Abstract:The fifth-order accurate explicit HWCNS(hybrid cell-edge and cell-node weighted compact nonlinear schemes) was used to solve Reynolds averaged NavierStokes equations. The grid convergence study of 30P-30N was performed by generating multi-block structured grids. The effects of HWCNS and the secondorder accurate MUSCL on pressure distribution and velocity profiles at typical stations were studied using SA turbulence model without regarding transition, furthermore the numerical and experimental results were compared and analyzed. The trapezoidal wing was numerically simulated using HWCNS and SA turbulence model, and the application performance of HWCNS for low-speed complex configuration flows was discussed by analyzing the aerodynamic characters and the pressure distribution.Simulation results indicate that the pressure distribution of 30P-30N is simulated with the fully turbulent model accurately; as for the trapezoidal wing, HWCNS shows good simulation performance when dealing with the attached flow and small flow separation.

Abstract:In order to evaluate the influence of transition on the vortex structure of delta wing, a numerical simulation of VFE-2 rounded leading edge delta wing was carried out by using a high-order scheme-weighted compact nonlinear scheme and the γ－Re_θ transition model. A comparisons between calculated results and experiment data indicate that the leading edge vortex begins at a certain distance of the wing apex and the transition has great influence on the onset of leading edge vortex. Using turbulence model without transition, the leading edge separation is delayed much, while with transition model the calculated results show a good agreement with experiment data. With transition model, numerical simulation on VFE-2 rounded leading edge delta wing at variation of the angle-of-attack was carried out. The calculated results which agree well with experiment data show that at a low angle-of-attack, there is no separation-induced leading-edge vortex, but with the increase of angle-of-attack the leading edge separation displays being closer to the trailing edge and moves upstream.

Abstract:In order to accurately simulate the transition in aeronautical engineering, the low speed flat plate data was adopted for the calibration of γ－Re_θ transition model based on high-order WCNS (weighted compact nonlinear scheme) on the platform of high-order numerical wind tunnel. Based on the calibrated transition model, the flow over the low speed airfoil was investigated. Comparison between the calculated results and the experiment data indicates that the γ－Re_θ transition model based on WCNS can predict the location of nature transition, bypass transition or separation transition very well and has low mesh sensitivity; only the transition model can calculate the drag coefficient accurately within a moderate Reynolds number range where the length of the laminar flow region is comparable to that of the turbulent flow region.

Abstract:According to the data interpolation problems between the old and new grid in the mesh reconstruction, a flow field information transmission algorithm based on the lattice format supported finite volume method was proposed. In order to realize information transfer between the two sets of the grid, the old cells were moved to the new grid cells by using the unstructured dynamic grid technology and the control equation was solved in time domain, then the datum was assigned to the new grid cells. Result shows that the interpolation error is not introduced in the process of information transmission, the theory precision of the method is equal to the precision of information transmission, and the verification results show that the proposed method is significantly better than that of the second order interpolation method.

Abstract:The influence of ducted fan profile parameters to aerodynamic characteristics was investigated. The threedimensional incompressible viscous NavierStokes equations and SST k-ω turbulence model were used to simulate the complex flow of a 2-blade propeller, which was based on the sliding mesh method. To demonstrate the feasibility of the method, the result was compared with the experimental data. The influences of the lip shape, diffuser angle, the height of duct on aerodynamic characteristics and the flow field were analyzed under the condition of hovering and within the limits of 3000 r/min to 8500 r/min. The thrust coefficient was produced by the ducted fan under the condition that the elliptical lip is smaller than the others, and its aerodynamic efficiency is very low. The power coefficient is the smallest when the diffuser angle is 8.2°. The flow separation emerges nearer to the duct under the propeller disk, with the increase of diffuser angle. The sensitivity of thrust coefficient to the change of ducted fan height is low. The power coefficient descends slightly with the increase of height.

