Tunnel Simulation Research Articles

Tunnel lighting calculation model based on bidirectional reflectance distribution function: Considering the dynamic changes in light transmittance in road tunnels

The current tunnel lighting calculation method does not completely consider the dynamic change in light transmittance in a tunnel and reflection characteristics of the tunnel sidewall. Thus, the measured and calculated values of road surface illuminance present a considerable difference, which seriously affects the tunnel lighting design and quality evaluation. To overcome this limitation, in this study, in addition to theoretical analysis and measured experiments, the changing trend in light attenuation is analyzed and a light attenuation model is established. Next, a bidirectional reflectance distribution function that can accurately reflect the reflection characteristics of tunnel sidewall is combined with the light attenuation model and calculation steps based on optical theory to construct a tunnel lighting calculation model considering light transmittance (TLCM-LT). Finally, theoretical calculation and actual measurement verification are conducted via an experimental tunnel simulation, and the results obtained using TLCM-LT are compared with the values calculated based on the Commission Internationale de l'éclairage (CIE), Illuminating Engineering Society of North America (IESNA), and Industry Standards of the People’s Republic of China (JTG) specifications. The results show that the average relative error of the TLCM-LT in a smoke-free environment is 1.31 %. In the presence of smoke, the average relative error of the model fluctuates in the range of 2.19–6.8 % with the change in light transmittance in the tunnel, which is significantly lower than the errors obtained based on the CIE, IESNA, and JTG specifications. Compared with a cement sidewall, the average increase rates in road surface illuminance and illuminance uniformity of the highly diffuse reflective sidewall are 23.21 and 3.65 %, respectively.

Interaction of Segmental Tunnel Linings and Dip-Slip Faults—Tabriz Subway Tunnels

In some subsurface urban development projects, bedrock faults intersecting with the tunnel path are inevitable. Due to the high costs of urban tunnel projects, it is necessary to study the behavior of such concrete structures under fault movement risks. Using an advanced 3D numerical finite difference code and a plastic hardening constitutive model for the soil, this paper examined the performance of the straight and oblique segmented structures of Tabriz Subway Line 2 under large deformations. The Tabriz Line 2 tunnel passes through a reverse fault called the Baghmisheh Fault. The fault–tunnel simulations were validated by centrifuge tests on the segmental tunnel for normal faulting. In the centrifuge tests and validation models, there was a maximum difference of 15%. According to the results of the Tabriz Line 2 tunnel under reverse faulting, segmental structures outperform no-joint linings when it comes to fault movement. During reverse fault movement, line 2 segments did not collapse but showed slight deformations. However, continuous structures collapsed under faulting, i.e., the structural forces created exceeded the section strength capacity. Among the segmental structures, the lining with oblique joints showed better behavior against faulting than the lining with straight joints. For better tunnel performance under fault movement, oblique joints should be used in segmental structures in faulting areas.

Structural Analysis of Tunnel using FEA

Tunnels are typically built for transportation, such as roads, railways, or canals, but they can also be used for other purposes, such as mining, sewerage, or water supply. Tunnels allow us to travel safely and efficiently through difficult terrain, and they provide us with access to essential resources such as water and energy. The objective of current research is to evaluate the structural characteristics of tunnel structure under geo-mechanical loading conditions. The structural analysis of tunnel is conducted using techniques of FEA. The CAD modelling and FEA simulation of tunnel is conducted using ANSYS simulation package. The shear stress, normal stress and deformation data are generated. From the generated data, the critical regions are identified and the lateral zone of tunnel is one of them. This region is likely to induce damage in the form of crack.

