Transient Thermal Deformation Research Articles

Finite element models for radiation effects in nuclear fusion applications

Deuterium-tritium fusion reactions produce energy in the form of 14.1 MeV neutrons, and hence fusion reactor components will be exposed to high energy neutron irradiation while also being subjected to thermal, mechanical and magnetic loads. Exposure to neutron irradiation has numerous consequences, including swelling and dimensional changes, comparable in magnitude to the peak transient thermal deformations occurring in plasma-facing components. Irradiation also dynamically alters the various thermo-mechanical properties, relating temperature, stress and swelling in a strongly non-linear way. Experimental data on the effect of neutron exposure spanning the design parameter space are very sparse and this highlights the relevance of computer simulations. In this study we explore the equivalence between the body force/surface traction approach and the eigenstrain formalism for treating anisotropic irradiation-induced swelling. We find that both commercial and massively parallelised open source software for finite element method (FEM) simulations are suitable for assessing the effect of neutron exposure on the mechanically loaded reactor components. We demonstrate how two primary effects of irradiation, radiation swelling and the degradation of thermal conductivity, affect the distributions of stress and temperature in the divertor of the ITER tokamak. Significant uncertainties characterising the magnitude of swelling and models for treating it suggest that on the basis of the presently available data, only an order of magnitude estimate can be given to the stress developing in reactor components most exposed to irradiation during service.

On the origins of transient thermal deformation of concrete

The conditions that lead to Transient Thermal Deformation (TTD), also called Thermal Transient Creep (TTC), of concrete subjected to various temperatures and compressive loads in sealed conditions are analysed and a model based on a two-scale porosity is proposed. In this model, water expands in the smaller pores and diffuses progressively to the capillary pores at the upper scale. It is then shown that the water overpressure in smaller pores and the duration of the diffusion process between the two scales of porosity control the TTD. It is also shown that creep or shrinkage before the temperature transition mitigates TTD. The aim is to provide a model able to predict the conditions for TTD to appear and the amplitude of the TTD under various thermo-mechanical conditions. The TTD model is implemented in an existing basic creep model, fitted and compared with different experimental results.

Transient Thermal Deformation of high performance concrete in the range 20 °C–40 °C

Transient Thermal Deformations (TTD) of High Performance Concrete (HPC) having various temperature and compressive loading histories in sealed conditions are investigated experimentally. The aim is to provide accurate data to quantify the transient thermal strain and to specify the conditions required to give rise to the phenomenon. The results are commented and hypotheses proposed to advise practitioners dealing with concrete structures concerned by the conditions of environment and loading that lead to Transient Thermal Deformation.

Unsteady-state thermal stress and thermal deformation analysis for a pressurizer surge line subjected to thermal stratification based on a coupled CFD-FEM method

In the pressurizer surge line, the phenomenon of thermal stratification may induce thermal stress and thermal deformation. Excessive thermal stress may result in thermal fatigue of the pipe structure, and excessive thermal deformation may destroy the pipe supports. The phenomenon of thermal stratification, and the induced thermal stress and thermal deformation in the pressurizer surge line would pose a threat on the safe operation of the nuclear power plants (NPPs). Therefore, it is very important to make an analysis to the thermal stratification, thermal stress and thermal deformation of the pressurizer surge line. In this study, a detailed unsteady-state computational fluid dynamics (CFD) analysis involving conjugate heat transfer (CHT) analysis is performed to obtain the transient temperature distributions of the pressurizer surge line under an overall out-surge case, and the thermal loads from the CFD calculations are then transferred to ANSYS Workbench Mechanical as body temperature loads for obtaining the transient thermal stress and the transient thermal deformation. With the coupled computational fluid dynamics-finite element method (CFD-FEM) analysis, the transient response characteristic of the surge line subjected to transient thermal stratification loadings are investigated and analyzed quantitatively. The positions where the maximal thermal stress occurs and where the maximal pipeline displacement occurs are determined, and the method for determining the degree of thermal deformation in the cross-section has been proposed. The coupled CFD-FEM method and the obtained conclusions in this study will be helpful for the design of the pipeline structures and the pipe supports to reduce the structural failure related safety accident.

An Accelerated Explicit Method and GPU Parallel Computing for Thermal Stress and Welding Deformation of Automotive Parts

An accelerated explicit method and GPU parallel computing program of finite element method (FEM) are developed for simulating transient thermal stress and welding deformation in large scale models. In the accelerated explicit method, a two-stage computation scheme is employed. The first computation stage is based on a dynamic explicit method considering the characteristics of the welding mechanical process by controlling both the temperature increment and time scaling parameter. In the second computation stage, a static equilibrium computation scheme is implemented after thermal loading to obtain a static solution of transient thermal stress and welding deformation. It has been demonstrated that the developed GPU parallel computing program has a good scalability for large scale models of more than 20 million degrees of freedom (DOFs). The validity of the accelerated explicit method is verified by comparing the transient thermal deformation and residual stresses with those computed by the implicit FEM and experimental measurements. Finally, the thermal stress and strain in an automotive engine cradle model with more than 12 million DOFs were efficiently computed and the results are discussed.

