Theoretical Velocity Research Articles

Mathematical model of velocity and distribution law in gas lift reverse circulation well washing flow field for drilling shaft sinking

To reveal the velocity distribution law of a gas lift reverse circulation well washing flow field in drilling shaft sinking, a velocity mathematical model of well washing flow field is established. The theoretical analytical solutions and velocity distribution laws in the drill pipe and bottom hole were provided and validated through numerical simulations and similar model tests. Furthermore, this study explores the impacts of mud circulation, wind pressure, rock debris, and mud properties on the flow field distribution, presenting the sensitivity order of the factors. This study indicated the following findings. (1) The velocity theoretical model of well washing flow field was validated through numerical simulation and similar model tests, and the relative error ranged from 4.2 to 18.5%, demonstrating the high consistency. (2) The rock debris and mud experienced slight and consistent deceleration within the drill pipe. Upon reaching the gas input end, the axial upward return of the multiphase flow resulted in a “jumping” sharp increase. (3) The mud circulation, wind pressure, and void fraction positively correlated with the multiphase fluid velocity in the drill pipe, but negatively correlated with the mud density and slag content. The axial upward velocity of the rock debris decreased with increasing particle size and density. (4) The sensitivity of each factor to the discharge speed of rock debris was summarized as follows: air content > mud circulation > wind pressure > mud density > rock debris density > rock debris particle size > slag content. These findings could offer a theoretical basis for selecting well washing parameters and enhancing drilling and washing efficiency.

Force-velocity-power variables derived from isometric and dynamic testing: metrics reliability and the relationship with jump performance

We investigated the convergent validity and intrasession reliability of force, velocity, and power (FVP) variables and the dynamic strength index (DSI) obtained from isometric midthigh pull (IMTP) and squat jump (SJ) testing. Fifteen male combat sports athletes (27 ± 5 years, 77 ± 9 kg, 1.76 ± 0.1 m, 14 ± 6% body fat) participated in a 2-days study. The first day involved testing familiarization, while the second was dedicated to IMTP and SJ testing. Maximal isometric force (Fiso) was obtained from IMTP, while mean force, mean velocity, jump height, and jump impulse (J) were gathered from SJ. To analyze the FVP, we calculated the linear relationship between force and velocity, which allowed us to obtain the slope of the relationship (SFV), the theoretical velocity at zero force (V0), and the theoretical maximal power (Pmax). DSI was obtained as a ratio from SJ peak force and Fiso. The convergent validity was investigated using Spearman’s ρ coefficients to assess the relationships between jump height and J with Fiso, V0, SFV, Pmax, and DSI. The intrasession reliability was assessed using intraclass correlation coefficients (ICC) and coefficient of variations (CV). All variables demonstrated acceptable reliability scores. ICC ranged from moderate to excellent, and the mean CV was <10%. We found a “very large” correlation between jump J and Pmax, while jump height was not correlated with any variable. In conclusion, the IMTP and SJ combination is a practical way to determine FVP producing capacities that can be reliably measured (intrasession). The Pmax, derived from FVP, was correlated with jump performance, which might evidence the convergent validity of the method.

Single-Ended Surface Acoustic Wave Pressure Resonators

Abstract Surface acoustic wave (SAW) sensors exhibit advantageous attributes for pressure detection, including compact dimensions, cost-effectiveness, facile integration, elevated sensitivity, and a high quality factor (Q value). In this study, the single-ended resonant configuration of SAW pressure sensing element based on ST-X cut quartz was simulated and fabricated. The influence of the interdigitated transducer (IDT) and applied pressure on the resonance frequency of SAW were simulated and analyzed. The designed phase velocity (3159.344 m/s) without IDT is closest to the theoretical phase velocity (3158 m/s) of SAW propagation in the substrate, and the relative error is about 0.043%. The designed phase velocity of SAW dropped to 3149.198 m/s due to the loading of the IDT mass. With an increase in applied pressure from 0 to 350 kPa, the resonance frequency of the SAW decreases from 157.05 to 154.02 MHz, yielding a maximum linear pressure sensitivity of approximately 8.6 kHz/kPa. The measured center frequencies of the fabricated single-ended SAW devices are predominantly clustered around 157 MHz, exhibiting a deviation of 0.46 MHz from the simulated results. The present work establishes a foundation for subsequent experimental investigations into pressure sensing.

