Short Tunnel Research Articles

A method for evaluating the safety of freeway tunnel sections based on driving comfort - a naturalistic driving study

Objective Driving comfort is crucial for tunnel safety because tunnel sections on freeways often introduce significant environmental changes that can compromise comfort and increase the risk of traffic accidents. This study aimed to quantitatively evaluate the driving comfort in tunnel sections and its implications for safety management. Methods Four indicators were used to assess the driving comfort: heart rate growth rate (Hrgr), skin conductance response (SCR), speed, and acceleration. The CRITIC weighting method was employed to calculate a quantitative driving comfort score, and the presence and severity of discomfort were used to evaluate the safety of each tunnel area. In addition, the evaluation was based on a naturalistic test consisting of Hrgr, SCR, speed, and acceleration data. A total of 32 participants were recruited based on a web-based questionnaire screening process, after which they were tested while driving through 30 tunnel sections on the roadway. These 30 tunnels included 14 short (< 500 m), 12 medium (500–1,000 m), and 4 long (1,000–3,000 m) tunnels. Results The results revealed that the four selected indicators exhibited minimal multicollinearity and effectively captured the driving comfort. Among the indicators, SCR had the most significant contribution to the driving comfort score. Most drivers did not experience substantial discomfort while driving through tunnels. The area where drivers were most susceptible to discomfort was the middle zones of tunnels. However, drivers were more likely to experience strong discomfort in the outside exit, entrance, and middle zones of short, medium, and long tunnels, respectively. Conclusions This study provides a comprehensive set of safety evaluation methods for tunnel sections on freeways, with a focus on quantifying the driving comfort. The findings provide theoretical support for freeway management personnel in implementing personalized controls in different tunnel areas with the aim of enhancing tunnel safety and mitigating the occurrence of traffic accidents.

Cluster Analysis of Freeway Tunnel Length Based on Naturalistic Driving Safety and Comfort

The tunnel is an important component of freeway operation safety, and its classification method is the foundation of a refined management of operation safety. At present, the impact of different categories of tunnels on driver safety, comfort, and driving behavior under naturalistic driving conditions is not clear, and there is a lack of classification methods for tunnels of different lengths in their operation stages. This paper was based on the driving workload, which effectively expresses the safety and comfort of drivers. In this context, naturalistic driving experiments in 13 freeways and 98 tunnels with 36 participants were carried out. The DDTW+K-Means++ algorithm, which is suitable for drivers’ driving workload time series data, was used for a clustering analysis of the tunnels. According to the length of the tunnel, the operation-stage tunnels were divided into three categories: short tunnels (&lt;450 m), general tunnels (450~4000 m), and long tunnels (&gt;4000 m). The length of the tunnel had a positive correlation with the drivers’ driving workload, while there was a negative correlation with the vehicle running speed, and the range of changes in the drivers’ driving workload and operation safety risks in general tunnels and long tunnels was higher than that in short tunnels. Road and environmental conditions are important factors affecting the driving workload. The entrance area, the exit area of tunnels, and the middle area of long tunnels are high-risk sections in the affected area of the tunnel. These research results are of great significance for the operation safety management of freeway tunnels.

Predicting of tunneling resistivity between adjacent nanosheets in graphene–polymer systems

In this work, the tunneling resistivity between neighboring nanosheets in grapheme–polymer nanocomposites is expressed by a simple equation as a function of the characteristics of graphene and tunnels. This expression is obtained by connecting two advanced models for the conductivity of graphene-filled materials reflecting tunneling role and interphase area. The predictions of the applied models are linked to the tested data of several samples. The impressions of all factors on the tunneling resistivity are evaluated and interpreted using the suggested equation. The calculations of tunneling resistivity for the studied examples by the model and suggested equation demonstrate the same levels, which confirm the presented methodology. The results indicate that the tunneling resistivity decreases by super-conductive graphene, small tunneling width, numerous contacts among nanosheets and short tunneling length.

Overcoming sub-threshold slope degradation by the advances of TFETSs materials

With the scaling of devices in the past few decades, a lot of problems arise include short tunnel effect and significant power consumption, in which sub-threshold slope is a considerate factor. However, Sub-threshold Slope of MOSFET is limited to 60 mV/decade at room temperature due to Boltzmann Tyranny. TFETs (Tunnelling Field Effect Transistors) are the most promising field-effect transistors candidates owing to its potential to overcome sub-threshold slope degradation. This article illustrates the main principles of TFETs and explains how TFETs can overcome sub-threshold slope degradation through tunnelling effect. Furthermore, this article introduces the advances of TFETs materials to optimize devices performances.

