Active vibration reduction in thick plates remains a significant challenge in structural control. This study proposes a novel method for optimizing the orientation of piezoelectric sensor/actuator pairs to enhance vibration suppression. The dynamics of thick plates are modeled using Mindlin plate theory and solved using the finite difference method. The optimization problem is addressed using a binary-coded genetic algorithm, with Singular Value Decomposition (SVD) of the modified control matrix as the objective function. Numerical simulations on a cantilever thick plate demonstrate that optimizing both patch orientation and location significantly improves vibration reduction. The proposed method achieves an average closed-loop dB gain reduction of up to 25.85% compared to location-only optimization and substantially outperforms both random and thin-plate-based configurations. These results highlight that alignment of piezoelectric patches with local strain directions is critical for maximizing electromechanical coupling and control effectiveness. The present framework offers a robust and efficient approach for designing high-performance active vibration control systems in thick plate structures, highlighting the combined importance of spatial placement and directional alignment for achieving superior performance and resource efficiency.

This paper presents a novel adaptive fault-tolerant control (AFTC) framework for systems with piezoelectric sensor patches, specifically targeting sensor faults and external disturbances. The proposed method ensures robust control of cantilever thick plates by integrating adaptive estimation to simultaneously handle sensor faults and system uncertainties, maintaining stability despite issues like drift, bias, loss of accuracy, and effectiveness. Unlike traditional approaches that address sensor faults individually, our method provides a comprehensive solution backed by Lyapunov-based stability analysis, demonstrating uniform ultimate boundedness under various fault conditions. Extensive simulations validate the controller’s superior fault compensation and disturbance rejection compared to Backstepping Sliding Mode Control (BSMC). Under fault-free conditions, the baseline controller achieves accurate tracking, while the AFTC shows significant improvement in trajectory tracking and adaptation when faults are introduced, with minimal performance degradation. This work extends fault-tolerant control strategies to complex systems, including those involving piezoelectric elements, providing a foundation for future research in this area, which has been largely unexplored.

Vertical axis wind turbines (VAWTs) are suitable for urban installations due to their low noise and operational independence from wind direction and speed. In this paper, novel explicit dynamical modeling of a rigid-flexible vertical axis wind turbine (VAWT) with three degrees of freedom (DOFs)—including fore-aft and side-side bending of the tower and rigid rotor rotation—is introduced for the first time. Another significant novelty is the development of generalized aerodynamic lift coefficients applicable across a wide range of Reynolds numbers, overcoming limitations found in previous aerodynamic models. To enhance rotor speed regulation and power output optimization, model predictive control (MPC) and fuzzy-sliding mode control (FSMC) strategies are proposed and evaluated under both normal and disturbed operating conditions. Simulation results demonstrate that the FSMC strategy significantly outperforms conventional MPC in robustness, reduced computational complexity, and precise rotor speed tracking.

Self-excited vibrations in drill-string systems are one of the main causes of failure and efficiency reduction in drilling operations.To suppress these vibrations, an active control strategy is proposed in this article based on a distributed drillstring model.Herein, the coupled axial-torsional dynamics of the drill string are taken into account.This coupling takes place through the bit-rock interaction, consisting of the cutting and the frictional components.The drill-string model is expressed as a neutral-type delay differential equation (NDDE) with constant and state-dependent state delays and constant input delays.As a first step in the novel controller design, a compensator is designed to mitigate the reflective waves at the top side of the string, which, in turn, results in the elimination of the neutral terms and some of the constant time delays in the delay system model.This supports a simplified next step of stabilizing controller design.Second, a new method is proposed to provide sufficient conditions for exponential stability with a prescribed minimal transient decay rate.Based on these conditions, a parametric feedback control law is designed.Finally, to make the controller causal, a predictor is designed which predicts the future state by only employing top-side measurements, available in practice.A simulation-based case study reflecting real-life scenarios is presented to illustrate the effectiveness of the proposed controller.It is also illustrated that the controller is robust against parametric uncertainties and measurement noise.

