Search Results (65)

Enhancing the explosive power output of the knee joints is critical for improving the agility and obstacle crossing of humanoid robots. However, a mismatch between the knee-to-CoM transmission ratio and jumping demands, together with power-loss–induced motor performance degradation at high speeds, shortens the high-power operating window and limits jump performance. To address this, this paper introduces a variable-reduction-ratio knee-joint paradigm in which the reduction ratio is coupled to the joint angle and decreases during extension. Analysis of motor output and knee kinematics motivates coupling the reduction ratio to the joint angle. A high initial ratio increases the takeoff torque, and a gradual decrease limits motor speed and power losses, extending the high-power window. A linear-actuator-driven guide-rod mechanism realizes this strategy, and parameter optimization guided by explosive jump control is employed to select the design parameters. Experimental validation demonstrates a high jump of 0.63 m on a single-joint platform (a theoretical improvement of $31.9\%$ over the optimal fixed-ratio baseline under the tested conditions). Integrated into a humanoid robot, the proposed design enables a 1.1 m long jump, a 0.5 m high jump, and a 0.5 m box jump. Full article

Unmanned aerial vehicles (UAVs) are regarded as a novel mode for urban air mobility, earning increasing attention on many commercial and civil applications. The risk of UAVs to people on the ground is heightened by airspace range and operational risks, and the quantitative ground risk buffer estimation are highly required to protect the people on the ground. In this work, a ground risk buffer estimation method based on the analysis of the UAVs dynamics is proposed. It is a 3D contour map, incorporated with flight test parameters, to determine the ground risk buffer for both, rotorcraft UAVs and fixed-wing UAVs. The contour map is generated through UAVs dynamics analysis and combines several parameter layers, including altitude and speed at moment of failure occurence, environment conditions and the lift-to-drag ratio. Each location of the map has associated a value that quantifies the area of the ground risk buffer for a specific test flight condition. The ground risk buffer determined by the current Specific Operations Risk Assessment framework using the 1-to-1 principle is provided for comparison. The proposed method exhibits greater safety margin and further proves the potential of the new estimation method in the perspective of risk quantification and practical engineering applications. Full article

Aiming at the speed chattering problem caused by high-frequency square wave injection in permanent magnet synchronous motors (PMSMs) during low-speed operation (200–500 r/min), this study intends to improve the rotor position estimation accuracy of sensorless control systems as well as the system’s ability to resist harmonic interference and sudden load changes. The goal is to enhance the control performance of traditional control schemes in this scenario and meet the requirement of stable low-speed operation of the motor. First, the study analyzes the harmonic error propagation mechanism of high-frequency square wave injection and finds that the traditional PI phase-locked loop (PI-PLL) is susceptible to high-order harmonic interference during demodulation, which in turn leads to position estimation errors and periodic speed fluctuations. Therefore, the extended state observer phase-locked loop (ESO-PLL) is adopted to replace the traditional PI-PLL. A third-order extended state observer (ESO) is used to uniformly regard the system’s unmodeled dynamics, external load disturbances, and harmonic interference as “total disturbances”, realizing real-time estimation and compensation of disturbances, and quickly suppressing the impacts of harmonic errors and sudden load changes. Meanwhile, a dynamic pole placement strategy for the speed loop is designed to adaptively adjust the controller’s damping ratio and bandwidth parameters according to the motor’s operating states (loaded/unloaded, steady-state/transient): large poles are used in the start-up phase to accelerate response, small poles are switched in the steady-state phase to reduce errors, and a smooth attenuation function is used in the transition phase to achieve stable parameter transition, balancing the system’s dynamic response and steady-state accuracy. In addition, high-frequency square wave voltage signals are injected into the dq axes of the rotating coordinate system, and effective rotor position information is extracted by combining signal demodulation with ESO-PLL to realize decoupling of high-frequency response currents. Verification through MATLAB/Simulink simulation experiments shows that the improved strategy exhibits significant advantages in the low-speed range of 200–300 r/min: in the scenario where the speed transitions from 200 r/min to 300 r/min with sudden load changes, the position estimation curve of ESO-PLL basically overlaps with the actual curve, while the PI-PLL shows obvious deviations; in the start-up and speed switching phases, dynamic pole placement enables the motor to respond quickly without overshoot and no obvious speed fluctuations, whereas the traditional fixed-pole PI control has problems of response lag or overshoot. In conclusion, the “ESO-PLL + dynamic pole placement” cooperative control strategy proposed in this study effectively solves the problems of harmonic interference and load disturbance caused by high-frequency square wave injection in the low-speed range and significantly improves the accuracy and robustness of PMSM sensorless control. This strategy requires no additional hardware cost and achieves performance improvement only through algorithm optimization. It can be directly applied to PMSM control systems that require stable low-speed operation, providing a reliable solution for the promotion of sensorless control technology in low-speed precision fields. Full article

