Wyniki wyszukiwania - Biblioteka Nauki

1

An accurate and stable pose estimation method for planar cases considering the line constraints between every two points

100%

Zhang Z. , Zhang H. , Zhang F. , Zhang S.

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tom Vol. 30, nr 2

235--258

EN

The current solutions for pose estimation problems using coplanar feature points (PnP problems) can be divided into non-iterative and iterative solutions. The accuracy, stability, and efficiency of iterative methods are unsatisfactory. Therefore, non-iterative methods have become more popular. However, the non-iterative methods only consider the correspondence of the feature points with their 2D projections. They ignore the constraints formed between feature points. This results in lower pose estimation accuracy and stability. In this work, we proposed an accurate and stable pose estimation method considering the line constraints between every two feature points. Our method has two steps. In the first step, we solved the pose non-iteratively, considering the correspondence of the 3D feature points with their 2D projections and the line constraints formed by every two feature points. In the second step, the pose was refined by minimizing the re-projection errors with one iteration, further improving accuracy and stability. Simulation and actual experiment results show that our method’s accuracy, stability, and computational efficiency are better than the other existing pose estimation methods. In the -45° to +45° measuring range, the maximum angle measurement error is no more than 0.039°, and the average angle measurement error is no more than 0.016°. In the 0 mm to, 30 mm measuring range, the maximum displacement measurement error is no more than 0.049 mm, and the average displacement measurement error is no more than 0.012 mm. Compared to other current pose estimation methods, our method is the most efficient based on guaranteeing measurement accuracy and stability.

2

Electrokinetic remediation technology of heavy metal contaminated soil based on improving soil electrical conductivity

100%

Liu J. , Zhang W. , Liu M. , Zhang H.

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tom Vol. 47, nr 4

5--17

EN

An electrokinetic remediation technique taking Cr(VI) as an example is proposed to improve the conductivity of contaminated soil, which significantly increases the current density in the soil. The improvement of soil conductivity was achieved by continuous spraying of NaCl solution with a concentration of 4 g·dm–3 on the soil surface. The distances of electrode pairs were 2.0 m and 1.5 m, respectively. The heavy metal-contaminated soil thickness was 25 cm, and the DC power supply voltage was 90 V. The experiment demonstrated that under the condition of continuous spraying of NaCl solution on the soil surface, the current density variation was related to the salt content in the soil, and the current density in the soil generally increased linearly with time. The effectiveness of soil remediation is related to the electric field strength and current density, and there exists an optimal electric field that can reduce the heavy metal content in the soil at any point by minimizing the electric field strength and current density. Most of the heavy metals can be concentrated within a diameter of about 15 cm around the anode under the optimal electric field, which can be remediated after removing the soil.

3

Investigation of lower limb injury under different contact stiffness for drivers during frontal crash

88%

Xiao S. , You S. , Tian T. , Wu J. , Zhang H.

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tom Vol. 24, no. 2

83--93

EN

Lower extremity injuries in AIS2+ were the most costly injuries through the statistical analysis of traffic accidents. This study aimed to investigate the response characteristics of the lower limb with different contact stiffness, in which knee cushion and foot cushion were applied. First, a model with a human body and a car was established, and the muscle function was activated in lower extremity of human model. Second, the deceleration pulse with a peak of 186 m/s2 was applied to the car to simulate the frontal crash. Then, four sets of simulations with different contact stiffness are conducted to obtain the lower limb responses. Results indicate that the maximum loading of the left and right legs during the impact was 1.29 and 1.22 kN, respectively. Meanwhile, the maximum moment were 28.82 and 52.17 Nm, respectively. The maximum stress of lower extremity was 87.35 MPa, and the maximum tibia index was 0.230. It was demonstrated that the injury risk of the femur in the groups with equipment of knee cushion and foot cushion was low, but the injury risk of the tibia increased at the same time. This study could provide a reference to the study of lower limb injury in a frontal impact.

4

Tool wear condition monitoring in milling process based on data fusion enhanced long short-term memory network under different cutting conditions

88%

Zheng G. , Sun W. , Zhang H. , Zhou Y. , Gao C.

