Cruciform Arrangement Research Articles

Failure intervention of transmission line tower primary legs using bi-angled cruciform retrofitting

Retrofitting has been suggested by researchers as an intervention measure against failure of transmission towers which needs to be done with minimal disruption. Retrofitting of the primary leg members of transmission line towers by bi-angled cruciform arrangement has been shown in literature to be effective. However, the influence of stresses and deformations existing in the leg member prior to retrofitting on the capacity of the final retrofitted member is not known. Therefore, this study assesses the effectiveness of bi-angled cruciform sections under preload conditions through experiment followed by a numerical study. The level of preload in the primary leg member with respect to its theoretical capacity, slenderness ratio and width-thickness ratio of the angle section were the parameters. The results suggest that bi-angled cruciform retrofit is more effective at lower slenderness and width-thickness ratios and the reduction in capacity of retrofitted member is more noticeable till 50 % preload after which the changes are not significant. While the former two parameters lead to lower load share in the retrofitting member, higher preloads however lead to more equal load share. The application of this retrofitting pattern is demonstrated numerically with a full-scale tower model simulated under code specified load cases. Critical load cases leading to tower failure before design loads were identified and the retrofitting was incorporated into the model for these load cases. The analysis showed that the final loads attained in these load cases improved by upto 70 % thus confirming the potential of this retrofitting technique in preventing tower failure.

Galloping of circular cylinder induced by downstream strip-plate in cruciform arrangement

It has been reported that two longitudinal vortices are periodically shed from a cruciform two-cylinder system in a uniform flow. These depend on the gap, s, between the two cylinders and can induce a vibration called the “longitudinal vortex-induced vibration”. In previous studies, the authors showed that stationary longitudinal vortices are formed by a cruciform circular-cylinder/strip-plate (CC/SP) system when the upstream cylinder is moving along the downstream strip plate, and that one of these longitudinal vortices, the necklace vortex (NV), generates a lift force that acts on the cylinder in the direction of the motion. The “stationary” position of the NV is believed to make the system unstable, leading to fluid-elastic instability vibration. This study measured the fluid force acting on the rotating upstream circular cylinder blade in a wind turbine-type CC/SP system, and the vibration behavior of a pendulum-type CC/SP system was investigated through wind-tunnel experiments. The lift force coefficient, together with the ranges for the gap ratio (s/d) and velocity ratio (λ=V/U) needed to achieve stationary positions, were obtained (d: diameter of the upstream circular cylinder, U: flow velocity, V: rotational velocity of cylinder). It was confirmed that a cross-flow vibration of the cylinder in the pendulum-type CC/SP system was induced, and an analytical method to predict the vibration amplitude was proposed based on the quasi-steady hypothesis. The vibration amplitude of the pendulum device was well predicted by the method using the lift coefficient, obtained through the wind turbine-type CC/SP experiment. In conclusion it was verified that the vibration was caused by the stationary formation of the NV. It was classified as galloping, although it did not occur for an isolated circular cylinder because of its axisymmetric cross-sectional geometry.

New modeling strategies for analyzing lateral-torsional buckling in class-4 steel structural members at elevated temperatures using beam-type elements

Fire is one of the main hazards that can affect steel buildings and bridges and was responsible, e.g., for the collapse of the Plasco building in Tehran, Iran, and the I-65 bridge in Birmingham, Alabama, USA. This vulnerability has motivated the development of advanced computational models to predict the response of steel structures to fire accurately. The mechanical response of slender steel members to fire is especially important because they fail prematurely by buckling at load values below their elastic strength. However, the structural analysis of these members typically requires advanced and complex FE models with shell elements, including initial geometric and material imperfections. These shell models are computationally expensive, complicating the carrying out of parametric and probabilistic studies. Therefore, there is a need to develop simple, accurate, and low-cost computational models as reliable as shell-type models. To overcome this knowledge gap, this paper presents two new modeling strategies that simulate the mechanical response of class-4 steel members subjected to lateral-torsional buckling in fire using Timoshenko beam-type finite elements, which significantly simplify the structural modeling. These strategies are called Fiber Beam Model (FBM) and Cruciform Frame Model (CFM) and include initial geometric and material imperfections and thermal strains. In the FBM, the steel member is represented by a single fiber of I-section beam elements, whereas in the CFM, a cruciform arrangement of rectangular beam finite element fibers idealizes it, making the CFM more complex to build than FBM. Both strategies were satisfactorily validated with experimental and numerical results of Test-1 and Test-3 carried out in the “Fire design of steel members with welded or hot-rolled class-4 cross-section” (FIDESC4) research project on a slender beam of class-4 section. Although both FBM and CFM correctly captured the LTB resistance of the tested beam, CFM can, in addition, adequately reproduce the local buckling failure and significantly reduced the computational time. That means complex fire engineering problems such as probabilistic and optimization analyses of thin-walled beams can be addressed more easily and accurately, representing an important step towards applying performance-based approaches in slender steel structures under fire.

