Y-axis Direction Research Articles

Dynamic simulation and adaptive heave compensation control of a wave-compensated gangway under random wave excitation

For high-precision position control of wave-compensated gangways under random wave excitation, the kinematic model is established based on the Denavit–Hartenberg parametric method. Desired motion parameters for each degree of freedom (DOF) are solved through multi-DOF motion decoupling calculations. The telescopic arm, pitching arm, and slewing seat are simplified as mechanical-hydraulic motor-driven systems or cylinder-driven systems. The nonlinear dynamic models for each system are deduced based on their structural composition and adaptive motion controllers are designed with the desired motion parameters as control targets. The gangway base's heave motion under random wave excitation is reconstructed and the electromechanical-hydraulic coupling dynamic model of the wave-compensated gangway under random wave excitation is coupled. Comparative testing with the traditional Proportional-Integral-Derivative control method shows that the displacement stabilization accuracy of the telescopic arm's tip in the x-axis and y-axis directions under the condition of scale 4 wave improved by 93.05% and 97.38%, respectively. This research provides a technical reference and reliable approach for dynamic analysis and high-precision control of wave-compensated gangways.

Research on intelligent cutting control technology of transverse moving machine for large cross-section roadheader

With the continuous development of the coal mine industry in our country, the cross-section of the roadway is getting larger and larger. The widely used EBZ series roadheader cannot complete the roadway cutting operation with a large cross-section at one time, so it usually needs to move the equipment left and right to complete all its cutting tasks. This paper studies the intelligent control technology of large cross-section roadway cutting, which mainly solves the positioning and attitude determination technology of roadheader in the large cross-section, and offers an accurate shape-cutting control technology and a path planning technology using a lateral moving machine. This paper proposes to combine the signals of laser sensor and fiber-optic inertial navigation system to form a combined positioning and attitude determination system, so as to make use of the advantages and avoid the disadvantages of their respective systems, and improve the accuracy of roadheader positioning and attitude determination. A swing kinematics model of the cutting arm is established, based on which the precise motion control of the first roadway section cutting and the second roadway section cutting can be realized. A key parameter calculation model of roadheader lateral moving machine is put forward to calculate the operation parameters for roadheader lateral moving machine path planning. Finally, the experimental research on intelligent cutting control technology of large cross-section roadheader is carried out in 12307 intelligent heading face of Wangjialing Coal Mine. The results show that the positioning error of the combined positioning and attitude determination system proposed in this paper is between 50-90 mm in the X-axis direction and between 25-45 mm in the Y-axis direction. The average attitude measurement error of heading angle is between 0.5 and 1.5°. This makes the technology appropriate for engineering use. The studied cutting control system achieves a cutting error of 25-50 mm for the first section, and a cutting error of 40-90 mm for the complete section. The complete section cutting error meets the ±100 mm cutting error requirement required in engineering. The intelligent cutting control technology of the lateral moving machine of the large-section tunnel boring machine studied in this paper can realize accurate cutting of the large-section tunnel of 5.6 meters. The research results of this paper provide a reference for the intelligent construction of heading faces.

Flow behavior and heat transfer characteristics of liquid film on vertical hot surface by inclined jet impingement

In this study, the flow behavior and heat transfer characteristics of the liquid film on the hot wall by inclined jet impingement are experimentally studied in detail. The effects of jet parameters, such as jet inclination angle, impingement distance, jet Reynolds number (Rej), and nozzle diameter are explored. The liquid film flow is visualized using a high-speed camera, and the surface temperature and heat flux are obtained by solving the inverse heat conduction problem. The results indicate that the liquid film shape is strongly affected by jet inclination angle but is almost unaffected by other parameters. As the inclination angle increases, the liquid film shape changes from elliptical to fusiform. In addition, the onset, enhancement, and disappearance of boiling cause the expansion and contraction of liquid film. The splashing rate is barely affected by jet parameters and remains within the range of 80–95 % under all conditions. The propagation of wetting fronts exhibits anisotropy. Except for the impingement distance, the position of wetting fronts along y-axis direction displays a high dependence on all parameters. The Rej and nozzle diameter have a significant effect on the heat flux at the impingement point and parallel flow zone, while the jet inclination angle and impingement distance only effect the impingement point. The visualization image proves that the droplet impingement pattern is the main reason for the increase in heat flux at higher impingement distances. Optimizing jet parameters can promote the wall to enter the rapid cooling stage in advance and increase maximum heat flux, thereby improving the maximum cooling capacity of the jet. Finally, an empirical equation is proposed to predict the maximum Nusselt number.

