Entry Velocity Research Articles

Slamming occurrence for a chemical tanker advancing in extreme waves modelled with the nonlinear Schrödinger equation

The relative motion and frequency of slamming occurrence for a chemical tanker advancing in irregular waves are studied in this work. The objective is to develop a numerical method for estimating the probability of slamming occurrence of a chemical tanker, under the two conditions: the relative vertical motion at the same longitudinal position of the ship being larger than the vertical distance from the still water to the concerned position, and the entry velocity exceeding one threshold velocity. Ship motions in extreme waves are firstly estimated by using a fully nonlinear time domain seakeeping programme, while the wave surface modelling is achieved by a nonlinear Schrödinger equation. Then, the probability of slamming occurrence on the bottom of a chemical tanker is predicted statistically based on the relative motions between the cross section of the ship and the wave surface. The numerical results are compared with the experimental data from model tests of a chemical tanker. The effects of the forward speed on the slamming occurrence are studied as well.

Blade shape optimization of liquid turbine flow sensor

Based on the characteristic curve analysis, the method using Δ(K2) square difference of meter factor at different flow rates was developed to evaluate the performance of turbine flow sensor in this study. Then according to the distribution of entrance velocity, it was supposed that reducing the blade area near the tip could decrease the linearity error of a sensor. Therefore, the influence of different blade shape parameters on the performance of the sensor was investigated by combining computational fluid dynamics(CFD)simulation with experimental test. The experimental results showed that, for the liquid turbine flow sensor with a diameter of 10 mm, the linearity error was smallest, and the performance of sensor was optimal when blade shape parameter equaled 0.25.

Passage of downstream migrant American eels through an airlift-assisted deep bypass

Traditional downstream guidance and bypass facilities for anadromous fishes (i.e., surface bypasses, surface guidance structures, and behavioral barriers) have frequently been ineffective for anguillid eels. Because eels typically spend the majority of their time near the bottom in the vicinity of intake structures, deep bypass structures with entrances near the bottom hold promise for increased effectiveness, thereby aiding in the recovery of this important species. A new design of a deep bypass system that uses airlift technology (the Conte Airlift Bypass) to induce flow in a bypass pipe was tested in a simulated intake entrance environment under controlled laboratory conditions. Water velocities of 0.9–1.5ms−1 could be generated at the bypass entrance (opening with 0.073m2 area), with corresponding flows through the bypass pipe of 0.07–0.11m3s−1. Gas saturation and hydrostatic pressure within the bypass pipe did not vary appreciably from a control (no air) condition under tested airflows. Migratory silver-phase American eels (Anguilla rostrata) tested during dark conditions readily located, entered, and passed through the bypass; initial avoidance rates (eels approaching but not entering the bypass entrance) were lower at higher entrance velocities. Eels that investigated the bypass pipe entrance tended to enter headfirst, but those that then exited the pipe upstream did so more frequently at lower entrance velocities. Eels appeared to swim against the flow while being transported downstream through the pipe; median transit times through the bypass for each test velocity ranged from 5.8 to 12.2s, with transit time decreasing with increasing entrance velocity. Eels did not show strong avoidance of the vertical section of the pipe which contained injected air. No mortality or injury of bypassed eels was observed, and individual eels repeatedly passed through the bypass at rates of up to 40 passes per hour, suggesting that individuals do not avoid repeated entrainment through the bypass. Airlift technology appears to be a viable method for increasing passage effectiveness for American eels through a deep bypass system.

An analysis of tube drawing process used to produce squared sections from round tubes through FE simulation and response surface methodology

Tube drawing process is an attractive manufacturing technique in automobile, medical, and aerospace industries. The quality of fabricated tubes is highly affected by drawing parameters, e.g., die geometry, material properties, friction conditions, and drawing ratio. In the present study, an extensive attempt has been made to find optimal combinations of drawing parameters, i.e., die angle, friction coefficient, tube entrance velocity, and deformation length regarding minimum drawing force and dimensional error as well as maximum linear and peripheral thickness distributions. A combination of finite element model, validated through trial experiments, and face-centered central composite design was used to design a matrix. Then, response surface methodology (RSM) was used to correlate empirical relationships between process factors and responses. The developed RSM models were then used to find the effects of tube drawing parameters on the mentioned performances. RSM was used further for the selection of optimum process parameters to achieve the desired quality regarding tube drawing performance in producing squared sections from round tubes. The results showed that to attain desired quality characteristics, the die angle of 7.5°, deformation length of 3 mm, friction coefficient of 0.3, and entrance velocity of 5 mm/min should be selected. A comparison between the optimal results and those derived from finite element (FE) model showed that the proposed approach would be able to predict optimal drawing process combinations with a high degree of accuracy.

