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Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper is concerned with the target tracking problem of an autonomous surface vehicle in the presence of a maneuvering target. The velocity information of target is totally unknown to the follower vehicle, and only the relative distance and angle between the target and follower are obtained. First, a reduced-order extended state observer is used to estimate the unknown relative dynamics due to the unavailable velocity of the target. Based on the reduced-order extended state observer, an antidisturbance guidance law for target tracking is designed. The input-to-state stability of the closed-loop target tracking guidance system is analyzed via cascade theory. Furthermore, the above result is extended to the case that collisions between the target and leader are avoided during tracking, and a collision-free target tracking guidance law is developed. The main feature of the proposed guidance law is twofold. First, the target tracking can be achieved without using the velocity information of the target. Second, collision avoidance can be achieved during target tracking. Simulation results show the effectiveness of the proposed antidisturbance guidance law for tracking a maneuvering target with the arbitrary bounded velocity. [ABSTRACT FROM AUTHOR]

Non-axisymmetric profiled endwalls have been shown to reduce losses and secondary flow both in cascades and in rig tests. This paper presents experimental results which quantify the benefits of loss reduction in the cascade with particular attention to accuracy. The paper compares the benefits achieved in experiment to the results predicted by computational fluid dynamics (CFD). The results show that both the experiment and CFD give significant reductions in secondary flow. A reduction of 31 percent in secondary loss has been measured for the best case, but the CFD gives only a small reduction in loss. Previous studies on the planar endwall have shown significant areas of transitional flow, so the surface flow has been studied with the aid of surface-mounted hot films. It was concluded that the loss reductions were not due to changes in regions of laminar and turbulent flow. [ABSTRACT FROM AUTHOR]

Aeroelastic instabilities such as flutter have a crucial role in limiting the operating range and reliability of turbomachinery. This paper offers an alternative approach to aeroelastic analysis, where the sensitivity of aerodynamic damping with respect to main flow and structural parameters is quantified through a surrogate-model-based investigation. The parameters are chosen based on previous studies and are represented by a uniform distribution within applicable intervals. The surrogate model is an artificial neural network, trained and tested to achieve an error within 1% of the test data. The quantity of interest is aerodynamic damping and the datasets are obtained from a linearised aeroelastic solver. The sensitivity of aerodynamic damping with respect to the input variables is obtained by calculating normalised gradients from the surrogate model at specific operating conditions. The results show a quantitative comparison of sensitivity across the different input parameters. The outcome of the sensitivity analysis is then used to decide the most appropriate action to take in order to induce stability in unstable operating conditions. The work is a preliminary study, carried out on a simplified two dimensional compressor cascade and it is aimed at proving the validity of a data-driven approach in studying the aeroelastic behaviour of turbomachinery. To the best of the authors' knowledge, this is the first time a data-driven flutter model has been investigated. The initial results are encouraging, indicating that this approach is worth pursuing in the future. The presented framework can be used as a redesign tool to enhance the flutter stability of an existing blade. [ABSTRACT FROM AUTHOR]

Stability issues in hybrid energy storage systems (HESSs) are the major concern, in addition to the control design challenges of individual modules. In this paper, the stability issues of Z + Z type cascade systems in HESS are focused. The stability issues of cascade systems have been studied for many years. Impedance ratio type criterions in the form of ZS/ZL or ZL/ZS have been proposed to solve these stability issues. However, existing ratio type criteria still have problems in some cascade systems. The terminal characteristics of submodule are studied and the different types of cascade system are defined in this paper. The validity of conventional impedance ratio type criterion would be influenced by the right-half-plane zeros (RHZ) in terminal impedance of submodules in the Z + Z type cascade system. Two improved criteria are proposed for the Z + Z type cascade system: one is improved ratio type criterion considering the RHZ in the terminal impedance of the submodule; the other one is sum type criterion which does not need the information about RHZ in terminal impedance of each submodule. Experimental evidences are provided to prove the validity of these two improved criteria. [ABSTRACT FROM AUTHOR]

In this paper, the long time behavior of a stochastic model is studied when the Contois growth rate is employed in reactor cascades. We first investigate the existence and uniqueness of the positive solution of the model. Then it is followed by the stochastic stability analysis of the equilibria, which is based on the so-called Lyapunov function. Our study shows that under certain condition, both the washout and non-washout equilibria are stochastically stable. At the end of this paper, numerical simulations are carried out to illustrate our theoretical results. [ABSTRACT FROM AUTHOR]

Nanofibers with high surface-to-volume ratio are of significant applications. This paper proposes a novel method for fabrication of particle-like beaded nanofibers and their daughter nanofibers, which are ejected from the surface of charged jets. Polyvinyl alcohol/ash solution is used in the electrospinning process. [ABSTRACT FROM AUTHOR]

