Journal of The Brazilian Society of Mechanical Sciences and Engineering最新文献

Throughout evolution, plants and animals have optimized their structure to thrive in a wide range of extreme environments, offering natural structures with both low mass and high-energy absorption capacities. Vascular plants have developed a specialized tissue known as the Xylem, which offers structural support and facilitates the transport of water, mineral nutrients, and signals throughout the plant. This study aims to enhance the crashworthiness of vehicles by adapting the Xylem structure to design an effective bio-inspired thin-walled structure. Several different crash tube configurations are considered first, and their crashworthiness performances are assessed based on two different metrics: specific energy absorption ((text{SEA})) and crush force efficiency ((text{CFE})), which are determined by using the finite element analysis software LS-DYNA. Then, the crash tube configuration with the best performance is chosen for further investigation. A surrogate-based optimization study is performed, and it is found that (text{SEA}) and (text{CFE}) are improved by 151% and 113% compared to an empty circular thin-walled crash tube. Furthermore, the simplified super folding element theory has been used for building a theoretical model that predicts the mean crushing force of the Xylem-mimicking structure. The simulation results and calculated values show a strong agreement, indicating that the proposed theoretical model is of high accuracy.

In this paper, the objective of path planning and control systems for robot is multifactorial. The method used for navigation algorithms based on is closed-loop random trees with quick search or CL-RRT. In this algorithm, each robot will grow a tree from its current location to the target or zone target is developed. The main advantage of this method is the ability to function in complex environments. For use this method, it is necessary that the CL-RRT algorithm for robot navigation online, be extended. In online mode, the robot does not have any information about the environment and through its sensors, which detect the environment and the ability to function in environments with obstacles dynamic and could face a new obstacle or the possibility of an obstacle’s dynamic (the other a robot) to change its direction during motion. Performance of the design path used with design the controller for robot in an environment with various obstacles is evaluated, and then this design is for a group of robots used. To coordinate among agents and to ensure that there is no conflict between them, there is strategy based on priority assignment and LOS method. The strategy used in a way that ensures that the collision between agents does not happen and benefits of the design methods path used to keep. As a result of this strategy can be divided into two parts, the first part of the prioritization robots and the second part of the strategy, no conflict robot is in motion. In this paper, the problem of forming a group of robots has been investigated. In other words, the agents move in the number of agents must be a specific form. The agents according to a number try to set form (originally defined) to its motion to follow, also when faced with obstacles or other agents of its priorities is no conflict with obstacles or other factors and this moment it is possible to change the shape of their, if this will happen again the situation changes be considered form to make its motion.

Bismaleimide resin (BMPN) matrix composites are widely used in aircraft load-bearing components. Their damage assessment and repair schemes after impact are always the important issues in the research of civil aircraft composite. In order to better understand their failure behaviors, especially after the cementing repair of the composite laminates, a three-dimensional finite element model of the BMPN matrix composite was established. The constitutive models of the 3D Hashin criterion and the B-K criterion were implemented through the ABAQUS subroutine USDFLD to simulate the damage behavior of composite laminates and adhesive layers, respectively. Through the simulation the influences of the layer setting of the patch and the layer property on the strength recovery after the repair process were compared and discussed. The results show that the failure mode of the parent laminate highly depends on the fiber angle, and the recovery effect of the repaired composite laminates can be significantly improved by adding additional layers with the increasing adhesive layer strength.

Composite material curved shell components are key parts of the new generation of high-speed aircraft and missile systems; grinding quality of these components directly affects service performance of the equipment. Optimizing processing process parameters with material removal depth and surface roughness as quality targets is an effective means to improve grinding quality. In this paper, flexible grinding disc is used to process such curved components; for this grinding method under flexible contact mode, deformation of the grinding tool is associated with actual geometric surface shape of the components, then a method for analysing deformation in grinding contact area is proposed combined with the compression physical characteristics of grinding tool, material removal depth prediction model is established based on this method, and processing path interval is optimized with the goal of uniform material removal. Surface roughness prediction model is obtained by conducting experiments and regression analysis, which can be combined with the material removal depth prediction model to achieve grinding quality prediction. In order to meet the actual processing quality requirements of achieving the target range of roughness, reducing material removal depth and improving machining efficiency, a multi-objective optimization method based on grey correlation analysis is proposed. Verification experiment results show that research of this article effectively achieves prediction of grinding quality and improvement of removal uniformity, optimal process parameter combination can reach material removal depth of 21.4 μm and surface roughness Ra of 1.31 μm, improves processing efficiency by 38.2%, improving the comprehensive grinding quality.

In this paper, the entropy production method with computational fluid dynamics technology is employed to study the effect of cavitation on the energy characteristics of the centrifugal pump. The modified cavitation model used in the numerical simulation is also verified by visualization experiments. The results show that the energy loss of the pump can be reflected by the entropy production and is the largest in the impeller. Moreover, the cavitation degree could greatly influence the energy loss of the pump. With the decrease in cavitation number, the vortexes and vapor distribution area increase in the impeller, leading to the increase in the total entropy production. The high entropy production region in the blade shifts to the outlet as the cavitation becomes serious.

