Tunnel Pressure Research Articles

The Semi-Air-Cushion Surge Tank: Design Principles and Case Study

Surge tanks are required to enable power and frequency governing of hydraulic machines in hydropower plants with pressure tunnels. To improve the hydraulic performance and reduce the construction costs, a new concept of semi-air-cushion surge tank (semi-ACST) is proposed. The semi-ACST can be particularly effective for upgrading and retrofitting of existing hydropower plants, when additional hydraulic machine capacity is added to an existing waterway. The key design element is a crown throttle, constructed as an inverted weir placed in the crown of the chamber. The purpose is to intentionally trap an air pocket during filling of the lower chamber. The air is released slowly through defined air pipes so that the air in practice contributes equivalent to added volume in the upper chamber. Thus, the semi-ACST improves the dampening of mass oscillation, without increasing the surge tank volume. The semi-ACST has been investigated and developed with multiphase 3D CFD simulations with RANS turbulence modelling. The design principles have been tested on the case-study Tonstad hydropower plant (960 MW). In the presented case study, the semi-ACST is proposed as an extension of one of the three exiting hydraulically coupled surge tanks.

Wind Pressure Field Reconstruction and Prediction of Large-Span Roof Structure with Folded-Plate Type Based on Proper Orthogonal Decomposition

The complex and diverse structural forms make it impossible to define universal shape coefficients for large-span roof structures, which usually need to be obtained by wind tunnel tests. However, the number of test measurement points is limited, which leads to obvious limitations in the study of wind loads on large-span roof structures. Taking a large-span folded-plate roof as an example, based on the wind tunnel pressure test results of the rigid model, the proper orthogonal decomposition (POD) method is used to reconstruct the wind pressure field of the roof using the first several eigenmodes. The wind pressure of several typical characteristic points is predicted based on four different interpolations methods, and the accuracy and feasibility of POD method in reconstruction and prediction of wind pressure field of large-span roof are analyzed and studied from multiple perspectives. The results show that the order of the selected structural eigenmodes has an impact on the reconstruction accuracy of the wind pressure field. The more orders are selected, the closer the wind pressure field reconstruction is to the true value. The reconstruction effect of the wind pressure field based on the POD method is related to the spatial position of the predicted point, and the reconstruction effect of the wind field based on the fluctuating wind pressure is obviously better than the that based on the mean wind pressure. When the POD method is used to predict the wind pressure of an unknown point, different interpolation methods can achieve ideal results. Among them, the bilinear interpolation method has the highest prediction accuracy, and the adjacent point interpolation method and Griddata V4 interpolation method only have certain errors in the low frequency region.

The Correlation of Carpal Tunnel Pressure with Clinical Outcomes following Ultrasonographically-Guided Percutaneous Carpal Tunnel Release.

Background: To evaluate the correlation between carpal tunnel pressure (CTP) and the clinical presentations, and to explore the possible predictors for the postoperative recovery pattern in patients with carpal tunnel syndrome (CTS). Materials and Methods: Consecutive patients with idiopathic CTS following percutaneous ultrasound-guided carpal tunnel release (UCTR) were enrolled. CTP was measured preoperatively and immediately after operation. The Boston Carpal Tunnel Questionnaire (BCTQ) and the cross-sectional area (CSA) of median nerve were recorded preoperatively and at 1, 3, and 12 months postoperatively. Results: 37 patients (37 hands; 8 men and 29 females; median age, 59.0 years) were enrolled. CTP significantly decreased immediately from 40.0 (28.0–58.0) to 13.0 (8.0–20.0) mmHg after UCTR. BCTQ scores significantly improved at 1 month postoperatively, and the improvement trend persisted until 12 months postoperatively (p < 0.001). Preoperative CTP was positively correlated with preoperative CSA and preoperative BCTQ scores (p < 0.05, all). Using group-based trajectory modeling, all patients were categorized into the “gradual recovery” or “fast recovery” group. Higher preoperative CTP was significantly associated with a faster recovery pattern (odds ratio: 1.32). Conclusions: Preoperative CTP was well correlated with the clinical presentations and might be a useful predictor for the postoperative clinical recovery pattern.

