Journal Center Research Articles

Analysis and Detection of Elastic Deformation of the Large-Scale Crankshaft in Non-Circular Grinding

Due to the discontinuous axis and the big ratio of length to diameter, the large-scale crankshaft is easy to generate the complex elastic deformation under the effect of the huge gravity and the clamping force on non-circular grinding machine. The distinctive deformation deteriorates the coaxiality of all the main journals and thus the grinding precision of crankpins in non-circular grinding. In this paper, the statics analysis of large-scale crankshaft has been conducted by using the finite element simulation. The overall deformation of crankshaft and the position offset of each main journal center without or with the auxiliary supports have been simulated and contrasted. The results manifest that the auxiliary support forces produced by the steady rests have the positive effect on the compensation for crankshaft deformation. On this basis, to satisfy the demand of position adjustment of the upper and lower support pads of servo-controlled open steady rest, the on-machine measurement method and device of the position of main journal center is proposed. And then the offset calculation model of the main journal center is deduced using the measured data. The measurement method and device are beneficial for the straightening of the crankshaft and the improvement of machining accuracy of crankpins in non-circular grinding.

Effects of turbulence on dynamic performance of accelerated/decelerated hydrodynamic journal bearing system

The hydrodynamic journal bearing system has found the wide spread application in high speed rotating machines such as compressors, gas turbines, steam turbines, etc. The rotors generally operate at high speed; therefore the lubricant flow in the clearance space of journal bearing does not remain laminar for accelerated/decelerated journals. Then, study of the dynamic response of the hydrodynamic journal bearing system considering superlaminar flow is needed. In this paper, the analysis is done for the fluid-low-field in the clearance space of hydrodynamic journal bearing system using short bearing assumption under laminar, transition and turbulent flow conditions. The positive pressure zone is established after deleting sub-ambient pressure around clearance space. Linear and non-linear motion trajectories at constant speed are obtained using the fourth order Runge-Kutta method. The non-linear motion trajectories during acceleration and deceleration are also obtained. Journal centre trajectories at constant speed and laminar flow, show the expected trend, i.e., system is stable below threshold speed curve, unstable above it, whereas for superlaminar flow, stable behaviour is found at some distance away from the stability curve. The behaviour during stopping/starting of journal centre trajectories is also obtained by non-linear equations of motion. The results also show the expected trend.

Nonlinear transient stability study of two lobe symmetric hole entry worn hybrid journal bearing operating with non-Newtonian lubricant

The present paper, deals with a theoretical study concerning the effect of non-Newtonian lubricant on the stability of a two lobe symmetric hole entry worn hybrid journal bearing, compensated with constant flow valve restrictor. Trajectories of journal center motion have been obtained by solving the nonlinear equation of motion for the journal center with the Runge–Kutta method. The numerically simulated results indicate that the non-Newtonian behavior of the lubricant has a profound influence on the journal trajectories and stability of a worn hybrid journal bearing. A proper selection of parameters such as offset factor, wear depth parameter and the non-linearity factor may provide better bearing stability.

Dynamic Simulation and Optimum Design for the Main Drive System of Reciprocating Compressor Considering Joint Friction

The dynamic optimization of a main drive system in a W-type compressor with friction of joints are studied by ADAMS , a special software for dynamical simulation. First the dynamical simulating model for the system is built considering joint friction in ADAMS . The dynamic response of the crankshaft journal center and dynamic reacting forces of the two rolling bearings are obtained on rated operating condition. Also the average value of the mechanical efficiency of reciprocating compressor was revealed .Then the mathematical model for dynamic optimization is presented, its objective function is mechanical efficiency of reciprocating compressor,and the design variable are the angle of cylinder lines and the rotation speed of crankshaft.The parametric simulating model is constructed in ADAMS to search the optimum solution.The relation between the design variable and objective value is disclosed through 'DOE' ,which is a function module in the design evaluation tools of ADAMS. Numerical results are available for the dynamic design of reciprocating compressor.

