Czeslaw M. Rodkiewicz

Localization of early atherosclerotic lesions in the aortic arch in the light of fluid flow

Abstract The blood flow characteristics of the human aortic arch region have been simulated on the open channel flow model. Experiments indicate existence of five separation regions and four stagnation regions. It is postulated that the atherosclerotic formations may commence and develop at these locations. To prove the thesis the early history of the atherosclerotic formations within the aortic arch of the rabbit have been, in vivo , experimentally determined. It was found that the atherosclerotic formations of the rabbit do commence and develop at the locations where there are separation and stagnation regions. As the consequence of the geometrical, flow and functional similarity the expectation is expressed that the atherosclerotic formations with in the aortic arch of the human will begin and develop at the similar locations.

On the Numerical Analysis to the Thermoelastohydrodynamic Lubrication of a Tilting Pad Inclusive of Side Leakage

Numerical solutions are obtained for the thermoelastohydrodynamic lubrication of a tilting pad based on the three-dimensional flow of lubricant. For elastic deformation, the pad is idealized as a uniform plate with free boundaries so that a displacement coefficient matrix can be established by the conventional finite difference method. For pressure distribution, a fast Newton-Raphsons approach is used in solving the generalized Reynolds equation, film thickness equation, inlet pressure buildup equation, and the force balance and moment balance equations of the pad, simultaneously. For temperature distribution, the finite difference method is carried out with the help of a sweeping scheme.

On the Design of Thrust Bearings Using a CFD Technique

A computational fluid dynamics (CFD) technique is used to examine fully submerged three-dimensional thrust bearings, including the effects of fluid inertia in both the thin film clearance and the groove. Making use of the advantage of the CFD technique, the present paper focuses on the optimum design of thrust bearings in terms of film ratio and fore-region volume size, given the bearing geometry. In contrast to the traditional lubrication analysis where inlet and outlet conditions were assumed to be known (ambient in most cases), the present investigation uses the so-called “spatial” periodic condition which is a more realistic approach to a practical situation. Load capacity and drag on the runner are obtained and compared among solutions of different bearing models. It is found that the flow within the groove significantly affects the load generated in the thin film clearance. Its effect on the drag developed in the film clearance is marginal. As the film ratio increases, the drag on the runner monoton...

Temperature maps for pin-on-disk configuration in dry sliding

Bulk and flash temperature maps are obtained by using a method incorporating an improved model for the individual real contact area. It is shown that the proposed method generates results which favourably compare with the experimental data available in the literature.

Time-dependent TEHL solution to centrally supported tilting pad bearings subjected to harmonic vibration

The bearing performance of a centrally supported tilting square pad, subjected to harmonic vibration, is analysed numerically. Thermo-elastohydrodynamic lubrication analysis considers simultaneously the heat transfer, elastic deformation of the pads working surface, side leakage, and the inlet pressure build-up effect. Governing equations with their boundary conditions are transformed into non-dimensional forms so that the problems non-dimensional parameters are obtained. An efficient procedure is developed to solve the problem numerically. By idealizing the pad as a uniform plate, a compliancy coefficient matrix is established to calculate the pads surface deformation due to various pressure distributions. At each time step the pressure is obtained by a fast Newton-Raphson method, whereas the temperature is determined by an efficient finite difference approach. A dynamic parameter is introduced to describe the effect of the pads periodic motion, which is found to be as important as the wedge effect when the dynamic parameter approaches unity.

Proposed TEHL Solution System for the Thrust Bearings Inclusive of Surface Deformations

The coupled fluid and solid governing differential equations and their boundary conditions are expressed in dimensionless form which yield dimensionless problem parameters. The proposed solution system uses an efficient hybrid numerical approach. The boundary element method is employed for heat transfer in the pad, a finite difference method for the lubricating oil film, a finite element method for the boundary deformations, and the Newton-Raphson method for the pressure equations. It is shown that the proposed solution system provides not only the opportunity to include the thermal and elastic effects but also, if required, incorporation of the inertia forces and of the fore-region pressure build-up.

The effects of temperature, elasticity and fore-region pressure build-up on the performance of centrally pivoted linear pad bearings

Abstract The performance of oil lubricated and centrally pivoted thrust pad bearings is investigated theoretically. The analysis considers simultaneously and individually the following factors: heat generation, heat transfer, elastic and thermal deformations of the bearing components, fore-region pressure build-up, and the inertia terms. In the mathematical model, governing equations with their boundary conditions are expressed in the dimensionless form. A hybrid numerical approach is then employed to solve the problem. The results are presented and discussed in terms of the applicable non-dimensional parameters.

Transient Thermal Effects in an Infinite Tilted-Pad Slider Bearing

The transient characteristics of an infinite tilted-pad thrust bearing are studied numerically for a step change in the slider velocity. Numerical solutions indicate that the effect of temperature-dependent viscosity is to lower the temperature of the lubricant film and reduce the load capacity and drag. This is particularly true for lower vlaues of the modified Reynolds number. It is also shown that the transient characteristics depend on the initial condition of the bearing and on the terminal speed of the slider.

On the TEHL Theory. Part I: Dimensionless Problem Formulation

Since the thermoelastohydrodynamic and elastohydrodynamic lubrication (TEHL and EHL) problems are predominantly heat transfer (HT) and/or fluid mechanics (FM) problems, it is proposed that the pertinent dimensionless quantities defined, in some instances tabulated, and commonly used in these branches of engineering science (HT and FM) should be used consistently and uniformly throughout for TEHL and EHL studies. In support of this, it is shown by some mathematical considerations that the published dimensionless quantities (in the TEHL and the EHL problems) can be converted into HT and FM parameters—such as the Reynolds number, Euler number, Eckert number, Prandtl number or Fourier modulus. It is indicated that such parameters have an immediately recognizable physical meaning.

Flow in Large Arteries

For centuries, the world within himself fascinated man as much as his near and distant environment. In particular the cardiovascular system was the object of attention of scientific observers like Aristotle and Leonardo da Vinci. However, the concept of the Circulation of the Blood was clearly presented by W. Harvey in 1628, in his famous De Motu Cordis et Sanguinis in Animalibus. The evidence provided was almost complete and reached into the present day understanding, except that Harvey could not see the passage of blood from the peripheral arteries to the veins. He speculated that there must be “pores” at these locations. These “pores” were in 1661 identified by Malpighi as the capillaries (K.D. Keele, 1978). Later in 1733 Stephen Hales, the Vicar of Teddington, published the first measurements of arterial blood pressure.