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

As an important element to maintain pressure stability in pipelines, back pressure valves play a vital role in high-pressure fluid control. With the continuous development of high-pressure flow control technology, the performance and adaptability of back pressure valves put forward higher requirements. At present, domestic and foreign back pressure valve products have problems such as poor adaptability to fluid media, insufficient wear resistance and easy to jam. Aiming at these problems, a new type of back pressure valve with jeweled ball seat structure is developed in this study, and the effects of opening degree, initial pump flow and stroke on the internal flow field and performance of the back pressure valve are investigated using water as the flow medium. Numerical simulation and experimental verification show that the inlet pressure can be up to 30 MPa, and under the highest pressure design condition, the fluid pressure flowing through the flow path between the spools will be reduced from high pressure to atmospheric pressure, with a jet appearing in the center of the outlet and a vortex forming in the area near the outlet wall of the slit.

The nonlinear factors, the external interference, and the coupling between the two hydraulic cylinders in the electro-hydraulic position servo system seriously affect the synchronous control accuracy. In this paper, based on the establishment of the state space equation of double hydraulic cylinders, the cross-coupling control structure was adopted, and the synchronous controller based on dynamic soft variable structure control was designed. The synchronous controller based on sliding mode control was used as a comparison for co-simulation and experimental analysis. The results showed that under the control of two synchronization controllers, the controlled dual cylinders could track the given positioning signal in a short time, and the synchronization error was always within the specified range. The synchronization controller based on dynamic soft variable structure control could shift smoothly without significant impact when the given positioning signal suddenly changes, avoiding the chattering problem in the sliding mode control.

The problem of diaphragmatic hernia (DH) and surgical procedures for its treatment in bovine have been widely reported by researchers. However, limited studies have been reported on the health monitoring of bovines post-DH surgery, especially to ascertain their reoccurrence for early diagnosis. This study highlights the fabrication and characterization of a DH sensor prepared by 3D printing (using 17-4 precipitation hardened (PH) stainless steel (SS) as conductor and polyvinylidene fluoride (PVDF) composite as dielectric) for health monitoring of bovine to ascertain its reoccurrence for supporting the early diagnosis. The study highlights the plastic strain deformation of the designed model for 3D printing (observed as 0 at 0.01645 MPa), followed by fatigue testing (observed as safe for 10⁸ cycles of loading) through finite element analysis (FEA) for the assembly of 17-4 PH SS and PVDF composite. The morphological and in vitro assessments were also carried out on 3D-printed functional prototypes. The results suggest that the 3D-printed DH sensor has acceptable mechanical properties (with a factor of safety of 12) and, hence, may be used as a commercial solution to ascertain the reoccurrence of DH in bovine.

The study aims to present new constants of ignition delay based on the Arrhenius model for two diesel fuel surrogates formulated from four components (n-Hexadecane, Heptamethylnonane, Decahydro-naphthalene, and 1-Methyl-naphthalene) as a function of temperature and pressure, obtained by simulation in an adiabatic, homogeneous and constant pressure reactor using the Cantera simulator. The reaction was considered stoichiometric, with a temperature and pressure range varying from 700 to 2200 K and 40 to 120 atm, typical values found in the combustion chamber of turbocharged compression ignition engines. It was found that two-stage combustion occurs for temperatures between 700 and 1000 K (for pressure of 80 atm). When the combustion occurs in two-stages, we detail the ignition delay of each stage, and its first-stage fraction are presented. Surrogate fuels was modeled in 35 and 45 cetane numbers and 48 and 35 threshold soot index, respectively, to compare low and medium fuels in cetane numbers. The main application of these models relates to stochastic combustion models, which require fast models with low computational cost. The main differential of this study refers to its description of two-stage combustion, if it occurs. The model does not consider the physical ignition delay, referring to atomization, mixing and heating of the fuel. Results were compared with models from the literature, showing good agreement and presented intermediate values when compared with the literature.

A novel hybrid approach combining Galerkin discretization and LTMM (Laplace-based transfer matrix method) is put forward to study the dynamics of cantilevered fluid-conveying pipes possessing potential periodicity and elastic supports. Firstly, the deduction for normalized modal functions of a periodic cantilevered beam additionally supported by a combination of linear and torsional springs via LTMM is reviewed. Secondly, the motion equation for a cantilevered pipe with the same material and cross-section moment of inertia as the former-mentioned beam is discretized through the Galerkin method. A hybrid method, abbreviated as LTMM-Galerkin, is then proposed by incorporating the obtained modal functions into the Galerkin method. Thirdly, the eigenfunction and steady-state displacement response are deduced by LTMM-Galerkin. Finally, numerical calculations are carried out, and the validity of LTMM-Galerkin is verified compared with existed methods including transfer matrix method, finite difference method, differential quadrature method, Green function method, and differential transformation method. LTMM-Galerkin can be radiated to study dynamics problems of fluid-conveying pipes with other supporting formats. Additionally, the creation process of this method can serve as a model for the development of other hybrid approaches.

