Journal of Military Science and Technology

Study the variation of the pitching frequency of sounding rockets

2024-10-26T04:30:31+00:00

Sounding rockets typically feature an axially symmetric design and are launched vertically to facilitate research and high-altitude atmospheric data collection. Manufacturing errors can cause axial asymmetry, leading to undesirable rocket trajectory dispersion. Sounding rockets are often designed to spin around their axis to mitigate these effects. However, axial spinning motion can resonate with short-period oscillations, creating large normal loads that may damage the rocket’s structures. This paper focuses on analyzing the variations in the pitching frequency, which may help predict the roll resonance phenomenon. In this study, the authors constructed a six-degree-of-freedom dynamic model for a sounding rocket, considering all aerodynamic problems and the variation of inertial characteristics. To determine the pitching frequency, an impulse is applied to the rocket to generate short-period oscillation. The Fourier transform is then used to analyze and obtain the frequency of the rocket while oscillating in space. The results demonstrate agreement with the theoretical model, thereby substantiating the validity of the current method. The findings of this research provide valuable recommendations for the design and manufacturing process of sounding rockets, which may help mitigate the adverse effects of motion resonance during flight.

Developing an algorithm for measurement of tilt angle for the base frame of a robot that transports patients through building stairs

2024-10-26T04:32:58+00:00

This paper presents a solution and algorithm for applying the Kalman filter algorithm to combine microelectromechanical measuring tools to determine the theoretical parameters of the basic frame in the structure of a human transport robot with people with mobility problems forth through the building's stairs. These parameters are the basis for forming an algorithm to automatically control the electric motors used in the seat posture control system and the robot's moving chain mechanism.

Research on the microstructure and mechanical properties of high-entropy alloys manufactured using 3D printing technology

2024-10-26T04:31:21+00:00

In this paper, the high-entropy alloy AlMnFeCrNiCu was fabricated using 3D printing technology from a mixture of pure metal powders. The microstructure and mechanical properties of the alloy were studied on thin wall samples. The results show that the alloy has a mixed structure of two phases: face-centered cubic and body-centered cubic. Tensile strength, yield strength, and elongation are 936 MPa, 563 MPa, and 32%, respectively. The alloy obtained by the 3D printing method demonstrates outstanding mechanical properties, which are both high durability but still ensure good ductility.

Bridging communication with machine learning in sign language recognition for Vietnamese

2024-10-26T04:28:34+00:00

Vietnamese Sign Language (VSL) serves as the primary language for deaf and hard-of-hearing individuals in Vietnam. This paper explores the sign language recognition process for VSL, emphasizing the role of machine learning in bridging communication barriers. We delve into the basics of VSL, detailing the one-to-one correspondence between hand signs and Vietnamese alphabet letters and address the formation of words through sequential hand signals and diacritics placement. Furthermore, the paper highlights the importance of pausing between words and the utilization of machine learning algorithms for automated sign recognition. Lastly, we conclude by discussing the potential applications and future directions of VSL recognition technology in Vietnam.

Evaluation of the effectiveness of camouflage patterns using visual methods based on target detection time and distance surveys

2024-10-26T04:31:37+00:00

Evaluation of camouflage effectiveness is the final step in research to create a set of camouflage products, for a scientifically based evaluation of the effectiveness of a set of camouflage products. In the article, the authors present a method for evaluating camouflage effectiveness experimentally based on the visual assessment of 10 observers in 2 stages: in the laboratory and in the field, from which the most suitable patterns are selected. The results after the survey determined 01 most suitable pattern for each background, with the shortest target detection range in mountainous terrain being L = 35 m (pattern R5), with the shortest target detection range in urban terrain being L = 30 m (pattern D1). The research results will be used to develop a complete camouflage effectiveness evaluation process.

