Shape Correction Factor Research Articles

Comparative Study of UPV and IE Results on Concrete Cores from Existing Structures

Dynamic non-destructive methods (NDT) are particularly attractive owing to their time and cost efficiency when compared to conventional uniaxial compressive strength tests. However, the results of these methods are highly scattered; therefore, they are primarily used for qualitative material characterization. One of the most important NDT results is the calculation of the dynamic Young’s modulus, which is associated to the uniaxial compressive strength (UCS) of concrete. The ultrasonic pulse velocity (UPV) is the most commonly used NDT. The limitation of this method is that it directly depends on knowledge of the Poisson’s ratio, and an assumption of its value must be made. This assumption results in highly scattered results. In contrast, the impact echo method (IE) can result in a dynamic Young’s modulus calculation without knowing the Poisson’s ratio. The limitation of this method is that it is dependent on the specimen’s slenderness, which in turn depends on the Poisson’s ratio. This study investigates the IE method’s applicability to short cylinders. A comparison of the UPV and IE methods is made, and the error in the dynamic Young’s modulus value derived by assuming Poisson’s ratio value in the UPV method is calculated. The authors conducted a numerical analysis and recently proposed the use of a shape correction factor (SCF) to apply the IE results for short cylinders, considering the influence of the slenderness (L/D) of the samples. For the first time worldwide, an extensive experimental study on 232 concrete samples with L/D ≈ 1.0 confirmed the wide spread of UPV test results and showed that it can lead to an error on Young’s Modulus determination by up to 50% owing to the adoption of an arbitrary Poisson’s ratio value. In contrast, using the SCF yields IE results with a ±2% error. A new methodology, ultrasonic pulse impact echo synergy (UPIES), is proposed by performing both UPV and IE tests on the specimens and using the SCF. The Poisson’s ratio and, consequently, the Young’s modulus can be accurately determined. Doi: 10.28991/CEJ-2024-010-09-03 Full Text: PDF

An improved optical length research on the physical boundary of particle-dispersed fuel

The Volumetric Homogenization Method (VHM) is one of the most commonly used methods for neutronics calculation in reactors or components. However, the use of VHM for the Double-Heterogeneous (DH) System may lead to a large deviation in reactivity calculation. The deviation of DH System using the VHM can be expressed by the theoretically modified optical length. When the theoretically modified optical length is less than 10−4, the deviation caused by the VHM will be less than 100 pcm. This paper points out that the existing theoretically modified optical length for some cases of DH systems is not accurate, and this method is only for pin cell. In this paper, by calculating a series of DH models and their corresponding VHM models, it is found that the water-uranium ratio and the shape of fuel region seriously affects the reactivity calculation deviation of particle-dispersed fuel, the original modified optical length does not take this into account, resulting in unacceptable errors. On this basis, the application of optical length to physical boundaries for DH system is further discussed and the shape correction factor is taken into consideration. Therefore, an improved optical length is proposed, which greatly expands the range of application of the physical boundary judgment methods for the double heterogeneity of dispersed particle fuel. The numerical results show that the accuracy of the improved optical length in defining the physical boundary of double heterogeneous system is higher than the theoretically modified optical length.

Formulation of justifiable wind loading distributions up tall buildings derived from HFFB measurements

For the general case of non-linear and combined sway and twist mode shapes, analysis of HFFB measurements gives rise to serious challenges and various techniques have been developed using significant assumptions. This is because it is not possible to directly obtain the distribution of varying fluctuating wind loads throughout the height of tall buildings. This paper proposes a straightforward HFFB-based wind load/twist distribution approach in the time domain to predict the wind-induced dynamic response of tall buildings. Using this framework, it is possible to overcome the deficiencies of mode shape correction factor approach, and the complexity and impracticality of alternative approaches for tall buildings. Two 1:300 scale rigid models of benchmark tall buildings, IAWE Buildings A and B, have been selected to perform a detailed wind tunnel investigation as subjects to evaluate this proposed HFFB approach study. Building A has complex 3D mode shapes combining sway and twist, whereas the simpler Building B has uncoupled linear mode shapes in sway and twist. The high frequency pressure integration (HFPI) wind tunnel technique was utilised to measure surface pressure information in separate tests to obtain the reference wind loading for validation of the HFFB predictions. Furthermore, a commonly used HFFB mode shape correction factor approach was used to estimate the dynamic wind responses which were compared to those from the proposed approach. From the comparison between the aerodynamic and dynamic wind results from proposed HFFB approach and reference HFPI results, it is found that the proposed HFFB approach can predict the vertical distributions of the wind forces and torque (wind loads) with acceptable accuracy for carrying out the conceptual stage of tall building design.

