Search Results (12)

The main shaft seal of offshore wind power equipment is one of the key components of wind power systems. However, wear issues between the seals and the main shaft caused by the intrusion of particulate matter in the environment have become a key factor affecting the service life of the equipment. To improve the surface performance of the main shaft, this study used laser cladding technology to prepare an Fe55 coating on the surface of QT-500 components. Through the wear experiments on HNBR seal pairs with the main shaft under different load conditions, this study thoroughly investigated the impact of the coating on frictional coefficients, wear mechanisms, and the wear morphology of metal surfaces. The experimental results show that the average hardness of the Fe55 coating is 533 HV, which is about 2.3 times the hardness of the substrate, and as the loading force increases, the wear form of the QT-500 metal changes from being dominated by pits to being dominated by furrows. In contrast, the wear form of the Fe55 coating is more inclined to furrows, and no pit formation is observed, indicating that the coating has improved the wear resistance of the surface. The frictional coefficient of the HNBR pair with the metal decreases with increasing load, and the frictional coefficient of the coating is lower than that of the substrate. As the loading increases, the wear morphology of the rubber surface transitions from furrows to pits, and the wear mechanism becomes abrasive wear. Full article

The field of civil engineering has witnessed significant development since the emergence of innovative control strategies that enhanced the construction of structures, imparting valuable resistance against dynamic loads like wind or earthquakes. Despite numerous articles highlighting the potential of various control approaches to reduce vibration, their effectiveness in mitigating the dynamic effects on structures under real-world conditions appears limited once implemented. A variety of factors, including practical constraints, the choice of the control system device, the shape of the structure, and the amount of control energy deployed, contribute to this lack of efficiency. Within this context, the literature primarily addressed the discrepancy between the mathematical model and the actual structure model, commonly referred to as parameter uncertainties, in the controller design process. In other words, logical continuity in this field involves the application of a more adapted control approach, which enhances performance by incorporating more practical aspects in the controller synthesis procedure. These aspects include the dynamics of the control device, high-frequency neglected modes, and the inherent limitations or constraints of the control equipment. Thus, this study treats two main active control systems, ABS and AMD. While applying an approach known as μ-synthesis, the robust control was retained because of its ability to include all these considerations when they act simultaneously. We used this control to make sure that a three-degree-of-freedom structure responds as little as possible to seismic requests, which are shown by an uncertain model. We then conducted a comparative study between these two systems, focusing on displacement reduction and control force, while exploring a classic AMD control system at the top of the structure and an ABS control system at the bottom. This approach proved to be a powerful way to deal with the uncertainties affecting the structure and achieve the stability design objectives, given the satisfying simulation results. Full article

The motor characteristics control method using the winding changeover technique can improve the matching ratio between the most frequent operating point of electric vehicle (EV) and the motor’s high-efficiency operating point, thereby enhancing the overall average efficiency of the drive system. This technology reduces back electromotive force and winding resistance by adjusting the effective number of motor winding turns according to the EV’s operating speed, ultimately improving the average efficiency. In this paper, we propose a winding changeover circuit and control method that maximizes the average efficiency in the main driving regions to extend the driving range per charge and improve the fuel efficiency of EVs. The proposed circuit is constructed using thyristor switching devices, offering the advantage of relatively lower overall system losses compared to conventional circuits. Due to the characteristics of the thyristor switching devices used in the proposed circuit, seamless winding changeover is possible during motor operation. Additionally, no extra snubber circuits are required, and the relatively low switch losses suggest the potential for improved efficiency and lightweight design in EV drive systems. To verify the proposed winding changeover circuit and control scheme, experiments were conducted using a dynamometer with an 80 kW permanent magnet motor, inverter, and the developed prototype of the winding changeover circuit. Full article

