Journal of Mechanical Engineering, Automation and Control Systems
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Potential of handheld laser beam welding
Get PDFSince 2023 at the latest, handheld laser beam welding systems (HLBW) gained interest by many companies. This is mainly due to two factors. Firstly, the cost of such a system has fallen considerably in recent years. Secondly, there is an economic pressure for the manufactures of welded products, partly due to the shortage of skilled workers. This publication addresses various aspects of HLBW, in particular the current state of the art and the potential applications. The higher throughput, less straightening work due to the lower heat input, and the use of less experienced personnel has to be mentioned here. However, welders still need to be qualified, especially to get informed about the hazards of laser radiation. In addition to welding, many systems for HLBW also include a cleaning function, some even a cutting function. The risks to be considered for both last mentioned are significantly greater, since on one hand, a touchdown or contact control is often omitted and on the other, the laser beam is conditioned for a longer working distance. For HLBW, the requirements of the process must be taken into account during the design phase already. This continues with edge preparation, e.g. pre-weld cleaning. HLBW is a supplement to traditional arc welding processes. Arc processes will be still used in the future as well, e.g. for small, complex geometries or in terms of accessibility. However, for longer welds, e.g. 1.5 m long 2 mm thick stainless steel sheets, HLBW sets currently the standard, especially with regard to the welding speed for manual welding
Impact of occlusal trauma on periodontal disease: a literature review
Get PDFPeriodontal disease can be defined as a chronic inflammatory process primarily associated with the accumulation of dental biofilm that affects the supporting periodontal and protective tissues of the periodontium, including root cementum, gingiva, alveolar bone, and periodontal ligament. However, evidence indicates that non-microbial factors, such as occlusal trauma, may also contribute to its progression. In this context, the need to investigate the possible correlation between loss of periodontal attachment and the presence of occlusal alterations, particularly those arising from repetitive traumatic loading, is emphasized. The present study aimed to critically analyze the existing scientific literature on the relationship between occlusal trauma and periodontal impairment. A total of twenty-eight articles were included, selected from the SciELO, PubMed, and Google Scholar databases, published between 1999 and 2025, using terms such as occlusal trauma, periodontal disease, inflammatory mediators, and periodontal inflammation. The qualitative analysis aimed to highlight convergences and divergences in the findings, thereby contributing to a deeper understanding of the factors that influence periodontal disease. The study revealed that, although occlusal trauma is not a causative factor of the disease, it exacerbates the destruction of already compromised tissues, highlighting the need for an integrated therapeutic approach for its management
Editor’s Letter. Jaw Functional Orthopedics courses. With the standard of social media, is chaos installed?
Get PDFCooling analysis and innovative design to increase heat transfer in sealed electronic devices
Get PDFOne of the most important problems of electronic devices is heating. Especially high-performance processors and electronic cards can draw significant power and therefore reach critical temperatures. Heating can lead to functional loss or failure of devices. Sealed systems are used in many areas today. Sealing is defined as not allowing two substances, water and dust, into a closed space. The purpose of our thesis is to design a new cooling system related to the cooling of sealed electronic devices. External flow ventilation will be used as active cooling, and a heatsink structure will be used as passive cooling. Then, the efficiency of this new design will be analyzed using CFD method. By keeping the device at reasonable temperature values, a new design example will be created, especially for cooling sealed structures. Analysis studies have been conducted according to different ventilation channels. As a result of these studies, reference data on how much heat can be drawn by different fin structures will be obtained. These reference data are aimed to provide an approximate cooling capacity estimation in projects where sealing is required. The data obtained as a result of the study are compared and presented in tabular form
Research on the influence of width-height ratio and internal friction angle of the TT mode on the trapezoidal sliding surface of backfill behind the retaining wall
Get PDFThe morphology of sliding surface is an important factor in the earth pressure analysis. To study the characteristics of the sliding surface of backfill behind a rigid wall, taking the translational mode of wall (TT model) as an example, a model test was conducted through a self-made test device, and numerical modelling and theoretical analysis were carried out. The research shows: (1) The finite sliding surface morphology starts from the heel of the wall and consists of multiple “straight lines”. The smaller the width-height ratio and the internal friction angle, the more the number of straight line segments of the finite sliding surface. (2) The “length factor” of the sliding surface is introduced and defined. Through normalisation processing, the width-height ratio, internal friction angle, and length factor are linearly fitted, showing a high degree of linear correlation. (3) The study of the width-height ratio, internal friction angle, and length factor yields a binary quadratic surface function, which shows a high degree of linear correlation. The study fills the research gap of the joint influence of the width-height ratio and internal friction angle on the folded-line type sliding surface. It proposes a quantitative calculation formula for the determination of the finite soil
MIMO radar river flow measurement based on space-velocity-time algorithm and adaptive correction model
Get PDFAccurate measurement of river hydrological characteristics is critical for assessing the impacts of flooding caused by meteorological and geomorphological factors. Flow velocity are key indicators in hydrological monitoring. Traditional measurement approaches, such as continuous-wave Doppler radar and pulsed radar systems, are typically mounted on bridges or fixed supports and offer only single-point measurements. These methods often suffer from limited detection range, low accuracy, and poor resistance to environmental interference. To address these limitations, this study proposes a three-dimensional flow detection framework based on multi-input multi-output (MIMO) radar sensors. By leveraging the high reliability and interference resistance of MIMO radar, along with a Space-Velocity-Time (SVT) algorithm that incorporates spatiotemporal information (two-dimensional surface velocity and time), the proposed method enables robust 3D river flow monitoring. In this study, comparative experiments were conducted on four rivers in China with different flow conditions, geomorphic features and weather environments. Results demonstrate that the proposed method achieves a measurement error of less than 5 % compared to acoustic Doppler current profilers (ADCP) and other conventional mechanical approaches, while also offering improved safety and real-time performance. Moreover, an adaptive flow correction algorithm is presented, which uses three optimized prediction models to compute the correction factor and reduces the mean streamflow measurement error to 0.79 % after correction, providing an effective solution for river gauging, flood control and flood resilience
