scholarly journals Experimental Research on Cavitation Evolution and Movement Characteristics of the Projectile during Vertical Launching

2021 ◽  
Vol 9 (12) ◽  
pp. 1359
Author(s):  
Siru Chen ◽  
Yao Shi ◽  
Guang Pan ◽  
Shan Gao
Keyword(s):  
High Speed ◽  
Cavitation Number ◽  
Small Scale ◽  
Scaled Model ◽  
General Process ◽  
Movement Characteristics ◽  
Shedding Frequency ◽  
The Stability ◽  
The Relationship ◽  
Launch Platform

Aiming at the problem of unsteady cavitation during a projectile’s vertical water-exit process, scaled model experiments were carried out based on the self-designed underwater launch platform and high-speed cameras, which focus on changes in cavitation shape and projectile posture. In this paper, the general process of the cavitation evolution and projectile’s movement is described; the relationship between the re-entry jet, local cavitation number and cavitation stability is discussed. Meanwhile, the effect of head forms and launch speeds on the cavitation evolution and movement characteristics is analyzed, including 60° cone, 90° cone and hemispherical head with velocity of 16.8 m/s, 18.5 m/s and 20.0 m/s, whose launch cavitation number is 0.714, 0.589 and 0.504. The results show that the attached cavities fall off from the bottom up under the influence of the end-re-entry jet and the shedding frequency declines when the launch cavitation number decreases. The cavitation growth of 60° cone is easily disturbed by the air mass near the launcher, the cavitation development of 90° cone is characterized by small-scale and high-frequency growth and shedding, while the hemispherical head is not prone to cavitation. Moreover, increasing the speed can improve the stability of cavitation development and the projectile’s movement.

scholarly journals Motion Characteristics After Ricochet: An Experimental Investigation

2020 ◽  
Vol 27 (2) ◽  
pp. 4-10
Author(s):  
Guoming Chen ◽  
Junhua Hu ◽  
An Liu ◽  
Jinfu Feng ◽  
Qingqing Hu
Keyword(s):  
High Speed ◽  
Initial Conditions ◽  
Incident Angle ◽  
Linear Functions ◽  
Small Scale ◽  
Residual Velocity ◽  
Angle Change ◽  
Motion Characteristics ◽  
The Stability ◽  
The Relationship

AbstractThe ricochet behaviour of the air–water trans-media vehicle (AWTMV) during water-entry crossing was experimentally investigated. Three types of small-scale AWTMV including cone, ogive, and flat nose were used in the test. The underwater trajectory, velocity, and inclination angle of projectiles during the ricochet process were obtained using a high-speed camera. The angle change of the AWTMV and the ratio of the residual velocity are introduced. Based on this result, the relationship between the ricochet responses and initial conditions was derived. The results of this study show that (1) a small incident angle and great velocity make the occurrence of ricochet behaviour easier, (2) the stability of the trajectory of projectiles with cone, ogive, and flat nose weakened in turn at the same initial conditions, (3) the angle change and the ratio of the residual velocity are linear functions of the incident angle and velocity.

scholarly journals Nonlinear Blade Stability for a Scaled Autogyro Rotor at High Advance Ratios

2020 ◽  
Vol 65 (1) ◽  
pp. 1-19
Author(s):  
Djamel Rezgui ◽  
Mark H. Lowenberg
Keyword(s):  
High Speed ◽  
Flow Speed ◽  
Numerical Continuation ◽  
Control Input ◽  
Nonlinear Phenomenon ◽  
Scaled Model ◽  
Underlying Mechanisms ◽  
Slowed Rotor ◽  
The Stability ◽  
Blade Pitch Angle

