Decrease In Rotational Speed Research Articles

Circular Asymmetry of Ocean Mesoscale Eddy

Abstract In the global ocean, mesoscale eddies frequently deviate from a circular shape [circular asymmetry (CA)]. On average, anticyclonic eddies display slightly larger asymmetry than that of cyclonic eddies. Both types of eddies exhibit larger asymmetry during the periods of generation and extinction and smaller asymmetry during the intermediate periods. CA’s spatial distribution is dominantly controlled by the eddy’s rotational speed, radius, meridional displacement, and the background oceanic circulation. A decrease in rotational speed, an increase in radius, moving poleward (toward the equator), and/or moving into regions with smaller (larger) mean dynamic topography can enhance the asymmetry of anticyclonic (cyclonic) eddies. A weak advective nonlinearity of the eddy, represented by the ratio of the eddy’s rotational speed to its translation speed, also helps to enhance the asymmetry. Eddy with an asymmetric structure may be important for marine mixing processes. Significance Statement Mesoscale eddies are often assumed to be circular and symmetric. However, global observations reveal that eddies frequently diverge from a circular shape, displaying circular asymmetry (CA). The asymmetric structure of eddy is poorly investigated in the global ocean, especially in regions close to the strong oceanic currents. This study reported the evolution of eddy’s asymmetric structure and its spatial distribution. Statistical results show that CA is dominantly controlled by the eddy’s rotational speed, radius, meridional displacement, and the background oceanic circulation. This study provides a new perspective on the evolution of eddy’s structure and may be important in oceanic mixing.

The effect of impeller height and rotation speed on the Kambala reactor desulfurization process

To improve the utilization efficiency of desulfurizer in the Kambala reactor liquid iron desulfurization process and prolong the life of the impeller, the height of the impeller and its optimal matching rotation speed are optimized. Through numerical simulation, the mixing effect of different height impellers under different rotation speeds is studied, the movement and distribution modes of desulfurizer particles are analyzed, the pumping capacity and power are calculated, and the influence of impeller height and optimal matching rotation speed on the desulfurization effect has been clarified. The numerical simulation results show that the optimization of impeller height and optimal matching rotation speed can improve the mixing effect. The height of the impeller increases, and its optimal matching rotation speed decreases. Based on the results, in existing models, it is recommended to run at 60 r/min with an impeller height of 800 mm for optimal mixing performance.

Study the Flow Capacity of Cylindrical Pellets in Hopper with Unloading Paddle Using DEM

The hopper is an important piece of basic equipment used for storing and transporting materials in the agricultural, grain, chemical engineering, coal mine and pharmaceutical industries. The discharging performance of hoppers is mainly affected by material properties and hopper structure. In this work, the flow capacity of cylindrical pellets in the hopper with the unloading paddle is studied. A series of numerical simulation analyses with the aid of the discrete element method (DEM) platform are carried out. Then, the discharging process is illustrated, and the flow capacity of pellets in the hopper is analyzed by the mass flow index (MFI), the dynamic discharging angle (DDA) formed in the discharging process and porosity among pellets. Furthermore, the effect of parameters such as hopper half angle, rotation speed of the unloading paddle and outlet diameter of the hopper is investigated. The results show that MFI increases with an increase in hopper half angle or outlet diameter and a decrease in rotation speed. Meanwhile, DDA and porosity decrease with the increase in the hopper half angle or outlet diameter and the decrease in the rotation speed. Finally, the MFI ~0.24 is identified as the criterion to distinguish the mass flow from the funnel flow for the hopper with an unloading paddle, and the optimization results are decided as follows: hopper half angle greater than 60°, outlet diameter greater than 60 mm and rotation speed between 45 rpm and 60 rpm. These results should be useful for providing a theoretical reference for the optimization design of feeding devices for swine feeders.

Investigation Of The Influence Of The Turbine Wicket Gates Closure Law Pattern On The Water Hammer Effect During Turbine Off-Design Operation

Hydraulic transients are accelerated by the wicket gate closing in hydroelectric power plants. When the wicket gate is closed, there is a sudden change in velocity due to the closure. Therefore, a study has been carried out here, wherein water hammers on different hydropower components use optimum closure laws: Fast closure laws, slow closure laws, and instant load rejection. Hammer V10i software was used to investigate the phenomenon of pressure transient. The results show that the maximum transient pressure is strongly influenced by a very short closing time and was increased to 41.24% from the slow to the fast closure.
 Furthermore, the results from instant load rejections reveal that the transient pressure will be less than the fast and slow closure. So, the closing law selection can positively influence the entire hydropower plant system. Furthermore, the results show that there was a decrease in pressure near the turbine during the different load rejections, Fast closure, slow closure, and instant load rejection, where 57.7%, 15%, and 0.46%, respectively, and the decrease in turbine rotation speed were as 5.1%, 60%, and 24% respectively. Moreover, results reveal that maximum and minimum flow variation reached -29.75% and 41.2% during the fast closure.
 