Wearable Haptics for Orthotropic Actuation Based on Perpendicularly Nested Auxetic SMA Knotting.

Smart wearable tactile systems, designed to deliver different types of touch feedback on human skin, can significantly improve engagement through diverse actuation patterns in virtual or augmented reality environments. Here, a perpendicularly nested auxetic wearable haptic interface is reported for orthotropically decoupled multimodal actuation (WHOA), capable of producing diverse tactile feedback modes with 3D sensory perception. WHOA incorporates shape memory alloy wires that are intricately knotted into an auxetic structure oriented along orthotropic dual axes. Its perpendicularly nested auxetic structure enables orthotropic actuation, allowing independent expansion and contraction along both x and y-axes, as confirmed by force-strain and displacement-time performance tests. Additionally, the perylene coating provides orthogonal electrical isolation to WHOA, allowing for stripe-specific localized actuation and enabling multiple tactile feedback modes. As an orthotropic wearable haptic interface, WHOA distinguishes between x-axis and y-axis directions and ultimately delivers multi-dimensional information regarding movements in 3D space through tactile feedback. As a result, when worn on the foot or arm, WHOA naturally delivers spatiotemporal tactile information to the user, facilitating navigation and teleoperation with 3D sensory perception.

Study on new thermal error compensation method for complex surface five-axis machining based on new experimental strategy

Five-axis machine tools are well-suited for processing complex surface parts. However, during the machining process, thermal error can have a significant impact on the machining accuracy. To propose an accountable on-line compensation method for five-axis milling, this paper developed a new experimental device for in-situ measurements of thermal-induced displacements in both X- and Y-axis directions. With the help of this self-developed device, a five-axis milling experiment was carried out to collect the temperature change of key thermal points and thermal-induced error during continuous impeller milling. A thermal error prediction model was established with collected data and a thermal error compensation system was developed for the five-axis milling accordingly. The following validation experiment showed that the surface profile error of the blades of milled impeller can be stabilized within the range of 0.1 mm with the help of proposed the thermal error compensation system. The results of the validation experiment proved the effectiveness of the proposed method for the reduction of thermal error during the five-axis milling.

Temporal adaptation of the postural control following a prolonged fin swimming.

Postural control deteriorates following a transition between two environments, highlighting a sensory conflict when returning to natural conditions. Aquatic immersion offers new perspectives for studying postural control adaptation in transitional situations. Our aim is to study immediate and post-task static postural control adaptation on land after a prolonged fin swimming exercise in total immersion. Standing static postural control was assessed in 14 professional or recreational SCUBA divers (11 men, 3 women; 33.21 ± 10.70years), with eyes open and closed, before, immediately after, and in the following 20min following a fully-immersed 45-min fin swimming exercise. Centre-of-pressure metrics (COP) including average position, amplitude, velocity, length and 95% ellipse were evaluated in medial-lateral (x-axis) and anterior-posterior (y-axis) directions with a force platform. The Romberg ratio was also assessed for each metric. A two-way repeated measures analysis of variance revealed a significant effect of the measurement period on COPx vel (p = 0.01), COPy vel (p < 0.01) and Length (p < 0.01), and of the visual condition on COPy vel (p < 0.01) and Length (p < 0.01). Eyes closed measures were systematically higher than eyes open measures despite there being no significant difference in the Romberg ratio in all periods. Post-immersion, the velocity and total trajectory of the centre of pressure remained systematically lower than baseline values in both visual conditions. Post-immersion, COP velocity and length significantly decreased, suggesting a sensory reweighting strategy potentially associated with ankle stiffening.

Stability of a viscous liquid film flowing down an inclined plane with respect to three-dimensional disturbances

An analysis is presented for the stability of a viscous liquid film flowing down an inclined plane with respect to three-dimensional disturbances under the action of gravity and surface tension. Using momentum-integral method, the nonlinear free surface evolution equation is derived by introducing the self-similar semiparabolic velocity profiles along the flow (x- and y-axis) directions. A normal mode technique and the method of multiple scales are used to obtain the theoretical (linear and nonlinear stability) results of this flow problem, which conceive the physical parameters: Reynolds number Re, Weber number We, angle of inclination of the plane θ and the angle of propagation of the interfacial disturbances ϕ. The temporal growth rate ωi+ and second Landau constant J2, based on which various (explosive, supercritical, unconditional, subcritical) stability zones of this flow problem are categorized, contain the shape factors B and β owing to the non-zero steady basic flow along the y-axis direction. A novel result which emerges from the linear stability analysis is that for any given value of Re, We and θ, any stability that arises in two-dimensional disturbances (ϕ = 0) must also be present in three-dimensional disturbances. For ϕ = 0, there exists a second explosive unstable zone (instead of unconditional stable zone) after a certain value of Re (or θ) due to the involvement of B and β in the expression of J2. This explosive unstable zone vanishes after a certain value of ϕ depending upon the values of Re, We and θ, which confirms the stabilizing influence of ϕ on the thin film flow dynamics irrespective of the values of Re, We and θ.

