Octagonal Cross-section Research Articles

INFLUENCE OF SUSPENSION GENERATION ON DUST EXPLOSION PARAMETERS

Combustion mechanisms of a suspension of solid particles in a gaseous mixture are studied with the aim of correlating the constant volume explosion characteristics with the initial state of the suspension at ignition time. Two vessels have been specially designed, one transparent with an octagonal cross section, allowing visualization and, the other steel made, able to support 50 bar overpressure to measure combustion characteristics. Particle dispersion in the chamber is achieved by means of the turbulent flow created by the discharge of pressurized air. Experiments were made with cornstarch particle suspensions. Evolution of the flowfield and dust distribution were recorded with high-speed imaging, LDV and PIV. The required delay to obtain an optimal mixture is between 500 and 700 ms. For a stoichiometric cornstarch dust-air mixture, explosion characteristics are in satisfactory agreement with results obtained by other researchers. Theses values decrease with initial rms velocity.

Finite-Element Analysis of Tapered Steel and Fiber-Reinforced Plastic Bridge Camera Poles

This paper presents experimental and finite element investigations of the load-deformation behavior of tapered steel and fiber-reinforced plastic (FRP) bridge camera poles subjected to cantilever bending type loading. Three full-scale experimental tests are conducted on one tapered octagonal steel cross section and two FRP circular cross-section poles to identify their load deformation characteristics. Three-dimensional isoparametric finite-element models of the poles are developed by considering the nonlinear coupling behavior between material, contact, and geometric effects. The elastoplastic solid elements with eight nodes are employed for the effective three-dimensional finite-element modeling and analysis. A surface-to-surface contact algorithm is used to simulate the interaction between contact surfaces. An energy-based convergence criterion is adopted to obtain the converged coupled nonlinear solutions. The obtained load-deformation results from finite-element analyses are compared with those of the experiments. The behavior of the finite-element models is examined by observing the effects of individual geometric variables on the load-deformation characteristics of the poles.

Fully nonlinear numerical wave tank (NWT) simulations and wave run-up prediction around 3-D structures

A finite-difference scheme and a modified marker-and-cell (MAC) algorithm have been developed to investigate the interactions of fully nonlinear waves with two- or three-dimensional structures of arbitrary shape. The Navier–Stokes (NS) and continuity equations are solved in the computational domain and the boundary values are updated at each time step by the finite-difference time-marching scheme in the framework of a rectangular coordinate system. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique developed for two fluid layers. To demonstrate the capability and accuracy of the present method, the numerical simulation of backstep flows with free-surface, and the numerical tests of the MDF technique with limit functions are conducted. The 3D program was then applied to nonlinear wave interactions with conical gravity platforms of circular and octagonal cross-sections. The numerical prediction of maximum wave run-up on arctic structures is compared with the prediction of the Shore Protection Manual (SPM) method and those of linear and second-order diffraction analyses based on potential theory and boundary element method (BEM). Through this comparison, the effects of non-linearity and viscosity on wave loading and run-up are discussed.

Finite element simulation of the axial collapse of metallic thin-walled tubes with octagonal cross-section

The present paper deals with the implementation of the explicit FE Code LS-DYNA to simulate the crash behaviour and energy absorption characteristics of steel thin-walled tubes of octagonal cross-section subjected to axial loading. The collapse procedure is successfully simulated and the obtained numerical results are compared with actual experimental data from small-scale models and useful concluding remarks pertaining to the design requirements of the crushing process are drawn.

A SIMPLIFIED NUMERICAL METHOD OF ANALYSIS FOR A CONCRETE-FILLED STEEL BRIDGE PIER WITH OCTAGONAL CROSS-SECTION

本論文は, コンクリートを充填した八角形断面鋼製橋脚の耐震設計のための簡易解析法を, 準静的繰り返し載荷実験との比較により検証, 提案したものである. ファイバー要素を用いた骨組解析に, 八角形断面鋼部材に充填されたコンクリートの圧縮実験より定式化された充填コンクリートの応力-ひずみ関係式と, FEMにより求めた外側鋼部材の局部座屈の影響を考慮した応力-ひずみ関係式を導入した. 実験供試体と同一の解析モデルにより, 一定死荷重の下, 降伏変位の整数倍を生じる水平荷重を繰り返し載荷した. 実験および簡易解析による荷重-変位履歴曲線を比較した結果, 簡易解析によって実用的に十分な精度で実験現象を追従できることを明らかにした.