The relationship between maximal lactate accumulation rate and sprint performance parameters in male competitive swimmers.

This study aimed to examine the relationship between the maximal lactate accumulation rate (ċLamax) and sprint performance parameters in male competitive swimmers. Seventeen male competitive swimmers volunteered to perform a 20 m maximal front crawl sprint without pushing off the wall from a floating position. ċLamax was determined by the 20-m sprint time and blood lactate measured before and after the 20 m sprint. For the sprint performance parameter, a 50 m time trial with the front crawl swimming stroke was conducted, and the times taken from 0 to 15 m, 15-25 m, 25-35 m, and 35-45 m were analyzed. A semi-tethered swimming test was conducted to investigate the load-velocity profile of each swimmer. From the load-velocity profile, theoretical maximal velocity (V0), maximal load (L0) and relative maximal load (rL0) were examined. The slope of the load-velocity profile was also determined. According to the results, ċLamax correlated with 50 m front crawl performance (r = -.546, p < .05). Moreover, a higher ċLamax was related to faster 0-35 m section time. Furthermore, ċLamax correlated with L0 (r = .837, p < .01), rL0 (r = .820, p < .01), and load-velocity slope (r = .804, p < .01). ċLamax is a good indicator of 50 m front crawl performance in male swimmers, and higher glycolytic power contributes to the faster time at the beginning of the sprint race. ċLamax could also evaluate the ability of a swimmer to apply force to the water during high-intensity swimming.

Submaximal force–velocity relationships during mountain ultramarathon: Data from the field

ABSTRACT This study presents a novel method for evaluating the submaximal velocity-force (V(F)) relationship in mountain ultramarathon races using crowdsourced data from Strava.com. The dataset includes positional data from 408 participants of the 171-km UTMB® 2023 race (9,850-m D+). The race was divided into 100-m segments. The mean net propulsive force and velocity were computed for each segment to describe the submaximal V(F) relationship as a rational function of three parameters. F1: propulsive force at 1 m · s−1; V0: theoretical maximum velocity on flat terrain; C: curvature parameter (the lower C, the more linear the V(F) relationship). The V(F) profile parameters were found to be F1 = 1.80 ± 0.33 N · kg−1, V0 = 2.36 ± 0.42 m · s−1, and C = 0.66 ± 1.81, with good independence between the parameters within a group of homogeneous performance. The best athletes had the highest F1, V0, and C values. V(F) parameters were affected by fatigue during the race, with decreases of 20.9%, 32.0%, and 59.8% between the first and second parts of the race respectively. These findings suggest that the V(F) relationship is an interesting original approach for studying performance and fatigability during mountain ultra-endurance races.

Improving Friction Sensitivity of Molecular Perovskite Energetic Material DAP‐4 by Polymer Binders Coated

AbstractThe high detonation and thermostability of the molecular perovskite energetic material DAP‐4 attracted a lot of interest, but its high friction sensitivity hindered its applicability. It is critical to minimize the friction sensitivity of DAP‐4 for future applications. DAP‐4‐based composites with core‐shell structures coated by polymer binders were devised and manufactured in this study. DAP‐4 was discovered to be polymer binder compatible, and the thermal breakdown temperature remained constant at 380°C. The friction sensitivity of DAP‐4‐based core‐shell composites increased from 36 N (raw DAP‐4) to 60 N (DAP‐4@Estane‐5703, DAP‐4@F2602, and DAP‐4@F2311) when 10% polymer binders were added as shell‐structured layers. Furthermore, their theoretical detonation performance was calculated, and each sample demonstrated superior performance. Among them, the theoretical detonation velocity of DAP‐4@F2602 reached 8081 m/s, and the heat of detonation was 5.118 kJ/kg. This provided proof‐of‐concept work for increasing the mechanical safety of molecular perovskite energetic materials.

Acute Changes in Hamstring Injury Risk Factors After a Session of High-Volume Maximal Sprinting Speed Efforts in Soccer Players.

