Zero impact: a large-scale study of uncitedness

This paper presents a large-scale study of the phenomenon ‘uncitedness’. A literature review indicates that uncitedness is related to at least three factors: Field, document type, and time. To explore these factors and their mutual influence further, and at much larger scale than previous studies, the paper focuses on seven subject areas (arts and humanities; social sciences; computer science; mathematics; engineering; medicine; physics and astronomy), seven document types (articles; reviews; notes; letters; conference papers; books; book chapters), and a 20-year publication window (1996–2015). Documents are searched in Scopus, and retrieved year-by-year, discipline-by-discipline, and for each individual document type (total: 29,472,184 documents; 7,508,741 uncited documents). The results show great variance in uncitedness ratios between subject areas and document types. This is probably caused by a somewhat tacitly agreed upon genre hierarchy existing in all subject areas, yet with important local traits and differences. The importance of the time-dimension is documented. Time to first citation varies a great deal between subject areas, and the uncitedness ratio is consequently shown to be quite sensitive to the length of citation windows.

     

Discharge of a gas-saturated liquid through a venturi

Equations are derived for determining the flow rate when a gas-saturated liquid discharges through a venturi.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.21, No. 5, pp.888–891, November, 1971.     

Vortex structures in a ceramic under high-velocity impact

A finite-element method in a two-dimensional axisymmetric formulation is used to analyze the characteristics of shock-wave processes in a ceramic plate under the impact of a high-speed cylinder. It is established that a vortex structure is formed and the evolution of the vortices is investigated. Pis’ma Zh. Tekh. Fiz. 23, 86–90 (December 26, 1997)     

Suppression of vibration localization in non-axisymmetric periodic structures

In this paper, mistuned non-axisymmetric periodic structures are considered. In such a structure, vibration localization, which results in large vibrations in some components of the structure, can occur. Such a behavior is due to mistunings in the structure components, small damping, and weak coupling between components. The efficacy of a passive technique (previously proposed by the author for axisymmetric structures) in suppressing vibration localization in mistuned non-axisymmetric periodic structures is examined. The technique is based on adding small components between components of structures. It is first shown numerically that the added components suppress vibration localization in mistuned structures. Then, this conclusion is rigorously proved by using the singular perturbation method. Application of the technique studied in the paper to comb drives of micro electro-mechanical systems (MEMS) is given.     

Suppression of delaminations in curved structures by stitching

A simple approach is presented for analysing the effects of stitching on the mechanics of delamination failure in curved structures subjected to opening bending moments. Advantage is taken of the existence of a steady-state cracking configuration which is amenable to analysis and yields conservative design limits. Design rules are derived for the minimum stitch density required to suppress delamination crack growth and to ensure the integrity of the stitches. The rules involve only geometrical factors and material parameters that are known or readily measured. Populations of initial delamination flaws are shown to be unimportant as long as they fall beneath a threshold length of several mm. An analytical result for delamination crack growth under cyclic loading is also derived.     

Observation of large-scale hydrodynamic structures in a vortex tube and the Ranque effect

The existence of large-scale structures in the form of a vortical double helix in a swirling Ranque flow is observed for the first time. The structure of the vortical double helix is visualized in real time by the method of Hilbert bichromatic filtering. The experimental result is interpreted on the basis that the most probable physical mechanism for the spatial energy separation in the gas flow (i.e., for the so-called Ranque effect) is viscous heating of the gas in a thin boundary layer at the walls of the vortex chamber and the adiabatic cooling at the center owing to the formation of an intense vortex braid near the axis. Pis’ma Zh. Tekh. Fiz. 23, 84–90 (December 12, 1997)     

Local characteristics of an axisymmetric impact jet

We present the results of an experimental investigation of the local characteristics of flow in an axisymmetric impact jet. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of the Reublic of Belarus,” Minsk: Institute of Thermophysics of the Siberian Branch of the Russian Academig of Sciences, Novosibirsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 4, pp. 615–624, July–August 1996.     

Emergence of coherent structures and large-scale flows in motile suspensions

The emergence of coherent structures, large-scale flows and correlated dynamics in suspensions of motile particles such as swimming micro-organisms or artificial microswimmers is studied using direct particle simulations. A detailed model is proposed for a slender rod-like particle that propels itself in a viscous fluid by exerting a prescribed tangential stress on its surface, and a method is devised for the efficient calculation of hydrodynamic interactions in large-scale suspensions of such particles using slender-body theory and a smooth particle-mesh Ewald algorithm. Simulations are performed with periodic boundary conditions for various system sizes and suspension volume fractions, and demonstrate a transition to large-scale correlated motions in suspensions of rear-actuated swimmers, or Pushers, above a critical volume fraction or system size. This transition, which is not observed in suspensions of head-actuated swimmers, or Pullers, is seen most clearly in particle velocity and passive tracer statistics. These observations are consistent with predictions from our previous mean-field kinetic theory, one of which states that instabilities will arise in uniform isotropic suspensions of Pushers when the product of the linear system size with the suspension volume fraction exceeds a given threshold. We also find that the collective dynamics of Pushers result in giant number fluctuations, local alignment of swimmers and strongly mixing flows. Suspensions of Pullers, which evince no large-scale dynamics, nonetheless display interesting deviations from the random isotropic state.     

