Mechanical Engineering Department

This paper presents a horizontal vibration isolator with electromagnetic planar actuator using multi hall-effect sensor network. The horizontal vibration isolator under study consists of two main parts: a passive vibration isolator and an electromagnetic planar actuator using multi hall-effect sensor network. A model of a planar actuator consists of 1D Halbach magnet array and a set of 3 phase coils is derived based on DQ decompositon and the muti hall-effect sensor is built to achieve the relation position of the magnet array and coil. Simulations and experiment model are performed to verify horizontal disturbance rejection of the vibration isolator.

This paper presents measurement of a putting golf ball jump motion using a vision sensor. After putting, a golf ball experiences bouncing, sliding and rolling sequentially. In particular, ball jump motion contains lots of important information related to impact such as jump number, height and length. Putting is simulated as a simple pendulum and golf ball jumps are measured using a vision sensor. The golf ball jump changes significantly according to impact errors such as impact timings. If an IMU sensor is attached on the putter head and relationship between variations of golf ball trajectory and IMU sensor signal is characterized, coaching information of golf putting to correct various impact errors can be provided only using IMU sensor.

This paper presents nonlinear controller design of horizontal vibration isolator based on Lyapunov Function. First we derive a mathematical model for an active horizontal vibration isolator with an electromagnetic planar actuator. Based on the model, a nonlinear control based on Lyapunov function is introduced to generate the vertical force. Optimal gains of the controller are determined considering settling time, and coil current. Finally, simulations are performed to verify the performance improvement of the horizontal disturbance rejection as well as reduction of its settling time. †Presenting Author

This paper presents an active control method for a quasi-zero stiffness (QZS) isolator using flexures based on a Lyapunov function. First, shown is a dynamic model of an active QZS isolator having indirect horizontal actuation. In the model, the control force is applied along the horizontal direction to compensate for vertical vibrations. Next, a nonlinear control algorithm for the active isolator is developed based on a Lyapunov function. Simulation of the active isolator model which consists of passive QZS isolators, sensors and actuator dynamic models is done to study the effects of control tuning gain on the system performances. In order to verify the active isolation performances, developed is an experimental model including an active QZS isolator, an exciter device and various sensors. Finally, experiments for such as impulse disturbance rejection and transmissibility are performed and the results show that the indirect horizontal actuation by the active QZS isolator using flexure attenuates impulse disturbance as well as isolates the base vibration effectively.

The Kaplan turbine is an axial propeller-type turbine that can simultaneously control guide vanes and runner blades, thus allowing its application in a wide range of operations. Here, turbine tip clearance plays a crucial role in turbine design and operation as high tip clearance flow can lead to a change in the flow pattern, resulting in a loss of efficiency and finally the breakdown of hydro turbines. This research investigates tip clearance flow characteristics and undertakes a transient fast Fourier transform (FFT) analysis of a Kaplan turbine. In this study, the computational fluid dynamics method was used to investigate the Kaplan turbine performance with tip clearance gaps at different operating conditions. Numerical performance was verified with experimental results. In particular, a parametric study was carried out including the different geometrical parameters such as tip clearance between stationary and rotating chambers. In addition, an FFT analysis was performed by monitoring dynamic pressure fluctuation on the rotor. Here, increases in tip clearance were shown to occur with decreases in efficiency owing to unsteady flow. With this study’s focus on analyzing the flow of the tip clearance and its effect on turbine performance as well as hydraulic efficiency, it aims to improve the understanding on the flow field in a Kaplan turbine.

omena
of pumps by Computational fluid dynamics (CFD). In order to accurately ascertain cavitation behavior, a comparison between
CFD and experimental data is a significant and essential process. The purpose of this study is to analyze cavitating behavior in multistage
centrifugal pumps numerically and experimentally. For this investigation an experimental set up was used to obtain cavitation performance
results. The CFD method was used to investigate the multistage centrifugal pump performance under developed cavitating conditions.
The Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST
turbulence model was adopted to account for turbulent flows. Numerical data were validated with experimental data and a good comparison
of results was achieved. Numerically, cavitation performances were obtained for different pump stages and the effects on cavitation
were described according to different NPSH (Net positive suction head). The occurrence of cavitation was also described according to
NPSH3% in the head drop lines and water vapor volume fraction on the impeller blade. The rapid drop in head at low NPSH was captured
for different flow conditions. It was found that for stage to stage performance, the head drop changes could be related to losses inside the pump. It was also shown that the simulation results can truly represent the development of the attached sheet cavitation in the impeller.

