Evolution of the Alfvénic correlation in the solar wind

Summary The radial evolution of Alfvénic correlation is such that its value decreases with increasing heliocentric distance. So far this behaviour has been interpreted as an increase in the local production of ?inward? modes interacting destructively with the ?outward? modes. This work, which deals with largescale turbulence, shows that local generation phenomena are not commonly found in the solar wind and that the Alfvénic character of the fluctuations mainly depend on the ?outward? modes alone. The interaction of these modes with density and/or magnetic-field structures convected by the wind causes their destruction and a consequent depletion of the Alfvénic correlation. The same effect would be obtained if ?inward? modes were really present. Our conclusions are that large-scale ?inward? modes are the spectral counterpart of non-propagating field and plasma structures convected by the solar wind and identified as both compression regions and pressure balance structures. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

THE THREE-DIMENSIONAL STRESS INTENSITY FACTOR UNDER MOVING LOADS ON THE CRACK FACES

The dynamic stress intensity factor history for a half plane crack in anotherwise unbounded elastic body,with the crack faces subjected to a tractiondistribution consisting of two pairs of combined mode point loads that move in adirection perpendicular to the crack edge is considered.The analytic expression for thecombined mode stress intensity factors as a function of time for any point along thecrack edge is obtained.The method of solution is based on the application of integraltransform together with the Wiener-Hopf technique and the Cagniard-de Hoop method.Some features of the solution are discussed and graphical results for various point loadspeeds are presented.     

Specific O₂⁻ generation in corona discharge for ion mobility spectrometry

This study deals with O₂⁻ generation in corona discharge (CD) in point to plane geometry for single flow ion mobility spectrometry (IMS) with gas outlet located behind the ionization source. We have designed CD of special geometry in order to achieve the high O₂⁻ yield. Using this ion source we have achieved in zero air conditions that up to 74% all negative ions were O₂⁻ or O₂⁻(H₂O). It has been demonstrated that the non-electronegative nitrogen positively influences the efficiency of O₂⁻ generation in O₂/N₂ mixtures. The reduced ion mobility of 2.27 cm² V⁻¹ s⁻¹ has been measured for O₂⁻/O₂⁻(H₂O) ions in zero air. Additional ions detected in zero air (less than 200 ppb CO₂) using the mass spectrometric and IMS technique were, NO₂⁻, N₂O₂⁻ (2.37 cm² V⁻¹ s⁻¹), NO₃⁻, N₂O₃⁻ and N₂O₃⁻(H₂O). The CO₃⁻ and CO₄⁻ ions have been detected after the introduction of 5 ppm CO₂ into zero air.     

Study of an alternative material to manufacture layered hydraulic hoses

Hydraulic hoses are components of umbilical cables and others subsea equipments. They are manufactured from thermoplastic polymers and are susceptible to collapse under external pressure, which can cause plastic strains around the circumference, leading to failure under internal pressure (bursting). This work studies an alternative hydraulic hose liner capable of support such load history, even after long time exposure to the hydraulic fluid. It is based on the comparison between the material currently used (Polyamide 11) and a fluorinated elastomer, Viton^®. Mechanical characterization, ageing tests as well as nonlinear finite elements simulations were accomplished to issue both performances. The results obtained showed that Viton^® liners are mechanically more suitable than Polyamide 11 liners to such hoses. The ageing tests showed compatibility between Viton^® and the hydraulic fluid. Considering that the external aramid layer is responsible to withstand the internal pressure in both cases, Viton^® can successfully replace Polyamide 11 for this application as well as others involving layered hoses under combined internal and external pressure.     

有限长FGM圆筒的热/机应力的解析解

利用微分方程的级数求解方法,分析了两端简支的有限长功能梯度圆筒的轴对称稳态热弹性问题,推导出了稳态温度场与应力场的解析解。分析中采用指数函数模型来描述FGM圆筒中材料性能在厚度方向的连续变化,同时忽略温度对材料性能的影响。另外,论文以金属钼和多铝红柱石制成的功能梯度圆筒为例,给出了稳态温度场和应力场的数值结果。     

Note on the surface wave due to the prescribed elevation

In the present paper, a study of the deep-sea water wave caused by an oscillatory wind stress due to the atmospheric depression, resulting in spiral cyclonic wind pressure on the surface of the sea is made. It has been observed that the motion of the water wave in the case of wind stress exhibits a greater elevation on the sea surface asg the acceleration due to gravity decreases and maintains the oscillatory nature with the increase of time. For the case of spiral cyclonic motion for which the sea surface experiences the elliptical pressure on the surface, the motion diminishes asg diminishes and oscillates with the variation of time. The motion also diminishes asymptotically as the radius vector of the elliptical pressure approaches unity.     

On the tribological characteristics of dynamically loaded journal bearing with micropolar fluids

The addition of the additives to the lubricant oil to enhance the characteristics of the lubricant will influence the performance of the bearings. Based on the theory of micropolar fluids, the tribological characteristics of a dynamically-loaded journal bearing are numerically studied. Comparisons are made between the Newtonian fluids and the micropolar fluids. It is shown that for a dynamically-loaded journal bearing, the micropolar fluids yield an increase not only in the friction force, but also in the friction coefficient. In addition, the oil film pressure and the oil film thickness are obviously higher than that of Newtonian fluids.     

Nonlinear oblique propagation of magnetohydrodynamic waves in the solar wind

Summary Oblique propagating magnetohydrodynamic waves with various wave forms and amplitudes are observed both at the Earth's foreshock and at comets. The possibility of interpreting some observational results in terms of nonlinear evolution of one- and two-dimensional hydromagnetic waves is investigated. For this purpose both analytical and numerical techniques are employed. It is found that an initial monochromatic wave changes its polarization giving origin to magnetosonic shocks and rotational discontinuities; the time evolution of density-magnetic-field correlation is studied, as a function of the plasma parameters and of the propagation angle. In the two-dimensional case both a transverse instability and a self-focusing effect may take place. Moreover, a two-dimensional magnetosonic solution is found, in which the density fluctuations are driven by the total pressure fluctuation as in a one-dimensional simple wave. These theoretical predictions compare well with the features observed in the solar-wind waves. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

An evolutionary method for optimization of plate buckling resistance

Optimization of plate buckling resistance is very complicated, because the in-plane stress resultants in the prebuckled state of a plate are functions of thickness distribution. This paper discusses the problem of finding the optimum thickness distribution of isotropic plate structures, with a given volume and layout, that would maximise the buckling load. A simple numerical method using the finite-element analysis is presented to obtain the optimum thickness distribution. Optimum designs of compression-loaded rectangular plates with different boundary conditions and plate aspect ratios are obtained by using the proposed method. Optimum designs from earlier studies and the methods of buckling analysis used to attain these results are discussed and compared with the designs from the proposed method. This paper also examines the reliability of the optimality criterion generally used for plate buckling optimization, which is based on the uniform strain energy density.