Round Corner Square Research Articles

Analytical calculation of stress intensity factors for cracks emanating from a quasi-square hole in an infinite plane

A new conformal mapping is proposed in order to solve stress intensity factor (SIF) problem in an infinite plane containing a traction-free square hole with two unequal cracks, analytically. To this end, Schwarts-Christoffel integral is expanded as sum of finite term series through Newton’s binomial formula to approximate the square hole to a rounded corner square one, which is called quasi-square. Next, the mapping function of cracked hole is expanded to a series of fractional expressions to combine with Muskhelishvili formulation. Finally, SIFs are presented for the remote tensile loading and the effects of crack length and radius of corners on the SIF are studied. To ensure the accuracy, results are compared to the available literature and FEM. Contrary to the previous researches, it was shown that the hole-shape had a considerable effect on the SIF for the small cracks though for large length cracks it is negligible.

Aerodynamic characteristics of a rounded-corner square cylinder in shear flow at subcritical and supercritical Reynolds numbers

Shear-inflow effects on flows past a rounded-corner square cylinder is investigated when Reynolds number (Re) increases from subcritical regimes (Re=2.2×104) to supercritical regimes (Re=1.0×106), with a focus on the latter Re in this study. The dimensionless shear parameter K ranges from 0 to 1.0. Results show that shear inflows have different effects on the aerodynamic characteristics of the cylinder in two Re regimes, and generally shear effects are smaller when Re is in the supercritical region. Specifically, mean and r.m.s pressure distributions remain in the same shapes under all shear inflows tested at supercritical Re; however they witness strong dependency on K at subcritical Re. Moreover, the directions of mean lifts at supercritical Re are opposite to those at subcritical Re. Correspondingly, the mean flow patterns observed in the uniform flow are overall preserved in shear flows at the supercritical Re: the free stream flows along the cross section and separates from the trailing corners on both sides of the cylinder, despite of the existence of small-degree asymmetry in the near-wake. However, the flow patterns are significantly changed at the subcritical Re by the sufficiently high shear inflows: the shear layer in suspension tends to reattach on the side wall of the high-velocity side and eventually separates from the trailing edge while the other on the low-velocity side becomes farther from the side wall. It results in the near-wake forming along an axis rotated in the clockwise direction from the horizontal axis, being opposite to the anticlockwise direction at supercritical Re. The mechanism for Re effects is further explored. The preservation of overall flow pattern at supercritical Re even under the strong shear effects is suggested mainly due to the greater favorable pressure gradient and the induced greater velocity acceleration before flow separation on the low-velocity side.

Shear effects on flows past a square cylinder with rounded corners at Re=2.2×104

The effects of planar shear inflows are investigated on flows past a rounded-corner square cylinder at Re = 2.2 × 104. The dimensionless shear parameter K ranges from 0.0 to 1.0. Strong dependency on K is found when K = 0–0.4. At K = 0.1, the flow fully separates on the high- and low-velocity sides despite asymmetry; the shear effects on aerodynamic characteristics have an overall similarity with those of sharp-corner square cylinders. At K = 0.4, the flow topology is changed significantly. Flow reattachment occurs on the high-velocity side, inducing a separation bubble. The low-velocity side is featured by a completely separated shear layer that is farther from the cylinder than at lower K, and by much weaker Karman vortices. This flow pattern results in very small mean pressures near the upper frontal corner, low r.m.s pressures on the bottom wall and a higher Strouhal number. When the local and extreme shear inflow at K = 1.0 is imposed with a high blockage ratio, the alternative vortex shedding is suppressed in the absence of interaction between two shear layers. The wake appears like a turbulent mixing layer which emanates from the trailing corner and rolls up to a series of large-scale coherent structures. However, the lower shear layer stays nearly stationary.

Supercritical flows past a square cylinder with rounded corners

Large-eddy simulations were used to investigate the supercritical aerodynamics of a square cylinder with rounded corners in comparison with those in the subcritical regime. First, the numerical methods, especially the dynamic mixed model, were validated on the basis of their prediction of supercritical flows past a circular cylinder. Then, the supercritical flows past a rounded-corner square cylinder were simulated and systematically clarified. Strong Reynolds number (Re) effects existed in the forces and local pressures as Re increased from o(104) to o(106). Changeover of flow patterns occurred as Re increased. At the supercritical Re, the free stream overall flowed along the cross sections of the cylinder, separated from the leeward corners and generated Karman vortices behind the cylinder. This pattern resulted in a much smaller recirculation region behind the cylinder compared with the subcritical flow. At the micro level, the flow experienced laminar separation and flow reattachment near the frontal corners, followed by the spatial development of turbulent boundary layers (TBLs) on the side faces and turbulent separation near the leeward corners. The feedback by large-scale primary vortex shedding and the small-scale turbulent motions in the high-frequency region with a slope of −5/3 were detected in the TBL. Their interaction affected the spanwise correlations of wall pressure fluctuations. The TBL on the side face differed from the zero-pressure-gradient flat-plate one; it was subjected to pressure gradients varying in space and time.