Maximal sprinting speed (MSS) overexposure is associated with increased risk of injury. This study aimed to describe changes in sprint performance-related factors and hamstring strain injury (HSI) risk factors after a high-volume sprinting session in soccer players. A high-volume sprinting session can induce acute changes in several sprint performance-related factors (sprint time and mechanical properties) and HSI risk factors (posterior chain muscle strength, hamstring range of motion, and dynamic lumbo-pelvic control [LPC], measured as changes in anterior pelvic tilt [APT] during maximal speed sprinting). Prospective observational case series. Level 4. Fifteen active male amateur soccer players participated. Changes in sprint performance-related factors and HSI risk factors were examined for 72 hours after high-volume MSS efforts (H-VMSSE) using a soccer-contextualized multifactorial approach. Muscle damage proxy markers (hamstring perceived soreness and creatine kinase) were also examined. H-VMSSE induced decrements in sprint performance-related factors. Significant reductions in theoretical maximal horizontal velocity (P < 0.01; effect size [ES], -0.71) and performance (P = 0.02; ES, -0.59) were observed for 48 and 72 hours after H-VMSSE. Small but significant reductions in posterior chain muscle force-generating capacity were detected for 48 and 72 hours after H-VMSSE for the nondominant (P < 0.03; ES, -0.60) and dominant (P < 0.04; ES, -0.40) leg. Finally, players exhibited persistent small, albeit nonsignificant (P = 0.06; ES, 0.53), decreases in dynamic LPC (APT increases) for 72 hours after H-VMSSE. H-VMSSE induced declines in both sprint performance-related factors and HSI risk factors. Sprinting can alter a player's anatomic structure by increasing APT during the maximum speed phase of the sprint. A soccer-contextualized multifactorial approach might allow for the regulation of MSS dosage depending on individual HSI risk factor status, thereby serving as a tailored "vaccine" for sprinting needs.

Horizontal and vertical dispersion in a wind-driven oceanic gyre model

This study addresses the horizontal and vertical dispersion of passive tracers in idealized wind-driven subtropical gyres. Synthetic particles within a closed basin are numerically advected to analyze their dispersion under different theoretical velocity fields. Horizontal dispersion simulations incorporate the classic wind-driven Stommel circulation along with (i) surface Ekman drift associated with the Stommel wind field and (ii) inertial effects due to particle size and buoyancy. Results reveal that the Ekman drift inhibits particle dispersion across the entire domain leading to tracer concentration in a quasi-stable distribution skewed toward the western side of the basin. Similar behavior is observed with inertial particles. The equilibrium state is quantified for different diffusivity values, particle sizes, and buoyancies. For vertical dispersion, simulations incorporate the three-dimensional Ekman velocity, which includes a negative vertical component, while ignoring inertial effects. Initially, surface particles accumulate around the gyre center while slowly sinking, but they disperse across the basin once they surpass the Ekman layer and are free from surface effects. Tracers sink more on the western side of the basin, regardless of horizontal diffusivity. On average, ignoring inertial effects, particles sink less with higher diffusivity and more with lower diffusivity, suggesting a potential for high horizontal distribution of sunken tracers in the ocean.

DISPERSION OF LAMB WAVES IN MULTILAYER STRUCTURES

Low cost, the possibility of online monitoring and high sensitivity distinguish the method of structural monitoring using Lamb waves from other available methods. Structural analysis based on Lamb waves in heterogeneous materials requires fundamental knowledge of the behavior of Lamb waves in such materials. This basic knowledge is critical for signal processing in determining possible damage that can be detected by the propagating wave. Recently, Lamb wave methods have been used to simultaneously survey large areas of composite structures. However, such methods are more complex than traditional ultrasonic testing because Lamb waves have dispersive characteristics, namely, the wave speed varies depending on the frequency, modes and thickness of the plates. Experimentally measured group velocities of Lamb waves in composite materials with anisotropic characteristics do not coincide with theoretical group velocities, which are calculated using the dispersion equation of Lamb waves. This discrepancy arises because in anisotropic materials there is an angle between the direction of the group velocity and the direction of the phase velocity. This work investigates the propagation characteristics of Lamb waves in composites, focusing on group velocity and characteristic wave curves. For symmetric laminates, a robust method is proposed by imposing boundary conditions on the mid-plane and top surface to separate symmetric and antisymmetric wave modes. The dispersive and anisotropic behavior of Lamb waves in two different types of symmetrical laminates is theoretically studied in detail. The dispersion of Lamb waves was studied for 10 symmetric and asymmetric modes. It is shown that only fundamental modes are not characterized by a cutoff frequency, which indicates the interaction of fundamental modes with composite layers in the low-frequency range. A high level of group velocity dispersion was discovered for the SH0 and S0 modes. It is concluded that in isotropic laminates, dispersion is characteristic of symmetric modes. It is shown that the frequency dependence of the group velocity of Lamb waves of laminar composites can be represented in polynomial form.

