Meccanica最新文献

Micro-vibration is an important issue that affects the observation accuracy and imaging quality of spacecraft. The micro-vibration of spacecraft has the characteristics of wide frequency (1–300 Hz) and low amplitude (μm level). Installing a micro-vibration isolation device on a disturbance source or precision payload is an effective method to suppress micro-vibration. In this paper, we propose a novel modeling method for a micro-vibration isolator with annular damping gap. Firstly, by cleverly utilizing the principle of effective area of bellows, the complex bellows are simplified into a single tube. Based on the axial vibration of the bellows, springs are used to equivalent the elasticity of the bellows, and the interaction between the fluid and bellows is considered in the model. Through this method, we greatly simplify the isolator and constructed a semi-analytical model. Then, we use the fluid–structure coupling analysis to evaluate the difference in describing the volume deformation between the single tube and the bellows with different wall thicknesses, and then propose a novel solution. We introduce the bellows volume deformation correction coefficient to modify the model. The effectiveness of the correction method for isolators with different wall thicknesses is discussed. Next, we conduct parametric research to analyze the influences of different wall thicknesses, viscosity, damping gap width and length, and excitation force amplitude on the isolation performance. Through our research, it is found that this annular damping gap has better adjustability for isolation performance than the damping orifice, which may help propose more combinations of design parameters suitable for different isolation performance requirements. Our proposed model is suitable for fluid viscous damper working at the frequency of 1–300 Hz, that used for spacecraft micro-vibration suppression (including magnetorheological dampers and adjustable damping orifice fluid viscous damper).

This paper proposes an exact completing method of generation of face-milled spiral bevel gears with uniform depth taper. This method ensures localized bearing contact without kinematic transmission errors in both directions of rotation. Both sides of the tooth are generated simultaneously using the same set of basic machine tool settings. A tip relief on the tooth surfaces is the only required microgeometry modification to achieve a smooth transition of load between consecutive pairs of teeth. An analytical approach to determine the basic machine tool settings and select the grinding cutter parameters has been also developed. The selection of the nominal cutter radius follows the recommendations of Information Sheet AGMA 22849-A12. The basis for alignment error compensation has been also established. Tooth contact and stress analyses demonstrate the advantages and limitations of the proposed method, making it suitable for applications with higher power demands for the drive side than for the coast side.

In the classical Coleman–Noll approach to the exploitation of second law of thermodynamics, the balance laws of mass, linear momentum and energy are regarded as differential bilateral constraints to be included in the entropy inequality. In recent years, the classical Coleman–Noll procedure has been generalized by considering also the gradients of the fundamental balance equations as constraints in the entropy inequality. In the present paper, a generalized Coleman–Noll procedure is applied to analyze viscoelastic solids with and without relaxation of the heat flux. It is proved that the relaxation of the heat flux does not ensure the hyperbolicity of the system of balance laws. An overview of the generalized exploitation procedures is provided as well.

This research introduces a novel active mass damper (AMD) that operates based on magnetic force. The proposed AMD utilizes magnetic force to control the damper’s and reduces the structural vibrations by the reaction force exerted by the mass onto the system. The utilization of magnetic force increases the performance of the AMD. The magnitude of the control force is determined by employing PID control based on the measured acceleration response of the structure on which the AMD is mounted. An experimental study is conducted to assess and evaluate the performance of the AMD. The study utilizes an experimental three-story shear frame as the testing platform, with the AMD mounted on the structure. The AMD’s mass is chosen to be approximately 3% of the total structural mass. A comparison of the obtained structural responses to those of the structure fitted with a passive mass damper shows the promising efficacy of the proposed AMD in reducing the structural responses across a broad frequency range. The results obtained from both experimental tests and analytical analyses provide confirmation of the effectiveness of the AMD within the range of the structure’s primary modes. The most significant points of the presented device are having a high performance in reducing vibration despite the small weight and efficiency in a wide frequency range by using magnetic force.

Manipulator arms in robots can be bulky and difficult to transport. Tensegrity mechanisms, which can be compact, deployed, and shaped to adjustable lengths, offer a promising alternative for robotic manipulators. This work develops a methodology for class 2 tensegrity mechanisms formed by cylindrical modules, using nonlinear programming to design a deployable tower capable of complex shape transformations, such as bowing. The study starts by deploying the structure from a compact shape into a tower, thereby enhancing its transportability and impact resistance. Next, a form-finding procedure assigns a bowing movement to the tower by pulling specific cables, using a kinematical method and nonlinear programming to achieve a stable configuration. Finally, the workspace of the mechanism is approximated through surface fitting, and three inverse kinematics functions are defined using artificial neural networks, sequential quadratic programming and a genetic algorithm. The example presented uses six quadruplex modules, but the floor and ceiling functions applied make it valid for any cylindrical tensegrity stacking.

