Maximum Head Research Articles

Associations Between Instrumented Mouthguard-Measured Head Acceleration Events and Post-Match Biomarkers of Astroglial and Axonal Injury in MaleAmateur Australian Football Players.

Advances in instrumented mouthguards (iMGs) allow for accurate quantification of single high-acceleration head impacts and cumulative head acceleration exposure in collision sports. However, relationships between these measures and risk of brain cell injury remain unclear. The purpose of this study was to quantify measures of non-concussive head impact exposure and assess their association with blood glial fibrillary acidic protein (GFAP), neurofilament light (NfL) and phosphorylated-tau-181 (p-tau-181) levels in male Australian football players. A total of 31 athletes underwent in-season (24h post-match) and post-season (> 5weeks) blood collections and/or wore HITIQ Nexus A9 iMGs measuring peak linear (PLA) and rotational (PRA) acceleration. Match footage was used to verify and code impacts. Blood GFAP, NfL, and p-tau-181 were quantified using Simoa and natural log transformed for analysis. Associations between post-match biomarkers and within match maximum single impact and cumulative PLA/PRA were assessed with linear mixed models. In-season versus post-season elevations were found for GFAP (mean difference 0.14, 95% CI 0.01-0.26, p = 0.033), NfL (mean difference = 0.21, 95% CI 0.09-0.32, p = 0.001) and p-tau-181 (mean difference = 0.49, 95% CI 0.33-0.65, p < 0.001). Post-match GFAP was associated with maximum single impact PLA (B = 0.003, 95% CI 0.0002-0.005, p = 0.036), cumulative PLA (B = 0.001, 95% CI 0.0002-0.002, p = 0.017), cumulativePRA (B = 0.01, 95% CI 0.002-0.02, p = 0.014), and impact number (B = 0.03, 95% CI 0.003-0.05, p = 0.029) within a single match. Change in NfL levels between two-matches correlated with cumulative PLA (r = 0.80, 95% CI 0.38-0.95, p = 0.005), PRA (r = 0.71, 95% CI 0.19-0.92, p = 0.019) and impact number (r = 0.63, 95% CI 0.05-0.89, p = 0.038). Maximum and cumulative head accelerations in Australian football, measured by iMGs, were associated with elevated blood biomarkers of brain injury, highlighting the potential of both technologies for head impact management in collision sports.

Sex and stature estimations from dry femurs of Northeastern Thais: Using a logistic and linear regression approach

BackgroundSex determination and stature estimation from skeletal remains are still crucial components in creating biological profiles in forensic anthropology. The femur is particularly valuable due to its high sexual dimorphism and correlation with stature. This study aimed to develop sex estimation models and stature reconstruction equations using femoral measurements in a Northeastern Thai population. Materials and methodThe 400 dry femora were measured for its six parameters including femur maximum length (FL), femoral shaft length (FSL), femur epicondylar breadth (FEB), femur maximum head diameter (FHD), femur midshaft circumference (FMC) and femur weight (FW). Then all parameters were analyzed by using logistic regression for sex estimation and linear regression for stature reconstruction. ResultsResults showed significant sexual dimorphism across all measured parameters, with FHD being the best predictor of sex (correction rate, 88.5 %). The optimized multivariate model achieved the highest accuracy (91.0 %). For stature estimation, sex-specific equations demonstrated superior accuracy compared to combined-sex models. The FL and FSL showed the strongest correlations with stature. ConclusionThis study demonstrated the importance of population-specific standards in forensic anthropology of the femur's reliability as a valuable tool for both sex determination and stature estimation. These results contribute significantly to forensic practice in Thailand, enhancing the accuracy of biological profile reconstruction in medicolegal investigations.