Dispersion of Traffic Pollutants in the Built Environment

Environmental modelling software can be useful for evaluating design interventions and formulating strategies to achieve a specific purpose, such as providing outdoor thermal comfort. It is less commonly used in predicting the dispersion of street pollutants. The aim of this research is to test selected morphological patterns with respect to their influence on wind conditions and the transport of traffic pollutants, and to verify the results against previous studies. The objective of the research is to evaluate relations between building typology in interactions with urban atmosphere. The method utilises a wind tunnel simulation with a static line source of emissions. Experiment results show that the exposed urban morphology models display an impact on flow conditions and consequently on the dispersion of traffic pollutants. At the same time, the results highlight the importance of urban aerodynamic perspective, particularly of urban spaces that can be expected to be subject to higher traffic pollutants in terms of urban air pollution.

Wind and structural response monitoring of a lighting pole for the study of downburst effects on structures

Wind excited response of structures due to downbursts has been studied using wind tunnel simulations, computational fluid dynamics applications, and analytical procedures in the previous two decades. However, the studies have not been validated with full-scale wind and structural response measurements. To fill this research gap, continuous wind-and-structural response monitoring of three slender structures was implemented through the European research council-funded project, THUNDERR. This paper focuses on one of the monitored structures, describing the monitoring system, the dynamic and aerodynamic properties, and the registered data during two downburst events. The wind-excited response of the monitored structure during two case studies of downbursts is analyzed. The correlation between the wind speed and structural displacement parameters was also studied and the square of mean wind speed was found to be highly correlated with the mean displacement and the standard deviation of the fluctuating displacement. The fluctuating components of wind speed and top displacement were found to be partially correlated. The simplicity of the selected structure, and the possibility of obtaining both the quasi-steady and resonant components of the structural response from strain registrations, will make this study a benchmark for the validation of methods and simulations of downburst wind load.

High-speed planar laser-induced fluorescence investigation of nitric oxide generated by hypersonic Mach reflections for computational fluid dynamics validation

In this article, the authors present an experimental investigation of the thermochemical relaxation regions downstream of symmetric Mach reflections generated in Mach 8.5 flows with stagnation enthalpies from 7 to 10 MJ/kg. The experiment was performed in the Hypervelocity Expansion Tunnel at the National Aerothermochemistry and Hypersonics Laboratory of Texas A&M University. The investigation focused on studying the nitric oxide morphology in the vicinity of a strong normal shock wave and shear layers. Experimental planar laser-induced fluorescence measurements at 250 kHz repetition rate with a quasi-simultaneous natural emission photography demonstrate a sufficient rejection of natural emission and reveal intricate flow structures in the shock vicinity. Steady computational fluid dynamics (CFD) flow solutions obtained with the US3D software were used to simulate laser-induced fluorescence signal levels for quantitative comparison against the experimentally acquired data. The investigation accomplished four objectives: complex flowfield visualization in the vicinity of the Mach stem with 4 μs temporal resolution, evaluation of the level of high-temperature chemistry effects introduced to the freestream by the expansion tunnel, both qualitative and quantitative CFD simulation validation, and cross-checking or introduction of fundamental properties of nitric oxide laser-induced fluorescence including absorption cross section for vibrationally excited states of nitric oxide and a collisional quenching cross section of nitric oxide by atomic nitrogen.

The effect of double-row wing bag sand barrier on wind prevention and sand fixation: wind tunnel simulation and field verification