Experimental study on vibration isolation performance of mining dump truck suspensions for improving ride comfort
Get PDFThis study addresses the challenge of reducing the transmission of low-frequency road excitation vibrations to the cab of mining dump trucks to enhance ride comfort. Given the harsh working conditions of these vehicles, a novel methodology combining experimental data collection and advanced signal processing techniques was developed. The research established a comprehensive vibration testing program aligned with earth-moving machinery standards, collecting vibration acceleration data under both idling and full-load operation at 35 km/h. To improve data accuracy, Singular Value Decomposition (SVD) was employed to denoise the experimental vibration data, effectively mitigating environmental interference. Subsequent Fourier transform analysis revealed the vibration energy transfer patterns of the vehicle suspension system in the frequency domain. The results indicated a significant vibration isolation rate of 89 % for the frame suspension system, contrasting with only 7 % for the cab suspension system. Notably, the cab seat suspension system was found to amplify low-frequency road excitations. Compared to previous methods, this study innovatively integrates SVD and Fourier transform techniques to provide a more accurate and detailed understanding of vibration transmission. The key result of achieving an 89 % vibration isolation rate for the frame suspension system demonstrates the effectiveness of the proposed methodology. This study offers practical optimization directions for improving suspension system performance and ride comfort in mining dump trucks, outperforming traditional approaches by providing a more comprehensive analysis and actionable insights for vibration isolation. The findings also serve as valuable references for addressing similar engineering challenges in heavy machinery
Random parametric nonlinear vibrations of a discrete mechanical system protected from vibration
Get PDFIn this work, the issue of checking the dynamics of nonlinear vibrations of a mechanical system protected from vibrations in case of random parametric excitations is considered. Using the Ito method, the analytical expressions of the mean square values of the absolute accelerations of the mechanical system and the dynamic absorber were determined. Statistical linearization method based on Davidenko's hypothesis was used to determine mean squared values. The average square value change of the random parametric vibration of the mechanical system protected against vibrations with the dynamic absorber at different values of the parameter describing the width of the vibration spectrum was analysed. It is shown that if the parameter describing the width of the vibration spectrum is taken smaller, the mean square value of the random parametric vibration of the protected object combined with the dynamic absorber will have a smaller vibration. At different values of the parameter of the hysteresis loop, the change of the mean square value of the random parametric vibration was analysed and appropriate conclusions were drawn
Bifurcation and chaos analysis of the floating raft vibration isolation system with quasi-zero-stiffness isolators
Get PDFThis paper presents an investigation into the nonlinear dynamic behaviors of the floating raft isolation system coupled with quasi-zero-stiffness isolators subject to multiple disturbance sources. First, the coupling effects between the excitation source and isolation system are considered. Also, the floating raft isolation model under multiple excitations and its motion equation are deduced, and then the dynamic responses are mainly investigated by using the techniques of time history diagram, spectrum diagram, phase diagram and Poincaré map, and the bifurcation diagram. Finally, the bifurcations of the mechanical isolation system with different parameters are analyzed through numerical methods, especially the effect of center distance and mass ratio. The result predicts that the floating raft shows an alternate phenomenon of periodic motion, quasi-periodic motion, and chaotic motion when the center distance and mass ratio vary. The motion state of the floating raft vibration isolation system is more sensitive to the mass ratio than to the center distance. The horizontal and rotational response of the system becomes very intense in the chaotic state, and the response amplitudes in the horizontal and vertical directions reach the same order of magnitude. Above all, the dynamic characteristics can provide the theoretic supporting for the dynamics, vibration control and its parametric optimization of the floating raft isolation system coupled with quasi-zero-stiffness isolators. This study will lay down the requirements for the engineering design and application of floating raft isolation equipment in large vessel
Fabrication and characterization of interdigital transducer structures as temperature sensors by two-photon lithography
Get PDFContinuous developments in the field of 3D printing techniques and equipment have enabled their usage in the field of electronics structures, circuits, and device fabrication in addition to many other fields. This advancement has enabled the potential fabrication of sensors using silicon-based micro or even Nanoelectronics. Currently, the manufacturing and packaging of such devices and structures are heavily reliant on lithography, which can be slow and can involve substantial processing requirements. In this paper, a temperature-sensing Interdigital Transducer (IDT) structure was designed and fabricated using Direct Laser Writing (DLW) based on Two-Photon Lithography (TPL), which is a high-resolution 3D printing technology. The TPL in a positive photoresist was combined with the physical vapor deposition method and the lift-off process to create gold IDT microstructures. The developed sensing structures were characterized using a network analyzer to determine the resonance frequency and its dependence on the temperature changes. The results showed that the IDT structures exhibit a linear response toward the changes in temperature with an average sensitivity of 0.123 MHz/°C. The most important advantage in producing the IDT structure with the additive manufacturing technique is that a very small-sized structure is produced error-free and efficiently