Numerical Study of the 3D MHD Radiative Flow of Williamson Nanofluid with Variable Characteristics Over a Double Stretching Sheet

The current study investigates the influence of variable thermal conductivity and mass conductivity on 3D MHD. The significance of this study lies in mass diffusion on a three-dimensional Williamson nanofluid fluid flow over a double stretched sheet. When thermal radiation and Hall current is present, the heat transfer process is explored to see how chemical reactions affect heat and mass transmission. Additional phenomena, such as momentum slip and convective boundary conditions, contribute to the model's uniqueness. The problem formulation becomes ordinary differential equations with application of the Von Karman similarity variable. Use of the bvp4c function in yields a numerical solution for the system of differential equations. Using MATLAB’s bvp4c function, a numerical solution to the differential equation system is obtained. A graphic is used to discuss the overall result of several metrics compared to the involved profiles. It is believed that as temperature-dependent thermal conductivity and viscosity increase, so does the temperature field. When the Williamson fluid and magnetic parameters rise, the velocity field decays in the x- and y-axis directions. To support the identified issue, a comparison between the current inquiry and a previously published work is also included.

An efficient and lightweight banana detection and localization system based on deep CNNs for agricultural robots

Accurate detection and localization of fruits in natural environments is a key step for fruit picking robots to achieve precise harvesting. However, existing banana detection and positioning methods have two main limitations in practical applications: a large number of model parameters that make deployment difficult, and a need for performance improvement. To tackle the above issues, a high-precision and lightweight banana bunch recognition and localization method was proposed and deployed on edge devices for application. First, a Slim-Banana model was proposed based on the improvement of YOLOv8l. In order to reduce the model calculation amount and maintain high performance, GSConv was introduced in the Slim-Banana model to replace the standard convolution, and combined with grouped convolution and spatial convolution. At the same time, the cross-stage local network (GSCSP) module was designed to reduce the computational complexity and the complexity of the network structure through a single-stage aggregation method. Then, the RealSense depth sensor is combined with TOF technology to perform image registration and 3D localization of the banana. Finally, the pipeline is deployed on the Nvidia Orin NX edge device and its performance and resource consumption in actual work are deeply analyzed. Experimental results show that the detection precision, recall, mAP and inference time of our method are 0.947, 0.948, 0.98 and 113.6ms respectively, the network memory size required is 4449MiB, and the average localization errors in the X-axis, Y-axis and Z-axis directions are 13.47mm, 12.87mm and 13.87mm respectively. To our knowledge, this is the first work that implements banana detection and localization on edge devices. Experimental results show that compared with existing methods, our method achieves better performance in complex orchard environments, achieving efficient and lightweight banana recognition and localization.

Experimental research on the mechanical properties of alkali-resistant glass fiber concrete acting as tunnel seismic isolation layer under periodic cyclic dynamic loading

The installation of seismic isolation layer is an effective measure to ensure the safe operation of underground projects such as tunnels during extreme seismic activities. Material parameters, mechanical properties, and design patterns of the seismic isolation layer are key research topics in exploring effective reduction of seismic response. This study mainly focused on the dynamic performance of the seismic isolation layer in tunnels. A series of drop hammer impact tests and laboratory shaking table tests were performed to reveal the seismic features of the seismic isolation layer under periodic external loading. The test results indicated that all cracks in the specimen initiated from the center and dispersed outwards under the cycle impact of the drop hammer. The incorporation of alkali-resistant glass fibers in concrete (AR-GFRC) effectively provided "reinforcement " and "crack resistance" under cyclic loading of the drop hammer, and the minimum number and width of cracks were observed at a 0.75 % HD fiber content and a 0.5 % HP fiber content. In the x- and y-axis directions, the seismic isolation layer effectively mitigated peak acceleration, strain response, and displacement at the tunnel vault and invert, but significant nonlinearity was identified. When the thickness of seismic isolation layer was 10 mm, the peak seismic response of the lining were minimum at a 0.75 % HD fiber content and a 0.5 % HP fiber content. However, the thickness of the lining was not directly related to the destruction of the lining. The tunnel mainly experienced shear deformation in the x-axis direction, with significant deformations from the left arch waist to the right arch foot (45°-225°), resulting in transverse cracking. The tunnel primarily underwent tensile and compressive deformation in the y-axis direction, with significant deformations occurring in the inverted vault (0°-180°), resulting in tension and circumferential cracks. This research can provide valuable data support and reference for the design and construction of underground projects such as tunnels.