Steady lift-force generation on a circular cylinder utilising a longitudinal vortex: Influence of geometrical parameters

A novel technique for producing a steady lift force on a circular cylinder in a uniform flow driven by the longitudinal vortex (LV) is developed. The LV forms behind the cylinder when a strip plate is located downstream in a cruciform arrangement. The upstream cylinder can stably move by itself via an aerodynamic effect of the LV-produced steady lift force. However, the effects of geometrical parameters on system performance have not been investigated. In this study, the effective parameters of the presented mechanism—the width ratio of the strip plate, W / d , and the exposed length ratio of the circular cylinder over the strip plate, l e / d —are numerically examined. An unsteady Reynolds-averaged Navier–Stokes simulation using a shear-stress-transport k–ω turbulence model is employed for this analysis. The experimental investigation in our wind tunnel laboratory is used to primarily validate the computational predictions. The distribution of the aerodynamic forces acting on the cylinder surface is continuously evaluated along the length span. Flow fields around the system are also visualised for discussion of the vortical effects. The results indicate that the proper parameters of the system needed to generate the available driving force for the moving cylinder are ( i ) a strip-plate width of 1.5 ​< ​ W/d ​< ​2.5, with W/d ​= ​2 being considered as the most suitable, and ( ii ) an optimal exposed length of the cylinder of l e ​= ​1.5 d . • Numerical results were validated with experimental data of the wind tunnel test. • Flow fields were numerically visualised providing vortical structures. • Aerodynamic-force distributions along the cylinder length were continuously investigated.

Numerical evaluation of particle collection efficiency of circular cylinders in cruciform arrangement

Numerical evaluation of particle collection efficiency of circular cylinders in cruciform arrangement

Study on instability of lift force by longitudinal vortex in a circular cylinder with a downstream flat plate in cruciform arrangement

Study on instability of lift force by longitudinal vortex in a circular cylinder with a downstream flat plate in cruciform arrangement

Numerical investigation of lift-force generation on a moving circular cylinder in a uniform flow driven by longitudinal vortex

A new concept for generating a steady lift force on a circular cylinder in a uniform flow is presented. A strip-plate is placed behind the upstream cylinder in a cruciform arrangement with a suitable gap distance, s, between them to employ the longitudinal vortex. The circular cylinder is driven by the aerodynamic effects of the longitudinal vortex induced steady lift force. In this paper, the system was examined using the unsteady Reynolds-averaged Navier–Stokes (URANS) approach with the shear-stress-transport (SST) k-ω model and adaptive wall function in the commercial CFD software, SC/Tetra. Two conditions were simulated for comparisons; i.e., the stationary-isolated cylinder and the parallel moving cylinder with a downstream strip-plate. Two effective parameters of the presented mechanism were investigated as the velocity ratio, VR, and the gap distance ratio, s/d. The wind-tunnel investigation in our laboratory was used for validation as well as the experiments, and other numerical results in the literature of the stationary-isolated cylinder, and the similar cases of flow over a free-end cylinder were employed for discussion. Three-dimensional structure of the longitudinal vortex and the limiting streamlines around the cylinder surfaces were numerically visualized. Distributions of the circumferential pressure and driving force coefficients were continuously evaluated along the cylinder axis.