Multistage centrifugal pumps with variable speed drives are currently widely used in a variety of industrial and commercial
applications. However, there are limitations to defining the efficiency of variable speed drive pumps. As an alternative method,
energy saving rates can be evaluated with flow patterns and mean duty cycles. Computational fluid dynamics (CFD) is being
used as a good tool to understand this and is less time consuming in terms of analyzing performances the experimental
method. Research attention was focused on the energy saving rates of a multistage centrifugal pump for variable flow with
variable speed drive through numerical and experiment methods. For this investigation Reynolds-averaged Navier-Stokes
(RANS) equations were discretized by the finite volume method and a two equations SST model was used to account for
three dimensional steady state flows. In the experimental system, an experimental set-up of a variable flow system was made
to obtain energy saving rates and computational results were validated. The energy saving rates of the pumps depend on the
flow patterns and specific mean duty cycles on which the machine or system operates. Mean duty cycles were divided into
different flow operating conditions and a weighting for the mean value was given for each segment according to interval time.
The pump system was operated at 5070% of maximum flow rates. The energy saving rates were obtained from input power
through CFD simulation and experimentally, and the mean duty cycle was obtained from flow patterns in the field of the pump.
Energy saving rates were evaluated as a function of mean duty cycle and input power of the system operation. The total energy
consumed for the constant speed drive was 25,922 kWh and for the variable speed drive pump was 17,687 kWh through CFD.
The total annual energy saving rates were annually 33.81% through computational and 31.77% through experimental method
with the variable speed drive system when compared to the constant speed drive system.

Nowadays centrifugal pumps are being widely used in the commercial, industrial and power plant applications and most of pumps operated by constant speed drive system. Therefore, pump consumes a huge energy of each nation’s total energy. But it could be operated in variable speed drive system which would be provided energy saving. The purpose of this study is to investigate the pump performance characteristics of the multistage centrifugal pump with the variable drive system. For this study an experimental set up of the system was constructed to achieve the centrifugal pump performances such as H-Q, η-Q, P-Q curves and operating points which interact between performance and system curves. In the variable speed drive system, a vector controlled inverter driving (variable voltage variable frequency) was installed in the experimental system. A numerical investigation also applied for getting the pump performances for the validation and reliability of the pump design development and also the pressure and velocity effects in internal flows of the pump are analyzed. For the numerical analysis, the Navier-Stokes equations were discretized by the finite volume method and two equations transport turbulence (SST) model accounts for three dimensional steady flows. In the experiment system, we also carried out system head performance of the three pumps in parallel to compare with one pump system head for its validation. In order to get the energy saving rate using the inverter control variable speed drive system instead of the constant speed drive system, it is necessary to identify the specific duty cycle of the pump operation cycle and operating system curve of the pump. Hopefully, this paper will be useful as a guide for identifying a method of implementing a variable speed drive system with inverter control in the variable flow and pressure system.

Cavitation is an abnormal physical phenomenon which can be generated in relatively low pressure regions in centrifugal
pumps. In predicting and understanding cavitation in the pumps, it is important to secure their efficiency and reliability. The
purpose of this study is to analyze the cavitation flows in centrifugal pumps with variable speeds through numerical methods.
The Rayleigh–Plesset cavitation model was adapted as the source term for inter-phase mass transfer in order to predict and
understand the cavitation performances. The Reynolds-average Navier-Stokes (RANS) equations were discretized by the
finite volume method. The two-equation SST turbulence model was accounted for turbulent flows. The numerical analysis
results were validated with experimental data and it was found that both results were in good accordance. The cavitation
performances were obtained for variable speeds with different temperatures and the effects on cavitation were described
according to different cavitation numbers. Cavitation performances were also observed for different centrifugal pump stages
(1st and 2nd). The performances of cavitation decreased with the increase of rotational speed. In addition, the development of
cavitation is elucidated according to the different temperatures, and the effects of water vapor volume fraction are discussed.

The purpose of this study is to understand the cavitation phenomena in centrifugal pumps through computational fluid
dynamics method. NPSH characteristic curve is measured from different flow operating conditions. Steady state, liquid-vapor
homogeneous method with two equations transport turbulence model is employed to estimate the NPSH curve in centrifugal
pumps. The Rayleigh-Plesset cavitation model is adapted as source term for inter-phase mass transfer in order to understand
cavitation phenomena in centrifugal pumps. The cavitation incipient curve is clearly estimated at different flows operating
conditions. A relationship is made between cavitation incipient and NPSH curve. Also the effects on water vapor volume
fraction and pressure load distributions on the impeller blade are also described.

Effective hydraulic turbine design prevents sediment and cavitation erosion from impacting the performance and reliability of the machine. Using computational fluid dynamics (CFD) techniques, this study investigated the performance characteristics of sediment and cavitation erosion on a hydraulic Francis turbine by ANSYS-CFX software. For the erosion rate calculation, the particle trajectory Tabakoff–Grant erosion model was used. To predict the cavitation characteristics, the study’s source term for interphase mass transfer was the Rayleigh–Plesset cavitation model. The experimental data acquired by this study were used to validate the existing evaluations of the Francis turbine. Hydraulic results revealed that the maximum difference was only 0.958% compared with the CFD data, and 0.547% compared with the experiment (Korea Institute of Machinery and Materials (KIMM)). The turbine blade region was affected by the erosion rate at the trailing edge because of their high velocity. Furthermore, in the cavitation–erosion simulation, it was observed that abrasion propagation began from the pressure side of the leading edge and continued along to the trailing edge of the runner. Additionally, as sediment flow rates grew within the area of the attached cavitation, they increased from the trailing edge at the suction side, and efficiency was reduced. Cavitation–sand erosion results then revealed a higher erosion rate than of those of the sand erosion condition.