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An accurate understanding of the elastostatic properties for flange-bolted joints is crucial in modeling the nonlinear dynamics. In this study, the elastostatics of the flange are investigated through finite element (FE) analysis and experimental test. It is shown that the axial stiffness exhibits bi-linear properties, and the flange appears axial-flexural coupling deformations under bending moments. Then, to understand the bi-linear axial stiffness properties and the influence of bolt preloads on axial and bending stiffnesses, the bolted T-stub joint is chosen as the object of study, and the relevant mechanical model is further presented based on linear elasticity. Meanwhile, the validity of the mechanical model is numerically verified. The analysis indicates that under tension and compression, the essence of the bi-linear axial stiffness is the differences in interface contact status, and the coupling deformations are induced by different tensile and compressive stiffnesses. In addition, both the tensile and bending stiffnesses increase with the increase of bolt preloads, while the effect of preloads on compressive stiffness is insignificant. • An equivalent mechanical model for the T-stub is presented to understand the elastostatics of flange-bolted joints. • The essence of the bi-linear axial stiffness properties are fully revealed. • The mechanisms of axial-flexural coupling deformations are investigated. • The influence of bolt preloads on axial and bending stiffnesses are discussed. [ABSTRACT FROM AUTHOR]

The trending integrations of Battery Energy Storage System (BESS, stationary battery) and Electric Vehicles (EV, mobile battery) to distribution grids call for advanced Demand Side Management (DSM) technique that addresses the scalability concerns of the system and stochastic availabilities of EVs. Towards this goal, a stochastic DSM is proposed to capture the uncertainties in EVs. Numerical approximation is then used to make the problem tractable. To accelerate the computational speed, the proposed DSM is tightly relaxed to a convex form using second-order cone programming. Furthermore, in light of the continuous increasing problem size, a distributed method with a guaranteed convergence is applied to shift the centralized computational burden to distributed controllers. To verify the proposed DSM, real-life EV data collected on UCLA campus is used to test the proposed DSM in an IEEE benchmark test system. Numerical results demonstrate the correctness and merits of the proposed approach. [ABSTRACT FROM AUTHOR]

In this study, considering the elastoplastic behavior of contacting asperities on micro-scale and the contact pressure distribution of bolted joint interfaces on macro-scale, an improved contact stiffness model is presented. Firstly, the bolted T -stub joint is chosen as the object of study, and the distribution of normal contact load over the interface under preload conditions is studied. Then, combining the continuity, smoothness and monotonicity of the constitutive relations of normal contact load-deformation in three different regimes of plastic- elastoplastic-elastic of contacting asperities, the contact stiffness of individual asperity is analytically derived. Meanwhile, the relation between the distribution of contact stiffness and the distribution of normal contact load for bolted joint interfaces is determined based on fractal theory. The presented model overcomes the shortcomings of the contact stiffness without elastoplastic behavior obtained from the MB model and reveals the inhomogeneous distribution features of interfacial contact stiffness in bolted joints. Finally, the finite element (FE) analysis for flange-bolted joints incorporating the proposed model and the relevant experimental verification are performed. The results show that the average error of the first 4-order natural frequencies between the FE results and the experimental ones is only 0.72%, and the predicted results in frequency-domain are consistent with the measured ones, which illustrates that the proposed model can be used in interface modeling of jointed structures. [ABSTRACT FROM AUTHOR]

Considering the non-uniformly distributed contact pressure, this study presents a new contact characteristic parameters (contact stiffness and damping) model for bolted joint interfaces. Firstly, to transform the contact pressure distribution into normal contact load distribution, the contact pressure distribution and its mathematical representation of single-bolted joint are studied. Subsequently, the relationships among contact stiffness distribution, contact damping distribution and normal contact load distribution are determined based on the improved MB model. It is found that the interfacial contact stiffness and damping exhibit significant inhomogeneous distributions. The proposed model overcomes the shortcomings of homogeneous distributions of contact stiffness and damping in bolted joints derived from previous models. In addition, the effects of bolt preload, tangential-to-normal contact load ratio and friction coefficient on the contact stiffness and damping are discussed in detail. Finally, the finite element (FE) analysis for beam lap structure with bolted joints incorporating the proposed model and the relevant experimental are performed to verify the validity of the modeling method. The results indicate that the proposed model can significantly improve the modeling accuracy of bolted joints. • A new contact characteristic parameters model for bolted joint interfaces is developed. • The inhomogeneous distribution characteristics of interfacial contact stiffness and damping are fully revealed. • The varying relations of contact stiffness and damping versus relevant parameters are discussed in detail. • The numerical results are entirely coincident with the experimental. [ABSTRACT FROM AUTHOR]

