Browse Topic: Computer simulation
Impact testing utilizing instrumented hammers and accelerometers is a widely adopted technique in dynamic testing. The mass loading effect of the accelerometer alters the dynamic response of the test structure, leading to deviations between the measured frequency response functions (FRFs) and their true values. Furthermore, the effects on the FRFs are contingent upon the positioning of the accelerometer, thereby causing the measured FRFs between two points to fail to meet the principle of reciprocity. This paper investigates the compensation method for the mass of a single accelerometer in impact testing. Compensation formulas for both origin–FRF and cross–FRF are derived using the frequency domain substructure decoupling method. Numerical simulations on a cantilever beam and experimental tests with milling tools validate the proposed methodology. The compensation formulas for FRFs presented in this paper are expected to enhance the measurement accuracy of FRFs in modal testing of small structures, particularly relevant for lightweight components in aerospace, aircraft, and transportation systems, where precise dynamic characterization is critical.
With the deepening of space exploration, deep space exploration missions face formidable challenges. Among these, intense solar radiation and high-temperature environments pose severe threats to precision instruments and equipment in space. Stray light suppression and protection against external heat flow inputs have emerged as critical technical requirements in the design of modern spacecraft over recent years. To address the demand of space applications, this paper proposes a cylindrical deployable sunshield with axial deployment capability. First, drawing on the 6UU/3UPU/3UKU mechanism as a foundational reference, the basic module was defined through in-depth analysis of the multi-layer Kresling origami pattern. Guided by the modular composition principle, these basic modules were further assembled into an integrated deployable support mechanism. Secondly, the overall kinetic and potential energy of the full mechanism system were computed and incorporated into the second-type Lagrange equation. To verify both the correctness of the established dynamic model and the reliability of follow-up simulation studies, an integrated validation strategy was implemented: SolidWorks was used for three-dimensional modeling and kinematic simulation of the mechanism, while Matlab was employed for numerical solving and result analysis of the dynamic model, with consistent outcomes from both tools confirming the model’s correctness.
High-speed wet clutches may experience dynamic instability between the friction plates, leading to rattling vibrations and a significant increase in drag torque. This study employs a homogeneous flow model to characterize the gas-liquid two-phase flow within a high-speed clutch. It establishes a dynamic model for the angular oscillation of friction plates. Finite-element numerical simulations and stability analyses were conducted. The results indicate that as the clutch speed difference increases, the density and viscosity of the two-phase flow decrease rapidly, leading to a sharp reduction in fluid stiffness and damping. Consequently, the friction plates become more susceptible to angular oscillation. The stability of angular oscillation is determined by two key parameters: dimensionless comprehensive stiffness and critical frequency ratio. Higher dimensionless comprehensive stiffness and a lower critical frequency ratio enhance oscillation stability. Numerical evaluations of various groove types reveal that as rotational speed and friction plate clearance increase, the fluid stiffness coefficient, damping coefficient, dimensionless comprehensive stiffness, and critical moment of inertia all decrease, thereby reducing angular oscillation stability. Among the tested groove geometries, enclosed grooves and spiral grooves exhibit superior stability due to their strong hydrodynamic effects, yielding the highest dimensionless comprehensive stiffness. The critical frequency ratio for the self-excited angular oscillation of friction plates is approximately 0.5, termed the half-frequency oscillation characteristic. Experimental data validate the proposed angular oscillation model and its frequency response, providing a theoretical foundation for performance prediction and stability optimization in high-speed clutch design.
To facilitate the development and application of bulb-flat titanium alloys in aerospace and automotive industries, this study selects TC4 as the research material and employs finite element simulation software to simulate the hot rolling process of TC4 bulb flat titanium. The temperature field, strain field, and metal flow velocity in each rolling pass are analyzed, and rolling experiments are conducted after optimizing the roll pass system. The results indicate that during the rolling process of TC4 bulb flat titanium, the head undergoes relatively smaller deformation, resulting in a slower temperature decrease, whereas the waist experiences greater deformation and a faster temperature drop. A significant temperature difference exists between the core and surface, which can be mitigated by appropriately increasing the roll temperature to reduce heat transfer. Prior to the K4 pass, the billet temperature drops to a level that may affect rolling performance, necessitating furnace reheating. Strain increases progressively with each rolling pass, with higher values observed at the waist compared to the head. A gradual strain transition occurs at the interface between the head and waist. Furthermore, the irregular design of the roll pass leads to a considerable difference in metal flow velocity between the upper and lower surfaces. During the K1 pass rolling, this imbalance can cause the guide guard to be displaced upward and result in roll wrapping. Without altering the roll diameter, shifting the entire roll pass system toward the side with higher metal flow velocity effectively reduces the linear velocity and prevents these issues, ensuring stable billet rolling. Rolling experiments successfully produced the final TC4 bulb flat titanium, thereby validating the feasibility of the optimized roll pass system and the rationality of the selected rolling parameters. It provides the possibility for its development and application in fields such as aircraft and automobiles.
The canard configuration has been widely adopted in short-range missiles. However, its main drawbacks include difficulties in roll control and a limited angle-of-attack (AoA) range. Compared to conventional canard missiles, the addition of a pair of control surfaces (referred to as “aileron”) behind the canard control surfaces achieves decoupling between the roll channel and pitch-yaw channel. To investigate the influence of ailerons on the aerodynamic characteristics of canard configuration missiles, numerical simulations were conducted for two typical flow conditions: subsonic (Mach 0.5) and supersonic (Mach2.0). The results show that the introduction of ailerons increases the normal force of missiles, causes the center of pressure to shift forward, and reduces the static stability of missiles, thus enhancing their maneuverability. When the ailerons control the roll channel, the effectiveness of the rolling moment remains consistent over the entire AoA range without adverse effects. However, when the canards control the pitch channel, the interference caused by the deflection of the canards on the ailerons leads to increased lift and generates additional nose-up pitching moments, which reduces the pitching moment effectiveness of the missile.
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