Complex systems are challenging to control because the system responds to the controller in a nonlinear fashion, often incorporating feedback mechanisms. Interdependence of systems poses additional difficulties, as cross-system connections enable malicious activity to spread between layers, increasing systemic risk. In this paper we explore the conditions for an optimal control of cascading failures in a system of interdependent networks. Specifically, we study the Bak–Tang–Wiesenfeld sandpile model incorporating a control mechanism, which affects the frequency of cascades occurring in individual layers. This modification allows us to explore sandpile-like dynamics near the critical state, with supercritical region corresponding to infrequent large cascades and subcritical zone being characterized by frequent small avalanches. Topological coupling between networks introduces dependence of control settings adopted in respective layers, causing the control strategy of a given layer to be influenced by choices made in other connected networks. We find that the optimal control strategy for a layer operating in a supercritical regime is to be coupled to a layer operating in a subcritical zone, since such condition corresponds to reduced probability of inflicted avalanches. However this condition describes a parasitic relation, in which only one layer benefits. Second optimal configuration is a mutualistic one, where both layers adopt the same control strategy. Our results provide valuable insights into dynamics of cascading failures and and its control in interdependent complex systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel extended state observer (ESO)-based line-of-sight guidance law for path following of underactuated marine surface vehicles in the presence of time-varying sideslip angle. A reduced-order ESO is employed to identify the vehicle sideslip angle caused by constant ocean disturbances when following a curved path or time-varying ocean disturbances. This guarantees that the sideslip angle can be timely and exactly estimated, and thus contributes to following the desired path with higher accuracy regardless of external disturbances induced by wind, waves, and ocean currents. The input-to-state stability of the closed-loop system is established via cascade theory. It is proven that the transient learning process can be shorten by increasing the bandwidth of the ESO. Both simulation and experimental results are provided to validate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular focus on spectral kinetic energy fluxes Π( K) computed in the isotropic wavenumber ( K) domain. The paper utilizes idealized two-layer quasigeostrophic (QG) models, realistic high-resolution ocean general circulation models, and present-generation gridded satellite altimeter data. Adding horizontal eddy viscosity to the QG model results in a forward cascade at smaller scales, in apparent agreement with results from present-generation altimetry. Eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies. Filtering the output of either the QG or realistic models before computing Π( K) also greatly increases the forward cascade. Such filtering mimics the smoothing inherent in the construction of present-generation gridded altimeter data. It is therefore difficult to say whether the forward cascades seen in present-generation altimeter data are due to real physics (represented here by eddy viscosity) or to insufficient horizontal resolution. The inverse cascade at larger scales remains in the models even after filtering, suggesting that its existence in the models and in altimeter data is robust. However, the magnitude of the inverse cascade is affected by filtering, suggesting that the wide-swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller-scale dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a cascaded H-bridge multilevel boost inverter for electric vehicle (EV) and hybrid EV (HEV) applications implemented without the use of inductors. Currently available power inverter systems for HEVs use a dc-dc boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV traction drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. A cascaded H-bridge multilevel boost inverter design for EV and HEV applications implemented without the use of inductors is proposed in this paper. Traditionally, each H-bridge needs a dc power supply. The proposed design uses a standard three-leg inverter (one leg for each phase) and an H-bridge in series with each inverter leg which uses a capacitor as the dc power source. A fundamental switching scheme is used to do modulation control and to produce a five-level phase voltage. Experiments show that the proposed dc-ac cascaded H-bridge multilevel boost inverter can output a boosted ac voltage without the use of inductors. [ABSTRACT FROM AUTHOR]

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics. [ABSTRACT FROM AUTHOR]

This paper describes a detailed experimental investigation into the effects of reverse compound lean (RCL) in a highly loaded axial turbine cascade. The geometry was designed using fully three-dimensional viscous CFD calculations to achieve a reduction in secondary flow. Traverses were made upstream and downstream with three-hole and five-hole probes to quantify the effects on the flow and losses produced by the leaned blade compared with a prismatic blade. These measurements were supplemented with blade static pressure measurements and surface flow visualization. It was found that the RCL blade produced higher overturning at the end-wall accompanied by higher secondary loss but this was constrained closer to the endwall. Near mid-span, the turning was reduced slightly but the overall turning for the row was unaltered. The mid-span showed much less loss, so that overall the loss was reduced by 11 per cent. An understanding of these effects may be gained by consideration of the three-dimensional effects produced by the RCL. [ABSTRACT FROM AUTHOR]

In the modern society, most networked critical infrastructures are coupled together and can be modeled as interconnected networks. Cascading failures caused by overload in interconnected networks are extremely complicated and still lack of corresponding researches. It is crucial to explore a systematic design and load management method for complex interconnected network. In this paper, a probabilistic heterogeneous capacity allocation model and a preventive load redistribution model are firstly proposed. Based on the novel models failure cascades in interconnected networks are studied in detail. Numerical simulations and analysis results show that robustness of interconnected network depends on the network topology, capacity allocation pattern and load management strategy. The novel models have guiding significance for the design and optimal management of robust interconnected infrastructure networks. [ABSTRACT FROM AUTHOR]

