Debris Velocity Research Articles

Sensitivity analysis of influencing parameters on slit-type barrier performance against debris flow using 3D-based numerical approach

Extreme rainfall-induced debris flow can be catastrophic to an urban area, and installation of slit-type barriers can prevent such damage while minimizing negative impact on environments. However, the performance of slit-type barriers against debris flows remains poorly identified partly due to the innate complexity in interactions between debris flow and solid structure. This paper investigated the flow behaviors of debris affected by slit-type barriers using the computational fluid dynamics (CFD) method, in which the numerical model based on the volume of fluid method was verified using the physical modeling results. The sensitivity analysis was performed by building metamodels to determine the primary parameters influencing the barrier performance against debris flows among various variables, in which the effect of input properties and design parameters, particularly the soil concentration in fluidized debris, initial velocity and volume of debris, the barrier height, and the opening ratio, was evaluated from the perspectives of the flow energy reduction and debris trapping. The initial velocity and volume of debris were found to play a significant role in determining the debris flow characteristics. A decrease in the opening ratio in the channel primarily facilitated the energy reduction and trapping due to the reduced opening size. However, the barrier height exhibited a limited effect when the height was sufficiently high to block the debris flow volume. In addition, it was observed that the double barrier system effectively increased the energy reduction while keeping the benefit of open-type barrier. The developed simulation method and obtained results provide an effective tool and an insight that can contribute to an optimum design of the debris-flow barrier.

Simulating Plasma Solitons from Orbital Debris Using the Forced Korteweg–de Vries Equation

Subcentimeter orbital debris is currently undetectable using ground-based radar and optical methods. However, pits in space shuttle windows produced by paint chips demonstrate that small debris can cause serious damage to spacecraft. Recent analytical, computational, and experimental work has shown that charged objects moving quickly through a plasma will cause the formation of plasma density solitary waves, or solitons. Due to their exposure to the solar wind plasma environment, even the smallest space debris will be charged. Depending on the debris size, charge, and velocity, debris may produce plasma solitons that propagate along the debris velocity vector; and it could be detected with existing sensor technology. Plasma soliton detection would be the first collision-free method of mapping the small debris population. The amplitude, width, and production frequency of solitons that may be produced by millimeter and centimeter-scale orbital debris will be described as a function of the debris’ size, velocity, and location (altitude, latitude, and longitude) about Earth. The characteristics of plasma solitons described here are necessary to evaluate the feasibility of orbital debris detection via soliton detection with future debris detection systems.

Simulating Damped Ion Acoustic Solitary Waves from Orbital Debris

Nontrackable orbital debris has become a great risk to Earth-orbiting spacecraft. Subcentimeter debris is currently undetectable using ground-based radar and optical methods. Recent analytical, computational, and experimental work has shown that plasma density solitary waves, or solitons, will be produced by orbital debris due to their electrical charge, and propagate along the debris velocity vector. The amplitude and velocity of solitons that may be produced by millimeter–centimeter-scale orbital debris, as well as the orbital altitudes, latitudes, and velocities where solitons can be produced as a function of debris size, have been previously described. The Chan–Kerkhoven pseudospectral method is used now to apply the damped forced Korteweg–de Vries equation, calculate the damping rate of the solitons, and estimate the resulting soliton propagation distance. It is demonstrated that Landau damping dominates over collisional damping for these solitons. Pinned solitons, which travel with the debris, do not experience significant damping due to the presence of the persistent debris force at the soliton location, and will continue to propagate until the debris enters a region where pinned solitons cannot be created. The median propagation distance for precursor solitons, which advance ahead of the debris, is 10 km for 0.5-mm-radius debris and 6 km for 0.5-cm-radius debris. With the current absence of a dedicated, calibrated, on-orbit debris detection sensor, plasma soliton detection would be the first collision-free method of mapping the small debris population. It is necessary to understand the damping of solitons in order to assess the feasibility of on-orbit debris detection.

