Thermal Structure Interaction Research Articles

Thermal-structure interaction characteristics of a high-speed spindle- bearing system

Abstract The neglection of thermal-structure interaction of high-speed spindle system may lead to the modeling error of the thermal characteristics. To improve the modeling accuracy, the thermal-structure interaction mechanism was analyzed and the closed-loop iterative modeling method of thermal characteristics was proposed to modify the heat sources and thermal boundary conditions of the spindle system in each substep. The heat generation of bearings and built-in motor, the convective coefficients and the thermal contact resistances (TCRs) of bearing joints were computed. The heat generation of bearings was calculated by the SKF bearing thermal model and the results were compared with that obtained by integral method. The heat generation of bearings was modified by considering the combined effect of the lubricant viscosity variation and thermally-induced preload of bearings. Moreover, a novel geometrical-mechanical-thermal model for TCRs was proposed by characterizing the rough surface morphology and by establishing the multi-scale contact mechanics of joint surfaces. To validate the effectiveness of the proposed method, the thermal characteristic experiments of the spindle system were conducted under different rotational speeds. The results showed that the modeling errors in the temperature field and thermal deformation are reduced significantly and that this model has the ability of thermal error compensation.

Post-fire damage assessment of Korean bridges using thermal–structure interaction fire analysis

To evaluate fire-induced damage to bridge structures, the thermal–structure interaction (TSI) fire analysis method is proposed, verified and applied to examine the behaviour of bridge superstructures with steel–concrete composite sections and prestressed concrete (PSC) exposed to fire loading. The proposed TSI fire analysis consists of two different modelling parts: thermal transfer analysis and thermodynamic structural analysis. The body temperature inside the structure is first calculated using fire curve boundary conditions in an overall non-linear transient thermal transfer analysis. Thermodynamic structural analysis is then performed based on the entire temperature and heat distribution in the structure. To validate the proposed method, comparisons are made with standard fire test results: the temperature distribution and the deflection of the steel–concrete composite superstructure agreed closely with the results of the standard fire test. The proposed fire analysis method is finally applied to two bridges with different superstructures (steel–concrete composite and PSC) damaged by recent fire events in Korea.

An internal penalty discontinuous Galerkin method for simulating a thermoelectric cooler

Compact modelling of a thermoelectric cooler in the computational fluid dynamics approach is essential for reliable product design in the telecommunication industry, particularly for the package design of the optical laser or the wavelength selective switch. When simulating these fluid thermal structure interaction problems numerically, stability and high order of accuracy are required to capture all of the necessary physics. The principle benefit of using the discontinuous Galerkin (DG) method is that it can produce a high order accurate scheme which can achieve an equivalent error compared to the lower order scheme with orders of magnitude lower computational effort. Based on the recent development of a framework for the computation of fluid thermal structure interaction problems within multi-solid domains using DG methods on unstructured grids([1,2]) ; this paper has proposed a detailed compact thermoelectric cooler (TEC) modelling method based on an existing black box like compact TEC model [4]. Close comparisons validate that both the detailed and the black box like compact model are accurate enough to simulate the conduction only case. When air convection is required to carry out a system-level thermal management optimization, the detailed compact modelling method is more reliable than the black box like compact TEC model. Furthermore, the thermal expansion of an operating TEC has been examined. Compared to the black box like compact TEC model, the simulation results of the detailed compact method have better agreement with electronic speckle pattern interferometry data.

Efficient uncertainty quantification for a hypersonic trailing-edge flap, using gradient-enhanced kriging

We present a numerical study on the uncertainty quantification (UQ) of aerodynamic forces acting on a hypersonic trailing-edge flap model, as a result of input uncertainties in the experimental boundary conditions. The complex fluid–thermal-structural interaction on aerodynamic surfaces of a hypersonic flight vehicle and fluctuations in flow conditions result in uncertainties in their aerodynamic characteristics. We run the numerical simulations in US3D to quantify these uncertainties. Altogether four input uncertain parameters—inlet flow velocity, density, temperature, and the model wall temperature—are considered. We obtain the aerodynamic forces from the primal solve, as well as gradient information from a dedicated sensitivity solver. We compare the surrogate-based UQ analysis using kriging as well as gradient-enhanced kriging (GEK), accounting for significant observation errors in the gradients, and quantify the accuracy of the output probability density function (PDF). The accuracy of the predicted output PDF converges faster for GEK than for kriging, implying the importance of the gradient information in order to reduce the computational cost—in the present case, the computational cost is reduced by a median speed-up of roughly 3.0 by exploiting the gradient information available from the sensitivity solver.

