Thermal-structural Finite Element Analysis Research Articles

Formulation of parameter limit values for the operation of a large concrete gravity dam

This study presents a coupled thermal-structural finite element analysis of a large concrete gravity dam in Bulgaria for exploring the dam response under different actual load combinations. The loads applied to the structure are caused by varying water level in the reservoir and ambient temperature typical for the respective seasons. The developed computational model was calibrated with real plumb measurements. Based on the performed analyses in the ANSYS environment, key limit values for the horizontal displacements measured by the plumbs in the dam as possibly caused by extreme combinations of ambient temperature and water level are formulated for further improvement of the dam operation.

Failure analysis of bolt connections in fired heater of a petrochemical unit

Abstract The main function of a fired heater in a petrochemical site is to produce supersaturated steam. Due to extremely difficult working conditions and high temperatures, there is a very high probability of failures in different parts of a fired heater. In the fired heater under study, tube guides are frequently damaged due to malfunctions and fractures in bolt connections. To investigate the nature of such fractures, Computational Fluid Dynamics (CFD), Finite Element (FE) method, Charpy impact test and fractography were used. To obtain the temperature of various components of the fired heater, a CFD analysis was carried out by considering the combustion process and modeling the central and side burners. Next, stress and displacement values in different components of the fire heater, particularly tube guides, were calculated using the uncoupled thermal-structural finite element analysis. It is found that when the dummy drain at the bottom of the tubes is stuck at the bottom of the fired heater, the expansion of tubes is impeded in addition to creating distortions in tube bundles and increasing the stress on the bolts of tube guides. Moreover, according to the performed tests, it is revealed that the increase in the stress of bolts leads to the activation of creep and Hydrogen embrittlement, causing the bolts to experience fractures in a considerably shorter amount of time.

Aerothermal–Structural Analysis of a Rocket-Launched Mach 8 Scramjet Experiment: Descent

This paper reports on the methodology and results of a weak-coupled aerothermal–structural analysis on the exoatmospheric and descent phase of the Mach 8 SCRAMSPACE flight-test engine. The passively cooled short-duration test engine was manufactured from common engineering materials including a 5 mm-thick aluminum aeroshell, an 8–10 mm aluminum inlet and combustion chamber assembly, and a 4–8 mm-thick carbon-phenolic thrust nozzle. Aerothermal heating and aerodynamic pressure on the external and internal flowpaths, including pulsed (5 Hz) fueling and combustion, were first solved using two- and three-dimensional computational fluid dynamics models. Results from these simulations where then used as boundary conditions to a three-dimensional transient thermal–structural finite element analysis model. The external aeroshell was found to maintain temperatures and stresses to within acceptable limits. Elevated surface temperatures along the internal flowpath were observed; however, the median stresses remained below material failure limits. This analysis indicates that, although the structure weakens and becomes more plastic, the vehicle integrity was maintained until the specified end of the experimental window. Results from this study demonstrate that, with careful design, thin-walled structures made from common engineering materials are suitable for short-duration hypersonic airbreathing flight-test engines without the need of active-cooling technology.

Thermal-structural analysis of regeneratively-cooled thrust chamber wall in reusable LOX/Methane rocket engines

To predict the thermal and structural responses of the thrust chamber wall under cyclic work, a 3-D fluid-structural coupling computational methodology is developed. The thermal and mechanical loads are determined by a validated 3-D finite volume fluid-thermal coupling computational method. With the specified loads, the nonlinear thermal-structural finite element analysis is applied to obtaining the 3-D thermal and structural responses. The Chaboche nonlinear kinematic hardening model calibrated by experimental data is adopted to predict the cyclic plastic behavior of the inner wall. The methodology is further applied to the thrust chamber of LOX/Methane rocket engines. The results show that both the maximum temperature at hot run phase and the maximum circumferential residual strain of the inner wall appear at the convergent part of the chamber. Structural analysis for multiple work cycles reveals that the failure of the inner wall may be controlled by the low-cycle fatigue when the Chaboche model parameter γ3=0, and the damage caused by the thermal-mechanical ratcheting of the inner wall cannot be ignored when γ3>0. The results of sensitivity analysis indicate that mechanical loads have a strong influence on the strains in the inner wall.

Thermal–structural analysis of large deployable space antenna under extreme heat loads

ABSTRACTLarge deployable space antennas may be exposed to severe thermal environments in future space missions; extreme heat loads will result in considerable thermal stresses and deformations which seriously affects the accuracy of the antenna's parabolic surface. In this study, thermal–structural finite element analysis of a deployable AstroMesh antenna under extreme heat loads was presented. Considering position and orientation with respect to the Sun and Earth, the antenna's temperature changing law under orbital heat fluxes was first evaluated to find the worst condition as loading point. Analyses for the antenna under different levels of extreme heat loads were then performed to obtain the temperature distributions utilizing an equivalent quarter antenna model. Based on the temperature calculation results and prestress designs, structural analyses were finally made to gain the resulting stresses and deformations. The analysis results show that the existing antenna may generate significant performance distortion under extreme thermal environments; so attentions for reliability and safety under such conditions should be taken seriously in future antenna works. Modeling and analysis method proposed in this article was validated to be contributive in antenna's thermal and precompensation designs.

