Search Results (18)

Objective: This study aimed to investigate the effects of a 12-week self-designed exercise game intervention on the kinematic and kinetic data of the supporting leg in preschool children during the single-leg jump. Methods: Thirty 5- to 6-year-old preschool children were randomly divided into an experimental group (EG) and a control group (CG). The BTS SMART DX motion capture analysis system was used to collect single-leg jump data before the intervention. The experimental group underwent a 12-week intervention, with self-designed exercise games conducted three times a week for 30 min each session, while the control group only participated in regular kindergarten recess activities and physical education classes. After the intervention, the same equipment was used to collect single-leg jump data again, and the kinematic and kinetic data were analyzed using Anybody 7.4 simulation software. Results: After the intervention, the experimental group showed significant changes in joint angles and joint torques, with a notable increase in the force exerted by dominant muscles such as the vastus medialis, vastus lateralis, and gastrocnemius and a significant increase in the ground reaction force. Although the control group also showed some changes in the dominant muscles, the changes were not as significant as those in the experimental group. Conclusions: A 12-week exercise game intervention significantly improved the technique and force characteristics of 5- to 6-year-old preschool children during the single-leg jump, making muscle exertion more focused and efficient and effectively enhancing explosive power and performance during the single-leg jump. Full article

Linear temporal logic (LTL) formalism can ensure the correctness of mobile robot planning through concise, readable, and verifiable mission specifications. For uneven terrain, planning must consider motion constraints related to asymmetric slope traversability and maneuverability. However, even though model checker tools like the open-source Simple Promela Interpreter (SPIN) include search optimization techniques to address the state explosion problem, defining a global LTL property that encompasses both mission specifications and motion constraints on digital elevation models (DEMs) can lead to complex models and high computation times. In this article, we propose a system model that incorporates a set of uncrewed ground vehicle (UGV) motion constraints, allowing these constraints to be omitted from LTL model checking. This model is used in the LTL synthesizer for path planning, where an LTL property describes only the mission specification. Furthermore, we present a specific parameterization for path planning synthesis using a SPIN. We also offer two SPIN-efficient general LTL formulas for representative UGV missions to reach a DEM partition set, with a specified or unspecified order, respectively. Validation experiments performed on synthetic and real-world DEMs demonstrate the feasibility of the framework for complex mission specifications on DEMs, achieving a significant reduction in computation cost compared to a baseline approach that includes a global LTL property, even when applying appropriate search optimization techniques on both path planners. Full article

This work applies the rarely seen explosive version of autoregressive modelling to a novel practical context—geological failure monitoring. This approach is more general than standard ARMA or ARIMA methods in that it allows the underlying data process to be explosively nonstationary, which is often the case in real-world slope failure processes. We develop and test our methodology on a case study consisting of high-quality (in situ) line-of-sight radar displacement data from a slope that undergoes a failure event. Specifically, we first optimally estimate the characteristic roots of the autoregressive processes underpinning the displacement time series preceding the failure at each monitoring location. We then establish and utilise a pivotal quantity for the autoregressive parameter ensemble to perform simulation-based hypothesis test/s for the explosiveness of the corresponding true characteristic roots. Concluding that a true characteristic root becomes explosive at some significance level implies that the underlying displacement process is explosively nonstationary, and, hence, local geological instability is suspected at this significance level. We found that the actual location of failure (LOF) was identified well in advance of the time of failure (TOF) by flagging those locations where explosive root(s) were identified by our approach. This statistical feedback model for ground motion dynamics presents an alternative and/or addition to the velocity threshold approach to early warning of impending failure. Full article

The frog-inspired jumping robot is an interesting topic in the field of biomechanics and bionics. However, due to the frog’s explosive movement and large range of joint motion, it is very difficult to make their structure completely bionic. To obtain the optimal jumping motion model, the musculoskeletal structure, jumping movement mechanism, and characteristics of frogs are first systematically analyzed, and the corresponding structural and kinematic parameters are obtained. Based on biological characteristics, a model of the articular bone structure is created, which can fully describe the features of frog movement. According to the various factors affecting the frog’s jumping movement, mass and constraints are added, and the complex biological joint structure is simplified into four different jumping structure models. The jumping ground reaction force, velocity, and displacement of the center of mass, joint torque, and other motion information of these four models are obtained through ADAMS simulation to reveal the jumping movement mechanism and the influencing factors of frogs. Finally, various motion features are analyzed and compared to determine the optimal structural model of the comprehensive index, which provides a theoretical basis for the design of the frog-inspired jumping robot. Full article