Lift Force Generation of a Moving Circular Cylinder with a Strip-Plate Set Downstream in Cruciform Arrangement: Flow Field Improving Using Tip Ends

A new concept of generating steady lift on a circular cylinder in uniform flow has been developed. A strip plate is placed behind a cylinder in cruciform arrangement with a suitable gap for employing the longitudinal vortex (LV). When the upstream cylinder moves parallel to the strip plate, the LV appears behind the moving cylinder near the crisscross region. The steady lift is produced by the aerodynamic effect of the vortex-induced suction flow. The vortex regime has a limited area, and the exterior is dominated by the wake which generates the negative driving force due to the drag. In this study, the negative portion near both free ends of the original cylinder was examined and restrained by attaching tip-end configurations for improving the flow field. Two types of added tip ends were evaluated that included the circular endplate and the semi-circular plate with a rectangular-shape bend. The unsteady Reynolds-averaged Navier–Stokes (URANS) simulation was employed. The numerical results were validated by the experimental data. The numerical investigation indicated that a negative lift is generated near the cylinder ends. When the accessory tip ends were employed, the semi-circular plate with a bend can suppress the disturbed flow and produce a positive lift, whereas only the circular endplate cannot.

Numerical simulation of flow past two circular cylinders in cruciform arrangement

Flow past two circular cylinders in cruciform arrangement is simulated by direct numerical simulations for Reynolds numbers ranging from 100 to 500. The study is aimed at investigating the local flow pattern near the gap between the two cylinders, the global vortex shedding flow in the wake of the cylinders and their effects on the force coefficients of the two cylinders. The three identified local flow patterns near the gap: trail vortex (TV), necklace vortex (NV) and vortex shedding in the gap (SG) agree with those found by flow visualization in experimental studies. As for the global wake flow, two modes of vortex shedding are identified: K mode with inclined wake vortices and P mode where the wake vortices are parallel to the cylinders. The K mode occurs when the gap is slightly greater than the boundary gap between the NV and SG. It also coexists with the SG gap flow pattern if the Reynolds number is very small ($Re=100$). The flow pattern affects the force coefficient. The K mode increases the mean drag coefficient and the standard deviation of the lift coefficient at the centre of the upstream cylinder because the wake vortices converge towards the centre. The mean drag coefficient and standard deviation of the lift coefficient of the downstream cylinder decreases because of the shedding effect from the upstream cylinder.

Observation of “Topological” Microflares in the Solar Atmosphere

We report on observation of the unusual kind of solar microflares, presumably associated with the so-called "topological trigger" of magnetic reconnection, which was theoretically suggested long time ago by Gorbachev et al. (Sov. Ast. 1988, v.32, p.308) but has not been clearly identified so far by observations. As can be seen in pictures by Hinode SOT in CaII line, there may be a bright loop connecting two sunspots, which looks at the first sight just as a magnetic field line connecting the opposite poles. However, a closer inspection of SDO HMI magnetograms shows that the respective arc is anchored in the regions of the same polarity near the sunspot boundaries. Yet another peculiar feature is that the arc flashes almost instantly as a thin strip and then begins to expand and decay, while the typical chromospheric flares in CaII line are much wider and propagate progressively in space. A qualitative explanation of the unusual flare can be given by the above-mentioned model of topological trigger. Namely, there are such configurations of the magnetic sources on the surface of photosphere that their tiny displacements result in the formation and fast motion of a 3D null point along the arc located well above the plane of the sources. So, such a null point can quickly ignite a magnetic reconnection along the entire its trajectory. Pictorially, this can be presented as flipping the so-called two-dome magnetic-field structure (which is just the reason why such mechanism was called topological). The most important prerequisite for the development of topological instability in the two-dome structure is a cruciform arrangement of the magnetic sources in its base, and this condition is really satisfied in the case under consideration.