Despite current research advances in aircraft dynamics and increased interest in the slowed rotor concept for high-speed compound helicopters, the stability of autogyro rotors remains partially understood, particularly at lightly loaded conditions and high advance ratios. In autorotation, the periodic behavior of a rotor blade is a complex nonlinear phenomenon, further complicated by the fact that the rotor speed is not held constant. The aim of the analysis presented in this article is to investigate the underlying mechanisms that can lead to rotation-flap blade instability at high advance ratios for a teetering autorotating rotor. The stability analysis was conducted via wind tunnel tests of a scaled autogyro model combined with numerical continuation and bifurcation analysis. The investigation assessed the effect of varying the flow speed, blade pitch angle, and rotor shaft tilt relative to the flow on the rotor performance and blade stability. The results revealed that rotor instability in autorotation is associated with the existence of fold bifurcations, which bound the control-input and design parameter space within which the rotor can autorotate. This instability occurs at a lightly loaded condition and at advance ratios close to 1 for the scaled model. Finally, it was also revealed that the rotor inability to autorotate was driven by blade stall.

scholarly journals A Study on the Relationship between the Design of Aerotrain and Its Stability Based on a Three-Dimensional Dynamic Model

Robotics ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 96
Author(s):  
Quang Huan Luong ◽  
Jeremy Jong ◽  
Yusuke Sugahara ◽  
Daisuke Matsuura ◽  
Yukio Takeda
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Three Dimensional ◽  
Vehicle Body ◽  
Directional Stability ◽  
Rigid Body Model ◽  
Body Design ◽  
The Stability ◽  
New Generation ◽  
The Relationship

A new generation electric high-speed train called Aerotrain has levitation wings and levitates under Wing-in-Ground (WIG) effect along a U-shaped guideway. The previous study found that lacking knowledge of the design makes the prototype unable to regain stability when losing control. In this paper, the nonlinear three-dimensional dynamic model of the Aerotrain based on the rigid body model has been developed to investigate the relationship between the vehicle body design and its stability. Based on the dynamic model, this paper considered an Aerotrain with a horizontal tail and a vertical tail. To evaluate the stability, the location and area of these tails were parameterized. The effects of these parameters on the longitudinal and directional stability have been investigated to show that: the horizontal tail gives its best performance if the tail area is a function of the tail location; the larger vertical tail area and (or) the farther vertical tail location will give better directional stability. As for the lateral stability, a dihedral front levitation wing design was investigated. This design did not show its effectiveness, therefore a control system is needed. The obtained results are useful for the optimization studies on Aerotrain design as well as developing experimental prototypes.

Weathervane Performance and Stability of Single Point Moored FOWTs Under Wind-Current Coexisting Field

2019 ◽  
Author(s):  
Sharath Srinivasamurthy ◽  
Kazuki Hashimoto ◽  
Kazuhiro Iijima ◽  
Yasunori Nihei
Keyword(s):  
High Speed ◽  
Single Point ◽  
Scaling Law ◽  
Water Tank ◽  
Scaled Model ◽  
Circulating Water ◽  
Osaka Prefecture ◽  
Unstable Oscillation ◽  
The Stability ◽  
Numerical Program

Abstract The objective of this study is to understand the weathervane performance and stability of FOWTs moored to SPM systems under wind and current coexisting field. Two types of FOWT systems, a semi-submersible and a spar (1/200 scale) are designed and manufactured based on Froude’s scaling law. A series of scaled model experiments are conducted and compared during wind-current coexisting field in a circulating water tank at Osaka Prefecture University, Osaka, Japan. Weathervane performance is evaluated under various conditions of wind and current. It is found during experiments that the weathervane performance of the SPM-FOWT systems is acceptable in rated wind and slow current condition. However, in the rated wind and high speed current condition, the weathervane performance is found to be not acceptable and unstable oscillation is observed. A numerical program is also developed to understand the behavior using the maneuvering equations. Further, attempts are made to understand the stability of SPM-FOWT systems based on Eigenvalue analysis.