Metallurgical Method of Determining Heat Transfer Coefficient in Simulations of Twin-Roll Casting

We herein suggest a metallurgical method using pure aluminum with no freezing temperature range to derive appropriate roll/melt interfacial heat transfer coefficients in simulation of twin-roll casting process. This method is inspired by the concept that the position of the kiss points where two solidifying shells encounter and the roll nip coincides under the condition where the roll load becomes zero as the roll rotation speed decreases. The conditions where the roll load becomes zero under various melt supply temperature conditions in the actual TRC process are found experimentally. These conditions are then applied to simulation models to derive heat transfer coefficient values. When comparing these values with those derived previously from the empirical relation for roll rotation speed and heat transfer coefficient, the conclusion is drawn that the deviation was reasonably low, around 10%.

Experimental investigation of wind turbine stress and power characteristics under dynamic changes in wind direction

ABSTRACT The dynamic inlet conditions of variable wind direction had an obvious influence on the response of wind turbine stress and power, and accurately analyzing their changing characteristics is of great significance to enhancing wind turbines’ stability and efficient operation. Experiments were performed in a wind tunnel, where the wind turbine was mounted on a rotating platform to simulate dynamic changes in wind direction at prescribed speeds and angles. The wind turbine’s stress and power were measured. Results show that the stress was minimally reduced by 4.4% (tower) and 1.7% (blade) when the wind direction change angle was small. Maximum stress reduction of 92% (tower) and 93% (blade) with increasing wind direction change angle. As the wind direction change speed increased, the magnitude of the drop in blade stress decreased by 6% ~32%. The decrease in power coefficient and rotational speed at small wind direction change angles and large wind direction change speeds were not significant, and the fluctuations were more obvious. The coupling of aerodynamic deterioration and inertial effects during dynamic changes in wind direction was one of the main reasons for the variations in the wind turbine power and stress response.

Effect of Residual Stress and Microstructure on the Fatigue Crack Growth Behavior of Aluminum Friction Stir Welded Joints.

Friction stir welding (FSW) has been adopted in the aerospace industry for fabricating structural alloys due to the low melting point and high thermal conductivity of aviation aluminum alloys. However, welding residual stresses can lead to secondary deformation in friction stir welded (FSWed) structures. Additionally, microstructural characteristics impact the crack growth rates and directions in these structures. Therefore, it is necessary to investigate the effects of residual stress and microstructure on the fatigue responses of FSWed joints. In this paper, we studied the fatigue crack growth behavior of two homogeneous and dissimilar FSWed joints with varying welding parameters, namely 2024-T3 and 7075-T6. The residual stresses were measured with the X-ray diffraction method. The dislocations and precipitates in different zones of the FSWed joints were analyzed via transmission electron microscopy (TEM). The results demonstrated that the residual stress significantly affected the fatigue crack growth rate and direction; the tensile residual stress promoted fatigue crack growth and offset the decrease in the fatigue crack growth rate that occurred due to grain refinement. The results of the microstructural analysis indicated that dislocation density and sliding resistance increased with the decrease in rotational speed and led to a decreased rate of fatigue crack propagation.

AN EXPERIMENTAL INVESTIGATION OF THE SPEED LOSSES IN POLY-V BELT SYSTEMS ON HOUSEHOLD DRYERS

A decrease in rotational speed in gear belt systems is one of the fundamental problems that affects the efficiency of the belt. Therefore, in this study, the speed loss behavior of a Poly-V gear belt drive system with two different designs has been experimentally investigated. In the study, experiments were conducted with two different home-type dryers; one used two belts and a stepped pulley to adjust the speed, while the other used a single belt to reach the required speed. The experimental studies were conducted with two different home-type dryers. The results were analyzed using statistical methodology to determine whether the normal distribution was suitable for the measurement results, and a pairwise comparison of the speed losses in the two systems was made. Additionally, the predicted formula for loss calculation was compared with the results of variance analysis (ANOVA), and it was found that very similar results were obtained. As a result of the experimental study and analysis, it was observed that the single-belt drive system is more efficient compared to the two-belt drive system. With the efficiency curve obtained from this study, it is possible to calculate speed loss and efficiency gain for similar belt drive systems.

