This page has only limited features, please log in for full access.
This study presents, experimentally, similarity and Froude number similitude (FNS) in the dimensionless features of two solitary waves propagating over a horizontal bed, using two wave gauges and a high-speed particle image velocimetry (HSPIV). The two waves have distinct wave heights H0 (2.9 and 5.8 cm) and still water depths h0 (8.0 and 16.0 cm) but identical H0/h0 (0.363). Together with the geometric features of free surface elevation and wavelength, the kinematic characteristics of horizontal and vertical velocities, as well as wave celerity, are elucidated. Illustration of the hydrodynamic features of local and convective accelerations are also made in this study. Both similarity and FNS hold true for the dimensionless free surface elevation (FSE), wavelength and celerity, horizontal and vertical velocities, and local and convective accelerations in the horizontal and vertical directions. The similarities and FNSs indicate that gravity dominates and governs the wave kinematics and hydrodynamics.
Chang Lin; Ming-Jer Kao; James Yang; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; Shih-Chun Hsieh. Similarity and Froude Number Similitude in Kinematic and Hydrodynamic Features of Solitary Waves over Horizontal Bed. Processes 2021, 9, 1420 .
AMA StyleChang Lin, Ming-Jer Kao, James Yang, Rajkumar Venkatesh Raikar, Juan-Ming Yuan, Shih-Chun Hsieh. Similarity and Froude Number Similitude in Kinematic and Hydrodynamic Features of Solitary Waves over Horizontal Bed. Processes. 2021; 9 (8):1420.
Chicago/Turabian StyleChang Lin; Ming-Jer Kao; James Yang; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; Shih-Chun Hsieh. 2021. "Similarity and Froude Number Similitude in Kinematic and Hydrodynamic Features of Solitary Waves over Horizontal Bed." Processes 9, no. 8: 1420.
The stage-discharge relationship of a weir is essential for posteriori calculations of flow discharges. Conventionally, it is determined by regression methods, which is time-consuming and may subject to limited prediction accuracy. To provide a better estimate, the machine learning models, artificial neural network (ANN), support vector machine (SVM) and extreme learning machine (ELM), are assessed for the prediction of discharges of rectangular sharp-crested weirs. A large number of experimental data sets are adopted to develop and calibrate these models. Different input scenarios and data management strategies are employed to optimize the models, for which performance is evaluated in the light of statistical criteria. The results show that all three models are capable of predicting the discharge coefficient with high accuracy, but the SVM exhibits somewhat better performance. Its maximum and mean relative error are respectively 5.44 and 0.99%, and 99% of the predicted data show an error below 5%. The coefficient of determination and root mean square error are 0.95 and 0.01, respectively. The model sensitivity is examined, indicative of the dominant roles of weir Reynolds number and contraction ratio in discharge estimation. The existing empirical formulas are assessed and compared against the machine learning models. It is found that the relationship proposed by Vatankhah exhibits the highest accuracy. However, it is still less accurate than the machine learning approaches. The study is intended to provide reference for discharge determination of overflow structures including spillways.
Shicheng Li; James Yang; Anders Ansell. Discharge prediction for rectangular sharp-crested weirs by machine learning techniques. Flow Measurement and Instrumentation 2021, 79, 101931 .
AMA StyleShicheng Li, James Yang, Anders Ansell. Discharge prediction for rectangular sharp-crested weirs by machine learning techniques. Flow Measurement and Instrumentation. 2021; 79 ():101931.
Chicago/Turabian StyleShicheng Li; James Yang; Anders Ansell. 2021. "Discharge prediction for rectangular sharp-crested weirs by machine learning techniques." Flow Measurement and Instrumentation 79, no. : 101931.
