Sequential Coupling Method Research Articles

Non-uniform variation characteristics of temperature field and corresponding thermal effect of longitudinal continuous slab ballastless track structure

The longitudinal continuous slab ballastless track structure (LCSBTS) easily suffers from interface and joint damage when subjected to extremely high-temperature loads, significantly affecting the running smoothness and safety of high-speed trains. This paper establishes a numerical model of the LCSBTS using the heat transfer principle and real-time shadow technology to replicate the time-varying evolution and spatial distribution of the temperature field. The corresponding thermal effect is obtained based on the sequential thermal-mechanical coupling method. The results show that the temperature variation and the corresponding thermal effect exhibit strong temporal-spatial non-uniformity on the horizontal and vertical planes of the LCSBTS. Solar radiation and heat convection are the dominant factors for the temperature field of the LCSBTS in the daytime and night, respectively, resulting in a higher temperature and greater thermal deformation on the sunny side than on the shady one. The temperature and vertical thermal deformation along the longitudinal direction vary periodically with a specific wavelength between the two adjacent rail support concrete blocks. The thermal deformation increments under the studied non-uniform temperature loads cause an interface damage increment. Finally, the consideration of a non-uniform temperature load produces remarkably different thermal effects from those given by the design temperature load.

Optimal design of electro-thermo-mechanical microactuators considering minimum length scale constraints

To ensure the manufacturability of compliant mechanisms, this paper presents a new approach for optimal design of electro-thermo-mechanical microactuators by employing minimum length scale constraints. A sequential coupling method is adopted to carry out finite element analysis for electric-thermal-mechanical coupling multiphysics. The inflection point fields of the solid and void phases are identified by structural indicator functions. The minimum length scales of the solid and void phases are adopted as constraints. The optimization objective is designed to maximize the output displacements of electro-thermo-mechanical microactuators. The validity of the proposed optimal design method is demonstrated through several numerical examples. In the optimal designs obtained by the proposed method, the minimum length scales of the two phases can be properly controlled. The electro-thermo-mechanical microactuator’s output displacements decrease when the allowable value of the minimum length scale is increased. The effects of different mesh discretizations and output spring stiffnesses on the optimized designs are discussed.

Numerical simulation method of the failure behavior of the UMo-Al monolithic fuel element

The UMo-Al monolithic fuel element has a special failure mode of blistering on the cladding surface under high temperature and high burn-up conditions. In order to provide an auxiliary means for the safety analysis and failure limit formulation of the fuel element, this study establishes a numerical simulation method of fuel failure behavior, considering the fracture behavior and the fission gas pressure acting on the cracks for the UMo-Al monolithic fuel element. Numerical simulation is based on ABAQUS software and the extended finite element method (XFEM) established by programming FORTRAN subroutines UMAT, UMATHT, and UAMP and using the thermo-mechanical sequential coupling method. Combined with Python to secondary develop ABAQUS with the FORTRAN subroutine, this study realizes the coupling of fission gas pressure load and crack propagation. This study obtained the failure threshold temperature, blistering height, area, and other blistering characteristics of the UMo-Al monolithic fuel element through numerical simulation of annealing experiments on L1P460 in RERTR-12. A comparison of the numerical simulation results with the RERTR-12 experiment shows that the method established in this study can effectively analyze blistering failures.

Coupled thermal-mechanical analysis of power electronic modules with finite element method and parametric model order reduction

This work presents a new approach for performing a parametric study and examining nonlinear material behaviours of a coupled thermal-mechanical model of a Power Electronics Module (PEM) by integrating the Finite Element Method (ANSYS-FEM) with Parametric Model Order Reduction (pMOR). The considered coupling method solves the thermal and structural models concurrently compared to the widely practised sequential coupling method. Instead of constant parameter values, which are generally regarded for pMOR studies, the temperature-dependent material properties of the wire material have been parametrised in the work using the pMOR method. A generalised 2D model has been regarded here for thermal-mechanical analysis with the pMOR approach, parametrising temperature-dependent coefficient of thermal expansion (CTE) and Young’s modulus (E) of the wire material to explore their impact on wire bonds. The matrix interpolation method has been applied here for the pMOR study, and PRIMA, a Krylov subspace-based model order reduction (MOR) technique, has been exercised for local model order reductions. A new efficient process of matrix interpolation, based on the Lagrange interpolation technique, has been developed to implement matrix interpolation in the parametric reduced order model (pROM). The local reduced order models (ROMs) have a degree of freedom (DOF) of just 8, compared to the full-order models’ (FOMs) of 50,602. The pROM provides an excellent solution and reduces computational time by 84% for the presented case.

