Abstract:Layerwise theory, proposed by Reddy, is a 3D analysis method for accurately analyzing composite laminated plates and shells. Without introducing any deformation and stress hypothesis, layerwise theory, compared with the classical equivalent single layer theories, has greater advantages for static and dynamic responses analysis of thick composite laminated plates and shells, especially for local interlaminar effects analysis. A review and recent research progress of the layerwise theory were presented, and its numerical solutions and applications were demonstrated as well. The basis of layerwise theory and its recent development were introduced. The implementation of layerwise finite element method and its refined models were discussed. The employment of layerwise theories for conducting static and vibration analyses and the damage model analysis of composite laminated plates and shells were outlined. And several future research trends were recommended in the end.

Abstract:The platelet technology has been in rapid development because of several features, including the special structure of flow channel, the precise size and location, and can provide solutions to difficult thermal and fluid flow problems. As a result, the platelet technology is a major technological innovation in the history of science and technology. The characteristics and development of platelet fluid devices were briefly introduced. Some typical new applications at home and abroad in recent years, such as platelet injector, platelet transpiration cooling nose-tip, platelet fluid mixer, platelet thruster of high speed ship and platelet muffler were summarized. Finally, the correlation of processing of platelet technology and 3D printing technology was described.

Abstract:The stochastic chaotic characteristics of supersonic two-dimensional airfoil were studied by Kapitaniak method. Nonlinear aerodynamics and aerodynamic moments of supersonic two-dimensional airfoil were deduced by the third-order piston theory. The 2 degree of freedom differential equation of motion of the airfoil with pitch cubic nonlinearity under stochastic disturbance was established and written in the form of 4-dimensional state equation. Then the system state equation was reduced to 2-dimensional by using the central manifold method. After that, the combination of the methods of cumulant neglect and non-Gauss truncated was used to obtain the two-dimensional probability density function and the probabilistic time-difference diagram of the system. Therefore, the Kapitaniak method was used to analyze the stochastic chaotic characteristics of the system under different disturbance intensities. Finally, the system response, Poincare cross-section diagram and the largest Lyapunov exponent were used to verify the stochastic chaotic characteristics of the system. The research is very important for the stability, safety and response characteristics of the supersonic two-dimensional airfoil in complex environment.

Abstract:The bi-stable composite materials can be widely used in the design of variable structures. Using ABAQUS/Standard(version 2018), a finite element analysis of the shell′s snapping process was conducted to simulate the snap-through process and snap-back process of the bi-stable cylindrical shells with anti-symmetric laminated carbon fiber composites. The distribution and trend of the stress on the cylindrical shell during the whole continuous process were discussed to give advice to the design of this type of variable structure. The results show that the stress distribution of the composite cylindrical shells is very different during the snap-through process, the snap-back process and the second stable state. Moreover, the maximum stress moment on the entire cylindrical shell does not overlap with the moment when the maximum load is applied, and has hysteresis.

Abstract:Special consideration must be applied in the analysis of fatigue life of composite materials due to its high scattering in mechanical property. The relationship between fatigue life Weibull shape parameter and residual strength shape parameter of M21C open-hole composite laminates were deduced based on the Sendeckyj equivalent static strength model and probability distribution of functions of random variables. The fatigue life shape parameter and fatigue threshold of M21C open-hole composite laminates were obtained through element tests and statistic analysis, which can provide support for the determination of LEF (load enhancement factor) and truncation levels for low loads of M21C composite material system.

Abstract:In order to study the influence of chamber pressure on thermo-structural response for the submerged nozzle of solid rocket motor, a simulation was carried out. By means of the commercial fluid software, based on the pressure solver, the flow field of pure gas in the nozzle was conducted and the temperature, pressure, and wall convective heat coefficients were obtained in the nozzle; according to the non-uniform pressure and non-uniform heat transfer coefficients obtained from the above flow field, using the finite element software, the thermo-structural problem of the submerged nozzle was solved at the pressure 6 MPa. Then, the ground firing test of solid rocket motor with the submerged nozzle was carried out, and the proposed numerical method is effective and accurate. By means of the same model and numerical method, the thermo-structural response of the submerged nozzle was solved at the pressure 9 MPa and 12 MPa, and the influence of combustion pressure on the thermal stress of throat insert was obtained. The simulation results show that during the entire operation process of solid rocket motor, the maximum hoop stress of throat insert is 103.9 MPa, which locates on the inner surface, and increases at first and then decreases with time; the hoop tensile stress increases at first and then decreases with the increasing of time for the throat insert, as well; with the increasing of pressure, the convective heat coefficients, the temperature and the hoop tensile stress increases, and the hoop compressive stress decreases for the throat insert.

