Arch-type Structures Research Articles

Flow control of wake around a wall-mounted cube using a horizontal hole of different diameters

This paper describes an experimental investigation of flow control for the wake around a wall-mounted cube using horizontal control holes (HCHs) of different diameters drilled from the center of the front surface to the rear surface of the cube. The cube has side lengths of D = 50 mm, and HCHs with diameters of d = 10, 12, and 14 mm are considered. The instantaneous velocity fields are measured at a Reynolds number of 7800 based on time-resolved particle image velocimetry in a water tunnel. The HCHs suppress the recirculation zone, turbulence intensity, and Reynolds stress, and these control effects gradually increase with the hole diameter. The issuing flow from the large-diameter HCH completely obstructs the development of the downwash flow to the bottom wall and decomposes the near-wake arch-type vortex into a double arch-type structure. As the hole diameter increases, the dominant frequency of the spectrum in the HCH wake increases. Proper orthogonal decomposition analysis indicates that the large-scale spanwise vortices are suppressed by HCH. In the dynamic evolution process of the cube wake, the HCH issuing flow hinders the interaction of shear flow on both sides, and the issuing vortices attract the spanwise vortices and accelerate their shedding.

Effect of Sweep on Dynamic Stall of a Pitching Finite-Aspect-Ratio Wing

An investigation of the effect of moderate sweep on three-dimensional (3D) dynamic stall of a pitching finite-aspect-ratio wing is performed by means of large-eddy simulations. The wings have an aspect ratio and a NACA 0012 section. Three values of sweep angle are considered, , and 30°. The flow parameters are freestream Mach number and chord Reynolds numbers . A sinusoidal pitching motion is considered with reduced frequency and minimum and maximum angles of attack of 4° and 22°. The unsteady flow structure is examined in order to provide a model of 3D dynamic stall over finite swept wings. For all configurations, the dynamic stall vortex evolves into an arch-type structure that is shed following its transformation into a ring vortex. For , there is a single and larger arch vortex centered about midspan. For the swept cases, arch vortices are formed on each side of the wing at a spanwise station that moves farther outboard with increasing sweep. For , the outer leg of the arch vortex interacts strongly with the wing tip flow and abrupt tip stall is observed.

A Conditionally Beta Distributed Time-Series Model with Application to Monthly US Corporate Default Rates

We consider an observation driven, conditionally Beta distributed model for variables restricted to the unit interval. The model includes both explanatory variables and autoregressive dependence in the mean and precision parameters using the mean-precision parametrization of the beta distribution suggested by Ferrari and Cribari-Neto (2004). Our model is a generalization of the βARMA model proposed in Rocha and Cribari-Neto (2009), which we generalize to allow for covariates and a ARCH type structure in the precision parameter. We also highlight some errors in their derivations of the score and information which has implications for the asymptotic theory. Included simulations suggests that standard asymptotics for estimators and test statistics apply. In an empirical application to Moody’s monthly US 12-month issuer default rates in the period 1972-2015, we revisit the results of Agosto et al. (2016) in examining the conditional independence hypothesis of Lando and Nielsen (2010). Empirically we find that: (1) the current default rate influence the default rate of the following periods even when conditioning on explanatory variables. (2) The 12 month lag is highly significant in explaining the monthly default rate. (3) There is evidence for volatility clustering beyond what is accounted for by the inherent mean-precision relationship of the Beta distribution in the default rate data.

A Conditionally Beta Distributed Time-Series Model with Application to Monthly US Corporate Default Rates

We consider an observation driven, conditionally Beta distributed model for variables restricted to the unit interval. The model includes both explanatory variables and autoregressive dependence in the mean and precision parameters using the mean-precision parametrization of the beta distribution suggested by Ferrari and Cribari-Neto (2004). Our model is a generalization of the ARMA model proposed in Rocha and Cribari-Neto (2009), which we generalize to allow for covariates and a ARCH type structure in the precision parameter. We also highlight some errors in their derivations of the score and information which has implications for the asymptotic theory. Included simulations suggests that standard asymptotics for estimators and test statistics apply. In an empirical application to Moody’s monthly US 12-month issuer default rates in the period 1972 - 2015, we revisit the results of Agosto et al. (2016) in examining the conditional independence hypothesis of Lando and Nielsen (2010). Empirically we find that; (1) the current default rate influence the default rate of the following periods even when conditioning on explanatory variables. (2) The 12 month lag is highly significant in explaining the monthly default rate. (3) There is evidence for volatility clustering beyond what is accounted for by the inherent mean-precision relationship of the Beta distribution in the default rate data.