Numerical investigation on thermal deformation of friction pair in hydro-viscous drive

Thermal deformation of friction pair has a significant effect on the working performance of hydro-viscous drive. In order to investigate the combined effect of temperature variation and constraints on the thermo-elastic-plastic deformation of friction pair in hydro-viscous drive during the soft-start, transient thermal deformation model is established for numerical simulation. Thermo-elastic-plastic constitutive equations coupled with thermal strain and mechanical strain are described in detail. Using the constitutive equations derived, indirect coupling numerical method based on the finite element program is developed and used to predict distributions of the temperature, displacement and stress of the disks. The research results show that there are three types of saucer-shaped warping deformation and one type of wave-shaped warping deformation with regard to different constraints. The characteristics of various kinds of displacement and stress are concerned with thermal conductivity and constraints. When the disks are under double constraints, the maximum stress that surpasses the yield stress appears in the disk. When the disks are not under any constraints, minimum stress leads to minimum displacement. To a large extent the deformation size is decided by the location and number of constraints.

Thermal error simulation and compensation in a jig-boring machine equipped with a dual-drive servo feed system

A jig-boring machine equipped with a dual-drive servo system can operate with high speed and accuracy. However, different friction behaviours and asymmetrical preloads of the double drive structures as well as asynchronous control over the master-slave motors can make the machine produce tremendous heat, causing uneven temperature distributions in the feed system and eventually leading to thermal deformation that reduces the positional accuracy of machines. To investigate the effects of thermal behaviours on machining accuracy, the thermal–structure finite element method was employed to analyse the transient thermal deformation and temperature field of the machine at different feed rates, considering boundary conditions such as the convective heat transfer coefficient and heat generation by motors, bearings, and screws. Additionally, a synchronous acquisition system was developed to measure the thermal behaviours, and the transient changes in temperature and deformation were compared with simulated values. Consequently, a synthetic thermal model was established to make accurate predictions based on the analysis of relationships between thermal error and equilibrium time, coordinate position and screw temperature. Finally, thermal error compensation was performed using a feedback integration method. The experimental data indicate that the finite element method model can accurately predict temperature distributions and thermal errors. Moreover, thermal errors were compensated at 24.1 °C and 22.6 °C with a feed rate of 18 m/min, and machining accuracy was increased by 73% and 62%, respectively.

Heat Transfer and Thermal Deformation Characteristics of Liquid-Cooled Laser Mirror

A coupled finite volume-element method is developed to simulate the transient thermal deformation of water-cooled mirror by considering fluid flow and convective heat transfer. The simulation process consists of two steps: the 3D finite volume models of fluid flow and heat transfer equation are solved to obtain the time-dependent temperature field by using CFD; then, the obtained temperature field used as final temperature field is unidirectionally coupled to the finite element model for solving the thermoplastic equation. It is concluded that fluid flow not only affects the magnitude of temperature rise and thermal deformation, but also affects the distribution of temperature and thermal deformation. The temperature gradient in the thickness direction ( z direction) is found to be much larger than that in transverse direction. It is found that the temperature and the consequent deformation of water-cooled mirror increase significantly in the first seconds and gradually become steady state in the subsequent time. Experiments are conducted to estimate the precision of numerical models, and the experimental results agree well with the simulated results.

FEM Simulation of Gas and Plasma Cutting with Emphasis on Precision of Cutting

To achieve truly effective automation or mechanization of the ship structure assembling line, it is necessary to maintain much higher precision in each manufacturing stage, such as cutting and welding, compared to that required for the system depending on skills of workers. Since the flame cutting is the first stage of the assembly and it determines large part of the accuracy problems, controlling the precision in the flame cutting is receiving more attention now. Although it has long been considered that residual plastic strain and the motion of the plate due to the transient thermal deformation are the main causes of the cutting error, hardly any studies have been conducted to investigate these factors theoretically and quantitatively. In this paper a computational method for simulating the cutting process, based on the thermal-elastic-plastic FEM, has been developed. The proposed method is verified by comparing the computations with the experimental results obtained for the plasma cutting.Using the FEM model, the residual plastic strain and the plate motion due to the transient thermal expansion are obtained respectively. Their effects are quantitatively discussed. The results show that these factors have great influences on the one-side cutting and small effects on the two-side simultaneous cutting. The influences of the residual stress existing in the plate before cutting are also investigated.

Thermal deformation of the active medium in a solid-state laser with natural cooling

An analytical expression is derived for the transient thermal deformation of the active medium in a periodic duty laser with natural cooling.

ホログラフィによる工作機械構造の3次元変形測定

The static, thermal and dynamic deformations of the machine tool structure are measured by means of holography. The whole optical system for laser holography is placed on the heavy reinforced concrete block supported by several air cushions. The double exposure method is used in the static and thermal tests, while the time average method is used in the dynamic tests to obtain the mode shape and vibration amplitude of the structure at a resonance frequency. The transient thermal deformation of the structure is evaluated by taking the interference photographs at a certain interval during the cooling-off period of the structure and by assembling these results in the preceding intervals. Holography is also proved useful to examine the mechanical behaviors of the machine interface.