Numerical characterization of local and global non-uniformities in the load distribution in ball screws

Load distribution in ball screws is a representation of the ball contact stress, and it is fundamental to understanding the behavior of these machine elements. This work aims to conduct a multi-variable analysis of the load distribution in ball screws. For this purpose, a numerical tool is developed for the generation and calculation of ball screw finite element (FE) models, which has been validated against the state of the art. This tool is based on the combination of an analytical contact model and the use of high-order FE models for the analysis of the load distribution of ball screws and stands out for its accuracy (less than 1% error against high-order FE models), adaptability, versatility (models are generated with more than 20 design variables and they can be introduced as components in larger models) and efficiency (being the computational time 1.25% of that of a high-order FE models) with respect to other existing models. Many different design variables (number of start threads, pitch, contact angle, ball size, slenderness and load arrangement) are studied in order to obtain a general characterization of the morphology of the load distribution in ball screws. Among them, the most influential variables on the load distribution and therefore on the structural behavior of ball screws are, load arrangement (with ratio r variations of up to 25% on the same ball screw) and slenderness (with ratio variations of up to 13% on ball screws with two turns of difference). The two most characteristic features, the non-uniformity at a local and global level are identified, along with as the possible causes of their appearance and the consequences that they may cause.

Kadar gula darah atlet sepak bola remaja setelah pemberian diet beban glikemik

Effect of diets with glycemic load arrangement on blood glucose levels in young soccer athletes Background: Carbohydrate arrangement considering the glycemic index (GI) and glycemic load (BG) are important to support the performance of athletes.Objective: To examine the effect of diets with glycemic load arrangement on blood glucose levels in young soccer athletes.Methods: Quasi-experimental study on 14 male young soccer players aged 15-18 years old at Terang Bangsa Soccer School. Each subject completed 4 trials separated by at least 7 days as a washout period. Diets provided consist of high GI with high GL diet (H-H), low GI with high GL diet (L-H), high GI with low GL (H-L), and low GI with low GL diet (L-L). Collected data were fasting blood glucose level (BGL 0), blood glucose level one hour after intervention (BGL 1), blood glucose level two hours after intervention (BGL 2), and blood glucose level after exercise (BGL 3).Results: The results of paired t-test analysis showed that there were differences between fasting blood glucose level and blood glucose level one hour after intervention, blood glucose level one hour after intervention and blood glucose level two hours after intervention, blood glucose level two hours after intervention and blood glucose level after exercise in the H-H and L-H diet group. In the L-L diet group, there were differences between BGL 2 and BGL 3. One-Way ANOVA analysis showed that there were no significant differences in blood glucose levels one hour after the intervention, blood glucose level two hours after intervention, and blood glucose level after exercise between groups.Conclusions: High glycemic load diets influence the increase in blood glucose levels at 1 hour postprandial and after exercise. Low glycemic load diets influence the increase in blood glucose levels after exercise. Diets with the arrangement of glycemic index and glycemic load did not affect blood glucose levels between diet groups.

An Optimal Phase Arrangement of Distribution Transformers under Risk Assessment

This paper presents a phase arrangement procedure for distribution transformers to improve system unbalance and voltage profile of distribution systems, while considering the location and uncertainties of the wind turbine (WT) and photovoltaics (PV). Based on historical data, the Monte Carlo method is used to calculate the power generation value-at-risk (VAR) of WTs/PVs installed under a given level of confidence. The main target of this paper is to reduce the line loss and unbalance factor during 24-hour intervals. Assessing the various confidence levels of risk, a feasible particle swarm optimization (FPSO) is proposed to solve the optimal location of WTs/PVs installed and transformer load arrangement. A three-phase power flow with equivalent current injection (ECI) is analyzed to demonstrate the operating efficiency of the FPSO in a Taipower feeder. Simulation results will support the planner in the proper location of WTs/PVs installed to reduce system losses and maintain the voltage profile. They can also provide more risk information for handing uncertainties when the renewable energy is connected to the distribution system.

Effect of Plastering Layer on Corrosion Resistances of Reinforced Concrete Beams

Reinforced concrete structures are subjected to deterioration due to many factors such as corrosion of reinforcing steel. Ultimate strengths of structural elements can be greatly affected by these deteriorating factors. There are numerous methods and techniques used to protect these structural elements. The mortar layer (Plastering) is considered the first defense line against all the deteriorating factors. The main goal of this research is to investigate to what extent the plastering layer can protect reinforced concrete beams against corrosion. The aim of the experimental program is to study the effect of plastering layer on corrosion resistance of reinforced concrete beams. Four reinforced concrete beams (1002001100 mms) and four Lollypop specimens (cylinders 100200 mms) were tested and described as follows: • A beam and a lollypop specimen without any plastering layer (control). • A beam and a lollypop specimen with traditional plastering layer (cement + sand + water). • A beam and a lollypop specimen with modified plastering (traditional plastering + waterproof admixtures). • A beam and a lollypop specimen with painted and modified plastering layer (traditional plastering + waterproof admixtures + external waterproof paint). These eight specimens were subjected to corrosion using accelerated corrosion technique, after that the four beams were tested in flexure under three point load arrangement while the four lollypops were used to calculate the total mass loss due to accelerated corrosion. The test results were used to figure out the effect of plastering layer on corrosion resistance of RC beams.

Influence of Wear on the Performance of Multirecess Hydrostatic Journal Bearing Operating With Micropolar Lubricant

The objective of the present work is to study theoretically the influence of wear on the performance of four-pocket capillary-compensated hydrostatic journal bearing operating with micropolar lubricant. In the present study, the lubricant containing additives and contaminants is modeled as micropolar fluid. The modified Reynolds equation for micropolar lubricant is solved using finite element method along with capillary restrictor flow equation as a constraint together with appropriate boundary conditions. The performance characteristics of a capillary-compensated four-pocket worn hydrostatic journal bearing operating with micropolar lubricant have been presented for a wide range of values of nondimensional external load, wear depth parameter, and micropolar parameters. The simulated results have also been presented for two different loading arrangements. In arrangement I, the load line acts through centers of the pockets, whereas in arrangement II, the load line bisects the land between two pockets. The simulated results suggest that a bearing lubricated with lubricant having higher micropolar effect has better static and dynamic performance characteristics as compared with Newtonian lubricant but the bearing lubricated with lubricant having higher micropolar effect is predominantly affected by the wear vis a vis static characteristics parameters as compared with Newtonian lubricant for both loading arrangements. However, in the case of stiffness and damping coefficients, loading arrangement II shows a significant higher enhancement in the value of direct stiffness and damping coefficients in z-direction due to micropolar effect as compared with load arrangement I. And also, the effect of wear on stiffness and damping coefficients in z-direction for bearing operating with micropolar lubricant is of same order as Newtonian lubricant for the loading arrangement II. A similar behavior is observed for the case of stiffness and damping coefficients in x-direction for loading arrangement I.

A multi-start random constructive heuristic for the container loading problem

This paper deals with the container loading problem which involves the selection of a subset of boxes, each box with a given volume, such that they fit in a single container and maximize its volume utilization subject to orientation and stability constraints. We propose a multi-start random constructive heuristic with a load arrangement that is based on maximal cuboids that fit in given empty spaces. Each instance is adaptively evaluated by a set of criteria, and at each step of the construction process one maximal cuboid is chosen probabilistically from a restricted list of candidates. In order to enhance the flexibility in the construction of a solution, a probabilistic reduction on such cuboids is allowed. Computational tests on several instances from the literature show that the proposed method performs better than other approaches.

Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes

This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169mm outer diameter and 14.33mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestractive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results.