Experimental and numerical study on effectiveness of various tie-rod systems in brick arches

Arch-type structures have long been used to span large openings. In many historical masonry structures, the stability of the arches or pillars upon which the arches rest has been ensured by wood or iron tension members, commonly called tie-rods. Limited studies in the literature and earthquake reconnaissance reports have already verified the critical role of tie-rods on seismic behavior of arch-type structures. Iron tie-rods in many historic arches are nowadays susceptible to damages due to excessive corrosion. Similarly, strong seismic excitations or large differential foundation settlements may result in severe damage, in the form of buckling or fracturing, on tie-rods of many historic arches. In such cases, the replacement of the damaged tie-rods using a practical, reliable and effective technique is essential to retain the stability of the structure. To the best knowledge of authors, there is no published work in literature on this specific restoration work. The main objective of this study is to investigate both experimentally and numerically the viability, practicality and efficiency of five different replacement techniques proposed for the tie-rods in historic masonry arches. With this aim, six masonry arches, one reference with no tie-rod and five repaired using various tie-rod connection details, were tested under compressive load. Using the actual nonlinear properties of the masonry units and mortar, which are determined as specified by the current national specifications, a numerical study was also conducted using a commercially available structural analysis program and the test results are compared by the numerical results. In this study, the experimental results are presented in comparison with these numerical results and comments on the tie-rods used on the arches are given in consideration of the obtained results. Furthermore, recommendations are offered to solve the problems of tie-rod applications encountered in restoration works.

Large-scale structures in dipole and quadrupole wakes of a wall-mounted finite rectangular cylinder

Large-scale quasi-periodic vortex structures shed behind a wall-mounted rectangular cylinder were reconstructed from conditional averaging of several planar particle image velocimetry measurements based on the phase of the pressure at the cylinder surface. The measurements were taken for a square cross-section cylinder with height-to-width ratio of h/d = 8 partially immersed in two nominally thin turbulent boundary layers of thickness-to-height ratios of δ/h = 0.09 and 0.32. The Reynolds number based on the diameter was 12,000. For the thinner boundary layer in the time-averaged wake, one stream wise vortex pair was present at the free end (dipole wake) while for the thicker boundary layer, another pair was also observed at the wall junction (quadrupole wake). The detailed description of the shed structures giving rise to these time-averaged vortex pairs indicates more complex connections than previously proposed arch-type structures, which implies different vortex dynamic processes in the wake. The structures obtained for the dipole and quadrupole wakes were similar at the free end but significantly different at the junction resulting in distinct imprint on the mean and turbulent fields.

Three-dimensional vortex formation on a heaving low-aspect-ratio wing: Computations and experiments

This paper addresses by means of high-resolution numerical simulations and experimental quantitative imaging the three-dimensional unsteady separation process induced by large-amplitude heaving oscillations of a low-aspect-ratio wing under low-Reynolds-number conditions. Computed results are found to be in good agreement with experimental flow visualizations and PIV measurements on selected cross-flow planes. The complex unsteady three-dimensional flow structure generated during dynamic stall of the low-aspect-ratio wing is elucidated. The process is characterized by the generation of a leading-edge vortex system which is pinned at the front corners of the plate and which exhibits intense transverse flow toward the wing centerline during its initial stages of development. This vortex detaches from the corners and evolves into an newly found arch-type structure. The legs of the arch vortex move along the surface toward the wing centerline and reconnect forming a ring-like structure which is shed as the next plunging cycle begins. Vortex breakdown, total collapse and reformation of the wing tip vortices are also observed at various stages of the heaving motion. At the relatively high value of reduced frequency considered, these basic flow elements of the complex three-dimensional dynamic stall process are found to persist over a range of Reynolds numbers.

Bistable Phenomenon of the Aerodynamic Forces on a Square Prism with the Aspect Ratio of 5

The flow around a finite-length square prism with aspect ratio of 5 is numerical investigated using LES at Red = 3900. The prism is mounted on a flat wall, with one end free. Based on the simulation results, it is found that the near wake is highly three dimensional under the effects of free-end downwash flow. The shear layers from prism side walls and free end form an arch-type structure. There are two typical flow modes presence in the near wake: first, the spanwise vortices are staggered arranged similar to that in 2D cylinder wake; second, the spanwise vortices are quasi-symmetrically arranged. These two modes occur alternately and intermittently. When the first mode occurs, the pressure on the prism side surface fluctuates periodically, corresponding to large values of drag and fluctuating lift coefficients; when the second modes occurs, there is no obvious pressure fluctuation on prism side surfaces, and the correspond drag and fluctuation life coefficients are significantly smaller than those for the first mode.

