Heat Source Model Research Articles

Research on the long-term operation performance of deep borehole heat exchangers array: Thermal attenuation and maximum heat extraction capacity

The long-term operation performance and thermal attenuation of deep borehole heat exchangers (DBHEs) array are important for their stable and safe operation. This paper proposed a semi-analytical method to quantitatively evaluate the 100-years operation performance of DBHEs array. Numerical simulation was utilized to determine the heat flux per depth of DBHE, while the finite line heat source model was modified to calculate the ground temperature variation. This allowed to obtain the ground borehole wall temperature, serving as a boundary condition for calculating the water temperature distribution in DBHE using an analytical solution. The results revealed that the line space of DBHEs array directly affected the allowed maximum accumulated heat extraction per DBHE per heating season (Qa,max). With line space decreasing from 100 m to 10 m, the Qa,max decreased from 0.3% to 19.1% compared to the single DBHE. Therefore, a line space larger than 30 m was recommended. Considering practical project with limited space, the inclined DBHEs were recommended in depth direction. For DBHEs array with a line space of 10 m at the surface ground and 100 m at a depth of 2500 m, Qa,max was only 3.2% smaller compared to the single DBHE, which showed an improvement over DBHEs array with a line space of 50 m. The proposed semi-analytical method could be applied in system design, to ensure the long-term safety and stability of DBHEs array.

Developed numerical Analysis of Residual Stress caused by Welding and Cutting in Steel Structures

AbstractThe welding and flame‐cutting process in the steel construction are commonly used, especially for the bridge structure. Some experiments about welding and cutting have been done separately by some researchers. The results from the experiments were also compared with the results from the numerical simulation under 3D or 2D models. The agreements between those results are as good as they predicted. Therefore, the numerical simulation is a better way to analyze the quality of the steel construction after welding and cutting without time‐consuming and a large amount of cost. But there are only a few research about the numerical simulation and the some of them are aimed to verify the experiments. In this study, the calculation about the residual stresses after welding and thermo‐cutting are considered from 3D‐model into 2D‐Model. The heat source model is simply regarded as curves of time and welding energy with the algorithm methods. And no matter the change of the parameters of the model and the heat source, the heat transfer and the residual stresses can be calculated with the 2D models as fast as possible. By the means of the finite element software Abaqus, the I‐profiles are easy to receive the job results with the input parameters. The influence of the welding and cutting process are visual and direct.

Effect of nanosecond pulsed laser parameters on texturing formation of metallic surface: Experiment and modelling

The laser ablation process is an indispensable tool in precision micromachining for fabricating micro/nanostructures with specific geometries and regulating physicochemical properties on target surfaces. However, the absence of studies on the effect of laser parameters on texturing formation and surface microstructure makes process control and the optimization of surface texturing challenging. In this study, a nanosecond pulsed laser process was employed to create the micro-texturing on the Al alloy surface, emphasizing the effect of process parameters on surficial grain structures and texturing formation. A three-dimensional (3D) heat transfer model based on the finite element (FE) method was developed to numerically visualize the shape-dimensional evolution of micro-texturing during laser ablation. A simplified but effective moving laser heat source model was proposed to predict the dynamic spatial and temporal distributions of heat generation and transfer. Material removal, which was dominated by surface evaporation in the pulsed laser process, was achieved using the element deletion method. Under various laser parameters, the model-predicted cross-sectional groove profiles agreed well with experimental measurements. In addition, the effects of laser power and scanning speed on the groove morphologies were investigated. The experimental findings and numerical models established in this study will provide guidance for precisely controlling pulsed laser parameters to achieve desired texturing structures and dimensions.

Effects of different friction stir welding processes on residual stress and deformation of Ti62A alloy joints

Residual stress induced by welding easily causes deformation and even fracture failure in welded structures. In this paper, a three-dimensional thermal-mechanical coupling finite element model of friction stir welding (FSW) was developed. The effects of different welding processes, namely conventional friction stir welding (C-FSW), stationary shoulder friction stir welding (SS-FSW), and bobbin tool friction stir welding (BT-FSW), on the temperature, residual stress, and deformation of welded joints were investigated by employing a heat source model and a force model to the welding analysis. The results reveal that a discernible disparity in temperature gradient is observed in the region ahead of the tool and behind it among various welding processes. The peak values of longitudinal residual stress along the surface and bottom paths of SS-FSW are reduced by 35.7% and 34.1%, respectively. In addition, the deformation at the initial end of the weld is slightly larger than that at the final end along the welding direction in three welding processes. Compared with other FSW processes, SS-FSW exhibits the smallest deformation, which is advantageous for improving assembly accuracy and enhancing the load-bearing capacity of weldments. The above results provide an important theoretical reference for the FSW process optimization of Ti62A alloy.