Linear variable parameter systems (LPV) are a very special class of nonlinear systems, which are suitable for controlling dynamic systems with parameter changes. Therefore, in this thesis, the problem of using variable parameter linear systems for controller design and stability analysis is raised. A designed controller must be able to reduce the adverse effects of disturbances in the output, for this purpose, in this research, by creating a compromise between the two functions of (H_{2}) and (H_{infty }) and combining them with the anticipatory control of the resistant model, a suitable method can be used to eliminate the effect A disturbance was achieved. The controller designed in this research, while stabilizing the system, in the presence of external disturbance, reduces the effect of external disturbance on the output under the control of the system. In general, the purpose of presenting this research is to provide an effective algorithm for controlling a variable parameter linear system with disturbance using the robust model predictive control method, which method presented in this thesis is based on solving the linear matrix inequality, also the proposed method has the ability to consider It has different restrictions on system states and system output. All the results obtained in different sections, including stability analysis, controller performance analysis, are shown using several validated practical examples and their effectiveness. In this thesis, solving optimization problems in the environment is done, as well as the case solvers. It is used to obtain auxiliary and controlling matrices.

In this paper, the nonlinear large amplitude vibrations of functionally graded material porous annular sector plates have been investigated. The effects of considering nonlinearity in scrutinizing the large amplitude thermally induced vibrations of the annular sector plates have been studied. Additionally, in this work, the effects of moisture distribution and the presence of material porosity are taken into account. Material and temperature distribution in the thickness direction of the plate cause changes in the hygro-thermo-mechanical material properties in the corresponding direction. To define the dependence of material properties on position and temperature, the power law distribution and the Touloukian formula are employed, respectively. Next, according to the classical theory of thermoelasticity, the one-dimensional heat conduction equation along the thickness direction of the plate is solved and the temperature profile is obtained. Afterward, knowing the temperature distribution, the nonlinear equations of motion, which are derived employing Hamilton’s principle, are solved for each time step. To numerically solve the equations, first, using the generalized differential quadrature method (GDQM), the spatial derivatives are discretized and a differential equation with only the time derivatives is achieved, then the time-dependent differential equation is solved utilizing the Newmark implicit time integration method. Finally, a parametric numerical analysis is conducted to investigate the effects of various parameters on the vibrational behavior of the plate.

The jet characteristics of the nozzles in high-pressure water scale removal systems are crucial to the quality of scale removal. The effects of different turbulence models, Reynolds numbers, and target distances on jet velocity, pressure, water volume, shear force, and descaling width and thickness in the free jet, wall jet, and stagnation zones were studied and compared with experimental data. It is found that the simulation results of the renormalization group (RNG) k-ε model are more closely matched to the experimental results. When the jet reaches approximately z = − 40 de, the velocity and dynamic pressure rapidly decay. The volume of water on the jet axial line gradually decreases at z = 0 to − 40 de. As the jet gradually approaches the surface of the slab, the peak and trough values of the vertical velocity along the striking force line near the wall gradually decrease. As the target distance increases, the volume of jet water, impact pressure, and wall shear gradually decrease, and the jet width gradually increases. As the Reynolds number increases, the volume of the jet water changes less, and the impact pressure and wall shear force increase rapidly. When the descaling pressure is 16 MPa, the impact force of the jet cannot meet the requirements of descaling. Based on research content, a dimensionless functional relationship between descaling width, thickness, strike pressure, target distance, and Reynolds number has been established.

In the present era dominated by Industry 4.0, the digital transformation and intelligent management of industrial systems is significantly important to enhance efficiency, quality, and the effective use of resources. This underscores the need for a framework that goes beyond merely boosting productivity and work quality, aiming for a net-zero impact from industrial activities. This research introduces a comprehensive and adaptable analytical framework intended to bridge existing gaps in research and technology within the manufacturing sector. It encompasses the essential stages of using artificial intelligence (AI) for modelling and optimizing manufacturing systems. The effectiveness of the proposed AI framework is evaluated through a case study on electric discharge machining (EDM), concentrating on optimizing the electrode wear rate (EWR) and overcut (OC) for aerospace alloy Inconel 617. Utilizing a comprehensive design of experiments, the process modelling through an artificial neural network (ANN) is carried out, accompanied by careful fine-tuning of hyperparameters throughout the training process. The trained models are further assessed using an external validation (Val_ext) dataset. The results of the sensitivity analysis indicated that the surfactant concentration (S_c) has the highest level of influence, accounting for 52.41% of the observed influence on the EWR, followed by the powder concentration (C_p) with a contribution of 33.14%, and the treatment variable with a contribution of 14.43%. Regarding OC, S_c holds the highest percentage significance at 72.67%, followed by C_p at 21.25%, and treatment at 6.06%. Additionally, parametric optimization (PO) shows that EWR and OC overcome experimental data by 47.05% and 85.00%, respectively, showcasing successful performance optimization with potential applications across diverse manufacturing systems.

To address the issue of machining errors in large rotary workpieces caused by geometric errors of heavy vertical lathes, this study focuses on measuring and modeling geometric errors of such lathes. By identifying the specific geometric errors that impact the machining accuracy of heavy vertical lathes and extracting the crucial ones, the study investigates the contribution degree of the error of geometric errors during the machining process of the wind turbine bearing raceways. The study combines the geometric error fitting function to predict the position error and profile error of feature points on the bearing raceway cross-sectional curve. It also performs an inverse evaluation of the contact angle of the wind turbine bearing raceways. The study aims to clarify the influence of crucial geometric errors in heavy vertical lathes on machining errors during the machining process of wind turbine bearings. The findings provide theoretical and practical guidance for the subsequent design and manufacture of heavy machine tools and the vertical turning process of large rotary workpieces.