Air entrainment at the intake of a bottom outlet often gives rise to air pockets in its conduit and formation of geysers. The outlet in question comprises a bulkhead gate, gate shaft, horizontal conduit, and exit. Operations show that it suffers from appreciable flow fluctuations and blowouts in the tailwater, which leads to gate operation restrictions. For the purpose of understanding the hydraulic phenomenon, both prototype discharge tests and three-dimensional computational fluid dynamics (CFD) modeling of two-phase flows are performed. The operational focus of the facility are small and large gate openings. The CFD results reveal that, with air entrained in the gate shaft, continual breakup and coalescence of air bubbles in the conduit typify the flow. At small openings below 1 meter, the air–water flow is characterized by either distinct blowouts of regular frequency or continuous air release. In terms of geyser behaviors inclusive of frequency, the agreement is good between field and numerical studies. At large openings, the gate becomes fully submerged, and the flow is discharged without air entrainment and blowouts. The paper showcases the air–water flow features in a typical bottom outlet layout in Sweden, which is intended to serve as an illustration of the study procedure for other similar outlets.
James Yang; Penghua Teng; Junhu Nan; Shicheng Li; Anders Ansell. Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation. Fluids 2020, 5, 203 .
AMA StyleJames Yang, Penghua Teng, Junhu Nan, Shicheng Li, Anders Ansell. Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation. Fluids. 2020; 5 (4):203.
Chicago/Turabian StyleJames Yang; Penghua Teng; Junhu Nan; Shicheng Li; Anders Ansell. 2020. "Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation." Fluids 5, no. 4: 203.
Chang Lin; Ming-Jer Kao; James Yang; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; Shih-Chun Hsieh. Particle acceleration and pressure gradient in a solitary wave traveling over a horizontal bed. AIP Advances 2020, 10, 115210 .
AMA StyleChang Lin, Ming-Jer Kao, James Yang, Rajkumar Venkatesh Raikar, Juan-Ming Yuan, Shih-Chun Hsieh. Particle acceleration and pressure gradient in a solitary wave traveling over a horizontal bed. AIP Advances. 2020; 10 (11):115210.
Chicago/Turabian StyleChang Lin; Ming-Jer Kao; James Yang; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; Shih-Chun Hsieh. 2020. "Particle acceleration and pressure gradient in a solitary wave traveling over a horizontal bed." AIP Advances 10, no. 11: 115210.
Owing to its effective energy dissipation and aeration, a stepped spillway is commonly used for flood release in hydraulic projects. Its conventional design features horizontal step surfaces. Designed for certain flow rates, it does not function satisfactorily at larger discharges. To improve this, layouts with inclined step surfaces, both downward and upward, are proposed. Computational fluid dynamics (CFD) modelling in 3D is performed to examine and compare their flow properties in the skimming flow. The results suggest that a shift from a downward to an upward layout leads to a gradual decrease in the flow velocity at the chute end; the latter exhibit higher energy dissipation efficiency. Moreover, equations are developed to estimate the velocity and energy loss. The flow velocity in the developing zone, described by a power law, shows a decline with an increase in the angle of inclination. The downward layout is subjected to somewhat higher risk of cavitation if implemented in a prototype. The extreme pressure loads acting upon an upward layout are larger, and a correlation is proposed for its prediction. On an inclined surface, either upward or downward, the pressure demonstrates an S-shaped distribution. On a vertical surface, the flow pressure increases, after an initial decline over a short distance, towards the chute bottom.
Shicheng Li; James Yang. Effects of Inclination Angles on Stepped Chute Flows. Applied Sciences 2020, 10, 6202 .
AMA StyleShicheng Li, James Yang. Effects of Inclination Angles on Stepped Chute Flows. Applied Sciences. 2020; 10 (18):6202.
Chicago/Turabian StyleShicheng Li; James Yang. 2020. "Effects of Inclination Angles on Stepped Chute Flows." Applied Sciences 10, no. 18: 6202.
