Trajectories Of Fragments Research Articles

Study on critical bounce and damage of tungsten alloy spherical fragments penetrating cylindrical concrete

Abstract Prefabricated fragment bomb will produce a large number of tungsten alloy spherical damage elements, causing damage to a wide range of targets. The phenomenon of bouncing projectile will deviate from the trajectory of fragments and affect the damage field of explosive projectile. In order to accurately obtain the influence of bouncing projectile on the residual damage of tungsten ball fragments, the damage of concrete targets caused by bouncing projectile is analyzed. The oblique penetration of tungsten ball fragments into concrete at different angles and speeds is simulated. Through the angle-by-angle approximation of cylinders and planes with different curvature radii at 1000m/s, the critical bounce angles in each case are obtained. Based on this, the critical bounce angle of each cylinder under medium and high speed conditions is obtained. The simulation results show that the critical bounce angle decreases with the increase of curvature, and the critical angle increases with the increase of velocity. The residual velocity angle of the projectile increases with the increase of curvature. The relationship between concrete damage degree and curvature and velocity is obtained. Based on the critical angle of penetration of concrete with different fragment flight parameters, the killing range of fragments can be corrected, and the accurate evaluation of the killing ability under the condition of bouncing projectile can be realized.

Diverse paths, stable differences – role of prior knowledge in learning biology over undergraduate years

ABSTRACT Undergraduate students enrol at university with diverse levels of prior knowledge and intuitive conceptions about essential biological topics. This longitudinal study explored the development of a conceptual understanding about three topics and how domain-specific prior knowledge affects this development. Undergraduate students (N = 50) of biological and environmental sciences participated in three measurement points – baseline (2019), follow-up 1 (2020), and follow-up 2 (2021) – where the same questionnaire with open-ended tasks was given. A mixed-methods approach was used for quantitative scoring of the answers and qualitative thematic analysis to describe the development of individual students’ conceptual understanding. The effect of prior knowledge was studied by dividing the students into two groups based on the baseline performance. The topic of evolution showed the most significant differences in prior knowledge and in knowledge gains. Students with lower prior knowledge experienced desirable shifts in their explanatory models about evolutionary processes, but an equal amount exhibited fragmented learning trajectories. Students with a more robust prior understanding of such an emergent phenomenon can more likely integrate scientific concepts in their knowledge framework. Implications for teaching in higher education are discussed.

Three-dimensional trajectories of irregular-shaped tunnel lining fragments in the flow environment caused by high-speed trains

High-speed railway tunnel lining fragments can cause collisions with trains and track blockages, severely affecting train operation. When a train passes through a tunnel where lining fragment is likely to occur, the train wind effect may significantly affect the trajectory of the lining fragment, making the location where the lining fragment is difficult to predict. For safety purpose, this study aims to analyze the impact of the initial circumferential position and shape of irregular-shaped lining fragments on their aerodynamic performance. Using on-site scanning and mathematical statistical methods, the shape characteristics and probability distribution of actual lining fragments in the tunnel are obtained. The aerodynamic behavior of irregular-shaped lining fragments with different initial positions and three typical aspect ratios (ARs) are investigated based on the overset grid method and the dynamic fluid–body interaction model framework as a high-speed train passes. The study found that the most representative lining fragments with an AR of three have a mass of 1.5 kg and are located 2.5 m from the tunnel centerline. The flight behavior of lining fragments shows distinct three-dimensional features, with both translation and rotation significantly affected by the aerodynamic effects of the train and the geometric shape of the fragments. The longitudinal and lateral translational distances of lining fragments at the top of the train decrease as their initial position moves further from the tunnel's centerline. With an increase in AR, both the longitudinal and lateral flight distances and average flight velocities of the fragments increase. The macroscopic flow field within the tunnel directly influences the motion characteristics of the lining fragments. Complex flow separation and circulation phenomena near the fragments result in uneven pressure differences acting on the smooth and rough surfaces of the lining fragments, causing irregular motion. The conclusions of this study provide a theoretical basis for assessing and preventing the impact of lining fragments on the operational safety of trains.