Eksploatacja i Niezawodność

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2021

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tom Vol. 23, no. 4

612--618

EN

Tool wear condition monitoring (TCM) is essential for milling process to ensure the machining quality, and the long short-term memory network (LSTM) is a good choice for predicting tool wear value. However, the robustness of LSTM- based method is poor when cutting condition changes. A novel method based on data fusion enhanced LSTM is proposed to estimate tool wear value under different cutting conditions. Firstly, vibration time series signal collected from milling process are transformed to feature space through empirical mode decomposition, variational mode decomposition and fourier synchro squeezed transform. And then few feature series are selected by neighborhood component analysis to reduce dimension of the signal features. Finally, these selected feature series are input to train the bidirectional LSTM network and estimate tool wear value. Applications of the proposed method to milling TCM experiments demonstrate it outperforms significantly SVR- based and RNN- based methods under different cutting conditions.

5

Strain measurement based on fixed wavelength transmission of tapered long-period fiber grating

88%

Tang Y. , Zhang H. , Zhang L. , Yu X. F. , Bai Y. F.

Optica Applicata

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2022

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tom Vol. 52, nr 4

511--519

EN

This paper studies the relationship between transmission intensity and strain based on tapered long-period fiber grating at a fixed wavelength. In experiments, tapered long-period fiber grating was prepared by the electric melting method. Experimental results show that two resonance peaks appeared at 1482 and 1537 nm, respectively. Here is the elaboration of the relationship between the resonant wavelength and the strain, its wavelength-strain sensitivity is 20 pm/με, and the linearity was negative. Then our next study was about the relationship between transmission intensity and strain at a fixed wavelength. The results show that the transmission intensity at a fixed wavelength is related to the exponent with strain. The coupled-mode theory is applied to simulate the relationship between fixed wavelength and strain. The simulation results matched the experimental results. Two fixed wavelength transmission intensity ratio was used, and the ratio showed a linear relationship with the strain, and the slope is –0.018 dB/με. Therefore, within the 0.01% resolution of our detector, we could resolve a 0.16 με strain change. We can select the appropriate light source and detector to achieve higher measurement accuracy. Thus, there is a great potential in fiber grating strain sensors.

6

Characteristic research of lower extremity injuries in elderly pedestrians during collisions

88%

Xiao S. , Zhang L. , Wu J. , Liu X. , Zhang H.

Acta of Bioengineering and Biomechanics

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2022

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tom Vol. 24, no. 4

95--108

EN

The aim of this research is to study the trend of pedestrian lower extremity injuries during vehicle-pedestrian collisions. Methods: In this study, pedestrian’s age, collision angle and pedestrian’s position are considered influencing factors. Nine experiments using a novel lower extremity mechanical model are designed with the orthogonal experiment method. Results: Under the same collision angle, collisions in the left and right positions caused more serious tibia injuries than the middle position. As for the collision angle, the tibial injury at +45° is more significant than the tibial injury at −45°, and the injury of oblique collisions is slightly greater than that at 0°. Moreover, tibial injury is more sensitive to research variables than femoral injury. When the collision angle and position are changed, the difference ratio of tibia stress is by 483.2% higher than that of femur stress. The axial force and bending moment of the quadriceps tendon in the left-position collision reach peak values, which are 3.83 kN and 165.98 Nm, respectively. The peak quadriceps tendon axial force is captured with the collision angle of −45°, and the peak quadriceps tendon bending moment is obtained with a collision angle of +45°. Conclusions: The effects of differences in impact position and angle on lower extremity injury in the elderly were analyzed, and the results of this study can be used as a reference for research on lower extremity protection.

7

An optimal 125-point scheme for 3D frequency-domain scalar wave equation

88%

Yang L. , Wu G. , Wang Y. , Li Q. , Zhang H.

