A NUMERICAL ALGORITHM FOR SINGULAR MULTI-POINT BVPS USING THE REPRODUCING KERNEL METHOD

Yuntao Jia,Yingzhen Lin 한국수학교육학회 2014 純粹 및 應用數學 Vol.21 No.1

In this paper, we construct a complex reproducing kernel space for sin-gular multi-point BVPs, and skillfully obtain reproducing kernel expressions. Then,we transform the problem into an equivalent operator equation, and give a numeri-cal algorithm to provide the approximate solution. The uniform convergence of thisalgorithm is proved, and complexity analysis is done. Lastly, we show the validityand feasibility of the numerical algorithm by two numerical examples.

Air rudder mechanism dynamics considering two elements: Joint clearance and link flexibility

Yuntao Li,Qiquan Quan,He Li,Dewei Tang,Zhonghong Li,Wenyang Fan,Zongquan Deng 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

Both the impact phenomenon in the clearance revolute joint and the link deformation will influence the dynamics of the air rudder transmission mechanism, which could reduce the flight quality of an aircraft. Given the effect of the two elements, a feasible simulation method with two improvements of previous methods is proposed to analyze the dynamic characteristics of the mechanism. In previous studies, the parameters of the contact force model in multi-body dynamics software were generally determined by experience, which may cause uncertainty in the calculation precision of the contact force. Furthermore, it is difficult to solve for the elastic link deformation in the practical mechanism using the available analytical methods due to the complicated section of the link. In this paper, a Continuous contact force (CCF) model was proposed and embedded in the ADAMS by developing a routine of the CCF model. Then, the flexible model was obtained by ANSYS to obtain the elastic link deformation. The experimental results indicate that the proposed simulation method can be effectively applied to predict the dynamic behavior of the mechanism.

Exponential Stability for Neutral Stochastic Differential Delay Equations with Markovian Switching and Nonlinear Impulsive Effects

Yuntao Qiu,Huabin Chen 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.2

In this paper, the problems on the exponential stability in p-th (p ≥ 2)-moment and the almost sure exponential stability for neutral stochastic differential delay equation with Markovian switching and impulses are analyzed. By establishing an impulsive delay integral inequality, the Lyapunov theorem on the exponential stability in p-th (p ≥ 2)-moment is given. Then, by using the Borel-Cantelli lemma, the almost sure exponential stability theorem is also proved. Two major advantages of these two results are that the differentiability or continuity of the delay function is not required, and that while considering the concerned problem, the difficulty coming from the simultaneous presence of the neutral item, the impulsive disturbance and the stochastic perturbations is overcome. An example is provided to examine the effectiveness and potential of the theoretic results obtained.

Natural Deep Eutectic Solvents as a New Extraction Media for Phenolic Metabolites in Carthamus tinctorius L.

Dai, Yuntao,Witkamp, Geert-Jan,Verpoorte, Robert,Choi, Young Hae American Chemical Society 2013 ANALYTICAL CHEMISTRY - Vol.85 No.13

<P>Developing green solvents with low toxicity and cost is an important issue for the biochemical industry. Synthetic ionic liquids and deep eutectic solvents have received considerable attention due to their negligible volatility at room temperature, high solubilization ability, and tunable selectivity. However, the potential toxicity of the synthetic ionic liquids and the solid state at room temperature of most deep eutectic solvents hamper their application as extraction solvents. In this study, a wide range of recently discovered natural ionic liquids and deep eutectic solvents (NADES) composed of natural compounds were investigated for the extraction of phenolic compounds of diverse polarity. Safflower was selected as a case study because its aromatic pigments cover a wide range of polarities. Many advantageous features of NADES (such as their sustainability, biodegradability combined with acceptable pharmaceutical toxicity profiles, and their high solubilization power of both polar and nonpolar compounds) suggest their potential as green solvents for extraction. Experiments with different NADES and multivariate data analysis demonstrated that the extractability of both polar and less polar metabolites was greater with NADES than conventional solvents. The water content in NADES proved to have the biggest effect on the yield of phenolic compounds. Most major phenolic compounds were recovered from NADES with a yield between 75% and 97%. This study reveals the potential of NADES for applications involving the extraction of bioactive compounds from natural sources.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2013/ancham.2013.85.issue-13/ac400432p/production/images/medium/ac-2013-00432p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac400432p'>ACS Electronic Supporting Info</A></P>