Liquid jet impact damage on zinc sulphide

Zinc sulphide is an important infra-red transparent window material. When used in forward-facing aircraft components, these windows can be damaged by the impact of rain drops. The drop impact is simulated using a high-velocity jet technique and the resulting damage is described quantitatively and qualitatively for impact velocities up to 600 m sec^–1. For the 0.8 mm jets used, which simulate 4 mm diameter drop impacts, no loss of strength was observed for impacts at or below 125 m sec^–1. The calculated threshold velocity for a 2 mm drop impact of 175±5 m sec^–1 agrees well with results obtained on whirling-arm installations. Visual examination of the impact damage emphasized the importance of careful specimen preparation.     

高层建筑环境振动TLD控制研究

调谐液体阻尼器(TLD)是一种典型有效的结构动力响应被动控制装置,可用于控制风致振动和地震响应。针对传统振动台缩尺试验的局限,该文采用振动台实时子结构试验研究了TLD对低层、中层和高层结构地震线性响应阶段及高层结构地震非线性响应阶段的影响。分别讨论了TLD频率与结构一阶频率比、TLD质量比以及地震激励幅值对TLD减震性能的影响规律。研究结果表明：当结构响应处于线性阶段时,TLD对加速度控制效果优于位移响应,相比于中低层结构,更适于高层结构减震;由于地震的随机性,对中低层结构位移响应有可能产生不利影响。当结构响应进入非线性后,受限于TLD较窄的减震频带,TLD对结构减震效果呈现较大的离散性。     

Jammed architectural structures: towards large-scale reversible construction

This paper takes a first step in characterizing a novel field of research—jammed architectural structures—where load-bearing architectural structures are automatically aggregated from bulk material. Initiated by the group of Gramazio Kohler Research at ETH Zürich and the Self-Assembly Lab at Massachusetts Institute of Technology, this digital fabrication approach fosters a combination of cutting-edge robotic fabrication technology and low-grade building material, shifting the focus from precise assembly of known parts towards controlled aggregation of granular material such as gravel or rocks. Since the structures in this process are produced without additional formwork, are fully reversible, and are produced from local or recycled materials, this pursuit offers a radical new approach to sustainable, economical and structurally sound building construction. The resulting morphologies allow for a convergence of novel aesthetic and structural capabilities, enabling a locally differentiated aggregation of material under digital guidance, and featuring high geometrical flexibility and minimal material waste. This paper considers (1) fundamental research parameters such as design computation and fabrication methods, (2) first results of physical experimentation, and (3) the architectural implications of this research for a unified, material-driven digital design and fabrication process. Full-scale experimentation demonstrates that it is possible to erect building-sized structures that are larger than the work-envelope of the digital fabrication setup.     

On the failure of a brittle material by high velocity gas jet impact

Failure of brittle solid bodies due to the impingement of a high velocity air jet on the body surface is studied, experimentally and theoretically. Using the linear elastic theory and stress distribution analysis, a general criterion for the failure of brittle materials impacted by a gas jet is derived. Several special cases of jet–solid body interaction including failure of thin and thick layers and cylindrical objects immersed in a crossflow gas stream are investigated and proper material failure criteria are developed. These criteria correlate the minimum jet peak impact pressure (PIP) required to break the material to the material's tensile strength and Poisson's ratio. A series of experiments were performed using a laboratory-scale apparatus. Gypsum cast on steel tubes forming cylindrical samples was used as the model brittle material. Experimental data and high-speed breakup movies are employed to understand the gas jet–solid body interaction and to validate the theoretical criteria developed for the material failure. It is deduced that the failure of cylindrical samples impacted by a gas jet is by the formation and propagation of cracks. However, when the impact jet diameter is small, the cracks cannot propagate, and the material is failed due to localized surface pitting. One of the practical applications of this research is in Kraft recovery boilers, where high velocity supersonic steam jets are employed to remove deposits accumulated on the outer surfaces of the steam tubes.     

