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

Designing safe and tailored strategies for robotic therapy requires the knowledge of patient joint torques, allowing control strategies to adjust the torque level provided by the robotic device according to the patient’s performance. Given the impracticability of measuring human joint torques directly, many works in the area have used estimation techniques that require complex calibration and signal processing or introduce uncertainty in their system modeling. This paper evaluates three disturbance observer techniques for estimating ankle joint torque as an alternative solution. Based on the generalized momentum and Kalman filter methodologies, the approaches were implemented on a robotic device for ankle rehabilitation. They were evaluated on six healthy voluntary users for sitting position movements. The techniques demonstrated effectiveness in estimating human joint torque across three distinct human–robot interaction modes, with performance evaluation through normalized root-mean-square error (NRMSE) metrics. Statistical analysis, including ANOVA, Kruskal–Wallis, and Dunn’s post hoc tests, was employed to assess approach performance and impact effects under different configuration settings. These analyses highlighted significant differences in performance among the techniques, enhancing the understanding of the estimation approaches and highlighting their potential integration into robotic rehabilitation settings.

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.