To propose a model for the coupled axial-torsional dynamics of a drilling bit with a non-uniform blade arrangement and to investigate the effects of multiple-regenerative effects and blade arrangement on the drilling vibration. The neutral-type time-delay model is used to model the drill pipes, which transfer the actuation force and torque to the bit. The employed bit-rock interaction law is a rate-independent law including both cutting and frictional effects. A novel method for determining the depth of cut, which is the key component in estimating the cutting forces, is developed to capture different phenomena, including multiple-regenerative effects. In this method, a functional description of the well surface pattern is presented to determine the depth of cut. Unlike the previous studies, the well surface pattern evolution is represented by an algebraic equation rather than a partial differential equation (PDE). Illustrative simulation results are presented for a representative case study, which demonstrates the validity of the proposed model even in the presence of multiple-regenerative effects. The effect of the non-uniformly arrangement of the blades on the drilling vibration is also discussed. It is shown that the non-uniform arrangement of the cutting blades can reduce the vibration amplitude in some operating conditions. The proposed model can capture the coupled axial-torsional dynamics of a drilling bit with a non-uniform blade arrangement and account for multiple-regenerative effects. The non-uniform arrangement of the cutting blades can be beneficial for reducing the drilling vibration in some cases. Disregarding the multiple-regenerative effects in the model can cause a considerable modeling error.

The first six vibration modes of a thick plate with 10 piezoelectric sensor-actuator pairs are suppressed using advanced beam elements based on the one-dimensional Carrera Unified Formulation (CUF). A three-dimensional model is developed by combining one-dimensional beam elements with two-dimensional Lagrange expansions in this paper. For the reduction of vibration of a thick cantilever plate, a PIDF type control is designed and tuned. Based on the results of the simulation, it can be concluded that the simulation of thick plate models with impulse inputs is efficient as well after model order reduction.

Accurate localization is crucial in the navigation of mobile robots. However, in other circumstances, single-sensor localization faces different challenges, including software and hardware problems or data outages. Sensor fusion is used in most autonomous vehicles (including aerial and ground vehicles) to overcome such challenges. In this paper, the localization of a mobile robot is studied in the presence of sensor faults. The mobile robot has two sensors: two Inertial Measurement Units (IMU) and wheel encoders. Regarding the fault-tolerant scheme, measurements of both sets of sensors are fused using an Interacting Multiple Model (IMM) Kalman filter based on both unscented and extended Kalman filters (UKF and EKF). UKF and EKF-based IMM are chosen for this study since the dynamic model of the localization is highly nonlinear. Regarding contributions, it should be noted that this scheme eliminates the need to model every single fault scenario and use an additional sensor to oversee the performance of the sensing system. Also, comparing this method with similar approaches adopted by other studies shows better performance regarding the cost of computations and RMSE. To evaluate performance, the outputs of the proposed filters are simulated and compared for different trajectories where the data of each sensor is intentionally corrupted to observe the fault detection capability. Simulations are performed for different trajectories and noises to demonstrate this method’s efficiency in different situations. In addition, the results of unscented and extended Kalman filter-based IMM are compared in terms of error and computational costs to evaluate their performance. Overall, simulation and experiments indicate accurate 3D estimations in all cases. Moreover, designated weights vividly show that sensor fault detection is achieved by both unscented and extended IMM Kalman filters, which enable complete fault isolation consequently. This approach provides mobile robots with a reliable and straightforward sensor fault detection and localization solution.

