Reduction Of Rotational Speed Research Articles

Numerical investigation of vehicle water entry with angle of attack

This paper investigates the water entry of a vehicle with angle of attack (AOA) through numerical methods, employing the volume-of-fluid multiphase flow model and overset grid technique. The validity of the numerical model is confirmed through experimental verification. Building upon this, the study analyzes the motion characteristics, cavity evolution, and flow field distribution of the vehicle during water entry, considering the influence of AOA and falling velocity. Numerical findings indicate that the collapse of the right side of the cavity induces a transient lateral force on the vehicle, resulting in vehicle tilting. Moreover, an increase in initial velocity delays vehicle tilt, while an increase in AOA reduces vehicle motion stability, leading to earlier tilting. Initially, the vehicle rotates counterclockwise around the Oz axis of the projectile coordinate system. Subsequent to cavity collapse, the vehicle experiences an opposing moment, leading to a reduction in rotation speed and eventual rotation in the opposite direction. Water impact triggers sudden changes in the vehicle's lift and drag coefficients, while cavity sticking induces a minor abrupt change in the lift coefficient. Following cavity collapse, both lift and drag coefficients exhibit significant oscillations. Unlike typical cavity collapse phenomena, the flow field on the right side of the vehicle undergoes alternating high-pressure and low-pressure regions.

ТЕОРЕТИЧЕСКОЕ ОБОСНОВАНИЕ ЧАСТОТЫ ВРАЩЕНИЯ ЛОПАСТНОГО ПОГРУЗЧИКА В ЦИРКУЛЯЦИОННОМ СМЕСИТЕЛЕ

The purpose of the research is to substantiate the critical rotation speed of the working body based on force analysis and modeling of the movement of particles of a bulk product in a horizontal loader with radial blades located in a circulation mixer. The research methodology involved substantiating the maximum rotation speed of the loader working body based on an analysis of the forces acting on particles as they move by the loader blades and fall into the tray during flight. Based on the obtained expressions, the values of the indicators were modeled to analyze and substantiate rational values. The implementation of a numerical analysis of the obtained expressions based on force analysis and process modeling with the Mathcad mathematical package made it possible to identify the critical values of the rotation speed of the working body of a paddle loader based on the condition for the possibility of material coming off the blade and the condition for the possibility of particles flying from the blade into the receiving tray. Due to the need for material to flow off the blades and the rotation speed reduction factor of 0.9, the rotation speed of a blade loader with an outer diameter of blades of 0.24 m and an inner diameter of 0.17 m should not exceed 77 min-1 . The highest rotation speed of the working body shaft at which particles of material will enter the receiving tray area from the outer end of the blade is 43 min-1 , and from the inner end - 73 min-1 . In the process of manufacturing a circulating mixer with a radial blade loader for experimental studies, it should be possible to change the rotation speed up to 43 min-1 . To test theoretical principles in exploratory experiments, it is necessary to provide for the possibility of changing the rotation speed of the blade loader shaft to 70 min-1 .

Feasibility study on improving the performance of the kitchen exhaust system by integrating a supercharging fan

Connecting a supercharging fan (SF) in series with the range hood is a practice way to better discharge the harmful oil fumes in residential kitchens, but a poor match SF may fail to help exhaust and even cause additional noise issues. This study aims to clarify how the SF rotation speed affects the operation of the existing range hood and explore the possible noise advantages of the series exhaust system. The computational fluid dynamics method was used to simulate the aerodynamic performance and internal flow of different exhaust systems. Analysis revealed that the system's exhaust capability can only be improved when the SF rotates fast enough, generating sufficient pressure rise to overcome its own flow resistance. Performance leading over the entire flow range is achieved when the SF rotates at 2500 rpm, where the pressure rise in the actual working range is increased by nearly 40%. These performance enhancements buy a rotational speed reduction of almost 300 rpm for the hood fan when the system's pressure remains unchanged. The airflow in the range hood thus decelerated by 14.5–18.2%, and the undesired reverse flows were also inhibited. The results obtained by full-scale kitchen experiments show that the sound pressure level of the series system was 0–1 dB lower than that of the original range hood in the same flow rate, and this decrement is maximum to 2 dB by inducing sound-absorbing treatment on the SF. This study provides preliminary guidance for integrating an SF in a range hood exhaust system, offering a novel view of its benefits and challenges.