Highlights • Selection of the d 1 determines the N S , at which detectivity reaches maximum. • d 1opt is higher for equal- than for matched-absorbers detectors. • D* MAX is slightly lower for equal- than for matched-absorbers detectors. • Detectivities are comparable for both type of interband cascade detectors. • Total absorber thickness is higher for the matched-absorbers detector. Abstract The paper presents the performance of the interband cascade type-II superlattice infrared photodetectors. Such photodetectors are made up of multiple stages, which are connected in series using an interband tunneling heterostructure. In this paper, we compare two different architectures of the cascade structure: equal absorber thickness in all stages and varied absorber thickness. In our calculation, in the case of equal absorber throughout the structure, we took into account electrical current gain. The selection of the first absorber thickness d 1 determines the number of possible stages N S , at which detectivity reaches maximum value, which is especially important in case of varied absorbers thickness to meet the quantum efficiency condition (equal quantum efficiency in each stage of the device). Optimal first absorber thickness d 1opt is higher for equal absorbers than for matched-absorbers detectors, but maximum value of detectivity is slightly lower. We compared theoretical results with experimental ones, obtaining good agreement. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of boundary layer skew on flow structure, total pressure loss, and flow control technique numerically on a high-loaded axial-flow compressor cascade. We have developed two new models respectively about loss evaluation and end wall flow control mechanism for more specific analysis. The result shows that boundary layer skew weakens the secondary flow and delays the generation of passage vortex when incidence approaches 0°. This results in a reduction of total pressure loss mainly (89.4%) due to relieved corner separation. However, as incidence exceeds a certain value (+7°), severe corner separation or even earlier corner stall can be induced by inlet boundary layer skew. Optimization procedure for profiled end wall at inflow condition of +7° incidence is further carried out to investigate the impact of boundary layer skew on flow control technique. The result shows that boundary layer skew should be counted in the optimization design of profiled end wall because of its significant influence on the development of end wall flow. The optimum profiled end walls for cases with and without boundary layer skew show great difference in the manner of end wall flow control. According to the improvement of cascades’ performance, end wall profiling seems more efficient in reducing loss when influenced by the boundary layer skew. [ABSTRACT FROM AUTHOR]

This paper deals with the trajectory tracking problem of a six-degree of freedom (6- DOF) quadrotor unmanned aerial vehicle ( UAV). The problem of simplified kinematics based on Euler angles is analyzed and the modified Rodrigues parameters ( MRPs) technique is introduced to model the rotational dynamics of the rigid body. A nonlinear system error model is established based on the trajectory tracking problem, and, due to the coupling property between the translational and rotational dynamics, we divide the complete closed-loop system into two reduced-order subsystems and a coupling term. The Rodrigues theorem is applied to analyze the internal connections between the coupling term and MRPs. Therefore, the global stability conclusions, by which the trajectory tracking controller of the quadrotor UAV could be designed based on the subsystem directly in future works, are proved based on several assumptions of the subsystems. Thereafter, the controllers, using the backstepping approach and nonlinear disturbance observer/sliding mode control approach, which stabilize the quadrotor UAV globally [ABSTRACT FROM AUTHOR]

This paper provides an audio 2-1 cascaded ΣΔ modulator using a novel gain-boost class-C inverter. The gain-boost class-C inverter behaves as a subthreshold amplifier. By introducing a gain-boost module, the inverter DC-gain is increased from 48 dB to 67 dB. The gain-boost class-C inverter consumes 57 μW at 1.2-V supply, where the gain-boost module consumes only 3 μW. In addition, an on-chip body bias technique is introduced to compensate the process and supply voltage variations of the class-C inverter. The proposed inverter-based ΣΔ modulator chip is implemented in 0.13-μm CMOS process, and achieves 86-dB peak-signal to noise and distortion ratio (SNDR) and 90-dB dynamic range (DR) over 22.05-KHz bandwidth at 1.2-V supply consuming 360 μW, which demonstrates that the gain-boost class-C inverter is particularly suitable for micro-power high-resolution applications. [ABSTRACT FROM AUTHOR]

Focus of this paper is aerodynamic investigation of tie-boss stabilization devices for extremely long rotor blades. This investigation covered measurements on multiple blade cascades and computational fluid dynamics (CFD) simulation of the flow past these cascades. Conclusions were drawn from results of the measurements and CFD and from the knowledge of prior investigation of the used blade cascade. Main focus of this paper is to describe influence of a tie-boss stabilization device on flow field in interblade channel. Tie-boss with more massive shape proved to cause lesser losses, while tie-boss with a tailored trailing edge showed lesser influence on flow turning. [ABSTRACT FROM AUTHOR]

