A Flexible-Segment-Model-Based Dynamics Calculation Method for Free Hanging Marine Risers in Re-Entry

In re-entry, the drilling riser hanging to the holding vessel takes on a free hanging state, waiting to be moved from the initial random position to the wellhead. For the re-entry, dynamics calculation is often done to predict the riser motion or evaluate the structural safety. A dynamics calculation method based on Flexible Segment Model （FSM） is proposed for free hanging marine risers. In FSM, a riser is discretized into a series of flexible segments. For each flexible segment, its deflection feature and external forces are analyzed independently. For the whole riser, the nonlinear governing equations are listed according to the moment equilibrium at nodes. For the solution of the nonlinear equations, a linearization iteration scheme is provided in the paper. Owing to its flexibility, each segment can match a long part of the riser body, which enables that good results can be obtained even with a small number of segments. Moreover, the linearization iteration scheme can avoid widely used Newton-Rapson iteration scheme in which the calculation stability is influenced by the initial points. The FSM-based dynamics calculation is timesaving and stable, so suitable for the shape prediction or real-time control of free hanging marine risers.

Quasi-three-dimensional hydrodynamics of the corona region of laser irradiation of a slab

This paper introduces and establishes a quasi-three-dimensional physical model of the interaction between a laser and a slab target.In contrast to previous one-dimensional analytical models,this paper innovatively fits the real laser conditions based on an isothermal,homogeneous expansion similarity solution of the ideal hydrodynamic equations.Using this simple model,the evolution law and analytical formulae for key parameters(e.g.,temperature,density and scale length)in the corona region under certain conditions are given.The analytical solutions agree well with the relevant results of computational hydrodynamics simulation.For constant laser irradiation,the analytical solutions provide a meaningful power-law scaling relationship.The model provides a set of mathematical and physical tools that give theoretical support for adjusting parameters in experiments.

Calculations of Chemical Reaction Dynamics for D+ H_2(j_i,ν_i=0)→DH(j_f, ν_f=0) + H

The constant Centrifugal potential approximation is Corrected so as to apply to the reactions of rotational excited reactants for D + H2 (j,, νi = 0 ) -DH(jf, νf = 0) + H. Our results show that the contributions from ji≠0 and Ωi terms are not negligible.

Diagnostic Calculation of the Oceanic Circulation

A 2-dimensional global free surface diagnostic model, combined with dynamic calculation, is used to investigate the world ocean circulation; the model has a horizontal resolution of 1/4°×1/4°. The simulated results agree well with the results of other modesl and observations. The distribution of Stream Function suggests that the main circulation systems in the wodd ocean have been represented, including oceanic currents strengthened in the oceanic western. Be close to the observed results, the net mass transport of the Kuroshio axes is estimated about 54Sv; The distribution of the horizontal circulation in each layer shows that the main circulation systems in the world ocean are well simulated, for example, the Kuroshio and the Antarctic Circumpolar Current can go down to the bottom layer, but the Gulf Stream cannot, and its direction reverses at the depths of 1000 to 2 000 m.

Peculiar diffusion behavior of AlCl_(4) intercalated in graphite from nanosecond-long molecular dynamics simulations

The diffusion property of the intercalated species in the graphite materials is at the heart of the rate performance of graphite-based metal-ion secondary battery.Here we study the diffusion process of a AlCl_(4) molecule within graphite—a key component of a recently reported aluminum ion battery with excellent performance—via molecular dynamics(MD)simulations.Both ab-initio MD(AIMD)and semiempirical tight-binding MD simulations show that the diffusion process of the intercalated AlCl_(4) molecule becomes rather inhomogeneous,when the simulation time exceeds approximately 100 picoseconds.Specifically,during its migration in between graphene layers,the intercalated AlCl_(4) molecule may become stagnant occasionally,and then recovers its normal(fast)diffusion behavior after halting for a while.When this phenomenon occurs,the linear relationship of the mean squared displacement(MSD)versus the duration time is not fulfilled.We interpret this peculiar behavior as a manifestation of inadequate sampling of rare event(the stagnation of the molecule),which does not yet appear in short-time MD simulations.We further check the influence of strains present in graphite intercalated compounds(GIC)on the diffusion properties of AlCl_(4),and find that their presence in general slows down the diffusion of the intercalated molecule,and is detrimental to the rate performance of the GIC-based battery.