Introduction: Most of the sand fixation technologies utilized locally and internationally are static or dynamic, making it challenging for a single sand fixation mode to function in a harsh environment. Therefore, the development of a sand fixation mode that combines resistance and consolidation has emerged as a trending topic in sand control research. Our team developed the wing bag sand barrier, which is a static and dynamic combination of sand fixation mode.Methods: In this study, we examined the characteristics of airflow velocity field and sand resistance near double-row wing bag sand barrier under different wind conditions to screen out the optimal mode of wing bag sand barrier. The analyses were conducted under nine configuration modes through the wind tunnel simulation experiment and the field experiment.Results: The inflection point of the airflow was always 5H on the windward side of the wing bag sand barrier, regardless of the wind speed. The protection range of the wing bag sand barrier with the same specifications was gradually weakened with the increase of the wind speed. However, there was an upward trend in both total sand accumulation and sand accumulation of each height layer. When the wind speed was slower than 8 m/s, the sand accumulation behind the barrier was mainly concentrated in the 0–10 cm height layer, and when the wind speed was 12 m/s, it was mainly concentrated in the 30–60 cm height layer. At the leeward side of the wing bag sand barrier, sand particles were rejected in the range of 0–30 cm; however, they were conducted in the range of 30–60 cm. The protective effect of the wing bag sand barrier simulated in the wind tunnel experiment was consistent with that of the field experiment.Discussion: For a wind speed of slower than 6 m/s, the recommended specification for the field-installed wing bag sand barrier was 25 cm × 20 cm or 30 cm × 20 cm. The specifications 25 cm × 20 cm and 25 cm × 25 cm were recommended at an inlet wind speed of 8 m/s. When the wind speed was greater than 12 m/s, the recommended specifications were 25 cm × 25 cm, 25 cm × 20 cm, and 20 cm × 25 cm.

Hyperbolic Paraboloid Tensile Structure—Numerical CFD Simulation of Wind Flow in RWIND Software

Tensile membrane structures combine a prestressed roofing envelope material and supporting elements. To design these structures, there is a set of recommendations in the European Design Guide for Tensile Surface Structures and some other national standards. However, currently, there is no official standard related to the design process of tensile structures in the European Union. The structure studied in this project is considered as permanent roofing of an external testing device in the shape of a simple hyperbolic paraboloid without enclosing walls. Snow and wind loads were analyzed as the most critical types of loading in the location. Determining the value of the snow load is relatively simple according to the European standard. However, in the case of the wind load, this shape is not considered in the European standard and needs to be solved experimentally or by numerical simulation in a wind tunnel. The present contribution focuses on numerical analysis of the wind flow in RFEM software and simulation of the wind tunnel in RWIND software.

Numerical investigations on dynamic responses of subway segmental tunnel lining structures under internal blasts

Numerical simulation of segmental lining tunnel subjected to internal explosive loading is carried out in this paper based on the arbitrary-Lagrangian-Eulerian (ALE) and finite element (FE) coupled algorithms. A high-fidelity FE model considering assembled features of segmental lining structure is established, and the mapping technique is adopted to accurately simulate the explosion process. The calculated overpressure histories and failure modes of the lining structure fit well with field test results of full-scale specimens, indicating the applicability and accuracy of the numerical model. A more comprehensive numerical model considered the practical service state of segmental lining tunnel is further built based on the verified model. Influences of mechanical properties and pressure levels of surrounding soils on dynamic responses of tunnel structure under internal explosion are investigated. Numerical results show that dominated deformation modes of the segmental lining tunnel under the action of internal explosion include opening deformation at the segmental joints of the charged ring and shear deformation between the adjacent rings. The modest explosion caused by terrorist bombing attacks may severely harm the shield tunnel structure and impair its service performance, especially if the tunnel is buried in soft soil at a shallow depth

Sensitivity Study of Highway Tunnel Light Environment Parameters Based on Pupil Change Experiments and CNN Judging Method

There is a sparsity of research regarding the nonlinear relationship between the sensitivity of the light environment parameters in the middle section of the tunnel under multi-factor conditions in multiple samples. Due to the lack of research, the present study was conducted in order to investigate said relationship. To determine the parameters of the eye-movement characteristics required for the convolutional neural network prediction evaluation, a tunnel simulation model was established using DIALux10 simulation software and a series of dynamic driving tests were conducted based on an indoor simulation experimental platform. Further, through employing the residual network ResNet to extract data features and the pyramidal pooling network module, a convolutional neural network judging model with adaptive learning capabilities was established for investigating the nonlinear relationship of sensitivity of light environment parameters. Following the test, the degree of influence on the diameter of the pupil for the different levels of each factor were: the optimal configuration of the staggered layout on either side of the lamp arrangement, the optimal 3 m height under the different sidewall painting layout height conditions, the optimal green painting color under the different sidewall painting color conditions, and the optimal 6500 k under different LED light source color temperature conditions. The results of the present study serve to expand the use of the convolutional neural network model in tunnel light environment research and provide a new path for evaluating the quality of tunnel light environment.