Rotational cross-shaped magnetized radio-frequency sputtering plasma source for uniform circular target utilization

A rotational cross-shaped magnetized radio-frequency (RF) sputtering plasma source was developed for uniform circular target utilization. The cross-shaped magnetized RF plasma was attained by inducing a linear E × Br drift motion using a cruciform arrangement of neodymium magnets, where E and Br are the electric field perpendicular and magnetic field parallel to the target, respectively. A two-dimensional magnetic field simulation clarified that the electrons are strongly magnetized by the Hall parameter at a magnitude 20 times that of the ions. Strong cross-shaped plasma discharges are observed. The temporal evolutions of the ion saturation current were measured by a Langmuir probe at various radial positions, and the time-averaged ion saturation current was found to decrease from the center to the outer area of the target. The target utilization percentage was found to increase from 73.6% to 86.3% when Fe pole pieces were incorporated on the cruciform arrangement of neodymium magnets.

Three-dimensional structure of longitudinal vortices shedding from cruciform two-cylinder systems with different geometries

In previous research the present authors have shown that cross flow vibrations can be induced on a cylinder by setting another cylindrical body downstream in cruciform arrangement with a certain gap s between them. These vibrations are excited by two longitudinal vortices (LVs), i.e. the trailing vortex (TV) and the necklace vortex (NV), shedding periodically near the cross of the system. In this study, LVs shedding from three cruciform systems, i.e. circular-cylinder/circular-cylinder (CC/CC), circular-cylinder/strip-plate (CC/SP) and square-cylinder/strip-plate (SC/SP) system, are observed from three directions using water tunnel and surface-die-streak technique to clarify their three-dimensional structure. The gap-to-diameter ratio s/d is set at 0.08 or 0.28 as the representative values of TV and NV, respectively. Formation of TV or NV depends on the system geometry s/d and Reynolds number Re. In the case of CC/CC, TV is formed at s/d = 0.08 and NV at s/d = 0.28 steadily when 1400 ≤ Re ≤ 2000, and they shed periodically when 3300 ≤ Re ≤ 5700. In the case of CC/SP, steady shedding of TV is observed at the both values of s/d in the lower Re range and periodic shedding is observed only for TV at s/d = 0.08 in the higher Re range, but with poorer periodicity. In the case of SC/SP, NV is formed at the both values of s/d and periodic shedding is not observed up to the highest value of Re = 5000 in this experiment.

Self-Assembled Molecular Gear: A 4:1 Complex of Rh(III)Cl Tetraarylporphyrin and Tetra(p-pyridyl)cavitand.

The components of a 4:1 mixture of Rh(III)Cl tetrakis(4-methylphenyl)porphyrin 1 and a bowl-shaped tetra(4-pyridyl)cavitand 4 self-assemble into a 4:1 complex 14•4 via Rh-pyridyl axial coordination bonds. The single-crystal X-ray diffraction analysis and variable-temperature (VT) (1)H NMR study of 14•4 indicated that 14•4 behaves as a quadruple interlocking gear with an inner space, wherein (i) four subunits-1 are gear wheels and four p-pyridyl groups in subunit-4 are axes of gear wheels, (ii) one subunit-1 and two adjacent subunits-1 interlock with one another cooperatively, and (iii) four subunits-1 in 14•4 rotate quickly at 298 K on the NMR time scale. Together, the extremely strong porphyrin-Rh-pyridyl axial coordination bond, the rigidity of the methylene-bridge cavitand as a scaffold of the pyridyl axes, and the cruciform arrangement of the interdigitating p-tolyl groups as the teeth moiety of the gear wheels in the assembling 14-unit make 14•4 function as a quadruple interlocking gear in solution. The gear function of 14•4 was also supported by the rotation behaviors of other 4:1 complexes: 24•4 and 34•4 obtained from Rh(III)Cl tetrakis[4-(4-methylphenyl)phenyl]porphyrin 2 or Rh(III)Cl tetrakis(3,5-dialkoxyphenyl)porphyrin 3 and 4 also served as quadruple interlocking gears, whereas 14•5 obtained from 1 and tetrakis[4-(4-pyridyl)phenyl]cavitand 5 did not behave as a gear. The results of activation parameters (ΔH(⧧), ΔS(⧧), and ΔG(⧧)) obtained from Eyring plots based on line-shape analysis of the VT (1)H NMR spectra of 14•4, 24•4, and 34•4 also support the interlocking rotation (geared coupled rotation) mechanism.