Hydrodynamic Ram Effect Caused by Debris Hypervelocity Impact on Satellite Tank

To study the hydrodynamic ram effect caused by the debris hypervelocity impact on the satellite tank, a numerical simulation of the spherical debris impacting the satellite tank at the velocity of 7000 m/s was carried out based on ANSYS/LS-DYNA software. The attenuation law of debris velocity, the propagation process of the shock wave and the deformation of the tank walls were investigated. The influences of the liquid-filling ratio, the magnitude, and direction of angular velocity on the hydrodynamic ram effect were analyzed. Results show that the debris velocity decreased rapidly and the residual velocity was 263 m/s when the debris passed through the tank. The shock wave was hemispherical, and the pressure of shock wave was the smallest at the element with an angle of 90° to the impact line. The maximum diameter of the front perforation was larger than that of the back perforation and the bulge height on the front wall was smaller than that on the back wall. With the decrease of the liquid-filling ratio, the diameter of the perforations and bulge height decreased. When the debris impacted the satellite tank with the angular velocity in the x direction, the debris trajectory did not deflect. When the debris impacted the satellite tank with the angular velocities in the y and z direction, the debris trajectory deflected to the negative direction of the z axis and y axis, respectively. The magnitude of the angular velocity affects the residual velocity of debris and the diameter of perforations.

An Inductive Debris Sensor for a Large-Diameter Lubricating Oil Circuit Based on a High-Gradient Magnetic Field

Wear is one of the main factors of machine failure. If abnormal wear was not detected in time during the operation of a mechanical system, it probably leads to catastrophic consequences. The wear debris in the lubricating oil circuit contains much information about equipment wear. Consequently, debris detection is regarded as an effective way to detect mechanical faults. In this paper, an inductive debris sensor based on a high-gradient magnetic field is presented for high-throughput lubricating oil circuits. The excitation coil of the sensor is driven by a constant current to generate a high-gradient magnetic field, and the induction coil is wound around the flow path. When wear debris cuts the magnetic line through the flow path, a corresponding induced voltage is generated. The experimental results show that the sensor output signal is linear with the drive current and the wear debris velocity. In addition, the shortest distance between the particles that the sensor output signals can be completely separated is 25 mm. When the distance is smaller, the induced signals are superimposed.

A model for thermal radiation from the Tunguska airburst

This paper develops a model for simulating the radiative flux reaching the ground originating from a meteor shock-layer and wake. The area of radiant burn measured for the Tunguska event provides a test case for the developed model. This model applies recently developed computational fluid dynamic simulations, which include the impact of ablation and radiation on the shock-layer flowfield, and ray-tracing radiation transport with atmospheric absorption. The impact of the meteor view angle is shown to significantly impact the radiative flux. Looking at the meteor along the flight path (head-on) results in lower radiative heating because it reduces the wake field of view, where the large radiating wake is shown to provide a significant contribution to the radiative flux (when viewed from the side). The impact of ablation on the ground radiative flux is negligible because the ablation products are limited to the optically-thick core of the wake. The resulting simulated radiative flux values are correlated as a function of velocity, altitude, view angle, and meteoroid radius. This correlation is then applied to potential Tunguska entry trajectories to provide a simulated ground heating footprint. Comparing this simulated footprint with the measured radiant burn area provides a metric for assessing unknown Tunguska entry parameters. Using this approach, the initial radius resulting in good agreement with the measured radiant burn footprint was found for a range of maximum debris cloud radii, entry angles, and velocities. The resulting optimal initial radii were between 30 and 45 m for the entire range of cases considered. This provides a valuable constraint on initial radius for complementary Tunguska studies, such as blast-wave simulations that aim to reproduce the tree-fall pattern.

Flood and Flash Flood Geo-Hazards in Malaysia

Floods are natural phenomena of geo-hazards that usually happened when experiencing prolonged heavy rainfalls. Floods in Malaysia can be categorized into monsoon floods and flash floods. Monsoon floods is caused of Northeast Monsoon season commences in early November and ends in March that brings heavy rainfall, particularly to the east coast states of Peninsular Malaysia and western Sarawak. Flash floods usually occur in areas with rapid development by a rapid rise in water level, high velocity, and large amounts of debris. Flooding that occurred in December 2014 can be classified as worst floods that affected several states in Peninsular Malaysia, and the worst affected is Kelantan state. This disaster was recorded more than 200,000 people were affected with 21 people were killed and gives a massive impact on people, properties, agriculture, livestock, and infrastructure facilities. Following the worst floods that hit Malaysia in 2014, the opinions and views from various parties such as subject matter experts was needed to produce mitigations and prevents of the flood disaster at once to minimize vulnerability to hazard.

