Movement Of Debris Research Articles

Selective accumulation of plastic debris at the breaking wave area of coastal waters

Over the last decades, plastic debris has been identified and quantified in the marine environment. Coastal and riverine input have been recognized as sources of plastic debris, whereas oceanic gyres and sediments are understood to be sinks. However, we have a limited understanding of the fate of plastic debris in the nearshore environment. To investigate the movement and distribution of plastic debris in the nearshore environment, we collected samples at three distinct locations: below the high tide line, the turbulent zone created by the combination of breaking wave and backflush (defined as the boundary), and the outer nearshore. We estimated the abundance and physical characteristics (e.g. density, hardness, etc.) of macroplastic and microplastics. Four times and 15 times more macroplastics and microplastics are observed, respectively, at the boundary than in the outer nearshore waters, which suggests an accumulation driven by the physical properties of the plastic particles such as density, buoyancy and surface area. We further report that highly energetic conditions characteristic of the boundary area promote the long-term suspension and/or degradation of low density, highly buoyant or large surface area plastic debris, leading to their preferential accumulation at the boundary. Contrastingly, denser and low surface area plastic pieces were transported to the outer nearshore. These results emphasize the role of selective plastic movement at the nearshore driven by physical properties, but also by the combined effects of several hydrodynamics forces like wave action, wind or tide in the resuspension, as well as degradation and transport of plastic debris out of the nearshore environment.

Repeated Impact-Based Capture of a Spinning Object by a Dual-Arm Space Robot.

This paper presents detumbling and capture of space debris by a dual-arm space robot for active space debris removal missions. Space debris, such as a malfunctioning satellite or a rocket upper stage, often has uncontrolled tumbling motion. It also has uncertainties in its parameters, such as inertial characteristics or surface frictional roughness. These factors make the debris capture missions difficult to accomplish. To cope with such challenging missions, we propose a detumbling and capture control method for a dual-arm robot based on repeated impact capable of suppressing the debris motion by repeatedly utilizing an effect of a passive damping factor in the contact characteristics. In this paper, as the initial step of a study on the repeated impact-based capture method, we assume that the capture target is a rocket upper stage that can be simply modeled as a cylindrical body and mainly has angular velocity motion in its principle axis of inertia. A motion tracking control law of an end-effector of the robot arm is introduced to maintain the repeated impact. The proposed control method enables the robot to accomplish the detumbling and capture without precise estimation of the inertial characteristics and surface frictional roughness of the debris. The validity of the proposed method is presented by numerical simulations and planar microgravity experiments using an air-floating system. In particular, the experimental evaluation shows the fundamental feasibility of the proposed method, and thus, the result contributes to a practical application.

Long-Term Rotational Motion Analysis and Comparison to Observations of the Inoperative Envisat

A new model for the analysis and prediction of the rotational motion of large space debris over a long term is outlined. A formulation for a high-order gravity-gradient torque is derived as well as the aerodynamic torque for a spinning spacecraft defined by a general surface geometry model. The comprehensive model is exercised for a coupled orbit-attitude propagation of the defunct satellite Envisat. An in-depth analysis of the simulation results reveals that, unlike what has been assumed previously, the likelihood of Envisat’s spin axis remaining stable is small. A distinct nutation of the spacecraft’s angular momentum vector about the orbit normal is predicted, having a period on the order of a few days. Although a decay of the angular rate is expected, the nutation motion of the spin axis is expected to become larger and faster with time, underlining a potential difficulty for a future active debris removal mission. A critical review of observational studies reported on Envisat’s rotational state is performed, in light of the knowledge gained from the simulations and with a comparison to the simulation results. Finally, recommendations for future observation campaigns to provide better estimates of Envisat’s angular motion are put forward.

Threshold of motion and settling velocities of mollusc shell debris: Influence of faunal composition

AbstractBioclastic particles derived from mollusc shell debris can represent a significant fraction of sandy to gravelly sediments in temperate and cool‐water regions with high carbonate productivity. Their reworking and subsequent transport and deposition by waves and currents is highly dependent on the shape and density of the particles. In this study, the hydrodynamic behaviour of shell debris produced by eight mollusc species is investigated for several grain sizes in terms of settling velocity (measurements in a settling tube) and threshold of motion under unidirectional current (flume experiments using an acoustic profiler). Consistent interspecific differences in settling velocity and critical bed shear stress are found, related to differences in shell density, shell structure imaged by scanning electron microscopy and grain shape. Drag coefficients are proposed for each mollusc species, based on an interpolation of settling velocity data. Depending on the shell species, the critical bed shear stress values obtained for bioclastic particles fall within or slightly below empirical envelopes established for siliciclastic particles, despite very low settling velocity values. The results suggest that settling velocity, often used to describe the entrainment of sediment particles through the equivalent diameter, is not a suitable parameter to predict the initiation of motion of shell debris. The influence of the flat shape of bioclastic particles on the initiation of motion under oscillatory flows and during bedload and saltation transport is yet to be elucidated.

