Modares Mechanical Engineering
Year:2025 | Volume:25 | Issue:5|Papers Count:6

Effective control strategies are necessary for enhancing wind turbine efficiency and lifespan. The purpose of this paper is to control the rotational speed of a wind turbine by adjusting the pitch angle of the blades. Initially, a one-degree-of-freedom closed-loop controller is designed based on the complementary sensitivity function, followed by a PID and a modified PID controller. Finally, their performance in tracking the desired rotational speed of the wind turbine, which includes step and sinusoidal signals, is compared. The 1DOF controller introduced oscillation, while the PID controller eliminated oscillation but exhibited steady-state error. To preserve the advantages of the PID controller and eliminate steady-state error, an integrator term (1/s) has been added to the controller. Consequently, the modified PID controller has been designed. The results of the modified PID controller show no steady-state error or peak overshoot percentage for step inputs. While, the PID and the one-degree-of-freedom closed-loop controller in tracking the step reference input result in steady-state errors of 1.464% and 0.497% and peak overshoot percentages of 23.688% and 84.389%, respectively. During the implementation of the one-degree-of-freedom closed-loop controller, significant oscillations occur while tracking the desired input. The oscillations occurring in the rotor speed can lead to increased fatigue in various wind turbine components, which is an undesirable outcome. However, no oscillations are observed in rotor speed with the PID and modified PID controllers. Finally, according to the obtained results, the modified PID controller demonstrates superior performance compared to the other controllers in tracking the desired rotor speed

Introduction The medial longitudinal arch (MLA) plays a role in foot function and injury prevention, particularly during growth. Its shape could be age-and chronic athletic loading-dependent. The aim of this study was to investigate the effect of participation in sports on MLA development in participants under the age of 20 years. Methods A cross-sectional study on 494 subjects (256 boys and 238 girls) aged below 20 years was undertaken. Subjects were divided into four age groups and further divided into athletes and non-athletes. Foot morphology was quantified using a 3D foot scanner, and the Arch Index was calculated. Independent T-tests were run to ascertain the effect of athletic status on the Arch Index for each age group. Results Athletes exhibited lower Arch Index values than non-athletes in some subgroups, most significantly in boys aged 12–15 and girls aged 16–19. These differences were statistically significant in some cases (p < 0. 05), and in others, borderline (e. g., p = 0. 05 and p = 0. 08). The effect size was small, and asymmetries between the right and left foot existed—greater in the left foot of boys and the right foot of girls. Conclusion The findings suggest the possible association of sport participation with higher MLA height during developmental years. However, due to small effect sizes and borderline statistical significance in some groups, the results need to be interpreted carefully. More prospective research is needed to establish the type, intensity, and duration of sport playing roles in MLA development.

Polymethyl methacrylate (PMMA) is extensively used in automotive, aerospace, and consumer products industries due to its favorable mechanical characteristics. Laser Transmission Welding (LTW) has recently gained attention as an advanced joining method for creating strong, narrow, and lightweight welds in thermoplastics like PMMA. This study examines the effects of three key process parameters—laser power, welding speed, and scan line spacing—on the LTW performance when bonding two transparent PMMA sheets using a fiber laser along a zigzag path. The main objective is determining the feasibility of practical welding at low laser power while achieving high joint strength. Experimental design and optimization were conducted using Analysis of Variance (ANOVA) and Response Surface Methodology (RSM). ANOVA confirmed that all three parameters significantly influenced lap-shear force. RSM results showed that higher laser power, lower welding speed, and reduced scan line spacing increased heat input and improved weld strength, with a maximum lap-shear force of 1256 N. In contrast, lower laser power, faster welding, and wider spacing reduced heat input and resulted in a minimum strength of 245 N. Desirability-based optimization identified optimal settings of 30 W laser power, 400 mm/s welding speed, and 0. 015 mm scan line spacing, predicting a lap-shear force of 1249. 2 N with 99. 3% confidence. The results demonstrate that zigzag LTW of PMMA is feasible at low power levels, attributed to uniform heat distribution and consistent melting achieved by the zigzag path.

Background Head stabilization plays a crucial role in locomotive tasks such as walking, but it can be impaired in individuals with unilateral vestibular disorder (UVD). This study aimed to evaluate the impact of UVD, environmental lighting, and gait speed on head stabilization during walking. The hypothesis was that people with UVD (PwUVD) restrict their head movements while walking, and faster walking speeds and darker environments would worsen head stabilization. Methods Eight PwUVD and nine healthy individuals were asked to walk along a 6-meter walkway at their preferred pace, as well as at 25% slower and 25% faster paces, either in normal or in dark environments. Motion analysis was utilized to measure head movement and calculate variability, range, and approximate entropy of the head kinematic data. Results Healthy individuals exhibited higher variability of head acceleration compared to patients in the forward (p=. 020), lateral (p=. 042), and vertical (p=. 001) directions. The lighting conditions had a significant impact on the variability of the vertical component of head acceleration (p=. 009). Gait speed also significantly influenced the variability of head acceleration in all directions (p<. 001). Furthermore, the range of head acceleration was greater in healthy individuals than in patients, particularly in the forward (p=. 006) and vertical (p<. 001) directions. PwUVD exhibited significantly higher approximate entropy of head displacement and velocity (p<. 033). Conclusion. Conclusion The findings suggest that head stabilization serves as a compensatory mechanism in PwUVD, particularly at higher gait speeds. However, walking in a dark environment limited the effectiveness of this strategy.

In contemporary robotics, enhancing performance accuracy remains a critical and ongoing challenge. As robotic systems are increasingly utilized in precision-demanding applications such as surgical procedures and industrial welding, the demand for higher accuracy in end-effector positioning continues to grow. Numerous techniques have been proposed to address this issue. This study introduces a novel methodology that integrates the pseudo-inverse approach for error estimation—based on Taylor series expansion—with forward kinematics to extract uncertainty parameters. The refined inverse kinematics solutions, obtained through the Newton-Raphson method, are implemented on a SCARA robot for validation. The proposed approach yields substantial accuracy improvements, achieving a 99.8% enhancement in the x-direction and a 99.8% error reduction in the y-direction, thereby underscoring its potential for high-precision robotic applications.

In this article, we introduce a new method which allows utilizing all the available sub-stencils of a WENO scheme to increase the accuracy of the numerical solution of conservation laws while preserving the non-oscillatory property of the scheme. In this method, near a discontinuity, if there is a smooth sub-stencil with higher-order of accuracy, it is used in the reconstruction procedure. Furthermore, in smooth regions, all the sub-stencils of the same order of accuracy form the stencil with the highest order of accuracy as the conventional WENO scheme. The presented method is assessed using several test cases of the linear wave equation and one- and two-dimensional Euler’s equations of gas dynamics. In addition to the original weights of WENO schemes, the WENO-Z approach is used. The results show that the new method increases the accuracy of the results while properly maintaining the ENO property