Roller Length Research Articles

Effect of inflow conditions on the free-surface properties of hydraulic jumps

Previous research has shown that the inflow conditions upstream of hydraulic jumps can affect flow aeration, bed pressures and turbulence. However, studies of the effects of inflow conditions on free-surface properties have not been conclusive and have lacked a comparison of partially and fully developed inflow conditions. Detailed measurements of the free-surface features in fully aerated hydraulic jumps with partially and fully developed inflow conditions have been conducted using a LIDAR. The results showed that the free-surface profile, the roller length, the free-surface and jump toe movements are strongly influenced by the inflow conditions. Hydraulic jumps with fully developed inflow conditions were of comparatively shorter length compared to partially developed hydraulic jumps, while they were characterized by stronger fluctuations, jump toe motions and frequencies as well as stronger energy loss across the hydraulic jump. Inflow conditions must be considered in determining the envelope of hydraulic jump motions with consequences for dissipator design.

Surf Zone Waves at the Onset of Breaking: 1. LIDAR and IR Data Fusion Methods

AbstractThis is the first of a 2‐part series concerning remote observation and wave‐by‐wave analysis of the onset of breaking in the surf zone. In the surf zone, breaking waves drive nearshore circulation, suspend sediment, and promote air‐sea gas exchange. Nearshore wave model predictions often diverge from in situ measurements near the break point location because common parameterizations do not account for the rapid changes that occur near the onset of breaking. This work presents extensive methodology to combine data from a line‐scanning LIDAR and thermal infrared cameras to detect breaking, classify breaker type, and measure geometric wave parameters on a wave‐by‐wave basis, which can be used to improve breaker parameterizations. Over 2,600 non‐breaking and 1,600 breaking waves are analyzed from data collected at the USACE Field Research Facility in Duck, NC, including 413 spilling and 111 plunging waves for which the onset of breaking was observed. Wave height is estimated using a spatio‐temporal method for wave tracking that preserves the sea surface elevation maximum and overcomes field of view limitations. Methods for estimating instantaneous wave speed are refined by fitting a skewed Gaussian function to each wave profile before tracking the peaks. Wave slope is estimated from a linear fit to the upper 80% of the wave face, which provides a robust metric and strong correlation with geometric wave slope defined relative to mean sea level. Finally, breaking wave face foam coverage is analyzed to assess common model assumptions about roller length for wave energy dissipation parameterizations.

Physical and computational study of a novel submerged entry nozzle design for twin-roll casting process

With significant emphasis on reducing the turbulence in the bath and the need for effective distribution of metal along the roller length in twin-roll casting, a novel submerged entry nozzle (SEN) configuration with two “gap regions” was provided. The “gap regions” of the new SEN divide the bath into two parts, the “upper melt bath” (casting region) and the “lower melt bath” (rolling region). The newly designed SEN was tested by using both full-scale water modeling experiments and numerical simulations. Results demonstrated that the turbulence could only be found near the rotating roller surfaces. The “gap regions” can make the near-wall flows more uniform. They can also prevent the instabilities in the “upper melt bath” to be transferred to the “lower melt bath”, thus improving the stability of the process. Moreover, the novel SEN can stabilize the meniscus where the initial solidification occurs. This is achieved by increasing the SEN immersion depth, which in turn, can enlarge the volume of the upper part of the bath.

Self-adaptive extreme learning machine-based prediction of roller length of hydraulic jump on rough bed

ABSTRACT In this study, the roller length of hydraulic jumps occurring on rough beds is modeled using the Self-Adaptive Extreme Learning Machine (SAELM) method. For this purpose, the parameters influencing the roller length are specified and four different SAELM models are developed based on them. A superior model is also established by analyzing the modeling results. For the superior model, the statistical values of the Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE) and correlation coefficient are calculated to be 1.720, 6.369 and 0.969, respectively. Also, the results of the SAELM superior model are compared with the Multilayer Perceptron Neural Network (MLPNN) and Support Vector Machine (SVM) methods. The analysis of the SVM, MLPNN and SVM models results reveals the effectiveness of the SAELM model. In this study, the uncertainty analysis of the SAELM, MLPNN and SVM models is also performed and the prediction error interval of 95% for the SAELM model is obtained which varies from −0.112 to +0.134.

