STUDY OF THE BILATERAL ASYMMETRY OF PLANTAR MECHANICAL PROPERTIES AS A BIOMARKER FOR THE DIFFERENTIATION OF DIABETIC CONDITION

Diabetes mellitus is a globally prevalent metabolic disease which results in altered plantar mechanical properties and foot ulcer. In this study, the bilateral asymmetry of mechanical properties for plantar soft tissue is investigated in healthy and diabetic conditions. Myotonometric signals are acquired from sub-metatarsal region of the plantar faces of healthy subjects and patients with varied diabetic age. Mechanical parameters such as dynamic stiffness and logarithmic decrement are extracted from the recorded signal. The asymmetry indices between right and left feet are computed. Statistical analysis shows that the spatial pattern of dynamic stiffness and logarithmic decrement varies significantly between healthy and diabetic subjects. The asymmetry index of dynamic stiffness in the fifth sub-metatarsal head can differentiate between healthy subjects and patients with both high and low diabetic age (p<0.05). The asymmetry index of logarithmic decrement is found to vary significantly between the healthy subjects and patients with higher diabetic age (p<0.05). These results indicate that bilateral asymmetry of myotonometric parameters can be exploited as a possible biomarker to differentiate diabetic patients from healthy subjects and can aid in the early detection of foot ulcer.

DEDETERMINATION OF THE LOGARITHMIC DECREMENT OF NATURAL VIBRATIONS OF BUILDINGS AND STRUCTURESTERMINATION OF THE LOGARITHMIC DECREMENT OF NATURAL VIBRATIONS OF BUILDINGS AND STRUCTURES

For the passport of buildings and structures, it is required to determine the logarithmic damping decrement. The proposed expressions [1, 2] to determine the decrement use the value of the Q-factor, however, an expression is known in which the damping decrement is determined through the logarithm of the ratio of the amplitudes of the damped signal. Comparison of the formulas for calculating the logarithmic decrement of vibrations was carried out using the example of data obtained when testing a beam with reinforcement.

Squeeze Film Damper Bearing With Double-Ended Beam Springs: Part II — Experimental Validation

To validate a new squeeze film damper (SFD) bearing design introduced in [1], a pair of 3.5 inch SFD bearings were manufactured and tested. Static spring compression test was conducted to prove the spring design stiffness calculated through the geometry parametric spring model. High cycle loading fatigue testing of the spring was conducted to validate the design spring fatigue limit. The entire SFD bearing assembly was inspected and checked through a SFD centering bench test before the rotor dynamic test. Unbalance response correlation and logarithmic decrement (Log. Dec.) measurement using the operational modal analysis (OMA) method were employed for the rotor-dynamic tests. An agreement was seen between the analysis and the experimental measurement. It was seen that the SFD bearing provided the extra damping as expected to suppress the unbalance vibration when passing through the critical speed and also improve the stability (Log. Dec.) of the rotor. It was found that the measured SFD damping was closer to the full film damping model when the squeeze oil film was sealed with O-rings. The SFD improved the logarithmic decrement of the rotor-bearing system from 0.07 to more than 0.21 as compared to the system without SFD.

Experimental study of parameters influencing the damping of particulate, fibre-reinforced, hybrid, and sandwich composites

In this study, we focus on the experimental determination of damping expressed by logarithmic decrement, damping ratio, and loss factor of particulate, continuous- and discontinuous- fibre reinforced, hybrid, and sandwich composites using the free vibration decay effect evaluated using the logarithmic decrement and half-power bandwidth methods. Composite materials with damping properties of magnitude several orders higher than that of traditional engineering materials are well known. However, in one study, we present different types of composite materials with different damping properties depending on various parameters such as ply angle, volume fraction, material configuration, reinforcement geometry, temperature, etc., which provide varied options to design the material arrangement of dynamically loaded components to maximize damping. Moreover, in this study, we determine typical time and frequency domain curves for individual types of analysed composites.

Experimental Investigation on Rotordynamic Characteristics and Rotor System Stability of a Novel Negative Dislocated Seal

Air-induced force generated in seals is one key factor on the stability of the rotor system. In this paper, a novel negative dislocated seal (NDS) was developed in respect of dislocated bearing theory, to reduce hydrodynamic pressure effect and air-induced force and improve rotor stability as well. A test rig was built to test rotordynamic characteristics and rotor stability of the NDS. The rotordynamic characteristics of seals were investigated based on the unbalanced synchronous excitation method, and seal-rotor system stability was evaluated by the identification method with an electromagnetic bearing exciter. The effects of both rotating speed and inlet/outlet pressure ratio on the rotordynamic characteristics and rotor stability of both NDS and conventional cylindrical labyrinth seal were experimentally investigated. The results show that with the increasing rotating speed, inlet/outlet pressure ratio is promising to reduce the direct stiffness coefficients of seals and the logarithmic decrement rate of seal-rotor system and enhance both cross stiffness and damping coefficient as well. Besides, the developed NDS effectively reduces cross-stiffness coefficients and increases direct damping coefficients and the logarithmic decrement rate of the seal-rotor system, relative to the conventional cylindrical seal. The proposed seal can effectively improve seal stability of turbomachinery.