Cheng Heming

Calculation of the residual stress of a 45 steel cylinder with a non-linear surface heat-transfer coefficient including phase transformation during quenching

Abstract From the TTT diagram of 45 steel, the CCT diagram was simulated by mathematical transformation, and the volume fraction of the constituents austenite, perisite, bainite and martensite in continuous cooling was calculated. The thermal physical and mechanical properties were treated as functions of the temperature and the volume fraction of the phase constituents. On the basis of a non-linear surface heat-transfer coefficient, the temperature field with phase transformation and non-linear surface heat-transfer coefficients was calculated using the finite-element technique. The experimental results for the temperature field coincide with the numeral solutions. Finally, the residual stress was calculated by means of the finite-element method.

Multi‐objective optimization design of a micro‐channel heat sink using adaptive genetic algorithm

Purpose – The purpose of this paper is to show how, with a view to the shortcomings of traditional optimization methods, a multi‐objective optimization concerning the structure sizes of micro‐channel heat sink is performed by adaptive genetic algorithm. The optimized micro‐channel heat sink is simulated by computational fluid dynamics (CFD) method, and the total thermal resistance is calculated to compare with that of thermal resistance network model.Design/methodology/approach – Taking the thermal resistance and the pressure drop as goal functions, a multi‐objective optimization model was proposed for the micro‐channel cooling heat sink based on the thermal resistance network model. The coupled solution of the flow and heat transfer is considered in the optimization process, and the aim of the procedure is to find the geometry most favorable to simultaneously maximize heat transfer while obtaining a minimum pressure drop. The optimized micro‐channel heat sink was numerically simulated by CFD software.Fin...

Estimation of the mechanical properties of a 42CrMo steel cylinder with phase transformation during quenching

Abstract The non-linear heat conduct equation with non-linear surface heat transfer coefficients was solved by means of the finite difference method and the non-linear estimate method, i.e. the temperature field can be obtained from the corrected surface heat-transfer coefficients of the specimen. From the TIT diagram of 42CrMo steel, its CCT diagram was simulated by mathematical transformation and the volume fraction of constituents austenite, pearlite, bainite and martensite in continuous cooling is calculated. Finally, the mechanical properties of the 42CrMo steel are estimated by a numerical method and the experimental relationships between time and temperature, the results obtained being compared with experimental results.

Computer simulation of turbulent flow through a hydraulic turbine draft tube

Based on the Navier-Stokes equations and the standardk-ε turbulence model, this paper presents the derivation of the governing equations for the turbulent flow field in a draft tube. The mathematical model for the turbulent flow through a draft tube is set up when the boundary conditions, including the inlet boundary conditions, the outlet boundary conditions and the wall boundary conditions, have been implemented. The governing equations are formulated in a discrete form on a staggered grid system by the finite volume method. The second-order central difference approximation and hybrid scheme are used for discretization. The computation and analysis on internal flow through a draft tube have been carried out by using the simplec algorithm and cfx-tasc flow software so as to obtain the simulated flow fields. The calculation results at the design operating condition for the draft tube are presented in this paper. Thereby, an effective method for simulating the internal flow field in a draft tube has been explored.

Determination of Surface Heat Transfer Coefficients of Cr12MoV Steel Cylinder during High-Speed Gas Quenching at Atmospheric Pressure

In the numerical simulation of quenching processes, establishment of the boundary conditions for the temperature field and stress field are very important. However, determination of the boundary conditions of the temperature field is very complicated. In order to simulate the thermal strain, thermal stress, residual stress, and microstructure of the steel during high-speed gas quenching at atmospheric pressure using a numerical method, it is necessary to obtain an accurate boundary condition of temperature field. The surface heat transfer coefficient is a key parameter. The explicit finite difference method, nonlinear estimate method, and the experimental relationship between temperature and time during quenching have been used to solve the inverse problem of heat conduction during gas quenching. The relationships between surface temperature and surface heat transfer coefficient of a solid cylinder are provided here. In addition, it is shown that this technique can determine the effective surface heat transfer coefficients during high-speed gas quenching.

Finite element analysis of temperature field with phase transformation and non-linear surface heat-transfer coefficient during quenching

The calculation of temperature field has a great influence upon the analysis of the thermal stresses and strains during quenching, and also upon the residual stresses and microstructure of the workpiece after quenching, too. In this paper, a 42CrMo steel cylinder was taken as an investigating example. From the TTT diagram of the 42 CrMo steel, the CCT diagram was simulated by mathematical transformation, and the volume fraction of phase constituents was calculated. The thermal physical properties were treated as the functions of temperature and the volume fraction of phase constitutents. Finally, the temperature field with phase transformation and non-linear surface heat-transfer coefficients was calculated with finite element method, and the corresponding functional of temperature was established.

The functional and its variational principle in coupled thermoelastoplasticity

In order to solve the coupled thermoelastoplastic problems by the finite element method it is necessary to establish suitable functional. In this paper, based on the thermoelastoplastic constitutive relation proposed by K.N. Rysinko and E.I. Blinov, the functional of coupled thermoelastoplasticity is derived by means of the nonlinear functional analysis theory.

Elementary Study of the Stability of the High‐fill Slope of A Certain International Airport

A certain 4D plateau international airport is to be built in a karst area with widespread heavy red clay strata. It is one of the major research subjects facing the engineering construction to use the red clay strata as the bearing stratum of foundation of the high‐fill section. By using the 3D finite element method, the stress, strain, deformation and stability of the high‐fill slope and foundation were simulated. The obtained results can be used as the basic and practical reference data for engineering construction.

Calculation of coupled problem between temperature and phase transformation during gas quenching in high pressure

The gas quenching is a modern, effective processing technology. On the basis of nonlinear surface heat-transfer coefficient obtained by Cheng during the gas quenching, the coupled problem between temperature and phase transformation during gas quenching in high pressure was simulated by means of finite element method. In the numerical calculation, the thermal physical properties were treated as the functions of temperature and the volume fraction of phase constituents. In order to avoid effectual “oscillation” of the numerical solutions under smaller time step, the Norsette rational approximate method was used.