A Novel Hybrid Clamped Three-level Converter

Yue Yuntao,Qiu Kekun,Lin Yan 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.6

A novel hybrid clamped dual-PWM three-level converter topology is proposed for induction motor drives in this paper. The switching states of hybrid clamp three-level converters increase to sixty-four from twenty-seven switching states of diode clamp three-level converters. In order to realize optimization of its redundant voltage space vectors by detecting voltage of clamp capacitor and difference of capacitor voltage in DC side, Generating an optimized switching pattern, The hybrid clamped three-level converter increases the voltage levels number, reducing the harmonics associated to the commutation frequency and limiting the dv/dt by all the switches . It can quickly balance the DC voltage, Realized system of 4-Quardant Running. the control circuit and main circuit was designed with DSP and CPLD, experimentation results proved it is very effective and practicability.

An Intelligent Fault Diagnosis Method for Imbalanced Nuclear Power Plant Data Based on Generative Adversarial Networks

Dai Yuntao,Peng Lizhang,Juan Zhaobo,Liang Yuan,Shen Jihong,Wang Shujuan,Tan Sichao,Yu Hongyan,Sun Mingze 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.4

In the fault diagnosis problem, where sample data of fault cases are imbalanced, data generation and expansion are performed based on a generative adversarial network to obtain balanced data for training. Combining a gated recurrent neural network and an autoencoder model, the GRU-BEGAN model for generating multiple time series data is proposed for the intelligent fault diagnosis of imbalanced nuclear power plant data. To guarantee the consistency of the probability distribution between the generated data and real data, the K-L losses are included as a part of the loss function of the generator. At the same time, the potential feature vector of the real data obtained by the discriminator encoder is introduced as a hidden variable in the generator, and the similarity between the generated data and the real data is controlled by introducing the hidden variables according to the probability to make the generated data diverse. For the imbalanced fault dataset of the nuclear power plant thermal–hydraulic systems, the proposed GRU-BEGAN model is used to expand the original data to obtain a balanced state. Then, a 1D-CNN fault diagnosis model is established based on a convolutional neural network. The experimental results show that the fault diagnosis accuracy of the total test data is improved by 1.45% after data expansion, and the fault diagnosis accuracy of the minority sample is improved by 6.8% after data expansion.

Comprehensive review on physical properties of supercritical carbon dioxide calculated by molecular simulation

Gaoliang Liao,Yuntao Du,Feng Zhang,Jiaqiang E 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.1

The applications of molecular simulation in supercritical carbon dioxide (S-CO2) and its mixtures are reviewed. First, an overview of physical properties of S-CO2 and CO2 models is given. Secondly, the accuracy of S-CO2 thermodynamic and transport properties calculated by different models is compared. It shows that Zhang’s model has relatively better global accuracy in calculating thermodynamic properties. EPM2, Zhang and Cygan models have similar accuracy when calculating transport properties based on equilibrium molecular simulation (EMD) method, but generally have higher deviations when calculating thermal conductivity. Therefore, EMD and non-equilibrium molecular simulation (NEMD) methods have been compared in calculating thermal conductivity. The results show that NEMD is better than EMD but the process is complicated. The structural properties are also discussed in this part. Thirdly, the applications of molecular simulation in S-CO2 binary organic, binary inorganic and multiple mixtures are reviewed. Finally, the summary and the prospect of future works are given.