Establishing an Initial Electron Beam Model with Monte Carlo Simulation for a Single 6 MV X-ray Medical Linac Based on Particle Dynamics Characteristics

Objective:In this study,we try to establish an initial electron beam model by combining Monte Carlo simulation method with particle dynamic calculation(TRSV)for the single 6 MV X-ray accelerating waveguide of BJ-6 medical linac.Methods and Materials:1.We adapted the treatment head configuration of BJ-6 medical linac made by Beijing Medical Equipment Institute(BMEI)as the radiation system for this study.2.Use particle dynamics calculation code called TRSV to drive out the initial electron beam parameters of the energy spectrum,the spatial intensity distribution,and the beam incidence angle.3.Analyze the 6 MV X-ray beam characteristics of PDDc,OARc in a water phantom by using Monte Carlo simulation(BEAMnrc,DOSXYZnrc)for a preset of the initial electron beam parameters which have been determined by TRSV,do the comparisons of the measured results of PDDm,OARm in a real water phantom,and then use the deviations of calculated and measured results to slightly modify the initial electron beam model back and forth until the deviations meet the error less than 2%.Results:The deviations between the Monte Carlo simulation results of percentage depth doses at PDDc and off-axis ratios OARc and the measured results of PDDm and OARm in a water phantom were within 2%.Conclusion:When doing the Monte Carlo simulation to determine the parameters of an initial electron beam for a particular medical linac like BJ-6,modifying some parameters based on the particle dynamics calculation code would give some more reasonable and more acceptable results.

Dynamic Motion and Tension of Marine Cables Being Laid During Velocity Change of Mother Vessels

Flexible segment model （FSM） is adopted for the dynamics calculation of marine cable being laid. In FSM, the cable is divided into a number of flexible segments, and nonlinear governing equations are listed according to the moment equilibriums of the segments. Linearization iteration scheme is employed to obtain the numerical solution for the governing equations. For the cable being laid, the payout rate is calculated from the velocities of all segments. The numerical results are shown of the dynamic motion and tension of marine cables being laid during velocity change of the mother vessels.

Negative thermal expansion in NbF_(3)and NbOF_(2):A comparative theoretical study

Thermal expansion control is always an obstructive factor and challenging in high precision engineering field.Here,the negative thermal expansion of NbF_(3)and NbOF_(2)was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation(QHA).We studied the total charge density,thermal vibration,and lattice dynamic to investigate the thermal expansion mechanism.We found that the presence of O induced the relatively strong covalent bond in NbOF_(2),thus weakening the transverse vibration of F and O in NbOF_(2),compared with the case of NbF_(3).In this study,we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms.The present work not only predicts two NTE compounds,but also provides an insight on thermal expansion control by designing chemical bond type.

Characteristics of water exchange in the Luzon Strait during September 2006

The Luzon Strait is the only deep channel that connects the South China Sea(SCS) with the Pacific.The transport through the Luzon Strait is an important process influencing the circulation,heat and water budgets of the SCS.Early observations have suggested that water enters the SCS in winter but water inflow or outflow in summer is quite controversial.On the basis of hydrographic measurements from CTD along 120° E in the Luzon Strait during the period from September 18 to 20 in 2006,the characteristics of temperature,salinity and density distributions are analyzed.The velocity and volume transport through the Luzon Strait are calculated using the method of dynamic calculation.The major observed results show that water exchanges are mainly from the Pacific to the South China Sea in the upper layer,and the flow is relatively weak and eastward in the deeper layer.The net volume transport of the Luzon Strait during the observation period is westward,amounts to about 3.25 Sv.This result is consistent with historical observations.

Quantum Mechanics Rate Constant for the N-I-ND Reaction

We present nonadiabatic quantum dynamical calculations on the two coupled potential energy surfaces （12A＇ and 22A＇） [J. Theor. Comput. Chem. 8, 849 （2009）] for the reaction. Initial state-resolved reaction probabilities and cross sections for the N＋ND→N2＋D reaction and N＇＋ND→N＋N＇D reaction for collision energies of 5 meV to 1.0 eV are determined, respectively. It is found that the N＋ND→N2＋D reaction is dominated in the N＋ND reaction. In addition, we obtained the rate constants for the N＋ND→N2＋D reaction which demand further experimental investigations.

