The paper summarized the experimental studies of adaptive structure vibration control in Nanjing University of Aeronautics and Astronautics (NUAA). Two kinds of experimental setups are constructed, i.e. an adaptive feedback control setup and an adaptive feedforward control setup. The former is used for free vibration control, and the control law is realized by the Intel 80X87 floating point processor. A Single Input and Single Output (SISO) control strategy is presented and extended to Multi-Input and Multi-Output (MIMO) systems. Its adaptabilities to the locations of sensors and actuators are also evaluated. The latter is suitable for forced vibration control, e.g. periodic vibration control and random vibration control. Its theoretical base is adaptive filtering theory. Its data acquisition and control law calculation are finished by the master/slave computers. The master computer — an IBM PC or a compatible PC — is responsible for data acquisition, and the slave computer — the TMS320C30 Digital Signal Processor (DSP) — calculates the control law. The results for both periodic vibration control and random vibration control are shown.

An on-board rotor-bearing system operating at high speed is inevitably subjected to additional inertial forces and parametric excitations caused by aircraft maneuvering flights. The differential equations of motion for a squeeze film damped rotor system moving with the aircraft during maneuvering flight are derived based on Lagrange’s principle. Transient characteristics of the rotor system considering instantaneous static eccentricity of journal in turning maneuver are calculated by Newmark-HHT integration method. The effects of forward speed, radius of curvature, and elastic support stiffness on transient responses are discussed subsequently. The results indicate that when the aircraft conducts a maneuvering flight, the whirl orbit of journal deviates from the center of the damper, and the deviation direction is determined by the centrifugal acceleration of aircraft and the additional gyroscopic moment. The journal performs a nonsynchronous whirl around the instantaneous static eccentricity. Its magnitude is related to the additional maneuvering loads and the stiffness of elastic support. Increasing forward speed or decreasing maneuvering radius, the rotor vibration will enter earlier into or withdraw later from the relatively large eccentric condition. The stiffness of elastic support has a great impact on transient characteristics of rotor-bearing system during maneuvering flight. Overall, using finite element modeling combined with mechanism analysis, a flexible and efficient approach is proposed to predict transient responses of engine rotor systems during aircraft maneuvering flights.

This paper studies the effect of the the caudal fin superimposed chordwise deformation on the propulsion performance. The calculation results show that the appropriate chord deformation of the caudal fin can effectively increase the propulsion efficiency. It describes the shape change of dolphin tail by mathematical formula, and studies the propulsion performance of dolphin tail by numerical method combined with morphing mesh technology. The quasi-propulsive efficiency is used to evaluate the propulsive efficiency of self-propelled objects. The results show that the active deformation of the caudal fin can effectively increase the propulsive efficiency and provide a theoretical basis for the design of the flapping bionic propeller.

The supercritical carbon dioxide (sCO 2 ) power generation system holds tremendous potential in nuclear, chemical and renewable energy utilization fields due to its compactness, security and high efficiency. However, the dramatic variation in the physical property of sCO 2 complicates the system analysis and optimization. Recent researches usually took simple stack of all governing equations of individual components as the physical model of system. Besides, based on the traditional heat transfer modeling method, some researches apply the segmentation method to take fluid property variation into consideration. These methods exacerbate the multivariate nonlinearity of the system and are not suitable to analyze complex sCO 2 thermal systems. Moreover, taking the consideration of the strong nonlinearity of sCO 2 system, most researches adopt single parameter analysis to obtain the optimum solution, which may not achieve global optimization. In this contribution, introduction of a new definition of thermal resistance of heat exchanger disassembles the original implicit nonlinear properties of heat transfer processes as the linear relation between inlet temperature difference of fluids and heat flow rate, and the explicit nonlinear expression of thermal resistance. For the nonlinearity caused by the variable properties of sCO 2 , segmentation is also used in heat exchanger modeling. However differently, the introduction of new defined thermal resistance enables the elimination of most intermediate variables produced by segmentation, which contributes to the connection of all segments in heat exchanger into a heat exchanger network. Furthermore, based on the system layout, the equivalent power flow diagram of the system is built to derive the corresponding governing equations revealing the overall transfer and conversion laws of heat. Combining the flow resistance balance equations of all components and the accompanying power flow processes constraints offers the inherent physical constraints among operating parameters. Benefit from the conciseness of system model, the genetic algorithm can be used for the model optimization. Taking thermal efficiency of the system as the optimization objective, the optimal matching of the operating parameters under variable working conditions is obtained.