The solution of a model problem of the atmospheric entry of a small meteoroid

Direct simulation Monte Carlo modeling (DSMC) is used to solve the problem of the entry into the Earth’s atmosphere of a small meteoroid. The main aspects of the physical theory of meteors, such as mass loss (ablation) and effects of aerodynamic and thermal shielding, are considered based on the numerical solution of the model problem of the atmospheric entry of an iron meteoroid. The DSMC makes it possible to obtain insight into the structure of the disturbed area around the meteoroid (coma) and trace its evolution depending on entry velocity and height (Knudsen number) in a transitional flow regime where calculation methods used for free molecular and continuum regimes are inapplicable.

WiFi 핑거프린트를 이용한 지하철 위치 추적 정확성 향상을 위한 연구

In this study, an WiFi fingerprinting method based on the k-nn algorithm was applied to improve the accuracy of location tracking of a moving train on a platform and evaluate the performance to minimize the estimation error of location tracking. The data related to the position of the moving train are monitored by the control center for trains and used widely for the safety and comfort of passengers. The train location tracking methods based on WiFi installed by telecom companies were evaluated. In this study, a simulator was developed to consider the environments of two cases; in already installed WiFi devices and new installed WiFi devices. The developed simulator can simulate the localized estimation of the position under a variety of conditions, such as the number of WiFi devices, the area of platform and entry velocity of train. To apply location tracking algorithms, a k-nn algorithm and fuzzy k-nn algorithm were applied selectively according to the underlying condition and also four distance measurement algorithms were applied to compare the error of location tracking. In conclusion, the best method to estimate train location tracking is a combination of the k-nn algorithm and Minkoski distance measurement at a 0.5m grid unit and 8 WiFi AP installed.

Kinematics of the deformation zone in plugless rolling of oil pipes

This article describes the process of plugless rolling of oil pipes. Correlations between caliber parameters and swaging were obtained. The mathematical model of the process of plugless rolling of pipes was made. Main parameters of the deformation zone were determined. A set of equations to determine the surface of the contact area of the round billet and the tool for two-roll and three-roll calibers was obtained. The velocity field of metal billets was presented. From the assumption that the axial component of the velocity vector changes according to the quadratic law and the metal entrance velocity in the deformation zone is connected with the exit velocity from the deformation zone by the reduction ratio, the dependence for the determination of this component of the velocity vector was obtained. The linear function of the radial component of the velocity vector was justified. From the relation of axial and radial components of the velocity vector by the tangent of the angle between the considered section and the vertical symmetry plane of the roll a dependence for the determination of the radial component of the velocity vector was defined. The third component of the velocity vector was determined subject to the incompressibility condition, which was defined for three-roll and two-roll calibers. Based on the determined components of the velocity vector, the components of the strain velocity tensor were defined for three-roll and two-roll calibers. The components of the strain velocity tensor were calculated for the case of rolling tubes in a three-roll reduction mill. The components of the strain velocity tensor were numerically estimated, and the components of the strain velocity tensor that may be neglected in engineering calculations were determined.

Investigation of water entry impact forces on airborne-launched AUVs

ABSTRACTAirborne-launched AUVs withstand great fluid impact force at the early stage when entering the water, which may cause damage to their structure and inner components in severe cases. Due to their large volume and mass, the major challenge involved in conducting experiments to measure the water entry impacts on real-life AUVs is the high demand for the experimental devices, finding a suitable site, and the cost of the experiments. Using a gas gun as launching device, water entry experiments using a full-size AUV model are conducted under various conditions. The axial and radial force changes that occur during the water entry process are obtained, and some accompanied phenomena such as cavitation and turnover under different water entry conditions are observed. Computational fluid dynamics (CFD) is used to simulate the water entry process of airborne-launched AUVs. The simulation results fit well with the experimental data, the latter of which show that both the water entry velocity and entry angle have a great influence on the impact load during the water entry process. These data can provide valuable reference information for AUV structure design and launch condition selection.

