Infinite Span Research Articles

Dynamic flexural strength of Aluminosilicate glass with a perspective of impulsive and quasi-impulsive responses: An experimental–numerical coupled evaluation

The flexural strength of glass is a critical design parameter for applications encountering impact loadings. However, the micro defects, specimen geometry, loading rate, and load transformation from a quasi-dynamic to quasi-impulsive state may influence the measurement accuracy. Due to the stochastic and amorphous nature of the material, an accurate determination of the flexural strength remains a challenge. In this two-fold study, a coupled experimental–numerical strategy was devised to evaluate the dynamic flexural strength. In the first phase, three-point bending experiments were conducted on a novel “Electromagnetic Split Hopkinson Pressure Bar (ESHPB)”. The incident stress signal and fracture time were recorded from experimental data, while the flexural strength was indirectly computed from a numerical algorithm. A quantitative comparison of the flexural strength with those in existing literature established the accuracy of the proposed methodology. Results of the study indicate that the specimen response became independent of the support conditions under impulsive loading. That being said, the specimen behaved like it had an infinite span length, and the measured flexural strength remained the same whether the specimen was supported or not. Besides, the specimen also maintained contact at the interfaces of the incident bar and fixture supports for the entire loading duration. In the second part of this study, the computed flexural strength was used to calibrate the existing JH-2 model. Numerical prediction of the damage propagation corroborated with that obtained from reprography images, though qualitatively. This work presents a precise and robust methodology to determine the dynamic flexural strength of brittle ceramics like Aluminosilicate glass over traditional experimental procedures to facilitate its adoption.

Flow noise radiated from a cylinder above a plate

The flow noise of an infinite span circular cylinder has been well documented over the past decades. In reality, cylinder flows are rarely isolated from any nearby boundaries. The addition of a large flat plate to one side of the cylinder created an asymmetric configuration, termed as the cylinder above a plate (CAP). Examples include roof racks and rail pantographs. Flow diagnostics of a CAP have been lacking when compared to the baseline unbounded cylinders, while the corresponding noise measurements have been practically absent. Recently, the rigid CAP configuration was systematically tested in subsonic, air flow. Cylinders with various cross-sectionalshapes were tested. Microphone measurements were used to characterize the noise generated by a CAP, while particle image velocimetry (PIV) was used to characterize the cylinder wake. When the gap between the cylinder and plate was reduced, the amplitude of the tonal noise radiated from the cylinder flow generally reduced, while acoustic directivity pattern was heavily modified. The correlated flow structures were weakened and pushed away from the plate, which strongly suggested a modulation of the fluctuating forces exerted on the cylinder. By Curle’s acoustic analogy, this was related to the modified acoustic noise and directivity.

NumericalStudy of Turbulent Flows over a NACA 0012 Airfoil: Insights into Its Performance and the Addition of a Slotted Flap

This work provides a comprehensive overview of various aspects of airfoil CFD simulations. The airflow around a 2D NACA 0012 airfoil at various angles of attack is simulated using the RANS SST turbulent flow model and compared to experimental data. The airfoil is then modified with a slotted flap and additionally the angle of the flap is altered. The flow model is subsequently coupled to a heat transfer model to compare the isothermal versus non-isothermal performance. The airfoil with the slotted flap shows increased CL and CD values compared to the standard NACA 0012. Larger flap angles further increase the CL and CD. The lift and drag coefficients show no difference in the non-isothermal model compared to the isothermal model, indicating the isothermal model is sufficient for this system. The 3D model without wingtips shows a similar CL to the 2D model as it effectively has an infinite span. Adding a wingtip reduces the lift coefficient, as the air can flow around the wingtip, increasing the pressure on top of the wing. Overall, these results match the behavior expected from wing theory well, showing how CFD can be effectively applied in the development and optimization of wings, flaps, and wingtips.