Experiment and numerical simulation of hydro-forming toroidal shells with different initial structure

In this paper, the effect of the initial structure on formation of toroidal shells is investigated for avoiding wrinkling in the hydro-forming process for manufacturing large elbows. The experimental results show that no wrinkling occurs on a toroidal shell with an octagonal cross-section. However, there are some tiny wrinkles on a toroidal shell with a hexagonal cross-section. The deformation process was simulated using an explicit dynamic finite element code LS-DYNA. The simulation results are basically in agreement with the experimental results. The reason for wrinkling is discussed. Research results show that wrinkling can be prevented by selecting an appropriate initial structure.

Computational Investigation of Shock-Enhanced Mixing: Application to Circular Cross Section Combustor

A computational investigation of shock-enhanced mixing applied to circular cross section combustors is presented. In a circular cross section combustor, there are shock wave intersections at the center axis that produce adverse effects on mixing characteristics. The purpose of this investigation is to analyze the adverse effects due to the shock wave intersections and to develop new combustor geometry minimizing the adverse effects and improving the mixing characteristics. Three-dimensional Navier-Stokes equations are used to calculate the motion of the mean flow. A κ-ω turbulence model is used to calculate the turbulent viscosity. It is shown that, in a circular cross section combustor, the shock waves intersecting at the center axis reduce the strength of the longitudinal vorticity and push the fuel downward. A change in the shape of the cross section of the combustor to an octagonal cross section results in a reduction of the adverse effects and an improvement of the mixing characteristics.

Longitudinal and flexural wave propagation in reinforced concrete columns

In order to investigate elastic wave propagation in reinforced concrete (RC) columns with regular rebar arrangements, longitudinal and flexural phase velocity spectra of the Floquet-type harmonic waves were computed. Floquet's theorem was applied to the regularly reinforced RC columns to incorporate the heterogeneity induced by longitudinal steel bars, tie bars, and concrete. The numerical solution of phase velocity spectra was obtained by utilizing a semi-analytical finite element (FE) method. Phase velocity spectra exhibit strong dispersion similar to the Pochhammer and Chree problem of homogeneous circular cylinders. It was found that this dispersion in acoustic (lowest) modes was not accurately predicted by the elementary theories. However, it was found that the acoustic mode shapes of the Floquet waves can be closely approximated by plane sections, consistent with the assumptions of elementary rod and beam theories. The effect of transverse steel, in the form of tie bars, on phase velocity spectra of acoustic modes was found to be negligible due to the small volume fractions. In addition, by considering square and octagonal cross sections, the effects on dispersion of both cross sectional geometry and increasing volume fractions of longitudinal bars were investigated by neglecting tie bars.

AN EVALUATION OF THE BOUNCE-BACK BOUNDARY CONDITION FOR LATTICE BOLTZMANN SIMULATIONS

The bounce-back boundary condition for lattice Boltzmann simulations is evaluated for flow about an infinite periodic array of cylinders. The solution is compared with results from a more accurate boundary condition formulation for the lattice Boltzmann method and with finite difference solutions. The bounce-back boundary condition is used to simulate boundaries of cylinders with both circular and octagonal cross-sections. The convergences of the velocity and total drag associated with this method are slightly sublinear with grid spacing. Error is also a function of relaxation time, increasing exponentially for large relaxation times. However, the accuracy does not exhibit a trend with Reynolds number between 0.1 and 100. The square lattice Boltzmann grid conforms to the octagonal cylinder but only approximates the circular cylinder, and the resulting error associated with the octagonal cylinder is half the error of the circular cylinder.

Automated design of waveguide components using hybrid mode-matching/numerical EM building-blocks in optimization-oriented CAD frameworks-state of the art and recent advances

Fast hybrid mode-matching/boundary-contour (MM/BC) and mode-matching/finite-element (MM/FE) waveguide building blocks are described for the optimization-oriented use in powerful circuit computer-aided design (CAD) tools and the automated design of waveguide components. The efficient electromagnetic (EM) CAD technique allows the accurate design of a comprehensive class of rectangular and circular waveguide components including realistic structures of higher complexity. The efficiency and flexibility of the hybrid CAD method is demonstrated at advanced EM design examples, such as broad-band circular-to-rectangular waveguide transitions including octagonal cross sections, waveguide resonator filters with rounded corners, optimum-shaped bends, dual-mode filters with coupling sections without tuning screws, ridged waveguide filters with rounded corners, and multiplexers. The designed components are directly amenable to cost-efficient fabrication techniques like computer-controlled milling methods. The theory is verified by available measurements.