Experiment study on fire extinguishing effects of airflow-water synergistic jet

As an important forest firefighting equipment in China, the 6 MF-30 pneumatic fire extinguisher has the problem of engine overheat resulting in rotational speed reduction during application. Adding water as a medium to form an airflow-water synergistic jet can improve the fire extinguishing effect. In this paper, through experiments, flow field analysis was carried out on the wood crib fire extinguishing scene and fire extinguishing effects were analyzed. It was found that the extinguisher with a rotational speed below a certain degree could not extinguish the wood crib fire. The airflow-water synergistic jet can effectively improve the fire extinguishing efficiency, greatly reduce the fire extinguishing time, and reduce the risk of reignition. The best effect is to use 4 nozzles to inject water into the outlet of the air duct, which can achieve the effect of direct injection with water pipe in the case of limited water source.

Theoretical and experimental analysis of the centrifugal micro hydrodynamic axial-thrust bearing

The novel centrifugal micro hydrodynamic axial-thrust bearing has been demonstrated to substantially mitigate the wear in hydrodynamic suspension micropumps. To further elevate the bearing performance, the flow mechanism is systematically analyzed via numerical simulations and experiments in this work. The effects of various properties of bearing on the performance are explored and explained. Results indicate that the load capacity augments with the growth of inlet-suction flow rate and with the reduction of rotational speed. Meanwhile, it initially decreases and then increases as fluid film thickness expands. Further, the bearing exhibits proper stiffness and adaptable anti-abrasion when thickness maintains 0.3 mm. This study provides a profound understanding of centrifugal micro hydrodynamic axial-Thrust bearing, and identifies its optimization measures.

Design and verification of Francis turbine working in sand laden hydro-power plant

Sand erosion is usually severe for hydraulic turbine operated in sediment-laden river hydro-power plant. Continuous erosion and abrasion in hydro-turbine components not only deteriorate the turbine performance but also bring frequent maintenance work. Thus, special attentions should be paid to anti-erosion performance besides the efficiency and stability during the hydraulic design stage. In this paper, the performances of a prototype Francis turbine used for a high head heavy sediment power station were investigated by reducing the rotational speed and using splitter runner. The hydraulic performance, anti-erosion characteristics and cavitation performance were focused and analyzed. The results proved that the velocity in the runner can be effectively reduced by lower the rotational speed, but the rotational speed reduction was also limited by the efficiency and velocity near the guide vane. The splitter runner can significantly improve the disorder flow in runner by re-distributing the velocity field. The erosion resistance of guide vane can be improved by increasing the pitch diameter of the guide vane appropriately. 3100 h of operation after commissioning further confirmed the anti-erosion and stability performance of the designed Francis turbine. This research provide a good reference for the Francis turbine design operated in heavy sediment hydro-power plant.

A Numerical Model for the Prediction of Performance Parameters and Hydraulic Losses in Centrifugal Pump Systems such as Turbine

The prediction of the energy performance of centrifugal pump systems such as turbines is one of the main needs to evaluate the viability of projects focused on energy recovery in high pressure flows rate. Due to the above, in this investigation, the construction of a numerical model has been carried out for the prediction of the performance parameters in pump systems such as turbines under different operating conditions. The analysis of the performance parameters includes the head, the generated power, and the efficiency. Additionally, the numerical model developed takes into consideration the hydraulic losses present in the impeller, the inlet pipe, and the pump volute. From the results obtained, it has been demonstrated that the proposed numerical model has the ability to predict the performance parameters of the pump as a turbine. It has been possible to obtain an average relative error of 2.82% and 3.52% in the prediction of the head and the efficiency of the PAT system. The analysis of the efficiency of the pump as a turbine has showed that this type of system could reach an efficiency of 84.7%. It has been evidenced that the rotation speed reduction causes a greater restriction in the efficient operating areas of the PAT system. In general, the proposed numerical model is an alternative tool to evaluate the behavior of centrifugal pumps as a turbine under different operating conditions.

