Effect of a two-phase wedge-sliding model on the ingredient drift of a stable mixed fluid and its computing method

A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of a stable system,and it is used to describe the ingredient distribution of a mixed fluid in a non-uniform stress field and to analyse its phase drift phenomenon.In the model,the drift-inhibition angle and the expansion-inhibition angle are also deduced and used as evaluating indexes to describe the drifting trend of different ingredients among the mixed fluids.For solving above two indexes of the model,a new calculation method is developed and used to compute the phase distributions of multiphase fluid at peak stress and gradient area stress,respectively.As an example,the flow process of grease in a pipe is analysed by simulation method and used to verify the validity of the model.     

Multi-bubble motion behavior of electric field based on phase field model

By coupling the phase field model with the continuity equation of incompressible fluid, Navier–Stokes equation,electric field equation, and other governing equations, a multi-field coupling model for multi-bubble coalescence in a viscous fluids is established. The phase field method is used to capture the two-phase interface. The motion and coalescence of a pair of coaxial bubbles under an external uniform electric field and the effects of different electric field strengths on the interaction and coalescence of rising bubbles are studied. The results show that the uniform electric field accelerates the collision and coalescence process of double bubbles in the fluid, and increases the rising velocity of the coalesced bubble.The electric field with an intensity of E = 2 kV/mm is reduced about 2 times compared with that without electric field in coalescence time. When the electric field strength is strong(E ≥ 1 kV/mm), the coalesced bubble will rupture before it rises to the top of the calculation area, and the time of the bubble rupturing also decreases with the increase of the electric field strength. The phase field method is compared with the simulation results of Lattice Boltzmann Method(LBM), and the shape of bubble obtained by the two methods is in good agreement, which verifies the correctness of the calculation model.     

Particle transport behavior in air channel flow with multi-group Lagrangian tracking

The particle motions of dispersion and transport in air channel flow are investigated using a large eddy simulation(LES) and Lagrangian trajectory method. The mean and fluctuating velocities of the fluids and particles are obtained,and the results are in good agreement with the data in the literature. Particle clustering is observed in the near-wall and low-speed regions. To reveal the evolution process and mechanism of particle dispersion and transport in the turbulent boundary layer, a multi-group Lagrangian tracking is applied when the two-phase flow has become fully developed: the fluid fields are classified into four sub-regions based on the flow characteristics, and particles in the turbulent region are divided accordingly into four groups when the gas–particle flow is fully developed. The spatiotemporal transport of the four groups of particles is then tracked and analyzed. The detailed relationship between particle dispersion and turbulent motion is investigated and discussed.     

Multi-bubble motion behavior of uniform magnetic field based on phase field model

Aiming at the interaction and coalescence of bubbles in gas–liquid two-phase flow, a multi-field coupling model was established to simulate deformation and dynamics of multi-bubble in gas–liquid two-phase flow by coupling magnetic field, phase field, continuity equation, and momentum equation. Using the phase field method to capture the interface of two phases, the geometric deformation and dynamics of a pair of coaxial vertical rising bubbles under the applied uniform magnetic field in the vertical direction were investigated. The correctness of results is verified by mass conservation method and the comparison of the existing results. The results show that the applied uniform magnetic field can effectively shorten the distance between the leading bubble and the trailing bubble, the time of bubbles coalescence, and increase the velocity of bubbles coalescence. Within a certain range, as the intensity of the applied uniform magnetic field increases, the velocity of bubbles coalescence is proportional to the intensity of the magnetic field, and the time of bubbles coalescence is inversely proportional to the intensity of the magnetic field.     

A multicomponent multiphase lattice Boltzmann model with large liquid–gas density ratios for simulations of wetting phenomena

A multicomponent multiphase(MCMP) pseudopotential lattice Boltzmann(LB) model with large liquid–gas density ratios is proposed for simulating the wetting phenomena. In the proposed model, two layers of neighboring nodes are adopted to calculate the fluid–fluid cohesion force with higher isotropy order. In addition, the different-time-step method is employed to calculate the processes of particle propagation and collision for the two fluid components with a large pseudoparticle mass contrast. It is found that the spurious current is remarkably reduced by employing the higher isotropy order calculation of the fluid–fluid cohesion force. The maximum spurious current appearing at the phase interfaces is evidently influenced by the magnitudes of fluid–fluid and fluid–solid interaction strengths, but weakly affected by the time step ratio.The density ratio analyses show that the liquid–gas density ratio is dependent on both the fluid–fluid interaction strength and the time step ratio. For the liquid–gas flow simulations without solid phase, the maximum liquid–gas density ratio achieved by the present model is higher than 1000:1. However, the obtainable maximum liquid–gas density ratio in the solid–liquid–gas system is lower. Wetting phenomena of droplets contacting smooth/rough solid surfaces and the dynamic process of liquid movement in a capillary tube are simulated to validate the proposed model in different solid–liquid–gas coexisting systems. It is shown that the simulated intrinsic contact angles of droplets on smooth surfaces are in good agreement with those predicted by the constructed LB formula that is related to Young's equation. The apparent contact angles of droplets on rough surfaces compare reasonably well with the predictions of Cassie's law. For the simulation of liquid movement in a capillary tube, the linear relation between the liquid–gas interface position and simulation time is observed, which is identical to the analytical prediction. The simulation results regarding the wetting phenomena of droplets on smooth/rough surfaces and the dynamic process of liquid movement in the capillary tube demonstrate the quantitative capability of the proposed model.     