Effect of vibration and airflow on separation of 6–1 mm fine coal in compound dry separation bed

The segregation behaviour of solid particles are affected by airflow and vibration in a compound dry separation bed. The distribution characteristics of airflow field on the bed surface have been systematically investigated by a novel method of regional air distribution, and the movement and segregation behavior of fine coal particles have been observed under different gas velocity. Meanwhile, the spatial distribution characteristics and ash variation of fine coal particles during the process of segregation and stratification were analyzed. The obtained results show that the airflow velocity of the bed showed a zonal air distribution characteristic of gradual decrease from the separation area to the clean coal section and the gangue section. The segregation and stratification of particles in the Y-axis and Z-axis directions of the bed surface can be enhanced by vibration. When the vibration frequency is 34 Hz, the probable error (E) is 0.08 g/cm3. The bed inclination and the bed grid height have a certain influence on the segregation behavior of fine coal.

Development of a machine vision-based weight prediction system of butterhead lettuce (Lactuca sativa L.) using deep learning models for industrial plant factory.

Indoor agriculture, especially plant factories, becomes essential because of the advantages of cultivating crops yearly to address global food shortages. Plant factories have been growing in scale as commercialized. Developing an on-site system that estimates the fresh weight of crops non-destructively for decision-making on harvest time is necessary to maximize yield and profits. However, a multi-layer growing environment with on-site workers is too confined and crowded to develop a high-performance system.This research developed a machine vision-based fresh weight estimation system to monitor crops from the transplant stage to harvest with less physical labor in an on-site industrial plant factory. A linear motion guide with a camera rail moving in both the x-axis and y-axis directions was produced and mounted on a cultivating rack with a height under 35 cm to get consistent images of crops from the top view. Raspberry Pi4 controlled its operation to capture images automatically every hour. The fresh weight was manually measured eleven times for four months to use as the ground-truth weight of the models. The attained images were preprocessed and used to develop weight prediction models based on manual and automatic feature extraction. The performance of models was compared, and the best performance among them was the automatic feature extraction-based model using convolutional neural networks (CNN; ResNet18). The CNN-based model on automatic feature extraction from images performed much better than any other manual feature extraction-based models with 0.95 of the coefficients of determination (R2) and 8.06 g of root mean square error (RMSE). However, another multiplayer perceptron model (MLP_2) was more appropriate to be adopted on-site since it showed around nine times faster inference time than CNN with a little less R2 (0.93). Through this study, field workers in a confined indoor farming environment can measure the fresh weight of crops non-destructively and easily. In addition, it would help to decide when to harvest on the spot.

Negative curvature fiber (NCF) polarization filter with large polarization loss ratio and ultralow loss in the terahertz range

A high-performance polarization filter based on the negative curvature fiber (NCF) with an asymmetric cladding structure is proposed and analyzed. The resonant effects of the x-polarization fundamental mode (XPFM) of the NCF are enhanced by the single-layer semi-elliptical tubes with a gradient wall thickness in the x-axis direction, while the anti-resonant effects of the y-polarization fundamental mode (YPFM) are strengthened by the nested double-layer elliptical tubes in the y-axis direction. The optimized structure shows a polarization loss ratio of greater than 100 in the range of 0.98–1.02 THz in addition to propagation losses of 0.94 dB/m and 7.43 × 10−4 dB/m at 1 THz for XPFM and YPFM, respectively. A polarization loss ratio of 1,276 is achieved and the polarization loss ratio is 6,321 at 0.98 THz. Our results show that the NCF polarization filter delivers better performance than recently reported filters in the terahertz band and the results reveal a new strategy to design high-performance polarization filters.