Effects of Cavitation on Periodic Wakes Behind Symmetric Wedges

1966 ◽  
Vol 88 (1) ◽  
pp. 163-176 ◽  
Author(s):  
J. O. Young ◽  
J. William Holl
Keyword(s):  
High Speed ◽  
Peak Frequency ◽  
Cavitation Number ◽  
Vortex Street ◽  
Maximum Value ◽  
Cavitation Bubbles ◽  
Sink Effect ◽  
Shedding Frequency ◽  
Simplified Analysis ◽  
The Cross

Measurements of the shedding frequency and spacing of cavitating vortex street wakes have been made for four wedge models having apex angles of 15, 30, 60, and 90 deg. The wake pattern made visible by the presence of cavitation bubbles enabled measurements of the shedding frequency and vortex street spacing to be taken. It was found that the cavitation produced negligible effects on the shedding frequency with decreasing cavitation number down to as low as half the incipient cavitation number. Further decrease in the cavitation number produced an increase in the shedding frequency to a maximum value followed by a decrease with a general decay to random shedding. The analysis of high-speed motion pictures demonstrated a general decrease in the cross-stream spacing of the two rows of vortices with decreasing cavitation number. The longitudinal spacing of vortices in the same row also decreased with decreasing cavitation number followed by a rapid increase at cavitation numbers lower than that producing the peak frequency. In a simplified analysis, it was hypothesized that the cavitation in the vortex cores caused a general sink effect in the shed wake. Modeling the cavitation with cylindrical cavitation bubbles, some agreement with the experimental results was obtained for the cross-stream spacing with decreasing cavitation number.

Hydrodynamic improvement by adding inlet baffles on centrifugal pump for reducing cavitation instabilities

2021 ◽  
pp. 107754632110474
Author(s):  
Zhicong Wei ◽  
Ran Tao ◽  
Ruofu Xiao ◽  
Honglin Hu
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Low Frequency ◽  
Cavitation Number ◽  
Center Frequency ◽  
Hydraulic Test ◽  
Rate Condition ◽  
Energy Characteristics ◽  
Cavitation Instability ◽  
The Relationship

Cavitation instability is a common phenomenon that causes vibration and noise of turbomachinery. In this study, an attempt is made to suppress the cavitation instability. A high-speed centrifugal pump with inducer is taken as the research objective. Four baffles are evenly arranged at the inlet of the inducer as a hydrodynamic improvement. The energy characteristics of the pump are measured on a closed hydraulic test rig. The pressure, vibration, and noise under different flow rates and different cavitation number are acquired for comparative analyses. Experimental results show that the energy characteristics changed after hydrodynamic improvement. The original pump is mainly affected by y-direction vibration and is clearly suppressed in the new pump. The low-frequency pressure pulsation under partial flow rate condition can be effectively suppressed. The baffles can also reduce the broadband center frequency at the pump outlet and change the relationship between center frequency and cavitation number. These results show that the hydrodynamic improvement at the inlet helps the suppression of cavitation instability of the high-speed centrifugal pump.

scholarly journals Experimental Study on Influence of Ventilation on Trajectory Characteristics of Free Motion of Supercavitating Vehicle

2019 ◽  
Vol 37 (4) ◽  
pp. 691-696
Author(s):  
Cheng Chen ◽  
Xulong Yuan ◽  
Yao Ren ◽  
Jianjun Dang ◽  
Xiyan Liu
Keyword(s):  
High Speed ◽  
Video Camera ◽  
Cavitation Number ◽  
Free Motion ◽  
Measuring System ◽  
Supercavitating Vehicle ◽  
Ventilation Condition ◽  
High Speed Video Camera ◽  
The Stability ◽  
Ventilation Conditions

In order to study the trajectory characteristics of supercavitating vehicle in free motion, a series of experiments were carried out on an unpowered vehicle under ventilation and non-ventilation conditions respectively. High-pressure gas was utilized to launch the vehicle. The flow pattern in free motion was captured by using a high-speed video camera, the variations in the motion parameters and the cavity pressure were simultaneously recorded by using the internal measuring system. The measured data under ventilation and non-ventilation conditions were analyzed in detail, giving the effect of the ventilation on the motion of the vehicle. The experimental results show that the cavitation number fluctuates around a certain value under the influence of both velocity of the vehicle and the ventilation flow rate, keeping the vehicle to stably move in the supercavitating state. Under non-ventilation condition, the vehicle moves stably at the state of supercavitating and double-cavity closed on at the cylindrical section of the vehicle. But the motion turns into instable when the cavity is closed at the shoulder of the vehicle. Therefore, to reduce the cavitation number by ventilation is beneficial to maintaining the stability of the vehicle.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