Adjoint-based robust optimization design of laminar flow wing under flight condition uncertainties

It is an inherent uncertainty problem that the application of laminar flow technology to the wing of large passenger aircraft is affected by flight conditions. In order to seek a more robust natural laminar flow control effect, it is necessary to develop an effective optimization design method. Meanwhile, attention must be given to the impact of crossflow (CF) instability brought on by the sweep angle. This paper constructs a robust optimization design framework based on discrete adjoint methods and non-intrusive polynomial chaos. Transition prediction is implemented by coupled Reynolds-Averaged Navier-Stokes (RANS) and simplified eN method, which can consider both Tollmien-Schlichting (TS) wave and crossflow vortex instability. We have performed gradient enhancement processing on the general Polynomial Chaos Expansion (PCE), which is advantageous to reduce the computational cost of single uncertainty propagation. This processing takes advantage of the gradient information obtained by solving the coupled adjoint equations considering transition. The statistical moment gradient solution used for the robust optimization design also uses the derivatives of coupled adjoint equations. The framework is applied to the robust design of a 25° swept wing with infinite span in transonic flow. The uncertainty quantification and sensitivity analysis on the baseline wing shows that the uncertainty quantification method in this paper has high accuracy, and qualitatively reveals the factors that dominate in different flow field regions. By the robust optimization design, the mean and standard deviation of the drag coefficient can be reduced by 29% and 45%, respectively, and compared with the deterministic optimization design results, there is less possibility of forming shock waves under flight condition uncertainties. Robust optimization results illustrate the trade-off between the transition delay and the wave drag reduction.

Attachment-line, crossflow and Tollmien-Schlichting instabilities on swept ONERA-D and Joukowski airfoils.

Linear stability analyses are performed to investigate the boundary layer instabilities developing in an incompressible flow around the whole leading-edge of swept ONERA-D and Joukowski airfoils of infinite span. The stability analyses conducted in our study are global in the chordwise direction and local in the spanwise direction. A neutral curve is drawn at a given leading-edge Reynolds number ReR and several overlapping regions, called "lobes", are identified on a physical basis. A detailed study of the marginal modes reveals the presence of attachment-line and crossflow instabilities, as well as modes whose features do not fall within the standards of a specific type. Connected crossflow/Tollmien-Schlichting modes, that show a dominant spatial structure reminiscent of Tollmien-Schlichting waves but whose destabilization is linked to a crossflow mechanism, have been identified. The comparison of several neutral curves at different ReR values reveals the greater stabilizing effect of the increase of ReR on the crossflow instability compared to the attachment-line instability. The influence of the airfoil shape is also studied by comparing the neutral curves of the ONERA-D with the neutral curves of the Joukowski airfoil. These curves reveal similar characteristics with the presence of distinct lobes and their comparison at constant sweep angle shows that, under the conditions studied, the ONERA-D airfoil is more stable than the Joukowski airfoil, even for crossflow instabilities. The absolutely or convectively unstable nature of the flow in the spanwise direction is also tackled and our results suggest that the flow is only convectively unstable.

Numerical study of the effect of sidewalls on shock train behaviour

Strongly coupled sequences of shock waves, known as shock trains, are present in high-speed propulsion systems, where the presence of sidewalls substantially modifies the boundary layer thickness, skin friction and streamwise pressure distribution. In the present contribution, scale-resolved numerical simulations are performed on supersonic channel (infinite span) and square duct flows to evaluate the effect of sidewall confinement with and without shock trains. Comparable secondary flow vortices are observed in the duct case with and without the presence of the shock train. The absence of a separation region at the leading shock of the duct case results in lower flow deflection compared with the channel case, leading to a reduced shock strength. The principal effect of the sidewalls is to cause a shock train that is approximately twice as long and composed of a larger number of shocks. A modification of previous models, based on a momentum thickness-based blockage parameter, leads to an improved collapse of the channel and duct cases.

Implementing a bivariate ordering and replacement policy for deteriorating systems with two failure types

AbstractFor plenty of existing maintenance policies in literature, it is always assumed that the spare unit for replacement is available at any time if needed, while this perquisite may be unrealistic or even impossible. In this paper, we investigate an ordering and replacement modeling framework for a deteriorating repairable system with two failure types, involving a repairable failure (Type I failure) and a nonrepairable failure (Type II failure). A regular order and an expedited order are both incorporated into the spare unit ordering policy while a preventive replacement and a corrective replacement are both considered into the replacement policy, of which the ordering and replacement policy is scheduled in regard to the number of repairable failures. The expected profit per unit of time over an infinite time span is maximized to seek the optimal solutions in terms of the renewal reward theorem with a recursive algorithm procedure. An illustrative example is designed to validate the applicability and effectiveness of the developed ordering and replacement policy. In addition, the sensitivity of the optimal ordering‐replacement policy is studied and the effect of some key characteristics on the optimal decisions is discussed.