Understanding the communication patterns between body segments of individuals can help us recognize the effects of neuromuscular deficiencies and the coordination challenges accompanying them, such as those likely to affect children with cerebral palsy. Intersegmental coordination can be influenced in cerebral palsy patients. This study compares the whole-body intersegmental coordination patterns observed in the sagittal plane in typically developing controls and patients with cerebral palsy (CP) during free-speed walking. There were ten age-matched children in each group walking at their preferred speed. Motion data were collected using the Vicon 3D motion capture system. The continuous relative phase was calculated using segment angles and angular velocities for each point in the sagittal plane. The relative phase analysis method was utilized to quantify coordination and stability by considering the mean absolute relative phase (MARP) and deviation phase (DP). The coordination and stability indices were determined for each side of the body and the gait swing and stance phases. Whole-body intersegmental analysis includes the relation between clavicle–thorax, thorax–pelvis, pelvis–femur, femur–tibia, tibia–foot, and foot–toe on either side. The Mann–Whitney U test was utilized to evaluate the mean values of DP and MARP between two groups on each side. The statistical analysis results demonstrated less coordination and stability in the CP group. Still, the difference between the CP and TD groups’ variability index is insignificant compared to the difference in the coordination index.

This study addresses the problem of designing a nonlinear feedback control strategy for horizontal axis variable speed wind turbines in the below-rated wind speed operating region (whether the wind turbine is offshore or onshore). The objective is to operate the wind turbines to maximum wind energy extraction while reducing the mechanical load. To overcome both issues, a robust nonlinear control strategy based on sliding mode control (SMC) is proposed which tries to seek for an improved performance. The proposed controller has been developed to compensate for negative consequences of external disturbances, measurement noises and unmodeled dynamics. This control strategy exploits a tracking controller that keeps an optimal value for the ratio between the rotor angular speed and the wind speed. For maximum wind energy extraction, the control algorithm employs the sliding mode state output feedback torque controller to provide robustness, combined with backstepping scheme to ensure better performance in the presence of matched and mismatched uncertainties. Next, a fuzzy logic system (FLS) approach is introduced to the backstepping sliding mode controller (BSMC) to achieve better mechanical loads prevention suffered by the transmission shaft by adjusting the parameters of the controller. Finally, multi-objective particle swarm optimization (MOPSO) algorithm is used to find the optimal values for the adjustable parameters of the proposed fuzzy BSMC (FBSMC). To validate the proposed control structure, FAST aeroelastic simulator is used. The obtained results illustrate that the presented control scheme has satisfactory performance.

This paper investigates nonlinear forced vibrations of homogeneous Euler-Bernoulli microbeams with clamped-clamped boundary conditions. Here, the nonlocal strain gradient theory is incorporated to achieve the governing nonlinear partial differential equation of motion, including mid-plane stretching and damping effects. Using the Galerkin approach, a reduced equation of motion is derived under a central harmonic force. The perturbation technique is employed to examine the nonlinear forced vibration behavior of microbeam. Frequency responses of microbeam are presented for primary, super-harmonic, and sub-harmonic resonances. Simulation results indicate role of size effect on the vibration behavior of microbeam. Moreover, the effects of different physical parameters on the vibration behavior of microbeam are studied. Finally, the proposed approach is compared with a numerical solution to demonstrate the accuracy and validity of the presented analytical solution.

In this paper, the vortex-induced vibrations (VIV) of two bladeless wind energy converters (BWECs) are investigated through wind tunnel experiments, CFD-FEM simulations reduced-order model. BWECs consist of a blunt body attached to the tip of two flexible coaxial beams. In BWEC1, the blunt body is a truncated conic cylinder, whereas in BWEC2 it is a right cylinder. Due to periodic shedding vortices, the BWECs undergo vibrations that can be converted to electrical energy. An analytical reduced-order model is derived for the BWECs by incorporating a semiempirical model for the fluctuating aerodynamic lift coefficient into the Euler–Bernoulli theorem for the flexible support. The reduced-order model involves two principal assumptions: linear mode shapes for the aerodynamic lift force and a semiempirical model for the lift coefficient. The objective of the present research is to study and validate the accuracy of these two assumptions. To this end, wind tunnel experiments were accomplished to measure the tip displacement and CFD-FEM simulations were performed to obtain lift force distribution. Parameters of the reduced-order model are obtained using a genetic algorithm that minimizes the least squared error between the results of the model and the measurements of the experiments. To examine the assumptions of the reduced-order model, further CFD-FEM simulations are performed. The results of the CFD-FEM simulations confirmed the validity of the presumed lift force mode shapes. Moreover, it is justifiably inferred that the semiempirical lift model is the source of inconsistencies between the model and the wind tunnel experiments in high wind speeds of the post-lock-in region. In conclusion, the proposed reduced-order model is shown to be adequately accurate near the lock-in wind speed, which is the most significant working condition of the VIV energy harvesters.

