Advances in Science and Technology Vol. 83

Abstract: A new constructive solution for the offshore wind power generation is to use floating wind turbines. An offshore wind farm situated sufficiently far away from the coast can generate more wind power and will have a longer operation life since the wind is stronger and more consistent than that on or near the coast. One of the main challenges is to reduce the fatigue of a floating wind turbine so as to guarantee its proper functioning under the constraints imposed by the floating support platforms. This paper will discuss the structural control issues related to the mitigation of dynamic wind and wave loads on the floating wind turbines so as to enhance the offshore wind power generation.

Abstract: The New Headquarters of Shenzhen Stock Exchange (NHSSE), located in Shenzhen, China, is a high-rise building with a height of 228 m. One salient feature of NHSSE is its huge floating platform. It is a steel truss structure assembled with a total of 14 steel trusses in six types. It overhangs from the main tower 36 m along the long axis and 22 m along the short axis at a height of 36 m above the ground. As a result, the huge floating platform has an overall plan dimension of 98 m × 162 m and a total height of 24 m, making it one of the largest cantilever structures in the world. In view of the uniqueness of the floating platform, a long-term structural health monitoring (SHM) system has been designed and implemented on NHSSE by The Hong Kong Polytechnic University. In this monitoring system, the strain and deflection of the cantilever structure are of the utmost concern. A total of 224 vibrating-wire strain gauges have been installed to measure the strain and a novel vision-based displacement tracking system has been employed to monitor the deflection. In addition, accelerometers and a wireless sensing network (WSN) are implemented to monitor dynamic responses and modal properties of the structure. This paper reports the monitoring results of stress evolution of NHSSE during the construction process of dismantling the shoring and modal properties of NHSSE under ambient vibration environment, as well as their comparison with the prediction results through finite element analysis.

Abstract: The data management system (DMS) is an essential part for long-term structural health monitoring (SHM) systems, which stores a pool of monitoring data for various applications. A robust database within a DMS is generally used to archive, manage and update life-cycle information of civil structures. However, many applications especially those to large-scale structures provide little support for visualizing the long-term monitoring data. This paper presents the development of an efficient visualized DMS by integrating 4-dimension (4D) model technology, nested relational database, and virtual reality (VR) technology. Spatial data of the 4D model are organized in nested tables, while real-time (temporal) monitoring data are linked to the 4D model. The model is then reconstructed by use of an OpenSceneGraph 3D engine. A user interface is developed to query the database and display the data via the 4D model. To demonstrate its efficiency, the proposed method has been applied to the Canton Tower, a supertall tower-like structure instrumented with a long-term SHM system

Abstract: Among structural concerns for the safety of rail transportation are internal flaws and thermal stresses, both of which can cause disruption of service and even derailments. Ultrasonic guided waves lend themselves to addressing both of these problems. This paper reports on two inspection systems for rails being developed at UCSD under the auspices of the US Federal Railroad Administration. Both systems utilize ultrasonic guided waves as the main probing mechanism, for the two different applications of flaw detection and thermal stress detection.

Abstract: Subsea infrastructures and broadly speaking any structure containing or surrounded by water such as water mains represent an important element of modern civilization. An arbitrary classification could consist of five groups: offshore structures that serve to extract oil or natural gas from the sea bead; communication cables; pipelines that carry oil and natural gas; naval vessels (ships and submarines); waterfront facilities such as piers, retaining walls, and docks. The occurrence of structural failure of any of these systems can have serious consequences for the people, the environment, and the economy. In this paper we describe the most important nondestructive techniques adopted to assess the health of offshore structures, pipelines, and marine facilities.

Abstract: In this study, an automated cable monitoring system using a NDE technique and a cable climbing robot is proposed. MFL (Magnetic Flux Leakage- based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults (LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the level of damage. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. In addition, the measured magnetic flux signal was visualized into a 3D MFL map for convenient cable monitoring. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

Abstract: This paper demonstrates damage detection in a smart sandwich panel with integrated piezoceramic transducers. The panel is built from a chiral honeycomb and two composite skins. A low-profile, surface-bonded piezoceramic transducer is used for high-frequency ultrasonic excitation. Low-frequency excitation is performed using a piezoceramic stack actuator. Ultrasonic sensing is performed using laser vibrometry. Nonlinear acoustics is applied for damage detection. The study is focused on sensor location analysis with respect to vibro-acoustic wave modulations. The paper demonstrates that when structure is damaged, the high-frequency “weak” ultrasonic wave is modulated by the low-frequency “strong” vibration wave. As a result frequency sidebands can be observed around the main acoustic harmonic in the spectrum of the ultrasonic signal. However, intensity of modulation strongly depends on sensor location.

Abstract: In the present paper, we introduce an application of two damage detection methods to a laboratory structure. One of the methods is based on autoregressive modeling of the signals involved, whereas the second one is based on subspace identification. Both have been tested in a tower that simulates a wind turbine. The results obtained are correct for the damages simulated by loosening some bolts of the different joints. The results show that the second method is computationally more efficient whereas the results are more stable in the first one.