Live monitoring of the distributed strain field in impulsive events through fiber Bragg gratings

In this paper, we propose a measurement technique based on local strain measurements to perform real-time reconstruction of the overall structural deformation and the distributed stress field produced by the impact of a body on a water free surface. In particular, we seek establishing a measurement chain capable of acquiring and elaborating the signals at high frequency, so that it can be utilized to study rapidly varying strain fields, such as those occurring in impulsive events. Fiber Bragg gratings are utilized to sense the local structural deformation. Experiments are conducted on flexible plastic wedges with variable deadrise angles impacting on a quiescent fluid surface. The experimental tests are performed in free fall and we explore variations of the entry velocity by varying the drop height. The structural deformation is reconstructed from point-wise strain measurements utilizing a modal reconstruction methodology. The impact dynamics are analysed through accelerometers and linear position sensors. Results show that the impact behaviour of the flexible body is characterized by a main overall deformation where the structure is distorted in the direction of the loading, whereby marked vibrations, whose amplitude increase with the entry velocity, dominate the dynamic response. The influence of the mode shapes considered in the present analysis on the accuracy of the results is also observed. The proposed methodology allows for a fairly high acquisition frequency, which translates into a real-time structural reconstruction technique. Results show that the proposed methodology can be a valuable tool for the live monitoring of structures undergoing impact events.

Experimental and numerical study of the slamming load on the bow of a chemical tanker in irregular waves

This paper presents calculations of ship motions, slamming occurrence probability and slamming loads on the bow of a ship hull in irregular waves. The results are compared with the experimental data from model tests of a 170m chemical tanker with Fn=0 in head seas. Ship motions are calculated by using a partially nonlinear time domain code based on strip theory. The probabilities of slamming occurrence at the bow are studied numerically and statistically, and compared with the experimental data. The experimental data are analysed statistically, to determine the relationships between the measured pressure and the entry velocity and with wave parameters. Two estimated significant slamming events are simulated by using the Arbitrary-Lagrangian Eulerian (ALE) algorithm, based on the calculated relative entry velocities in the numerical procedure.

Trajectory linearization control based tracking guidance design for entry flight

A novel use of trajectory linearization control( TLC) method was introduced in the guidance law design for hypersonic vehicle entry flight. By exploiting the inherent characteristics of time scale separation of entry vehicle dynamics,altitude and velocity could be controlled separately via outer and inner loop design.In the outer loop,path angle was used as pseudo-control for controlling the altitude. In the inner loop,the flight path angle command and velocity were tracked using bank angle and angle of attack as controls. A linear time-varying controller was designed for the feedback loop to stabilize the error dynamics. Feedback gains were computed online and are the symbolical functions of reference trajectory,therefore no explicit gain scheduling or mode-switching were needed. Extensive dispersion simulations show that this guidance algorithm can achieve precise trajectory tracking and is trajectory-independent. The simulations also show that an integrated entry guidance approach which combines the use of TLC-based tracking guidance law design and on-board reference trajectory planning can significantly enhance the autonomy and adaptability of entry flight.

EVALUATING CHANGES IN THE ELEMENTAL COMPOSITION OF MICROMETEORITES DURING ENTRY INTO THE EARTH’S ATMOSPHERE

We evaluate the heating of extraterrestrial particles entering the atmosphere using the comprehensive chemical ablation model (CABMOD). This model predicts the ablation rates of individual elements in a particle with a defined size, composition, entry velocity, and entry angle with respect to the zenith (ZA). In the present study, bulk chemical analyses of 1133 Antarctica micrometeorites (collected from the south pole water well) are interpreted using CABMOD. The marked spread in Fe/Si values in unmelted, partially melted, and melted micrometeorites is explained by the loss of relatively volatile Fe during atmospheric entry. The combined theoretical modeling and elemental composition of the micrometeorites (Mg/Si ratios) suggest that ∼85% of particles have a provenance of carbonaceous chondrites, the remaining ∼15% are either ordinary or enstatite chondrites. About 65% of the micrometeorites have undergone <20% ablation, while a further 20% have lost between 20% and 60% of their original mass. This has implications for understanding the micrometeorite flux that reaches the Earth's surface, as well as estimating the pre-atmospheric size of the particles. Our work shows that the unmelted particles that contribute ∼50% to the total micrometeorite collection on Earth's surface have a small entry zone: ZA = 60°–90° if the entry velocity is ∼11 km s−1, and ZA = 80°–90° for >11–21 km s−1.