Coupled Euler-Lagrange simulations of metal fragmentation in pipe bomb configurations

This paper details modeling of metal fragmentation of pipe-bomb configurations using the Euler-Lagrange code Zapotec. Zapotec couples the hydrocode CTH with the transient-dynamics finite element code Sierra/SM (also known as Presto) through a step-wise interchange of geometry, state data, and pressure. In this work, three experimental studies of pipe-bomb configurations were simulated using Zapotec, where the metal case was modeled using finite elements and the explosive was modeled with CTH. In the three examples, experimental and simulated debris distributions and early-time debris velocities generally showed excellent agreement. These studies both help build confidence in the use of Zapotec for simulating structural response under shock loadings.

Experimental investigation of tsunami-borne debris impact force on structures: Factors affecting impulse-momentum formula

This study investigates factors affecting tsunami-borne debris impact force on structures. Debris collision accelerations were measured at the contact point on the structure's seaward wall using disc- and box-shaped smart debris devices; the equation of motion was used to estimate the debris impact forces from the measured accelerations. Also, the impact force was measured at the base of the structure using a multi-axis load cell, and compared with the forces determined using the smart debris devices. The basic impulse-momentum formula was modified by the addition of coefficients, taking into account the added mass and the debris velocity. Debris shape also influenced the impact force. Deformability of the debris and flexibility of the structure both reduced the debris impact force.

A new Ballistic Limit Equation for thin tape tethers

Electrodynamic tethers represent one of the possible means to de-orbit defunct satellites from Low-Earth-Orbit at end of life. However, tethers survivability to orbital debris impacts is still debated because of the large area they expose to the space environment. Recently, increasing consideration has been given to thin-tape tether geometries, whose response to space debris threat is believed to be better than that of round wires. This paper describes a new Ballistic Limit Equation (BLE) applicable for thin tapes, to go beyond previous investigations referring at most to the impact resistance of round-wires (furthermore neglecting the damage dependence from the impact velocity and angle). In this paper, a new approach for BLE derivation is presented, which combines experimental results (in total 24 impact tests) and numerical simulations (in total 112 runs). The resulting BLE is non-monotonic with respect to the impact angle and presents a minimum at certain values of the impact obliquity, depending from the debris size and speed. In other words, the minimum particle diameter which is just able to cut a tape at a given velocity decreases with increasing impact obliquity up to a certain angle above which the damage is reduced due to early debris fragmentation triggered by shock waves propagating into the material. Notably, it has been observed that there is a minimum value of debris velocity v* below which no critical damage is possible and, furthermore, there is a minimum velocity-dependent value d* of debris diameter below which no critical damage is possible. This feature of BLE is extremely important, since it sets a minimum particle diameter for risk assessment and thus excludes a large part of the flux from risk computations. In conclusion, the newly-developed BLE confirms that thin tapes are significantly more resistant than round wires of equivalent cross-section; this is due to the intrinsic ballistic response of tapes, not only to their reduced cross-section at high impact obliquity.

Measurements of tsunami-borne debris impact on structures using an embedded accelerometer

ABSTRACTThis paper presents new experimental techniques utilizing a smart debris device for direct measurement of the impact acceleration forces associated with tsunami-borne debris that impact inland structures. The resulting experimental data will lead to advanced predictive capabilities of such forces for use in design guidelines. The measured debris acceleration data were used to calculate impact forces (mass × acceleration). An image processing technique was used to detect the debris impact angle. The debris impact tests were conducted using a disc-shaped smart debris device with masses of 550, 800 and 1000 g. For calculation of the debris force it was found necessary to include the mass of entrained water. The impact acceleration was found to be a function of debris mass, velocity, and contact duration. An equation is developed to allow estimation of the debris velocity for a known distance between the debris pick-up location by a tsunami and the structure.

Debris and shrapnel assessments for National Ignition Facility targets and diagnostics

High-energy laser experiments at the National Ignition Facility (NIF) can create debris and shrapnel capable of damaging laser optics and diagnostic instruments. The size, composition and location of target components and sacrificial shielding (e.g., disposable debris shields, or diagnostic filters) and the protection they provide is constrained by many factors, including: chamber and diagnostic geometries, experimental goals and material considerations. An assessment of the generation, nature and velocity of shrapnel and debris and their potential threats is necessary prior to fielding targets or diagnostics. These assessments may influence target and shielding design, filter configurations and diagnostic selection. This paper will outline the approach used to manage the debris and shrapnel risk associated with NIF targets and diagnostics and present some aspects of two such cases: the Material Strength Rayleigh- Taylor campaign and the Mono Angle Crystal Spectrometer (MACS).