Sex estimation by discriminant function analysis of long bones in prehistoric Southeast Asian populations

AbstractBiological sex estimation is an integral part of reconstructing the biological profile of an individual in forensic anthropological and bioarchaeological contexts. Formulating population specific discriminant function equations for metric variables is vital for reconstructing biological sex of fragmentary skeletal remains. This study aimed to develop multivariable and univariable sectioning point sex estimation equations from long bones of prehistoric Thailand and Cambodia people dated from 4700 to 1450 BP. A total of 481 individuals (236 females and 245 males) with 997 long bone measurements were analyzed. Discriminant function analysis was used to analyze sexually dimorphic measurements from long bones of humeri (177 females and 183 males), femora (169 females and 178 males), and tibiae (139 females and 151 males). Stepwise and direct multivariable functions offered the highest accuracies of 97.3% for humeri, 97% for femora, and 96.7% for tibiae. Univariable functions indicated that the recommended measurements for use in sex estimations with high cross‐validation accuracies are the humeral epicondylar breadth (89.1%), femoral maximum head diameter (87.1%), and tibial midshaft circumference (88.3%). These equations are applicable for use in sex estimation for the specific prehistoric Southeast Asian populations to improve our understanding of the prehistoric demography. Further evaluation and validation of the equations are required to test whether these equations can also be applied to estimate biological sex of contemporary Southeast Asian populations.

Responses of Vehicular Occupants During Emergency Braking and Aggressive Lane-Change Maneuvers.

To validate active human body models for investigating occupant safety in autonomous cars, it is crucial to comprehend the responses of vehicle occupants during evasive maneuvers. This study sought to quantify the behavior of midsize male and small female passenger seat occupants in both upright and reclined postures during three types of vehicle maneuvers. Volunteer tests were conducted using a minivan, where vehicle kinematics were measured with a DGPS sensor and occupant kinematics were captured with a stereo-vision motion capture system. Seatbelt loads, belt pull-out, and footrest reaction forces were also documented. The interior of the vehicle was 3D-scanned for modeling purposes. Results indicated that seatback angles significantly affected occupant kinematics, with small female volunteers displaying reduced head and torso movements, except during emergency braking with a upright posture seatback. Lane-change maneuvers revealed that maximum lateral head excursions varied depending on the maneuver's direction. The study concluded that seatback angles were crucial in determining the extent of occupant movement, with notable variations in head and torso excursions observed. The collected data assist in understanding occupant behavior during evasive maneuvers and contribute to the validation of human body models, offering essential insights for enhancing safety systems in autonomous vehicles.

Impact of Stage-Specific Irrigation on the Growth and Yield of Wheat

Stage-specific irrigation is essential for ensuring optimal water use at critical growth stages in wheat (Triticum aestivum), leading to increased yield and improved grain quality. Therefore, determining an appropriate irrigation schedule for wheat is crucial for enhancing productivity. Keeping this view in mind, an experiment was conducted at the farmer’s fields of Dinajpur Sadar Upazila, Dinajpur, Bangladesh from November 2020 to April 2021, aimed to evaluate the impact of irrigation schedules on the growth and yield of wheat (BARI Gom-33). A randomized complete block design (RCBD) with seven treatments and three replications was implemented. Treatments included varying irrigation timings: T0 (no irrigation), T1 (one irrigation at maximum tillering), T2 (one irrigation at booting), T3 (one irrigation at heading), T4 (two irrigations at maximum tillering and heading), T5 (milking dough), and T6(two irrigations at booting and milking dough). Key metrics assessed included plant height, leaf count, tiller number, dry matter, growth stages, grain number, thousand grain weight, and overall yield at different days’ intervals. Results indicated that irrigated treatments (T1-T6) significantly improved the parameters for growth and yield compared to the control (T0). Notably, T4, with two irrigations, yielded the highest grain production at 5.20 t/ha, followed closely by T6. These findings highlight the significance of proper irrigation scheduling for optimizing wheat yield, indicating that applying two irrigations at the maximum tillering and heading stages can significantly enhance agricultural productivity.

