Dynamic deformation monitoring of an offshore platform structure with accelerometers

In this paper, structural characteristics are evaluated by displacement and frequency indicators that indicate the real-time health status of offshore platforms. This paper uses an accelerometer to collect the dynamic response of the platform in the event of a ship collision. The main contributions of this research are reflected in three aspects. Firstly, based on Empirical Mode Decomposition (EMD) multiscale decomposition, the noise range is determined according to the scale and the average value of the standardized accumulation mode, and the original acceleration sequence is denoised. Secondly, two impact tests were carried out to understand the platform's structural characteristics under an external load. Combined with the FFT algorithm and Hilbert Huang transform, the three-dimensional information of the time, frequency, and energy is analyzed. Finally, a method of high-frequency dynamic displacement reconstruction is proposed. According to the extracted vibration frequency information, the parameters for the filter are reasonably set, and the denoised acceleration time sequence is processed with bandpass filtering and quadratic integration to obtain the high-frequency dynamic displacement of the structure. The results show that the high-frequency dynamic displacement of the accelerometer reconstruction is 1.5 mm. Two collision event frequencies, 1.477 Hz and 1.483 Hz, were successfully extracted from the north direction.

Uncertain Response Analysis of Fractionally-Damped Beams Based on Interval Process Model

In the uncertain vibration analysis of fractionally-damped beams whose damping characteristic is described using fractional derivative model, the uncertain excitation is usually modeled as a stochastic process. However, it is often difficult to obtain sufficient samples of the excitation to establish a precise probability distribution function for the stochastic process model in practical engineering problems. Hence, in this paper, a nonrandom vibration analysis method for fractionally-damped beams is proposed to obtain the dynamic displacement response bounds of the beams under the uncertain excitation. Specifically, the uncertain excitation applied to the fractionally-damped beam is treated as a spatial-time interval field, so that the dynamic displacement response of the beam is also a space-time interval field. The middle point function and the radius function of the displacement response of the fractionally-damped beam can be derived based on the modal superposition method and the Laplace transform, through which the bound functions of the dynamic displacement response can be obtained. In addition, several numerical examples are given to demonstrate the effectiveness of the proposed method.

Investigation of Dynamic Load in Superdeep Mine Hoisting Systems Induced by Drum Winding

Blair mine hoists powered by drum winding are a key equipment in the transportation of a superdeep mine shaft. The step changes of hoisting velocity and acceleration caused by coil and layer crossover of rope winding on the LeBus drum, which will excite impact responses of hoisting systems, cannot be ignored in the hoisting system with high velocity. The paper focuses on investigating the effect of drum winding on impact responses of superdeep mine hoisting systems. Firstly, the hoisting velocity and acceleration were precisely modelled and calculated according to the structure of rope groove of the LeBus drum; secondly, impact responses of the dynamic displacement and load were obtained by applying the established model; eventually, an experiment was performed, and then, the validity of the established model and the response mechanism was verified. The paper will provide good technical support for the design and optimization of the mine hoists in superdeep mine shafts.

Revealing the Dynamic Characteristics of Composite Material-Based Miura-Origami Tube

Although Miura origami has excellent planar expansion characteristics and good mechanical properties, its congenital flaws, e.g., open sections leading to weak out-of-plane stiffness and constituting the homogenization of the material, and resulting in limited design freedom, should also be taken seriously. Herein, two identical Miura sheets, made of carbon fiber/epoxy resin composite, were bonded to form a tubular structure with closed sections, i.e., an origami tube. Subsequently, the dynamic performances, including the nature frequency and the dynamic displacement response, of the designed origami tubes were extensively investigated through numerical simulations. The outcomes revealed that the natural frequency and corresponding dynamic displacement response of the structure can be adjusted in a larger range by varying the geometric and material parameters, which is realized by combining origami techniques and the composite structures’ characteristics. This work can provide new ideas for the design of light-weight and high-mechanical-performance structures.

An Improved Large-Field Microscopic Speckle Interferometry System for Dynamic Displacement Measurement of MEMS

The traditional microscopic speckle interferometer has limited applications in engineering due to its small field of view. In this paper, we propose a large-field microscopic speckle interferometer which embeds two doublet lens groups in the improved Mach–Zehnder optical path structure to expand its field of view. At the same time, the new system can reduce the coherent noise of reflected light in the optical path. We use this new system to measure the dynamic displacement process of the entire surface of the microchips. The experimental results show that our improved measurement system can achieve large-field, real-time and high-precision dynamic measurement of micro-electromechanical systems (MEMS).