Neutral cluster debris dynamics in droplet-based laser-produced plasma sources

The neutral cluster debris dynamics of a droplet-based laser-produced plasma is studied experimentally and analytically. Experiments were done imaging the debris with a high-speed shadowgraph system and using image processing to determine the droplet debris mean radial velocity dependence on laser pulse irradiance Ee. The data shows a power law dependence between the mean radial debris velocity and the incident irradiance giving with . A scaled analytical model was derived modeling the plasma ablation pressure on the droplet surface as the primary momentum exchange mechanism between the unablated droplet material and the laser pulse. The relationship between droplet debris trajectory and the droplet alignment with the laser was quantified analytically. The derived analytical model determines that the neutral cluster debris trajectory for an ablated droplet is a function of the laser profile fL, the droplet diameter D and the axial misalignment h between the laser axis and the droplet center. The analytical calculations from these models were found to be in good agreement with the measurements. This analysis has practical significance for understanding ablated droplet debris, droplet deformation by laser pulsing, and droplet breakup from very short timescale shocks.

Study on the Distribution of Removal Material of EDM in Deionized Water and Gas with Molecular Dynamics Simulation

In this paper, in order to clarify the distribution of removal material in EDM, a single pulse discharge process in both deionized water and gas was simulated by using molecular dynamics method. The research results showed that compared with the discharge in gas, discharge in deionized water would generate expanding bubble and flowing liquid, which could have removing, carrying, cooling and blocking effects on removal material. In addition, it was found that immediately after the discharge was ignited, the velocity direction of removal material mainly directed to the gap. But as the time went on, the velocity direction of removal material gradually deviated from the gap. The change of distribution of velocity direction along with the time could reflect the material removal and returning process. It was also found that the range of volume distribution of removal debris in the gap after the end of discharge in deionized water was larger than that in gas, but the velocity of the removal debris was lower than that in gas.

Flow Field Simulation and Experimental Investigation of Ultrasonic Vibration Assisted EDM Holes Array

Debris distribution in the bottom and side gap significantly affects machining performance of electrical discharge machining (EDM) of holes array. Therefore, the mechanisms of debris distribution and velocity field of flow field in the discharge gap between tool electrode and work piece during EDM process should be investigated. However, these mechanisms have not been fully understood because it is difficult to observe debris distribution process. In this paper, a two-dimensional model of flow field with liquid and debris phase for the bottom and side gap in ultrasonic assisted EDM of holes array was created by computational fluid dynamics. The debris distribution and velocity field of flow field in the bottom and side gap during an ultrasonic vibration cycle was investigated through the numerical simulation. The results show that holes in the center of the array are larger than those at the periphery, which is caused by difference of debris distribution. Machining experiments were conducted to verify the simulation results of debris distribution during EDM of holes array.

Landslide mobility analysis for design of multiple debris-resisting barriers

Multiple debris-resisting barriers have been commonly used worldwide to mitigate debris flows in drainage lines. However, a well-developed methodology to assess the mobility of debris flows with consideration of the obstruction of the barriers does not exist. A free-field debris-flow condition that omits the presence of multiple debris-resisting barriers is commonly considered in design, although the effects of the barriers could be critical in determining the dynamics of the landslide debris including debris velocity and debris thickness. This paper proposes a staged debris mobility analysis that accounts for the effects of multiple debris-resisting barriers. The staged analysis adopts solutions of a depth-averaged debris mobility model. The input parameters of the analysis have been established from field data and laboratory test results. Rigorous numerical simulations of debris flows intercepted by multiple debris-resisting barriers have also been undertaken using the three-dimensional finite element program LS-DYNA to provide results for benchmarking the output of the staged analysis.