Experimental and numerical study of crack damage under variable amplitude thermal fatigue for compacted graphite iron EN-GJV-450

Fatigue crack under variable amplitude thermal cycles is a common failure in combustion chamber components, proposing great challenges during the temperature reproduction of actual working condition. In this paper, this complicated thermal cycle was realized with pulsed laser experimentally, causing two kinds of damage such as the low cycle thermal fatigue (LCF) and high cycle thermal fatigue (HCF). A numerical model was developed to simulate the temperature, stress and strain under variable amplitude thermal cycles. The results showed that, there was good agreement between the measured temperature curve and the simulated results with different crack parameters. The observed crack depth at different cycles was consistent with the predicted ones. Furthermore, the mechanism of crack evolution under variable amplitude thermal fatigue was discussed. The calculated thermal-structural interaction depth of LCF thermal cycle was found to be larger than the HCF thermal cycle. The effect of LCF thermal loadings was associated with the initiation of major cracks, while the failure related to the superimposed HCF action was the acceleration of crack growth with a surface wedging process. This paper provides comprehensive experimental and numerical insights into the thermal damage process under variable amplitude thermal loading, showing a significant engineering value for failure analysis and design optimization of combustion chamber components.

Influence of Fluid–Thermal–Structural Interaction on Boundary Layer Flow in Rectangular Supersonic Nozzles

The aim of this work is to highlight the significance of Fluid–Thermal–Structural Interaction (FTSI) as a diagnosis of existing designs, and as a means of preliminary investigation to ensure the feasibility of new designs before conducting experimental and field tests. The novelty of this work lies in the multi-physics simulations, which are, for the first time, performed on rectangular nozzles. An existing experimental supersonic rectangular converging/diverging nozzle geometry is considered for multi-physics 3D simulations. A design that has been improved by eliminating the sharp throat is further investigated to evaluate its structural integrity at design Nozzle Pressure Ratio (NPR 3.67) and off-design (NPR 4.5) conditions. Static structural analysis is performed by unidirectional coupling of pressure loads from steady 3D Computational Fluid Dynamics (CFD) and thermal loads from steady thermal conduction simulations, such that the simulations represent the experimental set up. Structural deformation in the existing design is far less than the boundary layer thickness, because the impact of Shock wave Boundary Layer Interaction (SBLI) is not as severe. FTSI demonstrates that the discharge coefficient of the improved design is 0.99, and its structural integrity remains intact at off-design conditions. This proves the feasibility of the improved design. Although FTSI influence is shown for a nozzle, the approach can be applied to any product design cycle, or as a prelude to building prototypes.

Multi-objective reliability-based design optimization approach of complex structure with multi-failure modes

To make multi-objective reliability-based design optimization (MORBDO) more effective for complex structure with multi-failure modes and multi-physics coupling, multiple response surface method (MRSM)-based artificial neural network (ANN) (ANN-MRSM) and dynamic multi-objective particle swarm optimization (DMOPSO) algorithm are proposed based on MRSM and MOPSO algorithm. The mathematical model of ANN-MRSM is established by using artificial neural network to fit the multiple response surface function. The DMOPSO algorithm is proposed by designing dynamic inertia weight and dynamic learning factors. The proposed approach is verified by the MORBDO of turbine blisk deformation and stress with respect to fluid–thermal-structure interaction from probabilistic analysis. The optimization design results show that the proposed approach has the promising potentials to improve computational efficiency with acceptable computational precision for the MORBDO of turbine blisk deformation and stress. Moreover, Pareto front curve and a set of viable design values of turbine blisk are obtained for the high-reliability high-performance design of turbine blisk. The presented efforts provide an effective approach for MORBDO of complex structures, and enrich mechanical reliability design theory as well.

Thermal-deformation coupling in thermal network for transient analysis of spindle-bearing system

Transient analysis by thermal network method for complex structures like the spindle-bearing system is essential but insufficient. In this paper, the network approach was developed for spindle transient analysis in consideration of thermal-structure interaction. Firstly, the radial and axial deformation of spindle system during assembling process, deformation by thermal extension and centrifugal effect were all obtained. Then the transient analysis was deduced based on traditional steady model, the thermal-deformation coupling and some other time-varying parameters. Experiment results indicate that temperature by steady model is of large deviation, while by the transient model is much more accurate. Finally, the temperature rising curves, the balance time of the spindle system and temperature rise feature for continuous working conditions were all achieved and discussed.

Experimental investigation of the thermally induced vibration of a space boom section

Thermally induced vibration (TIV) is a typical failure of large-scale space structures. This paper reports a laboratory experiment that aims to investigate this unusual structural behavior of complex engineering structures. With the help of a Fourier finite element program, the fixing of a space boom section is well designed so that the TIV can be successfully observed. Although the observed torsional vibration mode is different from the bending vibration mode predicted by the classic theory based on a simple beam model, it can be successfully explained by the general thermal structural interaction theory. This demonstrates the validity of the theoretical model and the necessity of using finite element program to analyze complex engineering structures.

