Search Results (16)

This work presents an in-depth study on the system identification of a servo-valve controlled hydraulic cylinder operating under variable load. This research addresses the growing demand for improved control systems (enhancing time response, settling time, and precision) in variable load hydraulic actuators, such as those used in blade pitching systems of wind turbines. The paper begins by detailing the experimental setup, followed by the development of the system’s mathematical model, a fourth-order transfer function (TF). The experimental data collected by a proposed data acquisition system are used for the dynamic identification of the hydraulic setup using periodical signals as commands. All possible combinations of TFs up to order 8 are identified. After an initial visual preselection of the 15 most accurate ones, analyses comparing quality indicators between the measured (experimental) and the TF (simulated) step and sinusoidal responses are conducted to determine the most accurate TF. The paper concludes with the presentation and analysis of the dynamic model, identified as being a fourth-order TF, which replicates the system dynamics with the greatest fidelity. It provides an identification methodology with significant potential for industry practitioners aiming to improve, optimize, and enhance control strategies for variable load hydraulic actuators. Full article

This work aims to establish a numerical model to investigate the wave interaction induced by the motion of a submerged cylindrical wave energy converter. The results show that when the submerged cylinder is in forced sinusoidal heave motion, distinct hollows and humps are produced on the free surface. As the heave amplitude increased from 1 m to 1.8 m, the depth of the hollow increased by 454%, and the height of the hump increased by 370%. Along with strong nonlinear phenomena, the generation of up to the fourth harmonic on the free surface above the submerged body is found, and the highest amplitude of the second harmonic waves reached 68% of the primary frequency. This indicates that the energy distribution of the wave is decomposed and rebalanced, and some energy in the primary frequency accumulates towards higher harmonics. When the submerged cylinder is in forced sinusoidal surge motion, the free surface elevation decreases in a stepwise manner as the wave transitions from crest to trough. As the cylinder pitches, the elevation of the wave trough decreases by 5% compared to when the submerged cylinder remains static. Full article

During the loading process, significant external position disturbances occur in the electro–hydraulic load simulation system. To address these position disturbances and effectively mitigate the impact of uncertainty on system performance, this paper first treats model parameter uncertainty and external disturbances as lumped disturbances. The various states of the servo valve and the pressures within the hydraulic cylinder chambers are then examined. Building on this foundation, the paper proposes a nonlinear multi-mode variable structure independent load port electro–hydraulic load simulation system that is tailored for specific loading conditions. Secondly, in light of the significant motion disturbances present, this paper proposes an integral sliding mode active disturbance rejection composite control strategy that is based on fixed-time convergence. Based on the structure of the active disturbance rejection control framework, the fixed-time integral sliding mode and active disturbance rejection control algorithms are integrated. An extended state observer is designed to accurately estimate the lumped disturbance, effectively compensating for it to achieve precise loading of the independent load port electro–hydraulic load simulation system. The stability of the designed controller is also demonstrated. The results of the simulation research indicate that when the command input is a step signal, the pressure control accuracy under the composite control strategy is 99.94%, 99.86%, and 99.76% for disturbance frequencies of 1 Hz, 3 Hz, and 5 Hz, respectively. Conversely, when the command input is a sinusoidal signal, the pressure control accuracy remains high, measuring 99.94%, 99.8%, and 99.6% under the same disturbance frequencies. Furthermore, the simulation demonstrates that the influence of sensor random noise on the system remains within acceptable limits, highlighting the effective filtering capabilities of the extended state observer. This research establishes a solid foundation for the collaborative control of load ports and the engineering application of the independent load port electro–hydraulic load simulation system. Full article

A directional valve is a core component of the electro-hydraulic shakers in fatigue testing machines, controlling the cylinder or motor that drives the piston for reciprocating linear or rotary motion. In this article, a high-speed rotating directional valve with a symmetrical flow channel layout is designed to optimize the force on the valve core of the directional valve. A comparative analysis is conducted on the flow capacity of valve ports with different shapes. A steady-state hydrodynamic mathematical model is established for the valve core, the theoretical analysis results of which are verified through a Computational Fluid Dynamics (CFD) simulation of the fluid domain inside the directional valve. A prototype of the rotatory directional valve is designed and manufactured, and an experimental platform is built to measure the hydraulic force acting on the valve core to verify the performance of the valve. The displacement curves at different commutation frequencies are also obtained. The experimental results show that the symmetrical flow channel layout can significantly optimize the hydraulic force during the movement of the valve core. Under a pressure of 1 MPa, the hydraulic cylinder driven by the prototype can achieve a sinusoidal curve output with a maximum frequency of 60 Hz and an amplitude of 2.5 mm. The innovation of this design lies in the creation of a directional valve with a symmetric flow channel layout. The feasibility of the design is verified through modeling, simulation, and experimentation, and it significantly optimizes the hydraulic forces acting on the spool. It provides us with the possibility to further improve the switching frequency of hydraulic valves and has important value in engineering applications. Full article