Numerical Wind Tunnel Simulation for Pollutants Dispersion with Urban 2003

A CFD numerical wind tunnel software was made to simulate the air flow and diffusion of pollutants in urban areas. This softeware is very compact. With the collaboration of the modelling tool AutoCAD and the post-processing software Paraview, a set of standardized numerical simulation process of atmospheric diffusion has been established. The model of the software is based on Open Foam open-source platform, which can perform 3D large-scale parallel operation, and solve 3D Navier Stokes equations on Computer cluster. Based on the observation data of iop9 from the 2003 urban joint field study in Oklahoma City, Oklahoma, the numerical wind tunnel is further evaluated. The wind and concentration field in the near and middle regions, as well as the wind speed, wind direction, friction velocity and turbulent kinetic energy (TKE) profiles in the urban wake region are compared between the numerical wind tunnel and the urban 2003 field experiment. The results show that the numerical wind tunnel can be an economic and effective tool to simulate the diffusion of pollutants in urban areas.

Accuracy of equivalent model in band-to-band tunneling simulation of semiconductor nanowires

The accuracy of the equivalent model (EM) in the band-to-band tunneling simulation of semiconductor nanowires is investigated by constructing EMs for various semiconductor nanowires and calculating the tunneling characteristics with the non-equilibrium Green’s function method. As the target window is widened, the EM accurately reproduces not only the traveling states but also the evanescent states. The relative error of the maximum tunnel current is shown to decrease exponentially with the transport window size. It is also shown that semiconductor nanowires can be classified into two types (D-type and I-type) according to the dispersion of the evanescent mode connecting the valence and the conduction band edges, and that the D-type nanowires can be represented with a smaller EM basis size or high accuracy compared to the I-type nanowires.

Numerical modeling of open TBM tunneling in stratified rock masses using a coupled FDM-DEM method

The complex engineering characteristics of stratified rock masses make the comprehensive analysis of TBM tunneling more complex and difficult. In this study, an advanced modeling method based on the coupled finite difference method (FDM) and discrete element method (DEM) was proposed for the simulation of open TBM tunneling in stratified rock masses. The modeling and analysis process of the FDM-DEM numerical model was presented with the DLS Tunnel as the research background. Numerical results show that the displacement values and characteristics of the rock mass are consistent with the deformation of the surrounding rocks obtained from in situ monitoring. Severe shear and tensile fractures occur progressively in both rock blocks and bedding planes during TBM tunneling. The extent of the loosening area in the rock mass also continues to grow. The numerical model reproduces the progressive failure process of the stratified rock mass through the analysis of contact fracture events and the evolution of contact forces. The simulation of the interaction between the rock mass and the shield is accomplished by FDM-DEM coupling methods under the large-strain mode. This study presents an effective tool for the comprehensive analysis of open TBM tunneling in stratified rock masses.

Numerical Simulation of Wind Characteristics in Complex Mountains with Focus on Terrain Boundary Transition Curve