Recovery of phlogopite (mica) by hindered settling from molybdenum tailings in an ascending current separator based on particle shape differences

A novel gravity concentration approach for recovering phlogopite from molybdenum tailings in an ascending current separator (ACS) was proposed. The settlement behavior of coarse-grained minerals with different particle shapes was investigated. The results indicated that the particle shape difference between coarse-grained minerals brought about the gravity concentration of phlogopite. Phlogopite had a lower shape correction factor due to its flaky shape. Under the condition of the same particle size and solid volume concentration of the fluidized bed, the free and hindered settling terminal velocities of phlogopite were much lower than those of albite and calcite. The equal settling factors of phlogopite to albite and phlogopite to calcite in the hindered settlement process were 2.40–4.06 and 3.27–5.81, respectively, with solid volume concentrations ranging from ∼0.055 to 0.175. The operating parameters of the ACS during the phlogopite recovering process were optimized by response surface methodology with a three-level Box-Behnken design. Under optimum conditions, the K2O grade and K2O recovery of concentrate are 8.77% (phlogopite content is 92.41%) and 75.17%, respectively.

Extending the Gutowski model to kidney-bean and elliptically shaped fibers

Efforts by manufacturers to produce more cost-effective carbon fibers have resulted in fibers with irregular cross-section often referred to as kidney-bean shaped fibers. In this research, compaction experiments were performed with a modified laser light section method to evaluate the compaction behavior of kidney-bean shaped carbon fibers. The kidney-bean shaped fibers followed a different compaction behavior compared to the Gutowski model for circular fibers. Additionally, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which has implications in infiltration and consolidation efficiency for composites manufacturing. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the Gutowski model to fibers with irregular cross-sectional shapes. The modified Gutowski model provided an appropriate order of magnitude fit for the kidney-bean fibers. Furthermore, this modification to the Gutowski model recovered the original solution for circular fibers (cross-sectional aspect ratio = 1).

Pore Size Dependence of Permeability in Bicontinuous Nanoporous Media.

In this work, we employ many-body dissipative particle dynamics (mDPD) simulations to investigate the fluid flow process through bicontinuous nanoporous media, which are representative models for a broad class of nanoporous materials. The mDPD formulation includes attractive and repulsive interactions describing accurately fluid-fluid and fluid-solid interactions. As a mesoscale simulation method, mDPD can bridge the length and time scale gap between continuum and atomistic simulations. The bicontinuous nanoporous models are constructed considering a defined morphology, the porosity level, and varying pore sizes in the range from 3.41 to 13.63 nm. All models have a 0.65 porosity level and the same topology. The models provide a stochastic description of the morphology and pore size distribution and allow for a direct investigation of the dependence of permeability on the average pore size. The stationary nanoporous models are filled with fluid particles, and flow is induced by the action of confining pistons. Simulation results, obtained by imposing different pressure differences on the surfaces of the nanoporous media, indicate a linear pressure drop within the nanoporous model. Regardless of the complexities and different scales of the porous media considered, the steady-state fluid flow through the nanoporous models is proportional to the pressure gradient applied, in agreement with Darcy's law. The calculated pore size dependence of permeability is well described by the Hagen-Poiseuille law, considering a single shape correction factor that accounts for the flow resistance due to the complex nanoporous morphology. This work highlights the effect of the average pore size of a complex stochastic bicontinuous nanoporous medium on fluid properties. The results indicate rather a relatively simple dependence of permeability on the average pore size. The novel method we employ to generate the stochastic bicontinuous nanoporous structure allows the control of different geometric features that can be explored in future studies.