Real-Time Estimation of Tree Position, Tree Height, and Tree Diameter at Breast Height Point, Using Smartphones Based on Monocular SLAM

Precisely estimating the position, diameter at breast height (DBH), and height of trees is essential in forest resource inventory. Augmented reality (AR)-based devices help overcome the issue of inconsistent global point cloud data under thick forest canopies with insufficient Global Navigation Satellite System (GNSS) coverage. Although monocular simultaneous localization and mapping (SLAM) is one of the current mainstream systems, there is still no monocular SLAM solution for forest resource inventories, particularly for the precise measurement of inclined trees. We developed a forest plot survey system based on monocular SLAM that utilizes array cameras and Inertial Measurement Unit (IMU) sensors provided by smartphones, combined with augmented reality technology, to achieve a real-time estimation of the position, DBH, and height of trees within forest plots. Our results from the tested plots showed that the tree position estimation is unbiased, with an RMSE of 0.12 m and 0.11 m in the x-axis and y-axis directions, respectively; the DBH estimation bias is −0.17 cm (−0.65%), with an RMSE of 0.83 cm (3.59%), while the height estimation bias is −0.1 m (−0.95%), with an RMSE of 0.99 m (5.38%). This study will be useful in designing an algorithm to estimate the DBH and position of inclined trees using point clouds constrained by sectional planes at the breast height of the trunk, developing an algorithm to estimate the height of inclined trees utilizing the relationship between rays and plane positions, and providing observers with visual measurement results using augmented reality technology, allowing them to judge the accuracy of the estimates intuitively. Clearly, this system has significant potential applications in forest resource management and ecological research.

Thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load

Considering the importance of understanding the propagation of transient waves in the piezomagnetic solids, the thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load is investigated analytically in this paper. Using one-sided, two-sided Laplace transformation and Cagniard–de Hoop (CH) technique, an efficient and accurate analytical derivation for the solution of the anti-plane displacement, shear stress, magnetic potential, and induction in Laplace domain is presented. The study shows that the thermal stresses developed in x-axis and y-axis directions have significant influence on the transient response of the half-space. The magnetic induction B x increases obviously when the thermal stress is applied in x-axis direction, while it decreases when the thermal stress is applied in y-axis direction. Approaching time of magnetic induction B x and B y will become longer with higher thermal stress in x-axis direction. With the growth of the thermal stress in x-direction, contribution from the electromagnetic–elastic head (EH) wave increases, while the contribution from the shear elastic (SE) wave and the static value of shear stress decrease.

Research on Delamination Damage Localization of Carbon Fiber-Reinforced Polymer Curved Plate Using Lamb Wave

Carbon fiber-reinforced polymers (CFRPs) are extensively employed in the aerospace industry due to their excellent properties. Delamination damage occurring at critical locations in CFRPs can seriously reduce the safety of in-service components. The detection and localization of delamination damage using Lamb waves hold significant potential for widespread application in non-destructive testing. However, the choice of damage localization algorithm may produce different delamination damage localization results. This research presented an IRAPID (improved reconstruction algorithm for probabilistic inspection of defects) method derived from the RAPID (reconstruction algorithm for probabilistic inspection of defects) method, aiming to improve the accuracy and reliability of delamination damage localization. Three CFRP curved plates, including a healthy curved plate and two curved plates with delamination damage sizes of Φ20 mm and Φ40 mm, were prepared in the experiment. The detection experiment of the CFRP curved plate using lead zirconate titanate (PZT) as a transducer to excite and receive Lamb waves was conducted, and the influence of excitation signal frequency on the performance of the proposed method was discussed. Under the condition of an excitation signal frequency of 220~320 kHz and a step size of 10 kHz, the accuracy of the delamination damage localization method proposed in this paper was compared with that of existing methods. The experimental results indicate that the IRAPID algorithm exhibits good stability in the localization of delamination damage across the range of frequency variations considered. The localization error of the IRAPID algorithm for delamination damage is significantly lower than that of the DaS (delay-and-sum) algorithm and the RAPID algorithm. As the size of the delamination damage increases, so does the localization error. The accuracy of delamination damage localization is lower in the X-axis direction than in the Y-axis direction. By averaging the localization results across various frequencies, we can mitigate the potential localization errors associated with single-frequency detection to a certain extent. For the localization of delamination damage, Lamb waves at multiple frequencies can be employed for detection, and the detection results at each frequency are averaged to enhance the reliability of localization.

The transport of self-propelled ellipsoidal particles confined in 2D smooth corrugated channel

Directed transport of self-propelled ellipsoidal particles confined in a smooth corrugated channel with asymmetric potential and Gaussian colored noise is investigated. Effects of the channel, potential and colored noise on the system are discussed. Large noise intensity in the x-axis direction inhibits the transport in [Formula: see text] and [Formula: see text] directions. The directed transport speed [Formula: see text] has a maximum with increasing noise intensity in the y-axis direction. Proper size of the bottleneck is good for the directed transport of the ellipsoidal particles, but large or small size of bottleneck inhibits this directed transport. The transport reverse phenomenon appears with increasing load and self-propelled speed. Confined spherical particle is easier to produce directed transport than confined needlelike ellipsoid particle.

