Abstract: A simulation scheme of rotational motions for predictions of bump-type gas foil bearings operating at steady-state is proposed. The scheme is based on multi-physics coupling computer aided engineering packages modularized with computational fluid dynamic model and structure elasticity model to numerically solve the dynamic equation of motions of a hydrodynamic loaded shaft supported by an elastic bump foil. The bump foil is assumed to be modelled as infinite number of Hookean springs mounted on stiff wall. Hence, the top foil stiffness is constant on the periphery of the bearing housing. The hydrodynamic pressure generated by the air film lubrication transfers to the top foil and induces elastic deformation needed to be solved by a finite element method program, whereas the pressure profile applied on the top foil must be solved by a finite element method program based on Reynolds Equation in lubrication theory. As a result, the equation of motions for the bearing shaft are iteratively solved via coupling of the two finite element method programs simultaneously. In conclusion, the two-dimensional center trajectory of the shaft plus the deformation map on top foil at constant rotational speed are calculated for comparisons with the experimental results.
Abstract: This paper provides a robust stabilization method
for rotational motion of underwater robots against parameter
uncertainties. Underwater robots are expected to be used for
various work assignments. The large variety of applications of
underwater robots motivates researchers to develop control systems
and technologies for underwater robots. Several control methods
have been proposed so far for the stabilization of nominal system
model of underwater robots with no parameter uncertainty. Parameter
uncertainties are considered to be obstacles in implementation of the
such nominal control methods for underwater robots. The objective
of this study is to establish a robust stabilization method for rotational
motion of underwater robots against parameter uncertainties. The
effectiveness of the proposed method is verified by numerical
simulations.
Abstract: The control problem of underactuated spacecrafts has
attracted a considerable amount of interest. The control method for
a spacecraft equipped with less than three control torques is useful
when one of the three control torques had failed. On the other hand,
the quantized control of systems is one of the important research
topics in recent years. The random dither quantization method that
transforms a given continuous signal to a discrete signal by adding
artificial random noise to the continuous signal before quantization
has also attracted a considerable amount of interest. The objective of
this study is to develop the control method based on random dither
quantization method for stabilizing the rotational motion of a rigid
spacecraft with two control inputs. In this paper, the effectiveness of
random dither quantization control method for the stabilization of
rotational motion of spacecrafts with two torque inputs is verified
by numerical simulations.
Abstract: Tire noise has a significant impact on ride quality
and vehicle interior comfort, even at low frequency. Reduction of
tire noise is especially important due to strict state and federal
environmental regulations. The primary sources of tire noise are the
low frequency structure-borne noise and the noise that originates from
the release of trapped air between the tire tread and road surface
during each revolution of the tire. The frequency response of the tire
changes at low and high frequency. At low frequency, the tension
and bending moment become dominant, while the internal structure
and local deformation become dominant at higher frequencies. Here,
we analyze tire response in terms of deformation and rolling velocity
at low revolution frequency. An Abaqus FEA finite element model
is used to calculate the static and dynamic response of a rolling tire
under different rolling conditions. The natural frequencies and mode
shapes of a deformed tire are calculated with the FEA package where
the subspace-based steady state dynamic analysis calculates dynamic
response of tire subjected to harmonic excitation. The analysis was
conducted on the dynamic response at the road (contact point of tire
and road surface) and side nodes of a static and rolling tire when
the tire was excited with 200 N vertical load for a frequency ranging
from 20 to 200 Hz. The results show that frequency has little effect on
tire deformation up to 80 Hz. But between 80 and 200 Hz, the radial
and lateral components of displacement of the road and side nodes
exhibited significant oscillation. For the static analysis, the fluctuation
was sharp and frequent and decreased with frequency. In contrast, the
fluctuation was periodic in nature for the dynamic response of the
rolling tire. In addition to the dynamic analysis, a steady state rolling
analysis was also performed on the tire traveling at ground velocity
with a constant angular motion. The purpose of the computation
was to demonstrate the effect of rotating motion on deformation and
rolling velocity with respect to a fixed Newtonian reference point.
The analysis showed a significant variation in deformation and rolling
velocity due to centrifugal and Coriolis acceleration with respect to
a fixed Newtonian point on ground.
Abstract: This study investigates the mechanism of a Gyratory crusher-located in Golgohar mining and industrial Co. specifically with a focus on stresses distribution and fatigue failure of its main shaft. At first step, the cross section of the fractured shaft is studied, and the crack growth is analyzed. Then, the rotational motion of the shaft and the oil temperature of oil circuit of equipment are monitored. Condition monitoring is used to help finding a better modification. Based on the results of this study, the main causes of shaft failure are identified, and corrective solution is offered to increase crusher performance, especially its main shaft life. To predict the efficiency of the proposed modification, finite element simulation is performed, and its results are compared with the similar modified cases. The comparison and interpretation of simulation results confirm the efficiency of proposed corrective method.
