Transactions of Nanjing University of Aeronautics & Astronautics
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    2020,37(1):1-12, DOI: 10.16356/j.1005-1120.2020.01.001
    Abstract:
    The problem of correcting simultaneously mass and stiffness matrices of finite element model of undamped structural systems using vibration tests is considered in this paper. The desired matrix properties, including satisfaction of the characteristic equation, symmetry, positive semidefiniteness and sparsity, are imposed as side constraints to form the optimal matrix pencil approximation problem. Using partial Lagrangian multipliers, we transform the nonlinearly constrained optimization problem into an equivalent matrix linear variational inequality, develop a proximal point-like method for solving the matrix linear variational inequality, and analyze its global convergence. Numerical results are included to illustrate the performance and application of the proposed method.
    2020,37(1):13-26, DOI: 10.16356/j.1005-1120.2020.01.002
    Abstract:
    This paper summarized the recent development on Herglotz’s generalized variational principle and its symmetries and conserved quantities for nonconservative dynamical systems. Taking Lagrangian mechanics, Hamiltonian mechanics and Birkhoffian mechanics as three research frames, we introduce Herglotz’s generalized variational principle, dynamical equations of Herglotz type, Noether symmetry and conserved quantities, and their generalization to time-delay dynamics, fractional dynamics and time-scale dynamics, and put forward some problems as suggestions for future research.
    2020,37(1):27-39, DOI: 10.16356/j.1005-1120.2020.01.003
    Abstract:
    This study is to explore the influence of maximum aggregate size (MAS) on the failure and corresponding size effect of concrete materials under low strain rates. The failure process of concrete was simulated by the meso-scale numerical method considering the internal heterogeneity of concrete and strain rate effect. Based on the meso-scale method, the failure behavior of concrete specimens with different structural sizes and MAS was investigated. Also, the influence of MAS on the failure modes, nominal strength and corresponding size effect of concrete were studied at the meso-scale. The simulation results indicated that MAS has an obvious influence on the failure modes of concrete subjected to axial compressive and tensile loads. The nominal tensile strength increased as the MAS increased, while the nominal compressive strength increased first and then decreased as the MAS increases under quasi-static load. In addition, it was found that the size effect on nominal strength of concrete would be weakened with the increase of strain rate. When the applied strain rate reached 1 s-1, the size effect on nominal strength of concrete disappeard. Moreover, the MAS has an ignorable influence on the dynamic size effect of concrete under uniaxial compression and tension.
    2020,37(1):40-53, DOI: 10.16356/j.1005-1120.2020.01.004
    Abstract:
    Isolation technique of ground structure is a hot topic in the field of earthquake engineering and structure dynamics. Since soil-isolated structure dynamic interaction study is of great significance to enhance seismic performance of isolated structures and revision of relevant isolation specifications, research on dynamic interaction of soil-isolated structure has attracted more and more attention. Based on the basic theory of soil-structure dynamic interaction, we summarize and analyze the research status quo of soil-isolated structure dynamic interaction by means of theoretical analysis, numerical simulation, model test, prototype observation and seismic performance. After reviewing the results of previous research, we reveal that some key issues, which can be used to uncover dynamic interaction mechanism and seismic response characteristics of soil-isolated structures interaction system, should not be neglected. Based on the concept of seismic performance design and the latest research of soil-isolated structure dynamic interaction, we predict the future development of soil-isolated structure dynamic interaction by elastoplastic time history analysis method, seismic performance level and practical analysis method based on energy.
    2020,37(1):54-69, DOI: 10.16356/j.1005-1120.2020.01.005
    Abstract:
    Piezoelectric atomizers exhibit the advantages of structural simplicity, portability, low energy consumption, low production costs, and good atomization. They have been extensively used in various fields, including inhalation therapy, inkjet printing, and spray cooling. Here, the research of piezoelectric atomizers is first summarized from the perspectives of theoretical investigation and applications. Subsequently, the existing investigation and applications on piezoelectric atomizers are classified in terms of their functionalities. The functions of inkjet printing, spray cooling, and inhalation therapy are described in detail. Finally, the future trends in this field are analyzed. It is indicated that the vibrating-mesh atomizer has a promising prospect in the market, signaling strong demand especially in upgaraded consumption and medical scenarios.