The Contamination of the Lower Layer in Sloped Tunnel Fires

Fires in tunnels are a major concern due to the casualties they may cause. Therefore, forced ventilation is mandatory in long tunnels, despite the significant associated costs. In shorter tunnels, however, natural ventilation may be sufficient to comply with safety regulations. Accordingly, the analysis of natural fire smoke flow is relevant for tunnels shorter than 1000 m. This paper presents a computational investigation of the influence of the tunnel slope on the contamination of the cold lower layer with smoke and discusses how it impairs the user’s egress. Large-eddy simulations of the smoke propagation show three different regimes, namely, a quasi-horizontal tunnel behavior for a slope of 0.5%, a transitional behavior for slopes in the range of 1% to 5% and a quasi-forced ventilation behavior for a slope of 7%. The computational results are compared with the application of 1D equations to predict the upper layer temperature, the average mass flow rate, the upper layer mass flow rate, the upper layer velocity and the lower layer velocity. The distance from the fire to the location where the lower layer contamination with smoke starts is accurately predicted by the one-dimensional model for slopes of 2% and 3.5%. However, in the case of lower or higher slopes, the one-dimensional model performs poorly and needs further improvement.

Effect of contact number among graphene nanosheets on the conductivities of tunnels and polymer composites

Simple equations are expressed for tunnel conductivity, tunnel resistance and conductivity of a graphene-filled composite by the number of contacts and interphase part. More specially, the active filler amount is suggested by interphase depth, which changes the contact number. The conductivity of nanocomposite is presented by filler content, filler dimensions, tunneling length and interphase depth. The innovative model is surveyed by the experimented conductivity of real examples. Too, the impacts of numerous issues on the tunnel resistance, tunnel conductivity and conductivity of nanocomposite are discussed to validate the novel equations. The estimates agree with the experimented data and the impacts of several terms on the tunnel resistance, tunnel conductivity and conductivity of system are sensible. Thin and big nanosheets positively affect the nanocomposite’s conductivity, but thick nanosheets improve the tunnel conductivity. High conductivity is found at short tunnels, while the nanocomposite’s conductivity directly depends on the tunneling length. The dissimilar effects of these features on the tunneling properties and conductivity are described.

Double-flanged polypropylene technique: 5-year results.

To assess the long-term (5-year) results and complications of the double-flanged polypropylene technique in patients with capsular tension segment fixation, nonfoldable intraocular lens (IOL) scleral fixation, and foldable IOL scleral fixation. Santa Casa de Belo Horizonte and Centro Oftalmológico de Minas Gerais. Prospective case series. Eyes that underwent treatment using the double-flanged polypropylene technique between September 2016 to September 2021 were included. LogMAR visual acuity was recorded, as well as complications such as long-term polypropylene resistance, conjunctival erosion, conjunctival inflammation, flange exposure, internalization, endophthalmitis, retinal detachment, and cystoid macular edema. 71 eyes of 61 patients were evaluated. The mean follow-up period for these eyes was 28.2 ± 14.3 (min: 4; max: 60; median: 26) months. 173 flanges were performed. 13 cases with sub-Tenon flanges (7.5%) were observed. 5 exposed flanges (2.89%), presented after a mean of 1.8 weeks postoperatively, were observed. 1 patient with large flanges presented with conjunctival inflammation and hyperemia. 2 late internalized flanges (1.1%) and 2 recently internalized flanges (1.1%) were observed. 3 eyes (4.22%) had retinal detachment. Moreover, cystoid macular edema was detected in 3 eyes (4.22%). No cases of endophthalmitis were observed. The double-flanged technique was proven to be stable when the correct technical procedure was followed. However, complications can be observed, especially with short scleral tunnels and in eyes where the flanges were not buried inside the sclera.

Comparison of Short and Long-Tunnel Needle Track for Ahmed Glaucoma Valve Implantation in a Private Eye Center in the Philippines: A Retrospective Study.

