Load Oscillations Research Articles

Wind Tunnel Testing and Aeromechanics Predictions on Slowed Mach-Scaled Thrust Compounding Rotorcraft with a Trailing Propeller

A thrust compounded helicopter—a main rotor with a trailing propeller was tested in the Glenn L. Martin Wind Tunnel to evaluate its performance under different flight conditions. The main rotor rig consists of a hingeless hub with four fully instrumented NACA 0012 blades and a modified Robin fuselage. The propeller rig consists of a rigid Sensenich L26H propeller with four blades. Tunnel tests were carried out for the isolated propeller and thrust compounded rotor configurations. The isolated propeller tests were conducted with and without the fuselage installed ahead of it to understand the effects of the fuselage on propeller performance. The thrust compound configuration was tested at three different main rotor shaft tilt angles (αs): −4°, 0°, and 4° (fwd tilt, vertical, rearward tilt), advance ratios (μ) from 0.3 to 0.6, and multiple lift (CL/σ) and propulsive (CX/σ) trim targets. Main rotor hub loads, oscillatory blade structural loads, and propeller hub loads were measured for all the tests. The test data were verified with a full vehicle aeromechanical analysis using the University of Maryland Advanced Rotorcraft Code. The thrust compound configuration with the main rotor shaft tilt of 4° (rearward tilt) provided the best performance. Thrust compounding with rearward shaft tilt (4°) resulted in a 50% increase in the maximum aircraft lift-to-drag ratio compared to a single-rotor helicopter. Half peak-to-peak hub vibratory loads and blade bending loads decreased with thrust compounding. It was observed that for the same lift target (CL/σ), thrust compounding achieved 20% higher flight speeds than a single rotor.

Light load oscillation problem analysis and suppression of two-switch buck-boost converter

Light load oscillation problem analysis and suppression of two-switch buck-boost converter

OPTIMIZATION OF THE PROCESSES OF MOVEMENT AND ACCELERATION OF THE OVERHEAD CRANE TROLLEY IN THE MODE OF DAMPING UNCONTROLLED LOAD OSCILLATIONS

The paper deals with the modeling and optimization of the processes of movement and acceleration of a bridge crane trolley in the mode of damping uncontrolled oscillations of the load. For the dynamic system of a flat pendulum with vibration damping, which describes the oscillations of a bridge crane load on a flexible rope suspension in a separate vertical plane, it is proposed to use third-order time splines that model the motion and acceleration of the load suspension point in the horizontal direction of the trolley's movement. To determine the time dependence of the angle of deviation of the crane from the gravitational ver-tical, it is proposed to use the methods of classical calculus of variations (Euler-Poisson equation), which allow optimizing (minimizing) the value of this angle in the process of accelerating a trolley with a load sus-pended from the ropes of an overhead crane. An analytical solution to the problem of damping residual uncontrollable oscillations of the overhead crane load, which usually occur after full acceleration or braking of the load suspension point on the trolley, is obtained. To derive the dependencies, an analytical approach was used to calculate the value of the angle of deviation of the overhead crane's cargo rope from the gravitational vertical, depending on the acceleration and displacement of the load suspension point. The problem of loosening of a load moved by an overhead crane is considered and solved in a new way that allows to completely avoiding pendulum spatial oscillations of the load on a rope suspension. The mathematical apparatus of linear algebra (Kramer's rule, in particular) is used, which allows us to establish analytically the law of time motion of a rope with a load, the angle of deviation of which from the vertical takes minimum values in the process of acceleration of the cargo trolley.

Adaptive Sliding Mode Control of Quadrotor System with Elastic Load Connection of Unknown Mass

During quadrotor load transport, the cable’s elasticity exacerbates load fluctuations, which may result in platform instability or a potential crash. This paper introduced a model of the connecting cable as a spring-damper system and established the dynamic model of the suspension system based on Newton’s law. Nonsingular fast terminal sliding mode control (NFTSMC) was employed for attitude, position, and anti-swing controller design. Adaptive controllers were integrated into altitude control to address uncertainties related to load mass and cable length. The inclusion of an anti-swing controller into the position control loop effectively dampens load oscillations while ensuring accurate position tracking. Numerical simulations demonstrated that the proposed controller outperforms both the energy-based controller and the conventional linear sliding mode controller.

