Background : Competitive swimming is characterised by repetitive movements and is associated with a substantial burden of musculoskeletal injuries. However, descriptive epidemiological studies organising injuries according to both onset pattern and injured body region, including regions other than the shoulder, remain limited. This study aimed to describe the distribution of injury onset patterns and injured body regions among competitive swimmers seeking medical care. Methods : This retrospective descriptive study included competitive swimmers who visited a single medical institution between 2019 and 2024. Data on age, sex, competition level, diagnosis, injury onset pattern, and injured body region were extracted from electronic medical records. Injury onset patterns were classified as acute–sudden, repetitive–sudden, or repetitive–gradual. Injured body regions were categorised as follows: the trunk as head/face, neck, chest, thoracic spine/upper back, lumbosacral spine/buttocks, and abdomen; the upper extremity as shoulder, upper arm, elbow, forearm, wrist, hand, and fingers; and the lower extremity as hip/groin, thigh, knee, lower leg/Achilles tendon, ankle, and foot. The number and proportion of injury events with 95% confidence intervals were calculated, and the associations between injury onset patterns and injured body regions were explored using the chi-square test. Results : Overall, 615 injury events from 360 swimmers were analysed (mean age, 19.4 ± 6.5 years). Repetitive gradual-onset injuries were most frequently observed in the shoulder and lumbosacral spine/buttocks, whereas acute sudden-onset injuries were more commonly distributed in the lower extremity (χ² = 27.7, df = 4，p < 0.001), particularly at the ankle. Conclusions : Distinct distributions of injury onset patterns and injured body regions were observed in competitive swimmers seeking medical care, potentially providing baseline data that support future hypotheses and injury prevention strategies.
This study theoretically and experimentally investigates the sloshing behavior that occurs when a circular cylindrical rigid tank is subjected to horizontal harmonic excitation and the excitation frequency is close to the natural frequency of the sloshing mode (1, 1). The fluid velocity potential and free-surface elevation are assumed in Galerkin’s expansion forms to solve the corresponding partial differential equations. Subsequently, the ordering assumption for each sloshing mode leads to the derivation of second-order ordinary differential equations for seven sloshing modes, including the two orthogonal and degenerate (1, 1) sloshing modes. Linear viscous damping terms are incorporated into the modal equations of motion to represent the viscous effects of the fluid. These equations form an autoparametric system in which only the (1, 1) mode, with a diametral nodal line perpendicular to the direction of tank motion, is directly excited by the horizontal translation of the tank and nonlinearly couples with the remaining sloshing modes. Frequency response curves are obtained from the resulting equations using van der Pol’s method and are compared with experimental results to demonstrate the high accuracy of the calculated responses. To investigate the influence of the excitation amplitude on bifurcation point transitions, the corresponding bifurcation sets are calculated, and the oscillation patterns of sloshing—planar motion, swirl motion with constant and modulated amplitudes, and chaotic swirl motion—are presented as occurrence boundaries. Therefore, reliable and convenient modal equations for nonlinear sloshing behavior are provided, enabling easy prediction of actual sloshing phenomena.
Bayesian optimization is an effective framework for identifying optimal control parameters of excavation machinery from a limited number of costly trials. While it can improve excavation performance by increasing soil yield and reducing time or fuel consumption, unsafe or off-target parameter combinations must be avoided in real operations. Such cases—e.g., cylinder overload, excessive tire slip, or unstable bucket–soil interaction—are regarded as “failures” in this study. To address this issue, we propose a two-stage safe optimization method designed for automatic excavation control. In the first stage, we explore the success / failure boundary in a simulation environment, where failures can be evaluated without risking damage to vehicles, and estimate the safety probability distribution across the parameter space. In the second stage, this prior safety information is incorporated into a safety-weighted acquisition function for Bayesian optimization, introducing safety as a soft constraint and enabling risk-aware exploration of the parameter space. By separating offline boundary learning and online optimization, the proposed approach aims to reduce failure trials. The effectiveness of the method is evaluated through comparisons with existing safety-aware optimization approaches on known objective functions, as well as through a physics-based excavation simulation.
This study investigates the MnPh surface treatment applied to improve the tribological properties of steel and rolling fatigue life of gears, focusing on the wear behavior and tribofilm formation during the initial sliding stage. The MnPh-coated layer is almost completely worn off in a short time during sliding, exposing the roughness peaks of the base steel, at which wear mainly occurs. Since the MnPh treatment etches the base steel during the treatment process to roughen the surface, MnPh-treated and MnPh-removed disks are used to match the roughness and morphology of the steel surfaces. The wear rate of the MnPh-treated steel is higher than that of the MnPh-removed steel during the initial sliding stage, following which the wear rate of the MnPh-removed steel increases. The formation of a sulfur-based tribofilm is significant on the MnPh-treated steel, whereas the formation of a calcium-based tribofilm is significant on the MnPh-removed disk. The role of the MnPh treatment is comprehensively discussed through the relationship between the wear behavior and tribofilm formation during the initial sliding stage, which contributes to improving the fatigue life.