성능 개선된 대골형 파형강판의 설계 압축 및 휨 강도 평가에 대한 연구

The structures that use the bridge plates are considered to have advantages such as short work term, excellent economical efficiency and low maintenance cost. Bridge plates are being widely used for water ducts and eco-corridors as replacements of reinforced concrete ducts. Bridge plates are deep and have greater pitch as compare to conventionally deep corrugated steel plate. They are expected to be increasingly used in the future. The structures that use bridge plates have two forms, such as arch type and box type. The arch type structures are designed based on the compressive strength, and the box type structures, based on the moment in the plate member. In this study, the ultimate strength and moment strength of the connection part of the specimens were examined by their thickness. Static and bending tests used to evaluate the performance of bridge plate. Finally, These results were used in the design process.

Two Notable Arch Bridges on The Croatian Adriatic Highway

The construction of the Adriatic highway is one of the greatest financial and building projects that have ever been undertaken in Croatia. In this paper, two notable arch bridges on this highway are described in detail. The building of the new concrete arch Maslenica Bridge marked the beginning of construction of the new highway. The arch is of 200 m span with a rise of 65 m and was constructed by free cantilevering. The superstructure consists of eight simple-span precast prestressed girders made continuous and interconnected by concrete deck slab cast in situ. The bridge design was strongly influenced by the severity of the maritime environment and the high winds on the site. The Krka Bridge crosses the Krka River canyon in the proximity of the entrance to the environmentally very valuable and protected area of the National Park. The arch type structure was the logical choice for the canyon crossing. The reinforced concrete arch has 204 m span and 52 m rise. A slender composite steel–concrete superstructure was selected to blend more harmonically with the beautiful environment and to reduce weight and thus seismic forces at the highly seismic bridge site.

Two Notable Arch Bridges on The Croatian Adriatic Highway

The construction of the Adriatic highway is one of the greatest financial and building projects that have ever been undertaken in Croatia. In this paper, two notable arch bridges on this highway are described in detail. The building of the new concrete arch Maslenica Bridge marked the beginning of construction of the new highway. The arch is of 200 m span with a rise of 65 m and was constructed by free cantilevering. The superstructure consists of eight simple-span precast prestressed girders made continuous and interconnected by concrete deck slab cast in situ. The bridge design was strongly influenced by the severity of the maritime environment and the high winds on the site. The Krka Bridge crosses the Krka River canyon in the proximity of the entrance to the environmentally very valuable and protected area of the National Park. The arch type structure was the logical choice for the canyon crossing. The reinforced concrete arch has 204 m span and 52 m rise. A slender composite steel–concrete superstructure was selected to blend more harmonically with the beautiful environment and to reduce weight and thus seismic forces at the highly seismic bridge site.

The finite-length square cylinder near wake

This paper reports an experimental investigation of the near wake of a finite-length square cylinder, with one end mounted on a flat plate and the other free. The cylinder aspect ratio or height-to-width ratioH/dranges from 3 to 7. Measurements were carried out mainly in a closed-loop low-speed wind tunnel at a Reynolds numberRed, based ondand the free-stream velocity of 9300 using hot-wire anemometry, laser Doppler anemometry and particle image velocimetry (PIV). The planar PIV measurements were performed in the three orthogonal planes of the three-dimensional cylinder wake, along with flow visualization conducted simultaneously in two orthogonal planes (Red= 221). Three types of vortices, i.e. the tip, base and spanwise vortices were observed and the near wake is characterized by the interactions of these vortices. Both flow visualization and two-point correlation point to an inherent connection between the three types of vortices. A model is proposed for the three-dimensional flow structure based on the present measurements, which is distinct from previously proposed models. The instantaneous flow structure around the cylinder is arch-type, regardless ofH/d, consisting of two spanwise vortical ‘legs’, one on each side of the cylinder, and their connection or ‘bridge’ near the free end. Both tip and base vortices are the streamwise projections of the arch-type structure in the (y,z) plane, associated with the free-end downwash flow and upwash flow from the wall, respectively. Other issues such as the topological characteristics, spatial arrangement and interactions among the vortical structures are also addressed.