Numerical integration of an age-structured population model with infinite life span

The choice of age as a physiological parameter to structure a population and to describe its dynamics involves the election of the life-span. The analysis of an unbounded life-span age-structured population model is motivated because, not only new models continue to appear in this framework, but also it is required by the study of the asymptotic behaviour of its dynamics. The numerical integration of the corresponding model is usually performed in bounded domains through the truncation of the age life-span. Here, we propose a new numerical method that avoids the truncation of the unbounded age domain. It is completely analyzed and second order of convergence is established. We report some experiments to exhibit numerically the theoretical results and the behaviour of the problem in the simulation of the evolution of the Nicholson’s blowflies model.

Generalized periodic replacement policies for repairable systems subject to two types of failures

The purpose of this current research is to schedule generalized periodic replacement policies for a single unit system executing random working jobs. The system is subject to two types of failures when it has failed, including a minor failure (Type I failure), which can be thoroughly removed by the minimal repair and a catastrophic failure (Type II failure), which should be rectified by the corrective replacement. To be specific, four distinct periodic replacement models including a periodic replacement first model (Model A1), a modified periodic replacement first model (Model A2), a periodic replacement last model (Model B1), and a modified periodic replacement last model (Model B2) are investigated. The long run average cost rate (ACR) over an infinite time span under different situations is obtained theoretically and optimal periodic replacement interval for each condition is derived analytically. Numerical examples are exhibited to verify the derived results.

Radiation-induced instability of a finite-chord Nemtsov membrane

We consider a problem of stability of a membrane of an infinite span and a finite chord length, submerged in a uniform flow of finite depth with free surface. In the shallow water approximation, Nemtsov [“Flutter effect and emission in the region of anomalous and normal Doppler effects,” Radiophys. Quantum Electron. 28(12), 1076–1079 (1985)] has shown that an infinite-chord membrane is susceptible to flutter instability due to the excitation of long gravity waves on the free surface if the velocity of the flow exceeds the phase velocity of the waves and related this phenomenon with the anomalous Doppler effect. In the present work, we derive a full nonlinear eigenvalue problem for an integrodifferential equation for the finite-chord Nemtsov membrane in the finite-depth flow. In the shallow- and deep-water limits, we develop a perturbation theory in the small added mass ratio parameter acting as an effective dissipation to find explicit analytical expressions for the frequencies and the growth rates of the membrane modes coupled to the surface waves. We find an intricate pattern of instability pockets in the parameter space and describe it analytically. The case of an arbitrary depth flow with free surface requires numerical solution of a new non-polynomial nonlinear eigenvalue problem. We propose an original approach combining methods of complex analysis and residue calculus, Galerkin discretization, Newton method, and parallelization techniques implemented in MATLAB to produce high-accuracy stability diagrams within an unprecedented wide range of a system's parameters. We believe that the Nemtsov membrane plays the same paradigmatic role for understanding radiation-induced instabilities as the Lamb oscillator coupled to a string has played for understanding radiation damping.

Influence of separation structure on the dynamics of shock/turbulent-boundary-layer interactions

Shock/turbulent-boundary-layer interactions (STBLIs) are ubiquitous in high-speed flight and propulsion applications. Experimental and computational investigations of swept, three-dimensional (3-D) interactions, which exhibit quasi-conical mean-flow symmetry in the limit of infinite span, have demonstrated key differences in unsteadiness from their analogous, two-dimensional (2-D), spanwise-homogeneous counterparts. For swept interactions, represented by the swept–fin-on-plate and swept–compression–ramp-on-plate configurations, differences associated with the separated shear layers may be traced to the intermixing of 2-D (spanwise independent) and 3-D (spanwise dependent) scaling laws for the separated mean flow. This results in a broader spectrum of unsteadiness that includes relatively lower frequencies associated with the separated shear layers in 3-D interactions. However, lower frequency ranges associated with the global “breathing” of strongly separated 2-D interactions are significantly less prominent in these simple, swept 3-D interactions. A logical extension of 3-D interaction complexity is the compound interaction formed by the merging of two simple interactions. The first objective of this work is therefore to analyze the more complex picture of the dynamics of such interactions, by considering as an exemplar, wall-resolved simulations of the double-fin-on-plate configuration. We show that in the region of interaction merging, new flow scales, changes in separation topology, and the emergence of lower-frequency phenomena are observed, whereas the dynamics of the interaction near the fin leading edges are similar to those of the simple, swept interactions. The second objective is to evolve a unified understanding of the dynamics of STBLIs associated with complex configurations relevant to actual propulsion systems, which involve the coupling between multiple shock systems and multiple flow separation and attachment events. For this, we revisit the salient aspects of scaling phenomena in a manner that aids in assimilating the double-fin flow with simpler swept interactions. The emphasis is on the influence of the underlying structure of the separated flow on the dynamics. The distinct features of the compound interactions manifest in a centerline symmetry pattern that replaces the quasi-conical symmetry of simple interactions. The primary separation displays topological closure to reveal new length scales, associated unsteadiness bands, and secondary flow separation.