An Experimental Investigation on Thermal Conductivity and Viscosity of Graphene doped CNTs /TiO2 Nanofluid

2020 ◽  
Vol 17 (3) ◽  
Author(s):  
A.M. Zetty Akhtar ◽  
M.M. Rahman ◽  
K. Kadirgama ◽  
M.A. Maleque
Keyword(s):  
Thermal Conductivity ◽  
Zeta Potential ◽  
Base Fluid ◽  
Minimum Quantity Lubrication ◽  
Cutting Fluid ◽  
Cutting Zone ◽  
Observation Method ◽  
The Stability ◽  
The Relationship ◽  
Zeta Potential Analysis

This paper presents the findings of the stability, thermal conductivity and viscosity of CNTs (doped with 10 wt% graphene)- TiO2 hybrid nanofluids under various concentrations. While the usage of cutting fluid in machining operation is necessary for removing the heat generated at the cutting zone, the excessive use of it could lead to environmental and health issue to the operators. Therefore, the minimum quantity lubrication (MQL) to replace the conventional flooding was introduced. The MQL method minimises the usage of cutting fluid as a step to achieve a cleaner environment and sustainable machining. However, the low thermal conductivity of the base fluid in the MQL system caused the insufficient removal of heat generated in the cutting zone. Addition of nanoparticles to the base fluid was then introduced to enhance the performance of cutting fluids. The ethylene glycol used as the base fluid, titanium dioxide (TiO2) and carbon nanotubes (CNTs) nanoparticle mixed to produce nanofluids with concentrations of 0.02 to 0.1 wt.% with an interval of 0.02 wt%. The mixing ratio of TiO2: CNTs was 90:10 and ratio of SDBS (surfactant): CNTs was 10:1. The stability of nanofluid checked using observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured at a temperature range between 30˚C to 70˚C (with increment of 10˚C) to determine the relationship between concentration and temperature on nanofluid’s thermal physical properties. Based on the results obtained, zeta potential value for nanofluid range from -50 to -70 mV indicates a good stability of the suspension. Thermal conductivity of nanofluid increases as an increase of temperature and enhancement ratio is within the range of 1.51 to 4.53 compared to the base fluid. Meanwhile, the viscosity of nanofluid shows decrements with an increase of the temperature remarks significant advantage in pumping power. The developed nanofluid in this study found to be stable with enhanced thermal conductivity and decrease in viscosity, which at once make it possible to be use as nanolubricant in machining operation.

Predictive Failure Analysis of Solder Joints with Simultaneous High Speed EBSD and EDS

2018 ◽  
Author(s):  
J. Lindsay ◽  
P. Trimby ◽  
J. Goulden ◽  
S. McCracken ◽  
R. Andrews
Keyword(s):  
High Speed ◽  
Solder Joints ◽  
Phase Distribution ◽  
Bond Failure ◽  
Microstructural Parameters ◽  
Snpb Solder ◽  
Grain Orientations ◽  
Accelerated Thermal Cycling ◽  
The Relationship ◽  
Opening Up

Abstract The results presented here show how high-speed simultaneous EBSD and EDS can be used to characterize the essential microstructural parameters in SnPb solder joints with high resolution and precision. Analyses of both intact and failed solder joints have been carried out. Regions of strain localization that are not apparent from the Sn and Pb phase distribution are identified in the intact bond, providing key insights into the mechanism of potential bond failure. In addition, EBSD provides a wealth of quantitative detail such as the relationship between parent Sn grain orientations and Pb coarsening, the morphology and distribution of IMCs on a sub-micron scale and accurate grain size information for all phases within the joint. Such analyses enable a better understanding of the microstructural developments leading up to failure, opening up the possibility of improved accelerated thermal cycling (ATC) testing and better quality control.

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