Experimental and theoretical study on the burning and pulsation behaviors of hydrogen-containing and hydrocarbon jet flames

Hydrogen-containing and hydrocarbon fuels have been widely used in industrial production. Jet fires involving these fuels emerge frequently after leakage or explosion accidents for gas pipelines and processing equipments. To reveal the influencing mechanisms of inclination angle on the pulsation behaviors of jet fires, the burning experiments of hydrogen, syngas, methane and propane jet fires with a nozzle diameter (D) of 15 mm, inclination angles (θ0) of 0°∼90°, fuel flow rates (Qf)of 2.5–40 L/min were conducted. The variations of the global and spatial pulsation frequencies with inclination angle and fuel flow rate are sensitive to the fuel types. Subharmonic pulsation was found at large fuel flow rates (Qf>Qcri). For hydrogen-containing jet flame, a transition from natural pulsation to subharmonic pulsation occurs at a critical inclination angle (θcri). In this case, the transition height where the local pulsation frequency begins to be dominated by subharmonic pulsation, increases with the inclination angle. The local Richardson number (Riy) at the transition height is close to 1. The interaction between the inner and outer vortices increases with the decrease of inclination angle, resulting in decreased natural frequency at the nozzle exit. With the theoretical velocity and flame width at y/D = 2, a unified dimensionless model of natural pulsation frequency was developed, Sty=0.411/Fry0.5, reasonably predicting the natural pulsation frequency of jet flames under different conditions.

Investigation on the electro-magneto-thermoviscoelastic response of multilayer rotating hollow cylinder based on two-temperature theory and fractional-order viscoelastic systems

Hollow cylinder structures play a crucial role in scientific experiment and industrial production, and are widely used in various fields, including pipeline transportation of gases and liquids, high-speed engines, porous combustors, and other engineering equipments. As a result, they have garnered considerable academic interest over the years. However, as science and technology progress, studying hollow cylinders under a single physical field is no longer sufficient for real-world applications. Additionally, the classical viscoelastic model has become inadequate in accurately describing complex materials with properties that fall between elasticity and viscosity. Therefore, this article investigates the electro-magneto-thermoviscoelastic coupling behavior of an infinitely long rotating multilayer homogeneous hollow cylindrical conductor. In this study, based on the fractional-order three-phase lag thermoelasticity theory, the fractional-order viscoelastic system and the two-temperature theory are introduced to further increase the accuracy of the model. To solve the corresponding equations, the Laplace transform technique is employed, resulting in solutions with dimensionless physical quantities. Graphs and tables are used to make relevant comparisons and assess the effects of time, material layering properties, different thermoelastic theoretical models, fractional-order parameters and angular velocity on the considered physical quantities. Finally, the numerical results are discussed to reveal the dynamic response of a homogeneous multilayered hollow cylinder under the complex coupling of multiple physical fields.

Resistance training leading to repetition failure increases muscle strength and size, but not power-generation capacity in judo athletes.

Strength-trained athletes has less trainability in muscle size and function, because of their adaptation to long-term advanced training. This study examined whether resistance training (RT) leading to repetition failure can be effective modality to overcome this subject. Twenty-three male judo athletes completed a 6-week unilateral dumbbell curl training with two sessions per week, being added to in-season training of judo. The participants were assigned to one of three different training programs: ballistic light-load (30% of one repetition maximum (1RM)) RT to repetition failure (RFLB) (n = 6), traditional heavy-load (80% of 1RM) RT to repetition failure (RFHT) (n = 7), and ballistic light-load (30% of 1RM) RT to non-repetition failure (NRFLB) (n = 10). Before and after the intervention period, the muscle thickness (MT) and the maximal voluntary isometric force (MVC) and rate of force development (RFDmax) of elbow flexors were determined. In addition, theoretical maximum force (F0), velocity (V0), power (Pmax), and slope were calculated from force-velocity relation during explosive elbow flexion against six different loads. For statistical analysis, p < 0.05 was considered significant. The MT and MVC had significant effect of time with greater magnitude of the gains in RFHT and NRFLB compared to RFLB. On the other hand, all parameters derived from force-velocity relation and RFDmax did not show significant effects of time. The present study indicates that ballistic light-load and traditional heavy-load resistance training programs, leading to non-repetition failure and repetition failure, respectively, can be modalities for improving muscle size and isometric strength in judo athletes, but these do not improve power generation capacity.