Cavearhynchus, a new genus of tapeworm (Cestoda: Trypanorhyncha: Pterobothriidae) from Himantura lobistoma Manjaji-Matsumoto &amp; Last, 2006 (Rajiformes) off Borneo, including redescriptions and new records of species of Pterobothrium Diesing, 1850

A new genus of trypanorhynch cestode is described from the tubemouth whipray Himantura lobistoma Manjaji-Matsumoto & Last, 2006 in the South China Sea off Malaysian Borneo. Cavearhynchus foveatus n. g., n. sp. possesses four pedicellate bothria in a cruciform arrangement, a heteroacanthous, heteromorphous metabasal tentacular armature with five hooks per principle row and an alternating longitudinal file of intercalary hooks on the bothrial surface of each tentacle, but lacks prebulbar organs and gland-cells within the bulbs. It, thus, closely resembles taxa belonging to the lacistorhynchoid family Pterobothriidae Pintner, 1931. However, the new genus differs from other genera within this family in the possession of bothrial pits. Although a distinguishing characteristic of the superfamily Otobothrioidea Dollfus, 1942, representatives of this group exhibit two bothria and the bothrial pits are lined with spiniform microtriches, whereas the pit-like structures.of C. foveatus n. g., n. sp. entirely lack microtriches. Redescriptions of two species of Pterobothrium, namely P. lesteri Campbell & Beveridge, 1996 and P. platycephalum (Shipley & Hornell, 1906) Dollfus, 1930 are provided from material collected off Borneo and several localities off Australia. Moreover, new host and locality records are added for P. australiense Campbell & Beveridge, 1996 and P. pearsoni (Southwell, 1929) Beveridge & Campbell, 1989.

VIVs of a circular cylinder with a downstream strip-plate in cruciform arrangement

Earlier wind tunnel experiments by the present authors on the transverse vibration of a circular cylinder with a downstream counterpart in cruciform arrangement showed that either of the two longitudinal vortices – trailing or necklace vortices, depending on the gap-to-diameter ratio s/d – induces a resonant oscillation, like the Kármán-vortex-induced vibration (KVIV). In this study, the downstream cylinder is replaced by a strip plate with a width w comparable in magnitude with the cylinder diameter d, expecting that interference of a plate would be stronger than that of a circular cylinder. The characteristics of longitudinal vortices and VIV of the upstream cylinder are investigated through wind tunnel experiments over the range of Reynolds number 3000−22000, as well as a visualization experiment in a water tunnel at around Re=1700. When the system is fixed, the two longitudinal vortices (trailing and necklace) shed periodically over respective ranges of s/d for plates with 0.5≤w/d≤0.62, while the trailing vortex sheds periodically but the necklace vortex is not observed for plates with 0.75≤w/d≤1.0. When the cylinder is elastically supported for transverse vibration, the plate effectively suppresses KVIV, at distances further downstream for larger w/d plates. An unexpected effect is that KVIV is enhanced by the plate with 0.5≤w/d≤1.0 over a certain range of s/d. The two longitudinal vortices induce resonant vibrations under conditions of w/d and s/d correlating with their characteristics for the fixed system. The velocity ranges of the trailing vortices are much wider than for the case of the two-circular-cylinder system. The effects of the downstream plate on VIV can be utilized for oscillation control, i.e., not only to suppress but also to induce oscillations for beneficial purposes.

Influence of mass and damping ratios on VIVs of a cylinder with a downstream counterpart in cruciform arrangement

Previous wind tunnel experiments by the present authors showed that two kinds of longitudinal vortex induce cross-flow vibrations (LVIVs) on a circular cylinder accompanied by the vortex-synchronization (lock-in) by setting another cylinder downstream with proper gaps in cruciform arrangement, like the well-known Karman vortex induced vibration (KVIV) of a single cylinder. In this work, experiments on the three types of VIVs are carried out using a water tunnel to investigate influences of the mass ratio M R and the damping ratio ζ on the oscillation response. It is shown that the two LVIVs, i.e. the trailing- and the necklace-VIVs, occur in water flow over respective ranges of flow velocity U in spite of large differences in values of M R and ζ as compared with experiments in air flow. However, their influences on oscillation responses of the two LVIVs are largely different from each other, and also from the KVIV. They are compared by referring to the de-synchronization prediction based on the dimensional analysis and the equation on cylinder motion. The variation of behaviors among the three types of VIV are attributed to the differences among the three vortices in their threshold functions for synchronization and the vortex-synchronization functions which express the feedback effect of the cylinder oscillation on the alternating lift generated by the vortex.

