The simulation modeling of cutting processes represents a powerful scientific instrument for investigating stress-strain and thermodynamic processes in machined materials. Nevertheless, the principal obstacle to the extensive deployment of this scientific approach is inadequate precision of the resulting research outcomes. This is due to the complexity of formalizing the physical and mechanical forming pattern, considering all the dominant factors in building a high-quality cutting model. Additionally, there is a need for professional experience from the researcher to correctly describe the physical model of the material, as well as a logical selection of fracture criteria, among other factors. One of the most significant challenges in ensuring the accuracy of cutting modeling processes is formalization of the description of a rigid-plastic or elasto-plastic FEA model for analyzing the behavior of materials during machining. The article presents a scientifically based argument for the practicality of using these techniques in simulation modeling systems. It also provides practical recommendations for researchers on constructing an accurate FEA simulation model in DEFORM 2D. The conclusions drawn from the analysis of simulation studies of cutting-induced residual stresses for heterogeneous materials are confirmed by experimental investigations.

The present work deals with the identification of speed-dependent misalignment parameters in a multi-disk coupled rotor system supported on Tilting pad journal bearings (TPJB) and Active magnetic bearings (AMB). The stiffness matrix of misaligned coupling is modelled as the sum of static coupling stiffness (SCS) and additive coupling stiffness (ACS) matrices. The presence of parallel and/or angular misalignments gives rise to ACS matrix and its coefficients represent misalignment in/about a given direction. ACS coefficients are time dependent and a suitable mathematical function has been chosen to define the time varying nature of these coefficients. The global equations of motion (EOMs) are assembled and solved in time domain to obtain rotor vibration and AMB current data. This data is processed by full spectrum Fast Fourier Transform, and subsequently input to the identification algorithm. The stiffness and damping of TPJBs, stiffness of AMBs and ACS coefficients that correspond to misalignment are estimated at six different speeds along with speed-invariant disc unbalances, and SCS coefficients. The robustness of algorithm is tested against measurement noise and modelling bias. ACS coefficients have been identified within reasonable error margins. Finally, the method of application of the algorithm to real rotors is presented. The novelty of the work is the development of an inverse problem for the identification of parallel and angular misalignments in real rotors.

In this paper, the theory of screws is applied to the jerk analysis of the PUMA robot, one of the most popular serial manipulators in history. The higher order kinematic analyses of robot manipulators, such as the acceleration and the jerk, become relevant in improving, among other issues, the performance of robotic manipulators ameliorating the generation of impulsive forces, optimizing the path planning trajectory, reducing the noise, or making it possible to generate smooth trajectories. Numerical applications are provided with the aim to exemplify the versatility of the method of kinematic analysis employed in the contribution. As a consideration for non-experts in the subject, the contribution includes a brief review of the screw theory and its relationship with Plücker coordinates.

Exoskeletons of lower extremities are used mainly for gait treatment in physical rehabilitation. However, they are also capable of being involved in other types of exercises. Nevertheless, their structure needs to be adequately adjusted for such applications. To analyse approaches to that, this review paper investigates the mechanical designs of rehabilitation exoskeletons for lower extremities. The study seeks to identify best practices in designing and implementing these devices by analysing fifty-two articles. It covers aspects such as kinematic structures, materials used, types of drives, and the range of exercises. Standard design features include multiple degrees of freedom, primarily at the hip, knee, and ankle joints, and using lightweight materials to enhance mobility and reduce power consumption. The review also discusses the advantages of different driving systems. The findings provide valuable insights for developing effective and safe rehabilitation exoskeletons, contributing to improved patient outcomes in physiotherapy and rehabilitation settings.

In this paper, a novel analytical approach is proposed to predict the performance and onset criteria of a three-stage double-acting thermoacoustic Stirling oscillator (TDTASO). First, a coupled dynamic-thermodynamic model justifying the behavior of TDTASO is presented, taking into account Schmidt's theory assumptions. Subsequently, the manipulation of the obtained governing equations reveals that the considered Stirling oscillator is a physical regulator system. Thus, the onset criteria, which are the necessary conditions for designing such oscillators, are assessed based on a new analytical method resulting from a regulator-like model. Accordingly, the onset temperature difference is predicted corresponding to different dimensions of the resonator section in the TDTASO. Next, the sensitivity of the TDTASO to the inconsistency of resonators' dimensions is investigated. The results show that increasing the length of the mismatched water column results in a higher frequency. Finally, a prototype TDTASO is constructed and experimentally evaluated. Accordingly, the oscillator frequency is measured 3.14 Hz corresponding to the onset temperature of 163 C and the resonator length of 0.52 m. The experimental data demonstrate the effectiveness of the proposed analytical scheme in predicting the necessary conditions for designing the TDTASO.

