Advanced Engineering Forum Vols. 2-3

Abstract: With the constant development in the fields of Greenness, Environmental Protection and Energy Conservation all over the world, the improvement of foam cement technology is to bring about a revolution in the architectural material industry. The main component of the cement foaming machine is the delivery pump system, in which the peristaltic pump is the most important part. In this thesis, on the bases of study of peristaltic pump in imported machines, mathematical models are made and an approximate calculation of flow rate of the peristaltic pump is given through exhaustive analyses of the structure and the changes in the cross section before and after compression rolling. This research will also make it possible to analyze the pressure in the exit of the pump and deduce the power needed by the driven peristaltic pump according to the factors like the calculation of on-way pressure loss with the consideration of working altitude. This research is expected to provide a theoretic principle for the development of cement foaming technology.

Abstract: Cast molding is the main manufacture process in foundry, because the most disfigurements occurs in this step, while the foundry itself is a complex non-linear instantaneous transferring heat process, in which it should take the absorbing and releasing potential heat into account. In this paper, it simulates the temperature field changing process of the cast solidification in ANSYS software, gets the temperature field change rule for a typical cast, and analyzed the effect of different foundry technics parameters on composite interface temperature, which will provide numerical bases for optimizing foundry technics parameters in future.

Abstract: The mechanism withstands 220t high temperature molten steel. In case of damage, molten steel pours. There will be major security incidents. Therefore, it is necessary to calculate carrying capacity of the mechanism. However, the part of components of the mechanism is made up of a crisscross of steel plate. This is used to withstand the bending and stretching. If we rely on traditional mechanical analysis, a large number of simplifying must be adopted, and accuracy of the calculation can be reduced. Therefore, this paper uses the COSMOSWorks Plug-in of SolidWorks software to carry out finite element calculation of whole machine for the mechanism. It avoids these shortcomings mentioned above. And this makes bearing capacity calculation to be more close to the actual circumstances. And the results show that: (1) the maximum stress of parts in the mechanism is only 52.8Mpa and much less than permissible stresses of its materials. As a result, the mechanism has sufficient bearing capacity. (2) The maximum displacement of whole machine is 2.637 mm. And the displacement will cause dip angle when lifting molten steel and it is less than its allowable stiffness. Therefore, the deformation is to meet requirements for the mechanism. In conclusion, the finite element analysis of the whole machine avoids complex force analysis and simplification of structure. The calculation has high accuracy. It is one of effective methods in the design of intensity and stiffness of complex structures.

Abstract: Composite materials thin-walled structures are widely used as skin panel in flight vehicles in recent years. These structures will encounter severe complex loading conditions, which may be a combination of mechanical, aerodynamic, thermal and acoustic loads. Thin-walled structures subjected to this kind of loadings will exhibit nonlinear response; as a result, fatigue failure will occur. High temperature may cause large thermal deflection and stress, for some special conditions, may cause thermal buckling. Once the thermal buckling appears, the stiffness will change correspondingly, it will cause significant influence on the dynamic response and fatigue failure. Accordingly, it is important to research the nonlinear response of this kind of structures under elevated thermal environment. Nonlinear response and thermal pre-buckling/post-buckling behavior of a Graphite-Epoxy composite plate subjected to server thermal loading is numerically investigated in this paper. A composite laminated plate with clamped-clamped boundary conditions is chosen as simulated body, nonlinear finite element model is developed using the first-order shear deformable plate theory, Von Karman strain-displacement relations, and the principle of virtual work. The thermal load is assumed to be a steady-state with different predefined temperature distribution. The thermal strain is stated as an integral quantity of the thermal expansion coefficient with respect to temperature. Then the modes of the plate are analyzed, the nature frequencies and modal shapes are obtained. The critical temperature of buckling is calculated. The static nonlinear equations of motions are solved by the Newton-Raphson iteration technique to obtain the thermal post-buckling deflection. The Riks method is used to analyze static post-buckling behavior. In the numerical examples, four types of situations are studied, which include i) the buckling behaviors for different initial imperfections, ii) the buckling behaviors for different thickness to width ratios, and iii) The buckling behaviors for different width to length ratios; The critical temperature, the static thermal post-buckling deflection and the load to displacement relation are presented respectively. The influences of different boundary conditions on the buckling behaviors of the plate are achieved as well. The simulation method and results presented in this paper can be valuable references for further analysis of the nonlinear responses of thin-walled structures under complex loading conditions.

Abstract: Unsteady flow phenomenon occurs in a multi-stage axial compressor. The unsteady flow not only has significant influence on the performance of compressor and the stability of flow, but also can be an excitation source inducing Nonsynchronous vibration (NSV) of rotor blade. NSV is an aeroelastic phenomenon where the rotor blades vibrate at nonintegral multiples of the shaft rotational frequencies in operating regimes where classical flutter is not known to occur. Recently, more and more scholars pay attention to Rotating instabilities (RIs) as one of the unsteady flow phenomenon. RIs have been observed in axial flow fans and centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This research aims at revealing the relationships among the unsteady flow behaviors, characteristics of inner sound field and propagation, the vibration of rotor blade in multi-stage axial compressor. The noise in compressor and the vibration of rotor blade have been measured on a high pressure compressor rig testing. The transducer system is connected to the interior casing wall through the acoustic waveguide pipes. The noise is measured by 1/4 inch condenser microphones in different operating of the compressor. The time-domain wave of noise acquired at different work status of the compressor is transformed into frequency spectrum by Fast Fourier Transform (FFT) to investigate characteristics of sound field in multi-stage axial compressor. And the emphasis is focused on the frequency characteristics of the noise corresponding to blade nonsynchronous vibration. It is found that the vibration amplitude of the rotor blade suddenly increases in a pre-arranged structure adjustment and specific rotating speed, and noise signal with special frequency structures appears simultaneously. High amplitude levels of blade vibration have occurred on the first rotor of a multi-stage high pressure compressor. The frequencies are not in resonance with harmonics of the rotor speed. The frequency analysis show that the noise has a special frequency structures with combination of the appeared characteristic frequency and the blade pass frequency of rotor blade (BPF). Because the similarities between the frequency combination and the specific frequency structure of the fluctuating pressure when the rotating instability (RI) appears in the axial compressor have been identified, the acting mechanism of rotating instability may exist in this compressor, i.e. the vibrational excitation to the rotor blade may be aerodynamically caused and associated with a rotating flow instability in the compressor.

