• Wind and Structures
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• v.34 no.1
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• pp.15-27
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• 2022

This work comes within the framework of the "Benchmark on the Aerodynamics of a Rectangular Cylinder" that investigates a rectangular cylinder of length-to-depth ratio equal to 5. The present study reports and discusses velocity fields acquired using planar Particle Image Velocitmetry for several angles of attack and Reynolds numbers. In particular, for a cylinder depth-based Reynolds number of 2 × 10⁴ and zero incidence angle, the flow features along the lateral (parallel to the freestream) upper and lower surfaces of the cylinder are reported. Using first and second order statistics of the velocity field, the main flow features are discussed, especially the size and location of the time-averaged flow structures and the distribution of the Reynolds stresses. The variation of the flow features with the incidence is also studied considering angles of attack up to 6°. It is shown that the time-averaged flow is fully detached for incidence higher than 2°. For an angle of attack of 0°, the effects of the Reynolds number varying between 5 × 10³ and 2 × 10⁴ are investigated looking at flow statistics. It is shown that the time-averaged location of the reattachment point and the shape and position of the time-averaged main vortex are mostly constant with the Reynolds number. However, the size of the inner region located below the time-averaged shear layer and just downstream the leading edge corner appears to be strongly dependent on the Reynolds number.

• Composites Research
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• v.34 no.6
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• pp.380-386
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• 2021

This paper aims to improve the critical speed of power-take-off (PTO) shafts by using carbon fiber reinforced plastics (CFRPs). The PTO shaft was designed with titanium-CFRPs hybrid structure in order to compensate the low shear strength of CFRPs. Based on the requirements for PTO shafts, the dimensions of PTO shafts were determined through a parametric study. To evaluate the performance of the PTO shaft, a vibration test, a static torsion test, and a torsion durability test were performed. In the vibration test, the critical speed of PTO shafts was 20570 rpm, which was 7.5% higher than that of titanium shafts. Additionally, it was confirmed that the maximum allowable torque of the PTO shaft was 2300 N·m. Finally, under repeated load in the range of 11.3 to 113 N·m, the fatigue failure in the PTO shaft did not occur up to 10⁶ cycles.

• Advances in aircraft and spacecraft science
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• v.9 no.3
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• pp.169-193
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• 2022

By the present paper, both experimental and analytical models have been proposed to study the vibration behavior of partially bio-sourced sandwich panel with orthogonally stiffened core. For a variable mass fraction of Alfa fibers from 5% to 15%, impregnated in a Medapoxy STR resin, this panel were manufactured by molding the orthogonally stiffened core then attached it with both skins. Using simply supported boundary conditions, a free vibration test was carried out using an impact hammer for predicting the natural frequencies, the mode shapes and the damping coefficient versus the fibers content. In addition, an analytical model based on the Higher order Shear Deformation Theory (HSDT) was developed to predict natural frequencies and the mode shapes according to Navier's solution. From the experimental test, we have found that the frequency increases with the increase in the mass fraction of the fibers until 10%. Beyond this fraction, the frequencies give relatively lower values. For the analytical model, variation of the natural frequencies increased considerably with side-to-thickness ratio (a/H) and equivalent thickness of the core to thickness of the face (h_s/h). We concluded that, the vibration behavior was significantly influenced by geometrical and mechanical properties of the partially bio-sourced sandwich panel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.133-140
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• 2010

A series of triaxial test was performed in order to determine critical state parameters of calcareous Jeju sand, which comprises angular shape particles with many pores in the surface. It is observed that Jeju sand mainly shows the contractive behavior during triaxial shear due to high extreme void ratios and large compressibility. The peak friction angle of Jeju sand decreases slightly with increasing mean effective stress due to the particle crushing of carbonate materials. However, the peak friction angle of Jeju sand is higher than that of other silica sands because of the more angular particle shape. The critical state friction angle of Jeju sand gradually decreases when the mean effective stress at a critical state increases. Whereas, there is not a clear influence of void ratio on the critical state friction angle. Critical state parameters of Jeju sand are similar to those of calcareous sands, but significantly larger than those of common sands.