Motivated by the recent advances in additive manufacturing, a novel turbine end-wall aerothermal management method is presented in this two-part paper. The feasibility of enhancing purge air cooling effectiveness through engineered surface structure was experimentally and numerically investigated. The fundamental working mechanism and improved cooling performance for a 90 deg turning duct are presented in Part I. The second part of this paper demonstrates this novel concept in a low-speed linear cascade environment. The performance in three purge air blowing ratios is presented and enhanced cooling effectiveness and net heat flux reduction (NHFR) were observed from experimental data, especially for higher blow ratios. The Computational fluid dynamics (CFD) analysis indicates that the additional surface features are effective in reducing the passage vortex and providing a larger area of coolant coverage without introducing additional aerodynamic loss. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the dynamics of a fourth-order normal form near a double Takens-Bogdanov bifurcation. The reduced system of this normal form possesses eight pairs of homoclinic orbits for certain parameter values. The nonlinear time transformation method is applied to obtain an analytical approximation of the homoclinic orbit in the perturbed system and to construct the homoclinic bifurcation curve as well. Using numerical continuation, period-doubling and homoclinic-doubling cascades emanating from a codimension-2 bifurcation point are found. A codimension-2 homoclinic-gluing bifurcation point at which several homoclinic orbits concerning the origin glue together to form a new homoclinic orbit is also obtained. It is shown that in the vicinity of these bifurcation points, the system may exhibit chaos and chaotic attractors. [ABSTRACT FROM AUTHOR]

Separation in compressor cascade triggers flow loss and instability. This paper presents a passive flow control method by introducing a slot into the blade. The slot induces self-adapted jet, while the jet flow is used to suppress cascade’s separation. To study the flow control effect, experiments were conducted and flow field details were given by validated numerical simulations. The results show that a well-designed slot carries adequate jet airflow from pressure side (PS) to suction side (SS) due to the great pressure fall between the two sides. The jet airflow delays suction side separation within specific incidence angles, so the performance of cascade achieves considerable improvements. It enables to be concluded that the slot carries jet flow to SS separation zone, and then the self-adapted jet flow re-energizes low momentum fluid and suppresses vortices in the separation which are negative to the cascade flow. [ABSTRACT FROM AUTHOR]

The paper analyzes losses and the loss generation mechanisms in a low-pressure turbine (LPT) cascade by proper orthogonal decomposition (POD) applied to measurements. Total pressure probes and time-resolved particle image velocimetry (TR-PIV) are used to determine the flow field and performance of the blade with steady and unsteady inflow conditions varying the flow incidence. The total pressure loss coefficient is computed by traversing two Kiel probes upstream and downstream of the cascade simultaneously. This procedure allows a very accurate estimation of the total pressure loss coefficient also in the potential flow region affected by incoming wake migration. The TR-PIV investigation concentrates on the aft portion of the suction side boundary layer downstream of peak suction. In this adverse pressure gradient region, the interaction between the wake and the boundary layer is the strongest, and it leads to the largest deviation from a steady loss mechanism. POD applied to this portion of the domain provides a statistical representation of the flow oscillations by splitting the effects induced by the different dynamics. The paper also describes how POD can dissect the loss generation mechanisms by separating the contributions to the Reynolds stress tensor from the different modes. The steady condition loss generation, driven by boundary layer streaks and separation, is augmented in the presence of incoming wakes by the wake-boundary layer interaction and by the wake dilation mechanism. Wake migration losses have been found to be almost insensitive to incidence variation between nominal and negative (up to -9 deg) while at positive incidence, the losses have a steep increase due to the alteration of the wake path induced by the different loading distribution. [ABSTRACT FROM AUTHOR]

Two dimensional turbulence has a remarkable tendency to self-organize into large, coherent structures, forming a mean flow. The purpose of this paper is to elucidate how these structures are sustained and what determines them and the fluctuations around them. A recent theory for the mean flow will be reviewed. The theory assumes that turbulence is excited by a forcing supported on small scales and uses a linear shear model to relate the turbulent momentum flux to the mean shear rate. Extending the theory, it will be shown here that the relation between the momentum flux and mean shear is valid, and the momentum flux is non-zero, for both an isotropic forcing and an anisotropic forcing, independent of the dissipation mechanism at small scales. This conclusion requires taking into account that the linear shear model is an approximation to the real system. The proportionality between the momentum flux and the inverse of the shear can then be inferred most simply on dimensional grounds. Moreover, for a homogeneous pumping, the proportionality constant can be determined by symmetry considerations, recovering the result of the original theory. The regime of applicability of the theory, its compatibility with observations from simulations, a formula for the momentum flux for an inhomogeneous pumping, and results for the statistics of fluctuations will also be discussed. [ABSTRACT FROM AUTHOR]

This paper presents detailed flow-field measurements for a compressor cascade equipped with synthetic jet actuators for active flow control. The synthetic jets are mounted on the cascade sidewall and the suction side surface of the blade to reduce the total pressure loss caused by strong secondary flow structures developing in the passage. There are certain articles reporting that synthetic jets are well suited for flow control applications even in axial compressors and cascades. Most of them are focused on the parameter variation to optimize the efficiency of the control approach, still very little is known on the interaction of the synthetic jet actuators with the flow field. Detailed x-wire and pressure measurements were conducted to understand how synthetic jets influence the flow field and what causes the significant loss reduction in the cascade wake. It seems that the added momentum is not the key parameter for flow control with synthetic jets. In fact, the high mixing and the unsteadiness of the jets seem to amplify existing velocity fluctuations in the flow field. These increased fluctuations result in a shift of the shear layer between the flow separation and the surrounding flow, and thus in a dethrottling of the compressor cascade. Together with the increased mixing, loss reductions of approximately 10% can be reached using synthetic jet actuators. [ABSTRACT FROM PUBLISHER]