An energy-based chemo-thermo-mechanical damage model for early-age concrete

Cracking prediction and control in hydration process of mass concrete and structures has always been a challenging task. In this work, an energy-based chemo-thermo-mechanical damage model for early-age concrete is well established within the framework of thermodynamics and continuum damage mechanics. The evolution laws for the mechanical damage are driven by the work conjugate elastoplastic damage energy release rates to fully represent the microcracks closure-reopening effect, the anisotropy, and the aging effect of concrete relating to the degree of hydration. A formulation fitted from a large number of test data is introduced to simulate the thermal evolution during hydration process, resulting in an excellent approximation of the degree of hydration. When the degree of hydration is 1, the model is degenerated into the classical plastic damage model. The presented model is thus able to simulate the hydration process of early-age concrete and mechanical responses of concrete as well as reinforced concrete structures at any age. The model is implemented by user defined subroutine in Abaqus, in which a sequential coupling method is established. Several benchmark tests are successfully reproduced, indicating that the proposed model is capable of predicting the damage evolution and typical nonlinear behavior of early-age concrete and hardened concrete. The computational efficiency of the model is significantly improved compared to the classical ones due to the introduction of the fitting formulation of the thermal evolution and the sequential coupling method to reduce the nonlinearity of the system. The strategy allows the model to be applied in massive concrete structures during construction and provide valuable prediction as well as guidance for large scale engineering structures.

Progressive collapse resistance of RC frames subjected to localized fire

Fire is one of the accidental loads that can cause progressive collapse of buildings. However, the behavior of fire-exposed reinforced concrete (RC) frames to resist progressive collapse are still unclear. Therefore, a numerical study on the RC assembly based on the sequential thermal-mechanical coupling method is conducted. Fire effects on the failure mode, load-resistant capacity, and the evolution of load-resistant mechanisms of the RC frame are captured. The numerical results show that compressive arch action (CAA) and catenary action (CA) can develop in sequence for the specimens exposed to fire within a short fire duration of 30 min. The failure of the specimen is controlled by the fracture of beam rebars near the removed column. However, when the fire duration exceeds 60 min, the specimen is difficult to develop effective CA due to a decrease of over 80% in the tensile strength of the bottom reinforcement. The failure of the specimen is dominated by the fracture of the rebar at the cut-off point of the beam top rebar. Fire lasting for 30 min, 60 min, 90 min and 120 min results in a decrease of 41%, 72%, 77% and 78% in ultimate load, respectively. Increasing the span-depth ratio can upgrade the deformation capacity of the specimen, but it is adverse to the development of CAA. The effects of the reinforcement ratio on the failure mode, the ultimate load and deformation capacity are mild as the fire exposure duration increases.

Early warping deformation of high-speed railway CRTS III track slabs

Excessive flatness deviation issues in the track slabs of railway tracks make it difficult to achieve precise adjustments for both the track slabs and rails. This study aimed to analyze the deviation in flatness of the high-speed railway CRTS III track slabs. Experimental measurements were conducted on the warping deformation of the track slabs before water curing during the maintenance period. Six improved designs were implemented for the steaming process and structural construction. A numerical model was established to predict the warping deformation of the track slab before water curing, considering the temperature and humidity fields as driving forces. Using the sequential coupling method, the warping deformation of CRTS III track slab was calculated under the combined action of temperature field, shrinkage strain field, and prestressed tendons. Based on the results, it is concluded that: (1) High-temperature steam curing of the track slab increases the effective maintenance time and accelerates its strengthening rate. (2) Early shrinkage of the track slab is the primary factor causing warping deformation. (3) During the steam curing period, the warping deformation of the track slab can be controlled economically and effectively by employing secondary water spraying and presetting a reverse arch of 0.5 mm–0.8 mm.