Upper mantle structure of the northern Cascadia subduction zone

Previous knowledge of the structure of the Cascadia subduction zone north of the Canada–United States border has been derived from a variety of geophysical studies that accurately delineated the downgoing Juan de Fuca plate from the offshore deformation front to depths of ~50–60 km beneath south-central Vancouver Island and the Georgia Strait. Little is known, however, of the structure of the Cascadia subduction zone farther westward and to greater depths in the upper mantle. We have assembled a set of some 1100 teleseismic traveltimes from events recorded on the Western Canadian Telemetered Network to augment a previously existing data set recorded on the Washington Regional Seismograph Network. The composite data set is inverted for upper mantle structure below Washington, Oregon, and southwestern British Columbia. We analyze the new northern portion of the model between 48.5–50°N and 118–127°W, which provides the first images of the deep slab structure in this region. The model is parameterized using splines under tension over a dense grid of knots. The nonlinearity of the inverse problem is treated by iteratively performing three-dimensional ray tracing and linear inversion. Resolution tests performed with a synthetic slab model indicate that the deep structure is resolved by the data north to at least 50°N. The inversions are characterized by a quasi-planar, high-velocity body inferred to represent the thermal and compositional anomaly of the subducted Juan de Fuca plate. This body exhibits velocity deviations of up to 3% from the background reference model and extends to depths of at least 400–500 km. The depth contours of the slab in the upper mantle mimic those of the shallow slab by changing strike, in the latitude range 48.0–48.5°N, from north–south in Washington to northwest–southeast in southern British Columbia. This forces the development of two arch-type structures: a main arch observed in previous studies trending east–west over Puget Sound and a possible second arch extending northeasterly from the Georgia Strait into the British Columbia interior. A steepening of the deep slab dip from British Columbia south towards Puget Sound and complexity in the evolution of the arches in depth may be the result of a change in plate motions at 3.5 Ma associated with the detachment of the Explorer plate.

A note on in-plane vibrations of arch-type structures of non-uniform cross-section: The case of linearly varying thickness

This study deals with the determination of the first two natural frequencies of vibration of symmetric circular arches with linearly varying thickness carrying concentrated masses. Two situations are taken into account: (a) hinged arches; (b) clamped arches. The displacement amplitude is approximated by means of polynomial co-ordinate functions which include an optimization, exponential parameter γ. The frequency equation is generated by means of the Ritz method and the eigenvalues are then optimized with respect to the parameter γ.

Stability and optimum design of arch-type structures

Based on the Euler-Bernoulli Theory of the nonlinear inextensible plane elasticae, the concept of funicular or momentless design for arches is reviewed and equations determining the buckling load and transitional bending moments are derived. The results obtained for the buckling load of perabolic arches differs considerably from those found in the literature. Finally, the shape and the variable cross-sectional area of a funicular arch of constant stress is determined.

XUV spectra of the 1973 June 15 solar flare observed from Skylab. II - Intersystem and forbidden transitions in transition zone and coronal ions

An analysis is given of the intersystem lines of transition zone ions and high-temperature forbidden lines for the 1973 June 15 flare. The electron density in the erupting part of the plasma is at least approx.10/sup 13/ cm/sup -3/ at temperatures of approx.1.3 x 10/sup 5/ K. The density of the stationary component of the flare plasma at similar temperatures varies between approx.1.5 x 10/sup 11/ cm/sup -3/ and approx.10/sup 12/ cm/sup -3/. A density decrease observed in the stationary component occurs nearly simultaneously with an intensity enhancement of forbidden coronal lines such as Fe XII. These lines are believed to originate in arch-type structures. The electron density in the temperature regions approx.1.5 x 10/sup 6/ K is between 2 x 10/sup 10/ cm/sup -3/ and 2 x 10/sup 11/ cm/sup -3/. These regions appear to be stationary. Their motion relative to the observer is less than 4 km s/sup -1/. A continuous energy input is necessary to account for the transition zone emission. The transition zone emission arises in small regions, perhaps filaments.

Dynamic buckling of a two-degree-of-freedom mechanism

The dynamic buckling of a shell- or arch-type structure is investigated by studying the response of an idealized structural mechanism. A step load is applied to the apex of this bar linkage mechanism, and initial lateral displacements produce two-degree-of-freedom planar motions. The single-degree-of-freedom system is obtained by restraining the apex to vertical linear motion. The buckling load with planar motion is only slightly less than for the single-degree-of-freedom motion. However, the dynamic buckling load is much less than the static buckling load. Static load versus deflection curves are shown to be useful in evaluating the dynamic buckling. Energy surfaces are also helpful in determining the buckling load, if the trajectory of the apex planar motion can be determined. The trajectory of the apex motion can be investigated using phase plane plots. Configuration changes of the mechanism occur prior to the buckling, or snap-through, motion of the apex and significantly influence the trajectory, and, therefore, the ability of the mechanism to buckle.