Processing forced vibration test records of structural systems using the analytic signal

This article presents the use of the analytic signal procedure for processing the large volume of structural vibration data recorded in forced vibration tests. The analytic signal facilitates the computationally laborious task of extracting the steady-state amplitude for each response measure of interest from the recorded accelerations throughout the building at each operated frequency of the forced vibration source. The implementation of the signal processing procedure introduced here is illustrated in deriving the acceleration–frequency response curves from the forced vibration test of the first permanently instrumented building in Turkey. This reinforced concrete building, subsequently strengthened with cast-in-place reinforced concrete infill shear walls, is located in close proximity to the North Anatolian Fault. Later, system identification of the building yields the in situ structural system dynamic properties for the first translational and torsional vibration modes, which are compared with those identified from the ambient vibrations of the building recorded following its forced vibration test. The analytic signal procedure is a convenient tool for the rapid and correct derivation for mode shapes and associated frequencies and damping ratios from forced vibration testing of structural systems.

Wind Tunnel Measurement Systems for Unsteady Aerodynamic Forces on Bluff Bodies: Review and New Perspective

Wind tunnel tests have become one of the most effective ways to evaluate aerodynamics and aeroelasticity in bluff bodies. This paper has firstly overviewed the development of conventional wind tunnel test techniques, including high frequency base balance technique, static synchronous multi-pressure sensing system test technique and aeroelastic test, and summarized their advantages and shortcomings. Subsequently, two advanced test approaches, a forced vibration test technique and hybrid aeroelastic- force balance wind tunnel test technique have been comprehensively reviewed. Then the characteristics and calculation procedure of the conventional and advanced wind tunnel test techniques were discussed and summarized. The results indicated that the conventional wind tunnel test techniques ignored the effect of structural oscillation on the measured aerodynamics as the test model is rigid. A forced vibration test can include that effect. Unfortunately, a test model in a forced vibration test cannot respond like a structure in the real world; it only includes the effect of structural oscillation on the surrounding flow and cannot consider the feedback from the surrounding flow to the oscillation test model. A hybrid aeroelastic-pressure/force balance test technique that can observe unsteady aerodynamics of a test model during its aeroelastic oscillation completely takes the effect of structural oscillation into consideration and is, therefore, effective in evaluation of aerodynamics and aeroelasticity in bluff bodies. This paper has not only advanced our understanding for aerodynamics and aeroelasticity in bluff bodies, but also provided a new perspective for advanced wind tunnel test techniques that can be used for fundamental studies and engineering applications.

Study of the vibration transmission property of warp-knitted spacer fabrics under forced sinusoidal excitation vibration

The main content dealt with in this paper was to make a theoretical analysis of the vibration transmission property of spacer fabric as cushion materials. A forced vibration test with sinusoidal excitation was conducted, and the corresponding model of the vibration transmission coefficient was established based on a single-degree-of-freedom system. Experimental and theoretical vibration indexes, including natural frequency and the vibration transmission coefficient, were obtained from experimental and theoretical vibration transmission coefficient–frequency curves, respectively. After comparing theoretical parameters with experimental parameters, we were pleased to find out that their maximum vibration transmission coefficient and natural frequency showed good accordance with each other. Moreover, the effect of different parameters of spacer fabric on vibration transmission properties, including thickness, filament diameter, area density and inclination angle and arrangement of spacer filaments, were investigated, which is helpful to better design spacer fabrics with good vibration transmission.

Time Domain Analysis Approach for Riser Vortex-Induced Vibration Based on Forced Vibration Test Data

As oil and gas exploration and production are pushed into deepwater area, the offshore industry is facing more challenges for riser vortex induces vibration (VIV). Although frequency domain approach has been widely used for the riser VIV prediction and fatigue design, several assumptions need to be made. In addition, frequency domain approach cannot account for the variable current and riser nonlinear boundary conditions, such as top boundary response, the interaction between riser and guides in the hull and soil-SCR interaction. Considering above cases, several time domain codes have been developed for riser cross-flow (CF) VIV prediction. This paper presents a time domain approach based on forced algorithm. The exciting force is derived from the non-dimensional amplitude and frequency dependent lift coefficients from forced vibration test. The hydrodynamic damping model consists of empirical model and the extension of the lift curves. At each step, the displacement and velocity of each element would be obtained to calculate the response amplitude and frequency for the lift coefficient and damping. Expect for CF VIV, the mean drag force is also considered, which would be magnified by CF VIV. The model test at Delta Flume of Delft Hydraulics is simulated using the proposed approach, and the CF VIV responses and the mean drag displacement are predicted. The results match well with the measured data.

Testing and Analysis of the Dynamic Parameters of 3D Reciprocating Compressor Foundation

It is necessary to test dynamics parameters of foundations at construction ground of large-size dynamic machine base. This paper elaborate the test technology and data processing methods on the basis of the block forced vibration test with engineering example, and test results are analyzed and discussed.