Abstract:In recent years, multi-modal haptic rendering featured with multi-contact interaction has become a research focus in the human-computer interaction due to its ability to further enhancing the sense of reality. A multi-modal haptic rendering system for multi-contact interaction was presented, which is composed of Leap Motion sensor based multi-finger position detection module, vibration-based tactile rendering module, NRF51822 blue-tooth communication module, visual rendering module, and CHAI3D based virtual environment. To verify the efficacy and effectiveness of the proposed system, the virtual object contour recognition experiments and object pick-and-place experiments were carried out. Experiment results show that the average success rate for distinguishing geometric virtual objects is 87.9%, and the pick-and-place experiment with combined haptic rendering and visual rendering can lead to an average time saving of 47.7%, compared with that of single visual rendering condition. The proposed multi-contact haptic system features the virtues of low cost, small size, and simple control strategy, which lays out a profound foundation for the further development and application of multi-modal human-computer interaction.

Abstract:To solve the problem of coherent signals DOA(direction-of-arrival) based on the uniform circular array, a new VLPEA(virtual uniform linear array principal eigenvector analysis) algorithm was proposed. The uniform circular array was transformed into the virtual uniform linear array in space model by mode excitation, and the principal eigenvector matrix was obtained by data covariance matrix; the weighted least square method was introduced to get the linear prediction coefficient between each element in subspace matrix and to acquire estimation of DOA of coherent signals. Theoretical analysis and simulation results show that the proposed algorithm has good estimation accuracy, high resolution and low complexity.

Abstract:The cathode of MITL (magnetically insulated transmission line) of large scale pulse power plant can be more than ten meters, and the deflection of cantilevered structure end as a result of gravity might be as big as several centimeters. If without alignment measures, the gap error between anode and cathode will lead to obvious current loss. By taking reference of the alignment strategy of Hermes Ⅲ based on tilt spacers, a so called ‘Mini-MITL’ cathode was designed for the validation of alignment principle. According to the parameters of the designed cathode, as well as the rotating angels of the tilt spacers, a numerical coordinate model of key points of the cathode stalk was built. The vertical and horizon coordinates corrected by tilt spacers were thus got. For validation, coordinate measuring reference was built in SolidWorks environment. The coordinates of 3D simulation and numerical model matched well. The deflection of the designed cathode was simulated by SolidWorks Simulation. The rotating angles of tilt spacers were adjusted according to the simulation results to balance the vertical deflection and keep the horizon straightness. The alignment errors of vertical and horizon direction were both less than the threshold. Continuously adjusting strategy was studied based on the discretely adjusting strategy. The alignment accuracy was notably promoted after improvement.

Abstract:Artificial intelligence security is an important issue caused by rapid development of modern science and technology. Based on core papers obtatined from the Web of Science database, a scientometrics method and the visualized tool were used to explore the research distribution of countries, institutions, and research hot spots. A qualitative analysis framework was constructed for analyzing artificial intelligence security in integrated qualitative and quantitative perspectives. A preliminary exploration and evaluation of the development of artificial intelligence security technology was presented.

Abstract:Numerical investigation of a 80°swept delta wing rock characteristics was presented by solving N-S (Navier-Stokes) equations coupled with Euler rigid-body dynamics equations, and the influences of leading edge configuration and roll-axis installation were discussed. For the unsteady simulation of self-induced wing rock phenomenon, the Roe scheme and LU-SGS method with dual-time stepping approach were employed for NS equations discretization, the second order differential scheme was employed for Euler rigid-body equation discretization, and the loose-coupling approach for flow control equations and movement control equations was implemented. For the delta wing with a roll-axis located on the upper surface, three leading edge configurations, including upper beveled, lower beveled and double beveled were used for evaluating the influence on the amplitudes and bifurcation angles of delta wing rock. In view of the configuration equivalence of upper beveled delta wing and lower beveled delta wing, the influence of roll-axis installation was evaluated also. The results show that under a certain attack angle, all of the three delta wings with different leading edge configuration establish large and self-retained wing rock amplitudes, and the largest amplitude is observed with upper beveled delta wing, the double beveled delta wing takes the second place and the amplitude of lower beveled delta wing reaches the least degree. For the attack angle of 30°, the roll-over phenomena are observed at the delta wings with upper and double beveled leading edge configuration, and when the roll angle reaches to 180°, the oscillation amplitude remains unchanged.