In the last few decades, several innovations have been implemented in internal combustion engines to meet stricter emissions legislation and challenging targets related to energy efficiency. In this context, gasoline direct injection (GDI) engines adoption has been growing in the market as an economical and technically feasible route. These engines run on accurate fuel injection strategies, including multiple high pressure in-cylinder injections that improve mixture formation, expanding the possibilities for lean burn operation. In general, these strategies contribute to reduce fuel consumption and emissions. GDI fuel injectors have smaller mechanical tolerances and injection orifices diameters than those of PFI engines, which can lead to a higher sensitivity for obstruction by deposits. The GDI engine release in Brazil is relatively new, but included flex-fuel version innovations, allowing the use of Brazilian gasoline (25–27% v/v of anhydrous ethanol), hydrous ethanol, or any mixture of these fuels. Due to Brazilian market characteristics and the lack of information available in the literature, it is important to evaluate flex-fuel GDI injectors deposit formation. This investigation used an in-house patented engine test methodology, and the results showed the good quality of the Brazilian gasoline regarding low levels of injector deposits formation, under different engine operating conditions and, also, under critical fuel storage conditions (quality stress). The higher ethanol content in the gasoline, the fuel quality stress, the use of an in-house patented engine test methodology and the adoption of a flex-fuel engine in different operating conditions, including soak periods, contribute to this work novelty compared to the available literature. The paper also shows preliminary investigations of the deposit’s physicochemical nature, aiming to identify their characteristics and sources. Further research is recommended to improve knowledge in this area.

In this study, the performance of magnetohydrodynamic (MHD) generators working with seawater and with hot exhaust gas in a combined cycle was computationally investigated. The flow and electric potential coupled governing equations were solved using a commercial computational fluid dynamics code. For seawater applications, 2 geometries were studied: square-cross-section duct and helical channel. For both geometries, the influence of the magnetic field intensity, the flow rate and external electric circuit resistance on the device performance were analyzed. The energy structure of the MHD flow for the helical MHD generator was also analyzed. Finally, a combined power cycle equipped with the investigated MHD generators was studied to evaluate its effects on the thermal efficiency of the combined cycle. The results showed that the helical geometry resulted in 10, 30 and 44 times more electric power produced than the square-cross-section duct for Reynolds numbers of 10⁴, 10⁵ and 10⁶, respectively. An analysis of the energy structure in the helical MHD flow indicated that variations in the magnetic field modified the conversion of mechanical energy into electrical power and lost due to viscous and turbulence effects. It is also shown that for Reynolds numbers of 10⁵ and 10⁶, viscous and turbulence effects dissipate 60% of the mechanical energy lost in the MHD generator, independently of the Hartman number. The results of the MHD-based combined power cycle analysis revealed that the use of the MHD generator improved the thermal efficiency of the combined cycle around 24%, reaching values of 67.5% and 67.3%.

In this paper, a novel analytical model is proposed for calculating the tooth pair meshing duration of orthogonal face gears. Initially, the tooth surface equation, transition surface equation, and tooth width constraints are derived. Subsequently, the contact path of orthogonal face gears is determined based on the condition that the spatial position and normal vector of the contact point of the two tooth surfaces coincide respectively. Furthermore, an analytical model of the tooth pair meshing duration of the orthogonal face gears is established in accordance with the principle of gear meshing. Finally, the tooth pair meshing durations of orthogonal face gears in two cases (contact ratio 1 < ε ≤ 2 and 2 < ε ≤ 3) are discussed. The results show that when 1 < ε ≤ 2, at most two pairs of teeth and at least one pair of teeth are engaged in meshing simultaneously. The middle tooth pair contacts from the meshing-in point, passing through the double-single-double pairs of teeth meshing in sequence. When 2 < ε ≤ 3, at most three pairs of teeth and at least two pairs of teeth participate in meshing at the same time. The middle tooth pair contacts from the meshing-in point, successively transitioning through three-double-three-double-three pairs of teeth meshing. Single-tooth-pair meshing duration is absent.

This study presents a pioneering investigation into the energy absorption characteristics of thin-walled multi-cell tubes with DNA-like helical ribs under axial loading, marking the first such exploration in the literature. By systematically varying key design parameters—inner diameter, number of spirals, and spiral turns—we aimed to optimize the energy absorption performance of these complex structures. A total of 27 geometrically intricate multi-cell tubes were fabricated using fused deposition modeling (FDM) and subjected to rigorous axial compression tests. Crashworthiness metrics, including energy absorption, specific energy absorption (SEA), mean crash force (MCF), peak crash force, and crash force efficiency (CFE), were meticulously analyzed. Signal-to-noise ratio analysis and ANOVA were employed to discern the influence of design factors on these metrics. The findings revealed that the number of spirals significantly dictates the energy absorption capacity, with inner diameter exerting the least influence. Specifically, the inner diameter, spiral number, and spiral turns contributed 0.96%, 71.69%, and 17.69% to MCF; 13.03%, 59.22%, and 13.17% to SEA; and 0.13%, 47.39%, and 13.11% to CFE, respectively. Notably, the optimal selection of spiral and inner diameter parameters enhanced the SEA and CFE of the tubes by up to 166.62% and 169.70%, respectively. These results underscore the critical role of helical design in augmenting the crashworthiness of thin-walled multi-cell structures.

A numerical study was carried out to systematically investigate the effect of downstream attached splitter plates on the flow around three unequal spacing side-by-side arranged cylinders at the Reynolds number of 150. The lattice Boltzmann method and finite difference successive over-relaxation method are used simultaneously for the solution of the Navier–Stokes equations, in the formulation where the vorticity and the stream function are the field variables. Sixteen different unequal spacing combinations were chosen. The length of the downstream attached splitter plates is 1D, 2D, and 3D. In the case of a flip-flopping flow pattern without splitter plates, more than one peak was found in the power spectra. This study shows that downstream attached splitter plates reduce drag forces. A comparison is made between the cases with and without splitter plates in terms of the time histories of the drag and lift forces, vortex formation mechanisms, and dominant frequencies. The vortex patterns and downstream evolution are also discussed in detail using vorticity contours visualization. Power spectra analysis and fluid forces were presented upon reaching a steady state. Flow characteristics and fluid force coefficients change considerably with the addition of downstream attached splitter plates.