Nonlinear dynamics of flexible rotor supported on the gas foil journal bearings

Investigation on nonlinear dynamics of a flexible rotor supported on the gas foil journal bearings is attempted. A time domain orbit simulation is carried out that couples the equations of rotor motion, unsteady Reynolds equation and foil deformation. The unsteady Reynolds equation is solved using control volume formulation with power law hybrid scheme and Gauss–Seidel method. The nonlinear dynamic response is analyzed using disc center and journal center trajectories, Poincaré maps, Fast Fourier transforms and bifurcation plots. The analysis is carried out for different system parameters, namely, rotating speed, unbalance eccentricity, compliance and loss factor of gas foil bearing. The analysis reveals highly nonlinear behavior with periodic, multi-periodic and quasiperiodic motion of the disc and the journal center. The present analysis can be useful in designing and selection of suitable operating parameters of rotor bearing system.

The Analysis of the Deformation and Contact Lubrication Problem of HPD Diesel Engine Connecting Rod Bearings Based on the FFT Method and Flexibility Matrix Method

Based on the fast fourier transform (FFT) and flexibility matrix method, the effects of the FFT and flexibility matrix method on the distribution of oil film pressure, elastic deformation in the steady load and the journal center orbit of the connecting rod big-end bearings in the dynamic load are investigated. The results are shown that when the eccentricity ratio is more than 1, the maximum oil film pressure obtained by FFT method is bigger on both ends of the journal bearing and on its intermediate position is smaller. To the connecting rod big-end bearing, under the dynamic load condition, there is the same trend of the journal center orbit with two methods. However, with FFT method, the journal is largely deviated from bearing center.

A Dynamic Analysis of Reciprocating Compressor Transmission Mechanism with Joint Clearance

The dynamic behavior of a reciprocating compressor transmission mechanism with joint clearance is studied in this paper. A transmission mechanism virtual prototype model is built under software ADAMS. Revolute joint between connecting rod and crosshead pin is modeled with clearance by contact model based on the so called Impact-function, and four processes of cylinder pressure load is simulated by the IF function. Cylinder pressure load, amplitude of joint clearance, crank speed and flexibility of connecting rod is taken as influence factors. Four different cases were simulated. Joint contact forces, accelerations of compressor block and journal centre path are used to analyze the dynamic behavior. The presented results show that these factors play a significant role of dynamic behavior of mechanisms.

Application of computational fluid dynamics and fluid structure interaction techniques for calculating the 3D transient flow of journal bearings coupled with rotor systems

Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics (CFD)-fluid structure interaction (FSI) techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called “dynamic mesh” technique. A new mesh movement approach is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the journal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function (UDF). The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.

The Analysis of Lubrication for HPD Diesel Engine Piston Pin Bearing

Based on the unified Reynolds equation model and fast Fourier transform (FFT) method, the lubrication performance of the piston pin bearing for high power density diesel engine was studied by numerical simulation. First of all, through the coupled solving of a unified Reynolds equation and elastic deformation equation, the orbit of journal center for piston pin bearing is investigated. The eccentricity ratio of the piston pin bearing in vertical direction of the piston stroke is smaller, however it is much larger in the downward direction of the piston stroke, which indicate that the below area of the piston pin bearing bears greater load and occurs larger deformation. This is consistent with the reality that the below area of the piston pin bearing is prone to damage and wear. Secondly, the influence of the different bearing clearances and width on the minimum oil film thickness is discussed, The results show that the minimum oil film thickness is increased, while the width of piston pin bearing is increased or the clearance of piston pin bearing is decreased.