Wind load investigation of self-supported lattice transmission tower based on wind tunnel tests

Through a series of wind tunnel tests on a self-supported lattice transmission tower model, the wind loads on the tower were investigated in this paper. According to similarity laws, the scaled tower model was designed and fabricated, and the atmospheric boundary layer wind field of Category-B specified in Chinese load code was simulated in the wind tunnel laboratory. Based on the aeroelastic wind tunnel tests and the high frequency force balance tests, the dynamic vibrations, the nondimensional wind force coefficients and the generalized power spectral densities (PSDs) of dynamic wind forces were analyzed and discussed. For the convenient application, the empirical formulas of the generalized PSDs of dynamic wind forces were established and the nonlinear mode shape correction was introduced, which were verified via comparison between the aeroelastic tests and the calculated dynamic responses of tower top. It is indicated that the unfavorable wind attack angles may happen around θ = [15° 30°] and θ = [60° 75°] for this type of tower; the generalized PSDs of wind forces are unimodal in shape, and the corresponding effective bandwidths and the nondimensional frequencies of peaks vary with the wind attack angle θ, especially those of the cross-wind forces are larger than those of the along-wind forces obviously; the established empirical formulas of the generalized PSDs of dynamic wind forces and the derived nonlinear mode shape correction factor are applicable.

Measurement of Høgdahl neutron flux parameters in the SM1 subcritical reactor of the University of Pavia

Neutron flux of the thermal subcritical multiplication complex located at the nuclear pole of the University of Pavia was investigated to acknowledge the flux characteristics according to the Høgdahl convention in order to predict the expected activity of radionuclides while performing neutron activations. Flux parameters were evaluated by means of bare multi-monitor methods by preparing samples containing Au, Cr, Zn and Ni that were used to measure the epithermal shape correction factor, the conventional thermal to epithermal ratio and the thermal, epithermal and fast neutron fluxes in two irradiation channels of the facility.Despite high uncertainties affecting epithermal shape correction factors, thermal to epithermal ratios was measured with uncertainties ranging between tens and a few percent. In addition, conventional neutron fluxes were individually determined with a few percent level uncertainties, which are also suitable in applications requiring a known and/or ultra-stable neutron exposure.

Aerodynamic damping models for vortex-induced vibration of a rectangular 4:1 cylinder: Comparison of modeling schemes

Accurate modeling of vortex-induced force acting on a structure is of great significance to precisely evaluate its vortex-induced vibration (VIV). This paper systematically compares the capabilities of five aerodynamic damping models in simulating the VIV amplitudes of a line-like structure at various mass-damping conditions. These models are categorized into two types. Scanlan’s model, the polynomial model, and the describing function-based model, as the first type, can be utilized to calculate the VIV amplitudes in the entire lock-in range. The second type, including Larsen’s model and a newly-developed aerodynamic envelope model, that is designed to directly obtain the peak VIV amplitude. The relationships between aerodynamic damping of the aeroelastic systems and aerodynamic parameters of five models are established to convenience the identification of aerodynamic parameters. The aerodynamic parameters can be either identified based on the VIV decay-to-resonance and/or grow-to-resonance displacement signals at a single mass-damping condition, or based on the VIV steady amplitudes at various mass-damping conditions. Numerical examples involving the VIV analyses of a rigid rectangular 4:1 cylinder and two flexible cylinders are presented to compare the predictive capabilities of various models. The polynomial model and the describing function-based model can satisfactorily predict the VIV amplitudes at various mass-damping conditions, while the predicative capabilities of Scanlan’s model, Larsen’s model, and the aerodynamic envelope model may be comparatively lower. The underlying reasons for the different levels of accuracy of various models are discussed. Furthermore, it is demonstrated the mode shape correction factor of a flexible cylinder may be dependent not only on the mode shape, but also on other parameters such as the mechanical damping level.