Theoretical velocity of an object frictionally coupled to a two-mode vibrating plate.

Net velocity has been demonstrated for objects frictionally coupled to a flat plate that oscillates periodically in-plane with two frequencies, provided plate displacement is nonantiperiodic: the ratio of frequencies γ cannot be the ratio of two odd integers. We give a mathematical derivation of the experimentally determined dependence of mean velocity on the relative amplitudes of the two frequency modes, and the phase lag between the modes, when γ=2, and when the magnitude of plate acceleration is much larger than the magnitude of acceleration by static friction. The approach uses an analysis of the symmetry properties of the roots of trigonometric polynomials, without explicit determination of those roots. The behavior when γ=1/2, and specific phase lags that inhibit net velocity for general γ, are also determined.

Correlation of Road Safety Criteria with Occupant Safety Criteria in Impacts on Crash Cushions

Road restraint systems are used to protect vehicle occupants if the vehicle runs off the road and potentially collides with a dangerous obstacle. These road restraint systems must successfully pass the tests defined in EN 1317, or the Manual for Assessing Safety Hardware (MASH) before they are allowed to be installed. The safety assessment is carried out according to the criteria of ASI (Acceleration Severity Index), THIV (Theoretical Head Impact Velocity), OIV (Occupant Impact Velocity), ORA (Occupant Ridedown Acceleration), and PHD (Post-Impact Head Deceleration). Usually very old vehicles are used for these tests, and there is no assessment of occupant criteria such as HIC (Head Injury Criteria), chest deflection, etc. The objective of the study was to compare the occupant safety of vehicles that are commonly used in EN 1317 with vehicles that have improved safety equipment. Test results from two different vehicles (a commonly used vehicle in EN 1317 and a vehicle with improved safety equipment) and two different impact conditions (full overlap and an overlap of 50%) were compared. Measurement data from a Hybrid HIII 50th percentile anthropomorphic test device (ATD) (Denton ATD, INC.) was recorded during the tests to assess occupant safety. The tests have shown that vehicles with improved safety equipment perform better than vehicles that are commonly used in EN 1317-3 tests. The values for the occupant safety criteria assessed were well below the Euro NCAP (New Car Assessment Programme) or Federal Motor Vehicle Safety Standard (FMVSS) limits. However, the limits of the road safety criteria were in some cases considerably exceeded regardless of the vehicle. This has been observed in particular for the offset impact condition. THIV and OIV were supposed to be able to assess the risk of head injuries. However, these two criteria correlated negatively with the head criteria, HIC or a3ms. However, a positive correlation was found for the ASI with the HIC and the a3ms head acceleration. Even if some of the criteria for road safety correlate with the criteria for occupant safety, it is doubtful whether the criteria for road safety are suitable for assessing the risk of injury to vehicle occupants.

Numerical investigation of driver injury risks in car-to-end terminal crashes using a human finite element model

Although the safety performance of guardrail end terminals is tested using crash tests in the U.S., occupant injury risks are evaluated based on the flail-space model. This approach developed in the early 1980s neglects the influence of safety features (e.g. seatbelt, airbags, etc.) installed in late model vehicles. In this study, a vehicle (sedan, 1100 kg), a guardrail end terminal (ET-Plus) and a human body model (Global Human Body Model Consortium, GHBMC) were integrated to simulate car-to-end terminal crashes. Five velocities, two offsets, and two angles were used as pre-impact conditions. In all the 20 simulations, kinematics and kinetic data were recorded in GHBMC and vehicle models to calculate the GHBMC injury probabilities and vehicle-based injury metrics, correspondingly. Pre-impact velocity was observed to have the largest effect on the occupant injury measures. All the body-region and full-body injury risks increased with the increasing velocity. Meanwhile, the angles had a larger effect than offset to the change of full-body injury risk (9.1% vs. 0.3%). All the vehicle-based metrics had good correlations to full-body injury probabilities. Occupant Impact Velocity (OIVx), Acceleration Severity Index (ASI), and Theoretical Head Impact Velocity (THIV) had a good correlation to chest, thigh, upper tibia, and lower tibia injuries. All the other correlations (e.g. brain/head injuries) were not statistically significant. The results pointed out that more vehicle-based metrics (ASI and THIV) could help improve the predictability in terms of occupant injury risks in the tests. Numerical methodology could be used to assess head and brain injury probabilities, which were not predictable by any vehicle-based metrics.

