Three-dimensional Numerical Analysis Research Articles

Residual Stress Analysis at the Conductor–Insulator Interface During the Curing Process of Hair-Pin Motors

The curing process of hair-pin motor stator insulation is critical, as residual stress increases the risk of partial discharge and shortens a motor’s lifespan. However, studies on the stress-induced defects during insulation varnish curing remain limited. This research integrates three-dimensional numerical simulations and experimental analysis to develop a curing model based on unsaturated polyester imide resin, aiming to explore the mechanisms of residual stress formation and optimization strategies. A dual fiber Bragg grating (FBG) sensor system is employed for simultaneous temperature and strain monitoring, while curing kinetics tests confirm the self-catalytic nature of the process and yield the corresponding kinetic equations. The multi-physics simulation model demonstrates strong agreement with the experimental data. The results show that optimizing the curing process reduces the maximum stress from 45.1 MPa to 38.6 MPa, effectively alleviating the stress concentration. These findings highlight the significant influence of the post-curing temperature phase on residual stress. The proposed model offers a reliable tool for stress prediction and process optimization in various insulating materials, providing valuable insights for motor insulation system design.

Impact of Neighbouring Excavation on Diaphragm Wall under Seismic Loading

The existing diaphragm walls may be affected by the new structure as well as any excavation work required for the surrounding projects. During an earthquake, this effect can be more pronounced. It is therefore, suggested to create the diaphragm wall and the neighbouring excavation models with the intention of researching the influence of excavation upon diaphragm wall under dynamic conditions. For the investigation, a case study involving a diaphragm wall located in Noida was taken into account. The diaphragm wall and nearby excavation were modelled utilizing the Plaxis 3D program. By altering the space between the excavation and the diaphragm wall and entering the time-history acceleration data from an earlier earthquake, it was possible to examine the impact of the nearby excavation for the new construction on the diaphragm wall under dynamic conditions. The outcomes of three-dimensional numerical analysis were compared. The study has revealed that the wall's horizontal displacement increases with increasing the space between the wall and the excavation until it arrives at an approximate value that resembles the wall's horizontal deflection without nearby excavation. Graphs of shear force and bending moment were also compared and similar variations were found.

Thermal Hydraulic Performance and Characteristics of a Microchannel Heat Exchanger: Experimental and Numerical Investigations

Abstract This paper presents extensive fluid flow and Heat Transfer studies conducted through an experimental setup followed by a detailed three-dimensional (3D) numerical analysis of the same setup using a commercial package for computational fluid dynamics (CFD), known as cfd-ace® for additive-manufactured counterflow AlSi10 Mg microchannel heat exchangers (MCHEs). A detailed 3D computational model of the experimentally tested MCHEs was built and analyzed using the commercial software cfd-ace® for the same experimentally tested operating conditions. The computational model results are in good agreement with experimental data of tested MCHE within +2% to +7% and ∼0% to −13.5% variation for cold and hot fluids for the entire set of design of experiments (DoEs). This percentage disagreement may be due to various factors, such as manufacturing deviation within tolerance, longitudinal conduction, variation in the thermal conductivity of the material after heat treatment, variation in environmental temperature, sensor deviation, and surface roughness of internal channels. Instead of Stainless steel (SST), AlSi10 Mg was used because of its lower manufacturing cost because AlSi10 Mg was lighter than SST, though its thermal conductivity is almost ∼8–10 times more than that of SST. A higher thermal conductivity is not good for MCHEs because it leads to higher longitudinal conduction, which eventually degrades the performance of MCHEs in terms of effectiveness. MCHE effectiveness is also reduced by ∼12% to 18% owing to longitudinal conduction from ideal effectiveness.

Three-Dimensional Numerical Analysis of Seismic Response of Steel Frame–Core Wall Structure with Basement Considering Soil–Structure Interaction Effects

