Effect of Seal Locations of Pump-Turbine on Axial Hydraulic Trust

Axial hydraulic thrust is an important factor that affects safety and stability of pump turbine operation. Research and analysis of axial hydraulic thrust is of a great significance for guiding the safe and stable operation of a pumped storage power station. Since the runner shape of the pump turbine is flat and its radial dimension is large, an increase of leakage can happen easily. In order to reduce the leakage and improve the efficiency of the unit, a labyrinth ring seal is usually used in the upper crown and lower ring of the runner because the inner clearance of the seal has a great influence on the axial thrust. In order to study the influence of the change of labyrinth seal position on axial hydraulic thrust, a fluid domain model with a pressure balance pipe, upper crown clearance, and lower ring clearance is established for a pump turbine of a power station. The distribution position of labyrinth ring in the upper crown clearance is changed. The CFD numerical simulations are carried out under both 100% working load and 75% working load of turbine conditions, considering the flow in clearance areas. The research results of this paper have found that the axial hydraulic thrust of the 100% load condition is consistent with the change of the gap position compared with the 75% load condition. The amplitude of the change of the water thrust under the 100% load condition is greater. As the sealing position of the labyrinth ring in the upper crown gap moves away from the central axis, the resultant vertical and upward water thrust increases, and the operating efficiency of the unit first increases and then decreases. As the position of the labyrinth ring seal in the upper ring clearance moves away from the central axis, the resultant vertical and upward water thrust increases, and the operating efficiency of the unit first increases and then decreases. Defining the radial dimension ratio δ between the front clearance area and the total area of labyrinth ring, the closer δ is to 0.5, the unit efficiency is higher; the smaller that δ is, then the high pressure area in the upper crown clearance is smaller, and the hydraulic thrust force increases vertically. Considering a variety of factors, the clearance seal position has the optimal value. In the practical application of the project, the condition of excessive upward hydraulic thrust leading to the lifting of the unit can be avoided, and the phenomenon of excessive downward hydraulic thrust leading to the excessive load-bearing of the frame is evitable.

Study on Scanning Forming Methods of Machining Work-Piece Surface

In the process of machine tool cutting, there are strict geometric relations among the cutting edge curve / tool surface, machine tool movement and workpiece surface, and the machine tool movement is also related to the type of tool. Firstly, the forming methods of cutting workpiece surface are analyzed and summarized from the geometric point of view, and the scanning forming method and its geometric expression are studied, and the research technical route of forming turning scanning forming is put forward. Then, the mathematical modeling and Simulation of forming turning are carried out according to the proposed technical route. Finally, taking the groove of the inner ring of the formed turning ball bearing as an example, the mathematical modeling of the design surface of the workpiece and the machined surface of the workpiece is carried out. The radial dimension changes of the workpiece caused by the cutting force and tool wear are analyzed, and the simulation of the machined surface of the workpiece is carried out.

Investigation of effect of process variable on dimensional accuracy of FDM component using response surface methodology

Purpose Nowadays, rapid prototyping is emerging as end use product in low volume. The accuracy of the fabricated components depends on various process parameters. Process parameters used in this investigation are layer thickness (150, 200 and 250 µm), infill pattern (linear, hexagonal and star fill), raster angle (0°, 45° and 90°) and infill density (40, 60 and 80%). Linear and radial dimension of knuckle joint are selected for the response factor. Design/methodology/approach The experiments are design by using response surface methodology (RSM). Four design variables at three levels are used to examine their influence on percentage error in linear dimension and radial dimension of the component. A prototype Knuckle joint is selected as component. Minitab-14 software is used for the design of experiments. Findings Experimental measure data is analyzed by using “smaller is better” quality characteristics. A regression model for the forecasting of percentage error in linear and radial dimension is developed. The developed model is within precision range. The optimum level of process for linear and radial dimensions are obtained: layer thickness of 150 µm, Infill pattern of linear, Raster angle of 90° and infill density of 40%. Research limitations/implications It proves that both the mathematical model is significant and can be able to approximate the desired output value close to the accurate dimensions. While comparing the calculated F-values for both linear and radial dimension with the standard table (F-table, 0.05), it is found that at the given set of degree of freedom the standard F-values (6.61) is lower for that regression, linear, square and interaction source of the predicted model, for which p-values have already less than 0.05. It is desirable for significant process parameters. Practical implications The dimensional accuracy with respect to average percentage error of FDM produced knuckle joint is successfully examined. The effect of process parameters, namely, layer thickness, infill pattern, raster angle and infill density on average percentage error was investigated by RSM and analysis of variance table. Social implications The novelty of this work lies in the fact that only few studies are available in archival literature related to influence of these process parameters on percentage error in linear and radial dimension for Polycarbonate (PC) material. Originality/value The novelty of this work lies in the fact only few studies are available in archival literature related to influence of these process parameters on percentage error in linear and radial dimension for Polycarbonate (PC) material.

Experimental Study on Bearing Characteristics and Soil Deformation of Necking Pile with Cap Using Transparent Soils Technology

This paper will employ the transparent soil experiment technology to explore the influences of shallow necking on the vertical bearing capacity of single pile with cap. Model experiment is carried out on one intact pile and nine shallow necking piles. The load-settlement curves of all piles are obtained, which are used to study bearing characteristics of piles. The displacement fields of soil around piles are employed to investigate the reasons for the loss of vertical bearing capacity of piles with shallow necking. The vertical bearing capacity is greatly reduced which is caused by shallow necking. When the axial dimension of necking is the same, the larger the radial size is, the greater the loss of vertical bearing capacity is. When the radial dimension of necking is the same, the greater the axial size is, the greater the loss of vertical bearing capacity is. The soil near the pile shaft and under the pile cap produces a large area of vertical downward deformation, which causes the relative displacement between the pile shaft and the soil to greatly reduce. Therefore, it is easy that the necking piles with caps develop negative friction, which causes the vertical bearing capacity of piles to reduce. When the radial dimension of the shallow necking is 80% of pile diameter, the pile is easy to be damaged.