Abstract:In order to seek a sidewall compression method to weaken the interaction between swept shock waves of the same side and boundary layers, the three-dimensional flatplate boundary layer generated by the interaction of two swept shock waves of the same side and the flat-plate boundary layer was numerically studied. The flow mechanism of this three-dimensional boundary layer was analyzed. Also, the three-dimensional boundary layer was quantitatively compared with the one generated by one swept shock wave which has the same flow deflection angle. The results show that, in the case of two swept shock waves, the first swept shock wave makes the boundary layer next to the sidewall thinner, so the interaction between the second shock wave and the boundary layer in the attachment region becomes weaker, leading to the total effect that the interaction between two shock waves and the boundary layer is weaker than that at the one swept shock wave case; the total flow deflection angle of two swept shock waves is the same as one shock wave case, so the strength of the converged shock wave is essentially the same; the three-dimensional boundary layer generated by the swept shock is still conical, and the angle between the separation line and the inflow is essentially the same with the one swept shock case.

Abstract:In order to improve the computational performance of the WENO scheme, a new WENO scheme, namely WENO-E scheme was constructed, which reduces dissipation close to discontinuities. Based on the analysis of the algorithm for weighted factors in the classical WENO scheme (namely WENO-JS) proposed by Jiang and Shu, the new scheme was constructed by introducing indirect smooth indicator. Theoretical analysis shows that the WENO-E scheme can reach the same convergence order of WENO-JS with the same computational efficiency; while it can obtain smaller truncation errors at smooth parts of the solution and higher resolution close to the discontinuities with the same grids than the WENOJS. Subsequently, compared with the classical WENO scheme, when numerical experiments with the linear transport equation, the nonlinear Burgers equation and the one dimensional Euler system of equations are conducted, the WENO-E scheme achieves better numerical solutions.

Abstract:For the verification and validation of SSG/LRR-ωReynolds stress model, four typical two dimensional cases from NASA turbulence resources website were chosen, including zero pressure gradient flat plate, bump-in-channel, airfoil near-wake and flow over NACA0012 airfoil. A part of numerical results were in good agreement with that of CFL3D. For flow over NACA0012 airfoil, lift coefficients of Reynolds stress model and SA model were compared. It is obvious that near the stall angle of attack, Reynolds stress model has advantages over SA model. Based on these results, SSG/LRR-ωReynolds stress model was applied to the simulation of complex DLR-F6 wingbody configuration. Pressure coefficient in typical stations is comparable to that of experiment. Besides, small range of separation in the wing-body intersection is well captured. 

Abstract:Hypersonic low enthalpy laminar flows of double cone with 25°/55° geometry were simulated by using high-order WCNS (weighted compact nonlinear schemes), and their capabilities to accurately predict laminar shock wave/boundary layer interaction were examined. The simulations were performed through adopting the second order MUSCL, the third-order and the fifth-order WCNS as spatial discretization schemes, employing the secondorder dual time-stepping approach for time integration and using different flux functions, such as hybrid Roe-Rusnov, AUSMPW+ and Van Leer, for comparison. The effects of high-order methods on time and grid convergence, as well as the dissipation characteristics of flux functions, were analyzed. The numerical simulation results indicate that the highorder methods can obtain well-resolved results on coarse grid and eliminate the sensitivity of flux functions. However, the high-order methods need longer computational time to reach convergence. The computed results show good agreement with the experimental data, and the computational accuracy may be characterized as reasonable for most engineering purposes.

Abstract:For the influence of tail cavity on hydrodynamic damping force, a method was proposed by combing the rotating reference frames and cavity multiphase flow simulation techniques and solving the Reynolds averaged NS equations. Numerical research indicates that the unbalance of vehicle tail part pressure distribution has been relieved by tail cavity, which causes the reduction of hydrodynamic damping force. As the cavity expands, the decreasing rate trends tend to be slower. The tail cavity also changes the trend of damping force, which varies with the attack angle. Research reveals the necessary consideration of the effect of tail cavity on underwater vehicle hydrodynamic damping force design.

Abstract:Electromagnetic environment with a high efficiency based on single device supports has wide range of applications. But the efficiency of parallel ray-casting for rendering electromagnetic environment is restricted by the device. Based on researching the restriction of device for parallel ray-casting, a pixel interpolation method focusing on the restriction was presented. The number of rays was reduced when the parallel ray-casting rendering under device restriction couldn’t be completed immediately, namely, a part of pixels in the rendering image were generated by ray-casting and the rest pixels through interpolation. Pixel interpolation got rendering efficiency at the cost of image quality, so when image update paused, the interpolated pixels were regenerated to recover image quality. The experiments show that pixel interpolation obviously improves rendering efficiency when implemented on a low device. Compared with the rendering images of some volume data and the errors in these images, the electromagnetic environment data has the best rendering result, which proves that pixels interpolation is useable especially for rendering electromagnetic environment on a low device.