Hydrodynamic Characteristics of Preloading Spiral Case and Concrete in Turbine Mode with Emphasis on Preloading Clearance

A pump-turbine may generate high-amplitude hydraulic excitations during operation, wherein the flow-induced response of the spiral case and concrete is a key factor affecting the stable and safe operation of the unit. The preloading spiral case can enhance the combined bearing capacity of the entire structure, yet there is still limited research on the impact of the preloading pressure on the hydrodynamic response. In this study, the pressure fluctuation characteristics and dynamic behaviors of preloading a steel spiral case and concrete under different preloading pressures at rated operating conditions are analyzed based on fluid–structure interaction theory and contact model. The results show that the dominant frequency of pressure fluctuations in the spiral case is 15 fn, which is influenced by the rotor–stator interaction with a runner rotation of short and long blades. Under preloading pressures of 0.5, 0.7, and 1 times the maximum static head, higher preloading pressures reduce the contact regions, leading to uneven deformation and stress distributions with a near-positive linear correlation. The maximum deformation of the PSSC can reach 2.6 mm, and the stress is within the allowable range. The preloading pressure has little effect on the dominant frequency of the dynamic behaviors in the spiral case (15 fn), but both the maximum and amplitudes of deformation and stress increase with higher preloading pressure. The high-amplitude regions of deformation and stress along the axial direction are located near the nose vane, with maximum values of 0.003 mm and 0.082 MPa, respectively. The contact of concrete is at risk of stress concentrations and cracking under high preloading pressure. The results can provide references for optimizing the structural design and the selection of preloading pressure, which improves operation reliability.

Design and construction of GaInSn experimental facility for studies of mixed-convection MHD flows

A multifunctional liquid metal loop named MaTHE-XJTU (Magneto-Thermo-Hydrodynamic Experiments-Xi'an Jiaotong University) that utilizes eutectic alloy GaInSn as a working fluid has been designed and constructed. The function of the MaTHE-XJTU facility is to study the magnetohydrodynamic (MHD) flow and mixed convection characteristics under the coupling effect. The main operating parameters of the loop are: the maximum magnetic field intensity is 3T, the effective magnetic field region is 300 mm × 800 mm × 1000 mm, the maximum flow rate of electromagnetic pump (EM pump) is 8 m3/h, the maximum pressure head of EM pump is 0.5 MPa. The paper describes the major components and basic operation procedures of the loop, the related flow diagnostics method, and near-future experiments. This loop could provide a high-parameter experimental platform (Ha∼104, Gr∼109, Re∼104) for investigations that improve the present understanding of magnetohydrodynamic and heat transfer performance in liquid metal blankets.

A cavalpulmonary assist device utilising impedance pumping enhanced by peristaltic effect.

Fontan procedure, the standard surgical palliation to treat children with single ventricular defects, causes systemic complications over years due to lack of pumping at cavopulmonary junction. A device developed specifically for cavopulmonary support is thus considered, while current commercial ventricular assist devices (VAD) induce high shear rates to blood, and have issues with paediatric suitability. To demonstrate the feasibility of a small, valveless, non-invasive to blood and pulsatile rotary pump, which integrates impedance and peristaltic effects. A prototype pump was designed and fabricated in-house without any effort to optimise its specification. It was then tested in vitro, in terms of effect of pumping frequency, background pressure differences and pump size on output performance. Net flow rate (NFR) and maximum pressure head delivery are both reasonably linearly dependent on pumping frequency within normal physiological range. Positive linearity is also observed between NFR and the extent of asymmetric pumping. The device regulates NFR in favourable pressure head difference and overcomes significant adverse pressure head difference. Additionally, performance is shown to be insensitive to device size. The feasibility of the novel rotary pump integrating impedance and peristaltic effects is demonstrated to perform in normal physiological conditions without any optimisation effort. It provides promising results for possible future paediatric cavopulmonary support and warrants further investigation of miniaturisation and possible haemolysis.

