Dinamik yüklü radyal kaymalı yatakların teorik ve deneysel olarak incelenmesi
Theoretical and experimental investigation of dynamically loaded journal bearings
- Tez No: 19297
- Danışmanlar: DOÇ.DR. M. SAİT YÜCENUR
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1991
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 109
Özet
Ö2ET Bu çalışmada, dinamik yüklü Cyani hızın, yükün veya her ikisinin zamana bağlı olarak değiştiği radyal kaymalı yataklar, teorik ve deneysel olarak incelenmiştir. Çeşitli makinalarda, özellikle pistonlu makinalarda yataklar, büyüklüğü ve yönü değişen yüklere maruz kalırlar. Bu yataklarda eğer yüzeyleri ayıran bir akışkan filmi oluşursa, bu film yükün ve veya hızın değişimine bağlı ol ark değişecektir. Bu değişimin bilinmesi ve hesaplanabilmesi yatak performansının Önceden tahmini için gereklidir. Takdim edilen çalışma iki bölümden oluşmaktadır. Birinci bölümde dinamik yüklü radyal kaymalı yatakta yüzeyleri ayıran akışkan filminin zamana göre değişimi diğer bir deyimle mil merkezi yörüngesinin hesaplanması için yeni bir metod teklif edilmektedir. Yazılan bilgisayar programı ile değişken sınır şartları her an için elde edilmekte, böylece filmin yalnız pozitif basınç olan bölümü taşıma hesabına katılarak mil merkezi yörüngesi hesaplanmaktadır. Program kişisel bilgisayarlarla da çalışmaya elverişlidir. Açılımı dikdörtgen olan yataklar, sabit viskozite kabulü ve yan akım etkisi bir düzeltme faktörü ile dikkate alınarak simüle edilmektedir. Deneysel bölümde ise kurulan deney düzeniyle, sabit bileşenli sinusoidal yük kullanılarak, yatak davranışı çeşitli parametrelere bağlı olarak incelenmiştir. Bulunan teorik ve deneysel sonuçların genel olarak uyum sağladığı gözlenmiştir.
Özet (Çeviri)
SUMMARY THEORETICAL AND EXPERIMENTAL INVESTIGATION OF DYNAMICALLY LOADED JOURNAL BEARINGS In this study, dynamically loaded journal bearings are investigated both theoretically and experimentally. In internal combustion engines especially in reciprocating ones, bearings are effected by the loads that their magnitude and direction. In these bearings if a fluid film which seperates the surfaces, the thickness of the film will be varied as a result of the magnitude of the load and the shaft's speed changes. It is necassary to know and to calculate this variation of to predict the bearing performance. In the theoretical part of the study, Reynolds equation is. used to investigate the hydrodynamic journal bearings. Under the assumptions of with a constant viscosity and density. For the journal bearing without side leakage the Reynolds equation is as follows. dp > = 6 T) R -^s + 12 7? R2 V de " ae As the right-hand side of the above equation the first term 6 77 U R dh/d9t which represents the wedge effect and the second term represents the squeeze film effect. Squeeze film effect is very important for the film devel opted in dynamically loaded bearings. A physical model, for the dynamically loaded bearings is shown in Fig. 1. e and (p are variables which specify the position of the shaft center. For point A, the circumf erantial velocity U, and normal velocity V, can be easel ly obtained from this figure as follows U ^ co R V = - C s cos 9 - C s. 'ig. 1 Physical Model Loaded Bearings for the Dynamically The main problem for the theoretical investigation of dynamically loaded bearings is to determine boundary conditions. As know in journal bearing the integretin of Reynolds equation gives both positive and negative pressure region together. In dynamically loaded bearings, boundaries (boundary conditions) of the positive and negative pressure regions vary with time. By using the developed calculation method and computer program the boundary conditions which vary with time exist in these bearings, determined for the point of journal's center path each time. Using these boundary conditions only the positive pressure region is considered in investigation of bearings behaviour. The developed calculation algorithm is as follows. 1- A prediction ought to be made conditions Ccx,(3>. And then by using F and p of the time t the components of shaft center are calculated. for boundary , 40 , £. the velocity of 2- Substitution the values of F, ai, &, p, p in pressure equation, pressure distribution e and p in pressure equation, pressure aist.rj.Dut, ion is calculated. If ex and ft were the real boundary conditions the pressure distribution could be obtained as shown in Fig 2. However there is not such a state is mentioned. So a pressure distribution is obtained as in Fig 3. The number of the points on which the pressure is zero, are more than two. VİNFig. 3 C i. -r -3 IX3- Considering the zero pressure points in pressure distribution, the new ex,ft boudary conditions are defined. Turning back to the first step again, new shaft center velocities are found. This process is repeated until a pressure distribution is obtained as in Fig 2. At last, the real boundary conditions will be found step by step. It can be said that the proposed method is a guided trial and error method. For a unit bearing width, the carried load of the oil film can be obtained by integrating the positive pressure region by as follows. W = R f p cos (9) d& CX : v = ~ r J pce> cos it has been neglected the side leakage and its effect on the bearing pressure. This effect can be considered and be imported into the calculation by using a correcting factor . The load used in the calculation is Fca[ Ct). By defining a correcting factor we can write F, = f F, Ct> cal 0 real The correcting factor is obtained considering the previous studies on the journal bearings. A exaple for calculated shaft center path from a beginning point can be seen in Fig. 4. As seen for a steady state cylic load the center of shaft is staying on a closed curve. In the experimental study, by using an experimental rig the bearing behaviour are investigated depend on various bearing parametres. Bearing center path is observed on the oscilloscope screen. Two capasitive pick-up have been used to observe the film thickness variation. They have been fixed to the bearing budy which were mutually prependicular. Static and si nusoi dally varying forces are applied to the main bearing by way of two hydrostatic bearings, one above and below the bearing body CFig.S>. For the ratio of the loading frequency to the shaft frequency, the values of 1 are taken.a» XIXIIAs a results of present study the fol loving can be concl uded. By using the computer program based on the proposed solution method, the behaviour of dynamically load journal bearing can be investigated by employing a personal computer. The obtained -results given an opinion about the sufficiency of the method. In the bearing that they are subjected a cylic load or a load with a rotating component, the path of shaft center is a closed curve similar to an ellipse as seen in Fig. 4 In the calculated and drawn path, it has been seen that the effects of system parametres are as expected. For instance it is observed both theoretically and experimentally that as the frequency of the varying load increases, the curve of the path is getting smaller. It can be said that the bearings subjected high frequency load be have similar to the bearing with the constant load. The film is getting thinner as the relative bearing clearance increases, in other words, the path is developed in a region were there is larger eccentricity. Similar thing is observed by decreaing the viscosity. XIII
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