Study on the Surrounding Rock Pressure Characteristics of Loess Tunnel Based on Statistical Analysis in China

A method of load calculation in a tunnel was adopted in consideration of the state of covering depth. Due to the macropore characteristics of loess soil, the existing demarcation regulations of deep and shallow tunnels are inappropriate for large-section and shallow loess in highway tunnels. To determine the load of large-section loess tunnel and provide a proper reference for structural design, the theoretical basis for distinguishing depth of deep and shallow tunnels, as well as the characteristics of common calculation methods for surrounding rock load on depth, were analyzed. Through statistical analysis and significance analysis, the significance of the variation of surrounding rock pressure with cover depth was studied. Correlation analysis was carried out on significant results to fit the relationship between cover depth and surrounding rock pressure. The results showed that the surrounding rock pressure varied linearly with the cover depth, and the surrounding rock pressure was about 0.3 times the initial pressure in deep tunnels. The surrounding rock pressure of shallow tunnels did not change significantly with the cover depth, and the surrounding rock pressure was loose pressure. A method based on statistics was proposed to distinguish the cover depth threshold (CDT) of deep and shallow tunnels.

The axial fan design and commissioning test with nonuniform inlet flow

According to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel, combined with the fan aerodynamic efficiency and wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and flow rate in wind tunnel circuit is derived. So a new method for fan rotor blade setting angle adjustment to satisfy the fan performance at off-design point by getting the test results of fan operating parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Following the new method, the fan rotor blade setting angle adjusting value was provided directly only with the fan rotating speed and flow velocity in the wind tunnel test section, the adjusting target was achieved successfully by the new blade setting angle, the cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60m/s, the fan rotating speed is 570rpm, the deviation from the predicted fan rotating speed value of 575rpm is 0.9%. For the same test section flow velocity, the predicted value and the real value of the fan rotating speed are in good agreement, it proves that this method is reliable and accurate in practical application.

Effect of Earthquake on Pressure Arch above the Tunnel

Abstract In this paper, the changes in the pressure arch height above the tunnels subject to earthquake were analyzed by using theoretical, numerical, and experimental ways, respectively, and then, a corresponding formula was derived. The phenomenon of stress rotation and pressure arch around the tunnel under earthquake was found by illustrating the stress vector around tunnel. The force transmission method was used to analyze the change in pressure arch height of rectangular, horseshoe-shaped, and circular tunnels before and after earthquake, and then, a new method was presented to determine the pressure arch height above the tunnel under earthquake according to stress changes in surrounding rock. Then, the two methods were jointly used to analyze the pressure arch height above the tunnel. The results show that the tunnel shape has great effect on the shape of pressure arch, and the pressure arch height of deep tunnel varies little with depth. The changes in the shape and height of tunnel pressure arch before and after earthquake obtained from theoretical analysis and numerical simulation were finally verified by shaking table model tests. The research results in this paper may provide practical significance in seismic design of tunnel structures.

Overall Instability Failure Mechanism and Monitoring Strategy Research of the Shallow Tunnel under Unsymmetrical Pressure during Operation Period

Aiming at the safety of tunnel operation, based on the investigation and statistical analysis of a large number of operating tunnel diseases, comprehensively considering the interaction between the surrounding rock and the structure, this paper establishes the failure criteria for surrounding rocks and lining materials by using numerical limit analysis and theoretical analysis methods, analyzes the overall stability and instability failure mechanism on the shallow tunnel under unsymmetrical pressure during the operation period by using the strength reduction method in light of the operation safety of the tunnel, proposes the reasonable monitoring strategy, and also constructs monitoring index system. The analysis and research results show that the tunnel structure is affected by bias pressure due to the asymmetry of the terrain. The probability of disease in the bias pressure tunnel under asymmetric terrain conditions is significantly higher than that of the general terrain. The shallow tunnel under unsymmetrical pressure has experienced three development stages from shear failure to overall instability, including rock mass fracture and sliding, structural damage, and overall instability, which can be divided into eight processes. During operation, the key monitoring indicators of surface deformation are the subsidence and deformation of the slope top and the horizontal displacement of the slope itself, followed by the monitoring of the uplift and deformation at the bottom of the slope. Meanwhile, close attention should be paid to the structural stress states in the sliding direction and perpendicular to the sliding direction of the lining structure, which demonstrates that the principal compressive stress in the sliding direction is more sensitive than the principal tensile stress in perpendicular to the sliding direction and should be listed as the key monitoring and early warning indicators of the structural stress.