A diffluence‐confluence unit is an elementary component within a river system and presents a complex yet linked pattern of both flow and sediment transport in between. This study deals, by means of field investigations and numerical modelling, with morpho‐dynamics of such a unit on the lower Yangtze River reaches. The unit comprises, looking downstream, a secondary (left) course and a main (right) course. Field surveys are performed for measurements of flow discharge, sediment loads at selected locations and river bathymetry at certain intervals. The field data show that the reach is mainly composed of suspended load, whose amount exhibits a declining trend with the elapse of time. Simulations in 3D are made to complement the field data and clarify the basic features of the unit, especially the partitioning of flow and suspended sediment in the diffluence and their subsequent reciprocal adjustment in the confluence. The results indicate that approach flow variations have a bearing on the diffluence flow partition. To augment flow discharge in the left branch, a training wall is devised in the diffluence to modify the intake flow. Secondary flow structures are found to be more influenced by the thalweg curvature than the flow division. The “inlet step” or differential topography contributes to the unequal flow division. In the confluence, a two‐cell flow structure coexists, which may diminish along with the dynamical adjustment of the two waters. The classical bed discordance is also observed. With the typical flow and sediment features, the main course is prone to slight erosion, while the secondary branch faces up with gradual siltation. These findings contribute to the understanding of the alluvial behaviours of such units, and provide reference for studies in similar situations and river management.
Qiancheng Xie; James Yang; T. Staffan Lundström. Flow and sediment behaviours and morpho‐dynamics of a diffluence−Confluence unit. River Research and Applications 2020, 36, 1 .
AMA StyleQiancheng Xie, James Yang, T. Staffan Lundström. Flow and sediment behaviours and morpho‐dynamics of a diffluence−Confluence unit. River Research and Applications. 2020; 36 (8):1.
Chicago/Turabian StyleQiancheng Xie; James Yang; T. Staffan Lundström. 2020. "Flow and sediment behaviours and morpho‐dynamics of a diffluence−Confluence unit." River Research and Applications 36, no. 8: 1.
This study investigates experimentally similarity and Froude number similitude (FNS) in the dimensionless flow features of three solitary waves traveling on a 1:3 sloping beach. These three waves, designated as cases A, B, and C, respectively, have different heights H0 (=5.8 cm, 2.9 cm, and 1.815 cm) and still water depths h0 (=16.0 cm, 8.0 cm, and 5.0 cm), but identical ratios H0/h0 (=0.363). A high-speed particle image velocimetry system is employed to obtain the free surface profiles (FSPs) and velocity fields/profiles. These features include the free surface elevation (FSE)/FSP time series; velocity fields and profiles, positions, and propagation speeds of flow demarcation curves; times and maximum onshore distances of the maximum run-up heights (MRHs); and times and onshore distances of hydraulic jumps for cases A and B. When the swash tip of a solitary wave reaches the MRH, the contact point becomes almost immobile for a short time interval, with the contact angle changing from obtuse, via right, to acute angle. For cases A and B, the similarities in the dimensionless MRHs and times, at which the run-down motions of the wave tips start, are affirmed. These facts highlight that the swash tips and contact points are subject to complex interactions among gravity force, viscous friction, and surface tension of fluid. Case C, having the smallest length scale, is only focused on the arrival or starting time of the MRH or run-down motion and the MRH and used as a counterexample to demonstrate the absence of similarity or FNS due to the relatively prominent effects of viscous friction and surface tension.
Chang Lin; Ming-Jer Kao; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; James Yang; Po-Yu Chuang; Jie-Ming Syu; Wei-Chih Pan. Novel similarities in the free-surface profiles and velocities of solitary waves traveling over a very steep beach. Physics of Fluids 2020, 32, 083601 .
AMA StyleChang Lin, Ming-Jer Kao, Rajkumar Venkatesh Raikar, Juan-Ming Yuan, James Yang, Po-Yu Chuang, Jie-Ming Syu, Wei-Chih Pan. Novel similarities in the free-surface profiles and velocities of solitary waves traveling over a very steep beach. Physics of Fluids. 2020; 32 (8):083601.
Chicago/Turabian StyleChang Lin; Ming-Jer Kao; Rajkumar Venkatesh Raikar; Juan-Ming Yuan; James Yang; Po-Yu Chuang; Jie-Ming Syu; Wei-Chih Pan. 2020. "Novel similarities in the free-surface profiles and velocities of solitary waves traveling over a very steep beach." Physics of Fluids 32, no. 8: 083601.