Reducing Bird Collision Risk Per Megawatt by Introducing Longer Wind Turbine Blades

Renewable energy, including wind energy, remains one of the most effective options for controlling global warming. However, increasing wind turbine size (mainly blade size) implies expanding the blade swivel range (rotor sweep zone), and concerns have been raised about a possible increase in the number of bird collisions with the rotating blades. Conversely, an increase in turbine size, accompanied by a reduction in rotation speed might reduce the avian collision risk. The change in the number of collisions with increasing wind turbine size was analyzed using simple collision risk models. The results showed that with an increase in the length of the wind turbine blade, although the number of collisions per turbine increased monotonically, the number of collisions per megawatt generated decreased as a hyperbolic function. These models involved some assumptions for simplicity; therefore, their validity requires testing in wind-power replacement projects.

Optimization of Automotive Bosch-140 Alternator to use as a Generator for Small Wind Turbine

The generator is one of the costly elements of a small wind turbine. This paper developed a suitable low-cost small wind turbine generator, which can be modified to be easily manufactured. The experiment was conducted in two parts, the first part involves monitoring the current, voltage, power, and temperature for the Bosch 140 alternator before re-winding (initial case), and the second part includes monitoring of parameters (current, voltage, power) with modifying the alternator (Bosch 140) by re-winding depending on the results of the JAMG program simulation (last case). The Bosch 140 alternator was modified consistently by reducing the wire diameter to half to double the windings to evaluate the maximum torque. A genetic algorithm was used to optimize the stator’s design optimization to achieve a maximum torque of the magnet. The final result shows a good indication of the modified alternator’s efficiency, where it is increased by about 30% from the initial case, and the generation of voltage started at a low rotation speed. It was observed that the new optimization of claw-pole alternator provides fairly the double torque with at least 16% reduction in rotation speed.

Additional debulking efficacy of low-speed rotational atherectomy after high-speed rotational atherectomy for calcified coronary lesion.

We aimed to evaluate the additional debulking efficacy of low-speed rotational atherectomy (RA) after high-speed RA by using intravascular imaging. A total of 22 severe calcified coronary lesions in 19 patients (age, 74 ± 10years; 74% male) were retrospectively analyzed. All of these lesions underwent RA under optical coherence tomography (OCT) or optical frequency domain imaging (OFDI) guidance. At first, we performed high-speed RA with 220,000rpm until the reduction of rotational speed disappeared; then, low-speed RA with 120,000rpm using the same burr size was performed. OCT or OFDI was performed after both high-speed and low-speed RAs, and the minimum lumen area were compared. The initial and final burr sizes of high-speed RA were 1.5 (1.5-1.75) and 1.75 (1.5-2.0) mm, respectively. The number of sessions, total duration time, and maximum decreased rotational speed during high-speed RA were 11 ± 5 times, 113 ± 47s, and 4000 (3000-5000) rpm, respectively. During low-speed RA, the number of sessions, total duration time, and maximum reduction of rotational speed were 3 ± 1 times, 32 ± 11s, and 1000 (0-2000) rpm, respectively. The minimum lumen area was similar between after high-speed and after low-speed RA [2.61 ± 1.03 mm2 (after high-speed RA) vs. 2.65 ± 1.00 mm2 (after low-speed RA); P = 0.91]. Additional low-speed RA immediately after sufficient debulking by high-speed RA was not associated with increased lumen enlargement. There was no clinical efficacy of low-speed RA after high-speed RA.