Development of advanced biopolymer thin films of Carboxymethyl cellulose, Silver, and Zinc Oxide nanoparticles for avocado fruit preservation applications

2024-10-26T04:29:40+00:00

Nanomaterials in post-harvest preservation offer advantages such as non-toxicity, chemical residue-free protection, and effective inhibition of mold and bacteria. Due to their strong antimicrobial properties and their ability to form a thin nano-coating on fruit surfaces, even small amounts of nanoparticles provide extensive coverage, preventing microbial penetration. This technology significantly improves fruit quality and longevity during storage and transportation. In this work, we introduced an advanced biopolymer film of carboxymethyl cellulose (CMC) incorporating ZnO and Ag nanoparticles (NPs). Ag NPs and ZnO NPs demonstrated an outstanding antimicrobial inhibition property that can be used for fruit preservation. As a proof of concept, the biopolymer thin films enable to extend avocado ripening from up to 35 days. The sugar concentration variation, the hardness, and the weight loss of the avocado with and without the advanced biopolymer thin film integrated ZnO and Ag nanoparticles in 35 days were compared with each other to clarify the ripening reduction ability of the biopolymer thin film.

3D measurement of surface profile using Holography technique and Fourier transform method

2024-10-26T04:29:21+00:00

Holography has an important role in the field of 3D surface measurement due to its ability to simultaneously provide intensity and phase information of the measured surface with a single image. In this article, a computational and experimental method for 3D surface reconstruction of rough samples using Holography technique is proposed. Compared with white light interferometry, the proposed method has high stability due to no micro-displacement, fast measurement speed, and surface information extracted by a single frame and axial resolution reaching nanometer level. Fourier transform combined with noise filtering techniques is used to improve the accuracy of 3D surface measurement. The rough surface Ra = 0.2943 µm is successfully constructed by the proposed method with a deviation of ± 8 nm with a coverage factor of 3 compared with the measurement on white light interferometry. This study can be applied to high-precision 3D surface measurement, optical components, and micro-electromechanical structures.

Exploring physical layer security in underwater optical wireless communication: A concise overview

2024-10-26T04:32:11+00:00

Underwater wireless optical communications are a developing alternative to meet the increasing need for high-speed connections in oceans and seas. Optical wireless communications (OWCs) are more secure and less susceptible to eavesdropping compared to acoustic communications or radio frequency (RF) communications due to their narrow optical beam coverage and reliance on line-of-sight components. Nevertheless, the existence of a hostile eavesdropper can compromise the level of confidentiality achieved by OWC networks. This article provides a concise overview of the latest research conducted on physical layer security (PLS) in underwater optical wireless communication (UOWC). Furthermore, this work presents the relevant unresolved matters, approaches for enhancing secrecy performance, and potential areas for further research.

Microwave-assisted pyrolysis of plastic waste for liquid oil production

2024-10-26T04:30:14+00:00

In this work, the article presents the results of the production of fuel oil from plastic waste using microwave-assisted pyrolysis. Under the influence of microwave power, microwave absorption material, time, catalyst, polyethylene (PE), polypropylene (PP), polystyrene (PS) and mixture (34% PE + 33% PP + 33 wt% PS) were pyrolyzed to liquid oil. The results showed that with 500 g of raw plastic, 500 W microwave power, and 120 minutes, the carbon absorber accounted for 10 wt% (compared to plastic), catalysts accounted for 20 wt%, fuel efficiency reached 84% with PS and PP, 83% with PE, and 83.5% with mixed plastics. The oil obtained qualified the standards of FO No. 1 TCVN 6239:2019. The gas chromatography/mass spectroscopy GC/MS analysis (GC-MS) showed that the composition of the pyrolysis oil is mainly hydrocarbon from C7-C12.

Comparative greenhouse gas emissions inventory in Hau Giang province: Projections to 2030 and 2050

2024-10-26T04:33:32+00:00

Greenhouse gas (GHG) emissions are the primary cause of climate change, making the calculation and projection of GHG emissions in Vietnam mandatory in the Strategic Environmental Assessment (SEA) for strategies and plans, including adjusted plans. This study, therefore, forecasts GHG emissions levels up to 2030 and 2050 following the guidelines of the Intergovernmental Panel on Climate Change (IPCC) 2019 and 1996 versions, applied to the SEA of Hau Giang province’s Master Plan. The results are compared with the updated Nationally Determined Contributions (NDC) of 2022 and the Mekong Delta Regional Plan, aiming to provide a scientific basis for climate change mitigation strategies at both local and national levels, contributing to the goal of net-zero emissions.