Numerical Simulation Study on Ice–Water–Ship Interaction Based on FEM-SPH Adaptive Coupling Algorithm

To address the impact of layered ice and seawater on polar vessels navigating in icy waters, this study employs a coupled finite element method (FEM) and smoothed particle hydrodynamics (SPH) algorithm to simulate the collision dynamics between the bow and stern of a designated icebreaker and the ice layers. The foundational principles and deployment strategies of the coupling algorithm have been meticulously delineated, with a subsequent simulation conducted to model the trajectory of icebreakers navigating through stratified ice conditions. The ice load on the hull, the movement of broken ice bodies, and the temporal variation of ice resistance during collision were analyzed. The method’s applicability and precision were substantiated through a comparative analysis between the simulated ice resistance outcomes and the ice load estimations derived from the Lindqvist formula. Finally, the differences between the bow and stern icebreaking methods were compared. The research findings indicate that the coupling algorithm demonstrates high precision in simulating the navigation of icebreakers under layered ice conditions, aligning with actual scenarios. This provides a solid foundation for further exploration of the ice load on polar vessels. Furthermore, at equivalent speeds and ice thicknesses, stern icebreaking was observed to induce greater oscillations in ice load and yield a higher mean resistance compared to bow icebreaking.

Piecewise Time Polynomials-Based Control Methods for Obstacle Avoidance and Precision Positioning of Tower Crane Systems with Varying Cable Lengths

During the hoisting and lowering operations of a tower crane, dynamic variations in cable lengths significantly influence the oscillation frequency and amplitude of the load. These variations complicate the oscillation characteristics, heightening the challenge of balancing obstacle avoidance with precise positioning. To tackle this issue, we propose a trajectory planning and tracking control method that integrates hoisting control to reduce the impact of varying cable lengths on load swinging and achieve accurate positioning during obstacle navigation. A novel definition of swing angle is introduced to model the crane’s rigid and swinging components separately, enhancing model accuracy while simplifying complexity. A piecewise polynomial constructs the load trajectory in a low-dimensional flat space, which is then mapped to a high-dimensional generalized state space through a homeomorphic transformation, ensuring trajectory smoothness and traceability. A fractional-order sliding mode controller is employed to facilitate rapid and precise tracking of the actuated degrees of freedom, suppressing load oscillation while maintaining positioning accuracy. Experimental validation on a tower crane platform shows that the proposed strategy enables smooth obstacle avoidance and precise target point reaching, even with varying cable lengths.

Dynamic Soft Tissue Artifacts during Impulsive Loads: Measurement Errors Vary With Wearable Inertial Measurement Unit Sensor Design.

Characterize and model Inertial Measurement Unit (IMU) errors due to transient dynamic soft tissue artifacts excited by impulsive loads, such as foot strikes during running and jumping. We instrumented 10 participants (5 female, 5 male) with IMUs on the dominant leg. An ankle IMU measured reference vertical accelerations during impulsive loads and was cross-validated against vertical force measures. Two IMUs on the posterior shank and anterior shank were used to characterize errors caused by dynamic soft tissue artifacts with respect to the reference. Shank sensors' masses were varied to explore their effect on dynamic soft tissue artifacts. Both the posterior IMU and anterior IMU overestimated peak vertical accelerations during the impulsive load (gain of 2.18 ± 0.63 and 1.55 ± 0.35 respectively). The post- impulsive load oscillation duration and natural frequency varied with sensor mass according to an underdamped second-order system, with posterior IMU and anterior IMU durations of 326 ± 75 ms and 151 ± 50 ms respectively and natural frequencies of 9.79 ± 2.68 Hz and 18.22 ± 12.10 Hz respectively. Low-pass filtering reduced overestimation of peak vertical accelerations, but also attenuated the reference measure. Our study suggests dynamic soft tissue artifacts result in transient, but substantial measurement errors that may not be appropriately mitigated through low-pass filtering. However, these dynamic soft tissue artifacts can be modeled using an underdamped second-order system and used to estimate material properties of underlying soft tissue. We demonstrate that dynamic soft tissue artifacts can be modeled and potentially mitigated to improve accuracy in applications necessitating measurement of impulsive loads such as foot strikes.

