bob手机在线登陆学报自然版

2018, 38(3): .

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2018, 38(3): .

Abstract(557) PDF(418)

Abstract:

Aerodynamic Drag Reduction of Ahmed Model Based on Free Form Deformation

WANG Yi-ping, GUO Cheng-qi, WANG Tao, LI Shuai, YAO Yun-long

2018, 38(3): 221-228. doi:10.15918/j.tbit1001-0645.2018.03.001

Abstract(1303) PDF(682)

Abstract:
At present, the most common approach for vehicle aerodynamic drag reduction is trial and error method, which completely depended on the engineers' experience. Inevitably, this method is certain blindness and low efficiency. Moreover, it is quite difficult to parameterize the auto body in the aerodynamic optimization design. To solve these problems, a fast and effective parameterization method named FFD (free form deformation) was introduced into the vehicle aerodynamic optimization design. Firstly, taking the Ahmed model as the simulation object, sample space was constructed based on the orthogonal array experiment design, and FFD method was used to parameterize the model at each sample point. Secondly, the aerodynamic drag coefficient of each sample was confirmed by CFD simulation. Then, according to the sample space and computational results obtained by CFD, three kinds of approximate model were constructed, and the RBF model with highest credibility was selected to build the approximate model. Finally, the multi-island genetic algorithm was employed to get the optimal combination of the design variables. To validate the reliability of the final results, a new model was reconstructed according to the results of the optimization, and aerodynamic drag coefficient was computed by CFD again. The computational results show that the Ahmed model aerodynamic drag coefficient can be decreased by 51.96% after optimization, which confirms that FFD method deserves to be popularized in vehicle aerodynamic optimization design.

Hydrodynamic Lubrication Characteristics of Slipper/Swash Plate Pair in Axial Piston Pumps-Theory and Experiment

HU Ji-bin, ZHAO Hong-mei, JING Chong-bo

2018, 38(3): 229-234. doi:10.15918/j.tbit1001-0645.2018.03.002

Abstract(1222) PDF(750)

Abstract:
The hydrodynamic bearing ability of slipper/swash plate pair in axial piston pumps was studied under steady state. Considering the effect of centrifugal on the slipper tilt and analyzing the other forces on the slipper, a tribo-dynamic model of slipper/swash plate pair under steady condition was developed to study the law of hydrodynamic lubrication of oil film between the interfaces. The result shows that the gap between friction pair is always convergent wedged-shape and the tilting azimuth angle of slipper is around 170 degrees basically. This micro motion of slipper is helpful for the hydrodynamic lubrication film. The simulation result was testified well by the experiment.

Research on Gear Gridding Process of Material 18CrNi4A Based on Burn Control

WANG Yan-zhong, LIU Yang, WANG Duan, ZHANG Wei, ZHAO Xing-fu

2018, 38(3): 235-240. doi:10.15918/j.tbit1001-0645.2018.03.003

Abstract(813) PDF(546)

Abstract:
In order to improve the process and prolong the fatigue life of the gear made from Material 18CrNi4A,a new method was proposed to control the manufacturing process of gear and to prevent the grinding burns emerging in this process.Firstly,a model was developed based on ABAQUS finite element simulation method to simulate the gear grinding process and to analyze the influence of process parameters,such as grinding wheel speed and grinding depth,on the grinding temperature field of Material 18CrNi4A.And then,the influencing weights of each process parameter on the grinding temperature field were established to provide a reference for the study of grinding parameter control according as burn performance.Finally,a Material 18CrNi4A gear grinding test was carried out to verify the reliability of finite element simulation analysis result and to obtain the critical temperature of Material 18CrNi4A grinding burn.The analysis and test results can provide a certain theoretical guidance for the grinding process parameter decision of the Material 18CrNi4A gears.

Reducing CO₂Emission from Ship Based on Alkali Mechanism

WANG Zhong-cheng, LIU Xiao-yu, ZHOU Pei-lin, XU Le-ping

2018, 38(3): 241-246. doi:10.15918/j.tbit1001-0645.2018.03.004

Abstract(1044) PDF(524)

Abstract:
A NaOH solution was proposed to absorb CO₂from ship exhaust gas for the reduction of marine CO₂emission and achievement of green shipping.Firstly,CO₂absorption principle with NaOH solution was conducted and a mathematical model of absorption efficiency was deduced.After installing the newly designed CO₂absorption device on the 6135G128ZCa marine diesel engine,the factors,such as NaOH solution concentration and reaction temperature,were analyzed for influence on the CO₂absorption efficiency.Results indicate that ship's CO₂emission can be reduced over 20% after using NaOH solution under the full load conditions of the diesel engine.The results lay a foundation for the future study of marine emission decarburization technology.