In recent years, numerous studies highlighted the crucial role of the soil–structure interaction (SSI) in the seismic performance of basement structures. However, there remains a limited understanding of how this interaction affects buildings with basement structures under varying site conditions. Based on the three-dimensional (3D) numerical analysis method, the influence of the SSI on the seismic response of high-rise steel frame–core wall (SFCW) structures situated on shallow-box foundations were investigated in this study. To further investigate the effects of the SSI and site conditions, three types of soil profiles—soft, medium, and hard—were considered, along with a fixed-foundation model. The results were compared in terms of the maximum lateral displacement, inter-story drift ratio (IDR), acceleration amplification coefficient, and tensile damage for the SFCW structure under different site conditions, with both fixed-base and shallow-box foundation configurations. The findings highlight that the site conditions significantly affected the seismic performance of the SFCW structure, particularly in the soft soil, which increased the lateral deflection and inter-story drift. Moreover, compared with non-pulse-like ground motion, pulse-like ground motion resulted in a higher acceleration amplification coefficient and greater structural response in the SFCW structure. The RC core wall–basement slab junction was a critical region of stress concentration that exhibited a high sensitivity to the site conditions. Additionally, the maximum IDRs showed a more significant variation at incidence angles between 20 and 30 degrees, with a more pronounced effect at a seismic input intensity of 0.3 g than at 0.2 g.

Comparative analysis of hydrodynamic loads on bridge piers: assessing standards through numerical modeling

Currently, there is an alarming difference in the estimated actions on piers resulting from flash-floods and tsunamis as prescribed by international structural design codes. Previous studies have explored the interaction between surge waves and piers from a fluid-dynamics perspective, but there is no assessment about the relevance of the methods used in Structural Design to determine the hydrodynamic pressure resultants. To determine the degree of conservatism embedded in design, results from the different approaches are compared against validated numerical simulations. Three-dimensional numerical analyses were conducted using the OpenFOAM platform, employing the Large Eddy Simulation turbulence modeling approach to simulate the dam-break wave impacting the pier. The findings revealed that the maximum force was not necessarily caused by the stream’s first strike and could be sustained over time. The hydrodynamic pressure center consistently occurred at two-thirds of the stream depth, significantly impacting the overturning moments experienced by the pier. Identified inconsistencies between Codes underscore the need for revision of nonconservative approaches in predicting the design forces.

Three-dimensional numerical analysis of the effect of foundation stiffness on soil-structure interaction

Stiffness-related geometric characteristics are closely linked to the performance of structural systems. The influence of foundation stiffness on the soil-structure interaction (SSI) mechanism was investigated by numerical modeling of different building foundations. Numerical tools (PLAXIS 3D and TQS/CAD) were used for decoupling analyses of the interaction between the structural components. Results obtained from instruments installed in a building case study were used to refine the numerical calculations. Linear elastic constitutive models and beam elements were useful in reducing computational processes and ensuring study feasibility. The simulation results provided a satisfactory representation of field observations. Interaction between piles and the environment governs the relationship between foundation stiffness and uniform settlement. Rigid pile groups are achieved with greater pile length, diameter and spacing. This study highlights the different effects of pile geometric parameters on loading and unloading rates in pillars, demonstrating that the SSI mechanism is more sensitive to less rigid foundations, particularly those with greater pile embedment. It was concluded that numerical simulations to predict settlement as realistically as possible require understanding and selecting the most appropriate model and type of calculation.

Numerical Analysis of Hydrogen Behavior Inside Hydrogen Storage Cylinders under Rapid Refueling Conditions Based on Different Shapes of Hydrogen Inlet Ports

In order to investigate the effects of different shapes of hydrogen inlet ports on the behavioral characteristics of hydrogen in Type IV hydrogen storage cylinders under rapid refueling conditions, a mathematical model of hydrogen temperature rise and a three-dimensional numerical analysis model were developed. The rectangular, hexagonal, triangular, Reuleaux triangular, circular, elliptical and conical inlet ports were researched by using computational fluid dynamics methods. The results showed that, for the same refueling flow rate and cross-sectional area, the hydrogen temperature inside a cylinder with a rectangular inlet port is higher and the jet tilt angle is larger than for a hexagonal port, while the thermal stratification phenomenon is not obvious. The hydrogen temperature inside a cylinder with a triangular inlet port is lower than that with a Reuleaux triangle port and the jet tilt angle is larger, and neither has significant thermal stratification. The hydrogen temperature inside a cylinder with a circular inlet port is higher than that with an ellipse port, the jets are not tilted on either one, and the phenomenon of thermal stratification is prominent. Further analysis indicated that enlarging the cross-sectional area and increasing the refueling flow rate results in a higher hydrogen temperature and intensified thermal stratification and an upward-angled jet can effectively reduce or eliminate thermal stratification.

