Tunnel Study Research Articles

A wind tunnel study on cyclic yaw control: Power performance and wake characteristics

In this study, wind-tunnel experiments are used to investigate cyclic yaw control as a wake mitigation strategy aiming to improve wind farm power production. The control strategy is applied to a single wind turbine and a wind farm comprising of a column of three wind turbines in full wake state. The power performance of the wind farm is optimized by adjusting the control parameters, which include the yaw angle amplitude and yaw Strouhal number, and the wake flows are investigated using particle-image velocimetry measurements. The yaw angle of the controlled turbine is varied dynamically in a sinusoidal manner. A power gain of more than 10 % compared to an uncontrolled wind farm is achieved when the yaw angle amplitude and yaw Strouhal number are in the range of 10°–35° and 0.09-0.22, respectively, with a peak power gain of 15.2 %. The power consumed to generate the control is found to be small and predictable. Results from wake measurements reveal that by deflecting the wake cyclically, this control strategy can lead to relatively flattened mean wake velocity deficit profiles, faster wake recovery and very different wake turbulence intensity distributions, compared to the uncontrolled case. The results show that cyclic yaw control has a great potential in improving the power production of wind farms. A scaling of the control parameters based on the kinematic similarity between the wind-tunnel scale and utility-scale wind farms is also proposed.

Evaluation of passive flux samplers with different orifice sizes to measure ammonia volatilization losses

AbstractA common passive sampler used to measure NH3 volatilization losses in field studies has a nozzle with a 1‐mm, round orifice that reduces air flow to increase NH3 adsorption. This reduction in air flow, measured by the orifice's K value (0–1), implies a reduction in the amount of NH3 entering the sampler per unit of time, which may require a longer exposure to accumulate measurable quantities of NH3. Increasing the diameter of the orifice would increase the NH3 entering the sampler and possibly allow shorter exposure times, but it may also lead to increased NH3 bypass. The objectives of this research were to (1) determine the effect of wind speed on NH3 bypass in samplers with 1‐ or 2‐mm orifices, (2) determine the reduction in air speed in samplers with 1‐ or 2‐mm orifices by determining their K values, and (3) compare field NH3 volatilization losses measured with 1‐ and 2‐mm orifices. A laboratory study with wind speeds ranging from 0.6 to 10 m·s−1 showed that both orifice sizes had NH3 bypass at low and high wind speeds. Results from wind tunnel studies determined that flow was reduced to 63% (K = 0.63) in 1‐mm orifices and to 74% (K = 0.74) in 2‐mm orifices. Field studies indicated that 1‐mm orifices may measure greater NH3 volatilization losses than 2‐mm orifices at average low wind speeds when maximum wind speeds <10 m·s−1, but may measure equal or lower losses than 2‐mm orifices when several days occur with maximum wind speeds >10 m·s−1.

Analysis of the Interaction Damage Mechanism and Treatment Measures for an Underpass Landslide Tunnel: A Case from Southwest China

Previous studies have analyzed the damage of tunnels and slopes as a single entity, ignoring the interaction effect between the tunnels and slopes, which will have an impact on the accuracy of the damage mechanism and the safety of the treatment measures. In this paper, three types of simulation models are established—the natural state, after tunnel excavation, and after reinforcement measures—considering a case study of an underpass landslide tunnel in southwest China. Based on the theory of underpass landslide tunnels and the strength reduction method, the interaction damage mechanism of this underpass landslide tunnel is revealed, and a reasonable treatment plan is proposed. The analysis results show the following: there is an obvious interaction effect between the tunnel collapse and the slope instability; a large number of mudstones common in the surrounding rock of the tunnel have rheological properties, which amplify the influence of the interaction effect of the tunnel through the landslide; and the proposed comprehensive treatment measures of “rescue inside the tunnel cave + tunnel slope treatment” have strong pertinence and effectiveness, and they fundamentally address the tunnel collapse and the slope instability of the tunnel.