Accounting for spectral shape in a simplified method of analyzing friction pendulum systems

This paper examines the effect of subduction zone and basin amplified motions on the accuracy of using a simplified method to analyze Friction Pendulum Systems, which is the basis for many international code provisions. This method estimates the maximum displacement demand for Friction Pendulum System isolated structures from analyzing a single degree of freedom system with equivalent period and damping coefficient. Friction Pendulum Systems with equivalent natural period between 1.5 s and 5 s and equivalent damping ratio from 16% to 32% were considered when subjected to over 400 motions. The considered ground motions include crustal and subduction zone motions, with and without basin amplification effect. Ratios of analysis-to-design maximum displacements corresponding to each ground motion are computed. A displacement-spectrum shape correction factor is proposed to improve the accuracy of the simplified method. This correction factor takes into account the irregularity of the 5% damped displacement spectrum that depends on the equivalent period and damping ratio at design displacement of the isolation system.

Effect of mean flow on shape correction factor and acoustic properties of a compact acoustic filter

The inclusion of mean flow effects in the performance evaluation of acoustic filters has been found to be essential for achieving realistic results. There have been several efforts to predict and analyze the performance of filters by using plane wave theory, with and without mean flow. The present study is a step forward in this direction and examines the effect of mean flow on the shape correction factor in connection with the performance of a compact acoustic filter. The filter under consideration consists of two cavities, designed to attenuate noise in a wide frequency band by suitably varying cavity lengths. Performance of such filter has been predicted by a 1D acoustic model by including the convective effect of mean flow in the modified theory of Concentric hole Cavity Resonator (CCR). The Transmission Loss (TL) spectrum without flow featured sharp peaks and the mean flow is found to smoothen them out. TL peaks have also been observed to shift due to the convective effect of the mean flow. The most important finding of this investigation is the variation of shape correction factor with the flow, which was a constant in no flow condition. Therefore, an approximate relation has been established between the shape correction factor and mean flow Mach number, which is new of its kind. To validate the predicted results, experiments were conducted for flow speeds ranging from 6 m/s to 30 m/s in an impedance tube setup. Good agreements were observed between the experimental results and those predicted by the modified 1D model.

Stress intensity factors for axial semi-elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel-lined pressure tunnels and shafts considering weld shape

When for steel liners of pressure tunnels and shafts high-strength steels are used, welded joints are subject to the risk of hydrogen induced cold-cracking in the base material. Longitudinal butt welded joints are critical regions as they are loaded transversely. For an accurate engineering fatigue and fracture assessment, solutions for stress intensity factors (SIF) are required, considering the weld shape and the global behavior of the liner (i.e., geometrical imperfections and interaction with surrounding concrete and rock). In this study, SIF for axial semi-elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel liners are studied by means of the finite element method. At first the applicability of published parametric equations for SIF of elliptical cracks in plates is validated. Then the influence of the weld shape is assessed through a systematic parametric study. It is shown that the weld profile has a significant influence on SIF for semi-elliptical surface cracks while it has no significant influence on SIF for embedded elliptical cracks within the studied range of relative crack depth. Finally, a new parametric equation is proposed to estimate the weld shape correction factor for semi-elliptical surface cracks.

A study of fatigue crack growth from artificial corrosion pits at welded joints under complex stress fields

