Numerical Simulation on Oscillation-Sliding-Uplift Rock Coupled Motion of Caisson Breakwater Under Wave Excitation

Corresponding to the sliding and the overturning failure,the elementary motion modes of caisson breakwater include the horizontal-rotational oscillation coupled motion,the horizontal sliding-rotational oscillation coupled motion,the horizontal vibrating-uplift rocking coupled motion,and the horizontal sliding-uplift rocking coupled motion.The motion mode of a caisson will transform from one to another depending on the wave forces and the motion behaviors of the caisson.The numerical models of four motion modes of caisson are developed,and the numerical simulation procedure for joint motion process of various modes of caisson breakwater under wave excitation is presented and tested by a physical model experiment.It is concluded that the simulation procedure is reliable and can be applied to the dynamic stability analysis of caisson breakwaters.

Numerical simulation of bubble chaotic motion in a cavitating water jet

A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.

Numerical simulation and experimental verification of bubble size distribution in an air dense medium fluidized bed

Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.

Numerical simulation study of gob air leakage field and gas migration regularity in downlink ventilation

Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influence of natural wind pressure to analyze the stope face differential pressure, gob air leakage field distribution and gas migration regularity theoretically. Established a two-dimensional physical model with one source and one doab, and applied computational fluid dynamics analysis software Fluent to do numerical simulation, analyzed and contrasted to the areas of gob air leakage on size and gas emission from gob to working face on strength when using the downlink ventilation and uplink ventilation. When applied downward ventilation in stope face, the air leakage field of gob nearly working face, and the air leakage intensity were smaller than uplink, this can effectively reduce the gas emission from gob to working face; when used downlink ventilation, the air leakage airflow carry the lower amount of gas to doab than uplink ventilation, and more easily to mix the gas, reduced the possibility of gas accumulation in upper comer and the stratified flows, it can provide protection to mine with safe and effective production.

Numerical Simulation of the Effect of Air Distribution on Turbulent Flow and Combustion in a Tubular Heating Furnace

A three-dimension full-size numerical simulation of the effect of air distribution on turbulent flow and combustion in a tubular heating furnace was carried out. A standard k –ε turbulent model, a simplified PDF combustion model and a discrete ordinate transfer radiation model were used. The hybrid grid combining a structured and a non-structured grid was generated without any simplification of the complicated geometric configuration around the burner. It was found that the multistage combustion could reduce and control the peak value of temperature. At the same time, it was concluded that the amount of primary air had little effect on the global distribution of velocity and temperature in the furnace, but a great effect on that around the burner. It is recommended that 45% - 65% of the total amount of air be taken in in primary air inlets in the furnace. All the results are important to optimize the combustion progress.

Numerical simulation of dust distribution at a fully mechanized face under the isolation effect of an air curtain

At a fully mechanized working face of a coal mine as prototype,we investigated,by simulation,the flow field and dust distribution during the process of its isolation by a curtain of air,using the CFD software, Fluent.The results show that the air curtain installed on the shearer can effectively prevent the dust （especially the respirable dust）from diffusing into the work area of the operator,reducing the dust concentration on the side of the operator and greatly improving his working environment.The field application of the air curtain shows that the dust-isolation effect of an air curtain is quite noticeable.The isolation efficiency for respiratory dust is over 70%and,as well,it has good dust-isolation effect for nonrespiratory dust.The air curtain is a useful way to resolve the problem of dust-isolation at a fully mechanized working face.It has a practical background elsewhere with more extensive applications.

6-DOF Motion Assessment of A Hydrodynamic Numerical Simulation of A Semisubmersible Platform Using Prototype Monitoring Data

Hydrodynamic numerical simulations are used to conduct structural analyses and inform the design of engineered marine structures.In this paper,a hydrodynamic numerical model of“Nanhai Tiaozhan”(NHTZ)FPS platform was established according to its design specifications.The model was assessed with two sets of field monitoring data representing harsh and conventional sea states.The motion responses of the platform according to the measured data and the hydrodynamic simulation were compared by reviewing their statistical characteristics,distributions,and spectrum characteristics.The comparison showed that the hydrodynamic model could correctly simulate the frequency domain characteristics of the motion responses of the platform.However,the simulation underestimated the reciprocating motions of the floating body and the influence of slow drift on the motion of the platform.Meanwhile,analysis of the monitoring data revealed that the translational degrees of freedom(DOF)and rotational DOF of the platform were coupled,but these coupled motion states were not apparent in the hydrodynamic simulation.

Experimental Study and Numerical Simulation on Spray Characteristics of New-Type Air-Assist Nozzle

To investigate the spray characteristics of a new-type air-assist nozzle,three-dimensional laser phase Dopper analyzer( PDA) was used to measure the spray parameters. The external flow fields of the nozzle were simulated by means of computational fluid dynamics( CFD). The distributions of the diameter and the axial velocity for the droplets were analyzed respectively. The results indicate that,the mean diameter of the droplets fluctuates along the center axis. The distance between the measurement point and the nozzle increases,the axial velocity of the droplets decreases. The further the measurement point from the center axis is,the smaller the axial velocity of the droplets is. With the increase of the nozzle pressure drop,the axial velocity of the droplets improves while the mean diameter of the droplets is reduced,and the distribution uniformity of the droplets is better for the diameter. The simulation result agrees well with the experimental data. The average deviation ranges from 3.9% to 7.7%.