A Research of Optimization of the Forming Parameters to the Minimum Radial Dimension Error when Forming Sheet by HOTSPIF Technology

Single Point Incremental Forming (SPIF) technology has become popular and familiar for forming sheet, especially in single, small and prototype batch production in many fields such as medicine, aviation, automobile... However, sheet materials with high hardness and durability are difficult to deform and shape because of their high properties. In that case, if we determine a set of logical suitable technological parameters such as temperature T (°C), speed of forming Vxy (mm/min), vertical tool feed z (mm) and tool diameter D (mm) for single point incremental forming at high temperature (Hot SPIF) technology we will get high precision dimension product. The paper presents a study to optimize the main technological parameters when processing non-alloy Titanium sheet materials by HOT SPIF technology to get the smallest error in the radial direction of the product.

Viscous flow through microfabricated axisymmetric contraction/expansion geometries

We employ a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate a set of axisymmetric microfluidic geometries featuring a 4:1 contraction followed by a 1:4 downstream expansion in the radial dimension. Three devices are fabricated: the first has a sudden contraction followed by a sudden expansion, the second features hyperbolic contraction and expansion profiles, and the third has a numerically optimized contraction/expansion profile intended to provide a constant extensional/compressional rate along the axis. We use micro-particle image velocimetry to study the creeping flow of a Newtonian fluid through the three devices and we compare the obtained velocity profiles with finite-volume numerical predictions, with good agreement. This work demonstrates the capability of this new microfabrication technique for producing accurate non-planar microfluidic geometries with complex shapes and with sufficient clarity for optical probes. The axisymmetric microfluidic geometries examined have potential to be used for the study of the extensional properties and non-linear dynamics of viscoelastic flows, and to investigate the transport and deformation dynamics of bubbles, drops, cells, and fibers. Graphic abstract

System Performance and Process Capability in Additive Manufacturing: Quality Control for Polymer Jetting

Polymer-based additive manufacturing (AM) gathers a great deal of interest with regard to standardization and implementation in mass production. A new methodology for the system and process capabilities analysis in additive manufacturing, using statistical quality tools for production management, is proposed. A large sample of small specimens of circular shape was manufactured of photopolymer resins using polymer jetting (PolyJet) technology. Two critical geometrical features of the specimen were investigated. The variability of the measurement system was determined by Gage repeatability and reproducibility (Gage R&R) methodology. Machine and process capabilities were performed in relation to the defined tolerance limits and the results were analyzed based on the requirements from the statistical process control. The results showed that the EDEN 350 system capability and PolyJet process capability enables obtaining capability indices over 1.67 within the capable tolerance interval of 0.22 mm. Furthermore, PolyJet technology depositing thin layers of resins droplets of 0.016 mm allows for manufacturing in a short time of a high volume of parts for mass production with a tolerance matching the ISO 286 IT9 grade for radial dimension and IT10 grade for linear dimensions on the Z-axis, respectively. Using microscopy analysis some results were explained and validated from the capability study.

Influence of Flow Field's Radial Dimension on Ventilated Supercavitating Flow

To investigate the influence of flow field's radial dimension on the flow of the portion gas-leakage supercavity, based on the two-fluid multiphase flow model and SST turbulence model, considering the compressibility of ventilated gas, a 3D simulation model of ventilated supercavity was established to simulate the flow of the supercavitation, which was consistent with water tunnel experiment. The effect of flow field's radial dimension on ventilated supercavity's dimension and pressure distribution was studied. The results show that flow field's radial dimension has a significant effect on the ventilated supercavity's dimension and pressure distribution. When flow field's radial dimension ratio is 6.5 times lower than the maximum diameter of supercavity, the supercavity cannot be formed to completely enclose the underwater vehicle. With the increase of flow field's radial dimension, the pressure inside and outside the supercavity decreases, and there is a pronounced increase in supercavity dimension. When flow field's radial dimension ratio is 54.0 times greater than the maximum diameter of supercavity, the dimension and pressure distribution of ventilated supercavity remain unchanged, which coincides with the theoretical results. In addition, the calculation results provide a criterion for simulating the shape of ventilated supercavity in the open environment, which can be used to guide engineering practice.

Determination of Swelling and Dimensional Stability of Some Nigerian Timber Species

Aim: The absorption of moisture and dimensional distortion are the major shortcomings of wood utilization as building and furniture materials. This study was aimed at determining the moisture content, swelling ability and dimension stability of five selected timber species. Methods: The samples were collected with the help of the Forest Ranger from the Forestry Department of Enugu State, Nigeria, attached to the Nsukka timber market. The wood samples were evaluated for moisture content change, shrinkage or swelling (%) coefficient, amount of swelling and dimensional change. Results: The change in moisture content across the five species was in the order of Gmelina aborea < Milicia excels < Daniellia oliveri < Alstonia bonnie < Antiaris toxicaria. At 12hrs, Gmelina aborea recorded significantly (P < 0.05) the highest dimension change (46 ± 0.70%) in the radial dimension (direction) as compared to the other species except for Antiaris toxicaria. The swelling coefficient and the amount of swelling were observed to have a strong positive correlation with the dimensional change in the sampled wood. Conclusion: The lower swelling coefficient and the amount of swelling observed in Milicia excels among the five timber species, make it a more suitable species for industrial use.