Automatic control system for the electric drive of an overhead crane considering elastic connections

Purpose. Investigation of the peculiarities of the automatic control system of an overhead crane electric drive with regard to elastic connections.. Research methods. To achieve this goal, we used the methods of system analysis and modeling with the help of software tools. This made it possible to reflect accurately the processes occurring in the system, as well as to test various operating scenarios and their impact on the overall system efficiency. Results. The study considered the automatic control system of the electric drive and the importance of taking into account elastic connections. The proposed adaptive system uses the RBF neural network. The use of the proposed controller ensures resistance to disturbing influences and allows to level the load oscillations. The adaptability of the system is ensured by changing the parameters (load, speed of movement of mechanisms, stiffness, positioning accuracy, etc.) to meet the operating conditions of the overhead crane. Thanks to this, the system is able to operate efficiently even under variable loads and external influences. Computer modeling of the proposed control system was carried out, which confirmed its effectiveness under various operating conditions. Scientific novelty.This system provides damping of load oscillations and increases the crane positioning accuracy. This is achieved by comparing it with existing control methods according to various criteria. It is proposed to use an algorithm for adapting the parameters of the control system in real time (load, trolley speed, cable length, mechanism stiffness, etc.), which significantly improves (by 5-7% positioning accuracy, by 8-10% stability) the performance of the system. In addition, the study confirmed the ability of the system to adapt to different operating conditions (changed load, variations in travel speed, uneven external disturbances), ensuring the stability and reliability of its operation, which is especially important for ensuring continuous operation of the crane in industrial environments. Practical value. The use of this system can increase the overhead crane productivity by 5-10% compared to traditional control systems. Implementing the system in an industrial environment will significantly improve the efficiency and safety of the crane, as well as reduce maintenance and repair costs. In addition, this system can be used to modernize existing cranes, which will extend their service life and improve their reliability. This opens up new opportunities to improve the efficiency of industrial processes associated with the use of overhead cranes and provides better working conditions for operators.

Robust convex LPV control of a Helicopter-UAV transporting a suspended payload

This paper develops a robust integral sliding mode controller for a helicopter-type unmanned aerial vehicle with a suspended payload. The nonlinear model is rewritten by considering a convex Linear Parameter Varying model that captures the nonlinear system dynamics. Then, a controller is developed by considering a nominal integrator comparator scheme and a discontinuous control based on sliding modes. The first part of the controller is dedicated to tracking the desired trajectory, while the second is devoted to attenuating the effect of external disturbance through a sliding surface. A set of linear matrix inequalities obtained from a Lyapunov quadratic function gives sufficient conditions to compute the controller gains. Numerical simulations are carried out to illustrate the effectiveness of the proposed approach in tracking the desired trajectory and attenuating the load oscillations under the presence of external disturbance.

Fuzzy Logic Based Adaptive Parameter Estimation System in Moving Measurement Systems