Elastic-plastic solution of circular hydraulic pressure tunnel based on D-P criterion

This work provides new findings on the theory of D–P failure criterion applied to the study of the analytic solution of the radius and stress of tunnel plastic zone and the periphery displacement of hydraulic pressure tunnel under uniform ground stress field. It focuses on elasto-plastic rock masses with the stage of construction and operation. The results that are obtained are compared to other calculation techniques and show that: The elastic-plastic solution calculated based on the theoretical model is larger than that based on the D-P Criterion, indicating safer conditions. The principal stress varies with the internal water pressure, and it firstly decreases to zero and then gradually increase in the plastic zone. With the internal water pressure keeping increasing to a high level, the principal stress in the elastic zone changes from tangential stress to radial stress in the radial distance-enlarging direction, which tends to reach the geostress. In this condition, the radial distance is related to the value of internal water pressure. The calculation results of this study are demonstrated to be in good agreement with those of numerical simulation under the same conditions.

Flutter test of rudder with real servo actuator in continuous transonic wind tunnel

Flutter wind tunnel test is an important approach of investigation of transonic flutter characteristics of flight vehicle. Comparing with the blow-down wind tunnel, the long-running and low dynamic pressure capabilities of continuous transonic wind tunnel are very suitable for flutter test. The flutter safety protection and analysis of dynamic signals are developed. The safety protection control software, rapid reduction of Mach number and dynamic pressure, model debris catch screen are integrated, which can provide safety protection of test model and wind tunnel. During the test process, the flutter boundary can be achieved by interpolating the reciprocal of spectrum peak. The flutter tests of rudder are conduct through two methods of step and continuous varying dynamic pressure. It is illustrated that the error of flutter dynamic pressure is relatively small, less than 5% between the two methods. Meanwhile, the feedback effect of the real servo actuator on the flutter characteristics is hard to be obtained via numerical simulation. It is demonstrated that the flutter dynamic pressure has been increased by 10% due to the feedback effect.

Effects of slight flexion-extension and radial-ulnar deviation postures on carpal tunnel volume

BackgroundNon-neutral wrist postures are a commonly reported risk factor for carpal tunnel syndrome. It is unclear how slight flexion-extension and radial-ulnar deviation postures affect the carpal tunnel. The objective was to determine the effects of slight non-neutral postures by quantifying carpal tunnel volume. MethodsComputed tomography images were collected on ten cadaveric specimens in target postures of −20°, −10°, −5°, 0°, 5°, 10°, and 20° of flexion and − 10°, −5°, 0°, 5°, and 10° of radial-ulnar deviation. Surface meshes of the carpal tunnel, carpal bones, radius, and third metacarpal were generated with manual segmentation. Carpal tunnel volume was calculated as the volume between proximal and distal boundaries defined with anatomical landmarks and the orientation of the tunnel. The precise wrist posture of each scan was determined with inertial-based coordinate systems of the radius and third metacarpal. FindingsThrough multiple linear regression it was determined that, over the observed range of postures, flexion-extension angle does not have a significant effect (p = 0.99) while radial-ulnar deviation angle has a significant effect of −5.9 mm3/degree (p = 0.003). The findings were consistent with previous studies of postural effects on carpal tunnel pressure. InterpretationFor the treatment and prevention of carpal tunnel syndrome, results suggest that attention should be given to slight radial-ulnar deviation postures (<10°), while slight flexion-extension postures (<20°) are of lesser consequence to carpal tunnel volume.

The Relationship between Shear Wave Velocity in Transverse Carpal Ligament and Carpal Tunnel Pressure: A Finite Element Analysis

The Relationship between Shear Wave Velocity in Transverse Carpal Ligament and Carpal Tunnel Pressure: A Finite Element Analysis

Wind tunnel pressure data analysis for peak cladding load estimation on a high-rise building

A correct evaluation of wind loads on high-rise building cladding panels is essential to ensure safety while avoiding costly over-design. The estimation of peak design loads from wind tunnel tests requires post-processing pressure time histories to remove small-scale fluctuations that do not significantly affect the total load on cladding elements. This post-processing commonly employs a low pass filter with a time-scale that is linearly proportional to the ratio of a reference length scale and velocity. The objective of this study is to analyze the equivalence between the moving-average filter and the spatial averaging procedure, focusing on panels near the top corners and edges of a high-rise building. The real area-averaged pressure is calculated using high-resolution pressure measurements and compared to estimates obtained from moving-average filters with a range of time-scales. The error is within ±1Cp for most pressure tap locations and panels analyzed, although some locations near the top edge result in overestimates of the peak suction up to 3Cp. The optimal value of the proportionality coefficient defining the filter time-scale is shown to be dependent on both pressure tap location and panel size, suggesting that accurate estimates of area-averaged pressures based on single-point measurements require more advanced post-processing techniques.

