Biomechanical Response of the Root System in Tomato Seedlings under Wind Disturbance

Wind disturbance as a green method can effectively prevent the overgrowth of tomato seedlings,and its mechanism may be related to root system mechanics.This study characterized the biophysical mechanical properties of taproot and lateral roots of tomato seedlings at five seedling ages and seedling substrates with three different moisture content.The corresponding root system-substrate finite element(FE)model was then developed and validated.The study showed that seedling age significantly affected the biomechanical properties of the taproot and lateral roots of the seedlings and that moisture content significantly affected the biomechanical properties of the seedling substrate(p<0.05).The established FE model was sensitive to wind speed,substrate moisture content,strong seedling index,and seedling age and was robust.The multiple linear regression equations obtained could predict the maximum stress and strain of the root system of tomato seedlings in the wind field.The strong seedling index had the greatest impact on the biomechanical response of the seedling root system during wind disturbance,followed by wind speed.In contrast,seedling age had no significant effect on the biomechanical response of the root system during wind disturbance.In the simulation,no mechanical damage was observed on the tissue of the seedling root system,but there were some strain behaviors.Based on the plant stress resistance,wind disturbance may affect the growth and development of the root system in the later growth stage.In this study,finite element and statistical analysis methods were combined to provide an effective approach for indepth analysis of the biomechanical mechanisms of wind disturbances that inhibit tomato seedlings’growth from the root system’s perspective.

Numerical study on the blocking effect of skin on Flash-Ball Impact and damage assessment

To explore the response law of non-lethal large-size kinetic energy projectiles to blunt attack on skin tissue,and to evaluate the skin injury characteristics of the attacked personnel and the use safety of kinetic energy projectiles.Based on the LS-DYNA simulation software,a three-layer skin simulation model and a Flash-Ball rubber bullet model are established,and the force-time and deformation-time biomechanical corridors of the Flash-Ball rubber bullet impacting human skin tissue are obtained.The corridor curve and the energy transfer and diffusion are analyzed and compared.The safety evaluation of the damage caused by the rubber bullet shooting a human body at different distances is carried out using the empirical formula of the penetration limit.Finally,the safe shooting distance is obtained.The results show that the model used in the simulation has a good correlation with the experimental data,its biomechanical corridor characteristics are different from those of conventional vehicle impact and smallsize projectile response characteristics.The energy transfer and action time of medium and low-speed impact may cause greater damage.The fat layer is the largest energy absorption unit.The minimum safe shooting distance to ensure skin tissue from penetrating damage is 15.8 m,and the limit specific kinetic energy of skin damage is 7.88 J/cm^(2).This study can be extended to the study of biomechanical response law and safety evaluation under the impact of the same type of large kinetic energy projectile,which provides an important theoretical reference for the police to use large kinetic energy projectiles to conduct safe shooting in peacekeeping operations.

Biomedical response of femurs in male Wistar rat in chronic hypergravity environments

Bone is sensitive to mechanical stimulation and plays a loading-bearing role in the human body.However,regulation of bone biomechanical properties in chronic hypergravity environments is still unclear.In this study,male Wistar rats exposed to chronic hypergravity environments(4
g,8
g,10
g,and 20
g)for 4 weeks were set as the hypergravity groups,and rats exposed to the normal gravity as the control group.Morphology parameters and bone remodeling factors were obtained by means of micro-CT,Western blot,and q-PCR.Mechanical properties of femurs were measured utilizing three points bending test and creep test and were fitted into a viscoelastic-viscoplastic constitutive equation.The results indicate osteoporosis occurred in femurs of hypergravity groups.Accordingly,the protein and gene expressions of bone remodeling factors(OPG,RANKL,runx2)in hypergravity groups were significantly different from that in the control group,demonstrating that bone formation level increased and bone resorption level decreased.Meanwhile,mechanical properties of femurs in hypergravity groups showed that Young's modulus of femurs in the 20
g group was significantly higher than that in the control group.The viscoelastic-viscoplastic properties of bone tissue were changed in hypergravity environments.Among them,the 8
g group was closest to the control group in morphology and mechanical properties.To sum up,the biomechanical response regulation of rat femur under 4-20
g chronic hypergravity environments was presented.Hypergravity environments could lead to osteoporosis.The balance between bone formation and bone resorption would be disrupted in hypergravity groups due to bone adaptation.20
g environment has a significant effect on elastic modulus on femurs.Due to the difference in biomechanical response of femurs,the viscoelastic-viscoplastic characteristics of femurs have a nonlinear relationship with hypergravity values.Bone tissue was least affected by 8
g hypergravity in morphology and mechanical properties.

A study on the application of diffuse axonal multi-axis general evaluation for braininjury assessment in small overlap barrier crash test

Purpose:Head injury criterion(HIC)companied by a rotation-based metric was widely believed to behelpful for head injury prediction in road traffic accidents.Recently,the Euro-New Car AssessmentProgram utilized a newly developed metric called diffuse axonal multi-axis general evaluation(DAMAGE)to explain test device for human occupant restraint(THOR)head injury,which demonstratedexcellent ability in capturing concussions and diffuse axonal injuries.However,there is still a lack ofcomprehensive understanding regarding the effectiveness of using DAMAGE for Hybrid III 50thpercentile male dummy(H50th)head injury assessment.The objective of this study is to determinewhether the DAMAGE could capture the risk of H50th brain injury during small overlap barrier tests.Methods:To achieve this objective,a total of 24 vehicle crash loading curves were collected as input datafor the multi-body simulation.Two commercially available mathematical dynamic models,namelyH50th and THOR,were utilized to investigate the differences in head injury response.Subsequently,adecision method known as simple additive weighting was employed to establish a comprehensive braininjury metric by incorporating the weighted HIC and either DAMAGE or brain injury criterion.Furthermore,35 sets of vehicle crash test data were used to analyze these brain injury metrics.Results:The rotational displacement of the THOR head is significantly greater than that of the H50thhead.The maximum linear and rotational head accelerations experienced by H50th and THOR modelswere(544.6±341.7)m/s^(2),(2468.2±1309.4)rad/s^(2) and(715.2±332.8)m/s^(2),(3778.7±1660.6)rad/s^(2),respectively.Under the same loading condition during small overlap barrier(SOB)tests,THOR exhibits ahigher risk of head injury compared to the H50th model.It was observed that the overall head injuryresponse during the small overlap left test condition is greater than that during the small overlap righttest.Additionally,an equation was formulated to establish the necessary relationship between theDAMAGE values of THOR and H50th.Conclusion:If H50th rather than THOR is employed as an evaluation tool in SOB crash tests,newlydesigned vehicles are more likely to achieve superior performance scores.According to the current injurycurve for DAMAGE and brain injury criterion,it is highly recommended that HIC along with DAMAGE wasprioritized for brain injury assessment in SOB tests.