For safe spillway discharge of floods, attention is paid to the water flow. The resulting air flow inside the facility, an issue of personnel security, is sometimes disregarded. The spillway in question comprises two surface gates and two bottom outlet gates lying right below. Air passages to the outlet gates include an original gallery and a recently constructed vertical shaft. To understand water-air flow behavior, 3D CFD modelling is performed in combination with the physical model tests. The simulations are made with fully opened radial gates and at the full pool water level (FPWL). The results show that the operation of only the bottom outlets leads to an air supply amounting to ~57 m3/s, with the air flow rates 35 and 22 m3/s to the left and right outlets. The air supply to the right outlet comes from both the shaft and the gallery. The averaged air velocity in the shaft and the gallery are approximately 5 and 7 m/s. If only the surface gates are fully open, the water jet impinges upon the canal bottom, which encloses the air space leading to the bottom outlets; the air flow rate fluctuates about zero. If all the four gates are open, the total air demand is limited to ~10 m3/s, which is mainly attributable to the shear action of the meeting jets downstream. The air demand differs significantly among the flow cases. It is not the simultaneous discharge of all openings that results in the largest air demand. The flood release from only the two outlets is the most critical situation for the operation of the facility. The findings should provide reference for spillways with the same or similar layout.
James Yang; Penghua Teng; Qiancheng Xie; Shicheng Li. Understanding Water Flows and Air Venting Features of Spillway—A Case Study. Water 2020, 12, 2106 .
AMA StyleJames Yang, Penghua Teng, Qiancheng Xie, Shicheng Li. Understanding Water Flows and Air Venting Features of Spillway—A Case Study. Water. 2020; 12 (8):2106.
Chicago/Turabian StyleJames Yang; Penghua Teng; Qiancheng Xie; Shicheng Li. 2020. "Understanding Water Flows and Air Venting Features of Spillway—A Case Study." Water 12, no. 8: 2106.
Experimental results are presented regarding the free-surface elevations, velocity fields, and horizontal pressure gradients of dambreak-generated undular bores propagating over a horizontal bottom. Ultrasonic wave gauges, high-speed particle image velocimetry, and a flow visualization method are used to investigate the flow fields. Features of the full-depth velocity field and pressure gradient (equal to minus the sum of the local and convective accelerations) in the free stream over the boundary layer are elucidated with respect to the phase of the free-surface elevation and are categorized into four temporal stages. For stage I with rising free-surface elevations, a successive increase in the magnitude of the pressure gradient (with a negative value) corresponds to a favorable pressure gradient in the free stream. Around the zero-up/down-crossing phase of each leading wave evolving in stage II, the pressure gradient has a negative/positive maximum, revealing the maximum favorable/adverse pressure gradient in the free stream. However, the pressure gradient is zero at each crest or trough phase, showing an instantaneous zero pressure gradient. Within stage III characterized by a constant free-surface elevation, the pressure gradient is almost zero. In stage IV with descending free-surface elevations, the pressure gradient first increases from nearly zero to a positive maximum (representing the maximum adverse pressure gradient), then keeps this value for a period of time, and eventually decreases to zero. Subsequently, flow reversal with an increase in thickness over the bottom and free-stream velocity equal to zero takes place.
Rajkumar Raikar; James Yang; Ming-Jer Kao; Juan-Ming Yuan; Wei-Ying Wong; Ray-Yeng Yang. Features of the flow velocity and pressure gradient of an undular bore on a horizontal bed. Physics of Fluids 2020, 32, 043603 .
AMA StyleRajkumar Raikar, James Yang, Ming-Jer Kao, Juan-Ming Yuan, Wei-Ying Wong, Ray-Yeng Yang. Features of the flow velocity and pressure gradient of an undular bore on a horizontal bed. Physics of Fluids. 2020; 32 (4):043603.