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C(66). The shear failure under {110}{111} shear deformation occurring in process of tension may result in a small ideal tensile strength(~ 2 GPa) for NiTi. The unlikeness in the ideal strength of Ni Al and Ni Ti alloys is discussed based on the charge density difference.     

Magnetic and mechanical properties of Ni–Mn–Ga/Fe–Ga ferromagnetic shape memory composite

A ferromagnetic shape memory composite of Ni–Mn–Ga and Fe–Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni–Mn–Ga alloy,the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe–Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved.     

Particle path tracking method in two- and three-dimensional continuously rotating detonation engines

The particle path tracking method is proposed and used in two-dimensional（2D） and three-dimensional（3D） numerical simulations of continuously rotating detonation engines（CRDEs）. This method is used to analyze the combustion and expansion processes of the fresh particles, and the thermodynamic cycle process of CRDE. In a 3D CRDE flow field, as the radius of the annulus increases, the no-injection area proportion increases, the non-detonation proportion decreases, and the detonation height decreases. The flow field parameters on the 3D mid annulus are different from in the 2D flow field under the same chamber size. The non-detonation proportion in the 3D flow field is less than in the 2D flow field. In the 2D and 3D CRDE, the paths of the flow particles have only a small fluctuation in the circumferential direction. The numerical thermodynamic cycle processes are qualitatively consistent with the three ideal cycle models, and they are right in between the ideal F–J cycle and ideal ZND cycle. The net mechanical work and thermal efficiency are slightly smaller in the 2D simulation than in the 3D simulation. In the 3D CRDE, as the radius of the annulus increases, the net mechanical work is almost constant, and the thermal efficiency increases. The numerical thermal efficiencies are larger than F–J cycle, and much smaller than ZND cycle.     

Temperature-insensitive optical Fabry–Perot flow measurement system with partial bend angle

A flow measurement system consisting of an optical fiber Fabry–Perot(F-P) sensor and an elbow tube is proposed and demonstrated to realize flow measurements and eliminate thermal disturbance.Two F-P sensors are symmetrically mounted on the inner-wall surface of the elbow of 90° in order to eliminate the effect of thermal disturbance to the flow measurement accuracy.Experimental results show that the absolute phase difference is the square root of the fluid flow.It is consistent with the theoretical analysis,which proves that the flow measurement method can measure flow and eliminate the influence of thermal disturbance simultaneously.     

A three-dimensional solid-liquid two-phase turbulence model with the effect of vegetation in non-orthogonal curvilinear coordinates

A three-dimensional k-ε-Ap solid-liquid two-phase two-fluid model with the effect of vegetation is solved numerically with a finite-volume method on an adaptive grid to study water-sediment movements and bed evolution in vegetated channels. The additional drag force and additional turbulence generation due to vegetation are added to the relevant control equations for simulating the interaction between vegetation and flow. The flow structure and the bed-topography changes in a 60° partly vegetated channel be...     

Prediction of underwater target strength

1 IntroductionTarget Strength of underwater objects is an importallt parameter of the sonar equations.A method for the calculation of target strength using Lighthill's acoustic analogy approach ispresellted. Farassat's solution to the FW-H equation for the calculation of discrete noise ofsubsonic propeller in the free field is used. For a rigid bodys the suxface sound pressure inducedby incident sound wave could be obtained by united aerodynamics and aeroacoustics approach,which have been su…     

Influence of Rayleigh-Taylor Instability on Liquid Propellant Reorientation in a Low-Gravity Environment

A computational simulation is conducted to investigate the influence of Rayleigh-Taylor instability on liquid propellant reorientation flow dynamics for the tank of CZ-3A launch vehicle series fuel tanks in a low-gravity environment. The volume-of-fluid （VOF） method is used to simulate the free surface flow of gas-liquid. The process of the liquid propellant reorientation started from initially flat and curved interfaces are numerically studied. These two different initial conditions of the gas-liquid interface result in two modes of liquid flow. It is found that the Rayleigh Taylor instability can be reduced evidently at the initial gas-liquid interface with a high curve during the process of liquid reorientation in a low-gravity environment.     

Surface Corrugation in Rotational and Diffractive Scattering of O2 from LiF （001）

A quantum dynamic calculation on a five-dimensional O2/LiF （001） model system is performed using the multi-configuration time-dependent Hartree method. The obtained results show that the mechanism of rotational and diffractive excitation in details： Comparison with the rotational excited state, the initially non-rotational state is seen to favor the inelastic scattering in the rotational excitation process. The surface corrugation can damp the quantum interferences and produce a greater amount of rotational inelastic scattering at the expense of the elastic process in the rotational excitation process. The diffraction process and the average energy transferred into the rotational and diffractive mode are also discussed.     