A multi-platform approach to investigative journalism

Robert Rosenthal began his career in journalism at The New York Times, where he was a news assistant on the foreign desk and an editorial assistant on the Pulitzer-Prize winning Pentagon Papers project. He later worked at the Boston Globe, and for 22 years at the Philadelphia Inquirer, starting as a reporter and eventually becoming its executive editor in 1998. He became managing editor of the San Francisco Chronicle in late 2002, and joined the Center for Investigative Reporting as executive director in 2008. Rosenthal has won numerous awards, including the Overseas Press Club Award for magazine writing, the Sigma Delta Chi Award for distinguished foreign correspondence, and the National Association of Black Journalists Award for Third World Reporting. He was a Pulitzer Prize finalist in international reporting, and has been an adjunct professor at Columbia University Graduate School of Journalism and the University of California at Berkeley Graduate School of Journalism. The Australian Centre for Independent Journalism (ACIJ) invited Robert Rosenthal to speak about the transformational model of investigative journalism, which he has pioneered at the CIR, as the keynote speech at the ‘Back to the Source’ conference.

EDITORIAL: Independent journalism

Discussion about the role of journalism in universities too often leaves the impression that our main, and even only game, should be producing employees for major media corporations. This issue of Pacific Journalism Review assumes much more than that. The theme for the issue is investigative journalism, particularly material presented at the ‘Back to the Source’ investigative journalism conference hosted by the Australian Centre for Independent Journalism (ACIJ) and the Australian Broadcasting Corporation in Sydney in September 2011. This was the second regional investigative journalism conference; the first, hosted by the Pacific Media Centre, provided the theme for PJR (MIJT, 2011). These conferences, and indeed Pacific Journalism Review, are based on the notion that the goal of university based journalism is to develop links between journalists—whether full-time employees of major companies, freelancers, academics or students—in order to promote a more independent and critical culture of journalism in our region, without which democracy cannot flourish. This goal suggests a relationship much wider and more challenging than simply the production of qualified journalists.

Acoustic analysis of hydrodynamic and elasto-hydrodynamic oil lubricated journal bearings

The purpose of the present paper is to investigate the effect of elastic deformation of bearing liner on the acoustic behavior of oil lubricated journal bearings. Analysis is performed for hydrodynamic(HD) and elasto-hydrodynamic (EHD) lubrications. Dynamic behavior and acoustical properties are investigated through an analysis of pressure fluctuation calculated from the Reynolds equation governing the flow in the clearance space of the journal bearing. This is solved numerically using the finite difference method with the successive over relaxation technique. In elasto-hydrodynamic lubrication, the finite element method with in iteration scheme is adopted to solve both Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The results show that the sound pressure level of the bearing is markedly influenced by the flexibility of the bearing liner, the viscosity of lubricant and the load applied to journal. HD analysis shows that the journal centre's orbit, from a disturbed position, converges to the static equilibrium position faster than EHD lubrication. The results of the present paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings.

Mixed and Fluid Film Lubrication Characteristics of Worn Journal Bearings

The mixed and fluid film lubrication characteristics of plain journal bearings with shape changed by wear are numerically examined. A mixed lubrication model that employs both of the asperity-contact mechanism proposed by Greenwood and Williamson and the average flow model proposed by Patir and Cheng includes the effects of adsorbed film and elastic deformation is applied. Considering roughness interaction, the effects of the dent depth and operating conditions on the loci of the journal center, the asperity-contact and hydrodynamic fluid pressures, friction, and leakage are discussed. The following conclusions are drawn. In the mixed lubrication regime, the dent of the bearing noticeably influences the contact and fluid pressures. For smaller dents, the contact pressure and frictional coefficient reduce. In mixed and fluid film lubrication regimes, the pressure and coefficient increase for larger dents. Furthermore, as the dent increases and the Sommerfeld number decreases, the flow rate continuously increases.

Experimental Study of 3D Trajectory of Journal Center of Crankshaft Bearings in Multi-cylinder Internal Combustion Engine

Experimental Study of 3D Trajectory of Journal Center of Crankshaft Bearings in Multi-cylinder Internal Combustion Engine

박용엔진 크랭크 핀 베어링의 형상오차가 최소유막두께에 미치는 영향

Bearings of marine engines are operated under severe conditions because of dynamic load and low sliding speed. This paper deals with lubrication analysis of a crank pin bearing for a marine diesel engine. Journal center locus and oil film thickness are compared of crank pin bearing. In the past researches, journal bearings have been studied only about the surface of bearing. In addition to this conventional research, this paper analyzes the effect of roundness error of a journal and a bearing on the minimum film thickness. Numerical analysis has been studied by using Reynolds equation and also Half-Sommerfeld condition is applied as boundary condition. Futhermore, this study investigates the effect of roundness error change on the minimum film thickness. The results demonstrate that the bigger amplitude of roundness error yields, the lower minimum oil film thickness is. In comparison to previous research considered a journal and a bearing individually, the results considering a journal and a bearing together show that amplitude of roundness error of journal has very little effect on the minimum oil film thickness.