Geometry-Grid Generation for Three-Dimensional Multidisciplinary Simulations in Multistage Turbomachinery

A procedure is presented for automated and fast geometry-grid generation of three-dimensional, multistage, axial turbomachinery for multidisciplinary simulations involving fluid–thermal, fluid–structural, or fluid–thermal–structural interaction. The procedure rapidly generates geometry for solid airfoils and endwalls, thermal barrier coatings, heat transfer pedestals, cooling plenums, cooling flow control tubes, and interblade row endwall leakage slots as well as the computational grids for these components automatically based on prescribed input parameters. The computational grids that are generated in general consist of multiblock, point-matched structured grids. For the cooling flow control tubes, heat transfer pedestals, and interblade row leakage slots, the computational grids are embedded, multiblock, overset grids to allow for arbitrary placement to allow optimization without the need for regridding the entire domain. The techniques used to construct the geometry and various computational grids are described. Demonstration of the procedure is provided for a one-and-a-half stage film-cooled turbine and a single-stage compressor. The geometry parameterization, as well as the automated geometry and grid topology construction, makes this a unique and rapid approach for multidisciplinary grid generation of multistage turbomachinery configurations during design optimization.

The Effects of Dynamic Loading on Hysteretic Behavior of Frictional Dampers

During an earthquake excitation, a frictional damper may experience many cycles of dynamic loading. The effects of wear and heat induced by the cyclic loading result in the possible decay of the slippage load which subsequently reduce the energy absorption of the damper. In this paper, the effect of dynamic loading on hysteretic behavior of a special kind of frictional damper, namely, cylindrical frictional damper (CFD), is investigated by experimental means as well as numerical models which also account for coupled thermal-structural interaction. The damper is deemed to be more susceptible to thermal deformations due to the shrink-fit mechanism by which the device is assembled. The numerical models are validated experimentally and may be utilized for simulation of dynamic cyclic loading on frictional dampers. The results demonstrate that the slippage load is reduced gradually when subjected to consecutive cycles. This drift is attributed to thermal deformation. The verified numerical models are used to improve the geometry of the CFD. With the geometrical improvements implemented, the subsequent numerical studies confirmed that almost no degradation of the slippage load occurred. Furthermore, a dimensionless parameter is introduced by the authors which shows the effect of wear on the response of CFDs.

화재에 노출된 교량하부 강합성 구조물에 대한 열-구조 연성 병렬화재해석

The objective of this research is to evaluate of global and local damage for steel-concrete composite structures under highway bridge exposed to fire loading. To enhance the accuracy and efficiency of the numerical analysis, the proposed transient nonlinear thermal structure interaction(TSI) parallel fire analysis method is implemented in ANSYS. To validate the TSI parallel fire analysis method, a comparison is made with the standard fire test results. The proposed TSI parallel fire analysis method is applied to fire damage analysis and performance evaluation for Buchen highway bridge. The result of analysis, temperature of low flange and web are exceed the critical temperature. The deflection and deformation state show good agreement with the fire accident of buchen highway bridge.

Modeling and analysis of floating performances of stratospheric semi-rigid airships

In recent years, the study of semi-rigid airship has revived with the development of airships. Semi-rigid airships have some characteristics of rigid airships and non-rigid airships. Due to the flexibility of the envelope of the non-rigid airship, the variation of the temperature of the inner gas will lead to its structure deformation and affect its flight altitude. This paper develops the structural mechanics model, thermodynamic model and dynamic model of the semi-rigid airship, based on which nonlinear finite element analysis is employed for geometrically nonlinear deformation of the airship upper film in consideration of thermodynamics and structural mechanics coupling. Based on the thermal-structural interaction, the thermal characteristics and flight performances of the airship during floating flight are investigated. The 3-D solar radiation and temperature distribution of the airship skin and the temperature variation of the inner gas are presented to investigate the thermal performance of the airship, flight velocity, acceleration and flight altitude are simulated to investigate the flight performance, and the variations of the volume and pressure difference of the inner gas are calculated to provide a basis for structure design. The results of the simulation can be referenced for the design of the semi-rigid airship, and can be used for the further study on the attitude control of the airship during its floating flight.

On the use of system modes to model multibody flexible structures

This study has the purpose of bringing to light flexibility modelling issues in connection with multibody dynamic simulation. Towards this end, an examination is made of fundamental concerns that arise when one seeks to formulate equations of motion for simulation of dynamics and control of large flexible structures. Quantitative criteria are provided regarding modal discretization and model reduction techniques. In particular, the thermo-structural modelling and interaction effects on the system modal spectrum are investigated using system modes. This approach allows a more accurate modelling of the thermal–structural interaction in large flexible space structures.