Abstract:In cognitive wireless Mesh networks, the multiple-objective optimization problem with quality of service constraints is more complicated than the single objective optimization problem. To obtain the optimal multicast routing solution which satisfies the quality of service constraints and is aimed at minimizing the channel collision and the resource consumption, a problem solving framework which contains problem description, particle encoding, particle initialization, fitness function, particle flight, particle mutation, particle elimination circle, was proposed on the basis of particle swarm optimization. Adjacency matrix which shows the connection relation between nodes was used to represent particle. Three operation rules, particle flight operation and particle mutation operation were redefined. Simulation results show that the proposed algorithm can achieve the expected goal. It can achieve the effect of a lower resource consumption and a smaller channel collision value.

Abstract:Inspired by the circulatory secretion and paracrine of hormone, aimed at solving the problems such as low efficiency and complexity during the cellular communicating, a four-layer structural architecture for bioinspired self-healing hardware based on NoC (network on chip) and neighborhood connections was proposed. A self-healing hardware realizing an FIR (finite impulse response) filter based on the architecture was brought in to explain the architecture in detail. The hardware shows flexible routing ability and good fault-tolerant ability. It indicates that the structural architecture provides a new approach to design a self-healing hardware with high reliability. 

Abstract:In the high frequency of microwave, sea surface or ship target usually has the characteristics of electrically large size and very sophisticated structure, which imposes a huge computational burden for the electromagnetic modeling of the composite ship-sea scene. To simplify the calculation, based on the facet-model theory, the graphical electromagnetic computing method and the four path model, a hybrid method for the electromagnetic scattering computation of electrically-large composite ship-sea scene was presented. Under the precondition of guarantee calculation precision, the efficiency was improved obviously. The radar cross section of time-varying sea surfaces and ship target for different radar parameters were simulated and analyzed. The results show good agreement with the experimental data and the accurate numerical results, which demonstrates the correctness of the method. Application of the model to synthetic aperture radar imaging of marine scenes was developed. Simulation results demonstrate the effectiveness of the proposed method.

Abstract:Aimed at the limitation of conventional deceptive jamming in the CRPJ-SAR (chirp rate polarity jittered SAR), the sub-Nyquist sampling repeater jamming against CRPJ-SAR was investigated. The signal model of truncated sub-Nyquist sampling repeater jamming was built and the jamming effect of sub-Nyquist sampling repeater jamming on CRPJ-SAR was analyzed. Analytical formulas to calculate the number, location and amplitude of false targets were given and the various jamming effects with different sampling intervals were also addressed. The correctness of theoretical analysis was validated further by the simulation experiments.

Abstract:For the fact that the spoofer has no way to simulate the space distribution characteristic of the authentic GNSS（global navigation satellite system） signals, a detection technique based on carry phase difference was proposed. All errors of the detection were analyzed, and the multiple hypotheses testing the spoofing detection were built. Through theoretical analysis and simulation tests, the proposed spoofing detection method is verified. Results show that the longer the baseline of the array is, the smaller angle of incidence is, which leads to a better spoofing detection performance of the proposed method.

Abstract:According to similarity principles, an infrared imaging experimental test system based on scale model was set up, such work conditions as scale model based vehicle volume, submerged depth, movement, wake discharging, and etc, were designed so that the static and dynamic thermal wake detection tests of scaled vehicle were realized. The detectability of submerged vehicle thermal wakes on one side was determined, and the influencing factors at thermal wakes detection and changing rules of the wakes were found, which lays a foundation for future work. Scale model experimental tests show that the thermal wakes from submerged vehicle can be effectively detected out via the substantial changes of regional gray mean and gray mean variation.