Improving the efficiency of spark-ignited (SI) engines while simultaneously reducing emissions remains a critical challenge in meeting global energy demands and increasingly stringent environmental regulations. Lean burn combustion is a proven strategy for increasing efficiency in SI engines. However, the air dilution level is limited by the mixture’s ignition ability and poor combustion efficiency and stability. A promising method to extend the dilution limit and ensure stable combustion is the implementation of an active pre-chamber combustion system. The pre-chamber spark-ignited (PCSI) engine facilitates stable and rapid combustion of very lean mixtures in the main chamber by utilizing high ignition energy from multiple flame jets penetrating from the pre-chamber (PC) to the main chamber (MC). Together with the increase in efficiency by dilution of the mixture, nitrogen oxide (NO_X) emissions are lowered. However, at peak efficiencies, the NO_X emissions are still too high and require aftertreatment. The use of exhaust gas recirculation (EGR) as a dilutant might enable simple aftertreatment by using a three-way catalyst. This study experimentally investigates the use of EGR as a dilution method in a PCSI engine fueled by methane and analyzes the benefits and drawbacks compared to the use of air as a dilution method. The experimental results are categorized into three sets: measurements at wide open throttle (WOT) conditions, at a constant engine load of indicated mean effective pressure (IMEP) of 5 bar, and at IMEP = 7 bar, all at a fixed engine speed of 1600 rpm. The experimental results were further enhanced with numerical 1D/0D simulations to obtain parameters such as the residual combustion products and excess air ratio in the pre-chamber, which could not be directly measured during the experimental testing. The findings indicate that air dilution achieves higher indicated efficiency than EGR, at all operating conditions. However, EGR shows an increasing trend in indicated efficiency with the increase in EGR rates but is limited due to misfires. In both dilution approaches, at peak efficiencies, aftertreatment is required for exhaust gases because they are above the legal limit, but a significant decrease in NO_X emissions can be observed. Full article

Difficulty in thrust-matching between the cruise and vertical take-off and landing (VTOL) phases is one of the prominent issues faced by conventional VTOL fixed-wing drones. To address this issue, a propeller-induced lift-enhancing (PILE) biplane wing VTOL configuration is proposed with the goal of lift enhancement on the wing during the no-forward-speed VTOL phase. Numerical simulation methods are used to study and analyze the aerodynamic characteristics of this configuration in the cruise and VTOL phases. The results show that the favorable inducing effect of the propeller makes the PILE configuration have a good effect of increasing lift and reducing drag compared with a single wing of the same area during the cruise phase, improving the lift-to-drag ratio by 7.27%. During the VTOL phase, the optimal tilt angle of the propeller for the PALE configuration is 70°, matched with an installation angle of 5° for the aided wing. This parameter combination balances the total drag while also achieving a lift-to-thrust ratio of 1.12. As a result, the required thrust of the propeller is reduced under the same take-off weight, which helps to alleviate the thrust-matching problem and enables VTOL with a smaller power cost. Full article

The auxiliary power unit (APU), which is a compact gas turbine engine, is employed to provide a stable compressed air supply to the aircraft. This compressed air is introduced into the various aircraft components via the pneumatic servo system, thereby ensuring the normal operation of the aircraft’s systems. The objective of this study is to examine the impact of parameter variation on the transmission characteristics of an APU pneumatic servo system, with a particular focus on the aerodynamic moment associated with the operating process of a butterfly valve. To this end, a mathematical model of the pneumatic servo system has been developed. The accuracy of the mathematical model was verified by means of numerical simulation and comparative analysis of experiments. The simulation model was established in the Matlab/Simulink environment. Furthermore, the effects of throttling area ratio, fixed throttling hole diameter, rodless chamber volume of actuator cylinder and gas supply temperature on the transmission characteristics of the system were discussed in greater detail. The findings of the research indicate that the throttle area ratio is insufficiently sized, which results in a deterioration of the system’s linearity. Conversely, an excessively large throttle area ratio leads to a reduction in the controllable range of the load axis and is therefore detrimental to the servo mechanism of the flow control. An increase in the diameter of the fixed throttling hole or a decrease in the volume of the rodless cavity of the actuator cylinder facilitates a rapid change in flow rate within the rodless cavity and an increase in the response speed of the load-rotating shaft of the servomechanism. An increase in the temperature of the gas supply from 30 °C to 230 °C results in a reduction in the response time of the system by a mere 0.2 s, which has a negligible impact on the transmission characteristics of the system. Full article