Wind tunnel and CFD studies of wind loadings on topsides of offshore structures

This paper presents a comprehensive study of wind loads on various offshore platforms using both wind tunnel experiments and CFD at model scales. The platforms studied include an LNGC with simple topside geometry, a FPSO with complex porous blocks, and a JUP with mixed simple blocks and tall truss structures. The 3D-printing is used to fabricate experimental models to ensure consistency with CFD models. Sensitivity studies of mesh types, mesh independence, turbulence models, wind profiles and wind speed independence are conducted to achieve highly accurate and reliable simulation results. Comparisons between the CFD and experimental results of six loading components and surface pressure measurements at over 20 sensor locations for each platform show good agreement across various wind directions and geometries. The robustness of the experiments and CFD models can serve as a reference for future offshore wind loading studies. Detailed examinations of the wind fields surrounding the platforms and the effects of porosity levels on wind loading reveal unique internal flow structures that differentiate among the structures and provide explanations for variations in loading and discrepancies. These findings contribute to a better understanding of wind fields and loading on the superstructures of offshore platforms and can inform the design and operation of similar structures in the future.

The flow in the induction and entrance regions of lab‐scale wind farms

AbstractWith the increasing demand for wind energy, it is important to be able to understand and predict the available wind resources. To that end, the present wind tunnel study addresses the flow in the induction and entrance region of wind farms through particle image velocimetry, with focus on differences between actuator disks and two‐bladed rotating wind turbine models. Both staggered and aligned farm layouts are examined for three different incoming wind directions. For each layout, 69 disks or turbines are used, and the field of view ranges from 12 rotor diameters upstream of the farms to 8 diameters downstream of the first row. The results show that the induction, or blockage effect, is higher for the disks, even though the thrust (or drag) coefficient is the same. In contrast, the wake is stronger downstream of the turbines. The orientation and layout of the farm do not have a major impact on the results. Modal decomposition of the flow shows that the flow structure similarity between the disk and turbines improves downstream of the second row of wake generating objects, indicating that the substitution of wind turbines by actuator disks is more appropriate for wind farms than for the investigation of single wakes.

Assessing wind field characteristics along the airport runway glide slope: an explainable boosting machine-assisted wind tunnel study

Aircraft landings are especially perilous when the wind is gusty near airport runways. For this reason, an aircraft may deviate from its glide slope, miss its approach, or even crash in the worst cases. In the study, we used the state-of-the-art glass-box model, the Explainable Boosting Machine (EBM), to estimate the variation in headwind speed and turbulence intensity along the airport runway glide slope and to interpret the various contributing factors. To begin, the wind field characteristics were examined by developing a scaled-down model of Hong Kong International Airport (HKIA) runway as well as and the surrounding buildings and complex terrain in the TJ-3 atmospheric boundary layer wind tunnel. The placement of probes along the glide slope of the model runway aided in the measurement of wind field characteristics at different locations in the presence and absence of surrounding buildings. Next, the experimental data was used to train the EBM model in conjunction with Bayesian optimization approach. The counterpart black box models (extreme gradient boosting, random forest, extra tree and adaptive boosting) as well as other glass box models (linear regression and decision tree) were compared with the outcomes of the EBM model. Based on the holdout testing data, the EBM model revealed superior performance for both variation in headwind speed and turbulence intensity in terms of mean absolute error, mean squared error, root mean squared error and R-square values. To further evaluate the impact of different factors on the wind field characteristics along the airport runway glide slope, the EBM model allows for a full interpretation of the contribution of individual and pairwise interactions of factors to the prediction results from both a global and a local perspective.