Hydraulic jump on rough beds: conceptual modeling and experimental validation

Abstract The aim of this study was to assess and quantify the effect of channel bed roughness on hydraulic jumps based on sound physical theories. Assuming that integrated bed shear stress due to surface roughness changes linearly with supercritical velocity, a novel definition for the shear force coefficient and for roller length were obtained. Experimental findings and Pearson's correlation verify that the developed equations perform reasonably well and they prove that a linear correlation assumption between integrated bed shear stress and supercritical velocity is valid for a Froude number between 1.1 and 9.8. The shear force coefficient is defined in terms of the Reynolds coefficient and the supercritical flow velocity is directly related to the modified Reynolds number. A new analytical equation for roller length as a function of the modified Reynolds number was also developed and validated by using data from the experimental study.

Hydraulic jump control using stilling basin with adverse slope and positive step

ABSTRACT Water flow often releases excess energy after passing through gates and spillways. This energy should be reduced to avoid destruction of downstream structures. The hydraulic jump, a natural phenomenon, inevitably reduces incoming flow energy. In this research, effect of adverse slope and positive step on hydraulic jump characteristics including sequent depth ratio, jump length, roller length and energy losses were simultaneously investigated. In place of four adverse bed angle slopes of 0, 0.015, 0.03 and 0.05 (m/m) and three positive step heights of 0, 3 and 6 (cm) were tested. An analytical solution, based on momentum equation, was developed for estimating the sequent depth ratio with considering initial Froude number, bed slope and positive step height and its estimations were compared to the experimental measurements. Results showed that although both the adverse slope and positive step reduced the sequent depth ratio, jump length and roller length to a greater degree compared to the classic jump, the effect of adverse slope was greater than the positive step. Energy loss in the presence of adverse slope and positive step was greater than in the classic conditions. Furthermore, the result of the analytical solution was in good agreement with the corresponding experimental measurements.

Optimisation design for wind turbine mainshaft bearing based on lubrication reliability

The lubrication of the mainshaft bearing has a great influence on the safe operation of wind turbines. In this paper, an optimal design model of the mainshaft bearing of a wind turbine is established on the lubrication reliability analysis. The maximum rated dynamic load is set as the design objective. The roller number, roller diameter, roller length and wall thicknesses are design parameters. Constraints are formulated mainly based on lubrication reliability and structure consideration. In the lubrication reliability constraint model, the lubrication reliability criterion was determined by solving the minimum film thickness of numerical calculation model of grease EHL. The reliability of bearing lubrication is calculated by Monte Carlo Simulation, and uncertain variables based on sensitivity analysis are selected to improve calculation precision. In the structure constraints, range for the design variables is determined in terms of requirements of geometric structure and strength. Finally, the mainshaft bearing was optimised and analysed by genetic algorithms. The analysis results show that the rated dynamic load of bearing is improved from 1.3e6 N to 2e6 N. Meanwhile the lubrication reliability is improved about 10%. The model presented shows great advantages and practical usefulness in the mainshaft bearing research of wind turbines.