Abstract:Supercomputing is an important means to solve major challenges in the fields of national security, economic construction, scientific progress, social development, and national defense construction. It is a strategic high technology domain in the development of science and technology in various countries. Through investigation and empirical research, the roles of government and the enterprises as market players in catching up with world supercomputing technology pioneer were analyzed. For the requirement of strategic development, Chinese government has formed a solid accumulation of knowledge and talents through long-term funding under the condition of very limited financial capacity. To meet strategy of scientific and technological innovation, Chinese government has led cluster innovation across the country to achieve China′s supercomputing summit and built national supercomputer foundation facilities. To meet the strategy of comprehensive development, supercomputing applications are fully developed. At the same time, in accordance with the principle that the enterprises are the main body of the market, they achieve market breakthroughs by participating in supercomputing competition development and absorbs technology spillover from research body. The development model of supercomputing technology can provide experience for the other high-tech fields.

Abstract:Ice accretion affects flight safety severely. Intelligent ice accretion prediction is an important basis and support for the intelligent anti-icing and de-icing system design and safety design of aircraft. To solve the problem that there are multiple values of ice thickness in the normal direction of the same position of the airfoil surface with complex ice shape, a graphical ice accretion prediction method based on the transposed convolution neural network was proposed. The corresponding neural network structure, loss function and data specification of the prediction model were designed. The input of the prediction model was the data from flight and atmospheric conditions which directly affect ice accretion. The output of the prediction model is gray-scale image of ice shape. Ice shape data set was generated through numerical simulation method based on NACA0012 airfoil. To ensure the credibility of the generated data, wind tunnel test data was used to verify the numerical simulation method. Prediction model was established with five input parameters:liquid water content, median volumetric diameter, freezing time, temperature and flight speed, and was then trained and validated in simulation. The simulation results show that the proposed method can predict the ice shape quickly, and the main features of the predicted ice shape such as outline, upper and lower limits, position of ice horn and thickness fit well with the results of numerical simulation.

Abstract:Satellite stealth technology occupies a unique position in the space attack and defense system. It has certain similarities with the stealth technology applied on ground armored vehicles, warships, and aircraft. However, due to the different satellite development conditions and the space environment, satellite stealth technology faces greater challenges in its research and application. The requirements and conditions of satellite stealth technology were summarized on the basis of satellite engineering application. The international cutting-edge stealth technology was systematically reviewed. This research focuses on radar stealth methods, and infrared and visible light stealth methods. The technical bottlenecks and future prospects of satellite stealth were discussed, in the aim to promote the application of stealth technology on satellites.

Abstract:Aiming at the problem of high computational complexity of feature descriptors and low registration accuracy, a point cloud registration algorithm based on the differences of region′s feature information in different scales was proposed. In the aspect of feature descriptor, the neighborhood spaces with different scales were selected for the key points. The normalized eigenvalue vector differences and normal vector angles between the scales were calculated. The descriptor of key point based on neighborhood scale differences was created. It is simple and time-saving. For the key points searching, a key point extraction method based on shape index was designed. The obtained key points have better representative ability. For searching the corresponding relationship, a double screening method based on Euclidean distance was proposed to find the correspondence set. The global optimal searching algorithm based on global distance was designed to find the transformation matrix between two point clouds. The experimental results show that the registration algorithm has good accuracy and robust noise robustness.