In this work, a pioneering approach is proposed to enhance the efficacy of vertical axis wind turbines within the aerodynamic field. This innovative method involves integrating a bionic airfoil, inspired by the tail fin of a swordfish, along the trailing edge of the airfoil. To evaluate the impact of these biomimetic airfoils on wind turbine functionality, applications such as numerical simulations facilitated by computational fluid dynamics (CFD) and design of experiments (DOE) were employed. The primary objective of this study is to mitigate the flow separation phenomenon that occurs when wind turbines operate at low tip speed ratios (TSR < 4). The results indicate that the addition of the bionic tail delays the angle at which the peak torque appears, and enhances positive torque generation effectively within the phase angle range of 60° to 150°, suggesting successful suppression of the flow separation phenomenon. The presence of the tail also postpones the occurrence of dynamic stall, particularly near the trailing edge of the airfoil, and reduces losses associated with the expansion and shedding of dynamic stall vortices. As the tip speed ratio increases, the average power coefficient of the bionic airfoil exhibits a positive trend. Notably, at a tip speed ratio of 2.63, a significant increase in the average power coefficient of approximately 17% was observed. The analysis of the downstream wake of the wind turbine reveals that the bionic tail enhances the speed loss in the wake. This indicates that the blades can generate greater lift at a lower tip speed ratio, allowing the vertical axis wind turbine to operate effectively at low wind speeds, particularly in urban areas with significant development potential.

The present study investigated the dynamic characteristics of a novel inerter-enhanced non-traditional tuned mass damper, referred to as tuned series inerter damper (TSID), for structural vibration control. The proposed TSID model consists of a series layout of a spring, dashpot, and inerter, which is a mechanical two-terminal device whose resisting force is proportional to the relative acceleration between its terminals. Both time- and Laplace-domain representations of the TSID were presented, and closed-form solutions to the optimum parameters of the TSID controlled system were derived on the basis of the fixed-point theory. Parametric studies were conducted to investigate the influence of the mass ratio on the dynamic characteristics of the TSID controlled system in terms of the structural steady-state and transient responses. Comparison studies between the structure incorporated with optimally designed TSID and TMD suggest that the TSID can be advantageous over the traditional TMD in simultaneously controlling the structural displacement and damper stroke. The large practically achievable apparent mass of the TSID with a light physical weight makes it more attractive to serve as a viable option for structural vibration control.

This study investigates the physical and mechanical properties of concrete made with recycled aggregates, focusing on their reaction to acid attacks for sustainable construction in Cameroon. Despite initial challenges, such as lower density and higher water absorption in recycled aggregates, optimized concrete formulations can compensate, achieving comparable strengths to traditional concretes after extended curing periods. Recycled aggregates showed greater susceptibility to acid attacks, necessitating advanced protective strategies. Polynomial regression models enhanced the understanding of compressive strength evolution and degradation, proving vital for engineering predictions. The research advocates for the optimized use of recycled materials in construction, adhering to sustainability standards and contributing to environmental protection. Continued advancements in protective treatments and concrete formulations are essential for broadening the application of eco-friendly building materials.

This research deals with a numerical study of a drop impacting a moving film as a transient three-dimensional and its comparison with static film. For the modeling, the CLSVOF (Coupled Level Set and Volume of Fluid) method has been used for drop impact analysis. The parametric effects of film Reynolds number (830 < Re_f < 4478), non-dimensional film thickness (0.25 < h^* < 0.75), drop Weber number (249 < We < 1762), non-dimensional time (0.5 < τ < 4.0), and impact angle (0°, 30°, and 60°), on the interface evolution, was investigated. Further, the results have been compared to drop-impacting static film obtained by previous researchers, whereby in most cases consists of the results with drop-impacting static film have been observed. However, the drop impacting the moving film indicated a different behavior in some cases because of the unique effect of the moving film movement. Doubling the film velocity as well as a 57% reduction in the drop velocity, caused an 8.3% and 6.66% increase in the crown asymmetry and suppression of the downstream crown. The crown slip toward the downstream flow was observed in all cases. Doubling the fluid film velocity, on average, reduced the crown height by 18.5% and increased its diameter by 10.48%. However, its effect on the crater diameter was negligible (1%). An increase in the film thickness from 0.5 mm to 1 mm (h^* from 0.25 to 0.5), fed the upstream crown, and on average, increased its height by 10.57%. At a low impact velocity of 3 m/s (We = 249), the crown diameter was, on average, 26.7% larger than its diameter at the velocity of 7 m/s (We = 1358). By increasing the drop impact angle to 60 degrees and overcoming the effect of the fluid film velocity, the crown behavior was the same as its behavior with the drop impact on the static film. Finally, to predict the upstream crown height, downstream crown height, crown diameter, and crater diameter, four novel five-variable correlations (depending on τ, θ, Re_f, We, and h^*) are developed. It is concluded that a good agreement exists between the numerical data, and correlation results.

This study provides a reliability improvement control method for robotic arms with clearance joints. Firstly, the dynamical model of a six-DOF robotic arm with joint clearance is established, and the Archard model is utilized to describe joint wear, considering its effect on clearance evolution. The kinematic and dynamic characteristics of the robotic arm with clearances are analyzed concerning the contact and operation state variations. Then, the influence of clearance wear on the operational reliability of the robotic arm is studied as joint wear in the robotic arm contains interval uncertainty. To provide the uncertainty factors caused by the interval, we introduce Chebyshev functions to describe the dynamic response uncertainty and reliability. The non-probabilistic reliability index is given to evaluate the reliability of the robotic arm based on the stress intensity interference theory. Lastly, to improve operational accuracy and reliability, a novel compound control strategy containing collision force feedforward and PD feedback is carried out. It is compared with the traditional PD control strategy. Also, the sensitivity and robustness of the proposed compound control strategies are discussed. The results show that the proposed control strategy can effectively enhance the dynamics precision and reliability of the robotic arm, with satisfactory robustness. This study provides the control method for joint-worn robotic arms with undesired joint clearance, having significant potential applications for guaranteeing mission reliability in the fields of aerospace and industrial robotics.