Abstract: Future flight vehicle structures will encounter severe loading conditions, a combination of aerodynamic, thermal, acoustic and mechanical loads. Although the analysis methods for responses of structures under acoustic loads have been developed to some extent, but with thermal loads considered, the responses show fundamental differences, which complicate the analysis immensely. It was reported that hypersonic flight may give rise to surface temperature as high as and intense noise whose overall sound pressure level (OSPL) may reach 180dB. Thin-walled structures subjected to such loadings will exhibit nonlinear responses. Large temperature increments may cause thermal buckling, large thermal deflections and large thermal stresses superimposed on dynamic stresses, coupled with changes in material properties. Both the geometry change by thermal buckling and stiffness change by thermal stress account for the changes of natural frequencies and mode shapes. When the acoustic loading increases to a high enough level, the post-buckled structures will exhibit snap-through motion, a large amplitude nonlinear vibration between different equilibrium positions, which will introduce extra large mean stress. As a result, thermo-acoustic fatigue may be caused, which will reduce the structure's fatigue life dramatically. Therefore it is an urgent need to estimate the influences of thermal loads on the nonlinear response of structures. A numerical investigation of the influences of thermal loads on the dynamic response of thin-walled structure under thermo-acoustic loadings is implemented. With clamped-clamped thin flat plate selected, the response characteristics related to temperature are investigated by changing thermal loads. The thermal load is considered as constant both on the surface and across the thickness. The acoustic load is simulated using stationary Gaussian white noise. Firstly, a thermal buckling analysis is proceeded to obtain critical buckling temperatures, followed by modal analysis under different thermal loads. The pre-buckled and post-buckled mode frequencies and shapes are obtained. Then three types of snap-though motions are predicted: i) vibration around one post-buckled equilibrium position, ii) intermittent snap-through, and iii) persistent snap-through. The relations between thermal loads and the occurrence of snap-though is obtained together with results about the statistics characteristic of dynamic response and their relations with thermal loads, which include critical thermal buckling loads, natural frequencies and mode shapes, RMS response and snap-through frequency. Good agreements have been achieved with previous analytical solutions, which demonstrate the effectiveness and reliability of the method employed.

Abstract: Free axial vibrations of non-uniform rods are investigated by a proposed method, which results in a series solution. In a special case, with the proposed method an exact solution with a concise form can be obtained, which imply four types of profiles with variation in geometry or material properties. However, the WKB (Wentzel-Kramers-Brillouin) method leads to a series solution, which is a Taylor expansion of the results of the pro-posed method. For the arbitrary non-uniform rods, the comparison indicates that the WKB method is simpler, but the convergent speed of the series solution resulting from the proposed method is faster than that of the WKB method, which is also validated numerically using an exact solution of a kind of non-uniform rods with Kummer functions.

Abstract: This paper establishes a numerical procedure to predict the aluminum wheel performance during the impact test. The dynamic finite element solver, Ansys-Lsdyna970, is used. In order to save the computation time, the striker is assigned with an initial velocity, which is equal to the velocity reached during the free-fall period upon release. Mass scaling method is also utilized to further reduce computational time. Equivalent plastic strain is used as the damage indicator to judge pass or fail for the dynamic impact test. The true stress-strain curve is obtained from a uni-axial tensile test of A356-T6 samples machined from a prototype wheel. Simulation results show that plastic deformation tends to be localized around spoke-to-hub junction area. Studies on a recent prototype wheel revealed good correlation between experimental results and numerical prediction.

Abstract: Discrete element method (DEM) is applied to study the granular accumulation problem. Using Herz-Mindlin (no slip) model to simulate particles and container model is also established by software. When the container elevates, the process of granular falling and collision can be ob-served. Detailed analysis of that the impact of static and rolling friction coefficient for particles - particles, particles - flat on angle of repose is accomplished. The variation law is also further val-idated from the energy point of view. The results show that rolling friction has a greater impact on angle of repose than static friction, and rolling friction coefficient among particles play the more prominent role in the two kinds of rolling friction. The research method and results provide a the-oretical reference for the granular movement and DEM analysis.

Abstract: The paper determines the impact factors of high-speed spindle system including the centrifugal force, gyroscopic moments and the bearing stiffness softening, etc, then builds the general spindle-bearing FEM considering high speeds. Taking a motorized spindle as example, the effect of centrifugal force, gyroscopic effect, the radial stiffness and the coupling factors are analyzed qualitatively and quantitatively. Finally the research shows the variations of bearing radial stiffness, centrifugal force and gyroscopic moments have a significant effect on dynamics of spindle system in high speeds, while modeling the high speed spindle system, above factors must be considered.