Simulation of Welding Residual Stresses in Large Structures – First Results of Thermal Analyses

AbstractSimulation of welding residual stresses and distortions has been applied mostly for small‐scale components, smaller than those applied in civil engineering structures, due to the high requirements in computational capacities. In the present study, work hypotheses, which can reduce the computational load of welding simulations for an accepted sacrifice in accuracy, are discussed. A series of thermal analyses is carried out, in order to check the validity of the proposed modelling approaches, which refer to the application of simple weld heat source models and hybrid shell‐solid element models. Application of local‐global models is also discussed. The present study aims to work as a first step towards the establishment of an engineering approach for the simulation of welds in civil engineering structures with sufficient accuracy and reduced requirements for computational capacity.

Heat extraction analyses and energy consumption characteristics of novel designs of geothermal borehole heat exchangers with elliptic and oval double U-tube structures

The borehole heat exchanger (BHE) is an efficient and economic tool for extracting geothermal energy within ground source heat pumps (GSHPs). The layout and cross-section tube configuration of the BHE is one of the crucial bottlenecks that strongly influenced the effectiveness of the BHEs, which recently attracted numerous attention.Hence, the interest in retrofitting cost-efficient configurations of BHEs is recently regarded as an improvement pathfor maximizing geothermal energy production. In this study, novel geothermal borehole heat exchangers with elliptic and oval double U-tube (2U) configurations are investigated and compared to a traditional circular 2U BHE.This paper explains the development of traditional circular 2U-tube BHEs that makes an optimally designed model for maximizing the heat extraction rates and minimizing the energy consumption characteristics and BHE number. A 3-D numerical model was developed and validated by relevant field experiments (Tianjin geothermal project). The numerical study was performed on four cases corresponding to different widths of elliptic and oval 2U BHEs configurations. Furthermore, a sensitivity analysis was performed to parametrically investigate the impacts of key design and operational parameters on heat extraction performance. Additionally, a 3-D numerical model coupled with a finite line heat source model was also developed to perform case studies for energy consumption analysis for two goals of optimization. The results show that the oval 2U BHE (type II) outperformed the other investigated 2U BHE configurations, which increased the maximal and mean heat transfer rate by up to 54.0% and 12.30%, respectively, compared to circular 2U BHE. While the elliptic 2U-tube BHE (type II) was minimal pressure drop and energy consumption rates, which showed a pressure drop of 36.20% lower than the circular 2U BHE. In the case study findings, the utilization of elliptic 2U-tube BHE (type II) can not only reduce the BHE number by 6.70% but also minimize the energy consumption of the water pump and the entire system by 36.9% and 8.2%, compared to that of traditional circular 2U-tube BHE, respectively.

Numerical simulation and testing of laser-MIG hybrid-welding angle-structure sheets.

Numerical simulation and experimental investigation of laser-MIG hybrid angle-welding low-carbon 1.5-mm-thin SPCC steel sheets are presented in this work. The transient simulation analysis provides an access to the thermal-fluid phenomena prediction by employing a hybrid three-dimensional heat source model. Special attention is paid to the melt dynamic behaviors within the triangular molten pool affected by the Marangoni convection. The simulation results show that the temperature and its gradient distribution are symmetrical with respect to the laser beam, which is validated well by the experimental study. The microstructure of the welded joints was analyzed by scanning electron microscopy and transmission electron microscopy. The results show that the cross-section microstructures of welded joint are mainly composed of the weld zone, narrow heat-affected zone, and substrate. The semielliptic-like molten pool shape is consistent with that of the simulated results. The finer microstructure in the weld bead results from the rapid cooling rate of laser welding confirmed by the FEM calculation. The columnar and equiaxed dendrites are formed in the peripheral and central region of the molten pool, which is beneficial for the improvement of the microhardness.