Flow to a collector pipe laid under a stream bed

With the increase in population growth, there is tremendous pressure on the decision-makers to look for sustainable sources of safe and adequate water supply for different purposes. Therefore, during recent times, engineers are looking toward cost-effective process of water treatment. Collector wells constructed on the banks of a river are cost-effective means of supplying adequate and safe water supply to people living on the banks of a river. Collector pipes act as a carrier of water to the collector well. Collector pipes placed under a riverbed are the most effective in terms of quantity of water. Previously researchers have derived an analytical solution for potential and flow to the collector pipe under steady-state flow condition. In this study, an analytical method using conformal mapping has been suggested to estimate the potential at different locations in the flow domain. Further, expressions have been derived for estimating the quantity of flow to the collector pipe, entrance velocity, and the travel time of a parcel of water from the stream bed to the collector pipe along the shortest path. Using the travel time, the log cycle reduction in bacteria concentration has been found using logistic function.

述评:水井水力学—水流定律和几何学的影响

Water wells are an indispensable tool for groundwater extraction. The analytical and empirical approaches available to describe the flow of groundwater towards a well are summarized. Such flow involves a strong velocity increase, especially close to the well. The linear laminar Darcy approach is, therefore, not fully applicable in well hydraulics, as inertial and turbulent flow components occur close to and inside the well, respectively. For common well set-ups and hydraulic parameters, flow in the aquifer is linear laminar, non-linear laminar in the gravel pack, and turbulent in the screen and the well interior. The most commonly used parameter of well design is the entrance velocity. There is, however, considerable debate about which value from the literature should be used. The easiest way to control entrance velocity involves the well geometry. The influence of the diameter of the screen and borehole is smaller than that of the screen length. Minimizing partial penetration can help to curb head losses.

Main parameters of meteoroid motion during the fall of the Chelyabinsk meteorite shower on February 15, 2013

A rapid method is proposed for determining a meteoroid’s trajectory in the Earth’s atmosphere and its height and velocity at individual points. The method is designed for use with video material (regardless of the motion speed of the video recorder) for daytime bolide events. Kinematic parameters are obtained for the superbolide event followed by the Chelyabinsk meteorite shower on February 15, 2013. The (geodetic) azimuth of the meteoroid’s trajectory in the Earth’s atmosphere is 283.39° ± 1.7° (or 101.09° ± 1.7° toward the radiant). The radiant altitude over the site with observations of the end of the first fragmentation phase is 20.5°. The geodetic coordinates of the beginning of the bolide phenomenon and the point of suspension of the radiating material at the end of the first fragmentation phase are (64°00′02.74″ ± 2.1′ east longitude; 54°30′54.66″ ± 3.0′ north latitude) and (61°11′01.88″ ± 1.6′ east longitude; 54°52′06.68″ ± 3.1′ north latitude), respectively. The atmospheric entry velocity is 19.29 ± 0.89 km s−1. The height of the start of the light emission is 102.4 km; those of the main fragmentation phases are 28.0 and 24.4 km. The calculated elements for the heliocentric orbit of the Chelyabinsk meteoroid are: Q = 2.66 ± 1.20 AU, q = 0.73 ± 0.01 AU, a = 1.67 ± 0.10 AU, e = 0.57 ± 0.03, i = 7.07° ± 0.54°, Ω = 326.42°, and ω = 106.28° ± 2.54°. These parameters are compared with the results obtained by other authors.

An analytic expression for the sheath criterion in magnetized plasmas with multi-charged ion species

The generalized Bohm criterion in magnetized multi-component plasmas consisting of multi-charged positive and negative ion species and electrons is analytically investigated by using the hydrodynamic model. It is assumed that the electrons and negative ion density distributions are the Boltzmann distribution with different temperatures and the positive ions enter into the sheath region obliquely. Our results show that the positive and negative ion temperatures, the orientation of the applied magnetic field and the charge number of positive and negative ions strongly affect the Bohm criterion in these multi-component plasmas. To determine the validity of our derived generalized Bohm criterion, it reduced to some familiar physical condition and it is shown that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when entrance velocity of ion into the sheath satisfies the obtained Bohm criterion. Also, as a practical application of the obtained Bohm criterion, effects of the ionic temperature and concentration as well as magnetic field on the behavior of the charged particle density distributions and so the sheath thickness of a magnetized plasma consisting of electrons and singly charged positive and negative ion species are studied numerically.