Dynamic Characteristics and Simplified Numerical Methods of An All-Vertical-Piled Wharf in Offshore Deep Water

There has been a growing trend in the development of offshore deep-water ports in China. For such deep sea projects, all-vertical-piled wharves are suitable structures and generally located in open waters, greatly affected by wave action. Currently, no systematic studies or simplified numerical methods are available for deriving the dynamic characteristics and dynamic responses of all-vertical-piled wharves under wave cyclic loads. In this article, we compare the dynamic characteristics of an all-vertical-piled wharf with those of a traditional inshore high-piled wharf through numerical analysis; our research reveals that the vibration period of an all-vertical-piled wharf under cyclic loading is longer than that of an inshore high-piled wharf and is much closer to the period of the loading wave. Therefore, dynamic calculation and analysis should be conducted when designing and calculating the characteristics of an all-vertical-piled wharf. We establish a dynamic finite element model to examine the dynamic response of an all-vertical-piled wharf under wave cyclic loads and compare the results with those under wave equivalent static load; the comparison indicates that dynamic amplification of the structure is evident when the wave dynamic load effect is taken into account. Furthermore, a simplified dynamic numerical method for calculating the dynamic response of an all-vertical-piled wharf is established based on the P-Y curve. Compared with finite element analysis, the simplified method is more convenient to use and applicable to large structural deformation while considering the soil non-linearity. We confirmed that the simplified method has acceptable accuracy and can be used in engineering applications.

Dynamic responses of deep underground explosions based on improved Grigorian model

It is important to investigate the dynamic behaviors of deep rocks near explosion cavity to reveal the mechanisms of deformations and fractures. Some improvements are carried out for Grigorian model with focuses on the dilation effects and the relaxation effects of deep rocks, and the high pressure equations of states with Mie-Grüneisen form are also established. Numerical calculations of free field parameters for deep underground explosions are carried out based on the user subroutines which are compiled by means of the secondary development functions of LS-DYNA9703 D software. The histories of radial stress, radial velocity and radial displacement of rock particles are obtained, and the calculation results are compared with those of U.S. Hardhat nuclear test. It is indicated that the dynamic responses of free field for deep underground explosions are well simulated based on improved Grigorian model, and the calculation results are in good agreement with the data of U.S. Hardhat nuclear test. The peak values of particle velocities are consistent with those of test, but the waveform widths and the rising times are obviously greater than those without dilation effects. The attenuation rates of particle velocities are greater than the calculation results with classic plastic model, and they are consistent with the results of Hardhat nuclear test. The attenuation behaviors and the rising times of stress waves are well shown by introducing dilation effects and relaxation effects into the calculation model. Therefore, the defects of Grigorian model are avoided. It is also indicated that the initial stress has obvious influences on the waveforms of radial stress and the radial displacements of rock particles.

Identifying the crystal structure of T 1 precipitates in Al-Li-Cu alloys by ab initio calculations and HAADF-STEM imaging

Controversial experimental reports on the crystal structure of T 1 precipitates in Al-Li-Cu alloys have ex-isted for a long time,and all of them can be classified into five models.To clarify its ground-state atomic structure,herein,we have combined high-throughput first-principles calculations and CALPHAD,as well as aberration-corrected HAADF-STEM experiments.Employing the special quasi-random structure(SQS)and supercell approximation(SPA)methods to simulate the local disorder on Al-Cu sub-lattices,we find that none of the present models can satisfy the phase stability in Al-Li-Cu ternary system based on temperature-dependent convex hull analysis.Using the cluster expansion(CE)formulas,structural predic-tions derived from the five-frame models were performed.Subsequently,by introducing the vibrational contribution to the free energy at aging temperatures,we proposed a novel ground-state T 1 structure that maintains a coherent relationship with Al-matrix at the<112>Al orientation.The underlying phase transition between the variants of T 1 precipitates was further discussed.By means of ab initio molecular dynamics(AIMD)simulations,we resolved the controversy regarding the number of atomic layers con-stituting the T 1 phase and acknowledged the existence of Al-Li corrugated layers.The root cause of this structural distortion is triggered by atomic forces and bondings.Our work can have an positive impact on the novel fourth generation of Al-Cu-Li alloy designs by engineering the T 1 strengthening phase.