Abstract:Timing synchronization with the early/late loop scheme based on sequence detection was proposed for multi-h continuous phase modulation. The timing error detector was implemented by the survival metrics of Viterbi algorithm. The so-called S-curve and estimation variance were used for optimizing the acquisition range and tracking performance as well as eliminating false lock points of the loop. Using the PAM (pulse amplitude modulation) representation of multi-h CPM(continuous phase modulation), the proposed timing error detector is simplified. Simulation results show that the estimation range is as large as ±0.5 symbol period, and estimation precision is close to the modified Cramer-Rao bound at medium and low SNR(signal noise ratio), and it also has better estimation performance at high SNR. BER (bit error rate) with simplified schemes are derived. It is demonstrated that when the number of Viterbi metrics is reduced to 1/8 of the maximum likelihood sequence detection, the performance loss is only less than 0.5 dB for Mary or partial response of multi-h CPM.

Abstract:According to the problem of attitude control of satellite dynamic scanning imaging, the dynamic model of the satellite attitude was built and the specific requirement of dynamic scanning imaging tasks for attitude control was analyzed. Combined with the dynamic scanning imaging tasks, a typically attitude maneuver scheme was designed. The required control moment of the process of dynamic scanning imaging was estimated. A pitching maneuver control law based on the expected torque and real-time attitude of satellite was developed, and the steering law of five pyramid configuration gyros was given. A numerical simulation was presented for the designed control law based on a maneuver task. The simulation results proved that the proposed scheme can satisfy the requirement of attitude control of dynamic scanning imaging satellite.

Abstract:For solving the vibration control problem in complex excitation, the active control of magnetostrictive actuator of Jiles-atherton model in double-layer vibration isolation system was researched. Based on the traditional sliding mode control, a flexible neural network sliding mode control algorithm was proposed and the controller switching matrix was designed by the regularization method, then the updating formulas of the neural network weights and flexible mapping parameter were also established. Furthermore the control strategy was used for the active vibration control in double-layer vibration isolation system. Finally, the single frequency, multi frequency and random signal excitation were simulated and the results show that the flexible neural network sliding mode controller has a strong robustness and a good control effect.

Abstract:For the fact that the current fault diagnosis methods cannot detect soft fault effectively, a variable detection method based on electric servo system model was proposed for health simulation and evaluation. Common failures of electric servo system, such as motor module, controller and transmission mechanism were analyzed, and the mathematical models were built up for common health states. By injecting different health coefficients into the system, the characteristics of state variable were obtained, so the knowledge base was built up to locate the source of faults and to evaluate the changing trend of the failure parameter by health factors. Finally, the resistance of winding and the motor torque constant are chosen as health factors, the feasibility of health factors estimation algorithm is verified by simulation.

Abstract:The trajectory design for hypersonic glider vehicle subject to complex constraints is a multi-objective trajectory optimization problem. A multi-objective trajectory optimization method combining the boundary intersection method and the pseudospectral method was proposed. The multi-objective trajectory optimization problem was established based on the analysis of the features of trajectory for hypersonic glider vehicle. The multiobjective trajectory optimization problem was translated into a set of general optimization sub-problems by using the boundary intersection method and pseudospectral method. The sub-problems were solved by nonlinear programming algorithm. In the method, the solution that has been solved was employed as the initial guess for the next sub-problem. The maxima cross range and minimal peak heat problem was solved by the proposed method. The numerical results demonstrate that the proposed method can obtain the Pareto front of the optimal trajectory, which can provide reference for the trajectory design for hypersonic glider vehicle.

Abstract:Taking the limited control authority and guidance information of a gun-launched guided projectile into account, a novel three-dimension terminal guidance law based on the combination of the correction of the velocity direction via impact point prediction and continuous distribution of acceleration command was proposed. The deviations between the impact point of the projectile and the target were predicted on the basis of the series solutions of the nonlinear ballistic equations. According to the deviations, two methods to calculate the direction angle corrections of the current speed were addressed. The remaining flight time was designed as the correction time. The acceleration correction formulas were established through sharing the direction angle corrections of the current speed into the whole remaining guided flight to reduce the possibility of command saturation. By predicting the impact point and distributing the acceleration corrections continuously, the trajectory was shaped in real time. The simulation results show that the proposed guidance law is feasible and effective, and provides the performances of high precision with little requirements of control authority, and has great guidance and damage effects, which can provide reference for the application of the guided projectile.