STUDY ON PROPULSIVE PERFORMANCE OF TWO GEOMETRICALLY SIMILAR PODDED PROPULSORS

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

Analytical solutions of noncircular tunnels in viscoelastic semi-infinite ground subjected to surcharge loadings

The construction of noncircular tunnels at shallow depths has become increasingly common in urban areas to efficiently utilize underground space. In general, noncircular tunnels may cause high stress concentrations and large settlements. In addition, the stability of shallow tunnels affected by the structural loads/surcharge loads on the surface is too significant to ignore. This study presents new analytical solutions to efficiently predict the stresses and displacements around shallow noncircular tunnels in rheological rock. The key factors, i.e., any viscoelastic characteristics of the surrounding rock, arbitrarily distributed loads exerted on the ground surface, arbitrary tunnel shapes and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account. A noncircular tunnel in the half-plane was mapped into an anulus by employing the conformal mapping function. Then, the elastic solutions of the problem are obtained by complex variable theory combined with the mapping function. Based on the elastic solutions and the extended corresponding principle for the viscoelastic problem, time-dependent analytical solutions are obtained for the ground assuming any viscoelastic models. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. Then, a parametric study is finally performed to investigate the influence of the location or range of the surcharge, tunnel burial depth and lateral pressure coefficient on the ground stresses and displacements. The proposed analytical solution can provide insight into the mechanical behavior of shallow noncircular tunnels under surcharge loads, as well as an alternative method in the preliminary designs of future shallow tunnels.

Control of non-Darcian flow by consolidation grouting in the surrounding rocks of a concrete-lined pressure tunnel

A concrete-lined hydraulic tunnel is currently under construction for water diversion and power generation in the Yangjiang Pumped Storage Power Station, Guangdong Province. This tunnel will be subjected to a maximum hydrostatic pressure of ∼ 8 MPa during operation. This will present an extremely high pressure gradient in the surrounding rocks, which in turn may induce non-Darcian flow and even hydraulic fracturing in the fault and fracture system. How to control this unfavourable effect becomes one of the key technological issues for design and reinforcement of this tunnel. In this study, the groundwater flow behaviours in the surrounding rocks are investigated with Forchheimer’s law-based numerical simulations. The hydraulic properties are determined by in-situ packer tests and a universal correlation between hydraulic conductivity K and non-Darcian coefficient β (i.e., ). The performance of high-pressure grouting in suppressing the non-Darcian flow effect is quantified. The numerical results show that when the depth of grouting reaches 6 m, the grouting zone is effective in controlling the groundwater flow in the regime of Darcian flow in the fault zones and fracture network, and in reducing the amount of leakage out of the tunnel and lowering the risk of hydraulic fracturing in the surrounding rocks. This work provides valuable insights for understanding the role of consolidation grouting in controlling the groundwater flow behaviours in fractured rocks surrounding high-water pressure tunnels.

Numerical Modeling Method and Experimental Verification of Prestressed Lining with Unbonded Annular Anchors

Prestressed lining with unbonded annular anchors is a new type of lining used in hydraulic pressure tunnels. First, the key points of numerical modeling are analyzed based on the stress characteristics of the lining. Thus, the corresponding modeling methods are proposed: the contact relationship is set to simulate the different constraint effects of surrounding rock on the lining, the equivalent load and solid model are superposed to simulate the changing prestress state of anchors, and the nonlinear distribution of prestress loss is simulated by applying the gradient load in sections. Finally, based on the finite-difference software FLAC3D, the modeling analysis of Xiaolangdi pressure silt-releasing tunnel in an engineering case is conducted to verify the correctness of the modeling method presented in this study. The research shows that the new modeling method has a clear principle, fast modeling, and reliable results, which is of guiding significance to structure design.