Thermal analysis of ultrasonic vibration-assisted grinding with moment-triangle heat sources

AISI 9310 steel has garnered increasing attention for its superior mechanical properties in the manufacturing of transmission gears for helicopters and accessory transmission systems in aero-engines. The ultrasonic vibration-assisted grinding (UVAG) technique is a new potential method to machine tooth surface given the periodically changing trajectory between abrasive grains and the workpiece, contributing to enhancing heat transfer and thus solving sudden burns. The accurate prediction of grinding heat and the proposal of the associated control strategy are desired to ensure the machining quality. Combined with the separation coefficient model and the chip volume distribution of UVAG processes, a new moment-triangle (MT) heat source model was established. Subsequently, comparative analyses on grinding temperature with conventional grinding and UVAG process were performed using the conditional triangular heat source model and the proposed MT heat source model. Results show that the MT heat source model has a lower prediction error with an average error of 7.13%, which is improved by 7.33% compared with that of the triangular heat source model. The prediction accuracy for the maximum grinding temperature can be raised by 13.39% when the MT heat source model is applied in place of the other one under UVAG processes. In addition, the heat source model transits from triangular into uniform heat source gradually as the ultrasonic amplitude increases, and the transition rate is positively correlated with the ultrasonic amplitude. On this basis, the desired controlling strategy is proposed to enhance the machining performance of ultrasonic grinding processes and effectively reduce heat generations during grinding by increasing the ultrasonic amplitude, reducing the depth of cut and decreasing the workpiece speed.

Finite element analysis of butt joint of 316Ln steel thin plate welded by laser welding process

This study focuses on the FEM-based thermal analysis of laser welding for 1.5 mm thick austenitic stainless steel 316Ln, which is commonly used in high-temperature applications such as oil & gas industries and thermal power plants. The objective is to investigate the thermal behavior of the welding process and validate the FEM-based calculations with measured thermal cycles. The thermal cycles at a distance of 10 mm from the welding zone were measured using K-type thermocouples. To analyze the thermal behavior, a Finite Element Method (FEM) approach was employed using the SYSWELD software. The FEM-based calculated thermal distribution was then compared and validated against the measured thermal cycles. In order to accurately model the laser heat source distribution, two different heat source models were selected: a conical model and a combined double ellipsoidal plus conical model. The findings of this study provide valuable insights into the thermal characteristics of laser welding for austenitic stainless steel 316Ln. The validated FEM-based thermal analysis helps in understanding the temperature distribution and thermal effects during the welding process. Such knowledge is crucial for optimizing the welding parameters and ensuring the integrity and quality of the welded joints in high-temperature applications.

Distortion Analysis Method for Wire Arc Additive Manufacturing Component Using Thermomechanical Computation with Enhanced Separation and Deposition Algorithm.

This research is devoted to numerical and experimental analysis on deformation of completely removed component induced by wire arc additive manufacturing (WAAM). The component has the form of a hollow and rectangular thin wall made of deposition layer of stainless steel SS316L on top of substrate plate of mild steel S235. In this research, thermomechanical finite element analysis was applied with Goldak's double ellipsoid as heat-source model and isotropic hardening rule based on von-Mises yield criterion. A specialized numerical simulation software Simufact.Welding 2021 (SW) was utilized in developing the numerical model and the simulation of process enhanced with separation and deposition algorithm to predict the component deformation after removal of substrate. On determining the best possible mesh size, a sensitivity analysis was conducted before the advanced stage of model development. An advanced material modeling, the data of which were obtained based on the chemical composition of the evolved SS316L sample, was developed using an advanced material modeling software JMATPRO. For verification purpose, a series of WAAM experiments using robotic GMAW with synergic power source were conducted followed by the removal of substrate from component using machining process. Furthermore, component distortion was measured using industrial noncontact 3D scanner with structured blue light to fully capture the upper section deformation and compared with result of numerical computation. It can be concluded that this novel distortion analysis method using thermomechanical numerical computation with evolved material property and modified algorithms for substrate removal exhibits a surface deviation in vertical direction between 0.05 and 2.16 mm with acceptable pointwise and average error percentage of up to 3%.

Simulation of temperature field and residual stress in high-power laser self-melting welding process of CLF-1 steel medium-thick plate

To mitigate the adverse effects of residual stress and deformation during high-power laser welding, this study established a finite element model based on thermodynamic conditions for high-power laser welding of CLF-1 steel for nuclear fusion applications. The temperature field and residual stress of the weld were simulated by using the composite heat source model together with Gaussian model and conical model. The results showed that the temperature field simulation was in good agreement with the real temperature field. The simulation results of the weld metal (WM) and the heat affected zone (HAZ) in the cross sections were basically consistent with those of the real cross sections. Moreover, the margin of error between the simulation results and the real data was ≤ 1.3% (the largest error ≤0.04 mm). The Von Mises equivalent stress in WM was distributed irregularly, and its largest value was ≤ 220 MPa; the equivalent stress declined with an increase in distance from the center of WM. The transverse stress distribution in the center of WM was in accordance with the vertical stress distribution, which was essentially the same as the experimental data of the vertical stress. The simulation results of deformation in the Z direction of the weld showed that the maximum deformation was about -0.2 mm at the center of the weld corresponding to the length of 300 mm. In summary, the thermal source model, combined with laser welding process parameters, can provide high-precision prediction of stress variations and deformation control during the actual welding manufacturing process of the test blanket module (TBM) structure.