An Improved Heat Equation for Fully Coupled Thermal-Structural Finite Element Analysis Using Small Strain Formulation

In this paper an improved heat equation for fully coupled thermal structural finite element analysis is presented. In the problem solving process, mathematical formulation appropriate strain measures describing the onset and the growth of ductile and total damage and heat generation rate per unit volume for dissipation-induced heating have been employed. The model was implemented into a finite element code using an improved weak form for fully coupled thermal structural finite element analysis, an extended NoIHKH material model with internal damping for cyclic plasticity of metals capable of modelling ductile material behaviour in wide range of strain rates. A notched aluminium alloy specimen in cyclic tension using 2Hz excitation frequency and linearly increasing amplitude has been studied. The model verification showed excellent agreement with available experiments. A few selected analysis results are presented and briefly discussed.

An Improved Heat Equation to Model Ductile-to-Brittle Failure Mode Transition at High Strain Rates Using Fully Coupled Thermal-Structural Finite Element Analysis

In this paper a universal heat equation for fully coupled thermal structural finite element analysis of deformable solids capable of predicting ductile-to-brittle failure mode transition at high strain rates is presented. In the problem mathematical formulation appropriate strain measures describing the onset and the growth of ductile and total damage and heat generation rate per unit volume to model dissipation-induced heating have been employed, which were extended with the heat equation. The model was implemented into a finite element code utilizing an improved weak form for updated Lagrangian formulation, an extended NoIHKH material model for cyclic plasticity of metals applicable in wide range of strain rates and the Jaumann rate in the form of the Green-Naghdi rate in the co-rotational Cauchy’s stress objective integration. The model verification showed excellent agreement with the modelled experiment at low strain rates. Plastic bending of a cantilever has been studied at higher strain rates. A few selected analysis results are presented and briefly discussed.

Thermal–structural analysis of bi-metallic conformal cooling for injection moulds

In injection moulding process, cooling time greatly affects the total cycle time. As thermal conductivity is one of the main factors for conductive heat transfer in cooling phase of IMP, a cooling channel made by higher thermal conductive material will allow faster extraction of heat from the molten plastic materials, thus resulting in shorter cycle time and higher productivity. The main objective of this paper is to investigate bi-metallic conformal cooling channel design with high thermal conductive copper tube insert for injection moulds. Thermal–structural finite element analysis has been carried out with ANSYS workbench simulation software for a mould with bi-metallic conformal cooling channels and the performance is compared with a mould with conventional straight cooling channels for an industrial plastic part. Experimental verification has been carried out for the two moulds using two different types of plastics, polypropylene (PP) and acrylonitrile butadiene styrene, in a mini injection moulding machine. Simulation and experimental results show that bi-metallic conformal cooling channel design gives better cycle time, which ultimately increases production rate as well as fatigue life of the mould.

A Fully Coupled Thermal-Structural Finite Element Analysis of a Low-Carbon Steel Bar Using an Improved Material Model For Ductile-to-Brittle Transition at High Strain Rates

A Fully Coupled Thermal-Structural Finite Element Analysis of a Low-Carbon Steel Bar Using an Improved Material Model For Ductile-to-Brittle Transition at High Strain Rates

Thermal-Structural Finite Element Analysis of Injection Moulding Dies with Optimized Cooling Channels

One of the most important aspects of mould design in injection moulding is the provision of suitable and adequate cooling arrangements. Proper cooling channel design in the mould is an important aspect as it affects cycle time and quality of the injection moulded plastic part. A new cooling channel design with copper tube insert can reduce cycle time by optimal and uniform heat transfer in the mould. In this research work a comprehensive FEA transient thermal-structural analysis has been performed with ANSYS simulation software to understand robustness and longevity of an industrial plastic part mould with these cooling channels and compared with conventional straight cooling channels. Autodesk Moldflow Insight (AMI) also has been used to get essential process parameter values for analysis. Result shows that by inserting copper tube in the cooling channels, a mould can increase cooling efficiency and can last for higher number of cycles before fatigue failure, thus increasing production rate.

Constitutive equation with internal damping for materials under cyclic and dynamic loadings using a fully coupled thermal-structural finite element analysis

In this paper a universal constitutive equation with internal damping for materials under cyclic and dynamic loading is presented using fully coupled thermal-structural finite element analysis. The equation adapts the idea of a spring dashpot system connected in parallel for continuum utilizing appropriate deformation measures, which are independent of rigid body motion, thus enabling more precise numerical simulation of real material. In this work, mathematical formulation of the problem is presented and demonstrated in numerical examples using a solid bar in cyclic tension and a cross-shaped specimen in biaxial tension. Elastic and plastic loading cases with and without heat generation rate per unit volume were studied, where the heat generation rate was defined as 80% of the dissipated energy per unit time. Although the calculation results are in good agreement with the only experiment we could find in technical literature, more detailed tests are needed to draw final conclusions.

Process simulation of micro electro-discharge machining on molybdenum

Micro electro-discharge machining (micro-EDM) is an ideal process for obtaining burr-free machined micron-size apertures in many materials. Molybdenum is one of the most attractive high energy and power aperture materials due to its mechanical and physical properties, mainly its high melting temperature and relatively high thermal conductivity. In this paper, process simulation and residual stress analysis for the micro-EDM machining on molybdenum is presented. Material removal is analyzed using a thermo-numerical model, which simulates a single spark discharge process. Using the numerical model, the effects of important EDM parameters such as the pulse duration on the crater dimension and the tool wear percentage are studied. Experimental single-spark crater sizes are investigated using scanning electron microscopy and optical evaluation methods and the results compared to the model. Results from a coupled thermal-structural finite element analysis are also presented to show how the thermal action of the micro-EDM process affected the surface integrity of machined workpiece.