    2020,37(1):70-82, DOI: 10.16356/j.1005-1120.2020.01.006
    Abstract:
    Micro-behavior of pilots is one of the most remarkable aspects in flight safety research domain. The study of pilot’s micro-behavior and its function are of great significance to enhance active safety warnings of flight and evaluation of flight cadets. Based on the cognitive process of pilots, this paper explores the meanings and contents of previous research on the pilot’s micro-behavior. The history and research status of pilot’s micro-behavior are briefly introduced from the perspective of their psychology, physiology and physics. The current reviews mainly include the pilot’s characteristic, multi-information fusion, integrated cognitive and humanization about controlling environment, etc. The several methods of these studies are discussed, and the mechanisms, experimental contents and applicable conditions of pilot’s physiological, psychological and physical characteristics are analyzed. Meanwhile, the advantages and shortcomings of the existing research results are pointed out and analyzed. Combined with flight simulation experiment, the internal mechanism of pilot is explained. Furthermore, with the latest research in the modern flight field, and also from the specialization of application, the diversification of methodologies and the depth of investigation are provided, as well as the development trend of pilot’s micro-behavior analysis in the future.
    2020,37(1):83-87, DOI: 10.16356/j.1005-1120.2020.01.007
    Abstract:
    Foam-cored sandwich materials have been widely used in the civil engineering due to their advantages such as lightweight, high strength, and excellent anti-corrosion ability. However, the interfacial bonding strength of foam-cored sandwich materials is weakened at elevated temperatures. In practice, the effect of high temperature cannot be ignored, because the composites and foams are sensitive to the change of temperature in the environment. In this study, a series of single-leg bending beams were tested at different temperatures to evaluate the influences of high temperatures on Mode I/II mixed interfacial fracture of foam core sandwich materials. The temperature was from 29 ℃ to 90 ℃, covered the glass transition temperature of composites and foam core, respectively. The Mode I/II mixed interfacial crack prorogation and its corresponding interfacial strain energy release rate were summarized.
    2020,37(1):88-98, DOI: 10.16356/j.1005-1120.2020.01.008
    Abstract:
    Disturbance effect is one of the important factors for wind damage to large cooling towers. Existing studies on the wind-induced interference of cooling tower groups are aimed at the same size and the lack of wind-induced interference effects between cooling towers of different sizes. With the background of the additional cooling tower project at Shandong Luxi Power Plant in China, the rigid body pressure wind tunnel test is carried out to obtain 194 conditions for the three combinations of the existing four-tower combination (small size), the new two-tower combination (large size) and the six-tower combination surface wind pressure distribution. Numerical simulation of the surrounding flow field of the cooling tower group with the most unfavorable interference condition of the six-tower combination is conducted using the computational fluid dynamics (CFD) method. Based on this, the characteristics of the average and pulsating wind pressure distribution of the cooling tower surface under the six-tower combination are mainly studied, and the load interference coefficients of the large-sized cooling tower and the small-sized cooling tower under the three tower group combinations are compared. The velocity flow field and vorticity changes around the cooling tower group at unfavorable wind angles are analyzed, and the wind-induced interference mechanism between cooling tower groups of different sizes is mainly refined. Research shows that the interference effect between such cooling tower groups of different sizes is much larger than that of cooling tower groups of the same size, which is specifically manifested as the enhancement effect of small-sized cooling towers and the shielding effect of large-sized cooling towers. The interference coefficient of large-sized cooling tower groups increases by 28%, and the interference coefficient of small-sized cooling tower groups decreases by 6.4%. The airflow acceleration caused by the pinch effect between small-sized cooling tower groups has an adverse effect on large-sized cooling towers and can significantly increase the magnitude of local wind load. The shielding effect of large-sized cooling towers can reduce the overall wind load of small-sized cooling towers. The research conclusions can provide the basis of wind load value design for wind resistance design of such large cooling tower addition projects.