Laminated insulated glass units under blast loads: Experimental and numerical study

Laminated insulating glass units (IGUs), commonly used in modern buildings, are prone to shattering from explosive loads, causing significant damage and loss. Existing research on IGUs is constrained by a lack of experimental validation and comprehensive numerical analyses, as large-scale explosion tests are rarely reported due to safety and cost concerns. Furthermore, previous modeling efforts often oversimplify critical factors such as the supporting structure, component interactions, strain rate effects, hourglass energy, and failure criteria, leading to an inadequate representation of glass behavior under explosive loads. This paper addresses these gaps by conducting large-scale explosive test on glass system and utilizing sophisticated nonlinear dynamic analysis with LS-DYNA for simulation. The research considers the influence of the support system and incorporates detailed considerations of component interactions, constitutive relationships, and strain rate effects in the numerical simulations. The results confirm that the proposed model successfully replicates the crack patterns and damage observed in experimental test. Also, it accurately predicts the trajectory, quantity, and size distribution of glass fragments. The proposed modeling approach offers a more informed assessment of damage and improves the evaluation of glass safety in practical applications.

New method for calculating the windward area of irregular fragments

Average windward area is an important index for calculating the trajectory, velocity attenuation and terminal effect of explosive fragments. In order to solve the problems that existing theoretical method cannot calculate windward area of irregular fragment and experiment method is not convenient for automatic calculation and has low accuracy, a Monte Carlo subdivision projection simulation algorithm is proposed. The average windward area of arbitrary shaped fragments can be obtained with coordinate translation, random rotation, plane projection, convex-hull triangulation, concave boundary searching and sorting with maximum edge length constraint, subdivision area calculation, and averaging by thousands of cycles. Results show that projection area obtained by the subdivision projection algorithm is basically the same as that obtained by software method of computer aided design. Moreover, the maximum calculation error of the algorithm is less than 7%, and its accuracy is much higher than that of the equivalent ellipsoid method. The average windward area calculated by the Monte Carlo subdivision projection simulation algorithm is consistent with theoretical formula for prefabricated fragments, and the error is less than 3%. The convergence and accuracy of the Monte Carlo subdivision projection algorithm are better than those of the icosahedral uniform orientation method.

Modeling the Interaction of Proximal Fragments for Destructive Atmospheric Entry Analysis

The destructive atmospheric entry process is distinguished by the formation of several fragments due to the severe aerothermal loads encountered during the descent. The proximity of debris leads to shock wave interactions and collisions between bodies, influencing the overall dynamics of the fragments and affecting the prediction of demise and ground impact location. To account for these effects, the use of computational fluid dynamics is introduced to resolve the shock interaction patterns by employing a quasi-steady approach, and the use of a simple rigid-body collision model is introduced to represent the dynamics of fragments in the cloud of debris. The quasi-steady approach is assessed and validated by comparative analysis with a few studies in the literature. One of these examples is the rebuilding of the VKI’s experiment of a free-flying ring crossing a shock wave generated by the presence of a stationary cylinder. The impact of explicitly modeling collision dynamics in the trajectory of fragments and ground spread distance is validated by considering a set of relevant test cases from the literature and tested them for destructive atmospheric reentry of the Attitude Vernier Upper Module, the launcher VEGA upper stage.

Poetic Schemas

This article reads the affective charge of ethnonationalism and antiblackness in Puerto Rican poetics and performance. Moving from the “legible” affect in Afro–Puerto Rican feminist poet Julia de Burgos's ethnonational poetry to the “illegible” affect experienced on stage by Afro–Puerto Rican queer theater and performance artist Javier Cárdona Otero, this article provides a fragmented trajectory of the antiblack and white supremacist affective violence constitutive of art-making in Puerto Rico. In doing so, it locates an aesthetic collusion between ethnonationalism and antiblackness that in turn illuminates how the aesthetics of Puerto Ricanness can be antiblack, a claim that calls into question Puerto Rican nationalism's desire or need for ethnic difference.