Correlation analysis of structural characteristics of table tennis players' hitting movements and hitting effects based on data analysis

The increase in table tennis ball size and the decrease in table tennis ball speed and rotation speed in recent years have brought new challenges to the body strength of table tennis players and put new tests on the physical fitness and stability of the hitting action of the players. Improving the body strength can accelerate the rotation speed of the ball, improve the body quality and stability, and improve the accuracy of the ball. Basic skills training is a new method of modern sports training. After scientists studied it, they played a positive role in table tennis. The purpose of the paper is to discuss the impact of table tennis basic skills training, provide more space for the development of physical fitness training, provide the best training tools, and provide ways to improve the impact of hitting. The purpose of this document is to use the sports capture system to collect data from the structural characteristics of table tennis players, analyze the impact of various structural characteristics of the ball, and analyze the impact of various factors affecting table tennis players. In the process of a table tennis player's frontal downward spin stroke, the structure types of the player's frontal downward spin stroke were divided into two types: fast type and slow type according to the different lengths of the three stages of the player's stroke action. The experimental results proved that the optimized model applied to the correlation analysis between the structural characteristics of the stroke action and the stroke effect was stronger, and the accuracy was improved by nearly 5%, achieving the hypothesized goal.

Effects of chloride solution on the corrosion behaviour of dissimilar friction stir butt welded joints of aluminium alloys

The corrosion behaviour of dissimilar friction stirs butt welded joints of cold-rolled AA6061-T6 and additively manufactured AlSi10Mg aluminium alloys was investigated by immersion tests in aqueous sodium chloride and hydrogen peroxide solutions. Optical microscopy was employed to investigate corrosion responses and to understand the corrosion mechanisms of stir weld regions. For the same material positioning, with the decrease in tool rotational speed, the corrosion rate was observed to increase. At the same tool rotational speed, a weld joint having AA6061-T6 on the advancing side and additively manufactured AlSi10Mg on the retreating side exhibited a lower tendency to corrode towards the test solution. The predominant corrosion mechanism for the dissimilar friction stir butt welded joints was observed to be pitting corrosion.

Effect of process parameters on the mechanical properties of fiber‐reinforced thermoplastics fabricated by direct fiber feeding injection molding

AbstractGlass fiber‐reinforced polypropylene composites (GF/PP) were fabricated in this study by direct fiber feeding injection molding technology (DFFIM) equipped with specially designed plasticizing units. By analyzing the fiber length distribution, scanning electron microscopy micrographs, and the mechanical properties of GF/PP composites, the effect of three process parameters, namely the number of fiber bundles, screw rotational speed, and injection pressure, on the properties of GF/PP composites fabricated by DFFIM were investigated. The results show that the mechanical properties of GF/PP composites gradually increase as the fiber content increases and the screw rotational speed decreases; however, when the fiber content exceeds a certain range, the enhancement effect of mechanical property is reduced due to the increase of fiber breakage and fiber aggregation. Appropriately increasing the injection pressure can increase the fiber length and make the fiber and PP more tightly bonded, and the mechanical properties of GF/PP composites gradually improve, but the fiber breakage phenomenon is more severe under excessive injection pressure, the mechanical property enhancement effect is reduced or even the mechanical property is decreased due to the decrease of the fiber length.

Mass Transfer Behavior of a Rotating Packed Bed of Raschig Rings Suitable for Wastewater Treatment

AbstractThe mass transfer behavior of a rotating packed bed of Raschig rings was examined to increase the rate of liquid‐solid diffusion‐controlled reactions common in the production of fine chemicals, pharmaceuticals, and wastewater treatment. The aim was to measure the enhancing effect of the centrifugal force and the high area per unit volume of the bed, using diffusion‐controlled copper dissolution in acidified dichromate as the experimental approach and the bed rotation speed, the Raschig ring diameter, and the bed height as variables. A dimensionless mass transfer equation suited for scaling up and reactor design was used to correlate the data. Measurement of the specific mechanical power consumption ε of the rotating bed under different conditions revealed that the energy utilization efficiency increases with decreasing bed rotation speed.

Experimental Research on Performance Comparison of Compressed Air Engine under Different Operation Modes

An air-powered vehicle is a low-cost method to achieve low-pollution transportation, and compressed air engines (CAE) have become a research hotspot for their compact structure, low consumption, and wide working conditions. In this study, a pneumatic motor (PM) test bench is built and tested under different inlet pressures, operation modes, and three driving cycles. On the basis of the data obtained by sensors, power output, compressed air consumption rate, and efficiency are calculated to evaluate the pneumatic motor performances. The results show that with an increase in rotation speed, the output power and efficiency first increase and then decrease, and the compression air consumption rate decreases. With an increase in torque, the rotation speed decreases, and the power output and efficiency first increase and then decrease. With an increase in mass flow rate, the torque increases, the power output and efficiency first increase and then decrease. The pneumatic motor achieves the best performance under a rotation speed of 800–1200 rpm, where power output, efficiency, and compressed air consumption rates are 1498 W, 13.6%, and 10 J/g, respectively. The pneumatic motor achieves the best power output and efficiency under the UDDS driving cycle.