Three-dimensional modelling and numerical analysis of Pelton turbine runner buckets

Three-dimensional modelling and numerical analysis of Pelton turbine runner buckets

Catastrophe Information Characteristics and Prevention Measures of Water Inrush in Tunnel Approaching Fault with Different Water Pressure

In order to ensure the safety of the tunnel approaching the fault and prevent water inrush disasters, and then take reasonable protective measures, a fault-tunnel-surrounding rock is established by using a three-dimensional (3D) discrete element numerical analysis method, which takes into account the fluid-structure coupling effect. Based on the method of control variables, the catastrophe information characteristics of displacement and water pressure of the surrounding rock of the tunnel face and the corresponding characteristics of changes before the occurrence of water inrush disasters were studied under different fault water pressures during the excavation of the tunnel approaching the water-rich fault. The results show that, during excavation at the same step, displacement and its magnitude in the surrounding rock escalate as fault water pressure increases. The maximum pressure of the water in the surrounding rock is also constantly increasing. As tunnel excavation progresses, at constant fault water pressure, longer excavation distances result in greater axial displacement of the surrounding rock mass and increased water pressure at corresponding positions within the surrounding rock, leading to higher magnitude increases. As excavation proceeds, the displacement and water pressure in the surrounding rock and the increase of its amplitude continue to increase. Pre-reinforcement grouting techniques and pipe umbrella support systems that are very effective protective measures can be determined by a comprehensive approach integrating advanced geological forecasting methods, real-time water pressure detection, and the analysis of stress-strain and seepage pressure field variations in the surrounding rock mass.

Shaking-table tests and numerical simulations study of subway stations in loess region

The loess region in China, known for its high seismic activity and the extreme vulnerability of loess to earthquakes, presents a considerable threat to the seismic safety of underground structures, including subway stations. With the Xi'an Aerospace City subway station as the background, a subway station model was designed, and shaking table tests were conducted under various conditions to analyze the seismic damage and dynamic responses in this study. The study reveals the seismic vulnerable areas and dynamic response patterns of the subway station under different spectral earthquake actions. Simultaneously, a three-dimensional numerical modeling analysis accounting for soil-structure interaction, was conducted to explore the displacement response of the structure and soil. Results indicate a noticeable amplification effect on the acceleration of both the structure and the soil under seismic motion. The structure exhibits a suppressive effect on the acceleration amplification of the surrounding soil, diminishing with increasing seismic motion intensity. Different depths show varying differences in acceleration responses between the structure and adjacent soil. Structural strain responses and damage phenomena suggest that the central column is the seismic vulnerable area of the subway station. Additionally, the strain distribution of the structure exhibits a distinct spatial effect. The relative horizontal displacement between the structure and the soil follows certain patterns in the depth direction, with the structure experiencing smaller relative horizontal displacement than the soil under seismic action due to the constraining effect of surrounding soil on its displacement response. The experimental conclusions provide valuable reference points for the seismic design and analysis of subway station structures in loess regions.

Thermo-mechanical modelling of spalling around the deposition boreholes in an underground nuclear waste repository during its thermal phase

This paper presents a three-dimensional numerical analysis of multiple fracture growth leading to the development of excavation disturbed zones and spalling around deposition boreholes in a geological disposal facility. The development of fracture patterns is simulated with the Imperial College Geomechanics Toolkit, a finite-element based simulator that can model the simultaneous nucleation, growth, and coalescence of multiple fractures in quasi-brittle rock. In these simulations, fractures develop due to the stress concentrations around the borehole wall, caused by the local in situ stresses, and due to the thermal stresses caused by the radioactive decay of the waste. Fracture patterns, and the extent of the spalled zone, are computed after the borehole drilling, heating, and cooling stages, at the Forsmark repository site in Sweden. The effect of temperature on the nucleation and growth of spalling fractures, as well as on the reactivation of pre-existing fractures, is assessed qualitatively, by comparing fracture patterns, and quantitatively, in terms of the maximum spalling depth, width, and increase in the total fractured surface area. Overall, the simulations presented herein indicate that thermal spalling will increase the depths (away from the borehole) and angular widths of the spalled zone, but is not likely to lead to major increases in fracture aperture, and concomitant increases in hydraulic transmissivity and permeability of the spalled zone, above that which has already been caused by mechanical spalling.