Optimisation design for wind turbine mainshaft bearing based on lubrication reliability

The lubrication of the mainshaft bearing has a great influence on the safe operation of wind turbines. In this paper, an optimal design model of the mainshaft bearing of a wind turbine is established on the lubrication reliability analysis. The maximum rated dynamic load is set as the design objective. The roller number, roller diameter, roller length and wall thicknesses are design parameters. Constraints are formulated mainly based on lubrication reliability and structure consideration. In the lubrication reliability constraint model, the lubrication reliability criterion was determined by solving the minimum film thickness of numerical calculation model of grease EHL. The reliability of bearing lubrication is calculated by Monte Carlo Simulation, and uncertain variables based on sensitivity analysis are selected to improve calculation precision. In the structure constraints, range for the design variables is determined in terms of requirements of geometric structure and strength. Finally, the mainshaft bearing was optimised and analysed by genetic algorithms. The analysis results show that the rated dynamic load of bearing is improved from 1.3e6 N to 2e6 N. Meanwhile the lubrication reliability is improved about 10%. The model presented shows great advantages and practical usefulness in the mainshaft bearing research of wind turbines.

Development and Identification of Working Parameters for a Lychee Peeling Machine Combining Rollers and a Pressing Belt

This work describes the development, design, and parameter identification of a lychee peeling machine. The working principle of the machine combines two rollers with a pressing belt to separate the peel from the fruits. It was designed and its operational parameters identified on the basis of experimental data on the Thieu lychee, which currently covers about 80% of the plantation area in Vietnam. To this end, the first step was to measure the physical characteristics of the fruits, such as size, shape, and density. Moreover, the coefficient of static friction between lychees and rubber rollers, and the critical peeling force, were identified, with a view to optimizing the operational parameters later on. Results showed that a minimum tangential force of 10.5 N is needed to break the peel and separate it from the pulp. Based on the balanced force principle, various optimal machine parameters such as roller rotation speed, roller diameter, roller length, gap size between the two rollers, belt velocity, and minimum pressure of the belt were calibrated. In addition, spiral grooves were created on the roller surface to facilitate the motion of the fruits. The optimal results were roller size 900 × 100 mm (length × diameter), rotation speed 159 RPM, gap size between rollers 4 mm, belt size 850 × 60 mm (length × width), belt pressure 13.5 N, and belt velocity 140 mm/s. Using the design and operational parameters mentioned above, the machine was able to perform regularly at a throughput of 100 kg/h, as demanded by the current market. Moreover, it would be easily feasible to combine multiple pairs of rollers and pressing belts in order to increase throughput. The methodology for the design of this peeling machine and identification of working parameters with respect to experimental data could be applied in many other post-harvesting configurations.

Development of Coconut Dehusker Machine for Small Scale Industry

West Sumatra-Indonesia has potential to plant coconut due to the coastal location, sunshine level with average temperature 27oC. Coconut is a very productive plant. Coconut dehusking is one of the process that takes a lot of time and energy. Most of the farmer still using human manual labour with the help of tools made of iron or wooden crowbar that is mounted standing vertically with the blade facing upward about 80 cm from the ground. To increase the number of coconut products, it is designed the coconut dehusker machine. The main component of the machine were two rollers that rotate each other in opposite directions with each roller embedded iron-shaped nails that work to tear the coconut husk. Each roller has a different rotational speed. This machine has dimensions of 98 cm x 51 cm x 95 cm. Roller length is 50 cm and diameter 4 inches. The power source of the machine is a 2 HP electric motor, the speed was reduced by using 2 speeds reducer with the ratio of 1:20 and 1:30 respectively. From the performance test of this machine can dehusk 100 coconuts per hour. The operational basic cost of the machine equal to Rp 129.89 per coconut (about 1 cent) and Break Event Point is 12.387 coconut per year from the result of the performance test. From the economic analysis machine can be concluded that the use of this machine is better when compared to human labour which has limitation to duration and capacity.