Bifurcation of limit cycles in fluid film bearings

Rotors supported by journal bearings may become unstable due to self-excited vibrations when a critical rotor speed is exceeded. Linearised analysis is usually used to determine the stability boundaries. Non-linear bifurcation theory or numerical integration is required to predict stable or unstable periodic oscillations close to the critical speed. In this paper, a dynamic model of a short journal bearing is used to analyse the bifurcation of the steady state equilibrium point of the journal centre. Numerical continuation is applied to determine stable or unstable limit cycles bifurcating from the equilibrium point at the critical speed. Under certain working conditions, limit cycles themselves are shown to disappear beyond a certain rotor speed and to exhibit a fold bifurcation giving birth to unstable limit cycles surrounding the stable supercritical limit cycles. Numerical integration of the system of equations is used to support the results obtained by numerical continuation. Numerical simulation permitted a partial validation of the analytical investigation.

A Dynamic Solution Method for Dynamically Loaded Bearing

The crankshaft bearing in an internal combustion engine is a typical dynamically loaded bearing. In an engine, the crankshaft and bearing constitute an inseparable system. When operating, many mechanical actions in this system happen simultaneously and influence each other. This article presents a method to obtain the journal center trajectory that considers the interaction of the crankshaft and bearing. The dynamic equations of motion of the crankshaft and the Reynolds equations were solved simultaneously to determine (calculate) the load on the bearing, the dynamic response (journal center trajectory), and the tribological performance of the bearings. The numerical results show that the journal center trajectory of a crankshaft and tribological performance of bearings calculated by this method are remarkably different from those obtained by current methods.

Static Characteristics of Journal Bearings under Starved Lubricating Conditions

The static characteristics of journal bearings with an axial groove under starved lubrication are studied theoretically and a lubrication condition map is newly proposed. This map is represented using the contour map of the eccentricity ratio with the Sommerfeld number S in the horizontal axis and the dimensionless oil flow rate Qsup externally supplied in the vertical axis for the wide range of the operating conditions. It is found from the map that the eccentricity ratio increases with the decrease of Qsup. This tendency is more marked for a higher Sommerfeld number. Journal center loci show that the attitude angle decreases with Qsup. The degree of the starvation Λ and the oil supply rate Ψ are defined as the ratio of the dimensionless oil flow rate into the inlet of the oil film region to that obtained under the flooded lubrication condition and as the ratio of Qsup to Qsup* obtained under flooded lubrication conditions, respectively. The degree of starvation Λ varies with Ψ and the value of Λ can be determined by setting the value of Ψ. These facts suggest that the static characteristics and Λ are theoretically predicted once the value of Qsup or Ψ is determined.

Transient CFD Analysis of Multi-Lobe Bearings at 60000RPM for A Gas Turbine

Transient CFD Analysis of Multi-Lobe Bearings at 60000RPM for A Gas Turbine

Micropolar fluid squeeze film lubrication of finite porous journal bearing

In this paper, the effect of micropolar fluid on the static and dynamic characteristics of squeeze film lubrication in finite porous journal bearings is studied. The finite modified Reynolds equation is solved numerically using the finite difference technique and the squeeze film characteristics are obtained. According to the results obtained, the micropolar fluid effect significantly increases the squeeze film pressure and the load-carrying capacity as compared to the corresponding Newtonian case. Under cyclic load, the effect of micropolar fluid is to reduce the velocity of the journal centre. Effect of porous matrix is to reduce the film pressure, load-carrying capacity and to increase the journal centre velocity.