Fast and accurate weighing of the weighing systems used in industrial filling systems is of great importance in terms of increasing production capacity and maintaining product quality. In facilities that grind and process grain, machines and equipment are positioned horizontally and vertically on steel structures. Since these machines continuously perform grinding, transferring, filling, and emptying operations, they create continuous vibration in the mechanical systems they are connected to. Moving weighing systems are significantly affected by these mechanical systems. When the impact effect of pneumatic valves-controlled covers in moving weighing systems is added to these structural mechanical vibrations, there are significant waits and delays in weighing systems that measure performance. For this reason, in a performance measurement system in a flour mill, the measurement interval increases as the amount of weighing increases. For example, in a moving weighing system that performs 50 kg performance weighing, the measurement interval can increase up to 15 seconds, which is quite long. In this study, an applied study has been conducted to increase the weighing performance in moving weighing systems and to minimize the measurement interval. The data collection process in the study focuses on two main components: load cell data and IMU data. Thus, it is aimed to overcome the difficulties of traditional methods used in weighing systems, which are generally observed to be insufficient to combat slow and noisy data. The analysis techniques used in this study are Kalman Filtering, Dynamic Q and R Matrix Updates, Comparative Analysis and Statistical Analysis. The Kalman filter was used for the integration of Load cell and IMU data and was applied to filter out noise and oscillations in the weighing data and make more accurate weight estimates. The results obtained showed that the dynamic Kalman filtering method can provide faster and more accurate weighing results compared to traditional methods, with error rates varying between 0.4% and 1% for different combinations of Q and R values in measurements made on the scale. Dynamic Kalman filtering method effectively filters oscillatory and noisy load cell signals, with error rates of 0.7% to 1% for Q=0.02 and R=17 parameters, and error rates of 0.4% to 0.7% for Q=0.07 and R=13 parameters. was able to obtain more accurate weight estimates. This study has shown that the dynamic Kalman filtering method is a potential method that can be used in industrial filling systems. This method can contribute to increasing production capacity and maintaining product quality by providing faster and more accurate weighing results. In this respect, the research has a unique contribution. This method provides a revolutionary development in industrial weighing systems and fills an important gap in the literature.

Design and performance investigation of a sliding-mode adaptive proportional–integral–derivative control for cable-breakage scenario

AbstractControlling a cable-driven parallel robot (CDPR) when a cable breaks is challenging. In this paper, a sliding mode adaptive PID control is designed to ensure a safe guidance of the load when a cable fails. Indeed, regardless when a cable breaks, this control makes it possible enchanting the guidance of the load inside the remaining wrench feasible workspace. In other words, it allows reducing the load oscillation and then increasing the safety of the recovery manoeuvre. Performances are evaluated through simulations by considering a spatial CDPR and comparing the results with a PID control.

Oscillation mechanism and predictive model of explosion load for natural gas in confined tube

Gas explosion in confined space often leads to significant pressure oscillation. It is widely recognized that structural damage can be severe when the oscillation frequency of the load resonates with the natural vibration frequency of the structure. To reveal the oscillation mechanism of gas explosion load, the experiment of gas explosion was conducted in a large-scale confined tube with the length of 30 m, and the explosion process was numerically analyzed using FLACS. The results show that the essential cause of oscillation effect is the reflection of the pressure wave. In addition, due to the difference in the propagation path of the pressure wave, the load oscillation frequency at the middle position of the tunnel is twice that at the end position. The average sound velocity can be used to calculate the oscillation frequency of overpressure accurately, and the error is less than 15%. The instability of the flame surface and the increase of flame turbulence caused by the interaction between the pressure wave and the flame surface are the main contributors to the increase in overpressure and amplitude. The overpressure peaks calculated by the existing flame instability model and turbulence disturbance model are 31.7% and 34.7% lower than the numerical results, respectively. The turbulence factor model established in this work can describe the turbulence enhancement effect caused by flame instability and oscillatory load, and the difference between the theoretical and numerical results is only 4.6%. In the theoretical derivation of the overpressure model, an improved model of dynamic turbulence factor is established, which can describe the enhancement effect of turbulence factor caused by flame instability and self-turbulence. Based on the one-dimensional propagation theory of pressure wave, the oscillatory effect of the load is derived to calculate the frequency and amplitude of pressure oscillation. The average error of amplitude and frequency is less than 20%.

Aerodynamic performances and near wake of an Ahmed body under unsteady flow conditions