A Simulation Study of Debris Removal Process in Ultrasonic Vibration Assisted Electrical Discharge Machining (EDM) of Deep Holes †.

When machining a small hole with high aspect ratio in EDM, it is hard for the flushing liquid entering the bottom gap and the debris could hardly be removed, which results in the accumulation of debris and affects the machining efficiency and machining accuracy. The assisted ultrasonic vibration can improve the removal of debris in the gap. Based on dynamics simulation software, Fluent, a three-dimensional (3D) model of debris movement in the gap flow field of EDM small hole machining assisted with side flushing and ultrasonic vibration is established in this paper. The laws of different amplitudes and frequencies and different aspect ratios on debris distribution and movement are quantitatively analyzed. The motion height of debris was observed under different conditions. The research results show that periodic ultrasonic vibration can promote the movement of debris, which is beneficial to the removal of debris in the machining gap. When compared to traditional small hole machining in EDM, the debris in the machining gap were greatly reduced, which ensures the stability of the machining process and improves the machining efficiency.

Connecting flux, deposition and resuspension in coastal debris surveys

For decades, community groups and scientists have sampled coastal waste along shorelines to understand the distribution of debris. However, when debris is washed ashore or locally deposited, it may be washed away before it is removed or recorded. Using statistical models to understand the movement of debris in coastal processes may identify potential sinks of anthropogenic debris. We modelled arrival and departure of debris using data from repeated removal and marking experiments. Both the arrival and departure of debris were affected by the substrate of the shoreline and by seasonal changes (e.g. autumn and winter). Different substrates accumulated different types of debris. The backshore, coastal shape and wind exposure had all affected the departure but not the arrival of debris. Our findings suggest that areas with high accumulation have lower departure, rather than higher arrival of debris. The implication is that counting debris in dirty locations, as when cleanup activities are used for monitoring, will provide a misleading measure of the actual debris in adjoining waters. We found that onshore winds and lower profile backshore vegetation increase the departure of debris. Debris may be moving inland and accumulating in the backshore vegetation, suggesting the backshore vegetation could be a substantial sink of missing marine debris. Overall, inferring the state of plastic pollution in the ocean using one “snapshot” on shore may underestimate the output of debris from land-based sources, whilst overestimating ocean loads near sites that retain or accumulate high levels of debris.

Attitude motion of space debris during its removal by ion beam taking into account atmospheric disturbance

The paper is devoted to the issue of active large space debris removal. The contactless method of influencing space debris through the ion flow is considered. The main advantage of this method is absence of a dangerous and complex stage of space debris capturing or docking. In this study, the project “Ion Beam Shepherd” was taken as a basis. The aim of this paper is to study the effect of the atmosphere in LEO on the space debris behaviour during its removal. The equations of plane motion of space debris under the action of the ion beam, gravitational and aerodynamic forces and torques were obtained using Lagrange formalism. For calculation ion beam force and torque the self-similar model of ion engine plume exploration and fully diffused reflection model of ions interaction with the surface were used. Simulation of deorbiting the spent upper stage of the Cosmos 3M rocket was carried out. Phase portraits of the rocket stage attitude motion for various heights were constructed and analysed. It was shown that the motion of the stage around its centre of mass has a noticeable effect on the average ion beam force and descent time.

Restoration of low-informative image for robust debris shape measurement in on-line wear debris monitoring

Abstract As a significant technique in machine condition monitoring, wear debris analysis enables investigation of machine running condition with respect to debris features including size, quantity and morphology. In particular, being capable of providing more comprehensive morphological information, three-dimensional debris features are regarded essential and often acquired through a video-based debris imaging process. However, debris images captured often suffer degradation due to debris motion blur and lubrication contamination, that hinder reliable debris features extraction. To address the image degradation issue, a new method of wear debris image restoration is developed to reduce the effect of blur. In order to avoid the expensive computation involved in blind deconvolution methods, the debris image was restored using localized boundary features. Based on the fact that debris area and background area indicate distinctive brightness, a step edge model is applied to describe the original debris boundary. Localized kernels on each side of debris are then determined. Next, restorations are conducted with the estimated kernels to produce sharper debris profiles with respect to different motion features. Final restoration is conducted by fusing the restored profiles according to the maximum local sharpness. Experimental results have demonstrated that this method allows reliable features extraction from blurred image, improving the robustness of video based wear debris analysis.

