Tạp chí Kỹ thuật và Công nghệ Đại học Quốc gia Thành phố Hồ Chí Minh

The paper proposes a control system for bicycle robot based on a passivity-based method. Bicycle robot is a nonlinear, MIMO (multi input - multi output) system. The first input of bicycle robot is the steering torque and and the second input has a relation with the kinetic energy. Its two outputs are the velocity of the steering angle and the velocity of the rolling angle . Bicycle robot is shown to be a passivity system. Consider a control problem which the steering angle tracks a value of zero and the rolling angle tracks a value of zero in order that bicycle robot keeps its vertical balance. We use a new control signal so that the system is passivity with input và output y= , which are the velocity of the steering angle and the velocity of the rolling angle . Stabilization of the equilibrium point at origin uses a PI (proportional integral) passivity-based control. Simulation results are done with Simulink in MATLAB and have good results such as short settling time and small percentage of overshoot. The error of the steering angle comes to 0.01 after two seconds and the error of the rolling angle comes to 0.01 after two seconds. Stability analyses using the passivity theory show that the equilibrium point at origin is asymptotically stable in the case of PI passivity-based control because the system has a positive definite storage function Vb and the derivative of Vb is semi-negative definite and the system is zero-state observable.

In the MPM algorithm, all the particles are formulated in a single-valued velocity field hence the non-slip contact can be satisfied without any contact treatment. However, in some impact and penetration problems, the non-slip contact condition is not appropriate and may even yield unreasonable results, so it is important to overcome this drawback by using a contact algorithm in the MPM. In this paper, the variation of contact force with respect to time caused by the impact is investigated. The MPM using the Lagrange basis function, so causing the cell-crossing phenomenon when a particle moves from one cell to another. The essence of this phenomenon is due to the discontinuity of the gradient of the linear basis function. The accuracy of the results is therefore also affected. The high order B-spline MPM is used in this study to overcome the cell-crossing error. The BSMPM uses higher-order B-spline functions to make sure the derivatives of the shape functions are continuous, so that alleviate the error. The algorithm of MPM and BSMPM has some differences in defining the computational grid. Hence, the original contact algorithm in MPM needs to be modified to be suitable in order to use in the BSMPM. The purpose of this study is to construct a suitable contact algorithm for BSMPM and then use it to investigate the contact force caused by impact. Some numerical examples are presented in this paper, the impact of two circular elastic disks and the impact of a soft circular disk into a stiffer rectangular block. All the results of contact force obtained from this study are compared with finite element results and perform a good agreement, the energy conservation is also considered.

Traceability not only meets the social needs of product information transparency and reinforces the trust of consumers, but also meets the needs of enterprises for brand protection and enhances the competition in markets. Since a traceability system collects every necessary information at every stage in a supply chain, it is also an efficient tool for monitoring and optimizing the production procedure. Adopting information technology to digitalize the business process is an inevitable trend to improve the efficiency in information management and especially quickly detect fraud problems. However, with the digitized process via a computer software system, the challenge remains as to whether digitized data is real. The reality shows that changing digital data is easier than paper-based data. Thus, it is necessary to have a digitalized process and a secure mechanism for ensuring transparency, correctness, and consistency of data leading to more efficiency in incidents detection and trace problems tracing. An emerging technology, Blockchain, has attracted more attention after its great success in finance due to various dominant features in preventing data changes even from the internal system. Technically, Blockchain is a ledger that records the entire transaction history publicly on a network of peer-to-peer computers of the time. One common ledger will be shared among all collaborative organizations in an ecosystem to ensure data immutability and undeniable responsibility, thereby enhancing data transparency. Therefore, applying Blockchain technology in agriculture will improve the current traceability process, aiming to increase the responsibility of the objects in the process and transparency of information for consumers. In this paper, we propose a framework that utilizes Blockchain to robustize traceability systems. Additionally, our proposed framework is compliant with the GS1 standard to achieve high reliability and compatibility on a global scale.

The bootstrap is one of the method of studying statistical math which this article uses it but is a major tool for studying and evaluating the values of parameters in probability distribution. Overview of the theory of infinite distribution functions. The tool to deal with the problems raised in the paper is the mathematical methods of random analysis by theory of random process and multivariate statistics. Observations (realisations of a stationary process) are not independent, but dependence in time series is relatively simple example of dependent data. Through a simulation study we found that the pseudo data generated from the bootstrap method always showed a weaker dependence among the observations than the time series they were sampled from, hence we can draw the conclusion that even by re-sampling blocks instead of single observations we will lose some of structural from of the original sample. A potential difficulty by the using of likelihood methods for the GEV concerns the regularity conditions that are required for the usual asymptotic properties associated with the maximum likelihood estimator to be valid. To estimate the value of a parameter in GEV we can use classical methods of mathematical statistics such as the maximum likelihood method or the least squares method, but they all require a certain number samples for verification. For the bootstrap method, this is obviously not needed; here we use the limit theorems of probability theory and multivariate statistics to solve the problem even if there is only one sample data. That is the important practical significance that our paper wants to convey. In predictive analysis problems, in case the actual data is incomplete, not long enough, we can use bootstrap to add data.