Impact of Soil on the Penetration of Prefabricated Spherical Fragments and Its Protective Effect

As a natural environmental medium, soil has a wide range of sources and is often used as a material for building houses. It can also be used to construct simple protective structures in actual battlefield environments. In order to study the protective effect of sand on prefabricated fragments in practical situations, the authors conducted experiments on spherical tungsten alloy prefabricated fragments penetrating into sand using sand as the target medium. Natural sand (naturally generated rock particles with a particle size less than 4.75 mm) was selected as the sand, and the initial velocities of the fragments were 689 m/s~1761 m/s (fragment diameter 6 mm) and 596 m/s~1325 m/s (fragment diameter 11 mm), respectively. Based on the residual velocity of fragments and experimental phenomena in experimental data, the authors used LS-DYNA software to numerically simulate and compare the residual velocity of fragments and obtained a numerical model for sandy soil media and a calculation formula for the residual velocity of spherical fragments. Based on modeling equivalence in practical environments, the authors studied the impact of different attack angles on fragment trajectory deviation and found that fragments have the highest deviation values at 20° and 70° attack angles. They also analyzed the soil boundary effect within a small scale range, and the effect was significant when the vertical distance was less than 40 mm. The penetration resistance of different thicknesses of soil was calculated, and the maximum soil thickness under prefabricated fragment penetration at different speeds was obtained. The effective protective size of the soil under actual conditions was about 550 mm. This experiment provides a reference for the construction parameters of simple soil defense structures in actual environments.

Mitigating potentially hazardous asteroid impacts revisited

Contact. Potentially hazardous asteroids (PHA) in Earth-crossing orbits pose a constant threat to life on Earth. Several mitigation methods have been proposed, and the most feasible technique appears to be the disintegration of the impactor and the generation of a fragment cloud by explosive penetrators at interception. However, mitigation analyses tend to neglect the effect of orbital dynamics on the trajectory of fragments. Aims. We aim to study the effect of orbital dynamics of the impactor’s cloud on the number of fragments that hit the Earth, assuming different interception dates. We investigate the effect of self-gravitational cohesion and the axial rotation of the impactor. Methods. We computed the orbits of 105 fragments with a high-precision direct N-body integrator of the eighth order, running on GPUs. We considered orbital perturbations from all large bodies in the Solar System and the self-gravity of the cloud fragments. Results. Using a series of numerical experiments, we show that orbital shear causes the fragment cloud to adopt the shape of a triaxial ellipsoid. The shape and alignment of the triaxial ellipsoid are strongly modulated by the cloud’s orbital trajectory and, hence, the impact cross-section of the cloud with respect to the Earth. Therefore, the number of fragments hitting the Earth is strongly influenced by the orbit of the impactor and the time of interception. A minimum number of impacts occur for a well-defined orientation of the impactor rotational axis, depending on the date of interception. Conclusions. To minimise the lethal consequences of an PHA’s impact, a well-constrained interception timing is necessary. A too-early interception may not be ideal for PHAs in the Apollo or Aten groups. Thus, we find that the best time to intercept PHA is when it is at the pericentre of its orbit.

Mitigating casualty risks from primary fragmentation hazards

Primary fragmentation from detonation of high-explosive metal-cased munitions imposes significant risks to the safety of related personnel and the public. Barricades or other protective structures are commonly used to stop fragments and reduce casualty risks caused by detonated munitions when a sufficient safety distance cannot be guaranteed. This study aims to provide decision support for the positioning of barricades that can reasonably mitigate primary fragmentation hazards from the detonation of large calibre munitions using a probabilistic risk assessment approach. This approach enables a stochastic characterization of fragment ejections, stacking effects, fragment trajectories, human vulnerability and fragment hazard reduction by barricade. In a case study, the assessments of casualty risks and effectiveness of barricades were conducted for a single and a pallet of 155 mm projectiles. It was found that barricades with heights exceeding the height of munitions can significantly reduce the hazardous fragment densities and casualty risks beyond the barricade. The benefit of increasing the barricade height becomes marginal when it exceeds the height of munitions.