Effects of Additives on the Synthesis of Titanium Nitride Whiskers from Potassium Fluorotitanate (IV)

Titanium nitride (TiN) whiskers were formed on the outer surface of a graphite tube by heating potassium fluorotitanate (IV) (K2TiF6) above 1300°C in a stream of nitrogen. It is found that the addition of reduced metals has remarkable effects on the deposition temperature, shape, and yield of TiN. By addition of calcium, aluminium, and silicon, TiN whiskers were formed at 1100-1400°C on the outer surface of the graphite tube. By addition of magnesium, TiN whiskers were formed at 1200°C on the outer surface of the graphite tube. When aluminium and silicon were added, TiN whiskers were formed on the surface of residual additive. It is speculated that the reduced metals accelerated the reduction of titanium fluoride. The shape of the whiskers was observed by SEM. The cross section of whiskers on the graphite tube was mostly square, and that of whiskers on residual additive was mostly octagonal. It was suggested that the whiskers with a square cross section formed on the graphite tube grew in the ‹100› direction, and those with an octagonal cross section obtained on residual additive grew in the ‹112› direction.

Simulated Seismic Load Tests on Reinforced Concrete Columns

Simulated seismic load tests conducted on 11 reinforced concrete columns are described. The columns had a 400‐mm (15.7‐in.) square or octagonal cross section and contained various quantities of transverse reinforcement. The columns were subjected to either low, moderate, or high axial compressive loads and to reversible quasi‐state lateral loads that simulated severe earthquake loading. The tests were conducted to check an analytical approach for the determination of the available flexural ductility and the enhancement of flexural strength of columns with various levels of transverse confining reinforcement. The analytical approach for determining the quantities of transverse reinforcement required for confinement is shown to be conservative and to lead to equations more suitable for the design of transverse reinforcement for confinement than current code equations. Conclusions are also reached concerning the required length of the confined region in the potential plastic‐hinge zones of reinforced concrete columns.

Synthesis and structure of new sodium titanogallate Na xTi 2− xGa 4+ xO 10, containing one-dimensional channels

Sodium titanogallate, Na x Ti 2− x Ga 4+ x O 10 ( x ≅ 0.8), has been obtained as a new of a pseudo-ternary system of a Na 2OTiO 2Ga 2O 3. The phase has a monoclinic system with cell parameters of = 12.093 (2), = 3.0117 (5) = 10.4134 (9) (Å) and β = 92.29(1)°. Formation of Na x Ti 2− x Ga 4+ x O 10 is limited to a small area of the composition-temperature diagram. The structure has been determined using the single-crystal X-ray diffraction technique. One-dimensional channels of octagonal cross-section extending along the b-axis, where sodium ions are located, are contained in the structure. The conventional Fourier syntheses revealed the distribution of sodium ions to be broadened along the channel axis. These facts suggest channels of this sodium titanogallate are promising for ID conduction paths of sodium ions.

Simulated Seismic Load Tests on Prestressed Concrete Piles and Pile-Pile Cap Connections

The results of tests conducted in New Zealand on prestressed concrete piles and pile-pile cap connections subjected to simulated seismic loading are summarized. The piles were of prestressed pretensioned concrete with a 400 mm (15.7 in.) octagonal cross section and contained spiral reinforcement. The pile caps were of reinforced concrete. The range of pile-pile cap connection details tested included piles with ends embedded in the cap either with or without the ends of the longitudinal steel exposed, and the use of longitudinal steel dowel bars. The test results showed that well detailed prestressed concrete piles and pile-pile cap connections are capable of undergoing large post-elastic deformations without significant loss in strength when subjected to severe seismic loading.

