Journal of Science and Technique
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NGHIÊN CỨU ẢNH HƯỞNG CỦA MỘT SỐ THÔNG SỐ CÔNG NGHỆ ĐẾN KÍCH THƯỚC “TAI” KHI DẬP VUỐT LẦN ĐẦU CHI TIẾT HÌNH TRỤ TỪ VẬT LIỆU DỊ HƯỚNG SUS-304 BẰNG MÔ PHỎNG SỐ
Get PDFDị hướng là tính chất cố hữu của vật liệu tấm, đặc biệt là các loại tấm cán nguội. Khi dập vuốt chi tiết dạng hình trụ, các loại tấm này luôn xuất hiện “tai” trên miệng chi tiết, nghĩa là chiều cao chi tiết không đều theo các hướng khác nhau so với hướng cán. Dự đoán chính xác sự hình thành “tai” khi dập vuốt có ý nghĩa quan trọng đối với thiết kế công nghệ chế tạo các chi tiết dạng trụ. Bài báo này nghiên cứu ảnh hưởng của các thông số công nghệ bao gồm khe hở dập vuốt, hệ số ma sát tiếp xúc và lực ép biên đến kích thước “tai” khi dập vuốt chi tiết dạng trụ từ vật liệu dị hướng SUS-304. Phương pháp quy hoạch Taguchi được sử dụng trong đó mô hình vật liệu được xây dựng trên cơ sở các thí nghiệm thử kéo mẫu vật liệu thực. Kết quả cho thấy lực ép biên có ảnh hưởng lớn nhất đến chiều cao “tai” lớn nhất (48,53%), tiếp đó đến hệ số ma sát tiếp xúc (38,71%) và khe hở dụng cụ (12,76%)
WILDFIRE RISKS IN THE SOUTHWEST OF KY SON DISTRICT, NGHE AN PROVINCE – A MULTI-CRITICAL MODEL
Get PDFWildfires are considered one of the most common hazards in mountainous areas, posing a serious threat to flora, fauna, and humans. This article focuses on building a forest fire risk map based on GIS techniques in the southwest area of Ky Son district, Nghe An province. The selected factors to create the forest fire risk map include 9 indices: NDDI drought index, surface temperature, slope, elevation, distance to roads, distance to rivers and streams, distance to upland fields, distance to residential areas, and aspect. The results of determining the weights of these factors using the AHP hierarchical analysis technique show that drought and surface temperature are the two factors that have the greatest influence on the forest fire risk index. The limit values that lead to forest fire risks for the drought criterion are 0.2 - 0.4 mm and for the surface temperature criterion are 25 - 30°C. The area with high fire risk accounts for the largest proportion, 38%, covering an area of 24,519.78 ha, followed by the average fire risk with 21,012.48 ha, accounting for 33% of the entire study area. The area with extremely high fire risk occupies the smallest area, 1,283.76 ha (2%). While controlling wildfires is challenging, forest fire risk maps can detect areas with higher risk and mitigate them. Therefore, creating forest fire risk maps for the identified areas is necessary
USING A DISCRETE EVENT SIMULATION TOOL TO PREDICT THE SPEED OF SMALL CROSS SECTION TUNNELING BY DRILLING AND BLASTING METHOD
Get PDFCompared to medium- and large-sized underground tunnels, construction of small cross section tunnels has different conditions: in terms of construction organization space, vehicles and workers especially transportation in narrow roads thatonly one vehicle is allowed to pass. This article studies the small cross section tunneling construction in rocks with different coefficients of consolidation (fkp) and predicts the tunneling construction speed for the narrow segment by using EZStrobe software to simulate. The results are compared with the baseline model in case without narrow segmentation, and also indicate a reasonable number of transport vehicles should be used
FABRICATION OF PORTABLE TRIBOELECTRIC NANOGENERATOR BASED ON NATURAL LEAVES
Get PDFRecently, green triboelectric nanogenerators (TENG) have emerged as an alternative adequate power supply to solid-state chemical batteries to overcome certain drawbacks, including toxic materials, limited lifetime, or recharged requirement. In this paper, we demonstrated the fabrication of the natural and common leaf-based triboelectric nanogenerator (NF-TENG), which uses jackfruit, banana, and bamboo leaves as positive triboelectric layers. Among some fabricated NF-TENGs, the bamboo leaf-based TENG presents novel output characteristics, including the maximum output power density of 7 mW.m−2, the short-circuit current of 6 μA under the excitation power and the frequency supplied to the mechanical oscillator of 33.6 mW and 30 Hz. This NF-TENG can light up 18 green commercial LEDs simultaneously, which promises to be a novel solution for powering low-power electronic devices using different vibration energy sources
ACTIVATION OF PEROXYMONOSULFATE BY CuCoFe LAYERED DOUBLE HYDROXIDE FOR THE DECOMPOSITION OF LEVOFLOXACIN
Get PDFIn this study, we synthesized CuCoFe-LDH bilayer hydroxide catalysts in different Cu:Co:Fe ratios (1:1:1; 1:2:1, and 1:3:2) by hydrothermal method and applied them to activate PMS for decomposing levofloxacin. The obtained LDH samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results showed that CuCoFe-LDH (1:3:2) has the strongest ability to activate PMS and degrade levofloxacin. After 10 minutes of reaction (catalyst content of 200 mg/L, PMS concentration of 1.629 mM, pH 7, at 30 oC), the decomposition efficiency was 64.89, 83.93, and 92.58% for LDH with ratios of 1:1:1, 1:2:1, and 1:3:2, respectively. The influence of PMS concentration and reaction temperature on levofloxacin degradation was investigated. PMS at high concentrations was beneficial for the formation of active oxygen species. The degradation rate of levofloxacin was affected by temperature and the activation energy was 34.04 kJ/mol
