Theoretical studies of internal flow-induced instabilities of cantilever pipes

A theoretical analysis is made of the stability of a circular cross-section cantilever pipe containing an incompressible, inviscid fluid flowing uniformly and steadily in the axial direction. Beam and shell mode instabilities are examined. The study is based on the idea of obtaining a simple approximation for the fluid pressure and determining the importance of the downstream fluid behaviour. Results indicate that a pressure approximation (of the travelling wave type) can be made and that a reduction in the necessary numerical work can be achieved, with some small loss of accuracy, by making approximations to the in-plane inertia terms in the pipe equations.     

Peculiarities of deformation of compliant coatings with increased strength

Influence of elasticity module of coating material on the parameters of hard compliant coatings deformation has been analysed. Calculation using two-dimensional model has shown that maximum coating deformation is achieved at the ratio of flow rate U to the parameter C _t ⁰ = (E/3ρ)^0.5 approximately equal to 2.5, however, velocity of wall surface motion has first local maximum at U/C _t ⁰≈1. The range of coating parameters’ values at which compromise between its hardness and intensity of interaction with turbulent flow is provided has been determined. For rubbery materials with Poisson coefficient of about 0.5, correlations of the flow velocity and parameter C _t ⁰ shall be in the range 1÷1.5. It is shown that at such parameters, the mean square value of the coating surface deflection/inflection is less than the viscous sublayer thickness, its correlation with the wavelength is very small and equals (1÷5)·10⁻⁴. Such form of deformed surface fundamentally differs from the parameters of the wave wall in Kendall’s experiments which results are used for calculation of inverse influence of wall deformation on the flow. It was assumed that solid compliant coatings do not cause instability of interaction with the ambient flow.     

光子加速器的理论研究

研究了光子加速器(即利用等离子体中的朗谬尔波实现光脉冲频率上转换)所涉及的基本物理问题.文中导出了在存在朗谬尔波的条件下,光脉冲频率对于等离子体本底密度及电子密度扰动的依赖关系,并就最大频率转换、光脉冲俘获、波的加速位相(accelerating phase)以及位相滑动(phase slippage)效应进行讨论.     

Experimental investigation of electrohydrodynamic instabilities in micro channels

The European Physical Journal Special Topics - An electric field is applied to destabilize the interface between two Newtonian and immiscible liquids flowing in a rectangular micro channel. The...     

Experimental studies of compliant coatings for reduction of turbulent friction

Measurement results on turbulent friction are presented for nine single-layer compliant coatings in comparison with a polished solid surface streamlined by the water flow. Three experimental series separated by time passed after coating fabrication were carried out. Results on monitoring of the viscoelastic properties of coating materials are shown; they allow analysing coating aging effect as the instability factor of coating hydrodynamic efficiency. The work was financially supported by the US Navy Research Department (No. 000140210743).     

Drag reduction by compliant coatings made of a homogeneous material

The possibility of drag reduction due to compliant coatings of viscoelastic silicone rubbers has been tested experimentally. For this purpose, a series of single-layer coatings of various thicknesses was made of a homogeneous material. The experiments were carried out in a high-speed cavitation tunnel of Pusan National University. Dynamic viscoelastic properties of coating materials were carefully measured. The range of flow rates and coating thicknesses was calculated assuming that the coatings can interact intensively with the dynamic structures of the turbulent boundary layer only in the region of frequencies of their maximum compliance. The predicted range of coating parameters and flow velocities, in which the coatings reduce drag, is compared with experimental data.     

An investigation of oscillating instabilities in deflagrations with edges

We examine the Lewis-number-greater-than-1 stability of a deflagration sitting on a porous-plug burner with an inert coflow. The flame edges generated by the coflow influence the stability, and this influence is examined. Very wide flames display the same stability characteristics as unbounded flames (flames sans edges), but for moderately wide flames the instability is suppressed. A new two-dimensional instability can occur for narrow flames. There is a range of mass fluxes for which a monotonic decrease in burner (flame) width generates a transition from unstable flames to stable flames, to unstable flames, to quenching. The insertion of a cold probe into the combustion field can stabilize an unstable flame or destabilize a stable flame, depending on the point of insertion.     

水下翼型结构流噪声实验研究

为测量流激水下翼型结构的流噪声,提出了一种混响箱测量方法。在重力式水洞中搭建了一套实验测量系统,利用混响箱法测量了水下翼型结构模型的辐射声功率。在此基础上研究了流速及结构参数(厚度、肋、声学覆盖层)对其辐射声功率的影响。结果表明:当流速小于5 m/s时,辐射声功率随流速的6次方增长,符合偶极子的辐射规律;当流速大于5 m/s时,辐射声功率随流速的10土1次方规律增长,不再按偶极子的规律辐射;若对水下翼型结构模型加厚、加环肋及外部敷设黏弹性材料,均可在一定程度上抑制流噪声。此研究方法可对水下复杂结构的辐射声功率测量及结构优化设计提供一定的参考。     

A theoretical investigation of shell effects in deep inelastic collisions

The relative importance of three different influences of independent-particle shell structure on the nucleon transport process during heavy-ion collisions are discussed. Results of calculations for the 620-MeV⁸⁶Kr +¹⁹⁷Au system are presented.     

Strategy of a choice of single-layer compliant coatings for turbulent drag reduction

The main principles and methods of developing the single-layer monolithic compliant coatings for turbulent drag reduction are presented.     