Three-dimensional numerical analysis of twin tunnelling in two-layered soil strata

Tunnelling induces stress change and displacement in the ground. The excavation of a new tunnel in stratified soil can trigger different patterns of stress redistribution, which may adversely influence nearby tunnels. Research on multi-tunnel interaction has mainly been performed on the assumption of a uniform ground. The effects of different soil stratifications on tunnelling interaction remain poorly understood. In this paper, three-dimensional numerical parametric studies verified by previous centrifuge tests were carried out to analyse the twin tunnelling effects in two-layered soil. An advanced hypoplastic constitutive model that can capture stress-, path-, and strain-dependency of soil behaviour is adopted. Numerical cases investigated include perpendicular twin tunnelling in two sand layers with different relative densities and the location of the interface between the two sand layers. It is revealed that larger settlements and a wider surface settlement trough occur when tunnelling in two-layered soil strata than in a uniform ground. This is because of the wider and larger soil arch induced in two-layered soil strata. The structural response including tunnel deformation, induced bending moment, and induced hoop stress of the existing tunnel can be greater when tunnelling in layered soil strata than in a uniform ground owing to larger stress relief. Moreover, the combination of bending moment and hoop stress can exceed the M−N failure envelope of the structure in layered soil. A conventional simplified assumption of a uniform ground can underestimate of the influence of new tunnel excavation on existing tunnels, resulting in unsafe designs.

The performance of transmission pipelines on February 6th, 2023 Kahramanmaras earthquake: a series of case studies

AbstractThe Mw 7.8 earthquake that struck Kahramanmaras on February 6, 2023, caused significant damage to hydrocarbon and water transmission lines due to permanent ground deformations. Explosions occurred in the Kahramanmaras–Gaziantep Natural Gas transmission pipeline causing disruption of gas in the cities of Gaziantep and Hatay Fault Displacement Hazard. Water transmission pipelines were also damaged due to extreme fault offsets. This paper presents the findings from the earthquake affected zones. Particular attention was given to the performance of the 2600 mm diameter Duzbag–Gaziantep water transmission pipeline due to three reported challenges: (#1) The behavior of the pipe in the Duzbag tunnel, (#2) The pipe bend behavior at the fault crossing, and (#3) The pull-out of the pipe at valve room. Based on field observations, extreme damage forms at pipes were presented. A three-dimensional nonlinear numerical analysis was performed to simulate the observed damage of the reoriented water pipe at the fault crossing for Case #2. The nonlinear finite element model was able to capture the complex nature of the post-yield behavior of steel pipe as well as the damage locations along the pipe and their sequence of occurrences. As a mitigation measure for new pipes, the need for using flexible connections at critical crossings was highlighted. For existing pipes, the importance of developing secondary (by-pass) lines was emphasized.

Utilization of vortex flow pattern in the design of an efficient solar air heater

In this work, numerical and experimental analyses of a new model of circular solar air heater are carried out to examine the effect of employing vortex flow inside the air vessel of collector for convection enhancement. In three-dimensional numerical CFD-based analysis, the COMSOL Multi-physics is used to solve the flow equations for the turbulent forced convection airflow and conduction equation for the solid parts of the solar heater at different air mass flow rates in the range of 0.003 to 0.012 kg/s. In the calculation of turbulent stresses and heat fluxes, the RNG κ-∊ turbulence model is employed. The surface to surfaces (S2S) radiation model is used to consider the radiations emitted by the hot surfaces in collaboration with the energy equation. For validation, the theoretical findings are evaluated against the experiment. For the studied test cases with different values of solar irradiation and air mass flow rate, thermal efficiencies of up to 80 % are found. In comparison to the conventional rectangular-shaped solar air heaters with smooth ducts, more than 100 % increase in the value of thermal efficiency is delineated from the theoretical and experimental findings. This gain is attributed to the unique flow pattern in the developed solar collector.

Research on the Correction of Soil Pressure Distribution Pattern in Circular Working Wells in Soft Soil Areas

This paper investigates the distribution characteristics of earth pressure on circular caisson foundations in soft soil areas based on practical engineering considerations. Utilizing a three-dimensional numerical analysis model and a displacement-based method for earth pressure calculation, the lateral earth pressure on the retaining structure is examined. Adjustments are made to the distribution pattern of earth pressure on circular caisson foundations in soft soil areas. The study demonstrates that the radius of the caisson significantly influences the spatial distribution of soil pressure. Additionally, empirical formulas for the depth and radius of the reduction in soil pressure around circular caisson foundations are obtained through the research. Comparative analysis reveals that the modified earth pressure planar foundation beam method, which accounts for the arching effect, is simpler, features more mature parameter selection, and is more cost-effective than the three-dimensional finite element method. In comparison to the standard planar elastic foundation beam method for earth pressure, it aligns more closely with the actual direction of displacement.