Heading estimation algorithm for pedestrian navigation using a dual-foot-mounted IMU with a millimetre wave radar

Heading estimation is crucial in pedestrian navigation systems based on IMUs, but accuracy often suffers degradation due to error accumulation. This study introduces a novel heading estimation algorithm using dual-foot-mounted IMUs with a millimeter-wave radar to enhance accuracy. The algorithm includes a Single-foot Multiconditional Constraint Algorithm (SMC-A), adaptive step length constraint, and bipedal maximum heading difference constraint. Firstly, the SMC-A utilizes zero speed correction, zero angular rate updates, and self-observing heading error corrections through extended Kalman filtering. Then, the adaptive step length constraint limits pedestrian motion, and the bipedal constraint corrects heading errors. Finally, the Bipedal Multiconditional Constraint Algorithm (BMC-A) incorporates millimeter-wave radar measurements of foot distance. Experiments show heading deviations of 3.74° and 4.03° are obtained for the left and right feet over a 30-minute, 1.45 km trial. The new algorithm improves heading accuracy by 68.19 % and 70.67 % for the left and right feet, respectively, compared to traditional SMC-A.

Relationships Between Force-Time Curve Variables and Tennis Serve Performance in Competitive Tennis Players.

Fourel, L, Touzard, P, Fadier, M, Arles, L, Deghaies, K, Ozan, S, and Martin, C. Relationships between force-time curve variables and tennis serve performance in competitive tennis players. J Strength Cond Res 38(9): 1667-1674, 2024-Practitioners consider the role of the legs in the game of tennis as fundamental to achieve high performance. But, the exact link between leg actions and high-speed and accurate serves still lacks understanding. Here, we investigate the correlation between force-time curve variables during serve leg drive and serve performance indicators. Thirty-six competitive players performed fast serves, on 2 force plates, to measure ground reaction forces (GRF). Correlation coefficients describe the relationships between maximal racket head velocity, impact height, and force-time curve variables. Among all the variables tested, the elapsed time between the instants of maximal vertical and maximal anteroposterior GRF ( r = -0.519, p < 0.001) and the elapsed time between the instant of maximal anteroposterior GRF and ball impact ( r = -0.522, p < 0.001) are the best predictors of maximal racket velocity. Maximal racket head velocity did not significantly correlate with the mean or maximal vertical GRF or with the mean or maximum rate of vertical force development. The best predictor for impact height is the relative net vertical impulse during the concentric phase ( r = 0.772, p < 0.001). This work contributes to a better understanding of the mechanical demands of tennis serve motion and gives guidelines to improve players preparation and performance. Trainers should encourage their players to better synchronize their upward and forward pushing action during the serve to increase maximal racket head velocity. Players should also aim to improve their relative net vertical impulse to increase impact height through strength training and technical instructions.

Controlling Seepage Flow Beneath Hydraulic Structures: Effects of Floor Openings and Sheet Pile Wall Cracks

Using one opening (filter) within the floors of hydraulic structures is a known technique to relieve the seepage effects on their floors. In this study, a new method to control seepage flow by using two identical filters instead of one was tackled numerically. A comparative analysis of using one versus two filters was conducted for different thicknesses of the permeable stratum, apron size (b), filter length, and sheet pile wall depths. Results indicate that two filters are considerably more effective than using one where the overall uplift force, the maximum potential head, and the hydraulic exit gradient downstream of the floor are reduced to 42–56%, 42–51%, and 66–76%, respectively, compared to one filter, while slightly increasing seepage flow by 1–7%. Many reasons can lead to horizontal openings (cracks) appearing along the sheet pile walls beneath hydraulic structures. The current study tackled their effects on seepage flow for the first time and examined their impact on the floor. A crack in the upstream sheet pile wall can increase total uplift forces by up to 40%, while a crack in the downstream sheet pile wall can increase the hydraulic exit gradient by up to 230%

Effect of additively manufactured polymeric inserts on impact response of construction safety helmets