Compared to agricultural environments, afforestation sites are more complex, often presenting issues such as undulating and uneven terrain. These conditions lead to instability in hole digging depth and plant spacing during continuous movement, and the hole shape may not meet expectations. Additionally, the hydraulic system exhibits slow response speed and long steady-state time, affecting the quality of sapling planting. To address these issues, this paper designs an intelligent planting control system for intermittent hole digging under continuous dynamic movement, based on a large tree planter. The focus is on studying the dynamic accuracy of the hole digging cylinder to resolve the instability of plant spacing and planting depth in actual planting processes. Firstly, a motion trajectory model of the intermittent hole digging mechanism is established to obtain the relationship between the displacement trajectory of the rotating cutter and the displacements of the floating cylinder and the hole digging cylinder. Secondly, a mathematical model of the electro-hydraulic servo system is established to control the dynamic accuracy of the hole digging operation. Finally, a Simulink simulation model of the system is established to analyze the performance indicators of the hydraulic system during operation using step and sinusoidal excitation signals. The test results show that the displacement of the hydraulic piston rod can ensure a linear extension trend within the range of 0 to 0.4 m, and the extension distance of the hole digging cylinder in the planting system is 0 to 0.35 m, ensuring linear change within this stroke. When the system’s extension command is 1 V, the actual output is 0.6 m, with a relative error of less than 10% compared to the simulation value, indicating that the control strategy can effectively improve the dynamic performance of the system. When the hydraulic system is in a steady-state extension state at 50 to 58.6 s, the relative error with the simulation value is 7.3%, meeting the “double ten indicators” requirement. The research results clearly verify the superior performance of the proposed intelligent control system, and the proposed control strategy has great potential in practical applications, promising to improve afforestation quality by stabilizing planting spacing and planting depth. Full article

Photoacoustic (PA) velocimetry holds the advantage of detecting ultrasound signals from selective targets sensitive to specific wavelengths of light irradiation. In particular, it is expected to be applied for measuring blood flow in microvasculature. However, PA velocimetry has not been sufficiently investigated for small velocity ranges down to several tens of millimeters per second. This study evaluates the performance and uncertainty of PA velocity measurements using a single graphite cylinder (GC) as a moving object. A pair of short laser pulses irradiated the object within a brief time interval. The velocity was measured based on the cross-correlation peak of successive PA signal pairs in the time domain. The limiting measurement uncertainty was 3.4 mm/s, determined by the sampling rate of the digitizer. The object motion was controlled in a sinusoidal linear motion, realized using a loudspeaker. With the PA measurement, the velocity of the object was obtained with a time resolution in milliseconds and with directional discrimination. Notably, the PA velocity measurements successfully provided the local velocities of the object across a wide range, with the reference velocity obtained as the time derivative of the displacement data acquired using a laser displacement sensor (LDS). The PA measurement exhibited uncertainties ranging from 0.86 to 2.1 mm/s for the maximum and minimum velocities during the experiment. The uncertainties are consistent with those in stationary cases, and nearly constant in the investigated velocity range. Furthermore, the PA measurements revealed local fine velocities of the object, which were not resolved by the reference velocities of the LDS measurements. The capability of the PA velocity measurement was found to be advantageous for measurements of objects with dynamic variations in magnitude and direction. Full article

To obtain a more consistent droplet distribution and reduce spray drift, it is necessary to keep the entire spray boom parallel to the crop canopy or ground and maintain a certain distance from the spray nozzles to the crop canopy or ground. A high-performance boom active control system was developed for boom trapezoid suspension. The hydraulic system and hardware circuit of the boom control system were designed based on analyzing the configuration of active trapezoid suspension. The mathematical models of valve-controlled hydraulic cylinders and active boom suspensions were developed. Step response and frequency domain response analysis of passive suspension were conducted by Simulink simulations, and then key parameters of the boom suspension and hydraulic system were determined. A feedforward proportion integration differentiation (FPID) control algorithm was proposed to improve the tracking performance. The designed control system was assembled on a 24 m boom with trapezoid suspension. The response characteristic of the active boom control system was tested by the step signal and the sinusoidal signal from a six-degree-of-freedom hydraulic motion platform. Firstly, the tracking performance of the active balance control system for the PID (proportion integration differentiation) and FPID control algorithms was compared for a given 0.2 Hz sine signal. Then, for the ground-following control system, the response characteristics in challenging terrain and tracking performance in less challenging terrain were tested. Field experiment results indicate that the maximum rolling angle of the chassis was $3.896°$ while the maximum inclination angle of the boom was $0.453°$. The results show that the designed boom adjustment and control system can effectively adjust the boom motion in real time and meet the requirements of field operation. Full article