Mechanical Response of a Buried Pipeline to Permafrost Thawing Based on Sequential Coupling Method

Thawing permafrost has affected the structural integrity of buried warm pipelines in cold regions and poses an ongoing threat in the context of climate change. Therefore, characterizing variation in the engineering properties of pipeline foundation permafrost and its effect on the mechanical behavior of pipeline is important. In this paper, the ground temperature distributions around a buried warm pipeline and mechanical response of the pipeline to differential thaw settlement of foundation permafrost are investigated using thermal–mechanical sequential coupling simulation, based on the observational data collected from a selected monitoring site along the China-Russia crude oil pipelines in northeastern China. The results indicate that the thaw-induced settlement of pipeline foundation permafrost develops quickly with the formation and expansion of the thaw bulb in the first 10 years, and then increases slowly when the thaw bulb extends to the weathered granite. Differential thaw settlement will cause a significant change in the deformation and stress of the pipeline near the interface of strong and weak thaw settlement zones. When the length ratio of strong and weak thaw settlement zones is 1, the maximum stress of the pipeline with a thickness of 16 mm is approximately 45% of the allowable stress of X65 steel, and the pipeline remains safe for 30 years. However, the potential failure of the pipeline should be considered due to the continued ground thawing and warming and pipe material aging. Forthcoming research on this topic is needed to evaluate more carefully the structural integrity of buried pipelines in cold regions.

Simulation on seismic performance of the post‐fire precast concrete column with grouted sleeve connections

AbstractA simulation method with Abaqus software was adopted to analyze the seismic performance of post‐fire precast concrete column with grouted sleeve connections. First, the simulation was exerted on the column at ambient temperature and the grouted sleeve connection was simplified to be a single steel rebar. It is found that the yield load, lateral peak load and ductility coefficient from the simulation result are about 0.89, 0.85, and 1.02 times of those from the test respectively, which shows that the built finite element model is fit for the simulation analysis of precast concrete column and the simplified method of grouted sleeve connection is feasible. Then, a sequential coupling method was used to simulate the seismic performance of cast‐in‐place column after exposure to elevated temperatures. It is found that the highest temperature, load and ductility coefficient from simulation agree well with those of test, as the maximum difference is only 5.0%. Furthermore, simulations of post‐fire precast concrete columns with grouted sleeve connections were based on these practices and the findings as follows: as the elevating time becomes longer, the maximum difference of the highest temperature between the simulation and the theory decreases from 6.7% to 0.6%; compared to the condition at ambient temperature, the lateral peak load decreases linearly along with the elevating time ascending. Finally, a new expression was proposed to calculate the shear bearing capacity of post‐fire precast concrete column with grouted sleeve connections, which will be beneficial to the fire safety design of precast concrete structures.

Performance of RC beam-column assemblies during and after elevated temperature to resist progressive collapse

In practice, fire is one of the accidental loads that can result in the progressive collapse of buildings but the commonly used alternate load path (ALP) approach often ignores the impact of fire. Therefore, numerical models based on the finite element software ABAQUS are employed to investigate the performance of reinforced concrete (RC) beam-column assemblies during and after high temperature to resist progressive collapse. The thermal–mechanical sequential coupling method is used for analysis. The effects of fire durations, boundary conditions (middle or penultimate column removal) and side column subject to fire are studied. Previous test results demonstrated that compressive arch action (CAA) and catenary action (CA) are developed in sequence to prevent progressive collapse for the assemblies at ambient temperature. However, the numerical results show that the in-fire assemblies could not develop CA owing to severe degradation of rebar elongation and thus, the load resistance of in-fire assemblies controlled by CAA capacity. Further increasing fire duration to 90 mins, the CAA capacity of the assemblies decreases over 70% compared with that at ambient temperature. Since the rebar can recover most of its mechanical properties after cooling down, the assembly after fire (i.e., exposed to fire then cooled down) can also successively develop flexural action (FA), compressive arch action (CAA) and catenary action (CA) to resist progressive collapse, which is similar to that of intact RC frame at ambient temperature. Under the penultimate column removal scenario, the exterior side column of the post-fire specimen suffers large eccentric compression failure, which causes the highest collapse risk.