Accretion behavior and debris flow along interelectrode gap in μED-milling process

In microelectrodischarge milling (μED-milling) process, material removal occurs in the form of debris and these particles are predominantly spherical in shape with size varying from few nanometers to micrometers. The behavior of the debris particles in μED-milling is not well discussed in the literature, and this study will provide useful insight into the debris movement and its accretion on machining surfaces. Debris in its molten or cooled state will cause major issues in the μED-milling process such as secondary discharge and redeposition. Its presence at one location in large number gives rise to secondary discharge causing a disturbance in sparking, and its movement may affect the geometry of channel due to redeposition. The necessary drive for debris movement along the gap is provided by tool rotation. The experimental investigation of debris movement with dielectric at a gap of few micrometers is practically difficult due to complex phenomenon of the process. Thus, the present objective is focused to investigate the movement of debris and dielectric in the gap through simulation with consideration for fluid debris interaction and subsequent deposition. The effect of debris size, the position of injection, and the tool speed on the accretion of particles on the surface are analyzed by ANSYS Fluent. The trajectory of the particles, distance traveled, and accretion rate are calculated using discrete phase modeling. The 2D simulation results of accretion are compared with experimental surface micrographs.

SPOOK - A comprehensive Space Surveillance and Tracking analysis tool

Space Surveillance and Tracking (SST) is the ability to detect and predict the movement of space debris in orbit around the Earth. SPOOK (SPace Object Observations and Kalman filtering) is a versatile and highly configurable software tool developed by Airbus, for the detection, cataloguing and orbit prediction analysis of Earth orbiting objects. It provides an integrated framework for all the activities related with SST sensor architecture simulation. Throughout this paper, the functionalities of the tool are described and examples of different simulation scenarios are provided.

Numerical Analysis of Behavior on Opposing Unsteady Supersonic Jets in a Flow Field with Shields

Collision dynamics of opposing unsteady supersonic jets injected in background gas with shock waves were calculated to simulate double pulsed laser ablation. Since the jets are deflected by collision and the motion of debris is ballistic. This characteristic can be used to reduce the number of debris when shields are mounted in front of substrate. The flow of jets through installed shields is complicated by the interaction between shields and jets, and between shields and shock waves. We investigate influence of shield position on the shock waves and the jets by numerical calculations. Axisymmetric two-dimensional compressible Euler equations were solved using the finite volume method by using ANSYS Fluent 14.0.0 code. The shields with slit was mounted parallel to the direction of initially injected jets. In order to investigate the influence of shield position on the shock waves and the jets, the shield position and background gas pressure were adopted as parameters. The jets and shock wave are deflected by collision and they can pass through the slit of shields. The passed shock wave reflects at the substrate mounted behind the slits and it forces back the jet to decrease the jet velocity. The shield position governs the velocity and amount of the jet that reach the substrate.

Influence of Jet Flushing on Corner Shape Accuracy in Wire EDM

In wire electrical discharge machining (EDM), wire electrode easily breaks and the shape accuracy tends to decrease when cutting corner shapes. The wire electrode during the process is subjected to discharge explosive forces, electrostatics force with open voltage application and hydrodynamics force by jet flushing. Then, the wire always deflects in the opposite side of cutting direction. On the other hands, wire breakage is caused mainly by discharge concentrations at the same location due to much debris stagnation in the narrow machined kerf. Therefore, jet flushing of dielectric fluid with nozzles has been conventionally applied for smooth debris exclusion. However, excessive flow rate may promote large wire vibration and deflection. In addition, the influence of jet flushing conditions on the debris exclusion and wire deflection in the corner shape cutting has not yet been investigated so far. In this study, the flow fields and debris movements in the machined kerf during the corner shape cutting in 1st-cut wire EDM were simulated by CFD analysis. Also, wire deflection was discussed by a structural analysis of wire with stress distribution due to hydrodynamics force obtained by the CFD analysis. The results showed that the flow field and pressure field around the wire by jet flushing changed significantly just after changing the cutting direction at the corner. Furthermore, steady circulation area behind the wire disappeared temporarily just after the corner, and debris stagnation in the machined kerf decreased at that time. Additionally, the corner shape error with wire deflection was experimentally measured and compared to analytical result of wire deflection by hydrodynamics force. It was found that the influence of hydrodynamics force on wire deflection was as large as discharge explosive force under general 1st- cut conditions, which suggests that the influence of jet flushing on the corner shape accuracy is large under relatively high flow rate conditions.