Coexistence of superconductivity and charge-density waves: evidence from tunneling studies (Review article)

The review summarizes certain theoretical and experimental studies of the quasiparticle, J, and Josephson, IJ, currents between superconductors partially dielectrized with charge-density waves (CDWs). A relation between the Cooper and electron-hole pairings and their manifestations in high-Tc oxides have been analyzed. It was shown that the CDW fingerprints can be found in a lot of already observed dependences. All described results are considered in the framework of the historical context.

Specific Features of Grain Boundaries in Nickel Processed by High-Pressure Torsion

Publications on obtaining bulk nanostructured materials with special properties by various modes of severe plastic deformation, using nickel as an example, are briefly reviewed. Particular attention is paid to the state of grain boundaries, commonly referred to as nonequilibrium, or deformation-modified boundaries, revealed by electron microscopy, including scanning tunneling, Mossbauer spectroscopy, and diffusion studies. It is shown that contribution of specific state of grain boundaries to additional strengthening is often overestimated. In particular, in Ni processed by high pressure torsion, nonequilibrium grain boundaries are formed, which have increased energy and are ultrafast diffusion paths, but they contribute relatively little to the total strengthening.

Design and Implementation of a Quantitative Risk Assessment Model for UK Road Tunnels

One of the critical transportation infrastructures is road tunnels and fire safety is one of the important aspects of their operation. Interaction between the fire, tunnel users, traffic, and fire safety measures influences fires in road tunnels. Therefore, a complex model is required to analyse the risk and quantify the consequences. In this paper, a novel quantitative risk analysis model developed for UK road tunnels is presented consisting of a quantitative consequence analysis model and a quantitative frequency frequency analysis model. The proposed quantitative consequence analysis model is provided through three sub-models; queue model, distribution model, and egress model. The frequency analysis is via an event tree that takes into account the tunnel fire rate in UK road tunnels. After a brief description of this model, the proposed method is illustrated through a case study of an urban road tunnel. The effect of different emergency ventilation systems on societal risk and sensitivity of the model to pre-movement time, accident frequencies involving Heavy Good Vehicles (HGVs), tenability threshold temperature, and different burning vehicles were studied in this case study.

The damage mode and forced response characteristics of articulated lining structure: A case study of metro tunnel under a reverse fault action

With the continuous development of underground tunnel engineering, there have been a large number of engineering cases of tunnels crossing active faults, and the dislocation of active faults must have a greater impact on the structural safety of tunnels. Therefore, it is of great significance to study the stress characteristics and anti-dislocation design of tunnels crossing active faults. Based on the tunnel of Urumqi Metro Line 1 crossing the Wanyaogou reverse fault, a large-scale physical model test of shear dislocation of subway tunnel crossing the reverse fault is designed and carried out, and the mechanical behavior difference between conventional tunnel structure and articulated tunnel structure is compared and analyzed. The surface displacement, structural deformation, additional earth pressure, strain distribution, fracture distribution and other test results were monitored and recorded, and the forced response characteristics and failure mode of subway tunnel structure under the effect of stick–slip of reverse fault were studied in depth. The results show that the failure modes of conventional tunnel are mainly shear failure at the fault plane, while articulated tunnel is mainly large eccentric failure. Compared with the conventional tunnel, the deformation failure range, strain peak and total crack length of the articulated tunnel are obviously reduced. Besides, there is no spalling phenomenon similar to conventional tunnel. The structure still has a certain residual bearing capacity, that is, the articulated tunnel structure is more adaptable to the forced displacement of the fault, the stress state is better, and its rupture resistance is better. To sum up, the model test study reveals the forced response characteristics and rupture resistance of articulated tunnel structure under reverse fault conditions, which has guiding significance for similar tunnel engineering problems.