Activated carbon materials-derived from polyethylene terephthalate (PET) plastic waste using H3PO4 activation for Rhodamine B removal in aqueous solution

2024-10-26T04:32:26+00:00

Plastic items, which offer convenience, are ubiquitous in several manufacturing sectors and in everyday life. Polyethylene terephthalate (PET) is a highly popular synthetic plastic that is seeing a growing demand. Annually, a substantial quantity of PET plastic garbage is released into the environment. Hence, it is imperative to devise an efficient remedy for the disposal of PET plastic waste. This work employed PET waste plastic to produce activated carbon by the chemical activation method. The activating agent utilized was H₃PO₄ acid. An investigation was conducted to determine the impact of the impregnation rate of PET waste plastic with H₃PO₄, as well as the activating temperature and activating time, on the surface areas of activated carbon. The activated carbon was thoroughly analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analysis. The resulting product has a porous structure, a developed pore system, and a specific surface area of 892 m²/g, with effective adsorption capacity for RhB solutions with concentrations below 80 ppm (efficiency above 90%) in a neutral environment according to the Langmuir adsorption isothermal model, with a maximum adsorption capacity of 45.45 mg/g.

Investigation of the fabrication process of metal 3D printed powder by molten alloy dispersion method using centrifugation and high-pressure gas

2024-10-26T04:28:50+00:00

Atomization using centrifugation and high-pressure gas is considered to be a relatively new method of producing metal 3D printing powders. The metal powder made by this method is expected to obtain an adequate small-scaled size with the limitation of satellites stuck to the surface due to the reduction of the gas flow in the dispersion chamber. This work conducted experimental studies with aluminum alloy graded AlSi₁₀Mg. The manufactured metal powder was tested for corresponding technical properties of metal 3D printing powder, such as chemical composition, particle size distribution, morphological structure, etc. The investigation results have determined the influence of geometrical and technological parameters of the atomization process, including liquid metal flow, liquid metal overheating, and some structural parameters of equipment on the quantity and quality of the product.

Study on the treatment of landfill leachate using FeSO4.7H2O/NaOCl for Reactive Oxygen Species generation

2024-10-26T04:30:47+00:00

Leachate treatment is an urgent issue due to the high concentration of pollutants, which are difficult to treat using traditional technologies. Recently, reactive oxygen species (ROS) generating systems have been studied for potential applications. This paper presents the research results on the leachate treatment capability of the FeSO₄·7H₂O/NaOCl system. The study shows that the FeSO₄·7H₂O/NaOCl ROS-generating system is effective in treating leachate, reducing COD by nearly 80%, TDS by 71.2%, and changing the water color from dark black to light brown, while eliminating foul odors after 30 minutes of reaction at room temperature, pH = 6.9.

Compact form dynamic linearization CFDL and model-free adaptive control MFAC in discrete SISO system

2024-10-26T04:33:50+00:00

A class of SISO objects was dynamically linearized in compact form CFDL (Compact Form Dynamic Linearization) based on the pseudo partial derivative PPD. A newly modified model-free adaptive controller MFAC was synthesized for CFDL system via the solution of the object optimal problem. Simulation results showed the productiveness of the proposed modified algorithm.

A new algorithm for recognizing and estimating radar signal parameters

2024-10-26T04:33:15+00:00

This paper proposes a new algorithm based on image processing to recognize and estimate radar signal parameters such as carrier frequency, pulse width and modulation. The algorithm includes three steps. In the first step, banking filters are used for detecting and estimating signal carrier frequency. Time-frequency analysis is used in second step to extract signal feature. The last step is based on image processing for estimating pulse width and signal modulation. The simulated signals in MATLAB is used to evaluate performace of algorithm. Simulation results show that the proposed method is able to recognize and estimate parameter of single and multi-component signals.

