[Invited Papers] Angular Distribution of Incident Radiation on Tubular Solar Collentor with Planar Reflector

Zhifeng Wang 한국태양에너지학회 2004 한국태양에너지학회 학술대회논문집 Vol.- No.-

H∞ CONTROL FOR BATTERY/SUPERCAPACITOR HYBRID ENERGY STORAGE SYSTEM USED IN ELECTRIC VEHICLES

Zhifeng Bai,Zengfeng Yan,Xiaolan Wu,Jun Xu,Binggang Cao 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.6

This paper proposes a control strategy of a hybrid energy storage system (HESS) based on simplified 2th-order model. The HESS uses a bidirectional DC/DC converter to connect the supercapacitors (SC) with the battery. Two control objectives, the output current of the SC during the traction procedure and the charging current of the SC while regenerative braking, are regulated by using the DC/DC converter. Two H∞ controllers are designed to control the output and charging current of the SC to their reference values, which are generated by the energy management strategy (EMS). Experimental results show that the proposed control method achieves a satisfactory performance, including a low steady-state tracking error and high response speed when the load power varies in a wide range.

Complexity of cellular manufacturing systems based on entropy models

Zhifeng Zhang 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.11

Even structurally simple manufacturing systems can be operationally complex. This operational complexity can be colloquially defined as the uncertainty associated with managing the dynamic variations, in time or quantity, across information and material flows at the manufacturing systems interface. This paper proposes a means of measuring the information demands placed on cellular manufacturing systems, as a result of this uncertainty. A utility function for complexity is proposed according to the relationships between the complexity and utility in a manufacturing system and the underlying trend that the system becomes more and more complex in an everchanging environment is analyzed. This paper mathematically models the static entropy and the dynamic entropy of cellular manufacturing systems from an information-theoretic perspective. A unique feature of this measure is that it captures, in relative terms, the expected amount of information required to describe the state of the system. The measure provides flexibility in the scope and detail of analysis. Finally, an example is used to demonstrate the validity of the proposed methodology.

Design Method of Active Disassembly Structure Triggered by Temperature-Pressure Coupling

Zhifeng Liu,Yifei Zhan,Huanbo Cheng,Xinyu Li,Shaobo Pan 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

Active disassembly products often use active disassembly structures triggered by single temperature or pressure field as reversible joints. These structures can be triggered automatically in extreme or accidental circumstances, thus causing the low reliability of products. For improving the reliability of active disassembly products, working mechanisms of active disassembly structure triggered by temperature-pressure coupling is presented in this article. Through analyzing some typical active disassembly structures, this article presents the design criteria and methods of active disassembly structure triggered by temperature-pressure coupling. The feasibility of these design methods is proved by a case analysis. The results of research shows that the reliability of active disassembly structures triggered by temperature-pressure coupling is improved greatly, which can lay the foundation for the industrial applications of active disassembly methods.

An Empirical Study on the Utilization and Performance of the Korea-China FTA in Korean SMEs

Zhifeng Shen,Tae-In Kim,Lifu Chen 한국무역학회 2019 Journal of Korea trade Vol.23 No.4

Purpose - Based on the Korea-China FTA as the starting point, this paper makes an empirical analysis of the main influencing factors of the FTA utilization and performance of SMEs. Design/methodology - Taking into account the relationship between the internal and external environmental factors on FTA activities and performance of Korea’s SMEs, with PLS-SEM and data obtained by the questionnaire, Smart PLS was applied for the analysis. Findings - The recognition of FTA in SMEs has a significant positive effect on FTA utilization and performance, the international marketing orientation factor only has a significant positive effect on the performance, while the inadequate improvement of non-tariff barriers has a significant negative impact on FTA utilization. In addition, FTA activity has a significant mediation effect on two paths. Originality/value - This paper is of great practical relevance as a tool to enable SMEs to make effective utilization of Korea-China FTA and improve their imports and exports. The paper helps grasp the main factors affecting the utilization and performance of FTA for SMEs, also to establish FTA Business Model and FTA utilization plans for specific industries in the future regarding tariff and non-tariffs compatibility.

A Discriminative Model for Age Invariant Face Recognition

Zhifeng Li,Unsang Park,Jain, A. K. IEEE 2011 IEEE transactions on information forensics and sec Vol.6 No.3

<P>Aging variation poses a serious problem to automatic face recognition systems. Most of the face recognition studies that have addressed the aging problem are focused on age estimation or aging simulation. Designing an appropriate feature representation and an effective matching framework for age invariant face recognition remains an open problem. In this paper, we propose a discriminative model to address face matching in the presence of age variation. In this framework, we first represent each face by designing a densely sampled local feature description scheme, in which scale invariant feature transform (SIFT) and multi-scale local binary patterns (MLBP) serve as the local descriptors. By densely sampling the two kinds of local descriptors from the entire facial image, sufficient discriminatory information, including the distribution of the edge direction in the face image (that is expected to be age invariant) can be extracted for further analysis. Since both SIFT-based local features and MLBP-based local features span a high-dimensional feature space, to avoid the overfitting problem, we develop an algorithm, called multi-feature discriminant analysis (MFDA) to process these two local feature spaces in a unified framework. The MFDA is an extension and improvement of the LDA using multiple features combined with two different random sampling methods in feature and sample space. By random sampling the training set as well as the feature space, multiple LDA-based classifiers are constructed and then combined to generate a robust decision via a fusion rule. Experimental results show that our approach outperforms a state-of-the-art commercial face recognition engine on two public domain face aging data sets: MORPH and FG-NET. We also compare the performance of the proposed discriminative model with a generative aging model. A fusion of discriminative and generative models further improves the face matching accuracy in the presence of aging.</P>