Research on rotational angular velocity of preformed fragments

The rotational angular velocity of fragments under the driver of explosive products makes the fragments constantly flip during the trajectory, which has a huge effect on the velocity decay of the fragments. In order to more accurately calculate the residual velocity of the fragments during flight, it is necessary to study the rotational angular velocity of the fragments. Based on the paper target system, an experimental method for measuring the angular velocity of fragments is proposed. By using ANSYS/LSDYNA finite element software, the rotational angular velocity of preformed fragments under explosion is studied. A new meshing method is proposed to simulate the driven process of the explosive products on the fragments more accurately. The experimental results and the numerical simulation results are considered to be consistent within the margin of error. And at last, the distribution of fragment is studied base on numerical simulation. The research results provide a foundation for studying the trajectory of preformed fragments after explosive driven.

Study on Joint Damage of Double Prefabricated Fragments Penetrating Finite Thickness Concrete

In order to study the joint damage mechanism of multiple prefabricated fragments to finite thickness concrete targets, experiments on the damaging effect of a single fragment on a 300 × 300 × 100 mm concrete target were carried out, and the reliability of the simulation calculation model of single fragment damage to concrete was verified. On this basis, according to the trajectory of two fragments penetrating concrete, the double fragment penetration is divided into two penetration situations, that is, coplanar and heterogeneous. The orthogonal optimization method is used to carry out the joint damage simulation calculation of the double fragments to the concrete target by changing the fragment velocity, penetration angle, fragment spacing, and other factors. The simulation results show that the relationship between joint damage and fragment spacing is the largest when the fragment trajectories are coplanar, and the partial least squares regression coefficients affecting the joint damage time and surface joint length are 0.70 and 0.68 respectively. When the trajectory is different, the joint damage mode is relatively complex. Based on this, the joint damage degree analysis method between fragments is established, and each variable can explain 73.8% of the joint damage degree. It is found that the joint damage of the front pit area is the largest when the fragment is in different planes, and the PLS regression coefficient is −0.44. The hypothesis that joint damage is easy to occur in the area of the intersection line on the back of the target is analyzed and verified.

Fragmented care trajectories in municipal healthcare: Local sensemaking of digital documentation.

Since the 1990s, almost all healthcare organisations have had electronic health records (EHR) to organise and manage treatment, care and work routines. This article aims to understand how healthcare professionals (HCPs) make sense of digital documentation practice. Based on a case study design, field observations and semi-structured interviews were conducted in a Danish municipality. A systematic analysis based on Karl Weick's sensemaking theory was applied to investigate what cues HCPs extract from timetables in the EHR and how institutional logics frame the enactment of documentation practice. The analysis uncovered three themes: making sense of planning, making sense of tasks and making sense of documentation. The themes illustrate that HCPs make sense of the digital documentation practice as a dominant managerial tool designed to control resources and work routines. This sensemaking leads to a task-oriented practice which centres on delivering fragmented tasks according to a timetable. HCPs mitigate fragmentation by responding to a care professional logic, where they document to share information and carry out invisible work outside of timetables and scheduled tasks. However, HCPs are focused on solving specific tasks by the minute with the possible consequence that continuity and their overview of the service user's care and treatment disappear. In conclusion, the EHR system eliminates a holistic view of care trajectories, leaving it up to HCPs to collaborate in an effort to obtain continuity for the service user.

Bidirectional Multiple Object Tracking Based on Trajectory Criteria in Satellite Videos

Multiple object tracking (MOT) in satellite videos requires to detect all objects belonging to specified categories and identify each object, which plays a basic and necessary role in automatic driving, traffic surveillance and smart city. The traditional MOT methods in satellite videos mostly follow the detection-association framework. However, detection-association framework works under a strict assumption that all objects are correctly localized by the detector. In practice, MOT in satellite videos faces challenges such as low resolution, tiny objects, and the wide field of view, which leads to the degradation of detector performance. In order to reduce the impact of detector degradation, we propose a bi-directional multiple object tracking framework based on trajectory criteria (BMTC) in satellite videos. In BMTC, the SOT tracker carries out locating the objects between consecutive frames and the detector is just used for finding new objects. Therefore, it is less dependent on the detector performance. According to the characteristics of satellite videos, the trajectory criteria are designed to control the state of the tracker, which includes trajectory density, the limit of consecutive virtual motion predictions, and trajectory similarity measurement. Invalid fragment trajectory backtracking is implemented to alleviate the misalignment caused by the above subsection trajectory criteria. The method is validated on the VISO benchmark and SkySat-1 dataset. The experimental results show the improvement of completeness and accuracy, and the proposed tracker achieves state-of-art performance.