Hydraulic Jump below Abrupt Asymmetric Expanding Stilling Basin on Rough Bed

The present research describes a laboratory study of hydraulic jump in the abrupt asymmetric expansion stilling basin as an energy dissipator by changing the geometry of walls and bed roughness elements. The experiments were carried out in a horizontal flume with 10 m length, 0.5 m width, and 0.5 m depth for a range of the upstream Froude numbers ( F r 1 ) from 5 to 11. Four physical models with expansion ratio of α = 0.33, 0.5, 0.67, and 1 and asymmetry ratio of Δ = 0.16 were installed in the flume and two different heights of roughness elements ( h = 1.4 and 2.8 cm) were also considered. The results indicated that the sequent depth and the jump length as well as the roller length below abrupt asymmetric expansion on the rough bed were decreased in comparison to the same parameters of the jump in a prismatic channel with smooth bed. It was revealed that the roughness elements have the effective role on stabilization of the hydraulic jump location. The analysis of energy dissipation efficiency confirmed that the spatial jump in the abruptly expanded basin with roughened bed was more efficient than classical jump. In order to estimate the hydraulic jump characteristics, empirical relationships associated with expansion ratio of basin walls, relative height of roughness elements and upstream Froude number were proposed based on the experimental data that resulted in preliminary design of an abrupt asymmetric enlarged basin.

Gene expression programming-based approach for predicting the roller length of a hydraulic jump on a rough bed

ABSTRACT Hydraulic jumps are used for dissipating water flow energy after ogee spillways, chlorinating wastewater flow and other hydraulic purposes. This paper presents a concise and practical relationship based on Gene Expression Programming (GEP) to estimate the roller length of a hydraulic jump on a rough bed. K-fold cross validation (k = 10) is applied to validate the numerical results. Various models are developed in terms of the Froude number upstream of the hydraulic jump , ratio of sequent depth and the relative roughness . The model results are analyzed and compared to determine the superior model. The MARE and RMSE obtained for the best model are 0.079 and 1.965, while the correlation coefficient (R), scatter index and BIAS are 0.959, 0.101 and 0.003, respectively. To evaluate each input variable’s effect on the proposed model, Partial Derivative Sensitivity Analysis (PDSA) as well as uncertainty analysis is done for all GEP models. A number of artificial intelligence approaches are also compared. This study shows that the presented equation is simpler and more practical than other equations from prior studies.

A Thermal Elastohydrodynamic Lubrication Model for Crowned Rollers and Its Application on Apex Seal–Housing Interfaces

This paper presents a thermal elastohydrodynamic lubrication (EHL) model for analyzing crowned roller lubrication performances under the influence of frictional heating. In this thermal EHL model, the Reynolds equation is solved to obtain the film thickness and pressure results while the energy equation and temperature integration equation are evaluated for the temperature rise in the lubricant and at the surfaces. The discrete convolution fast Fourier transform (DC-FFT) method is utilized to calculate the influence coefficients for both the elastic deformation and the temperature integration equations. The influences of the slide-to-roll ratio (SRR), load, crowning radius, and roller length on the roller lubrication and temperature rise are investigated. The results indicate that the thermal effect becomes significant for the cases with high SRRs or heavy loads. The proposed thermal EHL model is used to study the thermal-tribology behavior of an apex seal–housing interface in a rotary engine, and to assist the design of the apex seal crown geometry. A simplified crown design equation is obtained from the analysis results, validated through comparison with the optimal results calculated using the current crowned-roller thermo-EHL (TEHL) model.

Improvement of Rolling Dynamics to Increase Roller Life in Ball Rolling

The downtime of ball-rolling mills is largely associated with the replacement of worn rollers. In the present work, the degree and location of critical roller wear are studied: the greatest wear is observed at the flanges in the billet-capture zone. The conditions required for billet capture and successful rolling are determined analytically. Variation in roller speed during billet supply is proposed. Tests are conducted with linear and quadratic variation in roller speed. The familiar formulas for the mean deformation rate are modified for linear and quadratic variation in roller speed. Experiments are conducted on the ball-rolling mill of AO EVRAZ Nizhnetagil’skii Metallurgicheskii Kombinat (NTMK), in rolling 60-mm ШЗГsteel grinding balls on a 40–80 rolling mill. In the experiments, the roller speed is varied manually according to a specified program, with billet capture by the rollers. It is found that speed variation significantly affects the mean pressure at the instant of billet capture. Time dependences of the torque and the mean contact pressure are plotted on the basis of calculation results and experimental data. Empirical characteristics with linear and quadratic variation in roller speed are presented. The permissible agreement of the calculated and empirical results is determined. The installation of a thyristor converter is proposed, so as to decrease the roller speed before billet capture and restore the speed to the rated value in specified fashion after capture. That yields a uniform distribution of the mean contact pressure over the roller length during automatic operation of the mill in different conditions. As a result, the roller wear is decreased, without loss of mill productivity. That reduces roller consumption and the mill downtime for roller replacement.