In recent years, an increasing number of projects have been developed in complex mountainous areas. The wind environment in mountainous areas, extremely complex due to the undulating terrain and diverse landscapes, is a key factor threatening the structural safety of buildings and their appurtenances in mountainous areas. Therefore, it is important to study the wind environment in complex terrain to clarify the wind resistance of structures in mountainous areas. Computational fluid dynamics (CFD) approaches are commonly used to examine wind fields in complex terrain; however, due to the limited range of terrain considered, direct modeling using terrain elevation data can result in truncated elevation differences, affecting the accuracy of numerical simulations. To address the problem of truncated elevation differences at terrain boundaries, the parameters of the wind tunnel contraction curve are optimized regarding the wind tunnel contraction section design principle. Moreover, several transition curves are analyzed and evaluated by numerical simulation methods, and a transition curve applicable to the terrain boundary transition form is proposed. The proposed terrain transition curves are applied to model the terrain of complex mountainous ski resort areas to be used in CFD numerical simulations. Furthermore, the accuracy of the numerical simulation is verified through a comparison with the field-measured data. Results indicate that the proposed method can accurately and effectively reflect the wind environment characteristics of a ski resort area. The proposed terrain transition curve provides a theoretical basis and case support for designing the terrain model boundary transition section, which can be used as a reference for wind tunnel and numerical simulation studies in complex mountainous areas.

An experimental and numerical study of turbulent oscillatory flow over an irregular rough wall

The hydrodynamics of turbulent oscillatory flow over a gravel-based irregular rough wall is investigated using laser-Doppler anemometry measurements of velocities in a large oscillatory flow tunnel and direct numerical simulation (DNS) of the Navier–Stokes equations. The same periodic irregular roughness was used for both experiments and DNS. Four flow shapes are investigated: sinusoidal, skewed, asymmetric and combined skewed–asymmetric. The experiments were conducted for target Reynolds numbers (based on the Stokes length and standard deviation of free-stream velocity) of$R_{\delta,\sigma }=800$and$R_{\delta,\sigma }=1549$; DNS was conducted for flows with target$R_{\delta,\sigma }=800$. Boundary layer thickness, bottom phase lead and friction factor are in good agreement with previous studies. For the first time, evidence of Prandtl's secondary flows of the second kind in oscillatory flow is presented. Turbulence structure is visualised using isosurfaces of$\lambda _{2}$(Jeong & HussainJ. Fluid Mech., vol. 285, 1995, pp. 69–94), revealing densely packed structures that grow stronger and weaker in correspondence with the free-stream velocity. Reynolds and dispersive stresses peak just below the highest roughness crest, with dispersive stress vanishing a short distance above the roughness. Bursts of turbulence kinetic energy and wake kinetic energy are generated each flow half-cycle, with variable behaviour depending on flow shape. Non-Gaussian turbulence statistics are observed that originate near the wall, becoming increasingly non-Gaussian far from the wall. Probability density functions of turbulence statistics can be closely approximated by a fourth-order Gram–Charlier distribution at most phases and elevations, though when statistics deviate more strongly from Gaussian, streamwise and wall-normal (spanwise) statistics are better described by a Pearson type IV (VII) distribution.

Journey through a virtual tunnel: Simulated motion and its effects on the experience of time

This paper examines the relationship between time and motion perception in virtual environments. Previous work has shown that the perception of motion can affect the perception of time. We developed a virtual environment that simulates motion in a tunnel and measured its effects on the estimation of the duration of time, the speed at which perceived time passes, and the illusion of self-motion, also known as vection. When large areas of the visual field move in the same direction, vection can occur; observers often perceive this as self-motion rather than motion of the environment. To generate different levels of vection and investigate its effects on time perception, we developed an abstract procedural tunnel generator. The generator can simulate different speeds and densities of tunnel sections (visibly distinguishable sections that form the virtual tunnel), as well as the degree of embodiment of the user avatar (with or without virtual hands). We exposed participants to various tunnel simulations with different durations, speeds, and densities in a remote desktop and a virtual reality (VR) laboratory study. Time passed subjectively faster under high-speed and high-density conditions in both studies. The experience of self-motion was also stronger under high-speed and high-density conditions. Both studies revealed a significant correlation between the perceived passage of time and perceived self-motion. Subjects in the virtual reality study reported a stronger self-motion experience, a faster perceived passage of time, and shorter time estimates than subjects in the desktop study. Our results suggest that a virtual tunnel simulation can manipulate time perception in virtual reality. We will explore these results for the development of virtual reality applications for therapeutic approaches in our future work. This could be particularly useful in treating disorders like depression, autism, and schizophrenia, which are known to be associated with distortions in time perception. For example, the tunnel could be therapeutically applied by resetting patients’ time perceptions by exposing them to the tunnel under different conditions, such as increasing or decreasing perceived time.