Design of a high power combiner in HF band

2024-10-26T04:29:56+00:00

Power combiners are commonly used in power amplifiers to achieve high power, especially in long-range and medium-range wireless communication device transmission systems. This paper proposes designing and implementing a high-power two-way power combiner operating in the HF (High Frequency) band, aiming to achieve an output power of over 1 kW. The power combiner is designed, implemented, and tested in the laboratory with the following achieved parameters: insertion loss between output and input better than 3.4 dB and isolation between inputs better than 26 dB. The experimental results showed that the proposed power combiner had better performance than existing combiners on the market. Mainly, power combining efficiency is over 88%, the standing wave ratio at ports is less than 1.25, and the operating temperature of the power combiner is less than 50 °C, meeting the set requirements.

Design of a high-power harmonic waveguide filter for radar transmitter

2024-10-26T04:31:03+00:00

In this article, we present the research results on the designing and manufacturing method of a high-power harmonic filter applied in the X-band transmitter system. The harmonic filter utilizes Waffle-iron filters and quarter-wavelength converters on the waveguide. As a result, the loss and ripple within the passband are improved, while meeting the requirements of cutting off high-order harmonics. Based on the application of microwave theory and simulation software tools, the research team have calculated, designed and manufactured a harmonic filter that meets all the requested specifications for application in X-band transmitter systems: Loss ≤ 0,12dB@8,9-9,6GHz; Reflection coefficient ≤ -20dB@8,9-9,6GHz; Frequency selectivity ≤ -40dB@2nd harmonic, 3rd harmonic, 4th harmonic.

Synthesis of optimal power tracking Pitch angle controller for wind turbines based on Fuzzy Logic System and Dynamic Surface Control

2024-10-26T04:32:42+00:00

This paper proposes a method to enhance the performance of Wind Turbin by a Fuzzy logic system. The fussy logic system is carried out as an intelligent system in order to determine a desired Pitch angle for each value of wind speech such that the Turbin’s power is maximum. To ensure that the pitch angle can track stably the desired angle, Dynamic surface Control is developed. The control quality of closed-loop system is analysed and simulated with different scenarios.

Synthesis of controllers based on linear matrix inequalities for a magnetic levitation system

2024-10-26T04:31:54+00:00

This paper presents the results of synthesizing controllers based on Linear Matrix Inequalities (LMIs) for a magnetic levitation system with a strongly nonlinear mathematical model: integral-state feedback control and sliding mode control. Comparative simulation results and evaluations of the controllers in MATLAB/Simulink software have demonstrated that the controllers perform well and are robust to changes in the mass of the object, with the object's position closely following the setpoint signal. However, in cases where system parameters change significantly, the control system with the integral-state feedback controller may operate inaccurately or even become unstable, whereas the sliding mode controller still ensures stability and robustness against changes in system parameters

Research and development of the dynamic multi-connection wireless sensor network model

2024-10-26T04:29:05+00:00

Wireless Sensor Networks (WSNs) consist of sensors connected wirelessly to collect information from the environment and transmit data to a central processing unit. WSNs are widely applied in healthcare, industry, and automation due to their ability to provide real-time information at a low cost. This research proposes a Dynamic Multi-Connection Wireless Sensor Network (DMC WSN) model integrated with Time Division Multiple Access (TDMA) to allocate transmission time efficiently, avoid signal interference, and enhance communication performance in production environments. Simulation results indicate that, when neither TDMA nor power control is employed, both the weakest sensor capacity and the average capacity are at their lowest levels. When the Max-Min algorithm is applied for power control, capacity is improved. Conversely, when TDMA is utilized, even without power control, both the weakest sensor capacity and the average capacity reach their highest levels. This demonstrates that TDMA significantly improves communication efficiency and ensures stable capacity for the DMC WSN model in production environments.