Development and application of an intelligent robot for rock mass structure detection: A case study of Letuan tunnel in Shandong, China

Determining the rock mass structure of an excavation face is important for the safe construction of tunnels. Traditional artificial detection poses a threat to personnel and property; thus, it is necessary to develop unmanned detection technology. This paper innovatively develops an efficient method for detecting joints in rock tunnels based on laser scanning, and an intelligent robot is then designed to achieve the automation of this method. The functionalities of the robot are realized by combining three modules, namely, a travel module, an automatic data acquisition module and a remote control and data transmission module. Based on the information obtained from intelligent robots, a data analysis method for estimating the location and orientation of structure planes and performing 3D tunnel fractures mapping in an underground environment is proposed. The reliability of the developed intelligent robot and the accuracy of the identification of rock instabilities are validated in field tests. The robot developed herein can be used as an effective tool to detect the instabilities of rocks in tunnels. In addition, the approach for the detection of rock joints as well as the design methodologies presented in this paper can also serve as a guide for other relevant intelligent equipment.

Numerical Modeling of Tunnel Support System in Himalayan Rock Masses for Seismic Resilience

This study uses numerical modeling in combination with rock mass classification approaches to develop tunnel support systems that are safe from earthquakes, ultimately contributing to the seismic resilience of the important infrastructure. A case study of tunnel in Himalayan region of Nepal has been considered for seismic assessment of tunnel supports in different geological conditions. For better quality rock masses (GSI>30), strain-softening model was used, and for weaker rock masses (GSI<30), elastic-perfectly-plastic model was used. To ensure safety in the case of extremely poor rock mass, shotcrete thickness had to be increased by 100 mm over that recommended by empirical methods. In both models, shotcrete in the sections with high overburden showed a significant decrease in FOS. Even though this type of unusual finding has also been reported in the Melamchi water supply tunnel after 2015 Gorkha Earthquake, no further studies to investigate the influencing factors have been done. While this condition occurred in the model used in this study because of the application of higher in-situ stress for sections with a larger depth of overburden, the actual reason for the occurrence of this situation as a result of an earthquake remains unexplained. Future research should take into account the effects of discontinuities, epicentral distance, aftershocks, and the incorporation of actual stress measurements from the field for numerical modeling.

Analysis of drivers’ preferences toward content and message format of variable message signs during tunnel emergency evacuation: A case study of Niayesh tunnel in Tehran

In the event of an emergency evacuation of a tunnel, variable message signs are one of the tools available to tunnel operators to communicate with tunnel users and play an important role in guiding them. In this study, the primary focus is to determine the most appropriate message for variable message signs in terms of content and format for tunnel emergency evacuations. This study evaluates the responses of drivers to the visual comparison between variable message signs by using stated choice methods. Using a binary logit model, the results indicate that drivers prefer the text message “Turn off the car, exit the tunnel” in two lines on the right side of the sign along with the green image of the emergency exit on the left side. Therefore, it is anticipated that the findings obtained and their application at the time of the tunnel disaster will reduce the likelihood of catastrophic accidents and mitigate their consequences.

On the wake characteristics of a model wind turbine and a porous disc: Effects of freestream turbulence intensity

Porous discs are the experimental counterparts of the numerical actuator disc concept and are frequently used in wind tunnel studies to reproduce the far-wake characteristics of wind turbines. The potential of using porous discs instead of wind turbines comes with the benefits such as operational easiness and design simplicity. This paper presents the results of an experimental study focusing on the wake development characteristics of a single porous disc and a single wind turbine under different freestream turbulence intensities but at similar Reynolds number conditions. The measurements are performed using two-dimensional two-component particle image velocimetry (2D2C PIV) technique up to seven diameters downstream distance in the wake of the models. The wake flows are analyzed in terms of the development of mean wake velocity deficit, wake decay, and wake turbulence characteristics. The results show that the wake recovery occurs faster for both the porous disc and the turbine with increasing freestream turbulence intensity. The wake width increases with the freestream turbulence intensity, indicating faster diffusion of the wake for both models. On the other hand, the wake width of the porous disc and the turbine is similar at the same turbulence intensity conditions, although they operate with slightly different thrust coefficients. Turbulent kinetic energy profiles in the far wake of the porous disc and the turbine, which are significantly different for the low turbulence intensity conditions, become similar for the high turbulence intensity case. The comparison of the turbulent kinetic energy, decay rate and production characteristics points to different turbulence mechanisms in the wake of the porous disc and the turbine. In the near wake, the wake decay rate and turbulent kinetic energy levels are higher in the porous disc case due to enhanced mixing levels associated with the grid-generated turbulence. In the far wake, the decay rate of the turbine wake is higher, most probably due to the breakdown of the tip vortices. When the freestream turbulence is increased, the differences in the turbulent wake flow characteristics diminish in the far wake, particularly after a 4.5-diameter downstream distance.