This paper experimentally characterizes unsteady effects and flow fields around the Ahmed Body, by analyzing global forces and detailed wake effects. The results are compared to those obtained under steady conditions, with varying wind tunnel velocities and different yaw angles between the model and the free stream. Unsteady fields are generated by means of oscillating blades positioned at the inlet of the test section, whose amplitudes and frequencies can be easily controlled. Specifically, low frequencies, around a few Hertz, as those in the typical range generating load oscillations on vehicles, are considered. The results in terms of force coefficients, obtained by a dynamometric balance, and velocity fields, obtained by Particle Image Velocimetry, are processed in order to derive time-average statistics and also phase-average statistics, as related to forcing blade instantaneous positioning. This type of analysis can be performed thanks to the high temporal resolution of measurement systems, around 100 Hz for the force measurements and around 4000 Hz for the velocity measurements. Results in steady conditions well compare with previous results in references, both as functions of wind tunnel velocity and yaw angles. In unsteady conditions, whatever amplitude is considered, time-average drag and lift coefficients and their dependence on yaw angle are consistently lower compared to the steady case. Phase-averaged coefficients in unsteady conditions can oscillate by around 20 % in comparison to time-average values and these fluctuations are strongly dependent on yaw angle and amplitude of oscillations, thus suggesting that they both contribute to instantaneous loads. Present investigations are related to improvements in set-up of control systems in assisted-driving (self-driving) vehicles.

Influence of High Strain Dynamic Loading on HEMA-DMAEMA Hydrogel Storage Modulus and Time Dependence.

Hydrogels have been extensively studied for biomedical applications such as drug delivery, tissue-engineered scaffolds, and biosensors. There is a gap in the literature pertaining to the mechanical properties of hydrogel materials subjected to high-strain dynamic-loading conditions even though empirical data of this type are needed to advance the design of innovative biomedical designs and inform numerical models. For this work, HEMA-DMAEMA hydrogels are fabricated using a photopolymerization approach. Hydrogels are subjected to high-compression oscillatory dynamic mechanical loading at strain rates equal to 50%, 60%, and 70%, and storage and loss moduli are observed over time, e.g., 72 h and 5, 10, and 15 days. As expected, the increased strains resulted in lower storage and loss moduli, which could be attributed to a breakdown in the hydrogel network attributed to several mechanisms, e.g., increased network disruption, chain scission or slippage, and partial plastic deformation. This study helps to advance our understanding of hydrogels subjected to high strain rates to understand their viscoelastic behavior, i.e., strain rate sensitivity, energy dissipation mechanisms, and deformation kinetics, which are needed for the accurate modeling and prediction of hydrogel behavior in real-world applications.

Adaptive Multi-Surface Sliding Mode Control with Radial Basis Function Neural Networks and Reinforcement Learning for Multirotor Slung Load Systems

While using multirotor UAVs for transport of suspended payloads, there is a need for stability along the desired path, in addition to avoidance of any excessive payload oscillations, and a good level of precision in maintaining the desired path of the vehicle. However, due to the nonlinear and underactuated nature of the system, in addition to the presence of mismatched uncertainties, the development of a control system for this application poses an interesting research problem. This paper proposes a control architecture for a multirotor slung load system by integrating a Multi-Surface Sliding Mode Control, aided by a Radial Basis Function Neural Network, with a Deep Q-Network Reinforcement Learning agent. The former will be used to ensure asymptotic tracking stability, while the latter will be used to suppress payload oscillations. First, we will present the dynamics of a multirotor slung load system, represented here as a quadrotor with a single pendulum load suspended from it. We will then propose a control method in which a multi-surface sliding mode controller, based on an adaptive RBF Neural Network for trajectory tracking of the quadrotor, works in tandem with a Deep Q-Network Reinforcement Learning agent whose reward function aims to suppress the oscillations of the single pendulum slung load. Simulation results demonstrate the effectiveness and potential of the proposed approach in achieving precise and reliable control of multirotor slung load systems.

A simple testing-analysis method to evaluate the mechanical characteristics of soils under cyclic loading

ABSTRACT This study presents a simple, yet robust testing methodology employed for investigating the mechanical behaviour of soils under cyclic loading conditions. Small cylindrical specimens of soil (10.5 mm diameter and 35.0 mm high) were subjected to oscillatory torsional loading in either strain sweep or stress sweep mode using the dynamic shear rheometer. Key mechanical properties, including dynamic shear modulus, phase angle, and energy dissipation capacity, were obtained and used to effectively identify threshold strain levels which differentiated the linear, nonlinear, and damage response of the soil. This study further applied the proposed method to stabilized soils to evaluate the effects of stabilizers on improving soil stiffness, while also considering their potential effects on increasing soil brittleness, which could ultimately lead to reduced resistance to fatigue cracking. The successful development of this testing protocol has the potential to evolve into a specification-type method due to its efficiency, repeatability, sensitivity, and fundamental robustness.