Effect of Overburden Depth and Stress Anisotropy on a Ground Reaction Caused by Advancing Excavation of a Circular Tunnel

The assumption of the Convergence–Confinement Method (CCM) is the analysis of the interaction behavior of the support and ground of a deep circular tunnel under an isotropic stress field. Aiming to improve this method, this paper proposes a discussion on the influence of the overburden depth and stress anisotropy. To consider the influence of the overburden effect, the ground reaction in different depths due to tunnel advancing excavation is investigated. Under anisotropic stress conditions, the analytical solutions of the stress/displacement in the plastic and elastic regions of this ground reaction can also be suitable for theoretical analysis in a consistent manner. The key factor in this study is the use of confinement loss, which can not only describe the simulation of tunnel advancing effects but also become a superimposed value of the incremental procedure. In addition, the calculation spreadsheets can be used to estimate and implement the theoretical analytical solutions into executable computational solutions. To check the validity of the analytical solution, finite element analysis is used to examine the distribution of stress/displacement around the tunnel, especially the distribution along the overburden pressure line in the circular tunnel cross-section. Comparing the analytical solution calculated by the incremental procedure with the result of the numerical analysis shows a consistent trend.

Simulation of Settlement-Free Tunneling by the Microtunneling Method

Simulation of Settlement-Free Tunneling by the Microtunneling Method

A Numerical Study on the Smoke Control System Performance for a Large Fire in a Long Tunnel

In this study, a numerical simulation was performed using the fire dynamics simulator to examine the performance of a smoke control system in the case of a large fire in a long tunnel. A regional long tunnel that facilitates frequent movement in the port area was simulated. The fire scenario was set as a heavy goods vehicle fire corresponding to a large fire based on the existing real-scale experimental research data. A jet fan with an inner diameter of 1250 mm used in the regional tunnel was included in the tunnel simulation. For the evaluation of the smoke control system performance, the effects of the flow rate and installation interval of the jet fan on the smoke behavior, visibility, and temperature was analyzed. As the flow rate of the jet fan decreased, backlayering was lengthened, which reduced the time to achieve life safety standard.

Towards a Wind Urbanism in Tropical Environments

One of the conditions for the proper functioning of passive comfort in humid tropical environments is access to natural ventilation in buildings. This notion of access to natural ventilation has taken on its full meaning during the current health crisis.
 Based on this observation established by a rich literature, we asked ourselves how to ensure the sustainability of the good functioning of natural ventilation in a humid tropical environment of a building in a built complex? This questioning led us to show the importance of the context through various dimensions: the chain of natural ventilation, the programmatic context, the climatic and geographical context, the regulatory context.
 Taking these parameters into account has allowed us, in the context of a case study, the eco-district Cœur de ville de La Possession, on the island of La Réunion, to develop a new conceptual approach associating urban planning and aeraulic engineering from the beginning of the design process for maximum efficiency.
 To this end, we initiated a new approach based on: co-design, the use of physical wind tunnel simulation at different scales, the integration of environmental, architectural and landscape recommendations at the scale of the district and of the buildings making up this district, in an enforceable urban planning regulation. This has enabled us, within the framework of this eco-district, to develop the concept of the right to natural ventilation, of the windy city and of the guarantee over time of the preservation of this potential.
 The transcription of this approach in other eco-neighbourhoods in a tropical environment seems to us to be a major challenge to be considered and which could even be extended to other climatic zones, in the context of current global warming.