Wave Nonlinearity Correction for Parametric Nearshore Wave Modelling

Zhang, C.; Zhang, Q.; Lei, G.; Cai, F.; Zheng, J., and Chen, K., 2018. Wave nonlinearity correction for parametric nearshore wave modelling. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 996–1000. Coconut Creek (Florida), ISSN 0749-0208.Many phase-averaged parametric nearshore wave models are based on the energy balance concept and use linear wave theory to calculate wave parameters (e.g., wave energy, wave height, wave setup). For a wave propagating into shallow water, however, its shape becomes skewed/asymmetric and the linear wave theory may not be appropriate. Seven cases of model-data comparison for regular wave transformation over sloping and barred beaches are carried out. It is shown that the model using linear wave theory underestimates the regular wave height near the breakpoint, and overestimates the breaking roller length in the surf zone. An empirical method is proposed to improve the performance of the parametric wave models in shallow waters by correcting the key model parameters to include wave nonlinearity effects. This includes (1) development of a new empirical formula for the nonlinear wave shape factor, (2) using a nonlinear wave celerity formula, and (3) implementing a new empirical formula for breaking roller slope. These formulas are functions of wave steepness and Ursell number. The proposed method systematically improves predictions of wave height, wave setup and roller evolution under regular wave transformation with different beach configurations. In particular, the peaks of wave height and mean water level near the breakpoint as well as the roller length variation in the surf zone are accurately captured by the wave nonlinearity-corrected model.

Multi-objective optimization of spherical roller bearings based on fatigue and wear using evolutionary algorithm

In Spherical Roller Bearings (SRBs) design the fatigue and wear lives are the most important factors. The fatigue life of bearing is connected to dynamic capacity (Cd) and wear life of bearing is linked with the elasto-hydrodynamic minimum film thickness (hmin). Multi-objective optimization (MOO) of SRBs has been considered in the present study. For SRBs optimization problem, two objectives (Cd and hmin), eight design variables, and twenty-two constraints have been considered. Bearing pitch diameter, roller diameter, number of rollers, effective roller length and the contact angle are five design geometrical variables and other three are constraint parameters. Objective functions have been optimized individually as well as simultaneously. Elitist Non Dominated Sorting Genetic Algorithm (NSGA-II) is used to solve a non-linear constrained optimization problem of the SRB design. A convergence methodology is performed to the bearing design for global optimum results. Results obtained from NSGA-II runs of MOO have been used to draw Pareto-optimal fronts (POFs). Optimum bearing dimensions are selected by considering the knee-point solution on the POFs. Results indicate that the dynamic capacity of optimized bearing got enhanced thus increase in life of the bearing. A sensitivity analysis is conducted to identify the sensitivity of objective functions with design variables. The sensitivity analysis plays an important part in deciding the tolerances, which can be provided to design variables for the manufacturing of optimized bearings. The results obtained from MOO problem have been compared with available literature and are found to be better.