Mechanical–Thermal–Electrical Coupling Modeling and Temperature Rise Characteristic of a Parallel Groove Clamp With Improved Representation of Contact Interactions

The electrical contact resistance and thermal contact resistance caused by the actual rough surfaces of parallel groove clamps exist during contact interactions, which affects the heat generation rate and thermal conductivity, and then the accuracy of multi-field coupling numerical simulation. Thus, first, a mechanical-thermal-electrical coupling model of the parallel groove clamp is created based on the improved representation of contact interactions. Then, a progressive sequential coupling method is proposed to improve the calculation accuracy and efficiency of the multi-field coupling. Meanwhile, the validity of the coupling model is verified by electrical resistance and temperature measurement experiments. Finally, the temperature rise characteristic of the parallel groove clamp is analyzed under normal and large current impact conditions. The results show that the experimental and numerical electrical resistance and temperature show a good agreement. The electrical resistance of parallel groove clamps stabilizes when the preload force is greater than the critical value, 5000 N. The highest temperature of parallel groove clamps is always located at the contact edge between the upper clamp block and branch line, and the influence of current intensity on temperature rise is significant under normal condition, while the effect of preload force is less. The large current impact mainly affects the transient temperature rise. However, the effect of the large current impact on steady-state temperature is negligible.

Simulation Analysis of Stress Field of Walnut Shell Composite Powder in Laser Additive Manufacturing Forming

A calculation model of stress field in laser additive manufacturing of walnut shell composite powder (walnut shell/Co-PES powder) was established. The DFLUX subroutine was used to implement the moveable application of a double ellipsoid heat source by considering the mechanical properties varying with temperature. The stress field was simulated by the sequential coupling method, and the experimental results were in good accordance with the simulation results. In addition, the distribution and variation of stress and strain field were obtained in the process of laser additive manufacturing of walnut shell composite powder. The displacement of laser additive manufacturing walnut shell composite parts gradually decreased with increasing preheating temperature, decreasing laser power and increasing scanning speed. During the cooling process, the displacement of laser additive manufacturing of walnut shell composite parts gradually increased with the increasing preheating temperature, decreasing scanning speed and increasing laser power.

Effect of fire on behavior of RC beam-column assembly under a middle column removal scenario

Fire is one of the accidental loads that can result in the progressive collapse of buildings. To investigate the structural behavior of reinforced concrete (RC) structures subjected to fire-induced progressive collapse, the sequential thermal-mechanical coupling (STMC) method is adopted. The STMC method includes two steps: firstly, the fire effects (temperature field) on the material properties of concrete and reinforcement are simulated. Secondly, the results of the first step are set as the initial condition of the RC beam-column assembly to study the structural behavior of the assembly subjected to a middle column removal scenario. The reliability of the simulation method is validated against the available test results. The influences of fire duration and fire range are studied based on the validated numerical model. It is found that the load resistance and deformation capacity decrease significantly as the fire duration exceeds 30 min. The load resistances of the RC beam-column assemblies under the fire durations of 30 min, 60 min, and 90 min are 35%, 26%, and 21% of that of the RC beam-column assembly under the ambient temperature, respectively. Fire duration of 18 min is found to be the critical one, less than and greater than which the failure of the RC beam-column assembly is controlled by the fracture of the beam bottom rebar near the middle column and the fracture of the beam top rebar at the location of rebar termination, respectively. The RC beam-column assembly subjected to a single-bay in fire scenario shows asymmetric structural behavior. Compared with RC beam-column assemblies under two-bay in fire scenario, the load resistances of RC beam-column assemblies subjected to single-bay in fire scenario are greater by 6%–30%. However, they achieve a similar deformation capacity as the failure of the RC beam-column assemblies subjected to single-bay in fire scenario is controlled by the failure of the bay in fire.