Comparative analysis of limit equilibrium and numerical methods for prediction of a landslide

Landslides that occur due to the rapid motion of a rock-mass are a primary risk in mountainous terrains and are a danger to human life and civil infrastructure. The application of geotechnical engineering methodologies for remedial purposes is to assess unpredictable behavior and the stability of the slope, and for analysis and design. The aim of the study is to quantify the global factor of safety (FOS) and describe a correlative and comparative assessment of the conventional Limit Equilibrium Model as compared with the advanced Numerical Model for the rock slopes of Amiya, Nainital, Uttarakhand in India utilizing Mohr-Coulomb failure criterion. The rock-mass characteristics were determined as a result of an estimation of the physio-mechanical properties of rock and debris from collected field samples with the help of the joint weakening coefficient for limit equilibrium (LE) and the numerical solution. Global FOS estimated by means of stability analysis procedures, such as Swedish slip circle, Ordinary method of slices, Modified Bishop, Janbu method, Finite difference static analysis, Finite element static, and Finite difference dynamic analysis, was found to be 0.65, 1.34, 1.38, 1.29, 1.57, 1.144, and 0.84, respectively. The results helped to deduce that the slope remains substantially stable and failure may only occur in the case of a down slope movement of rock debris (clastic mass of rocks) with a small local/global tremor. Combination of the LE technique and numerical approach (hybrid approach) has been found to be a better method for critical slip surface and FOS determination.

Study on Gap Flow Field Simulation in Small Hole Machining of Ultrasonic Assisted EDM

When machining a small hole with high aspect ratio in EDM, it is hard for the flushing liquid entering the bottom gap and the debris could hardly be removed, which results in the accumulation of debris and affects the machining efficiency and machining accuracy. The assisted ultrasonic vibration can improve the removal of debris in the gap. Based on dynamics simulation software Fluent, a 3D model of debris movement in the gap flow field of EDM small hole machining assisted with side flushing and ultrasonic vibration is established in this paper. When depth to ratio is 3, the laws of different amplitudes and frequencies on debris distribution and removal are quantitatively analysed. The research results show that periodic ultrasonic vibration can promote the movement of debris, which is beneficial to the removal of debris in the machining gap. Compared to traditional small hole machining in EDM, the debris in the machining gap is greatly reduced, which ensures the stability of machining process and improves the machining efficiency.

Yarkovsky-Schach effect on space debris motion

The Yarkovsky-Schach effect is a small perturbation affecting Earth satellites and space debris illuminated by the Sun. It was first applied to the orbit of LAGEOS satellites as an explanation of the residuals in orbital elements. In this work, we carry out several numerical integration tests taking into consideration various orbit and rotation parameters, in order to analyse this effect in a broader context. The semi-major axis variations remain small and depend on the spin axis attitude with respect to the Sun. We show that the force amplitude is maximised for orbits inclined with i≈ 20–30°. We also observe the influence on other orbital elements, notably on the orbit inclination. However, these effects are clearly observed only on long timescales; in our simulations, we propagated the orbits for 200 y. The Yarkovsky-Schach effect is thus confirmed to have a minuscule magnitude. It should be taken into account in studies requiring high-precision orbit determination, or on expanded timescales.

Influence of alternating side gap on micro-hole machining performances in micro-EDM

In the machining of micro-hole by micro-EDM, the narrow and uniform side gap leads to the difficulty in removing discharge debris from the working area, which causes frequent occurrence of abnormal discharges such as short circuit. In this study, a three-dimensional model with alternating side gap was proposed, based on which the flow field and movement of discharge debris in working gap were analyzed. Simulation results showed that the alternating side gap changed the flow field pattern in bottom gap, and the flow velocities both in bottom gap and side gap were increased as the enlargement of eccentric radius. In addition, when the alternating side gap was adopted, the concentration of debris particles in the bottom gap was dramatically decreased due to the improvement of flow field in the working gap, and the percentage of escaped debris particles was increased. Verifying experiments were carried out and the influences of alternating side gap on the micro-hole machining performances were addressed, which showed that both the material removal rate and aspect ratio of micro-hole were improved as the eccentric radius increases. Nevertheless, the eccentric radius still needs to be determined reasonably in consideration of the wear of electrode.