AbstractThe paper studies the effects of artificial corrosion pits and complex stress fields on the fatigue crack growth of full penetration load‐carrying fillet cruciform welded joints with 45° inclined angle. Parameters of fatigue crack growth rate of welded joints are obtained from S‐N curves under different levels of corrosion. A numerical method is used to simulate fatigue crack growth using different mixed mode fatigue crack growth criteria. Using polynomial regression, the crack shape correction factor of welded joints is fitted as a function of crack depth ratios. Because the maximum circumferential stress criterion is simple and easy to use in practice, fatigue crack growth rate is modified using this criterion. The relationship of effective stress intensity factor, crack growth angle and crack depth is studied under different corrosion levels. The simulated crack growth path obtained from the numerical method is compared with the actual crack growth path observed by fatigue tests. The results show that fatigue cracks do not initiate at the edge or bottom of pits but at the weld toes where the maximum stress occurs. The artificial corrosion pits have little effect on the effective stress intensity factor ranges and crack growth angle. The fatigue crack growth rates of welded joints with pits 1 and 2 are 1.15 times and 1.40 times larger than that of the welded joint with no pit, respectively. The simulated crack growth path agrees well with the actual one. The fatigue life prediction accuracy using the modified formulation is improved by about 18%. The crack shape correction factor obtained using the maximum circumferential stress criterion is recommended being used to calculate fatigue life.

Local scour around abutment in clay/sand-mixed cohesive sediment bed

New data on scouring around vertical and wing wall abutments embedded in clay/sand-mixed beds are reported and the mechanism of the scouring process is described. In total, 87 experimental runs on vertical wall abutments and 30 experimental runs on 45° wing wall abutments in cohesive beds were conducted. The effect of clay content, water content, bed shear strength and pier Froude number on maximum equilibrium scour depth, scouring process, and time variation of scour were investigated. Further, equations for estimation non-dimensional maximum scour depth for vertical wall abutments embedded in clay–sand mixtures are proposed as functions of pier Froude number, clay content (C), water content (Wc), and bed shear strength for 0.35 ⩽ C ⩽ 1; 0.19 ⩽ Wc ⩽ 0.44. In addition, shape correction factor for 45° wing wall abutments in cohesive sediment beds is evaluated.

The morphological and settling properties of ANAMMOX granular sludge in high-rate reactors

Digital macro photography and settling tests were carried out to investigate the morphological and settling characteristics of ANAMMOX granules in a high-rate reactor. The ANAMMOX granules could be divided into settling and floating granules. The settling granules with an average diameter of 2.96±0.99 mm were smaller than the floating granules with an average diameter of 4.58±1.22 mm. A settling model was established and validated to correlate the settling velocity with the density (ρG), mass shape factor (ψmass), shape-correction factor (characterized by sphericity (Φ(')) or roundness (ξ)) and projected area equivalent sphere diameter (dP) of ANAMMOX granules. The sphericity was more suitable than the roundness for describing the settling behavior. The sensitivity of four parameters was in the order of ρG,ψmass, dP and Φ('). Based on the settling model, ANAMMOX granules with diameter of 1.75-4.00 mm were supposed to be optimal for the ANAMMOX process.

Effects of particle diameter correction factor on the performance of cyclone collection efficiency models for an industrial application

A shape correction factor for flake-like particles is applied to six different previously reported models (Leith and Licht model, ideal laminar cyclonic flow model, ideal turbulent cyclonic flow model, mixed flow model, Zhang and Basu model, and Avci and Karagoz model) to calculate cyclone collection efficiency. The correction factor was obtained using an equivalent diameter concept based on particle volume and particle geometry. The results obtained after using this correction were compared to experimental data and it was found that the above mentioned models describe better the experimental collection efficiency data for particle diameters smaller than 20 μm in five of the six used models. Values for the D 50 were also calculated as well as their error compared to the experimental data. Error values for the D 50 calculation went from 77.8% to 7.7% for the Ideal laminar cyclonic flow model; from 92.9% to 70.3% for the Leith and Licht model, from 74.8% to 4.9% for the Mixed flow model; from 91% to 62.5% for the Avci and Karagoz model; from 87.7% to 48.6% for the Zhang and Basu model, and from 33.7% to 176% for the Ideal turbulent cyclonic flow model. These are promising results to predict collection efficiency more accurately for industrial processes that use cyclones.