In this paper, a wind energy conversion system based on a cascaded H-bridge multilevel inverter (CHBMLI) topology has been proposed to be used for the grid interface of large split winding alternators (SWAs). A new method has been suggested for the generation of reference currents for the voltage source inverter (VSI) depending upon the available wind power. The CHBMLI has been used as a VSI and operated in a current control mode order to achieve the objectives of real power injection and load compensation (power factor correction, load balancing, and harmonic compensation) based on the proposed reference generation scheme. In the field excitation control of SWA provides a single means vary the dc link voltages of all the CHBs simultaneously and proportionately. [ABSTRACT FROM AUTHOR]

ABSTRACT The concept of the sediment delivery problem was introduced into the literature in 1983 by Des Walling. This concept describes how only a fraction of sediment eroded within a catchment will reach the basin outlet and be represented as sediment yield, and that sediment storage mechanisms operating within a catchment explain this discrepancy. Since this paper was published, geomorphologists have been examining in great detail the fate of sediment eroded from the landsurface, and the pathways and timeframes of sediment transport and storage in catchments. However, to fully understand the internal dynamics of sediment flux requires a 'fresh look at the sediment delivery problem'. A framework is required that can incorporate the various processes involved in sediment movement from source areas through a basin to its outlet, and can take account of the spatial distribution of, and timeframes over which, these processes operate. This paper presents a conceptual framework for analysis of catchment (dis)connectivity that incorporates both spatial and temporal variability in the operation of the sediment cascade. This approach examines where blockages occur to disrupt these longitudinal, lateral and vertical linkages in catchments. Depending on the position of blockages (termed buffers, barriers and blankets), and their sediment residence time, various parts of a catchment may be actively contributing sediment to the sediment cascade and be switched on, or inactive and switched off. This paper discusses how such a framework can be used to model response times to disturbance and explain the manifestation of geomorphic change in catchments. The paper then highlights challenges geomorphologists face in applying such a framework to understand the internal dynamics of the catchment sediment cascades, and forecast how environmental change might affect the operation of sediment fluxes into the future. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

With the progress of “more electric aircraft,” introducing active power filter (APF) technology into the aircraft power system to improve its quality and reliability catches growing interest. In this paper, based on the analysis and modeling of the shunt APF with close-loop control, a feedforward compensation path of load current is proposed to improve the dynamic performance of the APF. The two H-bridge cascaded inverter is selected for the aeronautical APF (AAPF). Justifications for topology choosing and corresponding system control method are given. Furthermore, the global framework and operation principle of the proposed AAPF are presented in detail. A prototype with the load power of 7.2 kVA is built and tested in the laboratory. Experimental results verify the feasibility of the proposed AAPF and the high performance of the control strategy during steady-state and dynamic operations. [ABSTRACT FROM AUTHOR]

Analysis of economical aspects of centrifuge-based separation shows that the bulk of the cost is proportional to the number of centrifuges in a cascade. In this paper a program which is called MAKNO is used to obtain the velocity field in a centrifuge by solving popular purely axial flow in a gas centrifuge. Through using MAKNO and solving concentration equation in a single gas centrifuge a realistic function for α, separation factor, in relation to θ, cut, and f, feed flow rate is achieved. To minimize the number of centrifuges in a cascade one needs to determine optimal parameters, α, θ, and f. Finding the optimum solution requires a huge amount of calculation in classical methods. Recently, a genetic algorithm (GA) technique has attracted considerable attention among various modern heuristic optimization techniques. To optimize the parameters and the number of centrifuges for a given cascade a Real Coded Genetic Algorithm program, RCGA, is implemented and developed. It has been shown that the application of RCGA to this problem not only reduces the amount of calculation but also guarantees finding the best solution. It is found that, from an evolutionary point of view, the performance of the GA is excellent. [ABSTRACT FROM PUBLISHER]

Two-dimensional gyrokinetics is a simple paradigm for the study of kinetic magnetised plasma turbulence. In this paper, we present a comprehensive theoretical framework for this turbulence. We study both the inverse and direct cascades (the ‘dual cascade’), driven by a homogeneous and isotropic random forcing. The key characteristic length of gyrokinetics, the Larmor radius, divides scales into two physically distinct ranges. For scales larger than the Larmor radius, we derive the familiar Charney–Hasegawa–Mima equation from the gyrokinetic system, and explain its relationship to gyrokinetics. At scales smaller than the Larmor radius, a dual cascade occurs in phase space (two dimensions in position space plus one dimension in velocity space) via a nonlinear phase-mixing process. We show that at these sub-Larmor scales, the turbulence is self-similar and exhibits power-law spectra in position and velocity space. We propose a Hankel-transform formalism to characterise velocity-space spectra. We derive the exact relations for third-order structure functions, analogous to Kolmogorov's four-fifths and Yaglom's four-thirds laws and valid at both long and short wavelengths. We show how the general gyrokinetic invariants are related to the particular invariants that control the dual cascade in the long- and short-wavelength limits. We describe the full range of cascades from the fluid to the fully kinetic range. [ABSTRACT FROM AUTHOR]