Design of Combustor for Gas Turbocharging System

LIU Yang, MA Chao-chen

2018, 38(3): 247-254. doi:10.15918/j.tbit1001-0645.2018.03.005

Abstract(863) PDF(701)

Abstract:
A combustor of tumbling flow and recirculating flow was designed to satisfy the need of compact structure of diesel engine and to solve driving power shortage problem in the plateau with gas turbocharging system. Firstly, the internal temperature field and exit temperature distribution were analyzed by CFD numerical simulation and the main structural parameters of the combustion chamber were determined. Then the cold flow field of the combustor's dome was measured by the particle image velocimetry (PIV) to testify the tumbling flow, recirculating flow and capable steady blaze sections existing in the combustor's dome. Finally, a combustion experiment was implemented to analyze the oil deficient ignition and flameout. Experimental results show that, in a certain flow range, the gas oil ratio of both lean ignition and lean blowout is proportion to Mach number. Compared the total pressure recovery coefficient of the designed combustor with that of a same-sized recirculating-flow combustor, in the same flow, the total pressure of the designed combustor can increase by an average 2%.

Simulation of Vehicle Handling and Stability Based on Hydraulic-Electrical Energy Regenerative Shock Absorber

ZOU Jun-yi, GUO Xue-xun, FANG Zhi-gang, CHEN Zhen-fu, ZHANG Jie

2018, 38(3): 255-260. doi:10.15918/j.tbit1001-0645.2018.03.006

Abstract(1059) PDF(713)

Abstract:
Analyzing the influence of a proposed hydraulic-electrical energy regenerative shock absorber (HESA) on vehicle handling and stability in different simulation conditions,it was proved that the HESA possessed a basic level with traditional hydraulic damper,and it was provided with a feasibility of real vehicle experiments.At first,the principle and damping characteristics of HESA were studied.Secondly,different simulation conditions were selected,such as double lane changing,steering wheel angle step and fishhook test.And the yaw velocity,roll angle and lateral acceleration were selected as the evaluation indices to evaluate the HESA's influences on vehicle handling and stability.At last,the motor displacement,check valve cracking pressure and pipe diameter were taken as the main influential parameters to analysis the effect on vehicle handling and stability.The results can provide a theoretic foundation for suspension matching.

Analysis on Influencing Factors of Energy Consumption Characteristics of Electronic Hydraulic Braking System

HU Dong-hai, HE Ren, XU Xiao-ming, YI Feng-yan

2018, 38(3): 261-266. doi:10.15918/j.tbit1001-0645.2018.03.007

Abstract(791) PDF(706)

Abstract:
To solve the energy consumption problem existing in the electronic hydraulic braking system, a mathematical model was established for energy consumption analysis, and the effect of system parameters and structure parameters on energy consumption characteristics of electronic hydraulic braking system were analyzed based on this mathematical model. Analysis results show that, reducing the maximum system working pressure and diameter of brake wheel cylinder piston is beneficial to decrease the power consumption of electronic hydraulic brake system, but the change of the minimum system working pressure and the effective discharge of the accumulator have a little influence on it. Increasing the charging pressure of accumulator or reducing the effective discharge of accumulator and the diameter of brake wheel cylinder piston will make the accumulator smaller.

Vibration Fatigue Analysis and Experimental Study of Heavy Duty Truck Rear Axle

ZHANG Zhi-yuan, LIU Yu-mei, CHEN Tao, FAN Wen-feng

2018, 38(3): 267-271,299. doi:10.15918/j.tbit1001-0645.2018.03.008

Abstract(988) PDF(645)

Abstract:
To improve the durability of heavy tractor rear axle,the durability problem,such as rod-bracket failure,welding line and straight seam-weld crack was focused to be solved.Attempting to replace the welded axle with cast steel axle,several projects were carried out including the durability comparison between cast-steel axle and welded axle,the development of a virtual test platform for vehicle axle,and the virtual-test model examination by contrast experiment.A vibration fatigue analysis method was applied to solve cast-steel axle and welded axle life,and the bench test was taken to verify the simulation result.The simulation and test results identically show that the cast-steel axle is better than welded in fatigue life,the heavy tractor assembled with cast-steel axle can improve its structure reliability effectively.