The paper presents the numerical investigations for a light civil helicopter fuselage with the purpose of reducing the helicopter drag. Two numerical methods: Reynolds-Averaged Navier-Stokes (RANS) and a hybrid RANS-LES method: improved delayed detached-eddy simulation (IDDES) method are performed for the simulation of a prototype helicopter fuselage. The RANS method is validated by a modular helicopter fuselage with experimental data, while the IDDES method has already been used in other studies and good results have been achieved. The numerical results of the civil helicopter in terms of the aerodynamic coefficients obtained by the two methods are consistent with each other. Compared to the RANS method, the IDDES approach is capable of predicting the large separation flow of the fuselage/components and the small-scale vortices in the flow field. It is found that the hybrid method captures the periodically detached separating vortices behind the skid struts, while the flow at the same position simulated by the RANS method is still attached. Moreover, separating vortices, which develop diagonally upwards, are captured at fuselage/tail-boom junction by the hybrid method, whereas RANS simulation doesn't predict. Subsequently, the design of the helicopter drag reduction is carried out at α = 0 deg angle of attack and 0.2 Mach number through shape optimization based on the numerical simulations, and the numerical results are verified by the force tests. It shows that the optimization of the landing skids aims at reducing the strong Karman vortex shedding effect induced by the skids, which greatly decreases the total drag. Combined with the optimization of the fuselage/tail-boom transition, this approach suppresses the separation flow of the fuselage and reduces the pressure drag, and the adjustment of transition slope benefits of up to 1.18% drag reduction, while the extension of transition reduces the drag by 2.64%. The optimization of tail-boom layout demonstrates that lower tail-boom layout can contribute to a drag reduction by 4.37% (RANS) and 3.89% (test), respectively, when compared to the original tail-boom layout. [ABSTRACT FROM AUTHOR]

• Herbaceous peony stem diameter could be used to estimate stem strength. • Thickness of secondary cell wall contributed a lot to stem strength. • Three lignin monomers affected herbaceous peony stem strength. • Lignin deposition and secondary cell wall of the stem were observed. • CAD was a key gene controlling herbaceous peony lignin accumulation. Straight stems are highly important to herbaceous peony (Paeonia lactiflora Pall.) cut flowers. To clarify whether the microstructural and lignin characteristics are associated with P. lactiflora stem mechanical strength, eight cultivars were used to study their anatomical structure, secondary cell wall, lignin deposition, lignin content and structure, lignin biosynthetic enzyme activity and related gene expression levels. The results showed that stem diameter was a direct indicator estimating its mechanical strength. Simultaneously, the number of vascular bundles, area of vascular bundles, number of duct perforations, ratio of xylem to cross-section and thickness of secondary cell wall had significant positive correlations with stem mechanical strength. Moreover, three lignin monomers were all detected in the stem, and the contents of S-lignin, G-lignin and total lignin in high stem mechanical strength cultivars were higher than those in low stem mechanical strength cultivars as a whole, and lignin was deposited in the cell walls of the sclerenchyma, vascular bundle sheath and duct. Additionally, cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD) and polyphenol oxidase (PPO) activities in high stem mechanical strength cultivars were higher than those in low stem mechanical strength cultivars as a whole, and CAD might be the key gene among detected lignin biosynthetic genes. Consequently, microstructural and lignin characteristics were closely correlated with stem mechanical strength in P. lactiflora. These results would provide useful information concerning the physiological mechanism of stem strength. [ABSTRACT FROM AUTHOR]