The exhaust back pressure of diesel engines is becoming increasingly higher nowadays. In order to keep discharging exhaust unhindered and operating smoothly under high exhaust back pressure, a large reduction in engine maximum brake output is often observed, as well as increased fuel consumption and lower combustion efficiency with heavy exhaust smokes. In our previous study, “Applicability of Reducing Valve Timing Overlap for Diesel Engines under High Exhaust Back Pressure”, a reduced valve timing overlap of 12 °CA partially improves the brake output and BSFC for a fixed-geometry turbocharged diesel engine under high exhaust back pressures. A potential solution for restoring the brake output under high exhaust back pressures could be the use of variable-geometry turbochargers. In this study, a variable-geometry turbocharger is applied to a diesel engine to study the engine performance characteristics and applicability, especially the further improvement of brake output and the brake-specific fuel consumption of the engine. Continuing with the results of our previous research, a basic setting of 12 °CA for the valve timing overlap is set up for the subsequent engine performance simulations in this study (using GT-Power SW). Via simulation, exhaust back pressures of 25 kPa, 45 kPa, and 65 kPa gauge are studied for a turbocharged diesel engine. The results for the engine parameters, including brake output, brake-specific fuel consumption, compressor outlet temperature, turbine inlet temperature, intake air mass flow rate, and exhaust mass flow rate are analyzed. The results of the variable-geometry turbocharger, including turbocharger speed, pressure ratios and efficiencies of compressor and turbine are also analyzed. The results indicate that the brake output and brake-specific fuel consumption are effectively improved under full-load operation with an adequate variable-geometry turbocharger rack position. Operable ranges of rack position are also set up for different back pressures. Full article

This paper proposes an asymmetric hybrid tri-stable piezoelectric energy harvester for rotational motion (RHTPEH). The device features an asymmetric tri-stable piezoelectric cantilever beam positioned at the edge of a rotating disk. This beam is uniquely configured with an asymmetric arrangement of magnets. Additionally, an elastic amplifier composed of a vertical and a rotating spring connects the beam’s fixed end and the disk. This setup enhances both the rotational amplitude and vertical displacement of the beam during motion. A comprehensive dynamical model of the RHTPEH was developed using Lagrange’s equations. This model facilitated an in-depth analysis of the system’s behavior under various conditions, focusing on the influence of key parameters such as the asymmetry in the potential well, the stiffness ratio of the amplifier springs, the radius of the disk, and the disk’s rotational speed on the nonlinear dynamic response of the system. The results show that the asymmetric hybrid tri-stable piezoelectric energy harvester makes it easier to harvest the vibration energy in rotational motion and has excellent power output performance compared with the symmetric tri-stable piezoelectric energy harvester. The output power magnitude of the system at higher rotational speeds increases as the radius of rotation expands, but when the rotational speed is low, the steady-state output power magnitude of the system is not sensitive to changes in the radius of rotation. Theoretical analysis and numerical simulations validate the effectiveness of the proposed asymmetric RHTPEH for energy harvesting in low-frequency rotating environments. Full article

The ratio between blade height and chord, named the aspect ratio (AR), plays an important role in compressor aerodynamic design. Once selected, it influences stage performance, blade losses and the stage stability margin. The choice of the design AR involves both aerodynamic and mechanical considerations, and an aim is frequently to achieve the desired operating range while maximizing efficiency. For a fixed set of aerodynamic and geometric parameters, there will be an optimal choice of AR that achieves a maximum efficiency. However, for a state-of-the-art aero-engine design, optimality means multi-objective optimality, that is, reaching the highest possible efficiency for a number of operating points while achieving a sufficient stability margin. To this end, the influence of the AR on the performance of the first rotor row of a multistage, multi-objective, high-speed compressor design is analyzed. A careful setup of the high-speed aerodynamic design problem allows the effect of the AR to be isolated. Close to the optimal AR, only a modest efficiency variation is observed, but a considerable change in compressor stability margin (SM) is noted. Decreasing the AR allows for increasing efficiency, but at the expense of a reduced surge margin. This allows the designer to trade efficiency for stability. Increasing the AR, however, is shown to reduce both the surge margin and efficiency; hence, a distinct optimality in stability is observed for the analyzed rotor blade row. In this work, optimality in the surge margin with respect to the AR is observed, whereas there is a close to optimal efficiency. The predicted range from AR = 1.10 to AR = 1.64 is only indicative, considering that the definition of multi-objective optimality requires balancing efficiency and the surge margin and that the choice of balancing these two criteria requires making a design choice along a pareto optimal front. Full article