Influence of Section Size and Grain Size on the Microstructure Evolution and Mechanical Properties in Steel Grade AISI 5160

Steel grade AISI 5160, is a cost-effective straight chromium near eutectoid alloy steel used for several applications. The steel is used in thinner sections for application such as automotive leaf spring, knife etc. and in heavier section, the steel is used in applications such as wagon wheels, rails etc. The shallow hardenability of the steel generates a wide range of microstructures that influences the steel properties. The effect of normalizing, oil quenching and tempering was studied in a 140 mm thick round corner square (RCS) bar and 50 mm diameter bars of two different grain sizes. The microstructure evolution and its influence on the mechanical properties have been studied. The thicker 140 mm RCS bar showed pearlite in normalized and oil quenched condition. The pearlite in the oil quenched condition was extremely fine, resulting in superior mechanical properties. The 50 mm diameter bar with coarser grain size gave fully martensitic structure on oil hardening and a similar bar section with finer grain size showed the presence of pearlite in the matrix due to the influence of grain size on the hardenability. The study showed significant changes in microstructure as a function of section size, hardenability and heat treatment conditions. The study enabled proper choice of heat treatment for desired properties. The microstructure of other shallow hardenable near eutectoid steel was expected to show similar effect.

Experimental study on Re number effects on aerodynamic characteristics of 2D square prisms with corner modifications

Simultaneous pressure measurements on 2D square prisms with various corner modifications were performed in uniform flow with low turbulence level, and the testing Reynolds numbers varied from 1.0 x105 to 4.8x105. Experimental models were a square prism, three chamfered-corner square prisms (B/D=5%, 10%, and 15%, where B is the chamfered corner dimension and D is the cross-sectional dimension), and six rounded-corner square prisms (R/D =5%, 10%, 15%, 20%, 30%, and 40%, where R is the corner radius). Experimental results of drag coefficients, wind pressure distributions, power spectra of aerodynamic force coefficients, and Strouhal numbers are presented. Ten models are divided into various categories according to the variations of mean drag coefficients with Reynolds number. The mean drag coefficients of models with B/D < 15% and R/D < 15% are unaffected by the Reynolds number. On the contrary, the mean drag coefficients of models with R/D=20%, 30%, and 40% are obviously dependent on Reynolds number. Wind pressure distributions around each model are analyzed according to the categorized results.The influence mechanisms of corner modifications on the aerodynamic characteristics of the square prism are revealed from the perspective of flow around the model, which can be obtained by analyzing the local pressures acting on the model surface.

Heat Transfer Enhancement Around a Cylinder – A CFD Study of Effect of Corner Radius and Prandtl Number

Abstract An unsteady two-dimensional laminar forced convection heat transfer around a square cylinder with rounded corner edge is numerically investigated for Prandtl Number, Pr=0.01–1,000 and non-dimensional corner radius, r=0.50–0.71 at low Reynolds number, Re=100. The effect of gradual transformation of square cylinder into circular cylinder on heat transfer phenomenon is studied. The lateral sides of the computational domain are kept constant to maintain the blockage as 5 %. A structured non-uniform mesh is used for the computational domain and the Finite Volume Method (FVM) based commercial software Ansys FLUENT is used for numerical simulation. The heat transfer characteristics over the rounded corner square cylinder are analyzed with the isotherm patterns, local Nusselt number (Nulocal), average Nusselt number (Nuavg) at various Pr and various corner radii. It is found that the heat transfer rate of a circular cylinder can be enhanced 14 % by introducing a new cylinder geometry of corner radius, r=0. 51.

Void Closure in a Large Cross Section Bars Hot Rolled from a Low Alloy Steel Ingot Casting

The void closure phenomenon of a large size rolled bar made from an as-cast low alloy steel ingot of grade AISI 4130 has been examined. The study involved FEM based simulation of hot rolling of a four metric ton ingot casting to a final product of 320 mm round corner square cross section with a reduction ratio of 4.3. The rolling process was varied at two process conditions. The process variables considered included initial cooling time of the ingot from soaking pit before rolling, rpm, reduction and pass schedule. The defects in the product at the two rolling conditions were experimentally evaluated using ultrasonic technique during hot rolling and compared with void fraction in the simulation. Higher initial time of cooling of the ingot before hot rolling, lower rpm, higher reduction and lesser number of tilts gave products with least core defect which justified simulation results. The study brought out at every stage the load and torque distribution, effective strain, stress triaxiality factor, void volume fraction and void healing hydrostatic integration parameter in the model which had enabled void closure.

Prediction of the aerodynamic behavior of a rounded corner square cylinder at zero incidence using ANN

Abstract The aerodynamic behavior of a square cylinder with rounded corner edges in steady flow regime in the range of Reynolds number ( Re ) 5–45; is predicted by Artificial Neural Network (ANN) using MATLAB. The ANN has trained by back propagation algorithm. The ANN requires input and output data to train the network, which is obtained from the commercial Computational Fluid Dynamics (CFD) software FLUENT in the present study. In FLUENT, all the governing equations are discretized by the finite volume method. Results from numerical simulation and back propagation based ANN have been compared. It has been discovered that the ANN predicts the aerodynamic behavior correctly within the given range of the training data. It is additionally observed that back propagation based ANN is an effective tool to forecast the aerodynamic behavior than simulation, that has very much longer computational time.