A numerical study estimated the mixed convection around a sinusoidal cylinder inside a rectangular cavity. The key parameters for sinusoidal circular cylinders were the wavelength and Reynolds number (Re = 100, 500, and 1000) with a fixed Prandtl number of 0.7. The flow regimes were greatly affected by these parameters. The unsteadiness of the flow pattern was also affected by λ and Re. The results were analyzed by the thermal structure, vortical structure, and Nusselt number. Furthermore, the orthogonal enstrophy was used to quantify the three-dimensional flow characteristics, and the frequency of the surface-averaged Nusselt number for the heated bottom wall was used to analyze the unsteady characteristics. The heat transfer performance was enhanced by 6.6% at Re = 100 for λ = 3 compared to the circular cylinder. In addition, the heat transfer performance was enhanced by 6.6% and 2.6% at Re = 500 for λ = 2 and Re = 1000 for λ = 1, respectively, compared to the circular cylinder. Full article

A straight-line-type Sagnac optic fiber acoustic sensing system is proposed in this paper to adopt the application needs of no man’s plateau borderline for monitoring mechanical invasion. The Sagnac interference fiber loop is replaced by a straight-line fiber and a 1 × 2 coupler, and the length of the Sagnac interference fiber loop is shortened by close to 50%. The influences of delay fiber and sensing fiber on the sensing system are analyzed by theory calculation and simulation and the optimal lengths of delay fiber and sensing fiber were decided. The experiment system was set, and the sensing fiber was wound into titanium alloy cylinder to compose the sensing element. Experimental results show that the sensing system has a good response to 50−8000 Hz and 70 dB sinusoidal acoustical signals and can well distinguish the signals of different frequencies. Using a small-scale helicopter audio signal as the acoustical signal, the test results show that the response curve is consistent with the simulation results and the sensitivity reaches 30.67 mV/Pa. Full article

A numerical investigation is proposed to explore the flow past a novel wavy circular cylinder as a passive flow control, whose shape is determined by a sinusoidal function applied to its leading edge line, similar to studies with wavy leading-edge airfoils. The latter are motivated by the wavy-shaped tubercles found in the flippers of humpback whales, which are believed to improve their maneuverability. Our attempt is, therefore, to assess the effects of leading-edge waviness now on a simpler and canonical geometry: circular cylinders. The present work relies on iLES simulations conducted with Nektar++ at a Reynolds number of 3900. Besides the straight cylinder, two wavy geometries are assessed, which are determined by a single wavelength of 37.5% for two amplitudes, 3% and 11%, based on the mean diameter of the wavy cylinder. Our results showed that, contrary to what is usually the case with traditional wavy cylinders at similar Reynolds numbers, waviness caused a reduction in the near-wake recirculation length and an increase in the mean near-wake turbulent kinetic energy compared to the straight cylinder. This was followed by a reduction in base pressure (up to about 36%) leading to a rise in lift oscillations and also to a significant increase in the mean drag coefficient of up to about 28%. An attempt to detail the flow phenomena is provided, evidencing the emergence of counter-rotating pairs of streamwise vortices between peaks. It is argued that the differences observed in recirculation length, turbulent kinetic energy, and force coefficients start even prior to the formation of these coherent structures and end up with interactions with the near wake. Full article

An improved acoustic pick-up is presented to enhance the acoustic sensing sensitivity of the straight line-type Sagnac fiber optic acoustic sensing system. A hollow elastomer cylinder is introduced into the system, and the optical fiber is tightly wound around the cylinder to construct the pick-up. The theoretical analysis was finished, and it showed that the improved pick-up will bring in an extra phase change and let the phase difference increase almost an order. The extra phase change will enhance the sensing sensitivity correspondingly. The titanium alloy elastic cylinder was designed and manufactured. The experiment system was built, and a sinusoidal acoustic signal was used as the sound source. The tests were taken during 100–1500 Hz, and the experimental study showed that the sensitivity was more than 130 mV/Pa when the pick-up was used as the acoustic sensing element, and compared to the fiber only system, the sensitivity was enhanced more than 71.2%. The improved pick-up will be helpful in sound recognition and expand the application area of the Sagnac acoustic sensing system. Full article