円柱の下流に十字交差配置された帯状の平板による振動制御 : 第2報,帯状平板による渦励振の励起と抑制(流体工学,流体機械)

The specific aim of this work is to develop a new technique to control vortex excitations of a circular cylinder by utilizing interference of a downstream strip-plate in cruciform arrangement. In the previous paper, it is shown that the two longitudinal vortices, trailing vortex and necklace vortex, shed in the vicinity of the crossing of a fixed circular cylinder/strip-plate system. In this paper, the circular cylinder was supported elastically so as to allow cross-flow motion and influence of the strip-plate on vortex excitation was investigated with the same wind tunnel apparatus. The strip-plate suppresses Karman vortex excitation more effectively compared with a downstream circular cylinder. A wider strip-plate has a larger suppression effect. The trailing vortex induces vortex excitation when gap-to-diameter ratio s/d less than 0.3. When the strip-plate width w is equal to the upstream circular cylinder diameter d, the velocity range for longitudinal vortex excitation is 5 times wider than the case of the downstream circular cylinder. The necklace vortex excitations dose not occur for strip-plates with w/d&ge;0.75, as expected from the fixed-cylinder experiment. Longitudinal vortex excitation by downstream strip-plate occurs over a wide velocity range, and it can be easily controlled by s/d adjusting.

角柱のギャロッピングに対する下流平板の影響(流体工学,流体機械)

Galloping of a square cylinder can be suppressed by the downstream strip-plate set in cruciform arrangement with a gap s. In addition, another strong vibration is generated at certain conditions of the flow velocity and gap s. The specific aim of this work is to confirm generality of these phenomena for various dimension systems and nondimensional parameters by the wind tunnel experiment. When the width of the downstream strip-plate w is equal to the side length of the square cylinder d, the suppression of galloping and the strong vibration are observed for all the square cylinders. The effective region of suppression is affected by w. The strong vibration is confirmed to be the longitudinal vortex excitation from measurement of the dominant frequency of the velocity fluctuation near the cross and flow visualization.

Behavior of Steel Beam to Concrete-Filled Steel Tubular Column Connections after Exposure to Fire

A nonlinear finite-element analysis (FEA) model was developed in this paper based on the elastoplastic finite-element theory to analyze the load versus deformation relation of steel beam to concrete-filled steel tubular column connections. Six tests on steel beam to concrete-filled steel tubular (CFST) column connections using external ring after exposure to the ISO-834 standard fire were used to verify the theoretical model. The test parameters included the column cross-sectional type, the fire duration time, the level of axial load in the column, and the beam-column strength ratio. Each test specimen consisted of a CFST column and two steel beam segments in cruciform arrangement to represent an interior joint in a building. Three of the six composite connection specimens had circular cross sections and three had square cross sections. Five of the test specimens were simultaneously exposed to the standard ISO-834 fire condition. After they had cooled down to room temperature, each was tested under a cons...

The flow between a stationary cylinder and a downstream elastic cylinder in cruciform arrangement

Abstract The flow past a stationary circular cylinder and a downstream elastic circular cylinder in cruciform arrangement is investigated at a constant Reynolds number of 150. The virtual boundary method is employed in this study. After the validation of the numerical method, two cases are simulated. In Case 1, both cylinders are stationary. A critical spacing is found to be about three diameters ( L / D = 3 ) . Beyond this critical spacing, the modification of the wake of the upstream cylinder due to the presence of the downstream cylinder is limited to the mixed region, whereas below this critical spacing, the influenced region is significantly enlarged. In Case 2, we let the downstream cylinder vibrate in response to the fluid forces acting on it, and the vibration is modeled by a spring-damper-mass system. The results show that the peak amplitude of vibrations for the cruciform arrangement is lower than that for an isolated cylinder, and the resonance region is wider than that of an isolated cylinder.