Numerical Simulation Analysis of Temperature Distribution of NbC-Reinforced Ti-Based Composite Coating by Laser Cladding

In this article, three-dimensional numerical modeling of the laser cladding process by Ansys was proposed. The three-dimensional Gaussian heat source model was used to simulate the actual laser heat source to analyze the temperature distribution of the molten pool. The temperature distribution of the molten pool of TiAlSi + NbC coatings within different process parameters was obtained by simulation. To obtain finer simulation results, the thermophysical properties of TiAlSi + NbC powder and TiAlSi + NbC alloy were investigated, respectively. The temperature selection judgment mechanism, which is used to distinguish the powder and alloy elements, was built. The results showed that the laser power and laser scanning speed play a vital role in the temperature distribution along with the track width and the depth of the molten pool. The simulation values of the width and depth of the cladding layer under different processing parameters were obtained by using the temperature selection judgment mechanism and fitting. The results showed that the track width and depth had a positive correlation with the laser power, whereas they had a negative correlation with the laser scanning speed.

Experimental and numerical study on the distribution of temperature field and residual stress in a multi-pass welded tube joint of Inconel 617 alloy

The purpose of this study is to compare the residual stress generation during hot wire gas tungsten arc welding (HW-GTAW) welding and conventional gas tungsten arc welding (GTAW) in a multi-pass pipe weld of a nickel-based superalloy. HW-GTAW yields better mechanical properties at low heat input than conventional GTAW, and decreases the accumulation of residual stress significantly. The distribution of residual stress developed in the through-thickness direction is determined experimentally using the Deep hole drilling method. As a result of the analysis, it was observed that the highest residual stress arises in Fusion Zone (FZ) and Heat Affected Zone (HAZ). In the case of conventional GTAW the hoop stress was observed to be tensile and distributed over 70% of the weld whereas only 20% of the weld is found to be under tensile hoop stress in the case of HW-GTAW along the weld center. The results show that shrinkage at the weld HAZ region affects the stresses produced at the cylinder's outer surface. The bending effect created during the welding process is primarily responsible for the distribution of residual stresses in the weld zone. A comprehensive numerical analysis has been carried out using ABAQUS software to predict the level of thermal and residual stresses in the weld zone, FZ, and HAZ in the case of both welding process. A 2D finite element models have been developed to simulate the welding process using the ABAQUS FE tool based on coupled thermal-mechanical analysis. A double ellipsoidal heat source model has been developed using a DFLUX subroutine file to simulate the welding process during the numerical analysis. The predicted residual stresses were validated with the experimentally obtained results.

Segmented Line Heat Source Model for Thermal Radiation Calculation of Jet Fires in Chemical Plants

Abstract The jet fire caused by the leakage of combustible materials is one of the biggest threats to the safety of chemical plants. Thermal radiation of the jet fire brings severe damage to nearby facilities and people's health. To evaluate the damage of jet fires, a precise model for the calculation of thermal radiation is indispensable. Classical thermal radiation models of jet fires either have a lower prediction accuracy or a higher computation complexity. To overcome such deficiencies, this paper proposes a novel segmented line heat source (SLHS) model for jet fires. Because the length of the jet fire is often much larger than the width, the jet fire is viewed as a line heat source, with all the heat radiated from the centerline of the jet fire. The jet fire is divided into three segments along the flame length according to the temperature distribution and thermal radiation characteristics of the flame. Based on the SLHS model, three types of thermal radiation models called cone-cylinder-cone, ellipsoid-cylinder-ellipsoid, and ellipsoid-cylinder-cone models are built for computing the radiant heat flux distribution around the jet fire. The effectiveness and advantages of the proposed models are illustrated with the experimental data and a numerical simulation.