Binary Collisions of Water Drops in Presence of Horizontal Electric Fields: A Wind Tunnel Study

AbstractCoalescence/breakup characteristics of binary collisions of small water drops (dS = 0.4–1.8 mm diameter) with large drops (dL = 3–3.5 mm diameter) occurring in the absence/presence of horizontal electric field (EH) = 0, 100, and 300 kVm−1 have been investigated in a small vertical wind tunnel using a high‐speed digital camera. The coalescence efficiency (EC) of 0.299 observed for average diameters (dL = 3.2 mm, dS = 1.2 mm) in EH = 0 decreased to 0.244/0.211 when EH is increased to 100/300 kVm−1. The increase in the electric field reduces the probability of coalescence when Weber number (We) < 1. However, when We ≥ 1, an increase in We restricts the probability of coalescence. Our data, when plotted in the regime diagram in the We*‐p plane, delineates the collision outcomes in all‐electric field values but does show the overlapping of some data points in the adjacent categories. After a binary collision, the relaxation time for coalescence is higher than that for the breakup. Further, the relaxation time increases from the filament to sheet to disk mode of breakup in all‐electric field values. Fragment size distributions after the filament and sheet types of breakups differ and are differently affected by the applied electric field. Higher collision kinetic energy has a tendency to increase the number of fragments of the sizes between dL and dS. It is concluded therefore that, the effect of the electric field needs to be included in the estimation of drop growth and precipitation in clouds.

Yedoma. Part 3. Annals of geocryological research, study of radiocarbon age, the stable-isotope composition studies in the 21st century

The second decade and the beginning of the third decade of the XXI century in yedoma research were characterized by a variety of high-precision measurements of gas inclusions, molecular biomarkers, and DNA. The purpose of this paper is to analyze the most notable publications of 2010–2023 devoted to radiocarbon dating and stable isotope studies of yedoma in the Russian and North American Arctic. AMS dating and stable isotope analysis continued at Lomonosov Moscow State University (Yu.K. Vasil’chuk, A.C. Vasil’chuk, N.A. Budantseva, I.D. Streletskaya, Ju.N. Chizhova, J.Yu. Vasil’chuk), especially detailed on the yedoma of Batagay, Seyakha, Kotelny, and Faddeevsky islands. Active research was continued by the participants of the Russian-German expedition (A. Yu. Derevyagin, A. I. Kizyakov, S. Wetterich, T. Opel, J. Strauss, G. Grosse and L. Schirrmeister) on the yedoma sections of the New Siberian Islands. They studied the Batagay yedoma together with J. Murton and K. Ashastina. Researchers from the University of Fairbanks (M. Kanevskiy, Y. Shur, M. Jorgenson, and E. Stephani) studied in detail the yedoma of the Itkillik River valley, as well as new yedoma sections in the Fox Tunnel, where radiocarbon and isotope studies were also carried out by M.S. Lachniet and A. Sloat from the University of Las Vegas. Research has begun on molecular biomarkers and DNA (E. Willerslev, T. Jørgensen) in yedoma. The study of PAHs in yedoma ice wedges has also begun (Yu.K. Vasil’chuk). It is emphasized that isotopic data is not an end in itself for research; the next step, paleotemperature reconstruction based on these data, is necessary and logically justified. The accuracy and reliability of the proposed paleotemperature-isotope equations are considered.