Cantilevered and Linearly Tapered Thin‐Walled Members

In order to design a new power‐transmission tower built with a cantilevered and tapered thin‐walled steel member instead of the usual angle steel or pipe, the governing equations for a doubly symmetric and linearly tapered thin‐walled member are presented in a general way by means of Hamilton's principle. Closed‐form solutions are indicated for the static problems. Next, the exactness of the proposed elastic solutions is proven using numerical calculations for a cantilevered and linearly tapered thin‐walled member with a circular, octagonal, or rectangular transverse cross section. It is shown that the mechanical behavior of the cantilevered and linearly tapered thin‐walled members is remarkably different from that of the cantilevered thin‐walled member with uniform cross section and that the difference arises even for fairly small tapering angles. The effect of the transverse shear deformation for the current problem is shown to be negligible.

Plenum chamber effect on wind-tunnel resonance by the finite-elementmethod

A finite-element approach is developed for predicting the so-called frequencies of subsonic wind tunnels with plenum chambers. The resulting computer code has been applied to various wind tunnels. For example, the resonant frequencies for both the rectangular wind tunnel (rectangular cross section) and the NASA Langley Research Center 16 x 16 ft Transonic Dynamics Tunnel (octagonal cross section) have been calculated. Plenum chamber effects on wind-tunnel resonance is significant in a Mach number range of 0-0.5. The results are more accurate than theoretical values obtained by using an averaged homogeneous boundary condition on the slot. [B] b F {/) H i [K] [k] M [ m ] [M] |_7VJ p

Case study: Quantitative determination of the pedestrian comfort near a high-rise building

The paper presents a case study, carried out for an architect, to work out quantitative information about the pedestrian comfort near a proposed building. This building was designed with an octagonal cross-section, a height of 50 m and positioned between other buildings. The local wind speed and wind direction at ground level were determined in the wind tunnel by experiments with sand erosion and woollen filaments, using the existing architectural model of the site. The wind speeds were combined with the regional wind statistics and compared with existing acceptance criteria for pedestrian comfort. It has been shown, that such a procedure yields valuable information for the planning architect at reasonable cost and within a short time.

Report on the stanford octagonal magnetic monopole detector

After 1008 active (1150 elapsed) days of operation, the 476 cm2three-axis monopole detector has been shut down without observing any candidate events. This sets an upper limit for a cosmic ray flux of magnetic monopoles of 4.4 × 10-12cm-2s-1sr-1at 90% confidence level. We have constructed a 1.5 m2(averaged over 4π solid angle) superconducting monopole detector and are testing its performance. The sensing area includes only coincident events. The detector is an octagonal cross-section cylinder with an independent planar gradiometer loop (16.9 × 521.2 cm) on each side of the octagon. Originally constructed with copper traces covered by lead/tin solder, the loops have been converted to 2 mm wide × 50 μm thick niobium-titanium (NbTi) ribbon because of excessive noise in early tests. We expect to obtain a signal to noise ratio of about 10 with the new loops.

Subunit arrangement of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase

The structure of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) has been investigated by tilted-view electron microscopy of negatively stained monolayer crystals and image processing. The structure determined consists of a cylinder of octagonal cross-section with a large central hole. Based on this and other available evidence a model for the arrangement of the large and small subunits is suggested with the eight small subunits arranged equatorially around the core of eight large subunits.

Detailing of prestressed concrete piles for ductility

The role of spiral reinforcement in improving the ductility of concrete and the background to the New Zealand concrete design code equations for spiral reinforcement in potential plastic hinge zones are outlined. Tests and analysis of eleven full scale pretensioned prestressed concrete piles with a 400 mm octagonal cross section are reported. The tests were to determine the available ductility of the piles when subjected to large inelastic cyclic deformations from lateral loading which simulated severe seismic loading. The main variables of the tests were the amount of longitudinal nonprestressed reinforcement present, the applied axial load level, the amount of transverse spiral reinforcement present and the use of either Grade 275 or hard drawn spiral steel. The results showed that when the code specified quantity of spiral steel was present the piles were capable of undergoing very large post-elastic deformations when subjected to cyclic lateral loading without significant loss in load carrying ability. Piles with about 50% of the code specified quantity of spiral reinforcement were capable of reaching displacement ductility factors of at least ±4 providing the spiral spacing did not exceed about 4 tendon diameters. When the spiral reinforcement was provided by hard drawn wire the pile response was eventually limited by the fracture of the confining steel reinforcement, whereas piles with Grade 275 steel spirals did not suffer confining steel fracture.