Purpose Struck-by accidents (i.e. being hit by a falling object) are a leading cause of traumatic brain injuries in the construction industry. Despite the critical role of hard hats in minimizing such injuries, their overall design has not appreciably changed in decades. Therefore, this study aims to explore the potential benefits of modifying commercially available hard hat designs by incorporating a compliant cantilever and a sacrificial, energy-absorbing structure to enhance their protective capabilities against impacts. Design/methodology/approach This study involved conducting experimental impact tests to obtain the head acceleration attenuation using hard hats with a variety of compliant cantilever lattice insert designs. These lattice inserts were additively manufactured using three polymeric materials, including polylactide (PLA), acrylonitrile butadiene styrene, high-impact polystyrene and three porosity levels. A Hybrid III head/neck assembly was fitted with each hard hat design, and experimental drop tests were conducted using a 1.8-kg steel impactor dropped from 1.83 m. The maximum acceleration and head injury criterion (HIC) values were obtained for each test. Findings Analysis of variance revealed that HIC was significantly reduced for all lattices with 56% porosity (p &lt; 0.023) compared to the control (unmodified) hard hat. The most effective insert was found to be a PLA insert with 56% porosity, which reduced the HIC value by 38% compared to the control (unmodified) hard hat, with a statistically significant p-value of 0.018. Originality/value The data present in this study reveals that simple and inexpensive modifications can be made to existing hard hat designs to reduce injury risk from overhead impacts.

Research on the Flow Characteristics in the Gap of a Variable-Speed Pump-Turbine in Pump Mode

A variable-speed pump-turbine is the core component of a hydraulic storage and energy generation station. When the pump-turbine operates at a constant speed, its response to the power grid frequency is poor. In order to improve the hydraulic efficiency of the pumped storage unit, variable-speed units are used. However, there has been no numerical study on the effect of the rotational flow characteristics within the gap of a variable-speed pump-turbine. This paper calculates the flow characteristics within the gap of a variable-speed pump-turbine under three typical pump modes (maximum head minimum flow condition, minimum head maximum flow condition, and maximum speed condition). The research results indicate that the rotational speed significantly affects the pressure distribution, velocity distribution, and turbulent kinetic energy distribution within the crown and band gaps. The higher the speed, the larger the area of the high-pressure region before the runner inlet compared to other operating conditions, and similarly, the low-pressure area after the runner outlet is also larger than in other operating conditions. The change in speed mainly affects the internal flow field of the crown gap, with the most noticeable changes occurring in the pressure and flow velocity at the inlet and outlet of the crown gap. There is a clear trend of pressure drop and velocity increase within the gap as the speed increases. However, with the increase in speed, the pressure distribution and flow velocity within the band gap remain almost the same. In addition to speed changes, it is observed that the pressure within the gap and the flow velocity within the passages are also related to the head, especially in the condition of maximum head, where this relationship becomes more noticeable.

Evaluation of a novel head and neck restraint for harness-restrained children

Motor Vehicle Crashes (MVCs) are a common source of neck injury and, although rare, catastrophic neck injury occurs in restrained children up to age 10 years old. Recently, a head/neck support (HNS) that cradles the head during sleep was developed. The objective of this study was to determine if the HNS improves injury criteria measured on anthropomorphic test devices (ATDs) in front facing 5-point harness child restraint systems (FFCRS). Nineteen matched pair frontal impact sled tests were conducted with ATDs representing the 12 month old, or 3 or 6 year old child in FFCRS. HNS reduced HIC36 by median 22.2%, maximum resultant head acceleration (3ms clip) by 16.2%, head excursion by 8.2%, and neck tension by 12.2%. Providing supplemental restraint directly to the head has the potential to improve injury outcomes while not adding to harm during common misuse scenarios, but further research is needed to determine if these benefits persist in real-world crashes.

Gender differences in neck muscle activity during near-maximum forward head flexion while using smartphones with varied postures