This study aimed to compare the success and complication rates among patients implanted with Ahmed Glaucoma Valve (AGV) using the short and long tunnel technique through retrospective chart review. We reviewed 54 charts of adult patients who underwent AGV implantation using a Short-Needle Track (SNT) or Long-Needle Track (LNT) technique. Intraocular pressures (IOP), Best Corrected Visual Acuity (BCVA) and number of medications were recorded pre-operatively, and at Day 1, 3, 7, Month 1, 3, 6 post-operatively. Treatment success, occurrence of Hypertensive Phase (HP), complication and procedures done after AGV implantation were compared between the two groups using one-tailed Z-test of proportions. A total of 20 (LNT) and 21 (SNT) charts were included in the study. There was no significant difference between the median postoperative IOP, BCVA, and number of anti-glaucoma medications between the two groups at each time interval. The comparison between the occurrence of HP (P = 0.435) and success rates (P = 0.476) between the two groups yielded no significant difference. Flat/shallow anterior chamber (AC) was seen exclusively in three eyes (14%) in the SNT group (P = 0.039). There was one occurrence of plate exposure in the LNT group (P = 0.149). The LNT technique of AGV Implantation may be used as an alternative to the traditional SNT (with autologous graft). The long needle track offers the advantage reducing the risk of complications arising from shallow anterior chamber post-operatively.

Trends in the development of measurement microphones

Measurement microphones are, in principle, simple transducers that convert dynamic pressure fluctuations into an electrical output signal. The range of applications is, however, extremely wide-from measuring exceptionally low-level signals (below 0 dB; for example, measuring tiny insects) to the 190 dB signal of large rocket launches. The frequency range of interest spans from below 0.1 Hz for sonic boom measurements to 200 kHz or more for detailed investigations of very short impulses or wind tunnel scale modelling. At the same time, the individual application may mandate specific mounting conditions with specialized form factors for the microphone and associated preamplifier design. This trend towards application-specific testing has led to the development of a wide range of specialized microphones and accessories. Still, this wide variety of measurement microphones must measure accurately and be calibrated to be traceable to the basic unit of measure as, for example, defined by the SI system. This is ensured by maintaining reference to the basic IEC definition of measurement microphones in the IEC 61094 series of standards for microphones and calibration methods.

Anatomical predictors for suture-based closure of the patent foramen ovale: A multicenter experience.

NobleStitch EL is a novel suture-based technique used for patent foramen ovale(PFO) closure and an alternative to traditional double-disc devices without the need for antithrombotic therapy. However, successful closure rates are still unknown, and certain anatomies may be unfavorable for successful closure. We assessed the efficacy of the NobleStitch EL and sought to identify patient-related anatomical features associated with successful suture-based closure. We included 55 patients who underwent PFO closure with the NobleStitch EL in The Netherlands and Switzerland. Successful closure was defined as residual right-to-left shunt grade ≤1 with Valsalva maneuver at a cardiac ultrasound. Predefined possible anatomical determinants for effective closure included PFO length, atrial septal aneurysm, PFO entry- and exit diameter. Successful closure was achieved in 33 patients (60%). The PFO length was shorter in patients with successful closure compared to unsuccessful closure with a median length of 9.6 mm (IQR 8.0-15.0) versus 13.3 mm (IQR 11.4-18.6) on preprocedural ultrasound (p = 0.041) and 9.9 mm (IQR 8.0-13.1) versus 12.5 mm (IQR 9.7-15.4) on angiography (p = 0.049). Additionally, the PFO exit diameter and PFO volume were smaller in patients with successful closure than unsuccessful closure, with a mean diameter of 7.0 ± 3.1 mm versus 9.5 ± 3.8 mm (p = 0.015) and a median volume of 381 mm3 (IQR 286-894) versus 985 mm3 (IQR 572-1550) (p = 0.016). In our study cohort, the successful PFO closure rate using NobleStitch EL was relatively low (60%). With this alternative procedure, patients with a small PFO driven by a short PFO tunnel length and small exit diameter seem to be eligible for successful suture-based closure.