Chicago/Turabian StyleRajkumar Raikar; James Yang; Ming-Jer Kao; Juan-Ming Yuan; Wei-Ying Wong; Ray-Yeng Yang. 2020. "Features of the flow velocity and pressure gradient of an undular bore on a horizontal bed." Physics of Fluids 32, no. 4: 043603.
Shicheng Li; James Yang; Xin Ma; Xin Li. Flow features in a pooled fishway with V-shaped weir formation. Engineering Applications of Computational Fluid Mechanics 2020, 14, 1337 -1350.
AMA StyleShicheng Li, James Yang, Xin Ma, Xin Li. Flow features in a pooled fishway with V-shaped weir formation. Engineering Applications of Computational Fluid Mechanics. 2020; 14 (1):1337-1350.
Chicago/Turabian StyleShicheng Li; James Yang; Xin Ma; Xin Li. 2020. "Flow features in a pooled fishway with V-shaped weir formation." Engineering Applications of Computational Fluid Mechanics 14, no. 1: 1337-1350.
A sluice structure with multiple gates is often followed by an enlarging channel downstream. Experiments are conducted for different enlargement ratios in cross-section and Froude numbers at the gates. A large-scale PIV system is adopted to capture the surface flow field for examination of the flow features. The study shows that, despite the centrally placed sluice structure with symmetric outflow, a hydraulic jump occurs and the main flow downstream exhibits, in terms of expansion and deflection, a high degree of asymmetry and formation of large circulation zones. The degree of deflection increases significantly along the longitudinal direction for all the enlargement ratios except the smallest. The toe of the hydraulic jump is controlled at the upper edge of the sloping surface downstream of the gates. In light of outflow width, Froude number and enlargement ratio, the flow is classified into three regions. Immediately downstream, the effect of outflow width gradually decreases with increasing Froude number. Further downstream, the degree of deflection augments with increasing enlargement ratio, with circulation zones. At a given cross-section, the degree of expansion is positively related to the enlargement ratio. The study is expected to provide guidance for examination of similar issues of flow pattern and erosion protection design.
Yuejun Chen; James Yang; Jianzhong Yu; Zongfu Fu; Qingsheng Chen. Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure. KSCE Journal of Civil Engineering 2019, 24, 471 -482.
AMA StyleYuejun Chen, James Yang, Jianzhong Yu, Zongfu Fu, Qingsheng Chen. Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure. KSCE Journal of Civil Engineering. 2019; 24 (2):471-482.
Chicago/Turabian StyleYuejun Chen; James Yang; Jianzhong Yu; Zongfu Fu; Qingsheng Chen. 2019. "Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure." KSCE Journal of Civil Engineering 24, no. 2: 471-482.
A sluice structure with multiple gates is often followed by an enlarging channel downstream. Experiments are conducted for different enlargement ratios in cross-section and Froude numbers at the gates. A large-scale PIV system is adopted to capture the surface flow field for examination of the flow features. The study shows that, despite the centrally placed sluice structure with symmetric outflow, a hydraulic jump occurs and the main flow downstream exhibits, in terms of expansion and deflection, a high degree of asymmetry and formation of large circulation zones. The degree of deflection increases significantly along the longitudinal direction for all the enlargement ratios except the smallest. The toe of the hydraulic jump is controlled at the upper edge of the sloping surface downstream of the gates. In light of outflow width, Froude number and enlargement ratio, the flow is classified into three regions. Immediately downstream, the effect of outflow width gradually decreases with increasing Froude number. Further downstream, the degree of deflection augments with increasing enlargement ratio, with circulation zones. At a given cross-section, the degree of expansion is positively related to the enlargement ratio. The study is expected to provide guidance for examination of similar issues of flow pattern and erosion protection design.
Yuejun Chen; James Yang; Jianzhong Yu; Zongfu Fu; Qingsheng Chen. Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure. KSCE Journal of Civil Engineering 2019, 24, 471 -482.
AMA StyleYuejun Chen, James Yang, Jianzhong Yu, Zongfu Fu, Qingsheng Chen. Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure. KSCE Journal of Civil Engineering. 2019; 24 (2):471-482.