CFD simulation of turbulent flow of drill cuttings and parametric studies in a horizontal annulus

Understanding the mechanisms of cuttings transport and investigating the effects of different parameters is necessary to design an efficient cuttings transport process. Improper hole cleaning leads to the accumulation of drill cuttings in the well annulus and causes many problems such as rotational speed reduction, stuck pipe, circulation loss, and drill bit abrasion especially in horizontal drilling. In this study, computational fluid dynamics (CFD) were used for simulation of turbulent two phase flow in a horizontal annulus including a Herschel–Bulkley drilling fluid. The Lagrangian–Eulerian/discrete element method approach was adopted for description of the particle flow, interparticle and particle–wall interactions. Simulation results were compared and validated against published experimental data in the literature and j simulation results indicate that at constant drilling rate, the major factors that affects hole cleaning in horizontal wellbores are drill pipe rotational speed, drilling fluid rheology and velocity. Results of this study show the reliability of CFD analysis to simulate cuttings transport process which can minimize the difficult experimental measurements.

Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

Ti-6Al-4V alloy (Ti64) and SUS316L stainless steel rods were dissimilarly friction welded. Especially focusing on the detailed observation of interface microstructural evolution during the friction welding (FW), the relationship between the processing conditions, weld interface microstructure, and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L. A higher friction pressure produced a lower welding temperature in the FW, hence suppressing the thick intermetallic compound layer formation. However, hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate, high rotation linear velocity and high outward flow velocity of the Ti64. These harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’ mechanical properties. The rotation speed reduction and liquid CO2 cooling during the entire processing decreased the temperature increasing rate, rotation linear velocity and outward flow velocity of the Ti64 at the weld interface periphery. Therefore, they suppressed the formation of the harmful mechanically mixed layers, facilitated the homogeneous and sound interface microstructure generation, and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.

Investigation of Carbon Fiber Reinforced Polymer Composite Welding with a New Tool in Friction Stir Welding Method

Application of thermoplastic materials has increased dramatically in recent decades due to its recyclability, low density, resistance to chemical changes. The friction stir welding process is one of the new methods of solid state welding, which has recently undergone significant improvement. In this research, using a new tool Made of plain carbon steel st37 in friction stir welding and low cost turning machine, composite sheets of thermoplastic polymer base have 12% continuous carbon fiber in the form of buttocks with two rotational speeds of 250 and 355 rpm and two advance speeds of 5/6 and 9 mm/min Optical microscope images (OM) showed the complete connection of materials. Increasing the inlet temperature resulted in the formation and growth of cavities and converting them into tunnel cavities. In general, the parameters affecting the connection quality in this study included the main shoulder diameter and rotational speed, so that, based on the results of scanning electron microscopy (SEM), the increase in rotational speed resulted in the grinding of continuous carbon fibers and thus increased tensile strength. The results of the tensile test showed that the failure of the samples is due to microstructural changes in the HAZ, in the joint zone of the welding zone and the base materials. According to the results, it can be said that using this new tool in the friction stir welding method, because of the reduction of rotational speed compared to previous studies and the lack of use of a multi-axial milling machine, can save energy.

CFD analysis of number of blades on the performance of counter rotating wind turbine designed using blade element momentum theory under transient condition

Unsteady CFD simulations on the effects of number of blades on counter rotating wind turbine (CRWT) were carried out in order to investigate the performance and the flow characteristics. In this paper, 2-bladed and 3-bladed CRWT were designed using Blade Element Momentum Theory (BEMT) which comprised of S833, S834, and S835 airfoils. As a comparison baseline, a SRWT model which have similar design with front rotor of the 3-bladed CRWT would be also investigated. It was found that the SRWT had the same rotational speed with the front rotor of the 3-bladed CRWT. There was about 10.24 % and 11.79 % rotational speed reduction of the rear rotor from the front rotor of 2-bladed CRWTs and 3-bladed CRWTs, respectively. Both of 2-bladed CRWT and 3-bladed CRWT have higher total power than SRWT, thereby generating more larger velocity deficits in the wake flow.

Methods for rotational speed reduction for alternating current electric motors

The analysis of rotational speed reduction methods for alternating current electric motors are given, assigned to low-speed electric drives of various power levels. The integrated classification of electric machines of well-known types is given, the rotational speed reduction method being used as the basis. The main advantages and disadvantages, defining perspectives for the application in various low-speed electric drives, are explained. The approximate bounds of engineering expediency of the applications of the motors are given for obtaining certain assessments in selection of a type of the drive motor.