Structural Characteristics and Design of the New Prestressed Linings with Unbonded Annular Anchors

The new prestressed reinforced concrete lining with multi-layer (up to 2) multi-hoop (up to 2) un-bonded annular anchors (hereinafter referred to as MUAA lining) is a new type of structure suitable for hydraulic pressure tunnel. The structural characteristics and design concept of MUAA lining are put forward through comprehensively analysis on the structural system, annular anchor winding mode, internal force transfer process, anchorage block-out position and lining thickness. This lining produces radial precompressive stress of the concrete through the unbonded annular sealing curve anchor cable embedded in the jack tensioning lining, which makes full use of the superior tensile and imperforation performance of the prestressed concrete structure, and at the same time the surrounding rock is not required to provide all the reaction force. It can reduce load sharing of the surrounding rock by increasing the active prestress of anchors, and it is not limited by the geological conditions of surrounding rock, so it has broad engineering application value.

Effect of ergonomic Armrest® forearm support on wrist posture related to carpal tunnel pressure during computer mouse work

ObjectiveWe validated the effect of moveable arm support (Armrest®) on wrist posture during three standardized tasks. BackgroundThe use of the computer mouse has been increasing over the years and it has been identified as one of the occupational activities related to carpal tunnel syndrome (CTS). The main mechanism for CTS is carpal tunnel pressure (CTP) that could be estimated from the wrist posture. MethodUsing an electronic goniometer, we assessed wrist extension/flexion and ulnar-radial flexion in 15 participants (age: 34.8 [8.7] years) and calculated the time the wrist posture was outside the threshold values previously related to CTP. Specifically, we estimated time when wrist posture yielded >25 mmHg of CTP: wrist extension >32.7°; wrist flexion < −48.6°; wrist ulnar flexion >14.5°; and wrist radial flexion < −21.8°. ResultsAverage wrist extension/flexion tends to be 13.4° lower (p = 0.063), while radial-ulnar flexion was 13.2° lower (p = 0.025) when Armrest® forearm support was used in comparison to fixed forearm support. Furthermore, the time spent outside the threshold wrist extension was 25.8% (p = 0.018) lower and ulnar flexion was 37.2% (p = 0.017) lower when using Armrest® compared to a fixed forearm support. Results were independent from tasks. ConclusionArmrest® diminished the time spent outside the threshold values related to 25 mmHg of CTP indicative of CTS. ApplicationA moveable arm support is a simple and effective way to increase occupational health during computer mouse work.

Modelling and iterative learning control of internal pressure for high-speed trains under excitation of varying-amplitude tunnel pressure waves

Traditional control algorithm of shutting down the air ducts for a fixed period is not applicable to take both the riding comfort and the air quality inside high-speed train carriages into account in long tunnels. Inspired by the morphological similarity of the tunnel pressure waves generated by the same train passes through the same tunnel, an upgraded iterative learning control algorithm for suppressing the air pressure variation excited by the quasi-periodic varying-amplitude tunnel pressure wave is developed. Firstly, the mathematical model of the control system is established, in which the air ducts, gaps and random interferences are considered. Then, the methodology of determining the goal in each iteration is formed, and the implementation of the iterative learning control algorithm is discussed. Finally, simulations of the algorithm are carried out. The simulation results show that in the upgraded iterative learning control algorithm, both the goal and the output of the air pressure inside the carriage will converge into a range determined by the amplitude and random interferences. By comparing with the traditional control algorithm, the upgraded iterative learning control algorithm is more adaptable to meet the needs of riding comfort.

Retrofitting of Pressurized Sand Traps in Hydropower Plants

Unlined pressure tunnels in sound rock, combined with pressurized sand traps at the downstream end, allow for low-cost construction of hydropower tunnel systems. This design concept is utilized in hydropower plants across the world. Currently, many such power plants are being upgraded with higher installed capacity, which may result in challenges with the sand trap efficiency. A physical scale model test, accompanied by 3D CFD simulations of a case study pressurized sand trap, has been studied for economic retrofitting. The geometric model scale is 1:36.67 while the velocity scale and sediment scale are 1:1 (same average flow velocity and sediment size in model and prototype). This is currently an uncommon scaling approach but with several advantages, as presented in this paper. Various options for retrofitting were investigated. A combined structure of ramp and ribs was found to significantly improve the sediment trap efficiency. The main novelties from this work are the proposed design of the combined ramp and rib structure. Secondary results include an efficient setup for physical scale models of pressurized sand traps and a methodology that combines the benefits of 3D CFD simulations with physical scale models testing for sand trap engineering and design.