Abstract: New design of three dimensional (3D) flywheel system
based on gimbal and gyro mechanics is proposed. The 3D flywheel
device utilizes the rotational motion of three spherical shells and the
conservation of angular momentum to achieve planar locomotion.
Actuators mounted to the ring-shape frames are installed within the
system to drive the spherical shells to rotate, for the purpose of steering
and stabilization. Similar to the design of 2D flywheel system, it is
expected that the spherical shells may function like a “flyball” to store
and supply mechanical energy; additionally, in comparison with
typical single-wheel and spherical robots, the 3D flywheel can be used
for developing omnidirectional robotic systems with better mobility.
The Lagrangian method is applied to derive the equation of motion of
the 3D flywheel system, and simulation studies are presented to verify
the proposed design.
Abstract: New design of three dimensional (3D) flywheel system
based on gimbal and gyro mechanics is proposed. The 3D flywheel
device utilizes the rotational motion of three spherical shells and the
conservation of angular momentum to achieve planar locomotion.
Actuators mounted to the ring-shape frames are installed within the
system to drive the spherical shells to rotate, for the purpose of steering
and stabilization. Similar to the design of 2D flywheel system, it is
expected that the spherical shells may function like a “flyball” to store
and supply mechanical energy; additionally, in comparison with
typical single-wheel and spherical robots, the 3D flywheel can be used
for developing omnidirectional robotic systems with better mobility.
The Lagrangian method is applied to derive the equation of motion of
the 3D flywheel system, and simulation studies are presented to verify
the proposed design.
Abstract: Proton transfer and hydrogen bonding are two aspects
of the chemistry of hydrogen that respectively govern the behaviour
and structure of many molecules, both simple and complex. All the
theoretical enol and keto conformations of 1,3-diphenyl-1,3-
propandion known as dibenzoylmethane (DBM), have been
investigated by means of atoms in molecules (AIM) theory. It was
found that the most stable conformers are those stabilized by
hydrogen bridges.The aim of the present paper is a thorough
conformational analysis of DBM (with special attention on chelated
cis-enol conformers) in order to obtain detailed information on the
geometrical parameters, relative stabilities and rotational motion of
the phenyl groups. It is also important to estimate the barrier height
for ptoton transfer and hydrogen bond strength, which are the main
factors governing conformational stability.
Abstract: The Euler-s equation of motion is extended to include
the viscosity stress tensor leading to the formulation of Navier–
Stokes type equation. The latter is linearized and applied to
investigate the rotational motion or vorticity in a viscous fluid.
Relations for the velocity of viscous waves and attenuation parameter
are obtained in terms of viscosity (μ) and the density (¤ü) of the fluid.
μ and ¤ü are measured experimentally as a function of temperature for
two different samples of light and heavy crude oil. These data
facilitated to determine the activation energy, velocity of viscous
wave and the attenuation parameter. Shear wave velocity in heavy oil
is found to be much larger than the light oil, whereas the attenuation
parameter in heavy oil is quite low in comparison to light one. The
activation energy of heavy oil is three times larger than light oil.
Abstract: Falls are the primary cause of accidents in people over
the age of 65, and frequently lead to serious injuries. Since the early
detection of falls is an important step to alert and protect the aging
population, a variety of research on detecting falls was carried out
including the use of accelerators, gyroscopes and tilt sensors. In
exiting studies, falls were detected using an accelerometer with
errors. In this study, the proposed method for detecting falls was to
use two accelerometers to reject wrong falls detection. As falls are
accompanied by the acceleration of gravity and rotational motion, the
falls in this study were detected by using the z-axial acceleration
differences between two sites. The falls were detected by calculating
the difference between the analyses of accelerometers placed on two
different positions on the chest of the subject. The parameters of the
maximum difference of accelerations (diff_Z) and the integration of
accelerations in a defined region (Sum_diff_Z) were used to form the
fall detection algorithm. The falls and the activities of daily living
(ADL) could be distinguished by using the proposed parameters
without errors in spite of the impact and the change in the positions
of the accelerometers. By comparing each of the axial accelerations,
the directions of falls and the condition of the subject afterwards
could be determined.In this study, by using two accelerometers
without errors attached to two sites to detect falls, the usefulness of
the proposed fall detection algorithm parameters, diff_Z and
Sum_diff_Z, were confirmed.