Abstract:In order to study the relationship between horizontal attitude error angle and horizontal gravity disturbance of SINS (strapdown inertial navigation system) on moving base, the transfer function between horizontal attitude error and horizontal gravity disturbance on SINS mechanization was deduced in uniform linear motion in North-South direction and East-West direction. The distribution of zero and pole of transfer function was analyzed. In addition, the transfer function between horizontal attitude error angle and horizontal gravity disturbance was analyzed in integrated navigation mode. The amplitude-frequency characteristics of transfer function on SINS mechanization and integrated navigation mode were analyzed by simulation. Compared with the SINS mechanization, the cut-off frequency of integrated navigation mode was higher, and the attitude error angle of inertial navigation was affected by high-frequency gravity disturbance signals more obviously. Therefore, the INS needs higher resolution gravity disturbance data to compensate the gravity disturbance in the integrated navigation mode. However, there is a limit for the resolution of gravity disturbance used to compensate for the high-precision inertial navigation system. Too fine gravity disturbance data will only bring cost for measurement and storage instead of improving the attitude accuracy of the inertial navigation system.

Abstract:An acceleration measurement scheme with atom interference in optical waveguide at horizontal direction was presented. The optical structure, radical preparation and optical waveguide adiabatic loading were described in detail. In order to verify the measurement scheme by using the experiment means, the radical ⁸⁷Rb was cooled into Bose-Einstein condensate, then the splitting and combining of the ultracold radical was achieved by the Bragg diffraction and the process of atom interference was completed. The experiment results show that the interferometer can measure the axial acceleration of the optical waveguide, which is of reference value for the future study of multi-axis acceleration measurement.

Abstract:In order to solve the problem that deep-sea unmanned mobile platforms lack combined vector hydrophones which match their working depth, a large depth combined co-vibrating vector hydrophone was designed and developed with the thin aluminum alloy spherical shell as its vector channel and the piezoelectric ceramic ring as its sound pressure channel. The acoustic performance and pressure resistance of the hydrophone was verified by theoretical calculation, finite element simulation and experimental test. The size of the hydrophone is Φ85 mm, with the mass being 398 g, and the average density being 1 240 kg/m³. Its working frequency range is from 20 to 3 000 Hz. The vector channel of the hydrophone is cosine directional, and its sensitivity is -187 dB@ 500 Hz. The sound pressure channel has non-direction, with the sensitivity being -191 dB @ 500 Hz. This vector hydrophone has a working depth of 2 000 m. Sea tests show that this hydrophone can be applied on deep-sea unmanned platforms, such as underwater gliders, and can carry out acoustic detection missions,which means that it has great application values in the field of deep-sea acoustic detection.

Abstract:Using composite materials to replace aluminum alloy, steel or titanium alloy is of far-reaching significance. With the development of new material science, the advantages of direct extrusion fabrication are becoming increasingly prominent. In principle, direct extrusion fabrication is suitable for any paste or gel composite material with or without additives. The purpose of this study is to find out the general rheological parameters of thermosetting epoxy resin in the direct extrusion fabrication application by discussing the rheological properties and extrusion fabrication properties of the composite. The rheological behavior of the composite was designed by adding thickener. A gantry pneumatic extrusion 3D printer was designed and built to test and analyze the printing effect of composite materials. Combined with the experimental results, the influence of nozzle height on printing results was analyzed, and a calculation method suitable for critical value of nozzle height was proposed. The effects of shear rate, extrusion rate and extrusion pressure on the molding quality of materials were also analyzed. Aiming at the problem of multi-layer printing, a method for calculating the critical value of nozzle height of multi-layer printing was proposed. The above conclusions provide guidance methods for the extrusion 3D printing of composite materials.

Abstract:Aiming at the high-speed maneuvering target interception scenario, the conditions for the existence of the capture zone in the terminal guidance phase and the differential game guidance law were studied. The relative motion model of missile and target was established and the control dynamics model was introduced, and the relative motion model was reduced by terminal projection method. Based on the differential game theory, an analytic capture zone was derived, which can be used in the interception of maneuvering targets by a missile with dual control. The existence of the capture zone can ensure the accurate capture of any maneuvering target. The performance index function was re-selected, and the guidance problem of the target and the dual control missile with the collision angle constraint at the end was transformed into the zero-sum differential game problem, and the optimal interception strategy was solved. The simulation analyzed the existence of the capture zone of the dual control missile intercepting the target in several cases. Simulation results of the guidance law show that the differential game guidance law has better performance when intercepting high-speed maneuvering targets.