Thermo-mechanical properties of RTM-made carbon fibre/polyimide composite attaching collar under transient heating

This study focuses on the thermo-mechanical properties of Carbon Fibre/Polyimide Composite (CFPC) attaching collars under transient heating. The CFPC attaching collars were fabricated by a high-temperature resin transfer moulding process, and their thermo-mechanical properties under the conditions of simultaneous transient heating and bending load were investigated. The results show that the attaching collar tends to fail at 118% of the limit load. The failure mode includes the fracture of the connecting screws, local extrusion damage of the hole edges, and slight ablation damage at the outer plies. And there is no observable residual deformation in the composite attaching collar. Furthermore, considering that the material properties vary with temperature, a progressive damage model based on the sequential thermo-mechanical coupling method was established to study the failure mechanism of the attaching collar. Finally, the damage factor of the CFPC was calculated to assess the safety status of the attaching collar. The results show that the primary damage modes of the composite attaching collar are intralaminar failure, which mainly occurs at the heat insulation layer and the hole edges, and these slightly affect the structural bearing capacity. A good correlation between the experiment and FEA is obtained. The test methods and analysis models proposed contribute to the safety assessment of composite structures under transient heating.

Study on key mechanical properties of the flexible spoke non-pneumatic tire considering thermo-mechanical coupling

Based on the combination of numerical analysis and prototype test, this paper explores the key mechanical properties of the flexible spoke non-pneumatic tire under thermo-mechanical coupling, mainly including basic mechanical properties and fatigue properties. Based on the thermo-mechanical sequential coupling method, the structural field and temperature field of the flexible spoke non-pneumatic tire is analyzed, and the thermo-mechanical coupling analysis model is constructed by using the predefined field method. Based on the thermo-mechanical coupling analysis model, the basic mechanical properties of the flexible spoke non-pneumatic tire are investigated, and the J-integral method is used to predict the fatigue life of the non-pneumatic tire. The results show that the vertical displacement, the grounding area, and the axial displacement in the rolling process with thermo-mechanical coupling are similar to those without thermo-mechanical coupling, but each of them increases; based on the J-integral method, the predicted fatigue failure mileage of non-pneumatic tire is 2.67 × 104 km, and the fatigue failure mileage of indoor drum test is 2.44 × 104 km, which is basically consistent. The key mechanical properties of the flexible spoke non-pneumatic tire considering thermo-mechanical coupling are closer to the actual operating conditions. The development of this paper has important theoretical significance and application value for the development of tire safety technology.

The thermal-fluid-solid coupling effect in nuclear reactor vessel with direct vessel injection

Different from conventional cold leg safety injection, a newly designed reactor type CAP1400 directly connects the injection pipeline of the emergency cooling system with the pressure vessel. However, these structures have been found to potentially have adverse effects on the pressure vessel. This paper employs both physical experiment and numerical analysis to investigate the dynamic oscillating load and the structural response. A 1:9 scale model is adopted for the experimental section. The uncertainty of the measurement quantities is within 3%. The CFD code and the FEM code are used to simulate the transient fluid flow and solid structure deformation, respectively. The sequential coupling method is used for the thermal-fluid-solid coupling calculation. The overall error of the calculation is within ±10%. The result shows that the fluctuation of the physical quantity near the wall is caused by turbulence eddy and thermal mixing, and the flow, heat transfer and structural deformation near the wall of the pressure vessel are closely coupled. The effect of the turbulence eddy can be seen within the entire range of frequency measured, while that of the thermal mixing can be seen only within the low frequency range. The influence law of the loop flow ratio, the flow rate of the downcomer and the loop temperature difference in the structural response are obtained. Through the research of this paper, the law of interaction between the thermal-fluid load and the structural response under direct safety injection is more deeply understood. Thus, it provides a design reference for the safety of reactors.

Effects of bed geometric characteristics on hyporheic exchange

As an active ecotone between the surface stream and groundwater, hyporheic zone (HZ) plays a crucial role in hydrological and ecological processes. Previous numerical simulation and experimental studies have shown that hyporheic exchange can be affected not only by current but also by geometric characteristics of the streambed. However, the geometric characteristics that affect hyporheic exchange remain unclear. In this study, a one-way sequential coupling method was established to connect the river water flow and pore-water flow in the streambed. The change of flux at the interface, mass flux, depth, and area of hyporheic zone were investigated by altering the bed geometric characteristics, i.e. the depth, crest position, and shapes of bedforms. The results clearly demonstrate the following conclusions: (a) the hyporheic exchange flux, depth and area with wave-like bedform is greater than the triangular bedform. (b) The increase of the bed height accelerates the hyporheic exchange processes at the sediment–water interface. (c) A good linear relationship was found between the depth and area of the hyporheic zone. These results provide necessary theoretical understandings of hyporheic exchange, broadening the knowledge of mechanism of stream-streambed exchange processes.