Parameter design of solar optical reflection lighting system array for shadowless lighting in threshold zone of short freeway tunnel

A solar optical reflection (SOR) lighting system has been developed to illuminate the threshold zone of short freeway tunnel in the premise of zero energy consumption. To improve the limited illumination performance of SOR lighting system due to the obstruction of moving vehicles on reflected sunlight rays, this study develops a fast and simple parameter design method for shadowless lighting based on an array of multiple SOR lighting systems that makes reflected sunlight emit to the threshold zone from different angles. The effectiveness of shadowless lighting is verified by the application on a two-lane freeway of Shaanxi Province, China. Results show that the shadowless lighting can significantly improve the illuminance in threshold zone, and the improvement rate is higher for the area farther from the tunnel entrance inside the tunnel. In order to achieve shadowless lighting avoid both the vehicle and inter-system blocking on reflected sunlight, the systems should be installed roadside in a staggered array that: 1) their heights descend and lateral distances from the curb shrink in turn from near to far from the tunnel entrance, with as small vertical and horizontal deflection angles of the reflectors as possible, or 2) their heights remain identical with a reduction in the vertical deflection angles of the reflectors from near to far from the tunnel entrance.

Refining the NobleStitch PFO closure technique using an anatomy-tailored approach.

Key Points Patent foramen ovale (PFO) tunnel width and length can help predict successful closure after NobleStitch. A maximal tunnel width/shortest length ratio ≤0.61 is a good predictor of a significant (grade 2–3) residual right‐left shunt after a single stitch at follow‐up. Consideration of using two stitches for patients with large and/or short PFO tunnels should be made at the index procedure.

Prediction of along-wind loading on tall building based on two-dimensional aerodynamic admittance

The mismatch of simulated turbulence integral scale may occur in some wind tunnel model tests, especially in a short wind tunnel, which would lead to inaccurate prediction of the wind loading based on traditional aerodynamic admittance (traditional AAF) containing the three-dimensional effect (3D-effect). For this, a method for prediction of along-wind loading on tall building based on two-dimensional aerodynamic admittance (2D-AAF) is introduced. The key to the method is to identify the 2D-AAF which does not contain the 3D-effect through separating the 3D-effect from the traditional AAF. With this method, the 2D-AAFs of the along-wind loading of a CAARC building model in two turbulent flow fields with different turbulence integral scales are identified. As expected, the traditional AAF which contains 3D-effect changes with the turbulent flow field because 3D-effect is related to the turbulence integral scale. Different from the traditional AAF, the 2D-AAFs obtained in two different turbulent flow fields are almost consistent, confirming that the 2D-AAF is independent of the turbulence integral scale. An empirical expression for the 2D- AAF of along-wind loading of CAARC building is then proposed by fitting the experimental data. A comparison between the high-frequency-force-balance (HFFB) measurements conducted in a simulated boundary layer flow field and the prediction values shows that the reproduced spectrum of along-wind loading based on the 2D-AAF has high accuracy, verifying the validity of proposed prediction method.

Simulating of effective conductivity for graphene–polymer nanocomposites

The efficient conductivity of graphene-polymer systems is expressed supposing graphene, tunneling and interphase components. The volume shares and inherent resistances of the mentioned components are used to define the efficient conductivity. Besides, the percolation start and the share of graphene and interphase pieces in the nets are formulated by simple equations. Also, the resistances of tunneling and interphase parts are correlated to graphene conductivity and their specifications. Suitable arrangements among experimented data and model’s estimates as well as the proper trends between efficient conductivity and model’s parameters validate the correctness of the novel model. The calculations disclose that the efficient conductivity improves by low percolation level, dense interphase, short tunnel, large tunneling pieces and poor polymer tunnel resistivity. Furthermore, only the tunneling resistance can govern the electron transportation between nanosheets and efficient conductivity, while the big amounts of graphene and interphase conductivity cannot play a role in the efficient conductivity.