WCRT Optimization Scheme Based on Task Mapping and Cache Partitioning

GAN Zhi-hua, ZHANG Ming-quan, GU Zhi-min, ZHANG Ji-zan, TAN Hai

2018, 38(3): 272-278. doi:10.15918/j.tbit1001-0645.2018.03.009

Abstract(1203) PDF(618)

Abstract:
To reduce the worst-case response time (WCRT) of multi-core systems, an efficient approach based on the combination of task mapping and cache partitioning techniques was proposed in this paper. The allocating process was divided into two phases in the approach. In the first phase, the task with the worst-case execution time (WCET) based on the optimal cache size allocated was assigned to different cores. In the second phase, in order to meet the constraints of shared cache size, some mapped tasks were selected for callback of the cache size and readjustment of task mapping. At the same time, load balancing was considered in the two phases. Experiment results show that the proposed approach can reduce the WCRT of the systems and improve execution efficiency compared with previous techniques. The proposed approach can reduce WCRT of systems by up to 6.7% on average compared with GCP approach. The approach outperforms the LIP-based approach on execution efficiency.

Hand Gesture Recognition Based on an Improved Convex Shape Decomposition

PAN Zhi-geng, WANG Shun-ting, YAO Zheng-wei

2018, 38(3): 279-285. doi:10.15918/j.tbit1001-0645.2018.03.010

Abstract(913) PDF(806)

Abstract:
Hand gesture recognition has become one of the most natural way of human communication with computer, However, the recognition accuracy and efficiency of the traditional methods still need to be improved. In this paper, a novel method was proposed based on Kinect for static gesture recognition in real time. Firstly, a simple and feasible hand detection and segmentation method was put forward based on depth information and skin color information. Then, a improved convex shape decomposition method was developed to obtain hand skeleton, and a gesture recognition method was put forward based on comparing the geodesic paths between skeleton endpoints. Finally, a comparative experiment was carried out for a specific gesture set. The experimental results show that, this method can provided a good performance in recognition accuracy and efficiency of the algorithm.

Extraction Method of Archaeological Line Graph Based on 3D Model

ZHOU Ming-quan, LI Can, XIE Guo-dong, REN Pu

2018, 38(3): 286-292. doi:10.15918/j.tbit1001-0645.2018.03.011

Abstract(999) PDF(1011)

Abstract:
Archaeological line graph can not only show the shape characteristics of cultural relics, but also serve as their essential archives. It is obtained by manual work traditionally with high time-consuming and low accuracy as well as may cause new damage to cultural relics. In this paper, a new method was proposed based on a 3D model of cultural relics to generate archaeological line graph automatically, and was applied to debris models of Terracotta Warriors. First of all, the debris models were obtained by laser scanning and were pre-treated such as denoising, hole filling and simplification. Then, the feature points were extracted from the model according to the normal dispersion of vertex. At last, the contour was detected and the features line was drawn to complete line graph of the cultural relics. This method not only has low requirements for the primitive model but also own flexible perspectives and a high usability, it can significantly improve the efficiency of archaeological drawing.

Terracotta Warrior Blocks Matching Algorithm Based on Contour Curve and Feature Region

ZHAO Fu-qun, ZHOU Ming-quan, GENG Guo-hua

2018, 38(3): 293-299. doi:10.15918/j.tbit1001-0645.2018.03.012

Abstract(823) PDF(610)

Abstract:
A Terracotta Warrior blocks matching algorithm based on contour curve and feature region was proposed here in order to improve the matching accuracy and convergence rate. Firstly, the fracture surfaces and their contour curves were extracted, and each contour curve was divided into several parts, then the longest common subsequence algorithm was used to match the contour curves, achieving a coarse matching of the blocks. Secondly, the concavity or convexity of vertexes on fracture surface was calculated by volume integral invariant, and the fracture surface was divided into a number of concave and convex feature regions. Finally, the centroids of the feature regions were calculated and used to achieve fine matching of blocks with improved ICP algorithm. In the experiment, three types of algorithms were used to match the Terracotta Warrior blocks. The matching results show that the blocks matching algorithm based on contour curve and feature region can achieve complete matching and partial matching of Terracotta Warrior blocks much more accurately, and obtain a much higher iterative convergence rate in fine matching stage.

Parameters Identification of Particle Size of Heap Leaching Uranium Ore Based on Image Analysis

NING Zhi-gang, HAO Guang-peng, CHENG Xiong, SHEN Wen-bin, DING De-xin

2018, 38(3): 300-304,312. doi:10.15918/j.tbit1001-0645.2018.03.013

Abstract(774) PDF(435)

Abstract:
Digital image processing technology was used to measure particle size of uranium ore fragmentation and determine particle size distribution. Image guided filter was applied to ore image filtering for the first time, which could filter image noise and preserve ore image edge information. PCNN image segmentation algorithm based on between-class posterior maximum cross entropy criterion was used to segment ore image,which could reduce ore adhesion phenomenon. In order to solve ore adhesion phenomenon after first image segmentation, a digital image cutting algorithm based on concave point matching was proposed to secondly segment adhesive ore image, which could effectively separate adhesion ore image.The parameter measurement method based on shape features was used to measure particle parameters, which could improve measurable accuracy of particle parameters. The statistical distribution charts of ore particle size were drawn with particle parameters. Experimental data show that the method can improve measure accuracy and satisfy with practical needs.