    2020,37(1):99-107, DOI: 10.16356/j.1005-1120.2020.01.009
    Abstract:
    Vortex-induced vibration is likely to occur when subjected to wind loads because of low horizontal stiffness, resulting in internal force and large lateral amplitude. Long-term wind-induced vibration can not only affect the normal service and durability performance of chemical towers, but also seriously endanger the safety of towers in service periods, and cause property losses. In this study, a passive control method for suppressing wind-induced vibration of chemical towers is proposed. The flow around the flow field is guided by a pre-set air-blowing channel, thus destroying the unsteady vortex shedding in the wake region of the flow field and achieving the purpose of flow control. Two accelerometers are used to measure the vibration signal of the chemical tower model with and without the perforated pipe. The control effects of the spacing and the installation position of the perforated pipe are then studied. Experimental results show that the passive perforated pipe control method can effectively reduce the vibration amplitude of the chemical tower under wind loads, and decrease the potential wind-induced vibration.
    2020,37(1):108-119, DOI: 10.16356/j.1005-1120.2020.01.010
    Abstract:
    As high-rise cooling towers are constantly emerging, wind effects on this kind of wind-sensitive structures have attracted more and more attention, especially in typhoon prone areas. Terrain Type B turbulent flow fields under the normal wind and typhoon are simulated by active wind tunnel technology, and rigid-pressure-measurement model and aero-elastic-vibration-measurement model of a large cooling tower are built. The stagnation point, peak suction point, separation point and leeward point of the throat position shell are selected to analyze pressure coefficient, probability distribution, peak factor, power spectral density and dynamic amplification factor under normal wind and typhoon. It is clarified that there exists a significant non-Gaussian characteristic under typhoon condition, which also exists in structural response level. Resonance response ratio of the total response is higher during typhoon condition. The maximum value of dynamic amplification coefficient under typhoon field is up to 1.18 times over that under normal wind. The findings of this study are expected to be of interest and practical use to professional and researchers involved in the wind-resistant designs of super-large cooling towers in typhoon prone regions.
    2020,37(1):120-128, DOI: 10.16356/j.1005-1120.2020.01.011
    Abstract:
    The location of wind turbines on a continuous hilly terrain has an influence on its power outputs. A CFD-based approach is developed to investigate the complex aerodynamic interference between two wind turbines and the hilly terrain. In this approach, a new three-dimensional model of hilly terrain is established to analyze its viscous effect, and a wind shear is modelled through logarithmic function. They are coupled into the aerodynamics of wind turbine based on “FLUENT” software. Then we apply the proposed method to the NREL Phase VI wind turbines and compare with an experiment in the atmospheric boundary layer (ABL) wind tunnel to validate its accuracy. The simulation also investigates the power outputs of wind turbines on the flat ground and the continuous hilly terrain by changing the location of the wind turbine related to the hilly terrain and the shape of the 1st hill. The results show that the wind turbine located on the top of the 2nd hill has the maximum power; and that when the wind turbine is located on the downstream of the hill, the stall zone should be avoided, and the power of the wind turbine located on the side of the hill is higher than that of the wind turbine located on the front and rear of the hilly terrain.