Acta Geophysica

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2022

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tom Vol. 70, no 1

71--88

EN

To improve accuracy and efficiency of forward modeling in the frequency domain, a 125-point finite-difference scheme is proposed. At present, the optimized difference format based on the rotating coordinate system is widely used, but it only suitable for equally sampling interval, and the optimized difference format based on the average-derivative method can be applied to different spaced sampling while improving the sampling accuracy. In this paper, we firstly introduce a 125-point optimized scheme for the three dimensional scalar wave equation. Then, according to the optimized difference scheme, the 125-point optimized difference coefficient is calculated for different spatial sampling spacing ratios. Compared with the optimal 27-point scheme, grid points number reduces from 4 points to 2.5 per wavelength, higher efficiency and suitable for unequal directional sampling intervals. In addition, the higher accuracy of 125-point scheme means it requires more storage and computation cost. Numerical results show that the optimized 125-point difference format has higher accuracy than the classical 27-point difference format.

8

Research on beam supply control strategy based on sliding mode control

88%

Zhang H. , Dong H. , Zhang B. , Wu T. , Chen C.

Archives of Electrical Engineering

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2020

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tom Vol. 69, nr 2

349--364

EN

In the hybrid multiple H-bridge topology of beam supply, the load change of a DC/DC full-bridge converter can greatly affect the output voltage during onsite operation. An improved sliding mode control (SMC) strategy is thus proposed in this paper, where the rate of switching control is added to the law of system equivalent control to create a law that can realize a complete sliding mode control. Considering the special operating conditions of the load can have an influence on the performance of the controller, the impact of uncertainty existing in onsite conditions is suppressed with the proposed strategy utilized. The validity of the proposed strategy, finally, is verified by simulation, which proves the outperformance of the system in both robustness and dynamics.

9

P-Impedance and Vp/Vs prediction based on AVO inversion scheme with deep feedforward neural network: a case study from tight sandstone reservoir

75%

Mao X. , Han X. , Wu B. , Wang Z. , Zhang H. , Wang H.

Acta Geophysica

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2022

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tom Vol. 70, no 2

563--580

EN

The low-frequency component of seismic data is an inevitable part to obtain absolute P-impedance (Ip) and Vp∕Vs ratio of the subsurface, especially for the reservoir sweet spot. In this work, we train the deep feedforward neural network (DFNN) with band-pass seismic data and well log data to obtain favorable low-frequency components. Specifically, the Bayesian inference strategy is first applied to the pre-stack constrained sparse spike inversion process, obtaining an “initial” inverted band-pass parameters, which are subsequently used as input when applying the DFNN algorithm to predict low- and bandpass parameters. Moreover, the high linear correlation coefficient between the DFNN-based inversion results and the realistic well logging curves of the blind wells demonstrates that the DFNN-based inversion scheme exhibits strong robustness and good generalization ability. Ultimately, we apply the proposed DFNN-based inversion strategy to a tight sandstone reservoir located at the Sichuan basin field from onshore China. Both low- and band-pass Ip and Vp∕Vs inverted for the clastic formation of the Sichuan basin show a strong correlation with the corresponding Ip and Vp∕Vs logs.

10

Influence of cutting parameters and tool edge geometries on the machinability of AlSi aisi 52100 steel in hard whirling

75%

Song S. , Zhang Y. , Cheng J. , Zhang H. , Guan X. , Zuo D. , Shen X.

Engineering Transactions

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2023

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tom Vol. 71, iss. 3

399--417

EN

The synergistic effect of prepared tool edge and cutting parameters in hard whirling is still unclear, limiting its application in producing large precision ball screws. This paper aims to reveal the effect mechanism of cutting parameters and edge geometries in the whirling process to improve the stability of ball screw quality. A novel cutting force measurement strategy is proposed, and a systematic study of cutting force, surface quality and tool wear is implemented. The results show that small feed (less than 0.15 mm) and high cutting speed (more than 180 m/min) can ensure machining efficiency and improve surface quality. The machining quality can be improved when the edge radius is 10 µm, and the chamfer size is 0.1 mm × 20◦ . The tool with a 30 µm edge radius has a low probability of early failure, but the later wear is severe and timely sharpening is recommended. This study could guide cutting parameters and edge geometry optimization to improve the stability of the quality in hard whirling.