Finite element analysis of single-particle impact in abrasive water jet machining

This contribution presents an explicit finite element analysis (FEA) of a single abrasive particle impact on stainless steel 1.4301 (AISI 304) in abrasive water jet (AWJ) machining. In the experimental verification, the shapes of craters on the workpiece material were observed and compared with FEA simulation results by means of crater sphericity. The influences of the impact angle and particle velocity were observed. Especially the impact angle emerged as a very suitable process parameter for experimental verification of FEA simulation, where crater sphericity was observed. Results of the FEA simulation are in good agreement with those obtained from the experimental verification. The presented work gives the basis for further FEA investigation of AWJ machining, where influences such as particles rotation and other process parameters will be observed.     

Influence of the velocity profile on the heat transfer of a circular impact jet

The influence of the mean velocity profile in a round submerged jet on the heat transfer with a plane obstacle placed along the normal to the flow is investigated. A criterial relation for the heat transfer in the vicinity of the critical point is obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 3, pp. 393–398, March, 1988.     

一种适用于大型工程结构的分散振动控制方法

基于瞬时最优控制算法,提出一种适用于大型结构振动控制的分散控制方法。根据大型结构的有限元模型,将其划分为若干子结构,相邻子结构间的作用力视为对子结构的"附加未知扰动"。在子结构加速度响应部分观测情况下,依次运用卡尔曼预测估计和最小二乘估计法,分别对子结构的状态和子结构间的作用力进行估计,并在此基础上基于瞬时最优控制算法确定各子结构的最优控制力,继而施加于结构对其进行振动控制。将提出的分散振动控制方法应用于美国土木工程师协会(ASCE)提出的20层控制基准问题(benchmark problem),并与传统的集中振动控制方法进行相关振动控制指标的比较。结果表明提出的分散振动控制方法能取得满意的振动控制效果。因此,提出的分散振动控制方法适合应用于对大型结构的振动控制。     

A theory for the impact of a wave breaking onto a permeable barrier with jet generation

We model a water wave impact onto a porous breakwater. The breakwater surface is modelled as a thin barrier composed of solid matter pierced by channels through which water can flow freely. The water in the wave is modelled as a finite-length volume of inviscid, incompressible fluid in quasi-one-dimensional flow during its impact and flow through a typical hole in the barrier. The fluid volume moves at normal incidence to the barrier. After the initial impact the wave water starts to slow down as it passes through holes in the barrier. Each hole is the source of a free jet along whose length the fluid velocity and width vary in such a way as to conserve volume and momentum at zero pressure. We find there are two types of flow, depending on the porosity, β, of the barrier. If β is in the range 0 ≤ β < 0.5774 then the barrier is a strong impediment to the flow, in that the fluid velocity tends to zero as time tends to infinity. But if β is in the range 0.5774 ≤ β ≤ 1 then the barrier only temporarily holds up the flow, and the decelerating wave water passes through in a finite time. We report results for the velocity and impact pressure due to the incident wave water, and for the evolving shape of the jet, with examples from both types of impact. We account for the impulse on the barrier and the conserved kinetic energy of the flow. Consideration of small β gives insight into the sudden changes in flow and the high pressures that occur when a wave impacts a nearly impermeable seawall.     

Composite structures under ballistic impact

In the present study, investigations on the ballistic impact behaviour of two-dimensional woven fabric composites has been presented. Ballistic impact behaviour of plain weave E-glass/epoxy and twill weave T300 carbon/epoxy composites has been compared. The analytical method presented is based on our earlier work. Different damage and energy absorbing mechanisms during ballistic impact have been identified. These are: cone formation on the back face of the target, tensile failure of primary yarns, deformation of secondary yarns, delamination, matrix cracking, shear plugging and friction during penetration. Analytical formulation has been presented for each energy absorbing mechanism. Energy absorbed during each time interval and the corresponding reduction in velocity of the projectile has been determined. The solution is based on the target material properties at high strain rate and the geometry and the projectile parameters. Using the analytical formulation, ballistic limit, contact duration at ballistic limit, surface radius of the cone formed and the radius of the damaged zone have been predicted for typical woven fabric composites.     

Characterisation of impact damage in skin-stringer composite structures

In studies aimed at understanding the impact performance of structures made from carbon-fibre composites, effects of structural geometry, material type and impact location have been investigated in skin-stringer panels representative of aircraft structure. Effects were investigated for low-velocity impacts to the skin in the bay between stringers, over a stringer foot, and over a stringer centreline. Detailed studies of the impact damage at these locations were investigated using ultrasonic techniques, and optical and electron microscopy. The damage characteristics were explained in terms of the proportion of energy absorbed through damage, such as delamination, and elastic effects, such as structural response of the panel.