An equivalent volumetric heat source model for thermal conduction of plate forming by inducted line heating

An equivalent volumetric heat source model for thermal conduction of plate forming by inducted line heating

FEM Simulation of Pulsed Laser Welding of High-Carbon Alloy Steel: Using Different Heat Source Models

FEM Simulation of Pulsed Laser Welding of High-Carbon Alloy Steel: Using Different Heat Source Models

Estimation of heat source model parameters for partial penetration of TIG welding using numerical optimization method

Heat source parameters have a greater influence on the accuracy of numerical modelling for predicting residual stress and temperature field. Experimental measurements of stress and temperature during arc welding are cumbersome due to dynamic transfer of heat happening in a very short span of time. So, for modelling such a high temperature process, determining the heat source model parameters are critical. In this article, a novel method for figuring out the double ellipsoid heat distribution model’s heat source parameters is demonstrated. Here, finite element analysis (FEA) is done to predict the weld bead dimensions, thermal and structural cycles of tungsten inert gas (TIG) welding of AISI S304 stainless steel plates. 25 different sets of heat source parameters are generated for 100 and 120 A input power separately. Using this generated values, weld bead dimensions are determined from the simulation. The optimization is done with the Taguchi technique taking root mean square error (RMSE) value of heat source parameters and measured weld bead dimensions as response parameters. The model is validated using experimental data and the effects of each parameter on weld pool formation during TIG welding are also studied. Optimum values of heat source parameters for stainless steel AISI 304 at 100 A welding current are 2.3283, 2.3687 and 2.667, respectively, and that for 120 A weld current are 2.5909, 2.613 and 3.4949, respectively. The prediction of temperature and welding residual stress (WRS) distribution using optimizing heat source model parameters shows closer approximation with experimental results. The demonstrated model is very much reliable and simple to predict the heat source parameters for TIG welding with partial penetration with a very lesser number of operations and minimum error.

Enhanced heat source modeling in particle-based laser manufacturing simulations with ray tracing

Particle-based spatial discretization methods such as smoothed particle hydrodynamics (SPH) possess suitability for the high-fidelity simulation of laser manufacturing processes due to their capability in treating complex free-surface and multiphase problems. In such simulations, laser heat source modeling remains a central concern as the mechanisms governing the material deformations and phase changes strongly depend on the input laser energy and its distribution details. Ray tracing (RT) is a realistic and accurate approach for high-fidelity heat source modeling that can capture surface heterogeneity and multiple reflections. However, RT heat source modeling for particle-based numerical methods faces additional challenges rooted in the lack of explicit surface representation, intensive computational efforts, and implementation complexities. This work addresses these issues by proposing an enhanced and efficient RT heat source model for particle-based laser manufacturing simulations with negligible computational overhead and without requiring background nodes or surface mesh reconstruction. After validating the RT heat source model versus analytical and experimental results, we assess its computational performance through two test cases, showing that the computing workload imposed by our RT model is between 0.1% and 25% of the total runtime in different SPH-based laser manufacturing simulations. With the achieved efficiency and robustness, it becomes convenient yet advantageous to simulate processes like laser drilling and laser powder bed fusion with precision far beyond the conventional approaches using volumetric heat sources.

PRACTICE ORIENTED HEAT SOURCE MODEL CALIBRATION

The modelling of the thermal process is used as a tool in determination of the properties of the materials, subject to welding. One of the most important steps in the modelling is the calibration of the heat source model. This is a necessary condition for a given model to be used to solve practical problems. The standard practice in this regard is to calibrate the model by the shape of the melted zone or by the temperature cycles at set points. In the present work, the heat source model calibration based on the maximum temperatures measured at several surface points, at different distances from the seam line, is considered. The temperature cycles in the welded joint and the penetration depth were assumed by the model, calibrated in such non-destructive way. The calculated temperature cycles were compared with records of the temperature during welding. The actual penetration depth was measured by metallographic examination of samples and compared with the assumed penetration depth. The obtained results make it possible to evaluate the suitability of the proposed methodology for determining the cooling rate in the heat affected zone.

Heat source modeling, penetration analysis and parametric optimization of super spray MAG welding

Main drives, cutterheads and other critical components of tunnel shield machines require welding with thick plates that leave roots over 5 mm. Full penetration welds cannot be achieved by conventional Pulsed MAG welding methods. This article introduces Super Spray MAG Welding technology and investigates its penetrating regularities and mechanisms through high-speed camera images, finite element simulation, and microstructural analysis. An optimal welding procedure was generated using a combination of Genetic Algorithm and Back Propagation Neural Network. The data show that Super Spray MAG arc exhibits greater concentration and stability than traditional MAG arc, marking its strong qualities in emitting high-energy beams. The morphological solidification pattern of the molten pool closely matches the FEM simulation results of the composite Gaussian surface heat source model and peak linear attenuation Gaussian cylinder heat source. The welding current mainly affects the penetration of the weld, followed by the extension of the wire, and lastly the welding speed. Increasing the welding current can transition droplet transfer from globular to spray, as well as alter microstructure development and mechanical characteristics. Suggested parameters for penetrating the 5 mm root were put forward. The BPNN-GA model established can effectively predict weld formation, and points out the optimal welding parameters.