Blasting is a cost-efficient and effective technique that utilizes explosive chemical energy to generate the necessary pressure for rock fragmentation in surface mines. However, a significant portion of this energy is dissipated in undesirable outcomes such as flyrock, ground vibration, back-break, etc. Among these, flyrock poses the gravest threat to structures, humans, and equipment. Consequently, the precise estimation of flyrock has garnered substantial attention as a prominent research domain. This research introduces an innovative approach for demarcating the hazardous zone for bench blasting through simulation of flyrock trajectories with probable launch conditions. To accomplish this, production blasts at five distinct surface mines in India were monitored using a high-speed video camera and data related to blast design and flyrock launch circumstances including the launch velocity (v_f) were gathered by conducting motion analysis. The dataset was then used to develop ten Bayesian optimized machine learning regression models for predicting v_f. Among all the models, the Extremely Randomized Trees Regression model (ERTR-BO) demonstrated the best predictive accuracy. Moreover, Shapely Additive Explanation (SHAP) analysis of the ERTR-BO model unveiled bulk density as the most influential input feature in predicting v_f, followed by other features. To apply the model in a real-world setting, a user interface was developed to aid in flyrock trajectory simulation during bench blast designing. Full article

In the present study, a stochastic model of explosive ground motions applying the dimension-reduction method is proposed, and the reliability evaluation of a nonlinear frame structure under such excitations is realized by means of the probability density evolution method and an equivalent extreme-value-based reliability evaluation strategy. Firstly, the evolutionary power spectrum density function of the explosive ground motions is modeled by respectively identifying the normalized total energy distribution function and the frequency total energy distribution function on the basis of the measured motion records. In addition, an exponential model is constructed to forecast the seismic characteristics of the explosive ground motions based on the given distance to the explosive source and the charge quantity. Then, the representative samples of the explosive ground motions are simulated using the dimension-reduction method. The simulation results show that the generated acceleration samples have significant seismic characteristics of the explosive ground motions, and the accuracy is verified by comparing the second-order statistics with the sample set and the corresponding targets. Due to the fact that the probabilities of the representative samples simulated by the dimension-reduction method can compose a comprehensive probability set, it contributes to the refined dynamic response analysis and reliability evaluation of complex structures combining with the probability density evolution method. The accurate dynamic response analysis and reliability evaluation of a nonlinear frame structure illustrates the effectiveness of the proposed model and the dimension-reduction method for simulating the explosive ground motions. The numerical results demonstrate that the explosive ground motions have a substantial effect on the nonlinear behavior and the security of engineering structures. Full article

Aspects of mathematical and physical modeling of deflagration explosions emerging during atmospheric (outdoor) accidental explosions are addressed. It has been demonstrated that when physically modeling accidental deflagration explosions, a stoichiometric mixture in the shape of a sphere or hemisphere supported by the ground should be used. This allows us to research the parameters of blast loads for the worst-case accidental scenarios or address the accident using the most conservative approach. A technique has been provided allowing one to create a mixture of a given blend composition in the shape of a sphere or hemisphere supported by the ground in outdoor conditions. It has been demonstrated that there is an ability to conduct modeling studies of accidental atmospheric explosions. We have provided examples of modeling studies of accidental atmospheric explosions; a methodology for analyzing experimental results has also been reviewed. The article discusses the mathematical modeling of outdoor (unobstructed) accidental deflagration explosions. It has been demonstrated that it is most reasonable to base computational experiments on linearized (acoustic) equations of continuum motion, as the visible flame propagation rate emerging during explosive combustion is small (compared to the speed of sound). There has been a satisfactory agreement between the numerical analysis and the experimental data. Full article

As the demand and construction of cable-stayed bridges have increased, research on the safety of cable-stayed bridges in the event of natural disasters such as fires and explosions is actively being conducted. If a cable-stayed bridge is damaged by an unexpected natural disaster or accident, it can cause serious traffic congestion and huge economic losses. This study evaluates the usability of the cable-stayed bridge in the event of cable damage. Additionally, seismic performance and the impact of the damage are evaluated by numerical analysis. To achieve this goal, the cable-stayed bridge is modeled using 3D BEAM elements and two-node cable elements. Then, the impact of the damage was evaluated by gradually damaging the cable. The deflection, axial force of the girder, and cable stress changes under far-field ground motion (El-Centro earthquake) were reviewed. A representative dynamic analysis program LS-DYNA was utilized for the numerical analyses. The results show that the loss of a small number of cables does not affect the usability of the bridge. However, if five or more cables are continuously lost, or if an earthquake occurs when cables are already lost, excessive deflections and changes in the girders’ axial forces can cause usability problems. Full article