A novel thermo-hydraulic coupling model to investigate the crater formation in electrical discharge machining

A novel thermo-hydraulic coupling model was proposed in this study to investigate the crater formation in electrical discharge machining (EDM). The temperature distribution of workpiece materials was included, and the crater formation process was explained from the perspective of hydrodynamic characteristics of the molten region. To better track the morphology of the crater and the movement of debris, the level-set method was introduced in this study. Simulation results showed that the crater appears shortly after the ignition of the discharge, and the molten material is removed by vaporizing in the initial stage, then by splashing at the following time. The driving force for the detachment of debris in the splashing removal stage comes from the extremely large pressure difference in the upper part of the molten region, and the morphology of the crater is also influenced by the shearing flow of molten material. It was found that the removal ratio of molten material is only about 7.63% under the studied conditions, leaving most to form the re-solidification layer on the surface of the crater. The size of the crater reaches the maximum at the end of discharge duration then experiences a slight reduction because of the reflux of molten material after the discharge. The results of single pulse discharge experiments showed that the morphologies and sizes between the simulation crater and actual crater are good at agreement, verifying the feasibility of the proposed thermo-hydraulic coupling model in explaining the mechanisms of crater formation in EDM.

Theoretical and experimental study of magnetic-assisted finish cutting ferromagnetic material in WEDM

Abstract In this paper, a method of magnetic assisted is firstly proposed to improve the machining performance of finish cutting ferromagnetic material in WEDM, and theoretical and experimental study of this method is implemented to illustrate its improving mechanism. Firstly, a simple motion trajectory model of electron beam is established in forming discharge channel process, and it indicates that additional constant magnetic field can efficiently suppress the divergence phenomenon of electron beam and shorten discharge gap breakdown time. Besides, a set of single pulse discharge experiment agrees well with the inference of the simple electron beam motion trajectory model, and the discharge crater volume increases by 22.2% when 0.14 T magnetic field is applied to discharge machining. Secondly, the charged debris motion curve of magnetic assisted finish cutting is worked out, and it reveals that more charged debris can be washed away when the direction of Lorentz force is the same with dielectric flushing. Additionally, a set of continuous discharge experiment is accomplished to investigate the improving effect of constant magnetic field, and experiment result represents that significantly improvement (material removal rate (MRR) maximum increase by 44.0%, and surface roughness (Ra) maximum reduce by 30.5%) has been obtained. Eventually, by the method of multi-objective optimization, a group of Pareto optimal set of MRR and Ra is worked out to satisfy different requirement of practical manufacturing.

Tsunami-Driven Debris Motion and Loads: A Critical Review

Recent natural disasters, such as the 2004 Indian Ocean and 2011 Tohoku Tsunami, exhibited the importance of tsunami resistant infrastructure in high-risk coastal areas. The failure of critical infrastructure in tsunami-stricken communities has led to a recent emphasis on extreme loading conditions associated with tsunami events. One of the critical loads identified by previous research was debris loads. Debris is defined as solid objects entrained within the inundating flows and can range from construction materials to shipping vessels. The emphasis of tsunami loading has led to recent progression in the understanding of debris loads and effects, particularly in evaluating the impact of a single debris piece on a structure. The following paper reviews state-of-the-art research in tsunami-driven debris motion and loads and identifies future directions of research into debris loads and effects to aid in the design of tsunami-resistant infrastructure.

Study on the Gap Flow Simulation in EDM Small Hole Machining with Ti Alloy

In electrical discharge machining (EDM) process, the debris removed from electrode material strongly affects the machining efficiency and accuracy, especially for the deep small hole machining process. In case of Ti alloy, the debris movement and removal process in gap flow between electrodes for small hole EDM process is studied in this paper. Based on the solid-liquid two-phase flow equation, the mathematical model on the gap flow field with flushing and self-adaptive disturbation is developed. In our 3D simulation process, the count of debris increases with number of EDM discharge cycles, and the disturbation generated by the movement of self-adaptive tool in the gap flow is considered. The methods of smoothing and remeshing are also applied in the modeling process to enable a movable tool. Under different depth, flushing velocity, and tool diameter, the distribution of velocity field, pressure field of gap flow, and debris movement are analyzed. The statistical study of debris distribution under different machining conditions is also carried out. Finally, a series of experiments are conducted on a self-made machine to verify the 3D simulation model. The experiment results show the burn mark at hole bottom and the tapered wall, which corresponds well with the simulating conclusion.