슬릿트형 사방댐의 배치에 따른 토석류 흐름에 대한 영향: 축소모형실험 연구

Debris flows caused by heavy rainfall occur along long watersheds and travel at extremely rapid velocity. This phenomenon involves fast moving fluids induced by gravity and causes economic and societal damages when debris flows overflow to urban area. For this reason, barriers against debris flows have been widely employed. In particular, slit-type barriers are popularly used because of the minimum disturbance to surrounding environments. However, the performance of such slit-type barriers is not fully understood. This paper explores roles of spacing and angle of slit-type barriers on velocity reduction and trap ratio of the debris flows. The scaled physical modeling experiments were performed to examine the reduction of debris velocity and trap ratio and to assess the performance of debris flow barriers. The results indicate that the performance of barriers is heavily affected by spacing between slit-type barriers and angle of barriers from flow direction.

Modeling Debris Motion in Vibration Assisted Reverse Micro Electrical Discharge Machining Process (R-MEDM)

Reverse microelectrical discharge machining (R-MEDM) process is a recent variant of microelectrical discharge machining process capable of fabricating high aspect ratio arrayed microfeatures and textured surfaces. Efficient flushing of the debris particles from the interelectrode gap is essential for process stability, but extremely small interelectrode gaps ( $\sim 5~\mu $ m) make the dispelling of debris difficult, rendering the R-MEDM process infeasible for machining difficult-to-erode materials and creation of engineered/textured surfaces. It has been experimentally observed that the electrode vibrations facilitate the flushing of debris particles and improve the erosion rate, surface morphology, and dimensional accuracy of the machined features. Despite the obvious advantages, the vibration-assisted R-MEDM process, specifically the debris motion and dielectric flow under the effect of vibration, is not very well understood. Consequently, this paper is focused on computational modeling of the debris motion and its interaction with the dielectric fluid under low-amplitude vibrations imparted via a magnetorestrictive actuator. The effects of frequency and amplitude of the electrode vibration on the debris motion have been quantified. The higher local debris velocities and oscillatory motion due to flow reversal potentially reduce the debris agglomeration. As a result, the normal discharge duration, which is responsible for the material erosion, is increased and fabrication of arrayed features on difficult-to-erode materials and creation of surface texture over large areas become feasible. [2013-0394]

Physical modeling of baffles influence on landslide debris mobility

Debris flows surge downslope carrying destructive energy and can result in long runout distances. Structural mitigation is commonly installed along the flow path to impede debris flow mobility and protect downstream facilities. An array of baffles is a structural countermeasure frequently designed using empirical methods or prescribed to impede debris flow; nonetheless, its influence on reducing mobility is not well understood. A 5-m-long flume model is used to conduct a series of tests to systematically study the effects of varying baffle height, number of rows, spacing between rows, and degree of transverse blockage on mobility. Froude scaling is adopted to characterize initial upstream conditions. Debris runout, overflow, and frontal velocity reduction resulting from each baffle configuration used are examined. Experimental results reveal that it is imperative to adopt baffle heights taller than the approach flow depth (h) in order to suppress overflow and reduce runout. Adopting 1.5 h-tall baffles can reduce runout and peak overflow depth by 19 and 20 % compared to short baffles (0.75 h), respectively. A single row of baffles is ineffective in reducing frontal debris velocity, whereas increasing the array to three rows leads to 65 % reduction in runout and up to 57 % reduction in frontal velocity. Increasing spacing between successive rows from 0.25w to 0.5w can reduce runout by up to 37 %.

Fragmentation and debris evolution modeled by a point-wise coupled reproducing kernel/finite element formulation

A point-wise evolutionarily coupled reproducing kernel (RK)/finite element (FE) formulation was developed to model fragmentation processes induced by blast and impact loadings. In this coupled approach, each integration point defines a coupling zone so that very localized deformations and damage can be treated. A triggering criterion, such as a damage index for concrete or a critical effective plastic strain for steel, is employed to initiate the fragmentation process, which is realized by changing the morphology of the zone where fragmentation is indicated from a FE model to a meshfree model. The evolutionary coupling, whereby the FE zones can morph into meshfree zones, provides a convenient and more accurate domain from which to track the debris mass and velocity distributions, which is of great interest in many applications. To facilitate the fragmentation modeling, a flexible-to-flexible meshfree contact algorithm was implemented so that high velocity (up to 3000 m/s) impact penetration problems can be effectively analyzed by the coupled Lagrangian RK/FE formulation. Numerical results are shown for structures subjected to quasi-static, blast, and high velocity impact loadings using this coupled formulation and employing widely accepted constitutive models for concrete and steel. The examples show that the coupled formulation can be used to model material fragmentation and the evolution of debris using damage indicators provided by any validated material constitutive model.