Women frequently express heightened neck discomfort even though they exhibit smaller neck flexion (NF) during smartphone use. Differences in natural posture while using smartphones may result in varying muscle activation patterns between genders. However, no study focused on this issue. This study investigated the influence of gender on neck muscle activity and NF when using smartphones, ranging from slight (20°) to nearly maximal forward head flexion, across different postures. We analyzed smartphone usage patterns in 16 men and 16 women and examined these behaviors across different scenarios: standing, supported sitting, and unsupported sitting, at 20°, 30°, 40°, and the maximum head angles. During data collection, muscle activity was measured, expressed as a percentage of the maximum voluntary contraction (%MVC), in the cervical erector spinae (CES) and upper trapezius (UTZ), along with NF. Results show significant influences of gender, head angle, and posture on all measures, with notable interactions among these variables. Women displayed higher muscle activities in CES and UTZ, yet exhibited lesser NF, while using smartphones in both standing (12.3%MVC, 10.7% MVC, and 69.0°, respectively) and unsupported sitting (10.8%MVC, 12.3%MVC, and 71.8°, respectively) compared to men (standing: 9.5%MVC, 8.8%MVC, and 76.1°; unsupported sitting: 9.7%MVC, 10.8%MVC, and 76.1°). This study provides a potential rationale for gender-related disparities in injury outcomes, emphasizing that women experience higher neck and shoulder discomfort level, despite their smaller NF during smartphone use, as found in previous research. Additionally, the cervical flexion-relaxation phenomenon may occur when the head angle exceeded 40°. The near-maximum head angle during smartphone use might induce the cervical flexion-relaxation phenomenon, potentially aggravating neck issues. We recommend limiting smartphone usage postures that exceed the near-maximum head angle, as they are commonly adopted by individuals in the daily smartphone activities.

Optimisation of an On-grid Hybrid Energy System: A Case Study of the Main Campus of the University of Abuja, Nigeria

The challenge of meeting the energy demands of institutions and organisations in an economically viable and environmentally friendly manner is becoming more and more complex especially in developing countries like Nigeria. This work presents a resilient hybrid renewable energy system to supply the electric power requirement of the main campus of the University of Abuja, Nigeria, estimated as 900 kW at a consumption rate of 6300 kWh/day. HOMER software was used as the modelling tool for simulations, optimizations, and sensitivity analyses carried out to explore the feasibility of utilizing Abuja’s (MSW) in hybrid with the mini hydro power potential of River Wuye and solar PV resources to meet the load demand of the campus. The hybrid plant has the following component specifications:hydro resourcenominal flow rate is 14.5 m3/s; maximum head is 10 m and potential capacity is 885 kW;MSW plant specifications were determined to be 500 kW capacity, waste treatment of 2.3 ton/day; lower calorific value for MSW of 15.84 MJ/kg with the solar PV component having a capacity of 500 kW. Total installation cost for the hybrid plant for the 2 MW hybrid plant was determined to be ₦5.44 billion (US$7.225 million) with annual energy generation calculated to be 799,000 kWh/yr. The net present cost for the simulated system was found to be ₦ 9.37 billion ($12,486,120) with the corresponding LCOE being ₦55.2/kWh ($0.0736/kWh). The carbon emission was estimated to be 7.33 g per day which approximates to a net zero emission, demonstrating the environmental friendliness of renewable energy sources utilised. Sensitivity analysis performed on the system using project life span, inflation rate, solar irradiance, MSW’s lower heating value (LHV), capacity shortage and the annual average volumetric flow rate of River Wuye showed that the net present cost increased with increasing plant life while the levelized cost of energy reduces with increasing life from ₦55.02/kWh for plant life of 25 years to ₦43.73/kWh for 30 years.

Study on erosion characteristics of turbine in sediment-laden river

Abstract Sediment erosion of hydro turbines is prevalent and serious in the mountain river region. The effect of operating head and particle diameter on sediment erosion was investigated in this paper. A Eulerian-Lagrangian approach was applied to numerically simulate the solid-liquid flow in a Francis turbine under the minimum, design and maximum heads. Five typical diameters (0.1, 0.3, 0.5, 0.7, 0.9 mm) were firstly determined based on field measurements at a hydropower station. After tracking the trajectories of sediment particles, McLaury model was selected to predict the erosion rate. The results show that sediment erosion regions of runner blades are similar under different operating heads, while the sediment erosion rates amplify significantly with the increase of operating heads. The erosion rate of blade suction side is significantly higher than that of pressure side because of the effect of inter-blade vortices between runner blades. Sediment diameters also play an important role in accelerating erosion rate, which indicate that setting up sedimentation tanks to settle large-size sediment particles is a powerful method to alleviate sediment erosion. This study can provide a reference for erosion estimation and operational maintenance of hydro turbines in mountain river region.