For the same frequency, a vibrating screen usually can only achieve a circular or linear motion trajectory, which will lead to the phenomenon of screen clogging. The compound frequency vibrating screen can achieve various motion trajectories according to different frequency ratios, thus perfectly solving this problem. Thus, the multi-frequency control synchronization problem of the dual induction motor-driven vibration system based on the fixed speed ratio was studied. Firstly, by establishing an electromechanical coupled dynamics model of the vibration system driven by dual induction motors, the response equation of the fixed speed ratio vibration system was derived. Then, the master–slave control strategy was used to control the two induction motors through PID control optimized by a genetic algorithm. The slave motor tracked the main motor through the speed ratio method and achieved fixed speed ratio control synchronization. The simulation analysis showed that the two induction motors vibration system could not achieve self-synchronous motion with a fixed speed ratio, but by using the back propagation proportion-integral-derivative control (BP PID, PID based on BP neural network), we were able to achieve control synchronization with a fixed speed ratio. Herein, the arbitrariness of the fixed speed ratio parameter is also discussed, and controlled synchronous motion of the vibration system with a non-integer fixed speed ratio was realized. Finally, the simulation results were verified through experiments with the fixed speed ratio parameter n = 1.5, which verified the validity of the synchronization theory of fixed speed ratio control in vibrating systems and made it possible to apply it in compound frequency vibrating screens. Full article

Sound analysis is an important field of research for improving precision livestock farming systems. If the information carried by livestock sounds is interpreted correctly, it could be used to improve management and welfare assessment in this field. Therefore, we hypothesized that the nasal vocalization of a mother cow could have a calming effect on conspecifics. The nasal vocalization in our study was recorded from a mother cow (not part of the test herd) while it was licking its day-old calf. The raw sound was analyzed, cleaned from noises, and the most representative vocalization was lengthened to two minutes. Thirty cows having calves were randomly selected from eighty Hungarian grey cattle cows. Two test days were selected, one week apart; the weather circumstances in both days were similar. The herd was collected in a paddock, and the test site (a restraining crate with a headlock) was 21 m away from them. The cows from the herd were gently moved to the restraining crate, and, after the installation of the headlock, Polar^® heart rate monitors were fixed on the animals. The recording of the RR intervals was carried out for two minutes. On day one of the test, the processed nasal sound was played to every second cow during the heart rate monitoring. When the sound ended, the heart rate monitor was removed. On test day two, the sound and no sound treatments were switched among the participating cows. At the end of the measurement, the headlock was opened, letting the animals out voluntarily, and a flight test was performed along a 5 m distance. The time needed to pass the 5 m length was measured with a stopwatch and divided by the distance. The RR intervals were analyzed with the Kubios HRV Standard (ver. 3.5.0) software. The following data were recorded for the entire measurement: average and maximum heart rate; SD1 and SD2; pNN50; VLF, LF, and HF. The quasi-periodic signal detected in the sound analyses can hardly be heard, even when it is enhanced to the maximum. This can be considered a vibration probably caused by the basis of articulation, such as a vibration of the tongue, for example. The SD2/SD1 ratio (0.97 vs. 1.07 for the animals having no sound and sound played, respectively, p = 0.0110) and the flight speed (0.92 vs. 1.08 s/m for the animals having no sound and sound played, respectively, p = 0.0409) indicate that the sound treatment had a calming effect on the restrained cows. The day of the test did not influence any of the measured parameters; therefore, no effect of the routine was observed. The yes–no sequence of the sound treatment significantly reduced the pNN50 and flight speed values, suggesting a somewhat more positive association with the headlock and the effectiveness of the processed nasal sound. In conclusion, we have demonstrated that, by means of sound analyses, not only information about individuals and the herd can be gathered but that, with proper processing, the sound obtained can be used to improve animal welfare. Full article

The purpose of this experimental work was to investigate the role of the leading-edge wavy shape technique on the performance of small-scale HAWT fixed-pitch rotor blades operating under off-design conditions. Geometric parameters such as amplitude and wavelength were considered design variables to generate five different wavy shape blade models in order to increase the aerodynamic performance of the rotor with a diameter of 280 mm. A dedicated airfoil type S822 for small wind turbine application from the NREL Airfoil Family was chosen to fulfil both the aerodynamic and structural aspects of the blades. Rotor models were tested in a wind tunnel for different wind speeds while maintaining constant rotational speed to provide the blade-tip chord Reynolds number of 4.7 × 10⁴. The corrected tunnel data, in terms of power coefficients and tip-speed ratios, were compared first with the literature to validate the experimental approach, and then among themselves. It was observed that for minimal sizes of tubercles, the performance of the rotor increases by about 40% compared to the RB1 baseline rotor model for a low tip-speed ratio. Conversely, for the maximum size of the tubercles, there is a marked decrease of about 51% of the rotor performance for a moderate tip-speed ratio compared to the RB1 rotor model. Among these models, specifically, the RB2 rotor model with the smallest values of amplitude and wavelength provides a 2.8% higher peak power coefficient compared to the RB1 rotor model, and at the same time preserves higher performance values for a broad range of tip-speed ratios. Full article