Banding the Right Ventricular Assist Device Outflow Conduit: Is It Really Necessary With Current Devices?

Implantable left ventricular assist devices (LVADs) have been adapted clinically for right-sided mechanical circulatory support (RVAD). Previous studies on RVAD support have established the benefits of outflow cannula restriction and rotational speed reduction, and recent literature has focused on assessing either the degree of outflow cannula restriction required to simulate left-sided afterload, or the limitation of RVAD rotational speeds. Anecdotally, the utility of outflow cannula restriction has been questioned, with suggestion that banding may be unnecessary and may be replaced simply by varying the outflow conduit length. Furthermore, many patients have a high pulmonary vascular resistance (PVR) at the time of ventricular assist device (VAD) insertion that reduces with pulmonary vascular bed remodeling. It is therefore important to assess the potential changes in flow through an RVAD as PVR changes. In this in vitro study, we observed the use of dual HeartWare HVAD devices (HeartWare Inc., Framingham, MA, USA) in biventricular support (BiVAD) configuration. We assessed the pumps' ability to maintain hemodynamic stability with and without banding; and with varying outflow cannulae length (20, 40, and 60 cm). Increased length of the outflow conduit was found to produce significantly increased afterload to the device, but this was not found to be necessary to maintain the device within the manufacturer's recommended operational parameters under a simulated normal physiological setting of mild and severe right ventricular (RV) failure. We hypothesize that 40 cm of outflow conduit, laid down along the diaphragm and then up over the RV to reach the pulmonary trunk, will generate sufficient resistance to maintain normal pump function.

Novel motor design for rotating anode x-ray tubes operating in the fringe field of a magnetic resonance imaging system

Using hybrid x-ray∕MR (XMR) systems for image guidance during interventional procedures could enhance the diagnosis and treatment of neurologic, oncologic, cardiovascular, and other disorders. The authors propose a close proximity hybrid system design in which a C-arm fluoroscopy unit is placed immediately adjacent to the solenoid magnet of a MR system with a minimum distance of 1.2 m between the x-ray and MR imaging fields of view. Existing rotating anode x-ray tube designs fail within MR fringe field environments because the magnetic fields alter the electron trajectories in the x-ray tube and act as a brake on the induction motor, reducing the rotation speed of the anode. In this study the authors propose a novel motor design that avoids the anode rotation speed reduction. The proposed design replaces the permanent magnet stator found in brushed dc motors with the radial component of the MR fringe field. The x-ray tube is oriented such that the radial component of the MR fringe field is orthogonal to the cathode-anode axis. Using a feedback position sensor and the support bearings as electrical slip rings, the authors use electrical commutation to eliminate the need for mechanical brushes and commutators. A vacuum compatible prototype of the proposed motor design was assembled, and its performance was evaluated at various operating conditions. The prototype consisted of a 3.1 in. diameter anode rated at 300 kHU with a ceramic rotor that was 5.6 in. in length and had a 2.9 in. diameter. The material chosen for all ceramic components was MACOR, a machineable glass ceramic developed by Corning Inc. The approximate weight of the entire assembly was 1750 g. The maximum rotation speed, angular acceleration, and acceleration time of the motor design were investigated, as well as the dependence of these parameters on rotor angular offset, magnetic field strength, and field orientation. The resonance properties of the authors' assembly were also evaluated to determine its stability during acceleration, and a pulse width modulation algorithm was implemented to control the rotation speed of the motor. At a magnetic flux density of 41 mT orthogonal to the axis of rotation (on the lower end of the expected flux density in the MR suite) the maximum speed of the motor was found to be 5150 revolutions per minute (rpm). The acceleration time necessary to reach 3000 rpm was found to be approximately 10 s at 59 mT. The resonance frequency of the assembly with the anode attached was 1310 rpm (21.8 Hz) which is far below the desired operating speeds. Pulse width modulation provides an effective method to control the speed of the motor with a resolution of 100 rpm. The proposed design can serve as a direct replacement to the conventional induction motor used in rotating anode x-ray tubes. It does not suffer from a reduced rotation speed when operating in a MR environment. The presence of chromic steel bearings in the prototype prevented testing at the higher field strengths, and future iterations of the design could eliminate this shortcoming. The prototype assembly demonstrates proof of concept of the authors' design and overcomes one of the major obstacles for a MR compatible rotating anode x-ray tube.