Current disruption (CD) and the related kinetic instabilities in the near-Earth magnetosphere represent physical mechanisms which can trigger multi-scale substorm activity including global reorganizations of the magnetosphere. Lui et al. (2008) proposed a CD scenario in which the kinetic scale linear modes grow and reach the typical dipolarization scales through an inverse cascade. The experimental verification of the inverse nonlinear cascade is based on wavelet analysis. In this paper the Hilbert-Huang transform is used which is suitable for nonlinear systems and allows to reconstruct the time-frequency representation of empirical decomposed modes in an adaptive manner. It was found that, in the Lui et al. (2008) event, the modes evolve globally from high-frequencies to low-frequencies. However, there are also local frequency evolution trends oriented towards high-frequencies, indicating that the underlying processes involve multi-scale physics and non-stationary fluctuations for which the simple inverse cascade scenario is not correct. [ABSTRACT FROM AUTHOR]

This paper presents a possible and reasonable explanation of cascading failure in small-world modular networks. We aim to introduce the CML's method to interpret the mechanism of cascading failure in small-world modular networks with different rewiring probability of inner-module and inter-module. The cascade propagation of such networks with the different initial external perturbation is simulated. Additionally, it is found that the perturbation threshold has close relationships with the modularity, the mean node degree and the rewiring probability. Based on the numerical simulation, we can see that the larger mean node degree can delay the cascading failure process. Furthermore, the small value of rewiring probability and larger modularity can efficiently delay the breakdown caused by the cascading failure. It is particularly important for controlling the cascading failure process in small-world modular networks. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional two-objective procedure for minimizing dynamic loading and maximizing efficiency in multi-stage compressors. The procedure arises from the combination of an evolutionary algorithm and a CFD code, in which a sliding mesh technique and a time-dependent approach are implemented, enabling the study of unsteady rotor-stator interaction. The method is then applied to a two-stage compressor cascade (rotor-stator-rotor-stator). The results concerning the optimal set of geometrical parameters considered for optimization (axial distances between successive cascades, circumferential clocking between stators and between rotors) are finally presented and discussed. [ABSTRACT FROM AUTHOR]

The paper provides a method of selecting controller settings in cascade system when the controlled system may be considered as an inertial element connected to inertial element with time delay. The transfer function has been replaced with its expansion to Pade's series. The proposed method grounds on locating the roots of denominator of the transfer function describing the closed system. Step responses without any overshoot were achieved. The mathematical model of the controlled system may be used to describe a series of power engineering systems. [ABSTRACT FROM AUTHOR]

This paper proposes a secondary flow control concept using Endwall jet fence (EJF). A parametric investigation concerning the variations of the jet location along the axial and pitch-wise direction as well as the skew angle is conducted numerically to validate the potential of EJF in a high-speed compressor cascade with an inlet Mach number of 0.67. And then the interaction mechanisms between the EJF and the endwall secondary flow are discussed in detail. The results show that the EJF could reduce the corner separation and losses significantly by inputting transverse momentum component, inducing a concentrated jet vortex to block the pitch-wise migration of the passage vortex as well as enhancing the energy exchange between the endwall boundary layer and the mainstream. The jet location and the skew angle are important for the influence of EJF on the cascade performance. In this work, a maximum total pressure loss reduction of 11.6 % is obtained by the EJF located at 30 % of the axial chord and 10 % of the pitch with a skew angle of β = 40°, whereas the jet-to-inflow mass flow ratio is only about 0.4 %, validating the high efficiency of this flow control concept. For the off-design points, the EJF also shows appreciable potential on the endwall secondary flow control and loss reduction. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of improving the aerodynamic performance of low pressure turbine (LPT) blade cascades and developing low solidity LPT blade cascades through deflected trailing edge. A deflected trailing edge improved aerodynamic performance of both LPT blade cascades and low solidity LPT blade cascades. For standard solidity LPT cascades, deflecting the trailing edge can decrease the energy loss coefficient by 20.61% for a Reynolds number (Re) of 25,000 and freestream turbulence intensities (FSTI) of 1 %. For a low solidity LPT cascade, aerodynamic performance was also improved by deflecting the trailing edge. Solidity of the LPT cascade can be reduced by 12.5% for blades with a deflected trailing edge without a drop in efficiency. Here, the flow control mechanism surrounding a deflected trailing edge was also revealed. [ABSTRACT FROM AUTHOR]