Prediction and optimization of unsteady forced convection around a rounded cornered square cylinder in the range of Re

An unsteady two-dimensional laminar forced convection heat transfer around a square cylinder with the rounded corner edge is numerically investigated for Re = 80–180 and non-dimensional corner radius, r = 0.50–0.71 at Pr = 0.71 (Air). A structured non-uniform mesh is used for the computational domain discretization, and the finite-volume-method-based commercial code FLUENT is used for numerical simulation. The heat transfer characteristics over the rounded corner square cylinder are analyzed with average Nusselt number (Nu avg) at various Re and various corner radii. The heat transfer characteristic is predicted by gene expression programming (GEP), and the GEP-generated explicit equation of Nu avg is utilized in particle swarm optimization to optimize the corner radii for maximum heat transfer rate. The data required for the training the GEP model have been collected from the authors’ recent published article (Neural Comput Appl, 2015. doi: 10.1007/s00521-015-2023-8 ). It is found that the heat transfer rate of a circular cylinder can be enhanced 12 % by introducing a new cylinder geometry of corner radius r = 0.51.

Field investigation of axial monotonic and cyclic performance of reinforced helical pulldown micropiles

Helical piles are used increasingly to support new and existing foundations. This paper presents a field study on the axial monotonic and cyclic behaviour of steel fibre–reinforced helical pulldown micropiles. Test piles consisted of a round corner square helical pile with three helices attached to it, and a steel fibre–reinforced grout shaft. To assess the grout shaft contribution, one helical pile without a grout shaft was tested. Piles were instrumented with strain gauges to evaluate the load-transfer mechanism. This paper discusses the load–displacement response of this pile system, and load-sharing mechanism between the grout shaft and lead section. The study shows that the grout shaft significantly improves the helical pile axial performance. It was found that the load-transfer mechanism within the lead section is through individual bearing of each helix. Also, the findings demonstrate that the behaviour of this pile system is satisfactory under one-way cyclic loading conditions. The results suggest that the reinforced helical pulldown micropile is a viable deep foundation option for axial monotonic and one-way cyclic loading applications.

Synthesis and Gas Sensing Properties of SnO2 Microplatelets

SnO2 microplatelets were fabricated by oxidizing SnO microplatelets which were synthesized via dissolution-recrystallization with aid of sonication. The microplatelets were both characterized by X-ray diffraction, thermogravimetric analyses and differential scanning calorimetry, and field-emission scanning electron microscopy. The as- synthesized SnO2 microplatelets are consist of round corner square platelets structures with side length of 8–13 μm and thickness of 2–4 μm. The sensing properties of the sensors fabricated from SnO2 microplatelets were investigated at 4.5 V working voltage. Our results show that the sensors exhibit the excellent gas-sensing properties toward H2S in terms of sensitivity and selectivity.

Detached-Eddy Simulation of the Separated Flow Over a Rounded-Corner Square

Detached-eddy simulation (DES) is used to study the massively separated flow over a rounded-corner square. The configuration is an idealization of the flow around a forebody cross section rotating at high angle of attack. Simulations are performed at sub- and supercritical Reynolds numbers, between which experimental measurements show a reversal of the side force. DES predictions are evaluated using experimental measurements and contrasted with unsteady Reynolds-averaged Navier–Stokes (URANS) results. The computations are also subjected to a moderate grid refinement, a doubling of the spanwise period, an enlargement of the domain in the other directions, and the removal of any explicit turbulence model. The sub- and supercritical flows are computed at Reynolds numbers of 105 and 8×105, respectively, and with the freestream at 10deg angle of attack. Boundary-layer separation characteristics (laminar or turbulent) are established via the initial and boundary conditions of the eddy viscosity. Following boundary layer detachment, a chaotic and three-dimensional wake rapidly develops. For the supercritical flow, the pressure distribution is close to the measured values and both the streamwise and side forces are in adequate agreement with measurements. For the subcritical flow, DES side-force predictions do not follow the experimental measurements far enough to achieve reversal.

Hygrothermal bending of laminated composite plates with a cutout

Bending of laminated composite plates with a cutout subjected to moisture and temperature is investigated. An eight-noded isoparametric element, which takes transverse shear deformation into account, is used in the present analysis. Three types of cutouts are considered, namely, circular, rounded corner square, and square. The distribution of deflection and moment resultants are studied in anti-symmetric laminates for simply supported and clamped boundary conditions, subjected to uniform moisture and temperature.

Rotary In-Mold Stirring in a Cylindrical Continuous Casting Geometry

An analysis of in-mold rotary electromagnetic stirring forces and induced power is presented for a multilayer round continuous casting geometry. The required fields, forces, and power are derived using a convenient multilayer model that neglects end effects. Stirring characteristics are presented as a function of melt resistivity, slip, frequency, and mold wall thickness. Means of scaling these results to other round geometries are described, and the application of the model to the round corner square geometry is discussed.