On the Dynamic Fragmentation of Rock-Like Spheres: Insights into Fragment Distribution and Energy Partition

Fragmentation of blocks upon impact is commonly observed during rockfall events. Nevertheless, fragmentation is not properly taken into account in the design of protection structures because it is still poorly understood. This paper presents an extensive and rigorous experimental campaign that aims at bringing insights into the understanding of the complex phenomenon of rock fragmentation upon impact. A total of 114 drop tests were conducted with four diameters (50, 75, 100, and 200 mm) of rock-like spheres (made of mortar) of three different strengths (34, 23 and 13 MPa), falling on a horizontal concrete slab, with the objective to gather high-quality fragmentation data. The analysis focuses on the fragment size distribution, the energy dissipation mechanisms at impact and the distribution of energy amongst fragments after impact. The results show that the fragment size distributions obtained in this campaign are not linear on a logarithmic scale. The total normalised amount of energy loss during the impact increases with impact velocity, and consequently the total kinetic energy after impact decreases. It was also found that energy loss to create the fracture surfaces is a constant fraction of the kinetic energy before impact. The trajectories of fragments are related to the impact velocity. At low impact velocity, the fragments tend to bounce but, as the impact velocity increases, they tend to be ejected sideways. Although testing mortar spheres in normal impact is a simplification, the series of tests presented in this work has brought some valuable understanding into the fragmentation phenomenon of rockfalls.

‘Our home, your home?’ The precarious housing pathways of asylum seekers in Catalonia

This paper investigates the multi-layered barriers asylum seekers face in accessing secure and adequate housing in a host society through the case of Catalonia (Spain). While the existing literature mainly focuses on the effects of micro-level factors, we argue that these need to be analysed in combination with meso-level actors and macro-structural phenomena. Drawing on an exploratory survey of 300 international protection applicants and 60 semi-structured interviews with stakeholders and asylum seekers, we analyse their exposure to different dimensions of housing precariousness. Our research finds that, although certain individual characteristics such as age, sex and origin remain relevant in explaining housing pathways, these factors are strongly mediated by the role of NGOs and support networks, and by the structural features of the asylum system and housing market. We conclude that the complex interactions of these factors result in deeply unstable and fragmented housing trajectories that contribute to high levels of disorientation, precariousness, and exclusion among those seeking accommodation.

In Situ Measurement of the Fragmentation Behavior of Al/PTFE Reactive Materials Subjected to Explosive Loading, Part 2: Fragment Velocity and Trajectory Measurements

AbstractHigh‐speed optical diagnostics and image analysis methods are applied to implement an automated Kalman filter based tracking technique to measure fragment size, velocity, and trajectories for studying the fragmentation behavior of explosively launched Al/PTFE cylinders. Bivariate histograms of equivalent spherical diameters of fragments greater than 1 mm and their corresponding velocities are presented to describe the explosively‐driven fragmentation behavior of several Al/PTFE specimens. Spatial cross‐correlation of fragments is also implemented to optically determine, from high‐fidelity high‐speed images, the spatial distribution of fragment trajectories inside the diagnostic section. Sizes determined from the Kalman filter based tracking process are compared with the sizes determined from the high‐fidelity measurements in Part 1. Similarly, the velocities of discretely tracked fragments are compared to velocity estimates from the bulk fragment displacement calculated using a phase correlation routine.

Collisions between liquid droplets during the intersection of aerosol flows in a heated gas