    2020,37(1):129-142, DOI: 10.16356/j.1005-1120.2020.01.012
    Abstract:
    To find out the local buckling behaviors of glass fiber reinforced plastic(GFRP)-foam sandwich pipe suffering axial loading, a series of quasi-static axial compression tests are carried out in the laboratory. Comparing with the test data, systematic numerical analysis on the local buckling behavior of this sandwich pipe is also conducted, and the buckling failure mechanism is revealed. The influences of the key parameters on bearing capacity of the sandwich structure are discussed. Test and numerical results show that the local buckling failure of the GFRP-foam sandwich pipe is dominated basically by two typical modes, i.e., the conjoint buckling and the layered buckling. Local buckling at the end, shear failure at the end and interface peeling failure are less efficient than the local buckling failure at the middle height, and ought to be restrained by appropriate structural measures. The local buckling bearing capacity increases linearly with the core density of the sandwich pipe structure. When the core density is relatively high (higher than 0.05 g/cm3), the effect of increasing the core density on improving the bearing efficiency is less on the specimens with a large ratio of the wall thickness to the radius than on those with a small one. Local layered buckling is another failure mode with lower bearing efficiency than the local conjoint buckling, and it can be restrained by increasing the core density to ensure the cooperation of the inner and the outer GFRP surface layer. The bearing capacity of the GFRP-foam sandwich pipe increases with the height-diameter ratio; however, the bearing efficiency decreases with this parameter.
    2020,37(1):143-154, DOI: 10.16356/j.1005-1120.2020.01.013
    Abstract:
    Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent. However, majority of studies on blast walls have some shortcomings. The explosion test data are few. Most exsiting studies focus on the propagation of shock wave and the influence of blast wall on the propagation of shock wave. Discussion on the main parameters of blast wall design is meagre, such as the design of safety distance, the distance from the blast wall to the protective building, height and width of the blast wall. This paper uses the finite element programme LS-DYNA to design the blast wall. To analyze the convergence of the finite element model and to determine the mesh size of the model, this paper establishes several finite element models with different sizes of meshes to verify the model. Then, the overpressure distribution of the shock wave on the protective building is simulated to implement the blast wall design. The geometric parameters of the blast wall are preliminarily determined. And the influence of the safety distance on the overpressure of the building surface is mainly discussed, so as to determine the final design parameters. When the overpressure is less than 2 kPa, it is considered that there will be no damage to people caused by flying fragments. Eventually, the blast wall height is 3 m, the thickness is 1 m, and the safety distance is 35 m. The proposed method is used to demonstrate the design method, and the final design parameters of the blast wall can thus be used for reference.
    2020,37(1):155-163, DOI: 10.16356/j.1005-1120.2020.01.014
    Abstract:
    Valveless piezoelectric pump is widely used in the medical, however,there is a general and difficult problem to be solved:Low vortex and large flow rate are not compatible, resulting in the blood prone to thrombosis during blood delivery. In this paper, a new valveless piezoelectric (PZT) pump with streamlined flow tubes (streamlined pump) is proposed. The design method and the working principle of the pump are analyzed. The velocity streamlines are simulated, and the results demonstrate that there are no obvious vortexes in the flow tube of the streamlined pump. Five prototype pumps(two cone pumps and three streamlined pumps) are designed and fabricated to perform flow rate and flow resistance experiments. The experimental results illustrate that the maximum flow rate of the streamlined pump is 142 mL/min, which is 179% higher than that of the cone piezoelectric pump, demonstrating that the streamlined pump has a large flow rate performance. This research provides an inspiration for future research on simple structure, low vortex and large flow rate volume-type pumps, and also provides a useful solution for thrombosis preventing.
    2020,37(1):164-174, DOI: 10.16356/j.1005-1120.2020.01.015
    Abstract:
    During the process of deep-hole gun drilling, the shape of the chip is a significant factor affecting the final quality. The relationship between chip forming mechanism and process parameters has always been a complicated problem in deep-hole drilling. This paper investigates Ti6Al4V titanium alloy to address this issue. First, the four processes and influencing factors of forming spiral chips are analyzed theoretically. Second, the fracture mechanism of chips in drilling Ti6Al4V titanium alloy is analyzed by scanning electron microscopy. Finally, the influences of cutting speed, feed rate and coolant oil pressure on chip shape are analyzed through drilling experiments and fluid simulation. The relationship between chip compression ratio and surface roughness is obtained through chip thickness measurement. This research can provide a guide for optimizing parameters of deep-hole gun drilling on Ti6Al4V titanium alloy.
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