Theoretical Studies on Formation Mechanism of Resonance States for Na+I_2→Na^++I_2^-System

An extended linear combination of arrangement channels-scattering wave-function(LCAC-SW) quantum scattering dynamic method combined with ab initio quantum chemical calculation was used to study the formation mechanism of the resonance states for the collinear Na+I 2→Na ++I - 2 ion-pair formation process on Aten-Lanting-Los potential energy surface. The resonance energy and the resonance width or the lifetime for the first resonance peak were calculated. The resonance can be identified as the Feshbach type and the physical interpretation is given. The geometric structure of the resonance state for the title system has been optimized.

An integrated computational method for calculating dynamic thermal bridges of building facades in tropical countries

Identifying thermal bridges on building façades has been a great challenge for architects,especially during the conceptual design stage.This is not only due to the complexity of parameters when calculating thermal bridges,but also lack of feature integration between building energy simulation(BES)tools and the actual building conditions.For example,existing BES tools predominantly calculate thermal bridges only in steady state without considering the temperature dynamic behaviour of building outdoors.Consequently,relevant features such as thermal delay,decrement factor,and operative temperature are often neglected,and this can lead to miscalculation of energy consumption.This study then proposes an integrated method to calculate dynamic thermal bridges under transient conditions by incorporating field observations and computational simulations of thermal bridges.More specifically,the proposed method employs several measurement tools such as HOBO data logger to record the actual conditions of indoor and outdoor room temperature and thermal cameras to identify the surface temperature of selected building junctions.The actual datasets are then integrated with the simulation workflow developed in BES tools.This study ultimately enables architects not only to identify potential thermal bridges on existing building façades but also to support material and geometric exploration in early design phase.

具有直接Z型光催化机制的非金属BC4N/aza-CMP异质双层的光催化固氮性能

我们设计了一种不含金属的二维双层异质结构BC_(4)N/aza-CMP,该体系可在水溶液中将N2分子通过光催化作用还原为氨.通过密度泛函理论和非绝热分子动力学方法,我们发现该异质结构中的光生载流子遵循直接Z型迁移机制.这将有效分离光生电荷并使氮还原反应和氧发生反应分别在BC_(4)N层和aza-CMP层上进行,实现反应位点的空间分离.值得一提的是,BC_(4)N上的B原子可以有效吸附N2分子并激活N≡N键,这将降低氮还原反应的过电势并促进随后的质子化进程,且该异质双层具有适宜的带隙和带边位置,能够有效吸收太阳光并提供充足的驱动力来触发氧化还原反应,实现无任何牺牲剂辅助的光催化氨合成.本工作将为直接Z型固氮光催化剂的设计提供重要借鉴,并促进太阳能驱动的氨合成的发展.

Alloy-induced reduction and anisotropy change of lattice thermal conductivity in Ruddlesden–Popper phase halide perovskites

The effective modulation of the thermal conductivity of halide perovskites is of great importance in optimizing their optoelectronic device performance.Based on first-principles lattice dynamics calculations,we found that alloying at the B and X sites can significantly modulate the thermal transport properties of 2D Ruddlesden−Popper(RP)phase halide perovskites,achieving a range of lattice thermal conductivity values from the lowest(κ_(c)=0.05 W·m^(−1)·K^(−1)@Cs_(4)AgBiI_(8))to the highest(κ_(a/b)=0.95 W·m^(−1)·K^(−1)@Cs4NaBiCl_(4)I_(4)).Compared with the pure RP-phase halide perovskites and three-dimensional halide perovskite alloys,the two-dimensional halide perovskite introduces more phonon branches through alloying,resulting in stronger phonon branch coupling,which effectively scatters phonons and reduces thermal conductivity.Alloying can also dramatically regulate the thermal transport anisotropy of RP-phase halide perovskites,with the anisotropy ratio ranging from 1.22 to 4.13.Subsequently,analysis of the phonon transport modes in these structures revealed that the lower phonon velocity and shorter phonon lifetime were the main reasons for their low thermal conductivity.This work further reduces the lattice thermal conductivity of 2D pure RP-phase halide perovskites by alloying methods and provides a strong support for theoretical guidance by gaining insight into the interesting phonon transport phenomena in these compounds.