Abstract:In order to eliminate the effect of the disturbance gravity and improve the hit accuracy of ballistic missile, the equivalent theory based on the characteristics on the movement of ballistic missile and control system theory was established to compensate the effect of the earth disturbance gravity on motion parameters indirectly and meet the hit accuracy requirement. According to the characteristics of different compensation modes and compensation quantity, the compensation modes of embedded mode, fractional step mode and sectional mode, etc. were proposed, which provides a general framework and theoretical basis for compensating the influence of disturbance gravity to the movement of ballistic missile.

Abstract:According to the discontinuous characteristics of impulse correction projectile, a class of parameters optimization method for its control system was presented. Considering the two requirements of the correction cost and precision of impulse thrusters, the minimum amount of numbers of impulse thrusters and the control miss-distance were taken as a double-objective function, and it was put forward to select the time interval between the two neighboring impulse forces as design variable in condition of wind disturbance. Based on this, a modified particle swarm optimization algorithm was developed to improve the convergence speed of this optimization process. The simulation result indicates that the presented optimization algorithm can obtain the optimal solution efficiently, which provides a reference approach to find the optimal impulse correction parameters and work modes under wind disturbance.

Abstract:For the problem of the application of the scalar mixing of supersonic mixing layer in the combined cycle engine, the study progress of the supersonic mixing layer and the scalar mixing process in the supersonic mixing layer both at home and abroad was summarized. Then the methods for counteracting the shortcomings of the study on scalar transport and diffusion characteristics of supersonic mixing layer with high Reynolds number were proposed. Finally, some directions being worth studying deeply in the field were pointed out.

Abstract:In practical applications, fracture properties and fracture toughness of porous metal foam for bearing are very important. Based on ASTM standards, three-point bending of aluminum foam samples was used to determine I type fracture toughness. It is shown that the fracture of metal foam is brittle fracture. The deformation is localized in the thinnest regions of the cell walls surrounding the crack tip. With further loading, some cell walls existed fracture phenomenon and microcracks appear in the vicinity of the crack tip. With the increasing of load a main crack is initiated at the notch root or at the pre-crack by a coalescence of microcracks, and starts to propagate through the cell structure. The crack follows the weakest path through the structure and creates the secondary cracks and crack bridges. The main way of crack extension is I type fracture. According to the P-V curve characteristics, taking the force and displacement of the maximum load point to calculate the critical crack tip opening displacement, the average cracktip opening displacement is 0.051mm.

Abstract:In order to improve the design effectiveness of large flat bottom ship with groove, a calculation method with combination of RANS equations and VOF two-phase-flow model was proposed for a large flat bottom ship with groove. The dynamic development of air layer in the groove was found. Based on the analysis of air layer fluctuations with different flow velocity, the difference of air layer fluctuation characteristics between three-dimensional and two-dimensional was explained and the fluctuation similar law of air layer was obtained. Numerical results show that: fluctuations of air layer appear in the groove and the wavelength of air layer increases with the increasing of velocity; the wavelength is equal to 0.64 times of the square of velocity; air layer presents phenomenon of coherent and reflection at the side walls of groove, so the wave height and the thickness of local air layer are changed; fluctuations of air layer is satisfied with Froude similarity.

Abstract:In order to study the finite mass inflation dynamic behavior of parachute at an airdrop mission, the penalty coupling algorithm and the adaptive mesh technology were used to analyze the fluid-structure interaction characteristics between the flexible parachute structure and the surrounding incompressible flow field. The three dimensional dynamic opening profiles of parachute were numerically simulated and some parameters of parachute system like dropping velocities and drag coefficients were obtained; the influences of initial dropping velocity on filling time and drag area were compared; the trajectory was validated by the experimental data from airdrop tests. The computation results show that this method can efficiently simulate the dynamic characteristics of finite mass inflation in parachute system. The simulation results coincide with the test results.

Abstract:In order to analyze the track irregularity, the source of the periodical irregularity was introduced, and the simplified model of track irregularity and a levitation module model were built. Based on these models, the impact of track irregularity on the suspension was discussed. The gap fluctuation of the system was analyzed when stimulated by the different length wavelength of the track periodical irregularity. Considering the track power spectrum density in the Tangshan maglev experimental line, the sensitive wave length was pointed and some advice for the improvement of the track building was given. As the fact that many low-speed maglev tracks have been built, the way of adjusting parameters of the controller to reduce the disturbance from track periodical irregularity was studied.