Sandwich structures are extensively utilized as a structural component in different engineering applications such as aircraft, automotive and construction industries. For this reason, vibration damping behavior comes into prominence for structural health. Shear thickening fluid (STF) is a candidate smart material for vibration isolation in structural members due to its viscoelastic properties. In this work, we fabricated a novel concept by filling an STF into the extruded polystyrene (XPS) foam core of an aluminum face sheet sandwich structure to take advantage of STF rheology during vibrational loadings. In addition to consideration of temperature effect on STF based structures for the first time, STF usage has been extended to foam core sandwich systems with this design. The vibrational characteristics in these smart composites were analyzed by using modal analysis and therefore, natural frequencies and damping ratios were calculated for the structures. According to the results, STF inclusion in the sandwich structures leads to a significant development in the vibration attenuation properties whereas increasing temperature exhibits a disruption in the damping behavior.

Vibration attenuation of sandwich structures filled with shear thickening fluids

Smart polymer integrated cork composites for enhanced vibration damping properties

Self-balancing system of the disk on an elastic shaft

Nearly a century ago, the liquid self-balancing device was first introduced by M. LeBlanc for passive balancing of turbine rotors. Although of common use in many types or rotating machines nowadays, little information is available on the unbalance response and stability characteristics of this device. Experimental fluid flow visualization evidences that radial and traverse circulatory waves arise due to the interaction of the fluid backward rotation and the baffle boards within the self-balancer annular cavity. The otherwise destabilizing force induced by trapped fluids in hollow rotors, becomes a stabilizing mechanism when the cavity is equipped with adequate baffle boards. Further experiments using Particle Image Velocimetry (PIV) enable to assess the active fluid mass fraction to be one-third of the total fluid mass. An analytical model is introduced to study the effects of the active fluid mass fraction on a flexible rotor supported by flexible supports excited by bwo different destabilizing mechanisms; rotor internal friction damping and aerodynamic cross-coupling. It is found that the fluid radial and traverse forces contribute to the balancing action and to improve the rotor stability, respectively.

https://downloads.hindawi.com/journals/sv/2013/742163.pdf

Liquid self-balancing device effects on flexible rotor stability

The most prevalent problem in washing machines is the vibration incurred during the spin cycles. The balance of the washing machine plays an important role in reducing the vibrations from an unbalanced mass by injecting salt water into an automatic balancer. In this study, we determined the optimal dimension of layers and the amount of salt water for an automatic liquid balancer in order to minimize the maximum displacement of a low-speed spin cycle while satisfying the design constraint on the maximum displacement of a high-speed spin cycle. The maximum displacements for a specified design point were obtained by performing laboratory experiments. For design optimization, approximate models of the maximum displacements were created by employing radial basis function regression (RBFr) models based on the experimental data at full factorial design points. Then, an optimization algorithm was applied to the RBFr models to obtain the optimum solution. Using the proposed design approach, the optimal value of the maximum displacement of a low-speed spin cycle was reduced by 13.1%, compared to the initial value, while satisfying the design constraint on the maximum displacement of a high-speed spin cycle.

Experiment-based design optimization of a washing machine liquid balancer for vibration reduction

The paper describes a high-speed camera and a Particle Image Velocimetry (PIV) technique used on a transparent liquid balancing device for washing machines. Experimental results indicate that the baffle-liquid interaction renders fluid modes of vibration of circumferential and axial type. This complex swirl flow is comprised of two inertial waves; one of such waves is synchronous with the rigid body motion, while the other is a fluid backward traveling wave, thus enhancing the system damping capability. This damping phenomenon was revealed by the fluid flow visualization and Particle Image Velocimetry (PIV) technique employed. NOMENCLATURE

Dynamic performance of the leblanc balancer for automatic washing machines

Rotordynamic Optimization of Fixed Pad Journal Bearings Using Response Surface Design of Experiments

Improved design of a bladed hydraulic balance ring

\n A robust approach to investigate a tilting pad journal bearing (TPJB) as a whole tolerance stack-up assembly is presented. Normal component variation within actual design tolerances is considered. The vector loop is expanded via Taylor series for sensitive analysis. The bearing shell and tilting pad machined radiuses for each pad are found to be the more influential dimensional characteristics on the assembled clearance and preload. A leading edge relief (LER) was used to avoid unloaded pads fluttering, while maintaining a satisfactory bearing assembled clearance in the loaded pads throughout the resultant preload variation. Pivot flexibility and preload loss due to pad wear in service life were included in the preload variation assessment. Surface response multivariate multiresponse models were built for a 4-pad TPJB under load between pad (LBP) and load on pad (LOP) configurations. Desirability functions rendered the maximum and minimum rotordynamic coefficient and tribological parameter responses across speed. The LOP configuration showed more variation in the direct rotordynamic coefficients, while the LBP configuration indicated more sensitive cross-coupled coefficients with very strong sign change in some cases. Among the tribological performance parameters, the eccentricity and pad maximum pressure were more affected, followed by the minimum film thickness, and weakly by the power loss, and oil film temperature. The dispersion of the tribology parameters under normal manufacturing variation is found of importance. Four, and seven extreme geometrical state cases were identified for the LBP, and LOP bearing configurations, respectively.

Leonardo Urbiola-Soto

Papers

Liquid self-balancing device effects on flexible rotor stability

Dynamic performance of the leblanc balancer for automatic washing machines

Rotordynamic Optimization of Fixed Pad Journal Bearings Using Response Surface Design of Experiments

Improved design of a bladed hydraulic balance ring

Influence of Manufacturing Variation on the Dynamic and Tribological Performance of Tilting Pad Journal Bearings