Current Issue : April-June
Volume : 2022
Issue Number : 2
Articles : 5 Articles
To further study the fault mechanism and fault features of rolling bearings, a two-DOF rolling bearing fault dynamic model with
inner ring local defects considering the bearing radial clearance and time-varying displacement excitation is established based on
Hertz contact theory. By comparing the simulated fault signal with bearing fault test data in the time domain and frequency
domain, the accuracy of the established fault dynamic model is verified. Finally, the change rules of the characteristic parameters of
the bearing inner ring fault signal, including effective value, absolute mean value, square root amplitude, peak value, kurtosis
factor, pulse factor, peak factor, and shape factor, are simulated by the fault dynamic model. )e results highlight that the
proposed fault dynamic model is in good agreement with the experimental results. )e model can simulate the fault signal
characteristic parameters with the change of defect width, external load, and rotating speed effectively. )e study in this paper is of
engineering application value for bearing condition monitoring and fault diagnosis....
Liquid storage tanks are lifeline structures and strategically very important. Heavy damages or even collapse of these facilities
subjected to strong earthquakes may cause disastrous consequences. In this paper, the seismic response of a multistage series
liquid storage tank was simulated by a finite element method and verified by a scaled-down experiment.)estructural flexibility of
the tank and the liquid-structure coupling characteristics between the liquid and tank wall were considered in the research. A
multimass-block and spring model was employed to be equivalent to the longitudinal vibration of the liquid in the storage tank.
)e relationships between the connection springs and the elements of the stiffness matrix were explicitly deduced. )e seismic
response analysis of a four-stage series liquid tank was carried out, and the acceleration response, the stress response of the tank,
and the vertical vibration of the liquid were obtained. )e experimental results are in good agreement with the simulation results,
which verifies the effectiveness of the modeling method in this paper....
The reliability of the modelling system mainly depends on the simulation of underwater acoustic channel characteristics. The
reliability of simulator is improved because of the use of Bellhop in NS-Miracle. World Ocean Simulation System (WOSS) can
retrieve the data of marine environment by accessing the database of seabed depth, sound speed profile and seabed sediment,
and transmit them to Bellhop simulator automatically, so that the model is closer to the actual underwater acoustic transmission
channel than not using WOSS. In order to verify the reliability of NS2/NS-Miracle simulation system with WOSS, a centralized
underwater sensor network with five nodes is simulated on the integrated simulation system. The characteristic empirical
model, Bellhop Ray-Tracing model, and WOSS combined with Bellhop model are, respectively, adopted to simulate underwater
acoustic channel. The results of three types of simulation, such as average throughput, average delay, and packet error rate, and
simulation time are very close under the same condition. It proves that the accuracy of integrated simulation system is as
excellent as that of NS-Miracle. However, WOSS can automatically acquire the actual sea environment parameters and provide
them to the simulator, which can improve the authenticity of the simulation system. Furthermore, three MAC protocols, Aloha-
CS, CSMA/CA, and DACAP, are simulated on the integrated simulation system under the same condition including ocean
environment, network topology, and parameters. The results show that the performance of CSMA/CA is greater than the other
protocols in such networks. It also proves that the integrated simulation system can accurately simulate the relevant
characteristics of the MAC protocol....
Although the original proposal of microperforated panels by Maa consisted of an array of
minute circular holes evenly distributed in a thin plate, other hole geometries have been recently
suggested that provide similar absorption curves to those of circular holes. With the arrival of
modern machining technologies, such as 3D printing, panels microperforated with slit-shaped
holes are being specially considered. Therefore, models able to predict the absorption performance
of microperforated panels with variable hole geometry are needed. The aim of this article is to
analyze three models for such absorbing systems, namely, the Maa model for circular holes, the
Randeberg–Vigran model for slit-shaped holes, and the Equivalent Fluid model for both geometries.
The absorption curves predicted for these three models are compared with the measured curves of
three panels microperforated with spirally shaped slits....
To meet the practical application requirements of cardiac fixation during off-pump coronary
artery bypass surgery, a soft cardiac fixator with a flexible arm was previously designed. To enable
the soft cardiac fixator to adapt to uncertain external forces, this study evaluates the variable-stiffness
performance of the flexible arm. First, the flexible arm was simplified as a soft silicone manipulator
measuring 60 mm 90 mm 120 mm, which can actuate, soften, or stiffen independently along the
length of the arm by combining granular jamming with input pressure. Then, the soft manipulator
was modelled as a cantilever beam to analyse its variable-stiffness performance with granular
jamming. Next, based on theoretical analysis and calculations, many experiments were conducted
to evaluate the variable-stiffness performance of the soft manipulator. The experimental results
demonstrated that the variable-stiffness performance is influenced by the flexible arm length, the
size of the granules, and the input pressure....
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