In the present study, multiple-fan active control wind tunnel tests are conducted to investigate the aerodynamic forces on a 5:1 rectangular cylinder in sinusoidal streamwise winds with different angles of attack (AoA). The effects of the frequency, amplitude, and AoA of the sinusoidal flow on the statistical parameters, spectral characteristics, and spanwise distributions of drag, lift, and moment coefficients are analyzed. Results show that each force has two components: the one induced by the approaching velocity oscillation and the one induced by wake vortex-shedding—this is quite different from that in the smooth flows, where the fluctuating forces are totally due to wake vortex-shedding. For each force, changes of the two components and their relationship with the frequency, amplitude, and AoA are presented. The drag fluctuations are generally dominated by the approaching velocity oscillations, whereas the lift and moment are more sensitive to wake vortex-shedding. Therefore, the drag force has better spanwise correlations than the lift and moment forces. Meanwhile, at a non-zero AoA, the inflow amplitude has different effects on the vortex-shedding-induced component as that at a zero AoA. The differences of spanwise distributions between the sinusoidal flow cases and the smooth flow cases are analyzed. Full article

This mathematical model explains the behavior of sinusoidal radius activity in stagnation point three-dimensional flow of hybrid nanoparticles through a circular cylinder. The energy equation of heat source/sink effect and the mass equation of Arrhenius energy of activation and chemical reaction effects are incorporated. Self-relation transformations are adopted to reduce the PDEs to ODEs, then the RKF-45 method is solved with shooting proficiency. The nodal and saddle point action is studied in pertinent parameters for thermal, mass, and velocity curves. Further statistical values of skin friction, Nusselt number, and Sherwood number of both nodal and saddle points are portrayed in tables format. It is ascertained that higher values of activation energy and reaction rate enhance the concentration curve. In addition, the nodal point curves are always less than saddle point curves. Full article

Robotic forceps with a rigid-link joint mechanism is orthodox for current robotic-assisted surgery systems. However, external force estimation without force sensors during operations is difficult for such electrically driven forceps. This work introduces a pneumatically driven multi-DOF (DOF: degree of freedom) forceps using a rigid-link mechanism with less interference of the wire drive between joints and realizes external force estimation by utilizing high back-drivability of pneumatic cylinders. We developed a position controller with dynamic compensation of the mechanical friction, in which the rotational angles of the three movable joints of the forceps are independently controlled. Moreover, we designed an external force observer in the position controller by applying the disturbance observer scheme. The results of the performance evaluation experiments are as follows. First, in the joint position control experiments, smooth and stable controllability is confirmed for sinusoidal reference inputs with the mean absolute errors of less than 2°. The resolution of the joint position control is approximately 1° for the response of step increasing reference inputs, which is acceptable for laparoscopic surgery. Second, the external force observer can correctly estimate the translational and the grasping forces with less than 20% errors of the maximum output forces. The practical sensitivities of the external force estimation are better than 0.5 N for translational forces and 0.2 N for grasping forces. The achieved performance of the developed forceps can be applicable for interactive force control in some particular surgical tasks such as suturing, ligation, organ traction and exclusion. Full article

A cellular automata (CA) approach to modeling both Ostwald ripening and Rayleigh instability was developed. Curvature-driven phase interface migration was implemented to CA model, and novel CA rules were introduced to ensure the conservation of phase volume fraction of nearly equilibrium two-phase system. For transient Ostwald ripening, it is shown that the temporal growth exponent m is evolving with time and non-integer temporal exponents between 2 and 3 are predicted. The varying temporal growth exponent m is related to the particle size distributions (PSDs) evolution. With an initial wide PSD, it becomes narrowed toward steady state. With an initial narrow PSD, it becomes widened at first and then narrowed toward steady state. For Rayleigh instability, two cases (one with sinusoidal perturbation on the surface of the long cylinder, and the other with grain boundaries in the interior of the long cylinder) were simulated, and the breakup of the long cylinder was shown for both cases. In the end, a system containing long cylinders with interior grain boundaries was simulated, which demonstrated the integration of Rayleigh instability and Ostwald ripening relating to the spheroidization of the lamellar structure. Full article