• A rise in the gas temperature led to an increase in the number of secondary fragments. • At T g = 300–400 °C droplets with r d = 0.075–0.1 mm prevail. • A temperature rise contributed to a 2–3 times increase in area ratios S 1 / S 0. • At T g = 100–400 °C, droplets increased in size due to expansion of liquid on heating. • The motion of droplets in a heated gas led to a 10–30% change in their size due to evaporation. The paper presents the experimental findings on the water droplet collision behavior during the intersection of two aerosol flows in a high-temperature gas environment. Aerosol flows were produced by two strip pattern nozzles angled at 45° towards each other in the same plane. The resulting flow had an opening angle of 60°. The droplet impact angle (α d ) was varied from 0 to 90°, droplet radii ( R d1 , R d2 ) from 0.1 to 1.2 mm, and droplet velocities ( U d1 , U d2 ) from 2 to 12 m/s. The gas temperature in the droplet collision zone was varied using an induction heater with an internal volume of about 0.13 m 3 with viewing windows to record the key parameters (number, size, velocities, and trajectories) of liquid fragments before and after collision. The air temperature ranged from 20 to 400 °C in the experiments. Using a high-speed video camera, we recorded four collision regimes: coalescence, separation, disruption, and bounce. We also identified the main differences in the number and size of secondary droplets formed in an aerosol flow after the collision of two primary ones. A temperature rise led to an increase in the number of secondary fragments. The size distributions of secondary fragments are presented for three ranges of size ratios of initial droplets: Δ < 0.3; 0.3 < Δ < 0.7; Δ > 0.7. The impact of droplet collisions on their size variation rates was estimated at the gas temperature T g = 20–400 °C. Finally, we compared the contribution of this factor and evaporation without droplet-droplet collisions.

People with chronic wounds cared for at home in Belgium: Prevalence and exploration of care integration needs using health care trajectory analysis

BackgroundLittle is known about the prevalence of people with chronic wounds cared for at home and their care integration needs in Belgium. In high-income countries, chronic wounds are associated with ageing processes, chronic diseases and social and financial vulnerability, resulting in multiple needs. To meet these needs, many health care providers (with nurses figuring prominently) are involved. This can lead to fragmented health care trajectories and the need to strengthen care coordination. ObjectivesThis study aims to estimate the prevalence of people with chronic wounds cared for at home in Belgium. It also seeks to explore their health care trajectories and the risk of fragmentation of care to inform policy makers, care providers and research. DesignCross-sectional. Setting(s)Home care. ParticipantsRoutinely collected data of reimbursed care of 3467 people with a chronic wound cared for at home in 2018. MethodsWe applied a stratification method to our sample based on health care trajectories. First, we constructed individual sequences of care received during the year. Then we summarised the health care events using a K-mers approach. Finally, a multinomial mixture model was used on the previously obtained summary to cluster individuals according to their health care trajectories. Afterwards, other epidemiological, socioeconomic and health care use indicators were calculated for each health care trajectory group.We also estimated the prevalence of people with chronic wounds treated at home. ResultsWe constructed six health care trajectory groups for two age categories (<65 and ≥65 years) showing different intensity of care use and type of care. In some health care trajectory groups, generalist care was found to be predominant. In others, specialist care appeared more prevalent. Depending on the health care trajectory group, a significant proportion of people had multiple care providers involved (mainly nurses, medical specialists and GPs), and many of them also had multiple transitions between care settings.The prevalence of people with chronic wounds treated at home rises significantly with age: 0.3%, 95%CI (0.2%–0.4%) for people aged under 65, 2.5%, 95%CI (2.3%–2.8%) for people aged 65 and over. ConclusionA significant proportion of people with chronic wounds experienced multiple transitions and met many health care providers. This can lead to complex trajectories and risk of fragmentation. Nurses, who are intensively involved in wound care at home, with the appropriate skills, could play a ‘reference’ role to promote continuity of care and better coordination. RegistrationNot registered.

Reconstruction of fragmented trajectories of collective motion using Hadamard deep autoencoders

Learning dynamics of collectively moving agents such as fish or humans is an essential task in research. Due to phenomena such as occlusion or change of illumination, the multi-object methods tracking such dynamics may lose the tracks of the agents which may result in fragmentations of trajectories. Here, we present an extended deep autoencoder (DA) that we train only on the fully observed segments of the trajectories by defining its loss function as the Hadamard product of a binary indicator matrix with the absolute difference between the outputs and the labels. The trajectory matrix of the agents practicing collective motion is low-rank due to mutual interactions and dependencies between the agents that we utilize as the underlying pattern that our Hadamard deep autoencoder (HDA) codes during its training. The performance of this HDA is compared with that of a low-rank matrix completion scheme in the context of fragmented trajectory reconstruction.