Estimate of void fraction and air entrainment flux in hydraulic jump using Froude number

Hydraulic jumps are induced in hydraulic facilities for the purposes of energy dissipation or flow aeration. Presently there is no means for a simple estimate of void fraction distribution and air entrainment flux, without detailed physical modelling. This paper presents a semi-theoretical model to simulate the void fraction and velocity distributions in hydraulic jumps characterized by partially-developed inflow conditions. Relationships were established between the inflow Froude number, jump roller length and key parameters that determine the full expression of void fraction and velocity profiles. The proposed model enables accurate prediction of void fraction, longitudinal velocity, and air flux using the inflow Froude number. The results indicated considerable air flux contribution of free-surface aeration, in addition to the singular air entrainment at the jump toe, for moderate to large Froude numbers. A Froude number between 8 and 9 tended to achieve highest aeration rate with maximum total air flux in the roller.

The Load Distribution of the Main Shaft Bearing Considering Combined Load and Misalignment in a Floating Direct-Drive Wind Turbine

The main shaft tapered double-inner ring bearing (TDIRB) of floating direct-drive wind turbine system (FDDWT) is one of the most critical components in FDDWT, and its failure accounts for a large proportion of wind turbine malfunctions and faults. Over the past decades, a significant number of methods have been proposed to calculate the contact load distribution along the roller length in TDIRB, since the contact load distribution of roller is the key factor of fatigue life of TDIRB. Most of methods, however, neglected the misalignment of inner ring with respect to outer ring and friction force. In this paper, with the help of comprehensive and accurate quasi-static mathematical method, the contact load distribution of internal loads in TDIRB are analysed by considering the effects of combined loads, angular misalignment and friction force at different wind speeds for FDDWT. The simulation results show that the amount of combined load has an apparent effect on the contact load distribution along the TDIRB raceways and flanges in both rows. Furthermore, the slight change of tilted misalignment has a great influence on the contact load distribution. In addition, the slight angular misalignment easily produces noncontact zone for the bearing raceway in both rows, which is significantly disadvantage for the external load uniform transmitting to each roller.

Design and trial-produce of a special nail-tooth thresher for pulses crops

Pulses crops are widely distributed in China, but mechanization production-level of this crops is relatively low at present. So, a special nail-tooth thresher for pulses crops was carried out in this project to solve the problem of mechanical threshing. The roller diameter, speed, length, and nail-tooth structure, stripper concave screen, power device and cleaning system are determined by detailed theoretical calculation. Testing result of the trial-production prototype showed that the threshing roller with large diameter and low rotating speed, the nail-tooth threshing mechanism and the concave plate screen with large spacing are suitable for the broad bean thresher. The optimal combination is roller speed 400 /min, feed quantity 1.2 kg/s and concave tolerance 54 mm. Testing results showed that impurity content and breaking rate of the developed nail-tooth type broad bean thresher were respectively 1.09 %and 3.45%, It could improve the efficiency of the pulses crops threshing process significantly.

An Experimental Study of Hydraulic Jump in a Gradually Expanding Rectangular Stilling Basin with Roughened Bed

The paper presents the results of an experimental study carried out to investigate the effect of geometric and hydraulic parameters on energy dissipation and location of the hydraulic jump, with a change in the height of roughness elements and the divergence of walls in different discharges. Experiments were conducted in a horizontal rectangular basin with gradual expansion 0.5 m wide and 10 m long. Four physical models were fixed in the flume. The measured characteristics of the hydraulic jump with different divergences ratio (B = b1/b2 = 0.4, 0.6, 0.8, 1) and the inflow Froude numbers (6 < Fr1 < 12) were compared with each other and with the corresponding values measured for the classical hydraulic jump. The results showed that the tailwater depth required to form a hydraulic jump and also the roller length of the hydraulic jump and the length of the hydraulic jump on a gradual expansion basin with the rough bed were appreciably smaller than that of the corresponding hydraulic jumps in a rectangular basin with smooth and rough bed. With the experimental data, empirical formulae were developed to express the hydraulic jump characteristics relating to roughness elements height and divergence ratio of wall. Also, the applicability of some empirical relationships for estimating the roller length was tested.