Receptivity and stability of hypersonic leading-edge sweep flows around a blunt body

Abstract

Study of the ageing mechanisms of activated carbon supercapacitors by electrothermal simulation and experimental analysis

In view of the growing need for clean energy, supercapacitors (SC), especially those based on activated carbon (AC) and organic electrolyte are attracting great attention for their theoretically infinite life span. However, they still age much faster than expected due to certain mechanisms. Several researches is being conducted to understand these mechanisms, but so far, the chemical reactions at the phase boundary of the activated carbon electrodes and organic electrolyte have been very unclear. Some pathways have not yet been investigated; there is no research on the reactions that can take place between acetonitrile in the vapor phase and the oxides presented on the surface of activated carbons. For this reason, in this study, divided into two parts, the first based on a thermal simulation and the second based on an experimental study, we have systematically described the ageing mechanisms by determining the gas-phase reactions that can occur at the electrode–electrolyte interface. On the one hand, a thermal model of a supercapacitor cell using activated carbon and organic electrolyte technology has been developed. This model allowed us to study the temperature distribution of supercapacitors, and thus to determine the thermodynamic parameters related to the phenomena produced at the electrode–electrolyte interface. On the other hand, a thermo-gravimetric analysis coupled with gas phase infrared spectroscopy on the activated carbons of an aged supercapacitor of the same technology as that used in the simulation was carried out. The results obtained made it possible to identify the chemical groups produced by ageing.

Membrane flutter induced by radiation of surface gravity waves on a uniform flow

Abstract

Study of riblet drag reduction for an infinite span wing with different sweep angles

This paper studies the riblet drag reduction effect for an infinite swept wing under a low Reynolds number using a large-eddy simulation. The results show that the drag reduction ratio is not linear under different sweep angles. The maximum drag reduction ratio in this study is 9.5% for a wing with a 45° sweep angle. The local surface streamline angle and turbulence quantities are calculated to analyze the drag reduction mechanism. The results demonstrate that the riblets considerably suppress the Reynolds stresses above the wing upper surface, while the turbulence kinetic energy in the near wake is increased. A possible relaminarization phenomenon is observed at the middle part of the wing. Quasi-two-dimensional flow structures are observed near the wall, and a peak frequency is considered as the dominant frequency of the region.

Flutter and resonances of a flag near a free surface

We investigate the effects of a nearby free surface on the stability of a flexible plate in axial flow. Confinement by rigid boundaries is known to affect flag flutter thresholds and fluttering dynamics significantly, and this work considers the effects of a more general confinement involving a deformable free surface. To this end, a local linear stability is proposed for a flag in axial uniform flow and parallel to a free surface, using one-dimensional beam and potential flow models to revisit this classical fluid–structure interaction problem. The physical behaviour of the confining free surface is characterized by the Froude number, corresponding to the ratio of the incoming flow velocity to that of the gravity waves. After presenting the simplified limit of infinite span (i.e. two-dimensional problem), the results are generalized to include finite-span and lateral confinement effects. In both cases, three unstable regimes are identified for varying Froude number. Rigidly-confined flutter is observed for low Froude number, i.e. when the free surface behaves as a rigid wall, and is equivalent to the classical problem of the confined flag. When the flow and wave velocities are comparable, a new instability is observed before the onset of flutter (i.e. at lower reduced flow speed) and results from the resonance of a structural bending wave and one of the fundamental modes of surface gravity waves. Finally, for large Froude number (low effect of gravity), flutter is observed with significant but passive deformation of the free surface in response of the flag’s displacement.