Relationship Between Force-Velocity Characteristics and Sprint Performance in Elite Sprinters: A Pilot Study.

Sprinting is a type of running that consists of producing a short and intense effort in order to performmaximal speed in a short period of time. Sprinting is widely investigated because of the multiple and complex mechanismsinvolved. Sprint studies are now focusing on how to improve performance by focusing their analyses on the mechanicvariables. The hamstrings are part of the most important muscle groups duringsprinting because of their role of stabilization and propulsion, but they must be able to produce the maximum strength during a short moment, this ability is characterized by rate of torque development (RTD). The main of this study was to investigate the association between hamstring RTD (Nm.s-1.kg-1) and mechanicalvariables composed of maximal power output (Pmax) (W.kg-1), maximal theoretical velocity (V0) (m.s-1), and maximal horizontal force production (F0) (N.kg-1) on short sprints in elite sprinters. For this clinical trial, we used a research method based on data collection. A single group composed of four male and one female elite sprinters (age: 17.2 ± 1.79 years) has been included in this study. The sprinters performed a hamstring strength test, which included five trials of four seconds for each leg. This test required a portable dynamometer, the Kforce®, to collect 100 and 200 milliseconds RTD. Then the subjects were submitted to a sprint test. My Sprint® application has been used to collect the sprint mechanicalvariables. The sprint test included two trials; a starting block has been used for this test. A linear regression analysis was used between the rates of torque development and mechanicalvariables composed of maximal power output (Pmax) (W.kg-1), maximal theoretical velocity (V0) (m. s-1), and maximal horizontal force production (F0) (N.kg-1). No significant correlation was observed between 100 and 200 ms hamstring RTDand sprint biomechanical variables: maximal power output(Pmax) (W.kg-1), maximal theoretical velocity (V0) (m. s-1), and horizontal force production (F0) (N.kg-1). However, 100 and 200 ms RTD collected on the dominant leg tends to be more correlated with maximal theoretical velocity (spearman's rho = 0.80; p-value = 0.13) and Pmax output (spearman's rho = 0.70; p-value = 0.23) while for non-dominant leg, RTD tends to be more correlated with maximal power output (spearman's rho = 0.60; p-value = 0.35) and horizontal force production (spearman's rho = 0.70; p-value = 0.23). Hamstring RTD is not correlated with sprint biomechanical variables in elite sprinters. Further investigations must be made to study the observed trends in this study.

Combustion synthesis of TiC- high entropy alloy CoCrFeNiMn composites from granular mixtures

The advantage of combustion synthesis is the ability to produce composites from powders in a single technological step, using the heat of an exothermic reaction, in a fast and energy-efficient manner. Ceramic-metal composites TiC–High-Entropy Alloy (HEA) CoCrFeNiMn were fabricated by combustion synthesis from granular mixtures. The content of the metal binder components varied from 10 to 30 wt% and the combustion velocity and temperature gradually decreased as the binder content increased. Scaling up synthesis requires clarification of the parametric range for implementing a safe combustion mode. The impurity gas content and the range of safe conductive combustion were determined from known theoretical models and experimental combustion velocities of samples of granules of 0.6 and 1.1 mm size. The main phases of the product were titanium carbide with up to 3 at. % Cr and HEA CrCoFeNiMn with a reduced Mn content compared to the equimolar composition. The content of secondary phases Cr7C3 and carbon did not exceed 5 wt%. The use of granular mixtures solved the problem of significant sintering of exothermic powder mixtures containing metal binder during combustion. After synthesis, the granules retain their size and do not sinter together, making it easy to grind the sample and obtain a TiC-HEA composite powder.