Chicago/Turabian StyleYuejun Chen; James Yang; Jianzhong Yu; Zongfu Fu; Qingsheng Chen. 2019. "Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure." KSCE Journal of Civil Engineering 24, no. 2: 471-482.
Owing to effective aeration and energy dissipation, a stepped spillway is commonly used in a roller-compacted concrete (RCC) dam. However, its complex air-water flow features are far from being fully understood. Roughness density, step and cavity shapes are essential parameters. Numerical simulations are carried out to investigate their effects on hydraulic properties. In combination with the realizable k-ε turbulence model, the two-phase Mixture Model is used. The results indicate higher air concentrations for the spillway with rounded steps than the ones with trapezoidal steps; the roughness density and cavity shape show no observable effects on the aeration performance with cavity blockages. The characteristic air-water velocity for the trapezoidal steps layout is larger than that for the rounded steps. However, neither layout is sensitive to the roughness density; the velocity results for trapezoidal cavity and rounded cavity cases are almost independent of the roughness density. The velocity for all cases exclusive of trapezoidal steps increase with an increase in roughness density. The min. and max. pressures on the trapezoidal steps are slightly larger than those on the rounded steps; they increase with an increasing roughness density. The cavity shape and roughness density do not evidently influence the extreme pressures. Compared with the conventional step layout, chamfering the step edges slightly enhance the energy dissipation; partially blocking the cavities do not lead to any substantial change. In addition, the energy loss is not clearly related to the roughness density and step edge/cavity shape.
Shicheng Li; James Yang; Qiulin Li. Numerical Modelling of Air-Water Flows over a Stepped Spillway with Chamfers and Cavity Blockages. KSCE Journal of Civil Engineering 2019, 24, 99 -109.
AMA StyleShicheng Li, James Yang, Qiulin Li. Numerical Modelling of Air-Water Flows over a Stepped Spillway with Chamfers and Cavity Blockages. KSCE Journal of Civil Engineering. 2019; 24 (1):99-109.
Chicago/Turabian StyleShicheng Li; James Yang; Qiulin Li. 2019. "Numerical Modelling of Air-Water Flows over a Stepped Spillway with Chamfers and Cavity Blockages." KSCE Journal of Civil Engineering 24, no. 1: 99-109.
A traditional stepped spillway is prone to cavitation risks. To improve its hydraulic behaviors, distorted step faces and pool weirs are devised. By numerical modelling, comparative studies are conducted to look into the flow features. The pressures on step surfaces of the unconventional layouts exhibit 3D distributions. Pool weirs are essential in increasing both the min. and max. pressure loads. Pressures on the downstream bed show a unique pattern for V- and inverted V-shaped models, with the extreme pressures at the sidewalls for the former and at the central plane for the latter. Symmetrical secondary flows are formed in V- and inverted V-shaped cases with different patterns. Distributions of turbulent kinetic energy suggest differences in flow motions in all cases. Furthermore, the relative energy loss of flat setups is ∼5.4% lower than that of the pooled ones with the same step face angle; inverting the face angle does not give rise to noticeable change. The results provide reference for relevant projects.
Shicheng Li; Qiulin Li; James Yang. CFD Modelling of a Stepped Spillway with Various Step Layouts. Mathematical Problems in Engineering 2019, 2019, 1 -11.
AMA StyleShicheng Li, Qiulin Li, James Yang. CFD Modelling of a Stepped Spillway with Various Step Layouts. Mathematical Problems in Engineering. 2019; 2019 ():1-11.
Chicago/Turabian StyleShicheng Li; Qiulin Li; James Yang. 2019. "CFD Modelling of a Stepped Spillway with Various Step Layouts." Mathematical Problems in Engineering 2019, no. : 1-11.