Lean manufacturing technology has been applied in industry to eliminate wastes, enhance efficiency and increase competition ability. While some case studies were evaluated successfully, others faced with big challenges. Actually, lean was applied in different ways due to types and size of industry or organization. This paper would present an lean implementation process, in which lean tools are integrated in simultaneously. Requirements on system manufacturing capacity should be met, so necessary resources would be determined. Manufacturing layout and work flows would be created smoothly. The lean implementation process was applied in some case studies in garment industry with small and medium size, which show the efficiency and effectiveness of the lean technology in the practice systems. The research shows the good results on some performance key indexes such as productivity, ability to satisfy the orders and good working environment.

This paper applies isogeometric analysis (IGA) to simulate active control of the functionally graded material (FGM) plates by using piezoelectric material patches. This control helps to reduce the deflection of the plate under the effect of static load, which makes the structure more resistant to loading. IGA is built on the non-uniform rational basis spline (NURBS) basic function with many advantages such as: describing geometry exactly by approximating by higher order function and directly using this function to approach procedure. Furthermore, NURBS geometry has mesh flexibility and high continuity between elements, making the problem highly accurate. Three-dimensional model for plate-like structure consists of upper and lower layers made of piezoelectric materials, the middle layer is FGM. The obtained results will be verified with the published results to prove the efficiency of the proposed method for this problem. Through the obtained results, it is shown that IGA is used effectively for the active control problem by piezoelectric patches to reduce the displacement of FGM plates. The efficiency shown when using a small number of degrees of freedom but still ensuring the solution has accurate results when compared with the reference solution.

This research paper applies the blade element momentum theory on a horizontal axis wind turbine to study a 2-stage wind turbine with an independent rotating shaft, a type of small-scale wind turbine that has never been studied. The article also includes the Prandtl loss in the theory of the blade element momentum method to calculate the wind turbine so that the calculated power and efficiency are close to the actual efficiency instead of the consideration of ideal conditions. These theories have been around for a long time, but their applicability is still very high besides the use of modern computational tools such as computational fluid dynamics. Calculation results in the study are achieved by applying basic theories, then comparing with simulation results from Qblade software, a software that is commonly used in studies to calculate small and large-scale horizontal axis wind turbines and gives an error of less than 10%. This method is to ensure the objectivity and authenticity of the article. The proposed method in this study can be used to calculate various blade profiles of wind turbines. The paper aims to use the CL/CD ratio corresponding to a certain angle of attack as a specific case to optimize the calculation process, giving the problem can be automated.

Domestic hand sanitizers have been evaluated for their antibacterial activity according to Decision 120/2000/QĐ-BYT. However, the antibacterial ability was assessed with 10 minutes of the contact time, inconsistent with international standards and much longer than the actual hand washing time. Therefore, this study aims to test the antibacterial ability of dry hand sanitizer with some parameters, such as a list of tested bacteria, and at the same time, evaluate the antibacterial activity of some products being commercially available on the market. The results showed that the bacteria to evaluate the antibacterial activity selected were Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Serratia marcescens ATCC 14756. The exposure time between the reagent and bacteria was 20 - 30 seconds, and the initial bacterial density was approximately 108 CFU/ml. Ten hand sanitizers can reduce the number of bacteria by more than 3 log10. In conclusion, the study has helped improve the current evaluation process of hand sanitizer products according to Decision 120/2000/QD-BYT.

Based on the analysis and interpretation of drilling and petrophysics documents, the paper evaluates the hydrocarbon potential of the Oligocene sandstone set at field X. The paper presents some methods of gas classification based on gas chromatographic indicators and the hydrocarbon content in the drilling fluid. Besides, the paper also developed a process to analyze the fluid composition in the formation based on the Wh-Bh-Ch indexes on the gas peaks in the mud logging. The interpreted results from 8 gas peaks in the X-S16P well through the Oligocene sedimentary set identified potential oil and gas zones of field X, as well as the distribution of reservoir fluid. By comparing the results of well logging from GR, density, resistivity curves and the analysis of DST, it corrects the O&G behaviors at field X. The DST’s results of X-S16P well at X field in a depth interval of 2,827- 2,887m throughout the interlaced sandstone set indicate an oil flow rate of 8,826 barrels/day, which is coincident with the results of O&G behavior in mud logging; therefore, it’s concluded that the integration of mud logging with other petrophysical documents allows increasing the reliability of O&G potential evaluation. Furthermore, analyzing and evaluating different indicators to determine the gas composition throughout the drilling process is considered a quick way to predict and classify the products.

In recent years, the field of structural health monitoring (SHM) has been receiving the attention of many researchers. In particular, vibration-based structural damage detection methods have proven to be highly effective in civil engineering, mechanical engineering, aerospace engineering, … This paper presents a two-step procedure for damage detection in steel plane frame structures. In the first step, the damage locations in the frame are detected by Modal Strain Energy Index (MSEBI). This index is calculated on the difference from the modal strain energy value of every element before and after damage. In the second step, the damage extents are identified by Genetic Algorithm (GA). The objective function is established on the basis of the change of modal strain energy. A plane steel frame model is built by the finite element method. The results of the frame’s free vibration analysis are the input data of the proposed damage detection procedure. In order to improve the accuracy of the damage localization, the MSEBI is determined using the combination of the frame's first four bending mode shapes. The proposed method gives highly accurate results in detecting the damage’s location and extent for various damage scenarios.