Pentamode Structures Optimized by Machine Learning with Adaptive Sampling

Pentamode structures, gain increasing interest as insulation or stealth material. The enhancements in computers and clusters make it possible to investigate those structures not only in theory but also with simulations. Their applicability to mechanical wave dampening is the main focus of the present work, which leads to a structure with good damping and enough strength as the goal. Therefore, a parametrized geometry based on the diamond lattice is examined within a design space. A factorial testing plan investigates the boundaries and gives first hints on the structure's behaviour under compressive and oscillatory loading and also reveals the necessity of a multi objective optimization. Feed‐forward neural networks are then trained to predict the material properties action and mass specific stiffness utilizing adaptive sampling in order to save time and computational cost. An optimization procedure to gain the structure with lowest mass, highest stiffness, and best damping capabilities, which means lowest action, is successfully implemented and yields the best compromise solution for an equally balanced optimization. This structure is then investigated by finite element simulations and confirms the optimization as well as the neural network training, thus being the best trade‐off of all optimization targets.

Dynamic screening by plasticity in amorphous solids.

In recent work it was shown that elasticity theory can break down in amorphous solids subjected to nonuniform static loads. The elastic fields are screened by geometric dipoles; these stem from gradients of the quadrupole field associated with plastic responses. Here we study the dynamical responses induced by oscillatory loads. The required modification to classical elasticity is described. Exact solutions for the displacement field in circular geometry are presented, demonstrating that dipole screening results in essential departures from the expected predictions of classical elasticity theory. Numerical simulations are conducted to validate the theoretical predictions and to delineate their range of validity.

Flatness‐based sliding mode control for stabilizing a spherical pendulum on a quadrotor

AbstractThis paper presents the problem of transporting a suspended load by a quadrotor. A full model considering the quadrotor and the dynamics of the suspended load, in a three‐dimensional space, is proposed considering as control inputs the torques and the thrust force due to the motors. The solution proposed consists of simple control strategies based on the tangent linearization of the model, which is controllable and therefore flat. A sliding mode control technique is developed for the thrust force and torques associated with the Euler angles in order to track a desired trajectory of the vehicle in a three‐dimensional space with minimum oscillation of the suspended load. The control strategy results to be relatively simple to implement and achieves local stability of the tracking errors, as well as robustness to internal nonlinearities, which are neglected in the linearization process and other external disturbances. The attractiveness of the sliding surfaces and the stability of the tracking errors are formally studied using Lyapunov stability theory. Simulation results are given to show the performance of the proposed control strategy.

Energy Contribution Study of Blade Cavitation Control by Obstacles in a Waterjet Pump Based on mPOD and EEMD

Abstract It has been confirmed that the passive obstacles would substantially depress the leading-edge cavitation in a waterjet pump. Combined with the experiments and numerical simulations, this work revisits blade cavitation evolutions to demonstrate the stabilizing effects of obstacles on cavitation unsteadiness. The multiscale proper orthogonal decomposition (mPOD) and ensemble empirical mode decomposition (EEMD) are adopted to study the energy contributions regarding the cavitation-induced loading and thrust. The mPOD modes illuminate that the leading-edge loading oscillations of the obstacle blade are consequently eliminated where the cavitation is completely depressed and the obstacle cavitation wakes greatly contribute to loading excitation. The thrust statistics demonstrate that the thrust extremes and standard deviation in some revolutions can be well reduced as the large-scale leading-edge cavity depression. The adaptive spectra obtained by EEMD further illuminate that both the tonal and broadband components of blade thrust would be reasonably degraded to some degree. The pump with only one obstacle implementation, as an improvement strategy, is comparatively studied and indicates that single obstacle configuration presents positive effects on the leading-edge cavity depression owing to the pressure-raising effects and can reduce the un-necessary energy loss compared with two obstacles.