Previous work has shown that low-stagger contouring near the endwall of a nominally high-lift and high-stagger angle front-loaded low-pressure turbine (LPT) airfoil is successful in reducing endwall loss by limiting the development and migration of low momentum fluid associated with secondary flow structures. The design modification that leads to loss reduction in that study was determined from an intuitive approach based on the premise that reducing flow separation near the endwall will lead to reduced loss production. Those authors also relied heavily upon Reynolds-averaged Navier-Stokes (RANS) based computational tools. Due to uncertainties inherent in computational fluid dynamics (CFD) predictions, there is little confidence that the authors actually achieved true minimum loss. Despite recent advances in computing capability, turbulence modeling remains a shortcoming of modern design tools. As a contribution to overcoming this problem, this paper offers a three-dimensional (3D) view of the developing mean flow, total pressure, and turbulence fields that gave rise to the loss reduction of the airfoil mentioned above. Experiments are conducted in a linear cascade with aspect ratio of 3.5 and Re?=?100,000. The results are derived from stereoscopic particle image velocimetry (PIV) and total pressure measurements inside the passage. Overall, the loss reduction correlates strongly with reduced turbulence production. The aim of this paper is to provide readers with a realistic view of mean flow and turbulence development that include all the components of the Reynolds stress tensor to assess, at least qualitatively, the validity of high fidelity computational tools used to calculate turbine flows. [ABSTRACT FROM AUTHOR]

Effect of turbine endwall contouring on its aerodynamic performance has been widely studied, but only a few studies are available in the open literature investigating its effect on heat transfer performance; especially at transonic exit Mach number conditions. In this paper, we report a study of effect of contouring on endwall heat transfer performance of a high-turning high-pressure (HP) turbine blade passage operating under transonic exit conditions. The paper describes comparison of heat transfer performance of two contoured endwall geometries, one aerodynamically optimized (AO) and the other heat transfer optimized (HTO), with a baseline, noncontoured geometry. The endwall geometries were experimentally investigated at Virginia Tech's transient, blow down, transonic linear cascade facility at three exit Mach numbers, Mex= 0.71, 0.88(design) and 0.95, for their heat transfer performance. Endwall surface temperatures were measured using infrared (IR) thermography and local heat transfer coefficient (HTC) values were calculated using measured temperatures. A camera matrix model-based data postprocessing technique was developed to relate the two-dimensional images captured by IR camera to three-dimensional endwall contours. The measurement technique and the methodology for postprocessing of the heat transfer coefficient data have been presented in detail. Discussion and interpretation of experimental results have been augmented using aerodynamic CFD simulations of the geometries. Both the contoured endwalls demonstrated a significant reduction in the overall average heat transfer coefficient values of the order of 10%. The surface Stanton number distributions also indicated a reduction in the level of hot spots for most of the endwall surface. However, at some locations an increase was also observed, especially in the area near the leading edge (LE). The results indicate that the endwall contouring could significantly improve heat transfer performance of turbine passages. [ABSTRACT FROM AUTHOR]

The paper presents a detailed analysis of particle image velocimetry (PIV) measurements performed in a turbine cascade representative of highly accelerated low-pressure turbine (LPT) blades. Two cameras have been simultaneously used to observe a great portion of the suction side boundary layer with the highest possible spatial resolution, thus allowing us to solve the interaction process between impinging upstream wakes and the blade boundary layer. Four unsteady inflow conditions, characterized by different incoming wake reduced frequencies and flow coefficients, have been examined at fixed Reynolds number. The highly resolved flow fields have been processed to explore reduced frequency and flow coefficient effects on the boundary layer unsteady transition process and, consequently, on loss production. For a deep physical insight on the mechanisms responsible for loss generation, proper orthogonal decomposition (POD) has been applied at different phases of the wake passing period. This has provided the dominant structures affecting the cascade aerodynamics during the wake period. Moreover, the examination of POD modes has allowed us to show the effects induced by the parameter variation on the turbulent kinetic energy production and thus to the unsteady loss production mechanisms. [ABSTRACT FROM AUTHOR]

For effective validation of computational fluid dynamics (CFD) codes for design, numerical simulations must be compared and contrasted with experimental data sets which are well posed and measured. This paper presents, with the emphasis placed primarily upon the description and explanation of the experimental results, a test case designed for CFD validation concerning the flow field generated by the presence of tip clearance in an annular cascade turbine blade row. The test case is based upon a moderately loaded prismatic blade profile, operating with axial inflow and a nominal mid-span exit Mach number of 0.5. In addition to the case with no clearance, three gap heights, representing 1, 3 and 5 per cent of chord length have been selected. These tip clearances were chosen because they represent three conditions where the tip clearance is below, approximately equal to and substantially larger than the inlet boundary layer displacement thickness. At the leading edge this produces different behaviours, with the smallest gap producing a stagnation point, equivalent to the case without tip clearance, while the largest clearance allows throughflow over the leading edge into the tip gap. In the presence of larger tip clearances, the tip leakage flow induces a stagnating flow in the trailing-edge region, which results in a large area of blocked flow in the blade passage downstream of the trailing edge. [ABSTRACT FROM AUTHOR]