Landmines and explosive remnants of war are a significant threat in tens of countries and other territories, causing the deaths or injuries of thousands of people every year, even long after military conflicts. Effective technical means of remote detecting, localizing, imaging, and identifying mines and other buried explosives are still sought and have a great potential utility. This paper considers a positioning system used as a supporting tool for a handheld ground penetrating radar. Accurate knowledge of the radar antenna position during terrain scanning is necessary to properly localize and visualize the shape of buried objects, which helps in their remote classification and makes demining safer. The positioning system proposed in this paper uses ultrawideband radios to measure the distances between stationary beacons and mobile units. The measurements are processed with an extended Kalman filter based on an innovative dynamics model, derived from the model of a pendulum motion. The results of simulations included in the paper prove that using the proposed pendulum dynamics model ensures a better accuracy than the accuracy obtainable with other typically used dynamics models. It is also demonstrated that our positioning system can estimate the radar antenna position with the accuracy of single centimeters which is required for appropriate imaging of buried objects with the ground penetrating radars. Full article

Radars can be used as sensors to detect the breathing of victims trapped under layers of building materials in catastrophes like earthquakes or gas explosions. In this contribution, we present the implementation of a novel frequency comb continuous wave (FCCW) bioradar module using a commercial software-defined radio (SDR). The FCCW radar transmits multiple equally spaced frequency components simultaneously. The data acquisition of the received combs is frequency domain-based. Hence, it does not require synchronization between the transmit and receive channels, as time domain-based broadband radars, such as ultra wideband (UWB) pulse radar and frequency-modulated CW (FMCW) radar, do. Since a frequency comb has an instantaneous wide bandwidth, the effective scan rate is much higher than that of a step frequency CW (SFCW) radar. This FCCW radar is particularly suitable for small motion detection. Using inverse fast Fourier transform (IFFT), we can decompose the received frequency comb into different ranges and remove ghost signals and interference of further range intervals. The frequency comb we use in this report has a bandwidth of only 60 MHz, resulting in a range resolution of up to 2.5 m, much larger than respiration-induced chest wall motions. However, we demonstrate that in the centimeter range, motions can be detected and evaluated by processing the received comb signals. We want to integrate the bioradar into an unmanned aircraft system for fast and safe search and rescue operations. As a trade-off between ground penetrability and the size and weight of the antenna and the radar module, we use 1.3 GHz as the center frequency. Field measurements show that the proposed FCCW bioradar can detect an alive person through different nonmetallic building materials. Full article

This study investigated the effects of handheld-load-specific jump training on standing broad jump (SBJ) performance in youth athletes and the biomechanics changes involved. Methods: Fifteen male athletes (mean age, body weight, height, and body mass index were 14.7 ± 0.9 years, 59.3 ± 8.0 kg, 1.73 ± 0.07 m, 19.8 ± 2, respectively) underwent 15 SBJ training sessions over 8 weeks. The data were collected over three phases: before training, after training, and after training with 4 kg loading. Ten infrared high-speed motion-capture cameras and two force platforms, whose sampling rates were 250 and 1000 Hz, respectively, were used to record the kinematic and kinetic data. Visual three-dimensional software was used for the data analyses. Results: Jump performance and all biomechanics variables, including joint and takeoff velocities, ground reaction force, takeoff impulse, and mechanical outputs, improved after training. Conclusions: SBJ training under handheld loading resulted in considerable acute improvements as well as training transfer after 8 weeks. Moreover, explosive ability was effectively enhanced. The present findings serve as a reference for SBJ assessment and jump-related training. Full article

