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871.
Indoor air pollutants impact human health, comfort and productivity. The method of photocatalysis has been applied mainly
in flow reactors and little information is available on indoor air pollutant removal in airtight reactors. In the paper, experiments
were carried out to remove formaldehyde (HCHO), ammonia (NH3) and volatile organic compounds (VOCs) in the airtight and ventilated chambers. Results demonstrated that 90.4% of HCHO,
92.3% of NH3 and 57.9% of VOCs were removed in the amine adsorption process, while 67.5% (hereinbefore, these are the mass fraction) of
HCHO, 60.0% of NH3, and 61.2% of VOCs were removed in the photocatalytic process. However, ozone-assisted photocatalytic process showed great
potential to degrade indoor air pollutants in the ventilated chamber. Factors and mechanisms of the photocatalytic degradation
of HCHO, NH3 and VOCs were also discussed. 相似文献
872.
A method of underwater simultaneous localization and mapping (SLAM) based on on-board looking forward sonar is proposed. The
real-time data flow is obtained to form the underwater acoustic images and these images are pre-processed and positions of
objects are extracted for SLAM. Extended Kalman filter (EKF) is selected as the kernel approach to enable the underwater vehicle
to construct a feature map, and the EKF can locate the underwater vehicle through the map. In order to improve the association
efficiency, a novel association method based on ant colony algorithm is introduced. Results obtained on simulation data and
real acoustic vision data in tank are displayed and discussed. The proposed method maintains better association efficiency
and reduces navigation error, and is effective and feasible. 相似文献
873.
The asymmetric deformation and eccentricity problems of near hemispherical diaphragm under the uniform surface load are quantitatively
characterized in the paper. The analysis is based on a 3D finite element analysis (FEA) model established according to elastic-plasticity
and large displacement nonlinear finite element method. Besides, the deformation experiments are taken to validate the reliability
of FEA model which shows that the simulation results are in good agreement with the experimental results. Then, three angle
parameters, deflection angle β, circumvolving angle θ and distributing angle γ, are introduced and expressed to characterize the asymmetric deformation and eccentricity quantitatively. According to the
angle parameters, the inversion processes of uniform thickness diaphragm and varying thickness diaphragm are calculated respectively.
The inversion process of varying thickness diaphragm is much steadier than that of uniform thickness diaphragm. The present
results show that the asymmetric deformation process can be characterized by curve of three angle parameters (β, θ, γ) exactly, the degrees of eccentricity can be indicated by the final value of deflection angle and the eccentricity position
can be characterized by the final values of the three angle parameters. 相似文献
874.
Underwater gliders are highly efficient, buoyancy-driven, and winged autonomous underwater vehicles. Their dynamics are multivariable
nonlinear systems with unstable internal dynamics and thus their motion control is a significant challenge. To improve the
inherent efficiency and enhance the behavior of the underwater glider over a wide operating regime, a nonlinear feedforward
and feedback controller was developed. The nonlinear feedforward control design is based on a new stable inversion technique
which determines a causal and bounded solution for the unstable internal dynamics. The feedback control law was designed by
a quadratic optimal control method. Simulation results show that the derived control system is able to deal with nonminimum
phase system and successfully achieves the tracking of planned output trajectories from initial to final conditions. Furthermore,
the control effort is very low, which means the glider with limited power storage has longer range and higher endurance. 相似文献
875.
This paper presents experimental results of the post-fire behavior of tubular T-joints. The research aims at the failure modes
and the residual strengths of the T-joints after fire. Three tests of full-scale tubular T-joints are conducted. The first
one is carried out to study the mechanical behavior of T-joints under ambient temperature. The other two tests are performed
to study the influence of pre-load, heating and cooling phase on residual load-bearing capacity of the tubular T-joints. The
test results show that the sustained axial load on the brace has remarkable influence on the residual deflection of the T-joints
which is cooled down to room temperature. The results of the experiments also indicate that the axial load level and heating
and cooling history have more significant effects on the compressive stiffness of the T-joints than the residual strength.
In the numerical study, the result of finite element model agrees well with the test result. The work in this paper provides
a basis for further parametric analysis and theoretical study on the structural evaluation after fire. 相似文献
876.
In this paper, a kind of mathematic method for optimizing stretching process of large forgings is proposed. Distributions
of effective strain within forged ingots is described by a Gauss function, which is obtained from the simulation of flat-anvil
stretching process. Successive stretching is expressed by the superimposing Gauss functions. Optimized stretching process,
with both homogeneous and certain strain in the center of forgings, is presented by derivation of this function. The relationship
between effective strain and the values of feed is obtained during the successive stretching with a rotation angle of 90°
and a feed displacement of 1/2 anvil width. The optimization result is verified by finite element simulation. Optimized value
of feed obtained using this method can ensure both uniformity and forging penetration. It provides mathematic model and theoretic
basis of optimizing large forging stretching process. 相似文献
877.
22MnB5 is one of the most typical hot stamping boron steels. In order to study the effect of austenitizing temperature and
holding time on the mechanical properties of hot stamping boron steel 22MnB5, a series of quenching process are done. The
tensile strength and hardness of 22MnB5 samples are measured. The results show that 22MnB5 has a good quenching performance,
and the tensile strength and hardness of samples quenched in a water-cooled steel die are similar to those of water quenching.
The higher tensile strength and HRC hardness are achieved when austenitizing at temperatures of 880–910 °C. Holding at 910
°C for 5 min and then quenching gives rise to a better combination of tensile strength, hardness and ductility. 相似文献
878.
A numerical study on bank effects in shallow channels is carried out by using a first-order Rankine source panel method. A
container ship sailing along a vertical bank and a sloping bank at different forward speeds, different water depths and different
distances between the bank and the ship hull is taken as example. The sway force and yaw moment acting on the hull are calculated
and the influences of the speed, water depth and distance between the bank and ship hull on the hydrodynamic force and moment
are analyzed. This study can provide insight into the bank effects, as well as to give guidance on ship manoeuvring and control
in restricted waterways, which is helpful to the navigation safety. 相似文献
879.
The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity, which are
strongly influenced by molten pool profile that is influenced by VAR process. To better understand the effect of remelting
current on molten pool profile of titanium alloy ingot during VAR process, a 3D finite element model is developed by the ANSYS
software. The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.
The molten pool depth increases gradually from 30 to 320 s, then the change of molten pool depth is very small during the
steady state stage from 320 to 386 s, and lastly the molten pool depth becomes shallow after 386 s. The melting rate and temperature
of superheat increase with the remelting current increasing, which leads to the augment of molten pool volume. In the end,
the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA. 相似文献
880.
The quenching of a metal component with a channel section in a water tank is numerically simulated. Computational fluid dynamics
(CFD) is used to model the multiphase flow and the heat transfer in film boiling, nucleate boiling and convective cooling
processes to calculate the difference in heat transfer rate around the component and then combining with the thermal simulation
and structure analysis of the component to study the effect of heat transfer rate on the distortion of the U-channel component.
A model is also established to calculate the residual stress produced by quenching. The coupling fluid-thermal-structural
simulation provides an insight into the deformation of the component and can be used to perform parameter analysis to reduce
the distortion of the component. 相似文献