Under Different Working Conditions Carbon Oxides and Nitrogen Oxides Emission of n-Butanol and LNG in Diesel Engine

Through the establishment of covering substances such as CH4, C4H10O, nitride specific combustion reaction mechanism, carbon oxides and nitrogen oxides emissions can be simulated by CHEMKIN-PRO at the four fuel mixing ratios and same excess air coefficient, the Man 6S35ME-B9dual-stroke diesel engine was used as the experimental object. Changes in temperature, pressure, mole fraction of NO and mole fraction of CO2 in the reactor were investigated at 1.5, and the influence factors of crank angle on pollutant emission of marine diesel engine under various operating conditions were studied. The simulation results show that with the loss of the diesel engine rotating speed, exhaust temperature and exhaust pressure significantly reduced. In the meantime, the mole-percent of NO and CO2 decreased with the decrease of rotational speed. Compared with the rotational speed of 142 r/min, the molar mass of NO and CO2 in exhaust gas decreased by 54.7% and 24.1% at 89.5 r/min, respectively.

Study on the Emission Characteristics in Renewable Energy Combustion under Different Working Conditions of Marine Two-Stroke Diesel Engine

In this paper, MAN 6S35ME-B9 two-stroke diesel engine is taken as the research object. By constructing a detailed combustion reaction mechanism including CH4, C4H10O, nitrides and other substances, CHEMKIN-PRO is used to simulate the same fuel mixing ratio and excess air coefficient. Under the condition of 1.5, the temperature, NO mole fraction and NH3 mole fraction in the reactor change and study the factors affecting the pollutant emission of marine diesel engine with the crank angle under different working conditions. The simulation shows that with the decrease of diesel engine speed, the maximum temperature of combustion reaction and the temperature at exhaust opening are obviously reduced. At the same time, mole fraction of NO and NH3 decreases with the decrease of rotational speed, and there is no nitride production in the combustion reaction at 25%.

Role of sacrificing layer on glasses during ultrasonic machining (USM) - a review

Ultrasonic machining is a non-traditional, non-thermal material removal method; used to fabricate channels and drill holes in brittle materials such as glasses and wafers by using customized tools and ultrasonic vibrations. In this paper, different types of ultrasonic machining processes (Rotary, Stationary, Hybrid, and Micro) along with its process (Feed Rate, Tool Rotation Speed, Amplitude, Frequency, and Ultrasonic Power) and performance (MRR, Surface Roughness, Overcut, Edge Chipping, and Tool Wear) parameters have been studied. The role of sacrificing layers on glasses and silicon wafers during ultrasonic machining and their effect on various performance parameters have been extensively reviewed in this article. This article also presents a comprehensive and chronological review of ultrasonic machining and possible process and performance parameters on the wide variety of brittle materials extensively in different types of glasses used by various researchers. This provides optimized input and output parameters for their machining. In conclusion, MRR has been found directly proportional to Feed Rate, Tool Rotation Speed, and Ultrasonic Power. Surface Roughness has been observed to increase with the increase in Feed Rate and decrease in Tool Rotation Speed and Ultrasonic Power. Edge Chipping has been observed to be directly proportional to Feed Rate, Tool Rotation Speed and inversely proportional to Ultrasonic Power. It is also concluded that by incorporating Sacrificing Layer, overcut is decreased and the overall surface finish is increased. The objective of this paper is to study the significance of sacrificing layers and to provide optimized process parameters for ultrasonic machining of different glass types.

Prediction of M–A Constituents and Impact Toughness in Stir Zone of X80 Pipeline Steel Friction Stir Welds

This study explored a strategy for predicting the proportion of martensite–austenite (M–A) constituents and impact toughness of stir zone (SZ) on X80 pipeline steel joints welded by friction stir welding (FSW). It is found that the welding forces, including the traverse force (Fx), the lateral force (Fy) and the plunge force (Fz), are the key variables related to the change of welding parameters and influence remarkably the characteristics of M–A constituents and impact toughness of SZ. The impact toughness of SZ is commonly lower than that of the base material due to the formation of lath bainite and coarsening of austenite. The characteristics of M–A constituents in SZ are sensitive to the variation of welding parameters and respond well to the change of welding forces. The proportion of small island M–A constituents increases with the decrease in rotational speed and the increase in Fz. The increase in the amount of island M–A constituents is beneficial to improve the impact toughness of SZ. Based on the above findings, a machine learning (ML) model for predicting the M–A constituents and impact toughness is constructed using the force features as the input data set. The force data-driven ML model can predict the M–A constituents and impact toughness precisely and exhibits higher accuracy than ML built with welding parameters. It is believed that the high accuracy is achieved because the force features include more details of FSW process, such as the heat generation, material flow, plastic deformation, and so on, which govern the microstructural evolution of SZ during FSW.