A nano-scale mirror-like surface of Ti–6Al–4V attained by chemical mechanical polishing

Metal Ti and its alloys have been widely utilized in the fields of aviation, medical science, and micro-electromechanical systems, for its excellent specific strength, resistance to corrosion, and biological compatibility. As the application of Ti moves to the micro or nano scale, however, traditional methods of planarization have shown their short slabs.Thus, we introduce the method of chemical mechanical polishing(CMP) to provide a new way for the nano-scale planarization method of Ti alloys. We obtain a mirror-like surface, whose flatness is of nano-scale, via the CMP method. We test the basic mechanical behavior of Ti–6Al–4V(Ti64) in the CMP process, and optimize the composition of CMP slurry.Furthermore, the possible reactions that may take place in the CMP process have been studied by electrochemical methods combined with x-ray photoelectron spectroscopy(XPS). An equivalent circuit has been built to interpret the dynamic of oxidation. Finally, a model has been established to explain the synergy of chemical and mechanical effects in the CMP of Ti–6Al–4V.     

Non-intrusive flow measurement based on a distributed feedback fiber laser

We propose a new non-intrusive flow measurement method using the distributed feedback fiber laser(DFB-FL)as a sensor to monitor flow in the pipe.The relationship between the wavelength of the DFB-FL and the liquid flow rate in the pipeline is derived.Under the guidance of this theory,the design and test of the flow sensor is completed.The response curve is relatively flat in the frequency range of 10 Hz to 500 Hz,and the response of the flow sensor has high linearity.The flow from 0.6 m^3/h to 25.5 m^3/h is accurately measured under the energy analysis method in different frequency intervals.A minimum flow rate of 0.046 m/s is achieved.The experimental results demonstrate the feasibility of the new non-intrusive flow measurement method based on the DFB-FL and accurate measurement of small flow rates.     

Reliability analysis of stochastic structural system considering static strength, stiffness and fatigue

Multi-failures are possible to appear in the process of using the structural system, such as dead load failure, fatigue failure and stiffness failure. The expression of residual resistance is given based on the impact of random crack propagation in- duced by the fatigue load on the critical limit stress and section modulus in this paper. The failure modes of every element of the structural system are analyzed under dead and fatigue loads, and the influence of the correlation of failure modes on reliability of the element is considered. Failure mechanism and the correlation of failure modes under dead and fatigue loads are discussed, and the method of reli- ability analysis considering static strength, fatigue and stiffness is given. A nu- merical example is analyzed, which indicates that the failure probability is different for different use life and the influence of dead and fatigue loads on reliability of the structural system is different as well. This method of reliability analysis, in the pa- per, is better than the method only considering a single factor (or static strength, or fatigue, or stiffness, etc.) in the case of practical engineering.     

Electronic structure from equivalent differential equations of Hartree–Fock equations

A strict universal method of calculating the electronic structure of condensed matter from the Hartree–Fock equation is proposed. It is based on a partial differential equation(PDE) strictly equivalent to the Hartree–Fock equation, which is an integral–differential equation of fermion single-body wavefunctions. Although the maximum order of the differential operator in the Hartree–Fock equation is 2, the mathematical property of its integral kernel function can warrant the equation to be strictly equivalent to a 4 th-order nonlinear partial differential equation of fermion single-body wavefunctions. This allows the electronic structure calculation to eliminate empirical and random choices of the starting trial wavefunction(which is inevitable for achieving rapid convergence with respect to iterative times, in the iterative method of studying integral–differential equations), and strictly relates the electronic structure to the space boundary conditions of the singlebody wavefunction.     

Resonant charge transfer in slow Li~+–Li(2s) collision

The resonant charge transfer process for Li+–Li(2s) collision is investigated by the quantum-mechanical molecular orbital close-coupling(QMOCC) method and the two-center atomic-orbital close-coupling(AOCC) method in an energy range of 1.0 e V/u–104e V/u. Accurate molecular structure data and charge transfer cross sections are given. Both the allelectron model(AEM) and one-electron model(OEM) are used in the QMOCC calculations, and the discrepancies between the two models are analyzed. The OEM calculation can also give a reliable prediction of the cross sections for energies below 1 ke V/u.     

Stability and a fast calculation method of travel speed of pulse peak in convergence zone

A long-range sound propagation experiment was conducted in the West Pacific Ocean in summer 2013.The signals received by a towed array indicate that the travel speed of pulse peak(TSPP)in the convergence zones is stable.Therefore,an equivalent sound speed can be used at all ranges in the convergence zones.A fast calculation method based on the beam-displace-ment ray-mode(BDRM)theory and convergence zone theory is proposed to calculate this equivalent sound speed.The computation speed of this proposed method is over 1000 times faster than that of the conventional calculation method based on the normal mode theory,with the computation error less than 0.4%compared with the experimental result.Also,the effect of frequency and sound speed profile on the TSPP is studied with the conventional and fast calculation methods,showing that the TSPP is almost independent of the frequency and sound speed profile in the ocean surface layer.     

A Dugdale–Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals

The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.