Herbaceous peony (Paeonia lactiflora Pall.) is a popular high-end cut flower, but stem bending caused by low stem strength severely decreases its quality. To enhance stem strength, the regulatory effects of exogenous silicon were investigated in P. lactiflora. The results showed that silicon application enhanced stem strength by increasing the thickness of secondary cell walls and the layers of thickened secondary cells. Moreover, more lignin accumulated, particularly G-lignin and S-lignin, and the activities of lignin biosynthetic enzymes increased with silicon application. In addition, based on transcriptome analysis, silicon application induced the expression of genes participating in lignin biosynthesis pathway. Among them, hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyl transferase gene (HCT1) was isolated from P. lactiflora and found to be mainly localized in the cytoplasm of cells. Overexpression of PlHCT1 increased the layers of thickened secondary cells and lignin accumulation in tobacco, resulting in enhanced stem strength and demonstrably straight stems. Finally, silicon content, lignin content and PlHCT1 expression in P. lactiflora cultivars with high stem strengths were totally higher than those in cultivars with low stem strengths. These results indicated that silicon application enhanced stem strength by promoting lignin accumulation in P. lactiflora , which has prospects for stem quality improvement in general. [Display omitted] • Silicon increased the net photosynthesis rate and SPAD value. • Silicon enhanced stem strength by promoting lignin accumulation. • Silicon increased lignin biosynthetic enzyme activities and gene expression. • HCT1 expression was induced and localized in the cytoplasm of cells. • Overexpression of HCT1 increased lignin, resulting in enhanced stem strength. [ABSTRACT FROM AUTHOR]

• CCoAOMT could respond to drought stress in Paeonia ostii. • CCoAOMT was isolated, and its characteristics were clarified. • Overexpression of CCoAOMT conferred drought stress tolerance. • CCoAOMT could significantly altered G-lignin content. • Stress tolerance was caused by promoting lignin synthesis and ROS scavenging. Paeonia ostii is an emerging woody oil crop, but drought severely inhibits its growth and promotion in arid or semiarid areas, and little is known about the mechanism governing this inhibition. In this study, the full-length cDNA of a caffeoyl-CoA O -methyltransferase gene (CCoAOMT) from P. ostii was isolated, and determined to be comprised of 987 bp. PoCCoAOMT encoded a 247-amino acid protein, which was located in the nucleus and cytosol. Significantly higher PoCCoAOMT transcription was detected in P. ostii treated with drought stress. Subsequently, the constitutive overexpression of PoCCoAOMT in tobacco significantly conferred drought stress tolerance. Under drought stress, transgenic lines exhibited lower reactive oxygen species (ROS) accumulation, and higher antioxidant enzyme activities and photosynthesis. Moreover, the expression levels of senescence-associated genes were significantly downregulated, whereas the expression levels of lignin biosynthetic genes and PoCCoAOMT were significantly upregulated in transgenic lines. Similarly, transgenic lines produced significantly higher lignin, especially guaiacyl-lignin. These results suggest that PoCCoAOMT is a vital gene in promoting lignin synthesis and ROS scavenging to confer drought stress tolerance in P. ostii. [ABSTRACT FROM AUTHOR]

Despite extensive academic and commercial development, a comprehensive understanding of the principles necessary for high-yield production of carbon nanotubes (CNTs) is lacking, whether in oriented films, bulk powders, or other forms. In chemical vapor deposition growth of CNT films on substrates, trace contaminants of carbon, such as deposits on the reactor tube walls, are known to cause inconsistency in key production metrics, including CNT density and alignment. In this study, we show that trace exposure of the catalyst to carbon during initial heating of the catalyst film is a critical determinant of CNT yield, and this carbon exposure accelerates catalyst nanoparticle formation via film dewetting and increases the probability of CNT nucleation and the resultant density of the CNT population. By controlled exposure of the catalyst to a trace amount of carbon, we show up to a 4-fold increase in bulk mass density for a given forest height, an 8-fold increase in local CNT number density, and a 2-fold increase in the growth lifetime, relative to a reference condition. We discuss potential mechanisms to explain the role of carbon exposure on the probability of CNT nucleation from nanoparticle catalysts, supported by microscopy and gas analysis. Image 1 [ABSTRACT FROM AUTHOR]