Due to the peculiar physical properties, supercritical carbon dioxide (sCO 2 ) is considered as a promising working fluid in power generation cycles with high reliability, simple structure and great efficiency. Compared with the general thermal systems, the variable properties of sCO 2 make the system models obtained by the traditional modelling method more complex. Besides, the pressure distribution in the system will affect the distribution of the fluid properties, the fluid properties influencing the heat transfer process will produce an impact on the temperature distribution which will in turn affect the pressure distribution through the mass flow characteristics of all components. This contribution introduces the entransy-based power flow method to analyze and optimize a recompression sCO 2 power generation system under specific boundary conditions. About the heat exchanger, by subdividing the heat transfer area into several segment, the fluid properties in each segment are considered constant. Combining the entransy dissipation thermal resistance of each segment and the energy conservation of each fluid in each segment offers the governing equations for the whole heat transfer process without any intermediate segment temperatures, based on which the power flow diagram of the overall heat transfer process is constructed. Meanwhile, the pressure drops are constrained by the mass flow characteristics of each component, and the inlet and outlet temperatures of compressors and turbines are constrained by the isentropic process constraints and the isentropic efficiencies. Combining the governing equations for the heat exchangers and the constraints for turbine and the compressors, the whole system is modeled by sequential modular method. Based on this newly developed model, applying the genetic algorithm offers the maximum thermal efficiency of the system and the corresponding optimal operating variables, such as the mass flow rate of the working fluid in the cycle, the heat capacity rate of the cold source and the recompression mass fraction under the given heat source. Furthermore, the optimization of the system under different boundary conditions is conducted to study its influence on the optimal mass flow rate of the working fluid, the heat capacity of the cold source and the maximum system thermal efficiency. The results proposes some useful design suggestions to get better performance of the recompression supercritical carbon dioxide power generation system.

Performance improvement of heat recovery systems has huge potential for energy conservation but puzzles researchers due to the nonlinear coupled properties. The traditional modelling approaches focus on individual components, which introduces numerous non-independent variables and further complicates the system optimization. In this contribution, through the thermo-electric analogy method, the equivalent power flow diagram is built based on the system layout, then the corresponding governing equations are derived according to the circuitous philosophy, which reveals the overall transfer and conversion laws of heat. Then, by analyzing the pressure variations of fluids in various components, the flow resistance balance equations are established, which describes the pressure distribution in circulation loop. Moreover, through combining with the coupling relations between the temperatures and pressures of fluids, the inherent physical constraints among operating parameters are revealed by introducing few intermediate variables, which provides convenience for model computation. On this basis, through reasonably matching the mass flow rates of working fluids, the net power generation is maximized under variable working conditions. The optimization results indicate the parameters variation of flue gas significantly impacts the optimal operating state of system, while the empirical constant backpressure operation strategy apparently deviates from the optimums, and the most deviation reaches 8.2%.

Simulations of propeller E1619 of two models with different scales are presented using an in-house numerical code based on the solution of the Reynolds averaged Navier-Stokes equations for the purpose of analyzing the scale effect on propellers. Propeller open water performance at given advance coefficient was obtained and compared against experimental data, showing good agreement. In aspect of CFD results, scale effect is not obvious. ITTC’78 Performance Prediction Method is applied to correct both experimental and computational open water performance of model 1. Computational K T of model 2 and corrected K T of model 1 agrees well, but the difference between computational K Q of model 2 and corrected K Q of model 1 is not neglectable. The locations of the tip vortex core of the two models are similar to each other, and so is the pressure and fluid velocity distribution. The absolute value of pressure on the blades of the smaller model is higher than the bigger model. The fluid axial velocity around the smaller model is higher than the bigger model.

A dual-rotor system with an intershaft bearing subjected to mass unbalance and base motions is established. Using Lagrange’s principle, equations of motion for dual-rotor system relative to moving base are derived. Rotary inertia, gyroscopic inertia, transverse shear deformation, mass unbalance, and six components of deterministic base motions are taken into account. Using state-space vector, steady-state characteristics of dual-rotor system are analyzed through dual-rotor critical speed map, mode shapes, unbalance responses considering base rotations, frequency responses due to base motions, and shaft orbits. The results show that base translations just add external force vectors, while base rotations bring on parametric system matrices and additional force vectors. Base rotations not only change natural frequencies of dual-rotor system, but also break the symmetry of dynamic characteristics in the case of base lateral rotation. Excited by base harmonic translation, resonant frequencies correspond to whirl frequencies. The orbit remains circular under base axial rotation, while it becomes elliptical with a static offset under lateral rotation and then a complicated curve due to harmonic translation. When harmonic frequency of base translation gets close to dual-rotor excitation frequencies, obvious beat vibration appears. Overrall, this flexible approach can ensure calculation accuracy with high efficiency and good expandability.