Extended Periodic Inspection Policies for a Single Unit System Subject to Shocks

In this paper, two types of failures are taken into account to extend the classical periodic inspection policy for a single unit system when it has failed, in which type I failure can be rectified by a minimal repair and type II failure should be removed by a corrective replacement. More specifically, we investigate three extended periodic inspection models for a system subject to two kinds of distinctive shocks, i.e., a general periodic inspection model where the system is checked at periodic time epochs over an infinite time span (Policy A), a periodic inspection model with the consideration of quality warranty where the system is periodically checked within a maximal inspection number (Policy B), and a random periodic inspection model where the system is either periodically checked or randomly checked, whichever takes place first (Policy C). For each extended model, the average maintenance cost in one renewal cycle under special conditions is minimized to seek the optimal inspection interval theoretically and the numerical example is arranged to authenticate it analytically. Last but not least, comparisons are made among the extended models, indicating that the optimum solution varies from policy to policy.

Performance of Turbulence Models in Simulating Wind Loads on Photovoltaics Modules

The performance of five conventional turbulence models, commonly used in the wind industry, are examined in predicting the complex wake of an infinite span thin normal flat plate with large pressure gradients at Reynolds number of 1200. This body represents a large array of Photovoltaics modules, where two edges of the plate dominate the flow. This study provided a benchmark for capabilities of conventional turbulence models that are commonly used for wind forecasting in the wind energy industry. The results obtained from Reynolds Averaged Navier-Stokes (RANS) k - ε , Reynolds Normalization Group (RNG) k - ε , RANS k - ω Shear Stress Transport (SST) and Reynolds Stress Model (RSM) were compared with existing Direct Numerical Simulations (DNS). The mean flow features and unsteady wake characteristics were used as testing criteria amongst these models. All turbulence models over-predicted the mean recirculation length and under-predicted the mean drag coefficient. The major differences between numerical results in predicting the mean recirculation length, mean drag and velocity gradients, leading to deficits in turbulence kinetic energy production and diffusion, hint at major difficulties in modeling velocity gradients and thus turbulence energy transport terms, by traditional turbulence models. Unsteadiness of flow physics and nature of eddy viscosity approximations are potential reasons. This hints at the deficiencies of these models to predict complex flows with large pressure gradients, which are commonly observed in wind and solar farms. The under-prediction of wind loads on PV modules and over-estimation of the recirculation length behind them significantly affects the efficiency and operational feasibility of solar energy systems.

Establishment of TP53-knockout canine cells using optimized CRIPSR/Cas9 vector system for canine cancer research

BackgroundGenetic engineering technology such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system provides a powerful tool for developing disease models and determining gene functions. Recent interests in canine cancer models have highlighted the necessity of developing genetic engineering tools for dogs. In this study, we attempted to generate optimized CRISPR/Cas9 system to target canine tumor protein 53 (TP53), one of the most crucial tumor suppressor genes, to establish TP53 knockout canine cells for canine cancer research.ResultsWe constructed CRISPR/Cas9 vectors using each of three TP53 gene-targeting guide RNAs (gRNAs) with minimal off-target potential. After transfection, we obtained several clones of TP53 knockout cells containing “indel” mutations in the targeted locus which had infinite cellular life span, resistance to genotoxicity, and unstable genomic status in contrast to normal cells. Of the established TP53 knockout cells, TP53KO#30 cells targeted by TP53 gRNA #30 showed non-cancerous phenotypes without oncogenic activation both in vitro and in vivo. More importantly, no off-target alteration was detected in TP53KO#30 cells. We also tested the developmental capacity of TP53 knockout cells after application of the somatic cell nuclear transfer technique.ConclusionsOur results indicated that TP53 in canine cells was effectively and specifically targeted by our CRISPR/Cas9 system. Thus, we suggest our CRISPR/Cas9-derived canine TP53 knockout cells as a useful platform to reveal novel oncogenic functions and effects of developing anti-cancer therapeutics.

Wing-Propeller Interaction

Paper describes the effect of the distributed electric propulsion system (DEP) on the aerodynamic characteristics of the airplane wing. Using CFD simulation is described the influence of the wake of the propeller on the wing for various ratios of the propeller diameter to the wing chord. Unlike the normal case of wing-propeller interaction, periodic boundary conditions are used, i.e. a rectangular wing with infinite span with propellers installed periodically its span is considered. A wind tunnel experiment will be used to verify the calculations. Propeller thrust is set to compensate for airplane drag in horizontal flight, i.e. equal to the wing segment drag, which is increased by the corresponding part of the expected drag of other parts of the airplane. The increase of the drag was determined by the aerodynamic design of a generic airplane with DEP. The benefit of the work are the input data usable for the conceptual design of the airplane wing with DEP.