Experimental evaluation of organic Rankine cycle using zeotropic mixture under different operation conditions

The zeotropic mixture is a feasible way to improve the thermodynamics performance of organic Rankine cycle (ORC). A small-scale ORC experimental apparatus with a scroll expander was established. Then, the system performance using different zeotropic mixtures (including 0.75R245fa/0.25R141b, 0.5R245fa/0.5R141b and 0.25R245fa/0.75R141b) was tested and compared with the pure fluid of R245fa and R141b to determine whether the mixture fluid can improve the system performance. The experimental results show that the thermal efficiency and exergy efficiency of ORC system gradually increase with the increase of cooling water flow rate and the decrease of expander rotational speed. Under different working conditions, mixture fluids can produce more shaft power and have lower condenser exergy destruction than pure fluids. The zeotropic mixture is not always better than the pure fluid, while it can improve the thermal efficiency and exergy efficiency of the ORC system with an appropriate mass fraction. In the experiment, the best mass fraction of R245fa/R141b is 0.25/0.75, and its thermodynamic performance is significantly higher than that of R141b and R245fa. The maximum thermal efficiency and exergy efficiency of 0.25R245fa/0.75R141b are 5.58% and 23.2% respectively.

Thermal-fluid-structure coupling analysis of void defect in friction stir welding

Understanding the void defect formation mechanism and simultaneous predicting the tool service life in friction stir welding are critical for optimizing the welding parameters. However, the void defect formation mechanism in friction stir welding is not yet elucidated. In this study, a novel integrated thermal-fluid-structure coupling model of the friction stir welding process was proposed for simultaneous prediction of the weld formation and tool service life. A new non-uniform distribution model of the tool-workpiece contact pressure was proposed to describe the interaction between the tool and the workpiece. The void defect formation mechanism was quantitatively studied using the proposed integrated thermal-fluid-structure coupling model. The results show that the plastic material flows in the horizontal direction and can completely fill the cavity behind the tool for the welding condition of forming a sound weld. While the tool-workpiece contact interfacial frictional shear stress in the rear of the tool is decreased significantly which leads to a severe decrease in the plastic material flow velocity. Therefore, after bypassing the tool from the retreating side, the plastic material at the bottom of the weld stagnates, and void defect forms in the middle and lower part of the weld at the advancing side. The difference between the maximum and the minimum tool-workpiece contact pressure could serve as a numerical criterion to predict void defects. A sound joint is formed when the difference is lower than the critical value of 15 MPa, while a void defect is formed in the weld if it is higher than this critical value. The maximum equivalent stress acting on the tool is located at the pin root with severe stress concentration at a high welding speed. The front of the tool is subjected to tensile stress while its rear is subjected to compressive stress, therefore the tool is apt to fracture at its root under an inappropriate welding condition. The average normal stress of the tool varies periodically with its period consistent with the rotation period of the tool. The service life of the tool is decreased with the increase in welding speed and the decrease in rotation speed. The model is validated by experimental results.

Microstructures and mechanical properties of friction stir welded butt joints of 3003-H112 aluminum alloy to 304 stainless steel used in plate-fin heat exchanger

The valid joining of aluminum and steel plays an important role in support structure of heat exchanger, which was widely used in chemical, automobile and aircraft industries, etc. In this work, in order to improve the connection of aluminum to steel joints, the friction stir welding (FSW) method was applied to weld a 3003 aluminum alloy to a 304 stainless steel. The microstructures, mechanical properties and fracture mechanism of FSWed joints were studied. The results showed that an optimal joint was obtained at the rotational speed of 200 rpm, the traverse speed of 30 mm/min and the offset of 3.0 mm. The distance of root incomplete penetration increased with the raise of offset and the rotational speed. The offset had a more significant effect on the microstructure of the welded joints compared with the rotational speed. Both the tensile property and the microhardness of the stir zone improved with the decrease of rotational speed at the offset of 3.0 mm. The FSWed joints firstly generated stress concentration at the weld root during loading. With the further increase of the load, the weld root cracked and finally broke in the stir zone.