MP70-12 THE WIDE URETER AND THE SMALL BLADDER, THE CUFF-NIPPLE REIMPLANTATION RATHER THAN URINARY DIVERSION

You have accessJournal of UrologyCME1 Apr 2023MP70-12 THE WIDE URETER AND THE SMALL BLADDER, THE CUFF-NIPPLE REIMPLANTATION RATHER THAN URINARY DIVERSION Moneer Hanna and Wael Abosena Moneer HannaMoneer Hanna More articles by this author and Wael AbosenaWael Abosena More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003338.12AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Reimplantation of a dilated Ureter into an infantile small capacity bladder represents a surgical challenge. The surgical options for reflux megaureters who developed breakthrough urinary infections while on prophylaxis are temporary diversion (vesicostomy for bilateral and ureterostomy for unilateral megaureters). In cases of obstructed megaureter the options are ureterostomy and refluxing reimplantation. METHODS: Between 1995 and 2021, 46 infants aged 3 and 12 months were referred for surgical management following recurrent pyelonephritis while on prophylaxis (30 infants) and for worsening hydronephrosis (16 infants). There were 32 boys and 14 girls. The diagnosis was bilateral reflux megaureters in 18 and unilateral in 8 children. The other twenty children had bilateral obstructed megaureter in 9 and unilateral in 11 children. The radionuclide renal scan was performed in 43 children, and it showed reflux nephropathy in 35 kidneys with VUR and reduced function of more than 20% in 9/11 obstructed kidneys. A total of 73 megaureters were operated on. The ureteral tortuosity was straightened, and the caliber was reduced when indicated. Each ureter was reimplanted in a short (1 cm) submucosal tunnel, a cuff-nipple ureteral orifice was created in 62/73 ureters. Simple cuff-nipple without submucosal tunnelling in 11 ureters. RESULTS: The postoperative course was uneventful in all children and follow up US & VCUG were done at four months. Thereafter the follow-up continued by the pediatric nephrology service. The post operative US showed improved hydronephrosis in 59/73 kidneys and stable in 14 units. The VCUG showed no evidence of VUR in 58/62 (93%) of the group who had short tunnel and cuff-nipple reimplantation, in 4 ureters the VUR was downgraded to grade II. 10/11 (91%) of the ureters with the cuff-nipple without tunneling showed no evidence of VUR, and one ureter the VUR was grade II. 7 children had significant reflux nephropathy outgrew their renal function and underwent renal transplantation CONCLUSIONS: The time -tested Paquin dogma of tunnel length/width ratio of 5/1 was challenged by Lyons et.al, the latter contention was that the shape of the ureteral orifice (UO) is more important than the length of the tunnel for reflux prevention, (the cuff-nipple creates a volcano like UO). Recently Villaneuva et.al performed a parametric simulation study of ureteral collapse (LS-DYNA finite-element software). They confirmed Lyons observation. These observations would explain the high success rate which was achieved by the cuff-nipple technique. Source of Funding: none © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e1008 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Moneer Hanna More articles by this author Wael Abosena More articles by this author Expand All Advertisement PDF downloadLoading ...

Trends in the development of measurement microphones

Measurement microphones are, in principle, simple transducers that convert dynamic pressure fluctuations into an electrical output signal. The range of applications is, however, extremely wide—from measuring exceptionally low-level signals (below 0 dB; for example, measuring tiny insects) to the 190 dB signal of large rocket launches. The frequency range of interest spans from below 0.1 Hz for sonic boom measurements to 200 kHz or more for detailed investigations of very short impulses or wind tunnel scale modelling. At the same time, the individual application may mandate specific mounting conditions with specialized form factors for the microphone and associated preamplifier design. This trend towards application-specific testing has led to the development of a wide range of specialized microphones and accessories. Still, this wide variety of measurement microphones must measure accurately and be calibrated to be traceable to the basic unit of measure as, for example, defined by the SI system. This is ensured by maintaining reference to the basic IEC definition of measurement microphones in the IEC 61094 series of standards for microphones and calibration methods.

Finding shortcuts through collective tunnel excavations in a subterranean termite

Abstract Facilitating efficient resource transfer requires building an optimized transportation network which balances cost minimization with benefit maximization. For animals which forage for food located remotely, optimizing their transportation networks is critically related to survival. This process often involves finding and using the shortest route to save time and energy. Subterranean termites forage for wood resources by excavating underground foraging networks for search and transport. Because termites have no prior knowledge of food location during the food searching phase, establishment of a short tunnel between the nest and feeding site is difficult at the beginning of foraging. Thus, finding a short route should logically follow initial food discovery. However, it remains elusive as to how subterranean termites find the shortest route for food transportation. We simulated different scenarios using Coptotermes formosanus by providing different shapes and distances of pre-formed tunnels (straight, detour, and detour + twisting arenas) to food, where food items were located at a fixed distance from the arena entrance. Termites in the straight arena continuously used the pre-formed tunnel, showing negligible branching efforts. However, termites in the detour and detour + twisting arenas followed the pre-formed tunnel only for the initial few hours before excavating many branching tunnels. This branching activity ultimately resulted in termites finding shorter commuting routes than the pre-formed tunnels. In addition, the shortest established routes were widened over time. This study demonstrated that C. formosanus could actively alter tunnel networks to minimize the cost in food transportation by using short and wide tunnels.