The Pump-turbine Hydraulic Performance Research, Model Test and Operation in Yangjiang Pumped Storage Power Station

Abstract The Yangjiang Pumped Storage Power Station (PSP) is the largest unit rated output PSP that has been built in China, with a maximum water head of nearly 700m and a unit capacity of 400MW. The ultra high water head and its large range of the PSP means a significant difficulty during the dydraulic research and development of the pump-turbine. In this paper, it is introduced on model test and results in the EPFL and IWHR. It is studied on energy performance, cavitation, pressure pulsation and “S” characteristic of pump-turbine with splitter blade. The unit data analys after put into operaton indicat highly hydraulic stability and relative tiny vibration, which just verify the model test. As the model and prototype results show that Yangjiang pump-turbine is outstanding in various indexes and quite excellent in comprehensive hydaulic performance.

Strength Evaluation of the Flow Passage Stationary Structures of a Large Francis Turbine Unit

Abstract The multifield design and multifield coupling performance of the Francis turbine unit is a topic that needs to be studied deeply. In this paper, the strength evaluation of the stationary structures of the flow passage of a large Francis turbine unit under extreme conditions has been performed based on the fluid-structure coupling theory. The calculated stationary structures include the spiral casing, bottom ring, and head cover. The pressure load applied on the structures is 1.5 times the maximum head of the unit. The results show that there is stress concentration in the spiral casing, and the weld length with equivalent stress greater than 345 MPa reaches 800 mm; the maximum stress at the rib plate of the head cover reaches 357 MPa, which is greater than the yield limit 345MPa. Based on the evaluation results, the local and overall defects of the unit design can be found. The suggested strength evaluation methodology can provide references for the optimization of the unit and a theoretical basis for the operation of the unit.

Research on autonomous navigation system of greenhouse electric crawler tractor based on LiDAR.

The application of autonomous navigation technology of electric crawler tractors is an important link in the development of intelligent greenhouses. Aiming at the characteristics of enclosed and narrow space and uneven ground potholes in greenhouse planting, to improve the intelligence level of greenhouse electric crawler tractors, this paper develops a navigation system of electric crawler tractors for the greenhouse planting environment based on LiDAR technology. The navigation hardware system consists of five modules: the information perception module, the control module, the communication module, the motion module, and the power module. The software system is composed of three layers: the application layer, the data processing layer, and the execution layer. The developed navigation system uses LiDAR, Inertial Measurement Unit (IMU) and wheel speed sensor to sense the greenhouse environment and the crawler tractor's information, employs the Gmapping algorithm to build the greenhouse environment map, and utilizes the adaptive Monte Carlo positioning algorithm for positioning. The simulation test of different global path planning algorithms in Matlab shows that the A* algorithm obtains the optimal overall global path. In the scene of map 5, the path planned by the A* algorithm is the most significant, and the number of inflection points is reduced by 40.00% and 87.50%, respectively; meanwhile, the path length is the same as that of the Dijkstra algorithm, but the runtime is reduced by 68.87% and 81.49%, respectively; compared with the RRT algorithm, the path length is reduced by 7.27%. Therefore, the A* algorithm and the Dynamic Window Approach (DWA) method are used for tractor navigation and obstacle avoidance, which ensures global path optimality while also achieving effective local path planning for obstacle avoidance. The test results suggest that the maximum lateral deviation of the built map is 6cm, and the maximum longitudinal deviation is 16cm, which meets the requirement of map accuracy. Additionally, the results of the navigation accuracy test indicate that the maximum lateral deviation of navigation is less than 13cm, the average lateral deviation is less than 7cm, and the standard lateral deviation is less than 8cm. The maximum heading deviation is less than 14°, the average heading deviation is less than 7°, and the standard deviation is less than 8°. These results show that the developed navigation system meets the navigation accuracy requirements of electric crawler tractors in the greenhouse environment.