The hydrodynamic characteristics, including local and convective accelerations as well as pressure gradient in the horizontal direction, of the external stream of an undular bore propagating on a 1:20 sloping beach are experimentally studied. A bore with the water depth ratio of 1.70 was generated downstream of a suddenly lifted gate. A high-speed particle image velocimetry was employed to measure the velocity fields during the run-up and run-down motions. The time series of free surface elevation and velocity field/profile of the generated bore, comprising a pure bore accompanied by a series of dispersive leading waves, are first demonstrated. Based on the fast Fourier transform (FFT) and inverse FFT (IFFT) techniques, the free surface elevation of leading waves and the counterpart of pure bore are acquired separately at a specified measuring section (SMS), together with the uniform horizontal velocity of the pure bore. The effect of leading-wave-induced velocity shift on the velocity profiles of the generated bore are then evaluated at the SMS. To understand the calculation procedure of accelerations and pressure gradient, three tabulated forms are provided as illustrative examples. Accordingly, the relationships among the partially depth-averaged values of the non-dimensional local acceleration, convective acceleration, total acceleration and pressure gradient of the generated/pure bore acquired at the SMS versus the non-dimensional time are elucidated. The trends in the non-dimensional accelerations and pressure gradient of the external stream of generated bore are compared with those of the pure bore. During the run-up motion from the instant of arrival of the bore front to the moment of the peak level at the SMS, continuous decrease in the onshore uniform horizontal velocity, and successive deceleration of the pure bore in the onshore direction are evidenced, exhibiting the pure bore under the adverse pressure gradient with decreasing magnitude. However, the pure bore once ridden by the leading waves is decelerated/accelerated spatially and accelerated/decelerated temporally in the onshore direction during the rising/descending free surface of each leading wave. This fact highlights the effect of pre-passing/post-passing of the leading wave crest on the velocity distribution of generated bore. It is also found that, although the leading waves have minor contribution on the power spectrum of the free surface elevation as compared with that of the pure bore, the leading waves do play an important role on the magnitudes of both accelerations and pressure gradient. The largest magnitude of the acceleration contributed by the leading waves is around 26 times the counterpart contributed by the pure bore. Further, during the run-down motion right after the moment for the peak level of the bore, a linear increase in the magnitude of the offshore uniform horizontal velocity and a constant local acceleration with increasing time are both identified. The partially depth-averaged value of the non-dimensional pressure gradient is equal to a small negative constant (−0.0115) in the offshore direction, indicating that the bore is subject to a constant favorable pressure gradient.
Chang Lin; Wei-Ying Wong; Ming-Jer Kao; James Yang; Rajkumar V. Raikar; Juan-Ming Yuan. Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach. Water 2019, 11, 1556 .
AMA StyleChang Lin, Wei-Ying Wong, Ming-Jer Kao, James Yang, Rajkumar V. Raikar, Juan-Ming Yuan. Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach. Water. 2019; 11 (8):1556.
Chicago/Turabian StyleChang Lin; Wei-Ying Wong; Ming-Jer Kao; James Yang; Rajkumar V. Raikar; Juan-Ming Yuan. 2019. "Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach." Water 11, no. 8: 1556.
A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics (CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group (RNG) k – ɛ turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges.
James Yang; Penghua Teng; Chang Lin. Air-vent layouts and water-air flow behaviors of a wide spillway aerator. Theoretical and Applied Mechanics Letters 2019, 9, 130 -143.
AMA StyleJames Yang, Penghua Teng, Chang Lin. Air-vent layouts and water-air flow behaviors of a wide spillway aerator. Theoretical and Applied Mechanics Letters. 2019; 9 (2):130-143.
Chicago/Turabian StyleJames Yang; Penghua Teng; Chang Lin. 2019. "Air-vent layouts and water-air flow behaviors of a wide spillway aerator." Theoretical and Applied Mechanics Letters 9, no. 2: 130-143.
Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.
Qiancheng Xie; James Yang; T. Staffan Lundström. Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load. Fluids 2019, 4, 15 .
AMA StyleQiancheng Xie, James Yang, T. Staffan Lundström. Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load. Fluids. 2019; 4 (1):15.
Chicago/Turabian StyleQiancheng Xie; James Yang; T. Staffan Lundström. 2019. "Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load." Fluids 4, no. 1: 15.
Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structural upgrades. This has led to renewed laboratory model tests. For some dams, even computational fluid dynamics (CFD) simulations are performed. This provides the possibility to compare the spillway discharge data between the model tests performed a few decades apart. The paper presents the hydropower development, the needs for the ongoing dam rehabilitations and the history of physical hydraulic modeling in Sweden. More than 20 spillways, both surface and bottom types, are analyzed to evaluate their discharge modeling accuracy. The past and present model tests are compared with each other and with the CFD results if available. Discrepancies do exist in the discharges between the model tests made a few decades apart. The differences fall within the range −8.3%–+11.2%. The reasons for the discrepancies are sought from several aspects. The primary source of the errors is seemingly the model construction quality and flow measurement method. The machine milling technique and 3D printing reduce the source of construction errors and improve the model quality. Results of the CFD simulations differ, at the maximum, by 3.8% from the physical tests. They are conducted without knowledge of the physical model results in advance. Following the best practice guidelines, CFD should generate results of decent accuracy for discharge prediction.
James Yang; Patrik Andreasson; Penghua Teng; Qiancheng Xie. The Past and Present of Discharge Capacity Modeling for Spillways—A Swedish Perspective. Fluids 2019, 4, 10 .
AMA StyleJames Yang, Patrik Andreasson, Penghua Teng, Qiancheng Xie. The Past and Present of Discharge Capacity Modeling for Spillways—A Swedish Perspective. Fluids. 2019; 4 (1):10.
Chicago/Turabian StyleJames Yang; Patrik Andreasson; Penghua Teng; Qiancheng Xie. 2019. "The Past and Present of Discharge Capacity Modeling for Spillways—A Swedish Perspective." Fluids 4, no. 1: 10.
The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water–air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.
Penghua Teng; James Yang. Modeling and Prototype Testing of Flows over Flip-Bucket Aerators. Journal of Hydraulic Engineering 2018, 144, 04018069 .
AMA StylePenghua Teng, James Yang. Modeling and Prototype Testing of Flows over Flip-Bucket Aerators. Journal of Hydraulic Engineering. 2018; 144 (12):04018069.
Chicago/Turabian StylePenghua Teng; James Yang. 2018. "Modeling and Prototype Testing of Flows over Flip-Bucket Aerators." Journal of Hydraulic Engineering 144, no. 12: 04018069.
Mathematical formulations of two-phase flows at an aerator remain a challenging issue for spillway design. Due to their complexities in terms of water–air interactions subjected to high flow velocities, experiments play an essential role in evaluations of numerical models. The paper focuses on the underlying influence of the air–water momentum exchange in the two-phase Two-Fluid Model. It is modified to better represent the drag force acting on a group of air bubbles and the wall lubrication force accounting for near-wall phase interactions. Based on data from a large aerator rig with an approach velocity of 14.3 m/s, the models are evaluated for calculations of entrained air characteristics of a flow mixture. The air bubble diameter used in the modeling ranges from 0.5 to 4 mm as suggested by the experiments. In terms of air cavity configurations and aerator air demand, smaller air bubbles lead to better agreement with the test results. As far as air concentrations are concerned, the modified model gains by comparison. In the air cavity zone, smaller bubble sizes also provide better matches with the experiments. However, the near-base air concentration remains overestimated downstream from the impact area. The fact that the program user must pre-define a single air bubble size in simulations presumably limits the correct reproduction of near-base air concentrations and of their decay.
James Yang; Penghua Teng; Hongwei Zhang. Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility. Engineering Applications of Computational Fluid Mechanics 2018, 13, 48 -66.
AMA StyleJames Yang, Penghua Teng, Hongwei Zhang. Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility. Engineering Applications of Computational Fluid Mechanics. 2018; 13 (1):48-66.
Chicago/Turabian StyleJames Yang; Penghua Teng; Hongwei Zhang. 2018. "Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility." Engineering Applications of Computational Fluid Mechanics 13, no. 1: 48-66.