Using Newmark-Hilber-Hughes-Taylor (Newmark-HHT) integration method, transient characteristics of the dual-rotor system with an intershaft bearing subjected to mass unbalance and base motions during start-up are illustrated. Rotary inertia, gyroscopic moment, shear deformation, mass unbalance and deterministic base motions are considered. Due to variable angular velocities, additional stiffness matrices associated with rotating angular accelerations are also introduced in the equations of motion. The effects of base motion parameters on the dynamic characteristics of the dual-rotor system are discussed, including base axial rotation, lateral rotations, and harmonic translations. The results show that base axial rotation significantly changes the transient critical speeds and resonant amplitudes of the dual-rotor system. In the case of base lateral rotation, the center of the orbit is no longer on the bearing centerline, but with a dynamic offset. When increasing the rotating speeds, the dynamic offset becomes greater. Unlike base lateral rotation, base harmonic translation doesn’t result in dynamic offset, but it amplifies response amplitudes over the entire range of rotating speed. In conclusion, it provides a flexible approach with high efficiency and good expandability to predict transient responses of dual-rotor systems under base motions, and to prevent dual-rotor systems against potential excessive vibration in the design phase.

Using molecular dynamics (MD) simulations, we explore the structural stability and mechanical integrity of phosphorene nanotubes (PNTs), where the intrinsic strain in the tubular PNT structure plays an important role. It is proposed that the atomic structure of larger-diameter armchair PNTs (armPNTs) can remain stable at higher temperature, but the high intrinsic strain in the hoop direction renders zigzag PNTs (zigPNTs) less favorable. The mechanical properties of PNTs, including the Young’s modulus and fracture strength, are sensitive to the diameter, showing a size dependence. A simple model is proposed to express the Young’s modulus as a function of the intrinsic axial strain which in turns depends on the diameter of PNTs. In addition, the compressive buckling of armPNTs is length-dependent, whose instability modes transit from column buckling to shell buckling are observed as the ratio of diameter/length increases.

Through strain-induced morphological instability, protruding patterns of roughly commensurate nanostructures are self-assembled on the surface of spherical core/shell systems. A three-dimensional (3D) phase field model is established for closed substrate. We investigate both numerically and analytically the kinetics of the morphological evolution, from grooves to separated islands, which is sensitive to substrate curvature, misfit strain and modulus ratio between core and shell. The faster growth rate of surface undulation is associated with the core/shell system of harder substrate, larger radius or misfit strain. Based on a Ag core/SiO 2 shell system, the self-assemblies of protruding SiO 2 nano-islands are explored experimentally. The numerical and experimental studies herein could guide the fabrication of ordered quantum structures via surface instability on closed and curved substrates.

As the frequency of supply chain disruptions rises, businesses are increasingly realizing the value of supply chain resilience. A number of efforts has been devoted to define supply chain resilience or to develop risk mitigation strategies in order to maximize supply chain resilience. However, very few scholarly work has attempted to address how supply chain resilience should be quantified. This paper is dedicated to fill this gap by proposing a general framework for evaluating supply chain resilience. The proposed framework captures risks involved in the supply, the demand, the firm itself, and the external environment. In addition to risks, the framework also relates resilience to the supply chain’s risk prognosis capabilities, recover agility and recover time tolerance. Two example applications are used to demonstrate how this framework can be utilized to assess the effectiveness of risk mitigation strategies in supply chain design.

An experimental, flow visualization study was conducted for flow condensation in 1-mm diameter mini-gaps with a visualization window. The hydrophilic channel was composed of bare copper, while the hydrophobic channel was coated with Teflon AF™. An open loop steam experimental apparatus was constructed, and single-phase validation tests are presented. For flow condensation in the hydrophilic gap, filmwise condensation was observed for all cases with a mass flux range of 30–100 kg/m 2 s. In contrast, the hydrophobic channel promoted dropwise condensation at mass fluxes of 30 and 50 kg/m 2 s. Cycles of droplet nucleation, growth and coalescence, and sweeping were identified at both mass fluxes in the hydrophobic channel at steady state. Droplets departed at a smaller sizes and more frequently at the higher mass flux, demonstrating the effects of shear forces on droplet sweeping. Based on flow visualizations, three droplet sweeping methods were identified: interfacial shear stress, upstream droplets, and absorbing into rivulets.