A theoretical investigation of HeH+

Results are reported for the ground state (X¹Σ⁺) of the HeH⁺ ion. They include an improved Born-Oppenheimer potential curve, adiabatic corrections, and rovibronic energies for the three lowest vibrational states. The dissociation energy in the adiabatic approximation is found to be 14 873.6 cm^?1, and adiabatic effects decrease the two lowest vibrational spacings $\text{Δ}\text{G(}\text{1}\text{2}\text{)}$ and $\text{Δ}\text{G(}\text{3}\text{2}\text{)}$ by 0.9 and 0.8 cm^?1, respectively. The adiabatic rovibronic energies reported are thought to be accurate to within 1 cm^?1.     

A theoretical investigation of glide dislocations in BN/AlN heterojunctions

Glide dislocations with periodic pentagon-heptagon pairs are investigated within the theory of one-dimensional misfit dislocations in the framework of an improved Peierls-Nabarro (P-N) equation in which the lattice discreteness is fully considered. We find an approximate solution to handle misfit dislocations, where the second-order derivative appears in the improved P-N equation. This result is practical for periodic glide dislocations with narrow width, and those in the BN/AlN heterojunction are studied. The structure of the misfit dislocations and adhesion work are obtained explicitly and verified by first-principles calculations. Compared with shuffle dislocations, the compression force in the tangential direction of glide dislocations has a greater impact on the normal direction, and the contributions of the normal displacement to the interfacial energy cannot simply be ignored.     

A theoretical investigation of chirp insonification of ultrasound contrast agents

A theoretical investigation of second harmonic imaging of an Ultrasound Contrast Agent (UCA) under chirp insonification is considered. By solving the UCA’s dynamical equation analytically, the effect that the chirp signal parameters and the UCA shell parameters have on the amplitude of the second harmonic frequency are examined. This allows optimal parameter values to be identified which maximise the UCA’s second harmonic response. A relationship is found for the chirp parameters which ensures that a signal can be designed to resonate a UCA for a given set of shell parameters. It is also shown that the shell thickness, shell viscosity and shell elasticity parameter should be as small as realistically possible in order to maximise the second harmonic amplitude. Keller-Herring, Second Harmonic, Chirp, Ultrasound Contrast Agent.     

A theoretical investigation of electronic ground state of parent sulfur diimide

In this paper various properties of parent sulfur diimides (PSD) as the simplest member of sulfur diimides family have been considered using both DFT and ab initio methods employing correlation consistent basis set hierarchies. According to these calculations, EZ conformer is predicted to be the most stable conformer in accord with experimental observation, while its energy difference with ZZ conformer is completely minute. Comparison of microwave gas phase spectra and dense phase IR experimental data with theoretical calculations show a great coincidence. The properties of EE conformer have also been anticipated and its possible presence in dense phase have been discussed although no firm experimental data exists for this conformer. The possible pathways for interconversion between various conformers have been investigated and only two unimolecular type processes namely EZ ↔ EE and EZ ↔ ZZ interconversions have been established according to a pseudo-rotation mechanism as constituting the essential dynamic of system.     

A theoretical investigation of hydrolysis of borides and borohydrides of alkali metals

A theoretical investigation of phase transitions of components of chemical reactions in the course of hydrolysis of borohydrides of alkaline metals МВН ₄ (M = Li, Nа, K, Rb, etc.) and dehydrogenation of borohydrides is performed; these reactions giving different hydrogen yield are compared. The percentage of the extracted hydrogen is estimated and the temperature dependence of its concentration is revealed. The phase transformation diagrams are constructed using the experimental data.     

H_2在Al_nCr(n=1-7)团簇上吸附和解离的密度泛函研究

采用密度泛函理论中的B3LYP方法研究了H2在AlnCr(n=1-7)团簇上的吸附和解离.结果表明:AlnCr团簇结构与Aln+1团簇结构相似;物理吸附是H2以侧向的形式吸附在Cr原子上,H-H键长略微增长,H2的振动频率发生了红移;除了n=5外,其它AlnCr H2团簇的最稳定结构均是AlnCr团簇的最稳定结构与两个氢原子成键而成;AlnCr团簇向H原子转移了电荷;AlnCr H2团簇的平均结合能,垂直电离势和能隙均大于AlnCr团簇的,即AlnCr H2团簇比AlnCr团簇更稳定;Al7Cr对H2的化学吸附表现出较强的惰性,而AlnCr H2(n=1,2,6)则表现出较强的化学活性;由化学反应路径跟踪可知,通过改变AlnCr团簇中Al原子的个数可以调节H2的物理化学吸附行为.     

H2在AlnCr(n=1-7)团簇上吸附和解离的密度泛函研究

采用用密度泛函理论中的B3LYP方法研究了H2在AlnCr(n=1-7)团簇上的吸附和解离。结果表明：AlnCr团簇结构与Aln+1团簇结构相似;物理吸附是H2是以侧向的形式吸附在Cr原子上,H-H键长略微增长,H2的振动频率发生了红移;除了n=5外,其它AlnCrH2团簇的最稳定结构均是AlnCr团簇的最稳定结构与两个氢原子成键而成;AlnCr团簇向H原子转移了电荷;AlnCrH2团簇的平均结合能,垂直电离势和能隙均大于AlnCr团簇的,即AlnCrH2团簇比AlnCr团簇更稳定;Al7Cr对H2的化学吸附表现出较强的惰性,而AlnCrH2(n=1,2,6)则表现出较强的化学活性;由化学反应路径跟踪可知,通过改变AlnCr团簇中Al原子的个数可以调节H2的物理化学吸附行为。