Health Assessment of Cooling Fan Bearings Using Wavelet-Based Filtering

As commonly used forced convection air cooling devices in electronics, cooling fans are crucial for guaranteeing the reliability of electronic systems. In a cooling fan assembly, fan bearing failure is a major failure mode that causes excessive vibration, noise, reduction in rotation speed, locked rotor, failure to start, and other problems; therefore, it is necessary to conduct research on the health assessment of cooling fan bearings. This paper presents a vibration-based fan bearing health evaluation method using comblet filtering and exponentially weighted moving average. A new health condition indicator (HCI) for fan bearing degradation assessment is proposed. In order to collect the vibration data for validation of the proposed method, a cooling fan accelerated life test was conducted to simulate the lubricant starvation of fan bearings. A comparison between the proposed method and methods in previous studies (i.e., root mean square, kurtosis, and fault growth parameter) was carried out to assess the performance of the HCI. The analysis results suggest that the HCI can identify incipient fan bearing failures and describe the bearing degradation process. Overall, the work presented in this paper provides a promising method for fan bearing health evaluation and prognosis.

Technological solution to profile and generate the teeth of central gear for precessional gear drives

The transmission based on precessional gear pairs, mostly used for rotation speed reduction, has some important advantages relative to the common gear drives, such as the capability to produce very low transmission ratios, or the high loading capacity/dimensions ratio (due to the fact that all the teeth of a precessional gear pair are simultaneously in contact during its functioning). One among the likeliest constructive solutions for the precessional gear pair uses a satellite built with conical rollers. However, its practical use is restricted by the difficulty to realize the central gear teeth machining without using special and relative complicated devices. This paper introduces a technological substitutive profile for the central gear tooth, which enables the use of a simpler and more productive method for working it, without bringing major negative consequences regarding the teeth contact correctness or the drive loading capacity. The profile was found by analyzing the contact surface and the pressure angle evolution during the contact between conjugate teeth. The paper also presents technological solutions to generate the new tooth profile by milling it with a disk-tool or an end-mill cutter, together with methods to profile the required tools.

AN INVESTIGATION INTO THREE DIMENSIONAL TURBULENT FLOW OF NEWTONIAN LIQUID IN STIRRED TANKS MIXERS

The present work is concerned with the theoretical and experimental investigation of flow pattern of Newtonian fluid in liquid mixing process in stirred tank with flat blade impeller. A threedimensional model for mixing process was simulated. The effected parameters are rotation speed and impeller diameter. Continuity, momentum, and turbulent equations were solved by ANSYS package software 5.4 code with FLOTRAN/CFD based on Finite Element method. In the experimental work, two visualization methods are used in this work, the first method is the acidbase reaction visualization method and the second is the particle distribution visualization method.Different chemical materials were used in the first method, NaOH as a base, 2 4 H SO as acid and Methyl red as indicator, while polymer particles were used in the second method. The results of 3D model showed that the speed rotation directly affected the mixing zones, where the speed reduction by half decreasing the mixing zones approximately by half. Also the impeller diameter increasing clearly affected the mixing process where the mixing zones concentrated directly above and below the impeller. In the experimental work, the acid-base reaction visualization method showed that the mixing zones decreased due to the rotation speed reduction depend on the red and yellow colors, which describe the good mixing and poor mixing zones respectively. The mixing zones were concentrated directly above and below the impeller due to the impeller diameter increasing,. The particles distribution method showed that the mixing zones decreased due to the speed reduction, while the mixing zones concentrated directly above and below the impeller due to the impeller diameter increasing. The results showed a good agreement between the theoretical and experimentalworks in studying the effect of rotating speed, and impeller diameter .