A Highly Reliable In-VM Hidden Process Detection Countermeasure

YAN Guang-lu, LUO Sen-lin, LIU Wang-tong, PAN Li-min

2018, 38(3): 305-312. doi:10.15918/j.tbit1001-0645.2018.03.014

Abstract(878) PDF(457)

Abstract:
Executing malicious code via hidden process is a major way to carry out information attack. At present, hidden process detection methods based on In-VM model of virtualization platform can be attacked by circumventing and tampering with the relative data. To solve this problem, a highly reliable In-VM hidden process detection method was proposed. Firstly, an In-VM model and the memory protection mechanism of virtualization were developed to protect its detection code and relative kernel data from being maliciously changed. Secondly,by hijacking the system transfer function exactly and detecting the hidden process with a cross-view method, the detection algorithm was ensured from being circumvented. Finally, several typical Rootkits were built and chosen in experiments. The results show that, the proposed method can detect all kinds of hidden processes. Its detection code and relative kernel data cannot be tampered with and its detection algorithm and memory protection mechanism cannot be circumvented. And the developed memory protection mechanism has better performance in the system, showing a higher reliability and stronger pragmatic value.

Underdetermined DOA Estimation for Coprime Array Based on Noncircular Signal

WU Chen-xi, ZHANG Min, WANG Ke-ren

2018, 38(3): 313-319. doi:10.15918/j.tbit1001-0645.2018.03.015

Abstract(1164) PDF(702)

Abstract:
For underdetermined direction of arrival (DOA) estimation problems, a novel DOA estimation method was proposed for coprime array based on noncircular signals. Firstly,the cross covariance and elliptic covariance matrix of the coprime array output were vectorized,a virtual uniform array output was formed by reconnecting the data and wiping off the redundancy, making array aperture full expanded and the number of virtual array elements further increased. Then, according to the spatial sparsity of the incident signals, the DOA estimation problem was transformed into a continuous sparse recovery problem in continuous angle region, so as to eliminate the basis mismatch due to angle region discretizing with traditional sparse recovery arithmetic. Finally, the correlative convex optimization and polynomial root were solved to carry out the estimation of DOA. Theoretical analysis and simulation results show that, the proposed method can achieve excellent array expanding, high estimation accuracy and resolution capability.

An Improved Locating Algorithm Based on Double Baselines Rotating Interferometer

ZHANG Jin-xiu, TAO Hai-hong, WANG Yuan

2018, 38(3): 320-324. doi:10.15918/j.tbit1001-0645.2018.03.016

Abstract(855) PDF(497)

Abstract:
The traditional double long baselines interferometer (DLBI) requires the baselines to be strictly co-prime for locating. Besides, it is sensitive to the phase error and the performance becomes worse with higher fuzzy number. In this paper, an improved direction-finding algorithm with double baselines rotating interferometer (DBRI) was proposed to solve the drawback mentioned above. Two baselines with arbitrary length, rotating in the opposite direction with arbitrary palstance, were utilized to get the phase difference for locating. Finally, the computer simulations were carried out to verify the effectiveness and validity of the proposed algorithm. Results show that, the algorithm can obtain better location precision with high fuzzy number and robust to the phase error.

Monte Carlo Simulation for the Adsorption Behavior of Ethylene Oxide on HZSM-5 Zeolite

WU Qiong, LUAN Zhi-qiang, DAI Rong-ji, LI Kai, YE Ping-wei, ZHAO Li-feng

2018, 38(3): 325-330. doi:10.15918/j.tbit1001-0645.2018.03.017

Abstract(912) PDF(582)

Abstract:
In order to study the effects of silica-alumina ratio and changes in water content on the adsorption performance of epoxy ethane, a combined strategy of grand canonical Monte Carlo (GCMC) and isothermal-isobaric ensemble (NPT) was used to analyze the adsorption of ethylene oxide (EO) on HZSM-5 zeolite under different humidity on molecular level. The results show that, under two different relative humidity (RH) conditions, which are 30% and 90% respectively, the HZSM-5 zeolite with 25~120 Si/Al ratios have better adsorption performance of ethylene oxide with concentration 1 000 mg/m³.The adsorption quantity of HZSM-5 under low humidity is slightly higher than that under high humidity. At last, the simulation results were validated by experiment. It means that the simulation conditions and methods used are suitable for the adsorption process analysis of EO on ZSM-5. The simulation results provide a theoretical basis for seeking out the EO adsorption materials and optimizing the remove conditions of EO.

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