Study of the underground tunnel planning. Cognitive modelling

A study of the underground tunnel planning reliability for megacities is proposed based on the use of foresight and cognitive modeling methodologies. Using the foresight methodology allows, with the help of expert estimation procedures, to identify critical technologies and build alternatives of scenarios with quantitative characteristics. For the justified implementation of a particular scenario, cognitive modeling is used, which allows to build causal relationships based on knowledge and experience, understand and analyze the behavior of a complex system for a strategic perspective with a large number of interconnections and interdependencies. The suggested study allows the reliability planning of underground tunnels on the basis of reasonable scenarios selection and justification of their creation priority.

Global phase diagram of charge-neutral graphene in the quantum Hall regime for generic interactions

Monolayer graphene at charge neutrality in a quantizing magnetic field is a quantum Hall ferromagnet. Due to the spin and valley (near) degeneracies, there is a plethora of possible ground states. Previous theoretical work, based on a stringent ultra short-range assumption on the symmetry-allowed interactions, predicts a phase diagram with distinct regions of spin-polarized, canted antiferromagnetic, inter-valley coherent, and charge density wave order. While early experiments suggested that the system was in the canted antiferromagnetic phase at a perpendicular field, recent scanning tunneling studies universally find Kekul\'e bond order, and sometimes also charge density wave order. Recently, it was found that if one relaxes the stringent assumption mentioned above, a phase with coexisting canted antiferromagnetic and Kekul\'e order exists in the region of the phase diagram believed to correspond to real samples. In this work, starting from the continuum limit appropriate for experiments, we present the complete phase diagram of $\nu=0$ graphene in the Hartree-Fock approximation, using generic symmetry-allowed interactions, assuming translation invariant ground states up to an intervalley coherence. Allowing for a sublattice potential (valley Zeeman coupling), we find numerous phases with different types of coexisting order. We conclude with a discussion of the physical signatures of the various states.

A study of tunneling in triangular resonant tunnel diodes: Effect of barrier width, barrier height, pressure, temperature, and heterostructure strain

Using the transfer matrix, the transmission coefficient of electrons is examined in the triangular double-barrier semiconductor heterostructure. GaAs-based heterostructure is considered to study the role of barrier width, barrier height, pressure and temperature. The geometrical parameters of the heterostructures (barrier width and barrier height) and the external perturbation (pressure and temperature) influence the tunneling properties. The tunneling time of the electrons is also studied using Heisenberg's uncertainty principle. The account of the heterostructure strain is also discussed.

The role of near-façade flow in wind-dominant single-sided natural ventilation for an isolated three-storey building: An LES study

Wind-driven single-sided ventilation is present in many existing buildings globally, and its performance can be unreliable and challenging to improve. To address these performance challenges, a better understanding of the interconnected relationship between the external and internal flows is required. Therefore, a detailed assessment of this type of natural ventilation is vital. A detailed CFD analysis of wind-dominant single-sided natural ventilation is presented by adopting the Large Eddy Simulation method, validated using previous wind tunnel studies. An isolated cube, representing a three-storey building, was used to investigate four case studies with different opening positions on the building façade. The presence of parallel flow near the building façade and the effect this has, both on the structure of the flow at the opening and the internal secondary flow, is investigated. Results demonstrate that a mixing layer jet of air is the main structure of the flow at the opening. The flow characteristics of this jet are a function of how the external near-façade flow interacts with the building. It can be deflected or attenuated by the near-façade fluctuating pressure and vortex structures close to the opening. Tracer gas decay results show that only 3/5 of the flow at the opening contributes to effective ventilation in this type of natural ventilation. Comparisons between the ventilation rates for openings at different positions on the building façade demonstrate the importance of the pressure role at the opening in single-sided natural ventilation.