In mobile ad hoc networks (MANETs), geographical routing provides a robust and scalable solution for the randomly distributed and unrestricted movement of nodes. Each node broadcasts beacon packets periodically to exchange its position with neighboring nodes. However, reliable beacons can negatively affect routing performance in dynamic environments, particularly when there is a sudden and rapid change in the nodes’ mobility. Therefore, this paper suggests an improved Greedy Perimeter Stateless Routing Protocol, namely AFB-GPSR, to reduce routing overhead and increase network reliability by maintaining correct route selection. To this end, an adaptive beaconing strategy based on a fuzzy logic scheme (AFB) is utilized to choose more optimal routes for data forwarding. Instead of constant periodic beaconing, the AFB strategy can dynamically adjust beacon interval time with the variation of three network parameters: node speed, one-hop neighbors’ density, and link quality of nodes. The routing evaluation of the proposed protocol is carried out using OMNeT++ simulation experiments. The results show that the AFB strategy within the GPSR protocol can effectively reduce the routing overhead and improve the packet-delivery ratio, throughput, average end-to-end delay, and normalized routing load as compared to traditional routing protocols (AODV and GPSR with fixed beaconing). An enhancement of the packet-delivery ratio of up to 14% is achieved, and the routing cost is reduced by 35%. Moreover, the AFB-GPSR protocol exhibits good performance versus the state-of-the-art protocols in MANET. Full article

To promote energy saving, emission reduction, and sustainable development of high-speed trains, as well as achieve low-carbon operation of these trains. It is necessary to establish a fluctuating wind speed spectra model that can accurately describe the characteristics of the fluctuating wind speed field of the moving vehicle. This will help explore the effects of strong winds on the running resistance, energy consumption, safety, and comfort of trains. In this paper, based on Priestley’s evolutionary power spectral density (EPSD) theory, an efficient method was developed for generating the fluctuating wind speeds at the moving point under the non-stationary wind field. On such basis, the effects of different mean wind speeds, ground clearances, temporal modulation function parameters, and vehicle’s moving speeds on the time-varying correlation function ratio of fluctuating wind speed at fixed and moving points were analyzed. Subsequently, the relationship between the time-varying correlation functions of fluctuating wind speed at the fixed and moving points was established by analyzing the sensitivity of the above parameters, and a theoretical model of fluctuating wind speed spectra of the moving point under the non-stationary wind field was proposed. In addition, the relational expression of fluctuating wind speed spectra of the moving point under stationary and non-stationary wind fields was established, which was further validated using the fluctuating wind speed spectra model at the fixed points with different modulation function forms. The results demonstrated that the direct generation method can avoid n times of POD decomposition and $N_{\mathrm{s}}\sum _{j=1}^n{N}_q^{\mathrm{jj}}$ times of FFT calculation, improve the calculation speed, and save memory. The proposed fluctuating wind speed spectra model at the moving point under the non-stationary wind field is in good agreement with the corresponding target one, indicating the high accuracy of the proposed model. Meanwhile, it is also noted that the fluctuating wind speed spectra at the moving point under the non-stationary wind field can be obtained by modulating the spectra under the stationary wind field using temporal modulation function, which is the same as that of the fluctuating wind speed spectra at fixed points under the non-stationary wind field. Full article

Today, most humanoid mechanical fingers use an underactuated mechanism driven by linkages or tendons, with only a single and fixed grasping trajectory. This paper proposes a new multi-mode humanoid finger mechanism based on linkage and tendon fusion transmission, which is embedded with an adjustable-length tendon mechanism to achieve three types of grasping mode. The structural parameters of the mechanism are optimized according to the kinematic and static models. Furthermore, a discussion was conducted on how to set the speed ratio of the linkage driving motor and the tendon driving motor to adjust the length and tension of the tendon, in order to achieve the switching of the shape-adaptive, coupled-adaptive, and variable coupling-adaptive grasping modes. Finally, the multi-mode functionality of the proposed finger mechanism was verified through multiple grasping experiments. Full article