Bolt looseness detection and localization using time reversal signal and neural network techniques

Zhifeng Tang,Yuan-Feng Duan,Xiaodong Sui,Chung Bang Yun 국제구조공학회 2022 Smart Structures and Systems, An International Jou Vol.30 No.4

It is essential to monitor the working conditions of bolt-connected joints, which are widely used in various kinds of steel structures. The looseness of bolts may directly affect the stability and safety of the entire structure. In this study, a guided wave-based method for bolt looseness detection and localization is presented for a joint structure with multiple bolts. SH waves generated and received by a small number (two pairs) of magnetostrictive transducers were used. The bolt looseness index was proposed based on the changes in the reconstructed responses excited by the time reversal signals of the measured unit impulse responses. The damage locations and local damage severities were estimated using the damage indices from several wave propagation paths. The back propagation neural network (BPNN) technique was employed to identify the local damages. Numerical and experimental studies were conducted on a lap joint with eight bolts. The results show that the total damage severity can be successfully detected under the effect of external force and measurement noise. The local damage severity can be estimated reasonably for the experimental data using the BPNN constructed by the training patterns generated from the finite element simulations.

H2 Metabolism revealed by metagenomic analysis of subglacial sediment from East Antarctica

Zhifeng Yang,Yu Zhang,Yongxin Lv,Wenkai Yan,Xiang Xiao,Bo Sun,Hongmei Ma 한국미생물학회 2019 The journal of microbiology Vol.57 No.12

Subglacial ecosystems harbor diverse chemoautotrophic microbial communities in areas with limited organic carbon, and lithological H2 produced during glacial erosion has been considered an important energy source in these ecosystems. To verify the H2-utilizing potential there and to identify the related energy-converting metabolic mechanisms of these communities, we performed metagenomic analysis on subglacial sediment samples from East Antarctica with and without H2 supplementation. Genes coding for several [NiFe]- hydrogenases were identified in raw sediment and were enriched after H2 incubation. All genes in the dissimilatory nitrate reduction and denitrification pathways were detected in the subglacial community, and the genes coding for these pathways became enriched after H2 was supplied. Similarly, genes transcribing key enzymes in the Calvin cycle were detected in raw sediment and were also enriched. Moreover, key genes involved in H2 oxidization, nitrate reduction, oxidative phosphorylation, and the Calvin cycle were identified within one metagenome-assembled genome belonging to a Polaromonas sp. As suggested by our results, the microbial community in the subglacial environment we investigated consisted of chemoautotrophic populations supported by H2 oxidation. These results further confirm the importance of H2 in the cryosphere.

Study on modified differential transform method for free vibration analysis of uniform Euler-Bernoulli beam

Zhifeng Liu,Yunyao Yin,Feng Wang,Yongsheng Zhao,Ligang Cai 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.5

A simulation method called modified differential transform is studied to solve the free vibration problems of uniform Euler-Bernoulli beam. First of all, the modified differential transform method is derived. Secondly, the modified differential transformation is applied to uniform Euler-Bernoulli beam freefree vibration. And then a set of differential equations are established. Through algebraic operations on these equations, we can get any natural frequency and normalized mode shape. Thirdly, the FEM is applied to obtain the numerical solutions. Finally, mode experimental method (MEM) is conducted to obtain experimental data for analysis by signal processing with LMS Test.lab Vibration testing and analysis system. Experimental data and simulation results are illustrated to be in comparison with the analytical solutions. The results show that the modified differential transform method can achieve good results in predicting the solution of such problems.

Timoshenko beam-based stability and natural frequency analysis for heavy load mechanical spindles

Zhifeng Liu,Shiming Ma,Ligang Cai,Tieneng Guo,Yongsheng Zhao 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11

The heavy load mechanical spindle is an important functional component in a 5-axis computer numerical control (CNC) machine tool,which is used to process large and complex free-form surfaces. It is necessary to obtain the natural frequency and analyze the spindle stability for improving the machining precision. In this paper, Timoshenko beam theory is introduced to model the mechanical spindle shaft, where the centrifugal force and gyroscopic effects are considered. Stability of the heavy load mechanical spindle shaft is analyzed,and the buckling load of the spindle shaft is obtained under different rotational speeds. The natural frequency of spindle is investigated in a freedom and restraint state, respectively. Comparing the proposed method with the simplified hollow cylinder and shaft prototype in the freedom state, the results show that they are highly correlated with experimental results. For the restraint state, the axial load, rotational speed, gyroscopic effect, and centrifugal force are discussed, and all of these parameters affect the natural frequency. The proposed modeling approach can be used for spindle design and optimization in a given machining process and can be easily extended to other spindle design.