In this paper, a distributed model in terms of neutral-type time-delay equations is presented to investigate the global nonlinear axial-torsional dynamical behavior of a drilling string. A rate-independent bit-rock interaction law is employed for both cutting and frictional forces at the bit. A model is proposed for the estimation of the depth of cut which is valid in the case of bit bouncing and the bit reverse rotation. Illustrative simulation results are presented for a representative case study, which demonstrate the existence of the bit-bounce and reverse-rotation in some practical operating conditions, and indicates the need for taking the resulting multiple regenerative effects into account.

This article proposes an active control strategy to suppress self-excited coupled axial-torsional vibrations of a distributed drill-string system while the coupling takes place through the bit-rock interaction. The drill-string model is expressed as Neutral-type Delay Differential Equations (NDDEs) with constant and state-dependent state delays and constant input delays. As a first step in the novel controller design, an implementable input transformation is introduced, resulting in the elimination of the neutral terms from the equations of motion. This supports a simplified next step of stabilizing controller design. In the second step, a new analytic method named the “Eigenvector Contradiction Method” is proposed to provide sufficient conditions to ensure that all eigenvalues have real parts less than a prescribed value. Based on this criterion, an automated parametric feedback control law is designed. A case study simulation is presented to illustrate the effectiveness of the proposed control strategy.

SUMMARY In this article, a novel mechanism for planar one-legged hopping robots is proposed. The robot consists of a flat foot which is pinned to the leg and a reciprocating mass which is connected to the leg via a prismatic joint. The proposed mechanism performs the hopping by transferring linear momentum between the reciprocating mass and its main body. The nonlinear equations of the motion of the robot are derived using the Euler–Lagrange equations. To accomplish a stable jump, appropriate trajectories have been planned. To guarantee a stable response for this nonlinear system, a sliding-mode controller is implemented. The performance of the hopping robot is investigated through numerical simulations. The results confirm the stability of the hopping robot through the jump cycle on a flat surface and in climbing up and down ramp and stairs.

This paper uses the singular value decomposition approach to find the optimal distribution of a set of piezoelectric actuators and sensors in order to suppress the vibrations of a thick plate. The dynamic model of the system is derived using Mindlin plate theory and consequently, the finite difference method is employed to divide the thick plate to a finite number of nodes with appropriate horizontal and vertical distances. To compute the control force of piezoelectric actuators, the singular value decomposition approach for the column control matrix is supposed as the fitness function of an optimization problem. Through a genetic algorithm, the optimized solution is obtained. The results of numerical simulations indicate the optimal location achieved by the proposed method outperforms the previous results in suppressing the vibrations of a thick plate.