IMPROVED PROCEDURE FOR SPECTRAL ACCELERATION MATCHING IN DIFFERENT EARTHQUAKE SCENARIOS
Get PDFThe distinctive characteristics of near-field and far-field earthquake records have a critical influence on the seismic response of the structure, especially the frequency content and energy content. This study aimed at improving the ground motion linear scaling method, regarding the effect of near-field and far-field, for precise spectral matching between the response spectrum of real accelerations and the target elastic spectrum of TCVN 9386:2012. The common calibration methods are firstly presented and compared to evaluate the effectiveness of each one. The improvement of the Atkinson (ATK) linear scaling method by dividing the period range of interest is proposed and detailed by an application example. The results show that the proposed method is effective in matching the real ground motion to the target elastic spectrum
SIMULATION OF DISCRETE GUST ACCORDING TO AIRSHIP SAFETY STANDARDS
Get PDFOne of the factors that greatly affects the flight safety of airships is weather conditions and in particular, discrete gust with a speed equivalent to the speed of the airship. This article presented a method of numerical simulation of discrete gust according to flight safety standards. The discrete gust is considered from the bottom up with velocity in two forms: rectangular velocity distribution and variable velocity as a function of cosin. Research shows that in order for the velocity distribution to be most similar to the flight safety standards, it is recommended to choose a calculated area of size 25L × 10L × 2.5L. This simulation method can be used to study other discrete gust according to flight safety standards in the actual operation of airships
TUNING HYPERPARAMETERS OF SELF-ORGANIZING MAPS IN COMBINATION WITH K-NEAREST NEIGHBORS FOR IOT MALWARE DETECTION
Get PDFIn the Internet of Things, sensor devices often generate massive sensory data across multiple domains and applications. Identifying IoT malware from a huge amount of such IoT data is often a challenging task. In our previous studies, analytic techniques were applied to reduce dimensionality and discover valuable information from the original data. Particularly, the Self-organizing Maps (SOM)-based classifier with an AutoEncoder is used to create an end-to-end IoT malware detection model. However, the SOM-based classifier has a constraint that new instances may be incorrectly classified if they are mapped into unlabelled neurons in the SOM map. To address this issue, in this study, a novel hybrid between SOM-based classifier and well-known classification algorithms like K-Nearest Neighbors, Support Vector Machine, Softmax, Random Forest. In this hybrid, classification methods will help to correctly assign labels for instances mapped into the unlabeled neurons. In addition, this article investigates hyperparameter optimization methods for optimizing SOM hyperparameters. Our proposed methods were tested on the NBaIoT dataset with various experimental settings. Experimental results illustrate that SOMKNN often performs better than stand-alone techniques, including the SOM classifier
ĐÁNH GIÁ CHẤT LƯỢNG BỘ ĐIỀU KHIỂN TRƯỢT BẬC 2 BỘ CHUYỂN ĐỔI ZETA
Get PDFBộ chuyển đổi Zeta được sử dụng tiêu biểu trong máy tính, xe điện, đèn LED, lưới điện siêu nhỏ và lưới điện thông minh. Điện áp ngõ ra được đo từ ngõ ra mạch hở của bộ chuyển đổi. Để sử dụng hiệu quả bộ chuyển đổi này, điện áp ngõ ra của nó cần phải được điều khiển. Nghiên cứu này thiết kế và đánh giá chất lượng bộ điều khiển trượt bậc 2 (SOSMC) để điều khiển bám điện áp bộ chuyển đổi Zeta dựa vào sự thay đổi của chu kỳ làm việc. Bằng cách chọn hàm Lyapunov phù hợp, tính ổn định của bộ điều khiển được chứng minh. Kết quả mô phỏng với Matlab/Simulink cho thấy hiệu quả của giải thuật đề xuất với sai số bám tiến về 0, độ vọt lố là 0,0102 %, thời gian xác lập khoảng 0,0256 s và thời gian tăng đạt 0,0146 s. Ngoài ra, các hiệu suất sai số ADD, MSE, RMSE, MPE, MAPE và MRE cũng được sử dụng để đánh giá chất lượng của bộ điều khiển đề xuất
NONLINEAR STABILITY CONTROL OF INVERTED PENDULUM ON A CART USING LQR-BASED T-S FUZZY CONTROL
Get PDFThe inverted pendulum on a cart is a challenging and widely studied control problem in the fields of control systems and robotics. To address the need for more effective control strategies, this article presents a novel approach that combines the strengths of two powerful control techniques: Linear-Quadratic Regulator (LQR) and Takagi-Sugeno (T-S) fuzzy control. LQR control is well-established for stabilizing linear systems, but it faces limitations with nonlinear systems like the inverted pendulum. On the other hand, T-S fuzzy control excels in handling nonlinearities by approximating the system's behavior with local linear models. Our proposed approach leverages T-S fuzzy systems to approximate complex nonlinearities, while using LQR control for each local linear subsystem. The combined method's efficacy is substantiated by simulation results, specifically considering criteria such as stability under disturbance conditions, variations in the initial angle of the pendulum, and a comparative analysis between stability-only scenarios and those involving both swing-up and stability control