• Computers and Concrete
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• v.32 no.1
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• pp.75-85
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• 2023

This work utilizes simplified higher-order shear deformation beam theory (HSDBT) to investigate the vibration response for functionally graded carbon nanotube-reinforced composite (CNTRC) beam. Novel to this work, single-walled carbon nanotubes (SWCNTs) are distributed and aligned in a matrix of polymer throughout the beam, resting on a viscoelastic foundation. Four un-similar patterns of reinforcement distribution functions are investigated for the CNTRC beam. Porosity is another consideration taken into account due to its significant effect on functionally graded materials (FGMs) properties. Three types of uneven porosity distributions are studied in this study. The damping coefficient and Winkler's and Pasternak's parameters are considered in investigating the viscosity effect on the foundation. Moreover, the impact of different parameters on the vibration of the CNTRC beam supported by a viscoelastic foundation is discussed. A comparison to other works is made to validate numerical results in addition to analytical discussions. The findings indicate that incorporating a damping coefficient can improve the vibration performance, especially when the spring constant factors are raised. Additionally, it has been noted that the fundamental frequency of a beam increases as the porosity coefficient increases, indicating that porosity may have a significant impact on the vibrational characteristics of beams.

• Earthquakes and Structures
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• v.26 no.1
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• pp.31-48
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• 2024

In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.166-178
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• 2006

Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.

• Journal of the Korean Wood Science and Technology
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• v.2 no.2
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• pp.25-31
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• 1974

1. Various gluing qualities applying Resorcinol Plyophen #6000 were studied on aiming the strength relationships of laminated woods resulted by single species [poplar (Populus deltoides), larch(Larix leptolepis)], mixed species of (poplar and larch), preservatives, treated poplar the scarf joint with mixed species of poplar and larch and the scarf joint treated with preservatives. 1. 1 On the block shear and on the DVL tension test, the mean wood failure ratio showed an excellent value i.e., above 65% and the tangential strength for larch was higher than that of radial, but it was reversed for poplar as shown in Tables 1 and 2. 1. 2 The lamina treated with Na-PCP reduced slightly the strength but the limited strength allowed for manufacturing laminated wood was not influenced by treating Na-PCP as shown in Tables 3 and 4. 1. 3 The safe scarf ratio in the plane scarf joint was above 1/12 for larch and 1/6 for poplar regard less of the chemical treatment or untreatment as shown in Tables. 5, 6, 7 and 8. 2. In the normal and boiled state, the gluing quality of the laminated wood composed of single[poplar (Populus deltoides), larch (Larix leptolepis)] and double species (poplar and larch) glued with Resorcinol Plyophen #6000 were measured as follow, and also represented the delamination of the same laminated wood. 2.1 The normal block shear strength of the straight and curved laminated wood (in life size) were more than three times of the standards adhesion strength. And, the value of the boiled stock was decreased to one half of the standard shear adhesion strength, but it was more than twice the standard strength for the boiled stock. Thus, it was recognized that the water resistance of the Resorcinol Plyophen #6000 was very high as shown in Tables 9 and 10. 2. 2 The delamination ratio of the straight and curved laminated woods in respect of their composition were decraesed, in turn, in the following order i. e., larch, mixed stock (larch+poplar) and poplar. The maximum value represented by the larch was 3.5% but it was below the limited value as shown in Table 11. 3. The various strengthes i.e., compressive, bending and adhesion obtainted by the straight laminaced wood which were constructed by five plies of single and double species of lamina i. e., larch (Larix leptolepis) and poplar (Populus euramericana), glued with urea resin were shown as follows: 3. 1 If desired a higher strength of architectural laminated wood composed of poplar (P) and larch (L), the combination of the laminas should be arranged as follows, L+P+L+P+L as shown in Table 12. 3.2 The strength of laminated wood composed of laminas which included pith and knots was conside rably decreased than that of clear lamina as shown Table 13. 3.3 The shear strength of the FPL block of the straight laminated wood constructed by the same species which were glued with urea adhesives was more than twice the limited adhesion strength, thus it makes possible to use it for interior constructional stock.