Three-Dimensional Numerical Field Analysis in Transformers to Identify Losses in Tape Wound Cores.

To find the total core losses in 1-phase medium-frequency transformers, a 3D numerical field analysis was carried out. The proposed numerical modeling was based on the extended iterative homogenization method (IHM) developed by the authors. The achieved calculation results were validated by the corresponding values obtained experimentally, and a reasonably close agreement was obtained.

Three-Dimensional Numerical Analysis of Static and Cyclic Pull-out Response of Plate Anchors in Reinforced Soft Clay

Three-Dimensional Numerical Analysis of Static and Cyclic Pull-out Response of Plate Anchors in Reinforced Soft Clay

Numerical parametric study of embedded geosynthetic-reinforced soil abutment

Three-dimensional numerical analysis was conducted to investigate the performance of embedded geosynthetic-reinforced soil abutments. The numerical model was validated using field-monitoring data. A parametric study was conducted to investigate the key factors affecting the performance of the embedded abutment under the working conditions, including the pile offset distance, pile diameter, pile spacing, and bridge load. The piles exhibited a retaining rather than a pushing effect in these cases due to the relatively high stiffness and negative skin friction of the piles, thus reducing the loads exerted on the facing wall. The lateral displacement of the facing wall significantly increased as the pile offset distance decreased mainly due to the reduced anchor length of the reinforcement and enhanced retaining effect of the piles. As the pile diameter increases, the deflection of the facing wall is constrained by factors such as increased bearing width, limited displacement, and enhanced retention effect of thepiles. This is an efficient way to increase the pile density near the abutment centerline to control thedeformation of the facing wall. An increase in the vertical bridge load resulted in a decrease in negative skin friction, leading to increased foundation settlement and lateral displacement of the facing wall.

Three-dimensional numerical analysis of large-scale horizontal square anchors in geogrid-reinforced sand

This paper presents a comprehensive three-dimensional numerical investigation of horizontal square anchors embedded in geogrid-reinforced sand. Prior experimental studies have demonstrated notable enhancements in anchor uplift capacity when placed below geogrid reinforcement in soil. However, these results are limited to small anchor plates tested in laboratory conditions with over-reinforced sand. In contrast, this study focuses on large field-scale anchors and explores the influence of anchor width, embedment depth, reinforcement size, stiffness, and tensile strength on uplift capacity. The findings reveal that the optimal size for geogrid reinforcement is three times the anchor width. A diminishing improvement in uplift capacity with increasing anchor width was observed. Additionally, deeper anchor embedment reduces the uplift capacity improvement in geogrid-reinforced sand. The geogrid reinforcement is found to be more efficient in the case of shallow anchors placed in loose sand. The major contribution of this paper lies in the response analysis of large anchors and providing a better understanding of the uplift mechanism in geogrid-reinforced sand.

Time-dependent performance of large piled raft in clayey soil

In this study, three-dimensional numerical analysis has been performed to comprehend the time-dependent behavior of large piled rafts founded in saturated clayey soil, explicitly for the time of superstructure construction and post-construction up to the end of soil consolidation. The performance under different construction times for the corresponding unpiled raft and the piled raft with uniform pile length configuration of varying pile number, spacing, and length have been examined and then compared with that of non-uniform length configuration for the same total pile length. The dissipation of excess pore water pressure, average settlement, and differential settlement are presented and discussed in detail. A quicker dissipation rate of excess pore pressure is noted with either fewer piles, wider pile spacing, or shorter-length piles. An increase in construction time results in a lesser total average settlement at the end of consolidation. The piled raft with uniform pile length configuration shows a higher differential settlement than the unpiled raft. However, by adopting a suitable non-uniform length configuration, negligible differential settlement, higher load-carrying capacity, and a significant reduction in pile material volume can be achieved. Predictive expressions have been proposed to estimate the average and differential settlements of piled raft with uniform length configuration.