Analysis of fluid-solid-thermal coupling characteristics of axial-symmetric vectoring exhaust nozzle

Aiming at the problems of axial-symmetric vectoring exhaust nozzle (AVEN) mechanism due to its complex structure, which leads to the large amount of digital simulation calculation under the coupling of multi-physics, and it is difficult to establish the fluid domain model, a complex AVEN structure is proposed as the research object, the method of AVEN flow field simplify model in cylindrical coordinate system. This method simplifies the contact domain between the expansion regulator plate, the cruciform joint, the convergent regulator plate and the flow field into a cylindrical overall physical model, and constructs a fluid-solid coupling heat transfer physical model. The feasibility of the model is verified. The AVEN fluid-solid-thermal coupling digital simulation calculation is carried out using the sequential one-way coupling method. First, based on computational fluid dynamics, the AVEN fluid-solid coupling heat transfer calculation is carried out to calculate the coupling surface temperature and pressure field. Second, the calculated coupling surface temperature is used as the thermal analysis boundary condition. Then, the temperature field calculated by the thermal analysis and the pressure field calculated by the fluid-solid coupling heat transfer analysis are used as the boundary conditions of the structural strength analysis. Finally, fluid-solid-thermal coupling analysis of AVEN including aerodynamic load and thermal load is carried out. The calculation results show that the digital simulation method proposed in this paper can be used in engineering practice. The temperature and pressure of the AVEN coupling surface show a trend of first decreasing, then increasing, and then decreasing with the change of the position from the throat. Some AVEN mechanical components and parts have stress singular phenomena. The deformation of the AVEN structure is obviously affected by the thermal load, and the minimum change of rate is 9.54%, the maximum change of rate is 1845.37%.

Reducing Full-Field Residual Stress of Girth Weld With Thick Wall by Combining Local PWHT and Water Jet Peening

Abstract In this paper, a new controlling method combined local postweld heat treatment (PWHT) and water jet peening (WJP) was proposed to reduce full-field residual stress of girth weld with thick wall. The finite element analysis with sequential coupling method and experiment measurement were performed to study the residual stresses distribution before and after the new controlling method. The results show that the hoop and axial stresses through the thickness are all decreased greatly by using the new controlling method. As long as the new controlling method is used with appropriate parameters, the residual stresses on inner surface can be reduced from tensile stresses to compressive stresses, which greatly improve the resistance ability to stress corrosion of inner surface.

Thermal Mechanical Coupling Analysis of a Flexible Spoke Non-pneumatic Tire

A new type of non-pneumatic tire with a flexible spoke structure is proposed to solve traditional pneumatic tire defects, such as easy bursting, the requirement of real-time maintenance to keep tire pressure, and a complex manufacturing process. The thermal mechanical coupling characteristics of the flexible spoke non-pneumatic tire are studied in detail to obtain the steady-state temperature field distribution pattern under different operating conditions. A unit configuration method is proposed to build the 3D model of the flexible spoke non-pneumatic tire. Then, the thermal-mechanical sequential coupling method is used to analyse the deformation, energy loss and heat conduction of the flexible spoke non-pneumatic tire. Finally, the steady-state temperature field distribution pattern under thermal-mechanical coupling is obtained. The results show that the high temperature region of the non-pneumatic tire is mainly distributed in the middle bending part of the flexible spoke unit, and the temperature gradually decreases from the centre of the flexible spoke to the surrounding parts. The influence of load on the temperature change of non-pneumatic tire is greater than that of the driving speed. This study provides a theoretical basis and method guidance for solving the failure problem of the non-pneumatic tires under the action of thermal-mechanical coupling.