• Journal of the Korean Wood Science and Technology
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• v.35 no.6
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• pp.13-22
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• 2007

This study was carried out to scrutinize possibility of manufacturing pitch pine (Pinus rigida) glued laminated timber in order to add values of pitch pine trees. Also, it was investigated to improve bending performance of pitch pine glulam. Pitch pine was imported as one of major plantation species in Korean peninsula. Machine stress rated grades of pitch pine lumber mostly ranged between E7 and E9. which grades were more or less inferior to producing high quality glulam. However, the adhesive properties between pitch pine and pitch pine, and between pitch pine and Japanese larch (Larix kaempferi Carr.), such as shear bond strength, wood failure rate and de-lamination rate of bonded layer submerged in cold and boiling water, were higher than Korean Standard criteria. These properties are essential for manufacturing glulam with single species or multiple species. The modulus of rupture (MOR) of pitch pine glulam exceeded the criterion of Korean Standard for glulam strength grade but modulus of elasticity (MOE) was lower than the criterion. On the other hand, the bending performances (MOR and MOE) were improved 20 percent by mixing with Japanese larch laminar. It is effective to arrange higher quality Japanese larch laminar at the outer layer of glulam for improving bending performances. In conclusion, it is possible to use low quality pitch pine as laminar of structural glulam for adding values of pitch pine.

• Food Science of Animal Resources
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• v.34 no.3
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• pp.395-402
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• 2014

The current study was conducted to identify technology for the production of high quality pork, based on the meat consumption habits of consumers. Macsumsuk, a type of kaolinite (a clay mineral), and/or a mixture of herbs (Mori Folium, Sophorae Radix, Glycyrrhizae Radix, Citri Leiocarpae Exocarpium, and Pogostemi Herba) were added to the diets of fattening pigs. Sixty barrow pigs (4 kinds of treatment ${\times}5$ pigs/treatment ${\times}3$ replicates) were randomly assigned to either the Control (no additives), T1 (3% Macsumsuk), T2 (3% Herb mixtures), or T3 (3% Macsumsuk + 3% Herb mixtures) groups, and were fed the diets for 60 d. Dressed weights were in the order of T1 ($93.40{\pm}4.68kg$) > T2 ($91.40{\pm}6.52kg$) > Control ($88.80{\pm}1.57kg$) > T3 ($86.80{\pm}2.01kg$). Back-fat thickness of the Control animals ($23.2{\pm}1.03mm$) was significantly greater than that of the various treatment groups (p<0.01). Numeric values representing the carcass yield and quality grade were higher for all the treated groups than the Control group, thought the difference was not statistically significant. Crude fat content was significantly higher in the Control group ($2.23{\pm}0.34%$) than in the treated groups (p<0.05). The addition of both Macsumsuk and herb mixtures into the diets of the pigs significantly reduced cooking loss of the pork compared to the Control (p<0.05). No statistically significant changes were observed in the shear force (average $5.87{\pm}0.54kg/cm^2$), water holding capacity (average $54.59{\pm}3.16%$), or CIE values of the pork, whereas cholesterol levels significantly decreased (p<0.01) in those fed Macsumsuk and/or the herb mixtures. No significant changes in fatty acid composition, total saturated fatty acid (SFA), total unsaturated fatty acid (UFA), or UFA/SFA ratios were observed by any of the treatments. In conclusion, the results obtained from this study suggest that the addition of Macsumsuk and/or herb mixtures into the diets of growing and fattening pigs improves the pork quality by reducing cooking loss, decreasing cholesterol content, and enhancing sensory characteristics.