigid grinding spindle supported by a pair of angular contact ball bearings are studied. A computer program was developed to simulate the dynamic behaviour of the spindle and results are presented in the time, frequency, and waterfall diagrams. Results from the simulations for different spindle speeds show the characteristic ball passage frequency (BPF) (varying compliance) and its harmonics due to non-linear Hertzian contact between the balls and the races for even a defect free bearing. This behaviour is, of course, predicted theoretically, but most of the previous simulations only give the effect of BPF when it coincides with the natural frequencies of the system or under specific conditions. This paper will be a guide for researchers studying vibrations of a spindle supported by ball bearings as it describes the details of the theoretical background of the modelling and simulation.

Dynamics of Externally Pressurized Air Bearing With High Values of Clearance

Performance parameters such as critical speed and stability are affected by various design parameters such as supply pressure, clearance between shaft and rotor (air film thickness), bearing diameter and length etc. for externally pressurized gas lubricated bearing. Literature about effects of supply pressure is generally analyzed with clearances which are lower than 100 μm. Externally pressurized gas lubricated bearings with small clearance have some practical disadvantages such as difficulties in manufacturing process and price. So, externally pressurized air bearing may become widespread with usage of higher values of clearance in the bearing. However, there is limited number of study investigating the dynamics of externally pressurized air bearing with high values of clearance. In this study the effect of supply pressure was investigated on the dynamic of an externally pressurized gas lubricated bearing with increased clearance. The flow between shaft and rotor was modeled using Reynold’s Equation which is known fluid equation of motion. And this model was solved by Alternating Direction Implicit (ADI) numerical solution method. Dynamics of the rotor was investigated for different elevated (increased) clearances.Copyright

Non-Stationary response of a vehicle obtained from a series of stationary responses

Ride characteristics of a vehicle moving on a rough ground with changing travel velocity are analyzed in this paper. The solution is difficult due to the non-stationary characteristics of the problem. Hence a new technique has been proposed to overcome this difficulty. This new technique is employed in the analysis of ride characteristics of a vehicle with changing velocity in the time/frequency domain. It is found that the proposed technique gives successful results in modelling non-stationary responses in terms of a series of stationary responses.

Intrusion Detection Using Seismic Signals and Classification with Support Vector Machine

Seismic signals which are generated by human footsteps could be used in intrusion. Feature extraction is the most important step of the target detection and classification. In this study, vibration signals, which are generated by human steps, are analyzed for intrusion detection. A test set-up is established for measuring seismic signals equipped with a seismic accelerometer and experiments are performed according to different measurement scenarios. Crest factor and kurtosis values of raw data and discrete wavelet transform (DWT) analysis results are examined. Three different features matrices are generated using crest factor and kurtosis value of raw data and DWT analysis data. Detection and no-detection cases are divided into two groups and three support vector machine (SVM) classifiers are modeled using data. The results show that, detection distance increases with improved feature matrix generated with DWT crest factor and kurtosis values of data, which also decreases the error rate of the classifier.

Numerical Investigation of Rotor-Bearing Vibrations with Tilted Externally Pressurized Air Lubricated Bearing

In this study, vibrations of a rotor-bearing system supported by tilted air bearing are numerically investigated. Air flow between rotor and bearing surfaces is modelled using Reynolds equation with an introduced new clearance function for tilted air bearing. In order to calculate air film forces, Reynolds equation is solved using Differential Transform and Finite Difference hybrid numerical solution method. Dynamic motions of the rotor-bearing system supported by air bearings are modelled with air film forces in four degrees-of-freedom. In order to investigate effects of the bearing tilt on the vibrations of the rotor, one of the air bearing is modelled with a certain amount of tilt angle and the model is simulated for different rotor angular speeds.

ZEMİN TİTREŞİMLERİ ÖLÇÜMÜ VE ANALİZİ İLE İNSAN HEDEFLERİN TESPİTİ

Hareket halindeki insanlar zemin uzerinde birbirlerini takip eden darbeler seklinde zorlamalar olustururlar. Darbeler sonucu zeminde bir takim duzensizlikler olusur ve bu duzensizlikler sonucu olusan titresimler darbe kaynagindan sismik dalgalar seklinde yayilirlar. Zeminde olusan bu titresimlerinin olculmesi ve analizi ile insanlarin varliginin algilanmasi ve tespiti mumkundur. Bu calismada hedef tespiti amaciyla sismik sinyaller toplanmis ve belirli zaman araliklarina bolunerek incelenmistir. Bu sinyallerin olculebilmesi icin bir deney altyapisi kurulmus ve belirlenen olcum senaryolari dâhilinde bir takim deneyler gerceklestirilmistir. Test sonuclari zaman ve frekans tanim bolgelerinde analiz edilmistir. Kullanilan analiz yontemleri ile insan adimi karakteristigi cikarilmis, adim kaynakli darbelerin zeminde olusturdugu zorlamalar incelenmis ve farkli yuruyus stillerinde bir insanin olusturdugu sismik sinyal bilesenleri tespit edilebilmistir. Elde edilen sonuclar, titresim analizi ile hedef tespiti ve tanimlamasi yapilabilecegini ortaya koymaktadir.

GERÇEK YOL GİRDİSİNE MARUZ İKİ SERBESTLİK DERECELİ ÇEYREK TAŞIT MODELİNİN SÜRÜŞ KARAKTERİSTİĞİNİN İNCELENMESİ

Bu makalede duzgun olmayan bir yolda hizi degiserek seyahat eden bir tasitin surus karakteristigi analiz edilmistir. Problemin duragan olmayan yapisindan kaynaklanan cozum zorlugunu asmak icin yeni bir yontem gelistirilmis ve bu yontemle hizi degisen bir tasitin surus karakteristigi zaman/frekans bolgesinde analiz edilmistir. Kullanilan bu yeni teknigin duragan olmayan sureclerin bir seri duragan cevaptan elde edilmesinde basarili bir sekilde uygulanabilecegi iki serbestlik dereceli bir ceyrek tasit modeli kullanilarak gosterilmistir.