Earth-covered magazine has some characteristics that are safer than the above-ground magazine and are more economical than underground magazine. To investigate the pressure distribution and the structural failure under the internal explosion, the scaled tests of the earth-covered magazine were conducted under a 0.5 kg TNT explosive charge. The overpressure in the 0°, 90°, and 180° directions outside the structure and the debris distribution were obtained. The numerical simulations were constructed in LS-DYNA software to analyze the test results. The results show that the external overpressure has a directional characteristic that the maximum and minimum overpressure appear in 0° and 180° directions, respectively. In the double logarithmic coordinate system, the overpressure peaks in three directions are linearly related to the scaled distance. Most of the fragments in the 0° direction hit the ground within the front range of ±60°, and the further fragments (40 m or more) were confined to a limited sector within the front range of ±30°. The internal explosion numerical simulation shows that the concrete cracks first appeared at the roof and the ground, and then the damage occurred at the intersection of the walls, and then the damage occurred at each surface. The maximum debris velocity of the side and rear walls is lower than that of the front wall due to the limitation of the soil. The motion equations of the debris combined with numerical simulation can be adopted to predict the projection distance of fragments. Full article

Globally, there are several critical infrastructure networks (water and gas networks) whose disruption or destruction would significantly affect the maintenance of vital societal functions, such as the health, safety, security, and social or economic well-being of people. They would also have significant local, regional, and national impacts as a result of the inability to maintain those functions, and would have similar cross-border effects. The main objective of this article is to investigate by comparative numerical studies the structural response of three types of buried pipes made of different materials, primarily steel, concrete, and high-density polyethylene, resulting from the impact of the environment through exceptional external actions, such as explosions at the surface of the land in the vicinity of the laying areas. The dynamic transient analysis of the equation of motion with the application of the explicit integration procedure was performed with the ANSYS numerical simulation program. This study allows designers to solve complex problems related to the quality of the laying ground of water networks to canals. The knowledge accumulated gives us the possibility to correctly specify the optimal economic and technical value of the ratio between the laying depth of pipes and their diameter, the importance of the radius ratio of the pipe and the thickness of its wall, and, importantly, the improvement of the quality of the foundation ground. Following the results obtained, it is estimated that the optimal economic and technical value of the ratio between the laying depth of the pipes (H) and their diameter (D) is 3, regardless of the material from which the pipe is made. Full article

For many years, seismological research mainly focuses on translational ground motions due to the lack of appropriate sensors. However, because of the development of devices based on Sagnac effect, measuring rotational waves directly comes available. In this work, a portable three-component broadband rotational seismometer named RotSensor3C based on open loop interferometric fiber optic gyroscope (IFOG) is designed and demonstrated. Laboratory tests and results are illustrated in detail. The self-noise ranging from 0.005 Hz to 125 Hz is about $1.2\times {10}^{-7}{\mathrm{rads}}^{-1}/\sqrt{\mathrm{Hz}}$, and with the harmonics compensation the scale factor variation over $\pm {250}^{\circ }/\mathrm{s}$ is lower than 10 ppm (parts per million). The misalignment matrix method is adopted to revise the output rotation rate. In a special near field experiment using the explosive source, the back-azimuths and phase velocity are estimated by the recorded acceleration and rotation rate. All the results prove the practicability of this new rotational sensor. Full article

The use of uncrewed aerial systems (UAS) increases the opportunities for detecting surface changes in remote areas and in challenging terrain. Detecting surface topographic changes offers an important constraint for understanding earthquake damage, groundwater depletion, effects of mining, and other events. For these purposes, changes on the order of 5–10 cm are readily detected, but sometimes it is necessary to detect smaller changes. An example is the surface changes that result from underground explosions, which can be as small as 3 cm. Previous studies that described change detection methodologies were generally not aimed at detecting sub-5-cm changes. Additionally, studies focused on high-fidelity accuracy were either computationally modeled or did not fully provide the necessary examples to highlight the usability of these workflows. Detecting changes at this threshold may be critical in certain applications, such as global security research and monitoring for high-consequence natural hazards, including landslides. Here we provide a detailed description of the methodology we used to detect 2–3 cm changes in an important applied research setting—surface changes related to underground explosions. This methodology improves the accuracy of change detection data collection and analysis through the optimization of pre-field planning, surveying, flight operations, and post-processing the collected data, all of which are critical to obtaining the highest output data resolution possible. We applied this methodology to a field study location, collecting 1.4 Tb of images over the course of 30 flights, and location data for 239 ground control points (GCPs). We independently verified changes with orthoimagery, and found that structure-from-motion, software-reported root mean square errors (RMSEs) for both control and check points underestimated the actual error. We found that 3 cm changes are detectable with this methodology, thereby improving our knowledge of a rock’s response to underground explosions. Full article