Textile composites can be manufactured utilizing both synthetic and natural fibers, such as Corypha gebanga fiber, being a viable option. The weaving of Corypha gebanga fiber with cotton thread in a plain weave configuration enables its application as a reinforcement material in textile composites involving a resin matrix. This research aims to investigate the mechanical characteristics of plain woven Corypha gebanga fiber textile fabric-reinforced polymer hybrid composites made from epoxy resin. This study utilized four different variations: a control group without any treatment, and three treatment groups using solutions with NaOH concentrations of 2.5%, 5%, and 7.5%. The result showed that NaOH concentrations above 2.5% seem to have a detrimental effect, as indicated by the gradual decrease in mechanical performance observed in the 5% and 7.5% NaOH-treated specimens. The decrease in tensile strength suggests that prolonged exposure to alkaline conditions leads to permanent alterations in the cellulose structure and morphology. The optimal concentration of NaOH for maximum mechanical performance enhancement is found to be 5%, which balances the removal of impurities and the avoidance of excessive fiber damage. Microscopy image analysis showed that fiber pullout occurred in all specimens tested that were cut in the direction of the warp during tensile testing. The onset of fracture was characterized by the resin breaking initially, followed by the fibers stretching and ultimately breaking.

This research presents an enhanced methodology for diagnosing bearing faults using Variational Mode Decomposition (VMD) based on L-Kurtosis analysis. The proposed method focuses on selecting optimal parameters for VMD to extract the mode containing the most information related to the fault. The selection of these parameters is based on comparing the energy ratio of each mode and the absolute difference in L-Kurtosis between the Intrinsic Mode Function (IMF) with the highest energy and the original signal. The extracted mode is further refined using a specified kurtosis rate threshold to ensure the most relevant significant modes are captured. The proposed methodology was tested using real fault data from the CWRU, XJTU-SY, and a real-world wind turbine dataset related to electric motors and wind turbine systems. The results demonstrated high accuracy in fault detection compared to other methods such as the Gini Index, correlation, and traditional decomposition techniques like EMD. Furthermore, due to the simple computational nature of the improved VMD method, it is faster and more efficient compared to methods that rely on complex calculations or frequency band analysis, making it suitable for applications requiring real-time, reliable fault diagnosis

The impact of a simple trailing-edge plain flap on the aerodynamics of the SD7037 airfoil have been studied in this paper using computational fluid dynamics at Reynolds number of 3×105 across various low angles of attack and flap deflection angles. The computational model was evaluated by using Star CCM+ software with κ--ω SST turbulence and gamma transition model to solve Navier-Stokes equations. The accuracy of the computational model has been confirmed through comparison with experimental data, showing a high level of agreement at low angles of attack. The findings revealed that specific combinations of angles of attack and flap deflection angles could increase the lift-to-drag ratio by over 70% compared to baseline conditions, benefiting airfoil performance, particularly during takeoff. Some combinations, however, resulted in decreased performance and should be avoided. The results also showed that with the increase of either the angle of attack or the flap deflection angle, the pitching moment increased.

Flow control is studied to improve the aerodynamic performance of an aerofoil. A strategy for maintaining the near-wall flow structure with a given spatial scale, developed within the framework of interdisciplinary research, is used. The proposed active flow control method is based on the application of spanwise arrays of mechanical, thermal, or plasma vortex generators. The latter are found most versatile and efficient for the formulated goal. Aerodynamic coefficients measured in the specified wind tunnel are discussed for the 12.5% supercritical airfoil model. The model is controlled by the spanwise array of pulsating high-voltage plasma discharges. This multi-actuator system provides a sufficient number of control parameters such as pulse duration and repetition rate, the distance between the neighboring actuators (space scale of generated disturbances), and the plasma array location along the airfoil chord. Measurements in a range of Reynolds numbers of Rec=(3-7)x105 showed growth of a maximal lift coefficient CLmax up to 10% and the stall angle by 1.5°-3.5° accompanied by drag reduction up to 7%.

This paper presents a mathematical model for the flow of micropolar fluid in a horizontal channel filled with an anisotropic porous medium, bounded by two parallel plates—where the upper plate is stationary, and the lower plate moves at a constant velocity. The flow, driven by both a constant pressure gradient and the movement of the lower plate, is governed by the Darcy-Brinkman equation. Using no-slip and no-spin boundary conditions, we analytically derive expressions for the velocity, microrotational velocity, and stress distributions. The study provides a graphical analysis of the flow behavior influenced by key parameters such as the Darcy number, porous medium anisotropy, anisotropy angle, and the micropolar fluid’s material parameters. Furthermore, the effects of the material parameters and Darcy number on shear stress and couple stress are thoroughly investigated. The findings have applications in modeling fluid flow in striated or fractured rock formations.