A Method for Generating Malware Countermeasure Samples Based on Pixel Attention Mechanism

Xiangyu Ma,Yuntao Zhao,Yongxin Feng,Yutao Hu 한국인터넷정보학회 2024 KSII Transactions on Internet and Information Syst Vol.18 No.2

Studies have shown that malware has become a primary means of attacking the Internet. Therefore, adversarial samples have become a vital breakthrough point for studying malware. By studying adversarial samples, we can gain insights into the behavior and characteristics of malware, evaluate the performance of existing detectors in the face of deceptive samples, and help to discover vulnerabilities and improve detection methods for better performance. However, existing adversarial sample generation methods still need help regarding escape effectiveness and mobility. For instance, researchers have attempted to incorporate perturbation methods like Fast Gradient Sign Method (FGSM), Projected Gradient Descent (PGD), and others into adversarial samples to obfuscate detectors. However, these methods are only effective in specific environments and yield limited evasion effectiveness. To solve the above problems, this paper proposes a malware adversarial sample generation method (PixGAN) based on the pixel attention mechanism, which aims to improve adversarial samples' escape effect and mobility. The method transforms malware into grey-scale images and introduces the pixel attention mechanism in the Deep Convolution Generative Adversarial Networks (DCGAN) model to weigh the critical pixels in the grey-scale map, which improves the modeling ability of the generator and discriminator, thus enhancing the escape effect and mobility of the adversarial samples. The escape rate (ASR) is used as an evaluation index of the quality of the adversarial samples. The experimental results show that the adversarial samples generated by PixGAN achieve escape rates of 97%, 94%, 35%, 39%, and 43% on the Random Forest (RF), Support Vector Machine (SVM), Convolutional Neural Network (CNN), Convolutional Neural Network and Recurrent Neural Network (CNN_RNN), and Convolutional Neural Network and Long Short Term Memory (CNN_LSTM) algorithmic detectors, respectively.

Numerical Simulation of the Influence of Tip Clearance on the Performance of Centrifugal Cold Compressor

Maofei Geng,Yuntao Song,Anyi Cheng,Hansheng Feng 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.1

To improve the efficiency of the Experimental Advanced Superconducting Tokamak (EAST) subcooled helium cryogenic system, a centrifugal cold compressor (CC) was investigated as an alternative to the oil ring pump. A numerical simulation method was applied to analyse variations in CC performance parameters, pressure ratio and polytropic efficiency. Results indicated that the performance curve of the CC and warm compressor (WC) were similar. The tip clearance at the design point was 0.2 mm and increased to 0.231 mm when the CC was operated at 4 K. This increase in tip clearance resulted in a 0.86% drop in the pressure ratio and a 0.54% drop in polytropic efficiency. To verify the simulation model, experiments were done using cold nitrogen.

Flexural Durability and Chloride Diffusion Equation of TRC-Strengthened Beams under a Chloride Environment

Shiping Yin,Yuntao Hua,Yulin Yu 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.6

In this study, the chloride ion diffusion and structural performance of beams reinforced with textile-reinforced concrete (TRC) were evaluated. The parameters investigated were chloride concentration, sustained load and number of textile layers. The results demonstrate that the content and diffusion coefficient of chloride increased with increasing chloride concentration. Higher chloride concentrations accelerated the crack propagation and deflection changes and caused the reduction of the load-carrying capacity of the beams. The sustained load promoted the chloride transport of the TRC, increasing the chloride ion content and diffusion coefficient and causing substantial damage to the microstructure of the TRC. In addition, the performance (such as cracking resistance, deflection and flexural capacity) of beams with a large sustained load ratio decreased to a less extent than did the performance of the unloaded beams. The content and diffusion coefficient of chloride in the unstrengthened beams were obviously larger than those in the strengthened beams, but increasing the textile layers number had little influence on these factors. In addition, for the unstrengthened beams, the cracks and deflections developed rapidly, and the load decreased greatly, especially the cracking load. Finally, in accordance with Fick’s second law of diffusion, a chloride diffusion equation in TRC layers under new boundary conditions was proposed.