Three-dimensional-printed patient-specific instrumentation is an accurate tool to reproduce femoral bone tunnels in multiple-ligament knee injuries

PurposeMultiple-ligament knee reconstruction techniques often involve the creation of several bone tunnels for various reconstruction grafts. A critical step in this procedure is to avoid short tunnels or convergences among them. Currently, no specific template guide to reproduce these angulations has been reported in the literature, and the success of the technique still depends on the experience of the surgeon. The aim of this study is to analyze the accuracy and reliability of 3D-printed patient-specific instrumentation (PSI) for lateral and medial anatomical knee reconstructions.MethodsTen cadaveric knees were scanned by computed tomography (CT). Using specific computer software, anatomical femoral attachments were identified: (1) on the lateral side the lateral collateral ligament (LCL) and the popliteal tendon (PT) and (2) on the medial side the medial collateral ligament (MCL) and the posterior oblique ligament (POL). Four bone tunnels were planned for each knee, and PSI with different directions were designed as templates to reproduce the planned tunnels during surgery. Twenty 3D-printed PSI were used: ten were tailored to the medial side for reconstructing MCL and POL tunnels, and the other ten were tailored to the lateral side for reconstructing LCL and PT tunnels. Postoperative CT scans were made for each cadaveric knee. The accuracy of the use of 3D-printed PSI was assessed by superimposing post-operative CT images onto pre-operative images and analyzing the deviation of tunnels performed based on the planning, specifically the entry point and the angular deviations.ResultsThe median entry point deviations for the tunnels were as follows: LCL tunnel, 1.88 mm (interquartile range (IQR) 2.2 mm); PT tunnel, 2.93 mm (IQR 1.17 mm); MCL tunnel, 1.93 mm (IQR 4.26 mm); and POL tunnel, 2.16 mm (IQR 2.39). The median angular deviations for the tunnels were as follows: LCL tunnel, 2.42° (IQR 6.49°); PT tunnel, 4.15° (IQR 6.68); MCL tunnel, 4.50° (IQR 6.34°); and POL tunnel, 4.69° (IQR 3.1°). No statistically significant differences were found in either the entry point or the angular deviation among the different bone tunnels.ConclusionThe use of 3D-printed PSI for lateral and medial anatomical knee reconstructions provides accurate and reproducible results and may be a promising tool for use in clinical practice.

Numerical assessment of dielectrically-modulated short- double-gate PNPN TFET-based label-free biosensor

A comprehensive investigation of dielectrically modulated Ge-source short double-gate PNPN tunnel FET (SG-PNPN TFET) based label-free biosensor is presented. Short gates and counter-doped pockets in the SG-PNPN TFET architecture improve band-to-band tunneling, which subsequently raises the device's drain current sensitivity. On the source side of the device, a nanocavity is created between the gate and the SiO2 layer. The sensing performance of the device was evaluated using the effect of the dielectric constant and charge density of the biomolecules. The non-ideal performance of the biosensor can be understood by analyzing the consequences of steric hindrance and irregular probe placement. The concave profile has the highest value of sensitivity among all the non-uniform profiles considered (including ascending, descending, concave, and convex). The sensitivity comparison of the proposed TFET biosensor with other FET-based biosensors revealed that the SG-PNPN TFET could function admirably as a low-power biosensor with improved sensitivity.

Modeling and stability investigation on the governor-turbine-hydraulic system with a ceiling-sloping tail tunnel

For a hydropower system with a relatively short tail tunnel and wide variation of tail water level, the ceiling-sloping tail tunnel (CSTT) is often recommended. Considering various flow patterns and traveling free-surface-pressurized interface in the CSTT, stability modeling and analysis of the governor-turbine-hydraulic system shows more challenging. Based on state equations analysis, an improved nonlinear model considering transition part, and a new linear model for downstream free-surface flow are derived. Further comparative analysis indicates that, by introducing these models, water flow characteristics in transition part have positive effect on operation stability with an around 4.0% increase of attenuation rate, while that of downstream free-surface flow has a negative effect with a 21.8% decrease rate on the absolute value of negative attenuation factor. For stability optimization of the CSTT, to properly increase its bottom width is preferable, herein with a 6.2% increase of attenuation rate for a 2.0 m increase of bottom width, while a reasonable ceiling slope should be optimized considering the counteraction effect of upstream pressurized flow and downstream free-surface flow. The new developed models and further discussion for the hydropower systems with a CSTT will greatly improve system's stability evaluation and advance the development of renewable energy.