Papers by Author: Lie Yu

Abstract: Circumferential rod-fastened rotor is one kind of extensively applied structures of gas turbines which work at high temperature to expand hot gas and generate power. The steady-state temperature distribution of the turbine rotor as well as the thermal deformation and stress state were calculated through a thermo-mechanical analysis. A cyclic model of a four-disc rod-fastened turbine rotor assembly was built. A thermal analysis was carried out to obtain the steady-state thermal map of the turbine rotor with the thermal boundary conditions calculated through heat transfer empirical correlations. A static structural analysis was performed to derive the deformation and stress field under both thermal and mechanical loads which incorporate both the pre-tightening force of the rods and the centrifugal force of the rotor itself. The thermo-mechanical results are compared to the result with only mechanical loads applied. The comparison shows the steady-state thermal loads have an influence on the stress state of the rotor and the deformation of the rods.

Abstract: The bolted joint is the important fastening parts of structures. Its fatigue and self-loosing will affect the safety of the system. In this paper, the finite element contact models are built to analyze the mechanical property of bolted joint numerically. The stress, strain and clamping force when the bolted joint is subjected to preload, axial force and transverse load are investigated. The results show that the bolt is the most dangerous part of bolt-nut connected member. The clamping force of bolted joint will gradually lose with the increasing loading cycles of cyclic transverse load which generally explains the stress loosing rule of bolted joint.

Abstract: High-speed couplings are the key parts of micro-turbomachinerys. They are assembled to shafts by interference fits, which can transfer large torque, are easy to produce and offer significant cost advantages. Considering of the influences of the torque, rotational speed and temperature variation, the interference fits between couplings and shafts have to be analyzed accurately in order to save the construction cost and reducing risk of invalidation accidents. In this paper, a model of the interference fit between a coupling and a shaft is developed to study the determine parameters of the interference value. Using the classic elastic plane stress theory, the exact solutions of the radial stresses, hoop stresses and radial displacements are obtained. Three determine parameters (the torque, angular velocity and temperature variation correction terms) are derived in order to calculate the interference value. Taking a high-speed microturbomachinery for example, the numerical results show that the interference value is dependent of the ratios of inner radius to outer radius of the coupling and shaft significantly. The torque, angular velocity and temperature variation correction terms are in the same order of magnitude. The present analytical solutions are expected to be useful in the structure design of the interference fit between a high-speed coupling and a shaft.

Abstract: Finite element equation of the nonlinear dimensionless Reynolds equation, based on the Galerkin finite element method, was derived. Three key points of solving the equation was studied in detail, i.e. Boolean matrix was calculated under the nonlinear conditions, and a method of integrating discrete element equations was provided; Nonlinear algebraic equations set, resulted from integrated finite element equations, was obtained and a method how to substitute boundary conditions into the algebraic equations was presented; A method of calculating the Jacobi matrix of the equations set were described in this paper. All of them are crucial to solve the nonlinear Reynolds equation and helpful for promoting the further research on compliant foil gas bearing.

Abstract: In this article, a metal diaphragm coupling is introduced. It is assembled by interference fit with the shafts. Based on two axial vibration styles, self-exited vibration and external exited vibration, of the coupling, physical model of the coupling is established. Stiffness and damping of the coupling are also solved and analyzed. Then, natural vibration of the coupling is researched and natural frequencies are acquired by analyzed and simulated method. Finally, axial vibration response of the coupling was presented based on a calculation example. Techniques are presented which permit the coupling designer to predictably modify the coupling and thereby make in-place retrofits should an axial resonance condition occur in the field.

Abstract: Vibration characteristics of a misaligned rotor with asymmetric shaft stiffness are studied. The system consists of two shafts connected by a flexible coupling with parallel misalignment, two rigid disks attached at the middle of each shaft and one of the shafts has asymmetric stiffness. The governing ordinary differential equations are derived using Lagrange dynamics and integrated through numerical methods. The effects of asymmetry, eccentricity and misalignment are studied through the peak-to-peak lateral vibration amplitude at different rotor speed. Simulation results show that the amplitude peaks at the natural frequency associated with unbalance and parallel misalignment, while half the natural frequency associated with the asymmetric shaft stiffness. This study may contribute to enrich understanding of the vibration of a rotor system under the cases of eccentricity, parallel misalignment and asymmetric shaft stiffness.

Abstract: Based on the nonlinear theory, the unbalanced responses of the gas-lubricated journal bearing-rotor system are investigated. A time-dependent mathematical model is established to describe the pressure distribution of gas-lubricated journal bearing with nonlinearity. The rigid rotor with gyroscopic effect supported by self-acting gas journal bearing with three axial grooves is modeled. The differential transformation method is employed to solve the time-dependent gas-lubricated Reynolds equation, and the dynamic motion equation is solved by Newmark-β method. The unbalanced responses of the rotor system supported by finite gas-lubricated journal bearings are analyzed by bifurcation diagram, orbit diagram, Poincaré map. The numerical results reveal periodic, period-4 motion of nonlinear behaviors of the system.

Abstract: Two-phase thin solid films consisted of Au nanoparticles imbedded in an amorphous matrix were prepared via a series of galvanic replacement reactions between chloroauric acid solution and reducing metals. The Au nanoparticles were in situ crystallized from the amorphous films rather than precipitated from solution directly. Amorphous films with partly crystallized Au nanoparticles only existed stably in dilute chloroauric acid solution. The higher concentration of chloroauric acid evidently promoted the strain-induced crystallization process and accelerated the crystallization of amorphous films into Au nanoparticles with many stacking faults, twins and dislocations. The coexistence of amorphous and crystalline Au nanoparticles makes it possible to synthesize two-phase nanostructured films.

Abstract: In this paper, a simplified nonlinear finite element for bump foil forming process of foil air bearings is developed. The bump foil is dealt with as flexible deformable body, the upper die and lower die are considered as the rigid body without deformation. The friction model between bump foil and dies with velocity-dependent friction forces is described by arctan function. The forming process of SS304 Stainless Steel bump foil under different loads is investigated with rigid-plastic finite element method. The simulation results are compared with theoretical values and experimental results. Therefore more feasible process parameters are obtained to fabricate the bump foils.

Abstract: Distribution of static interference pressure between a thin-wall flexible cup and a flexible shaft fluctuates heavily along the axis of the cup and is quite different from pressure distribution of common interference styles. In this article, aiming at solving distribution of static interference pressure between a thin-wall flexible cup with much thicker bottom and a hollow flexible shaft, mechanical model and mathematical model of solving the problem were built based on classic thin shell theory. Special difference is that precise special solution of bending equation of thin cylindrical shell was used to substitute the special solution which is original from bending deformation of thin cylindrical shell in no moment status. And a brand new general solution, the relational expression between bending deformation of thin wall of the cup and distribution of the static interference pressure, was obtained. Then, a method used to solve the pressure distribution was presented by solving integral equation and applying superposition principle for the first time. Through using the method to solve an example and comparing calculated results with FEM results, it was proved that the method is correct and effective.