Comprehensive Analysis of Connectivity and Permeability of a Pore-Fracture Structure in Low Permeability Seam of Huainan-Huaibei Coalfield.

The connectivity and permeability of the coal seam pore structures control the occurrence and migration of coalbed methane. Coal samples were used from Huainan-Huaibei to reconstruct three-dimensional models of the pores and an equivalent pore network model, Statistical pore structure characteristic parameters. The pore structure of the coal reservoir was analyzed from the direction of multidimensional and multiangle. It shows that based on quantitative analysis, the representative Elementary volume of 500 × 500 × 500 was the most suitable experimental volume. The Y-axis direction of the Renlou sample had poor pore connectivity compared to that of other samples. Large volume connected pores dominated their pore systems. In terms of coal sample pore connectivity, the coal samples from the Liuzhuang and Qidong regions had pore connectivity better than those from the other regions. The pore connectivity of the Liuzhuang coal samples was the best. In terms of coal permeability, the Liuzhuang sample had better permeability than the other three samples, and the permeability was the best in the Y-axis direction. For all the combinations of the different types of throats, the shorter the throat, the greater the equivalent radius and the better the permeability. Conversely, the worse the permeability. During gas injection production, the closer the gas injection area was to the gas injection well, the poorer the connectivity and the lower the permeability over time. Near the production area, where the CO2 did not reach the production area, the fracture porosity and effective connected porosity of the coal reservoir increased over time. When CO2 reached the production area, the change in its connected pore structure was consistent with the change in the connected pores in the gas injection area. With this study, the coal seam pore structure on a microscale was characterized. A comprehensive analysis of the coal reservoir pore connectivity and permeability was completed. The study results are significant for the exploration and development of coalbed methane in the Huainan-Huaibei coalfield.

Evaluation of Core Stability and Foot Kinematics of Taekwondo Athletes

To score in taekwondo competition requires faster kicking. Among the factors that influence kicking velocity, core stability is important, but the relationship between core stability and kicking velocity in taekwondo is unclear. The aim of this study was to investigate the association between core stability and foot segmental COM velocity at the moment of kick. A total of 13 taekwondo instructors (gender: male, height: 172.6±7.3 cm, weight: 64.3±11.78 kg, age: 29±4 years) participated in this study. The center of mass velocity of the left foot segment at the moment of the kick and the level of core stability was measured using the Sahrmann core stability test. During the Naraechagi, the velocity of the foot segment COM relative to the laboratory origin at the moment of the aerial phase kick was positively correlated in the forward and backward directions X-axis. Moderate correlation in the left and right direction Z-axis. Very strong correlation in the up and down direction Y-axis. Through the current experiment, we found a strong correlation between core stability and kicking speed in the forward and backward and up and down directions. Therefore, we believe that adding core stability training to taekwondo training has the potential to increase kicking speed.

The study on the properties of a metamaterial composed of star-shaped auxetic and curved-beam multi-stable structure

This article presents the design of a new metamaterial with adjustable Poisson’s ratio and multi-stability, which combines two common metamaterial structures: star-shaped auxetic and multi-stability. The range of negative Poisson’s ratio variation for the unit structure is 0.2433. The negative Poisson’s ratio shows an increasing trend followed by a decrease with the increase in compression displacement. The peak compression displacement is 12 mm, and the peak negative Poisson’s ratio is −0.1499. Simultaneously, the structure exhibits good shape memory properties, with a shape memory recovery ratio of R rx = 94.18% in the y-axis direction and R ry = 91.20% in the x-axis direction. The shape memory recovery time is 35.10 s. The combination of experimental testing and finite element analysis was employed to verify the functionality of the adjustable Poisson’s ratio in the structure. Special attention was given to investigating the structural parameters such as the type of curved-beam, the angle of the star-shaped structure, the width of the star-shaped structure, and the connection method for their effects on the shape memory effect and the range, peak value, and peak compression displacement of the negative Poisson’s ratio in the unit structure. Based on the characteristics of the novel metamaterial, including a significant increase in stiffness upon compression and controllable deformation sequence, it can be used as a buffering device in protective engineering and civil engineering applications.