This paper describes a methodology for planning rehabilitation of small-scale irrigation systems in dry zones where the hydrologic database is poor. The methodology includes a two-stage decision-making process. The first stage relates to selection of cascades (meso-watersheds) within the basin for rehabilitation planning. The second stage is concerned with selection of tanks within a cascade and the type of rehabilitation components to be planned, taking into consideration the resource potential of the cascade and the socioeconomic factors of farmers. The methodology has been field-tested in Sri Lanka and shown to be efficient. A key principle underlying this approach is that development of any use of water within a basin must be viewed in the context of the whole basin to avoid conflicts over water use. Another principle is that hydrological and non-hydrological criteria must be used together to evaluate water resources development proposals. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of a hybrid 13-level inverter, which consists of three cascaded H-bridges per phase. Each H-bridge produces 5-level voltages. The proposed approach can be extended to any desired number of levels. Extensive simulation results of the proposed inverter are presented. Several aspects as total harmonic distortion factor of the inverter output currents, and voltages, harmonic content, frequency spectrum distribution, and switching power losses are studied to determine an optimal operation point of the inverter. The simulations are validated by hardware-in-the-loop experimental results. [ABSTRACT FROM AUTHOR]

The sediment (dis)connectivity concept is the water-mediated transfer of sediment between different compartments of a catchment sediment cascade involving four possible dimensions or linkages (longitudinal, lateral, vertical and temporal). Quantifying the strength of these linkages within and between compartments provides a means to understand the internal sediment flux dynamics of a catchment. The aims of this paper are to examine (1) the dynamics of longitudinal and lateral (dis)connectivity by quantifying patterns of erosion and deposition that occurred during a catastrophic flood, and (2) how the patterns of connectivity can be changed through management actions that better utilise floodplain sediment storages. Multi-temporal LiDAR and air photos are used to quantify volumetric change with respect to geomorphic settings and units. The results show that over the length of the trunk stream, the high-magnitude event was net depositional with high longitudinal sediment disconnectivity. At the reach scale, an alternating pattern of high and low longitudinal connectivity associated with contraction and expansion zones was evident. The efficiency of sediment transfer from the uppermost compartment to the most downstream compartment decreased exponentially, while the strength of lateral connectivity increased for each expansion reach. Modelling results show that increasing channel boundary roughness along expansion reaches with riparian revegetation can increase the frequency of lateral connectivity and floodplain sediment storage, thereby decreasing reach-to-reach connectivity and reducing end-of-catchment sediment delivery. This contrasts with the current trend of building levees along the bank tops of expansion reaches, which decrease lateral connectivity and increase reach-to-reach connectivity. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel transcritical cascade-Organic Rankine Cycle (C-ORC) system was proposed for recovering multi-grade waste heat from a typical heavy-duty diesel engine. The C-ORC comprises a high temperature ORC loop (HT-Loop) and a low temperature ORC loop (LT-Loop) for recovering waste heat from engine exhaust gas (EG), exhaust gas recirculation (EGR), jacket water (JW) and charge air (CA) in a cascaded pattern. The basic thermodynamic evaluation on energy and exergy aspects were covered in the companion piece-‘Part A-thermodynamic evaluations’, indicating that the proposed C-ORC possesses great heat-recovery capacities and efficiency-promotion potentials. The techno-economic evaluations in Part B of this paper will further explore the performance of the C-ORC system based on costs and benefits in order to reveal its practical benefits. Four techno-economic indexes are mainly focused on: component-to-system cost ratio (CSCR), electricity production cost (EPC), depreciated payback period (DPP) and savings-to-investment ratio (SIR). Under rated engine conditions, working fluids were initially compared to find the most economical fluids for the HT-Loop and the LT-Loop respectively. Results indicated that toluene and R143a still make the perfect match for the C-ORC with the lowest EPC (0.27 Dollar/kW h), DPP (7.8 years) and the highest SIR (1.6). As to component-to-system cost ratio (CSCR), the cost of expanders and heat exchangers together account for more than 3/4 of the total system cost, and the expander of the LT-Loop is the most costly single component. The C-ORC’s techno-economic performance was further evaluated based on engine’s practical operating conditions. Results showed that, under available conditions, the CSCR of expanders is within 25.9–48.0%, and it gradually increases as engine’s speed and torque increase; the CSCRs of heat exchangers and pumps are within 31.1–54.8% and 17.7–22.5% respectively. The EPC, DPP and SIR are within 0.27–0.48 Dollar/kW h, 8.5–20.5 years and 0.85–1.6 respectively, and according to their similar variations, an increase in engine speed will evidently benefit three indexes. In addition, the increasing torque will also improve the indexes to some extent. Summarily, the techno-economic evaluations in Part B of this paper further reveal the C-ORC’s merits and drawbacks, and in order to improve its full performance, provide directions for optimizations for higher system capacities and commercial potentials. [ABSTRACT FROM AUTHOR]

In this paper, we develop sufficient conditions for uniform asymptotic stability of interconnected dynamical systems that are not in cascade form. We show that the stability analysis of a two-subsystem interconnection can be reduced to ensuring the stability of the first nonisolated subsystem with respect to its own state vector (partial stability) and the stability of the isolated second subsystem. In addition, based on the above results, we provide a control design framework for nonlinear systems where the control objective reduces to stabilization of only a part of the system state while guaranteeing the stability for the entire state of the system. We validate the efficacy of the proposed control framework via simulations and experiments using the wheeled mobile robot platform. [ABSTRACT FROM AUTHOR]