Nitric Oxide (NO) provides myocardial oxygen demands of the heart during exercise and cardiac pacing and also prevents cardiovascular diseases such as atherosclerosis and platelet adhesion and aggregation. However, the direct in vivo measurement of NO in coronary arteries is still challenging. To address this matter, a mathematical model of dynamic changes of calcium and NO concentration in the coronary artery was developed for the first time. The model is able to simulate the effect of NO release in coronary arteries and its impact on the hemodynamics of the coronary arterial tree and also to investigate the vasodilation effects of arteries during cardiac pacing. For these purposes, flow rate, time-averaged wall shear stress, dilation percent, NO concentration, and Calcium (Ca2+) concentration within coronary arteries were obtained. In addition, the impact of hematocrit on the flow rate of the coronary artery was studied. It was seen that the behavior of flow rate, wall shear stress, and Ca2+ is biphasic, but the behavior of NO concentration and the dilation percent is triphasic. Also, by increasing the Hematocrit, the blood flow reduces slightly. The results were compared with several experimental measurements to validate the model qualitatively and quantitatively. It was observed that the presented model is well capable of predicting the behavior of arteries after releasing NO during cardiac pacing. Such a study would be a valuable tool to understand the mechanisms underlying vessel damage, and thereby to offer insights for the prevention or treatment of cardiovascular diseases.

This paper studies the control of a brachiating robot imitating the locomotion of a long armed ape. The robot has two revolute joints, but only one of them is actuated. In this paper, after deriving dynamic model of the robot, the Controlled Lagrangians (CL) method is used to design a controller for point to point locomotion. The CL method involves satisfying a number of equations called matching conditions. The matching conditions are derived using the extended λ-method in the form of a set of partial differential equations (PDEs). Solving the PDEs, a class of controllers is found that satisfies the matching conditions. The fittest controller in the class of controllers is then chosen by particle swarm optimization algorithm. Performance of the developed controller is investigated by numerical simulations. Finally, experiments are performed to validate theoretical results.

In this paper, an optimal control method is proposed for a piezoelectric vortex-induced vibrations (VIV) energy harvester. The harvester comprises a blunt cylinder attached to the tip of a flexible beam. The beam is a composite cantilever that is partially covered by piezoelectric plates. A nonlinear model is derived for the VIV of the harvester by using the Euler-Lagrange principle with the unsteady aerodynamic force due to vortex shedding. To achieve the maximum energy production, an optimal controller is designed using the model predictive control (MPC) method. The MPC design problem turned out to be a linear quadratic optimization problem that is solved by efficient numerical methods. The closed-loop response of the MPC scheme is studied through extensive numerical simulation for several working conditions. The results showed that, compared with the conventional methods, the MPC scheme significantly increases the output electrical power of the VIV harvester. (c) 2020 American Society of Civil Engineers.

This study is concerned with the design of a nonsingular decoupled terminal sliding mode controller for a class of fourth-order under-actuated uncertain nonlinear systems with unknown external disturbance. For the unmeasured disturbance, a disturbance observer with finite-time convergence of estimation error to zero is proposed. The nonsingular decoupled terminal sliding mode controller is designed by utilizing the output of the proposed disturbance observer. Also, an input saturation constraint and control singularity are considered in the controller design. The finite-time stability and convergence of the disturbance observer are proved for the closed-loop system. In addition, the control of an electrostatically actuated Timoshenko nanobeam subjected to Casimir force is simulated to demonstrate the effectiveness and performance of the proposed control scheme.

Drill strings are subjected to complex coupled dynamics. Therefore, accurate dynamic modeling, which can represent the physical behavior of real drill strings, is of great importance for system analysis and control. The most widely used dynamic models for such systems are the lumped element models, which neglect the system distributed feature. In this paper, a dynamic model called neutral-type time delay model is modified to investigate the coupled axial–torsional vibrations in drill strings. This model is derived directly from the distributed parameter model by employing the d'Alembert method. Coupling of axial and torsional vibration modes occurs in the bit–rock interface. For the first time, the neutral-type time delay model is combined with a bit–rock interaction model that regards cutting process in addition to frictional contact. Moreover, mistakes made in some of the related previous studies are corrected. The resulting equations of motion are in terms of neutral-type delay differential equations with two constant delays, related to the oscillatory behavior of the system, and a state-dependent delay, induced by the bit–rock interaction. Illustrative simulation results are presented for a representative drill string, which demonstrates intense axial and torsional vibrations that may lead to system failure without a controller.