Design and characteristic analysis of flame cutting nozzles for ultralarge-thickness steel ingots

The cutting thickness of the flame cutting nozzle mainly depends on the characteristics of the cutting oxygen jet, and in the process of designing and manufacturing a flame cutting nozzle with an ultralarge thickness, it is impossible to carry out multiple experiments to optimize the design due to the difficulty in testing, safety, manufacturing cost, environmental pollution, and other problems. In this paper, the Laval-type cutting oxygen orifice channel was first designed by theoretical calculation, the pressure, velocity, Mach number, and density distribution characteristics of the cutting oxygen jet were investigated by numerical simulation, and the reliability and adaptability of the numerical simulation results were verified by experiments. Then, the numerical simulation comparison and estimation method of jet characteristics with the general-purpose G301-7# nozzle was used to study the cutting oxygen orifice channel of the ultralarge thickness flame cutting nozzle. The results show that under the condition of a 19 mm throat diameter and 10 atm inlet pressure, it was estimated that the length of cutting oxygen flow from the design nozzle can reach 1800 mm and the cutting thickness can reach 2500 mm based on the density value; the length of cutting oxygen flow can reach 2000 mm and the cutting thickness can reach 3800 mm based on the velocity value; the length of cutting oxygen flow can reach 1600 mm according to the value of the oxygen quality fraction; and the cutting thickness can reach 2800 mm based on the oxygen mass fraction content. Finally, trial production of the nozzle design, verification of the cutting test, the nozzle with a cutting thickness of 2500 mm at an oxygen pressure of 7 atm, and the cutting quality were all good.

Sprint Acceleration Mechanical Outputs and Lower Limb Injuries: A Follow-Up of Sprint, Jumps and Combined Events Athletes during an Athletics Season

Problem: We aimed to explore the potential association between sprint running horizontal force production capacities (the theoretical maximum horizontal force that the lower limbs can produce at zero velocity: FH0, and the theoretical maximum velocity until which they can produce force (velocity at zero force): v0 ) and occurrence of lower limb injuries (LLI) in athletics (track and field) athletes through a season. Methods: We performed a prospective cohort study with data collection of FH0 and v0 and their week-to-week changes (dFH0 and dv0 , respectively) and LLI in 16 athletes practicing sprints, jumps or combined events in the same training group during the 2021/2022 season (37 weeks). We performed a multivariable binomial logistic regression with LLI (yes/no) as the dependent variable, and FH0 and v0 , dFH0 and dv0 as explanatory variables, adjusted for individual athletes and LLI during the previous week (yes/no). Risk indicators were presented as odd ratios (OR) and 95% confidence intervals (95% CI). › Results: The multivariable binomial logistic regression showed that a higher FH0 was associated with lower LLI risk (OR=0.12 (95%CI: 0.00-0.89). Conclusion: Lower FH0 was associated with higher risk of sustaining a new lower limb injury during the next week. Although caution should be taken on these preliminary results (e.g., small athletes’ sample, missing measurements, few confounding factors included), monitoring the FH0 could be one additional relevant approach to detect LLI in athletics.

Study on the free surface evolution and slamming pressure of curved-wedge water entry using a Riemann-smoothed particle hydrodynamics method

The present study aims to provide a deep understanding of curved wedge water entry. It involves a numerical simulation investigation into the kinematic and dynamic properties of water entry for two curved wedges with deadrise angles of 25° and 35°. The meshless Riemann-smoothed particle hydrodynamics (SPH) model embedded with an acoustic damper is developed to simulate these violent water entries. The validation of the Riemann-SPH accuracy is confirmed through comparison with experimental data, and subsequently, we make a systematical simulation study on curved wedge water entry, including a comparative study of free surface evolution and pressure distribution at different curvatures and drop heights. Furthermore, the kinematics analysis of velocity and displacement of curved wedges and time domain characteristics of slamming pressure loads on both sides of the wedge are investigated. It is revealed that the pressure distribution is symmetrical, with high-pressure regions forming near the bottom of the wedge and gradually propagating outward. The free surface profiles are symmetrical, with deeper depressions formed by sharper wedges. The entry depth and velocity are correlated with the initial theoretical entry velocity, and the rate of speed decline varies with the curvature of the wedge. The slamming pressure loads exhibit distinct time-domain patterns, with lower pressure loads by sharper wedges.