Analysis of hydroelastic slamming through particle image velocimetry

Predicting the hydrodynamic loading experienced by lightweight structures during water impact is central to the design of marine vessels and aircraft. Here, hydroelastic effects of flexible panels during water entry are studied through particle image velocimetry. Experiments are conducted on a compliant wedge entering the water surface in free fall for varying entry velocities, and the pressure field is indirectly evaluated from particle image velocimetry. Results show that the impact is responsible for prominent multimodal vibrations of the wedge, and, vice versa, that the wedge flexibility strongly influences the hydrodynamic loading. With respect to rigid wedges, the hydrodynamic loading exhibits marked spatial variations, which control the location of the minimum and maximum pressure on the wetted surface, and temporal oscillations, which modulate the direction of the hydrodynamic force. These experimental results are expected to aid in refining computational schemes for the analysis of hydroelastic phenomena and provide guidelines for structural design.

Numerical Simulation of Oblique Towing Tests and Rotating Arm Tests for a Submarine Model in Same Grid Topology

The numerical simulation of oblique towing tests (OTT) and rotating arm tests (RAT) for a submarine model was undertaken with the same grid topology. As for the OTT simulation, to improve the efficiency and accuracy of the computation, the drift sweep procedure was adopted. In contrast with the steady drift case, rotating motion for a submarine is more complex. The rotating reference frame was adopted to deal with the rotation problem. The Coriolis force and centrifugal force due to the computation in a body-fixed rotating coordinate system were treated explicitly and added to the momentum equations as source terms. The user-defined boundary conditions were coded to give the correct magnitude and direction of entrance velocity. Lastly, the computed forces and moments as a function of drift angle during the two kinds of simulations were compared with experimental results, as well as literature values. They always show the correct trend. The flow field and streamline patterns in rotating motion were depicted. It indicates that the method used in the paper is reliable and the same grid topology can be used for the simulation of two simplified maneuvers.

Nonextensive statistics and the sheath criterion in collisional plasmas

The Bohm criterion in an electropositive plasma containing nonextensively distributed electrons and warm ions is investigated by using a steady state two-fluid model. Taking into account the ion-neutral collisions and finite temperature of ions, a modified Bohm criterion is derived which limits both maximum and minimum allowable velocity of ions at the sheath edge (u0i). It is found that the degree of nonextensivity of electrons (q) and temperature of positive ions (Ti) affect only the lower limit of the entrance velocity of ions into the sheath while the degree of ion collisionality (α) influences both lower and upper limits of the ion velocities at the sheath edge. In addition, depending on the value of q, it is shown that the minimum velocity of positive ions at the sheath edge can be greater or smaller than its Maxwellian counterpart. Moreover, it is shown that, depending on the values of α and Ti, the positive ions with subsonic velocity may enter the sheath for either q &amp;gt; 1 or −1 &amp;lt; q &amp;lt; 1. Finally, as a practical application, the density distribution of charged particles in the sheath region is studied for different values of u0i, and it is shown that monotonical reduction of the positive ion density distribution occurs only when the velocity of positive ions at the sheath edge lies between two above mentioned limits.

Numerical Assessment of Similitude Parameters and Dimensional Analysis for Water Entry Problems

The prediction of impulsive loads deriving from the sudden impact of a solid body on the water surface is of fundamental importance for a wide range of engineering applications. The study of hull-slamming phenomena largely relies on laboratory scale experimental investigations and on simplified analytical models. The aim of this paper is to quantitatively assess the interplay between the relevant nondimensional parameters for the water entry of a two-dimensional body, evidencing the similitude conditions that allow the transition from scaled experiments to real size applications. This assessment is performed through the numerical study of the hydrodynamics induced by the water impact of a two-dimensional wedge. The fluid flow is considered incompressible. First of all numerical simulations are validated by comparison with experimental data from the literature and with the Wagner seminal theory. Afterwards, a thorough computational study is performed by systematically varying all the relevant parameters, such as the nondimensional entry velocity and acceleration. We conclude by evidencing some design prescriptions that should be adopted in order to facilitate the transition of laboratory scale experiments to real scale applications.