• This work presents a method for absolute flow velocity measurement in spectral domain optical coherence tomography (SDOCT). • The probe arm of SDOCT is mounted on a dividing head which can change the incident angle of the probe beam. • By rotating the dividing head and reading the scale, Doppler angle of flow can be achieved. • The method is demonstrated with capillary phantom and blood flows of chicken embryo in vivo. Abnormal blood flow in the early stage of embryonic heart can lead to cardiac defects. Thus, accurate flow measurement in the embryonic heart is important for related studies. Optical coherence tomography (OCT) is a noninvasive imaging approach which can provide flow velocity distribution information with high spatial and temporal resolution. However, OCT is only sensitive to velocity components parallel to the probing beam. To measure absolute flow velocity, additional information, such as Doppler angle, is required. Here, we propose a practical method to measure Doppler angle by introducing a dividing head to probe the arm of OCT. The incident angle of the probe beam can be controlled by rotating the dividing head. With the scale of the dividing head, rotating angle can be obtained. In each measurement, probe beam is adjusted to a proper angle by real time flow monitoring. Then, the probe beam is rotated perpendicularly to the flow velocity, i.e. Doppler angle is π/2 , and the Doppler angle can be calculated. This method is validated by capillary phantom. Last, blood flow in the early stage of chicken embryo is measured in vivo by the proposed method. [ABSTRACT FROM AUTHOR]

• A new pattern bundle with a smaller wire diameter of peripheral rods was proposed. • The comparative study between the new bundle and the conventional one was carried out by RANS-based CFD simulation. • The better flow and heat transfer performance was obtained for the new pattern bundle. In this paper, a new pattern bundle with a smaller wire diameter of peripheral rods was proposed. By decreasing the wire diameter of peripheral rods, the flow area of peripheral sub-channels is reduced diverting more coolant towards the central sub-channels. This would lead to a more uniform sub-channel temperatures distribution. To analyze the flow and heat transfer performance of the new bundle, the comparative study between the new bundle and conventional one was carried out by RANS-based CFD simulation. It was found that decreasing the partial wire diameters, the uniformity of coolant flow distribution is improved, resulting in a more homogeneous temperature distribution. The local transverse pressure difference characterizing global swirl motion is smaller, resulting in a weaker sweeping flow in peripheral sub-channels. Moreover, the obvious sweeping flow also could be observed in inter-connected sub-channels due to the smaller wire diameter of peripheral rods. At last, Nusselt number and friction factor are the parameters targeted for the investigation, and the results show that the thermal-hydraulics performance of the new bundle has been significantly improved. Through the research of this paper, the qualitative understanding of fuel assembly structure optimization could be provided for the core design in future. [ABSTRACT FROM AUTHOR]

The expanding process of turbulent separation bubble induced by a horn ice on the leading edge of an airfoil for business jet was investigated numerically with IDDES. Through comparing with the experiment results of critical stall condition, the fidelity of method for detailed simulation of ice-induced separation was verified firstly. Then the separation bubble under post-stall conditions was investigated in the aspects of both the features of averaged static flowfield and the behaviors of transient shear-layer vortices. The averaged results manifested that during the stall process, the bubble expanded with stretching and deformation for reattachment line and turbulence region were shifted towards trailing edge and spread continually. The corresponding extending and descending of pressure plateau with weak pressure gradient resulted in an early but mitigated stall pattern consequently. From the transient flowfield, it was observed that the entire evolution process of bubble was driven by the hairpin-type vortices generated from the shedding shear-layer with K-H instability. The propagation direction of these shear-layer vortices was affected by the entrainment of external flow. Under the post-stall condition, the motion of vortices towards the wall was delayed with the increasing of incidence and the interaction between vortices and wall was weakened correspondingly, which leaded the gradual decrease of reattachment effect and the continuous expanding of recirculation region. [ABSTRACT FROM AUTHOR]