Single-configuration FPP method에 의한 실리콘 웨이퍼의 비저항 정밀측정

Precision measurement of silicon wafer resistivity has been using single-configuration Four-Point Probe(FPP) method. This FPP method have to applying sample size, shape and thickness correction factor for a probe pin spacing to precision measurement of silicon wafer. The deference for resistivity measurement values applied correction factor and not applied correction factor was about 1.0 % deviation. The sample size, shape and thickness correction factor for a probe pin spacing have an effects on precision measurement for resistivity of silicon wafer.

Hygroscopic property of water-soluble organic-enriched aerosols in Ulaanbaatar, Mongolia during the cold winter of 2007

The hygroscopic properties of the water-soluble matter extracts of atmospheric aerosols collected at an urban site (47.92° N, 106.90° E, ∼1300 m above sea level) in Ulaanbaatar, Mongolia during the cold winter of 2007 were investigated using a hygroscopicity tandem differential mobility analyzer (H-TDMA). Dynamic shape correction factor (χ), the ratio of the actual drag force on a non-spherical aerosol particle to that on a sphere of equivalent volume, of the laboratory generated water-soluble matter (WSM) was found to be 1.09–1.38 (avg. 1.23 ± 0.10), implying that particles generated from the WSM are highly non-spherical. The reduction in the mobility diameter can cause ∼11% underestimation in a hygroscopic growth factor at 85% RH. The hygroscopic growth factors at 85% RH (g(85%)), defined as the ratio of the particle diameter at 85% RH to that at RH < 10% (initial dry diameter), of the WSM (initial dry particle diameter = 100 nm) were 1.32–1.50 (avg. 1.40 ± 0.06). The g(RH) of the water-soluble organic matter (WSOM) was retrieved from the measured g(RH) of the WSM and using the ZSR (Zdanovskii–Stokes–Robinson) approach and the thermodynamic aerosol inorganic model (AIM). We found that the g(85%) of the WSOM were in the range of 1.11–1.35 (avg. 1.22 ± 0.08), which are comparable to those of the biomass burning aerosols.

Investigation of internal bremsstrahlung radiation accompanying forbidden β-decay of 169Er and 170Tm

The internal bremsstrahlung (IB) spectrum accompanying the β-decay of the first forbidden β-transitions of 169Er and 170Tm is studied. The IB was measured using a scintillation γ-spectrometer. It was analyzed by the variable width peeling-off-method, and then corrected by applying the proper corrections. The analyzed and corrected IB spectrum was compared with those calculated according to the original theories of Knipp and Uhlenbeck (1936) as well as of Bloch (1936) (KUB), the coulomb corrected theory of Nilsson (1956), Lewis and Ford (1957), and detour transitions of Ford and Martin (1969). Also, a new trial was carried out by applying the shape correction factor C 1 of the first forbidden β-transition suggested by Konopinski and Uhlenbeck (1935, 1941) on the Fermi β-decay theory to the calculated IB based on Nilsson's theory. It is called modified KUB (M.KUB). The experimental results are in a good agreement with the theoretical calculations of forbidden β-transition of Ford and Martin (1969), and M.KUB. It is observed that the Coloumb contribution into IB spectrum is larger for lower β-endpoint energies in case of the sources of same Coulomb charge ( Z) and different β-endpoint energies.

クリープ変形を伴う免震建物の風応答性状に関する研究

This study proposes analytical methods for determining wind responses of base-isolated high-rise buildings with creep deflection and clarifies characteristics of their modal forces and responses. The following results are derived. Modal forces on a base-isolated building are calculated easily by multiplying those on a conventional building with a linear mode shape function by the proposed mode shape correction factor. It is shown that the proposed methods for determining wind responses of base-isolated high-rise buildings with creep deflection are appropriate. Creep deflections are insensitive to fluctuating wind forces, so creep deflections and wind responses can be calculated separately. Shifts of the mean wind response of a base-isolated building due to plastic characteristics of isolation devices occur, but they behave almost elastically in the along-wind direction. However, the isolation layer moves inelastically in the across-wind and torsional directions. The standard deviation response calculated from the wind force for a certain direction is equal to or greater than that derived from 3 components of wind forces simultaneously. However, the mean response considering the former is smaller than that considering with the latter.