A numerical simulation study on active species production in dense methane-air plasma discharge

Recently, low-temperature atmospheric pressure plasmas have been proposed as a potential type of ＇reaction cartier＇ for the conversion of methane into value-added chemicals. In this paper, the multi-physics field coupling software of COMSOL is used to simulate the detailed discharge characteristics of atmospheric pressure methane-air plasma. A two-dimensional axisymmetric fluid model is constructed, in which 77 plasma chemical reactions and 32 different species are taken into account. The spatial density distributions of dominant charged ions and reactive radical species, such as ＋ ＋ ＋ ＋ CH4, CH3,N2,02, H, O, CH3, and CH2, are presented, which is due to plasma chemical reactions of methane/air dissociation （or ionization） and reforming of small fragment radical species. The physicochemical mechanisms of methane dissociation and radical species recombination are also discussed and analyzed.

Design and Numerical Simulation of Low-Fiber Hollow Spindle in Air-Jet Vortex Spinning

Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is simulated numerically. The negative pressure effect is much bigger at the top of low-fiber hollow spindle than that in Murata No.861,which is more conducive for single fiber to get into the channel of hollow spindle. The tangential velocity in 0-3 mm at the top of hollow spindle increases and the fluctuation of radial velocity is much stronger,which enhance the wrapping effect. In the addition,the distribution of axial velocity remains the same.

Numerical Simulation and Experimental Research on Indoor Environment Separated with Down-Feed Air Curtain

Indoor environment separated with down-feed air curtain was numerically simulated and experimen-tally researched. Indoor airflow and temperature fields separated with air curtain were numerically simulated. Re-sults show that both polluted airflow and thermal air current can be separated with a down-feed air curtain to pre-vent contaminants from spreading in the room space. In a test chamber, the smoke of burning Tibetan incense served as the source of contaminants, and the probe test shows that 1.0 μm is the prevailing diameter of the smoke particles. During the release of the smoke, the particle concentration of the indoor air was tested with a laser particle counter at the points of three different heights from the floor when the air curtain was running or not. Experimental results show that the higher the test point is located, the lower the particle concentration is, implying that the sepa-rating or isolating effect decreases as the air velocity of the curtain reduces along with the height descends. Accord-ing to both simulation and experimental results, down-feed air curtain can separate indoor environment effectively when the supply air velocity of air curtain is not less than 3 m/s. In order to strengthen separation effect, it is sug-gested that the supply air velocity be speeded up to 5 m/s.

Reliability Analysis for Air-Gap Detonation Transfer Interface by Numerical Simulation

In order to reduce the test samples in the reliability design and assessment,the function process of air-gap detonation transfer interface was simulated by LS-DYNA software.The stress nephograms for the detonation transfer processes of six kinds of design parameters were analyzed.The results show that when the length of air-gap is between 2 and 18 mm,the detonation can be normally transferred which is consistent with the test result of NeyerD method.The result has referential value for design and analysis of similar products.

Numerical Simulation of High Temperature Air Combustion Flames Properties

High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.

Numerical simulation of gas-liquid two-phase jet flow in air-bubble generator

Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.

Numerical Simulations of the Equations of Particle Motion in the Gas Flow

Under the assumption of considering the gravity and without gravity, two different acceleration models to describe particle’ motion in the gas flow are formulated, respectively. The corresponding numerical simulations of these models do not only show the trend of the velocity of the particle in different density and particle diameter sizes, but also the relationship between the maximum particle velocity and its diameter size.

Numerical simulation of high temperature air combustion in aluminum hydroxide gas suspension calcinations

The high temperature air combustion(HiTAC) process in gas suspension calcinations(GSC) was studied by using a CFD software FLUENT that can simulate the three-dimensional physical model of GSC with the k-epsilon turbulent viscous model, PDF non-premixed combustion species model, P1 radiation model, thermal and prompt NO pollution model. The simulation vividly describes the distributions of the temperature, velocity and consistency fields. Finally, the optimal operation conditions and igniter configuration of particular fuel combustion are obtained by analyzing and comparing the simulation results. And the emission quantity of NOx, CO and CO2 deduced from computation can play a role as reference. These optimal and estimated values are beneficial to practical operation.

Numerical simulation of a thixocasting process for AISI420 stainless steel air-turbine blade

A new technology,semi-solid casting(thixocasting) method,was used to replace the conventional hot forging process to form AISI420 stainless steel air-turbine blade.The power law cut-off(PLCO) material model in Procast software was used to simulate the thixocasting process.The thixocasting process was simulated.The results show that the reasonable technology parameters for air-turbine blade thixocasting process are obtained:billet temperature 1 483-1 485 °C,piston velocity 12-15 m/s and die temperature is about 400 °C.

Study of 3-D Numerical Simulation for Gas Transfer in the Goaf of the Coal Mining

In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.

Numerical Simulation of Viscous Flow Around a Rolling Cylinder with Ship-Like Section

Two-dimensional unsteady incompressible viscous flow around a rolling cylinder with ship-like section is numerically simulated by employing the computational scheme previously developed by the authors, in which the continuity and momentum equations are satisfied simultaneously at each time step for oscillating flow. The numerical results show that the motion of vortices around a rolling ship hull is cyclical. It is found that the location of the vortices is very similar to the existing experimental result. Using these simulation results, we can calculate the roll damping of ships including viscous effects.

Numerical Simulation of Dynamic Response of A Net Cage for Flatfish in Waves

A numerical model of flatfish cage is built based on the lumped mass method and the principle of rigid body kinematics. To validate the numerical model, a series of physical model tests are conducted in the wave flume. The numerical results correspond well with the data sets from physical model test. The effect of weight of bottom frame, height of fish net and net shape on motion responses of fish cage and tension force on mooring lines is then analyzed. The results indicate that the vertical displacements of float collar and bottom frame decrease with the increase in the weight of bottom frame; the maximum tension force on mooring lines increases with the increasing weight of bottom frame. The inclination angles of float collar and bottom frame decrease with the increasing net height; the maximum tension force increases obviously with the increase of net height.