The prevailing approach to the wind resistance design of transmission towers is rooted in the quasi-static method. However, this methodology faces criticism for neglecting tower-line coupling dynamics. Despite efforts to boost structural wind resilience, the research on tower failure mechanisms, especially under extreme winds considering tower-line coupling, is limited. To address this gap, the wind-induced dynamic failure modes of the transmission tower-line system are investigated in this paper. The consistent discrete random flow generation method is employed to simulate the fluctuating wind field for transmission lines. Incorporating the compressive buckling mode of angle steel, the plastic hinge model of the frame element is employed to simulate mechanical nonlinearity. A typical transmission tower-line system is concerned, with a finite element model established for a three-tower, four-line coupled configuration. The findings reveal that the wind-induced collapse of the transmission tower is directly triggered by the buckling failure of the compressed main members, with the vulnerable section located beneath the lower cross-arm. The transmission tower experiences bidirectional bending and compression instability under an unfavorable wind direction. In contrast, the traditional pushover collapse modes of the transmission tower cannot fully capture the characteristics of the collapse failure, mainly due to the ignorance of the transverse wind force action induced by the coupling effect. This research underscores the importance of incorporating lateral dynamic considerations into transmission tower designs and advocates for optimizing strategies to mitigate wind-induced collapse modes. Full article

In view of the great impact of the pipeline system in a delayed coker unit (DCU) on production and operation safety, we applied computational fluid dynamics (CFD) to investigate the flow in a fractionator overhead vapor line connected to an air cooler in a previous study. The causes of the pipeline damage and the strategies to alleviate the occurrence of the damage were discussed. It is found that if two 24″ pipes are connected and five 18″ pipes are also connected, the force uniformity can be improved, and the forces on the caps, reducers, and T-junctions can be reduced. In this paper, we further applied the finite element method to perform structure analysis to confirm the strength of the original and the improved pipeline system. It is found that the static stress is larger when the pipelines are connected. The first four modes of the pipeline vibration are primarily affected by the vibration of the 30″ main pipe, while the fifth and the sixth modes are primarily affected by the vibration of the smaller pipes. In the case of a magnitude 1 earthquake (parallel mode) and a magnitude 2 wind, the maximum harmonic response stresses (stresses obtained from harmonic response analysis) occur at the same locations. After the pipelines are connected, some positions of the maximum harmonic response stresses are shifted from the 30″ main pipe to the 24″ pipe. In terms of the wind effect, the pipelines connected or unconnected can both withstand moderate typhoons of magnitude 13 without fatigue damage. In terms of the seismic effect, the pipelines connected can withstand a strong earthquake of magnitude 5(+) without fatigue damage, while the pipelines unconnected can withstand a very strong earthquake of magnitude 6(−) without fatigue damage, which is better than the pipelines connected. Under the action of a magnitude 17 severe typhoon, the stresses for the pipelines connected or unconnected are both lower than the yield strength and the ultimate tensile strength (UTS). There is no danger of immediate damage in terms of the wind effect. The pipelines connected or unconnected can withstand magnitude 7 earthquakes up to accelerations of 1718 gal (17.18 m/s²) and 2236 gal (22.36 m/s²), respectively, without exceeding the UTS. The pipelines unconnected are slightly better than the pipelines connected in terms of earthquake resistance. The purpose of this series study is to explore the flow development and the structural strength of the DCU pipeline system to improve its operational safety. Full article

The present paper investigates the fundamental characteristics of wind loading on vaulted (cylindrical) free roofs based on a wind tunnel experiment and a computational fluid dynamics (CFD) analysis using Large Eddy Simulation (LES). In the wind tunnel experiment, wind pressures at many points, both on the top and bottom surfaces of rigid roof models, were measured in a turbulent boundary layer. The wind tunnel models, including the tubing system installed in the roof and columns, were made using a 3D printer, which made the roof thickness as small as 2 mm, whereas the span B was 150 mm and the length L ranged from 150 to 450 mm. The rise-to-span ratio f/B ranged from 0.1 to 0.4. Pressure taps were installed along the center arc and an arc near the roof edge (verge) of an instrumented model with a length-to-span ratio of L/B = 1. The value of L/B of the tested models was changed from 1 to 3 using one or two dummy models, which had the same configuration as that of the instrumented model but no pressure taps. The wind direction θ was changed from 0° (perpendicular to the eaves) to ±90° (parallel to the eaves). The CFD simulation was carried out only for limited cases, that is, f/B = 0.1 and 0.4 and θ = 0° and 45°, considering the computational time. The effects of f/B, L/B, and θ on the mean (time-averaged) and fluctuating wind pressures acting on the roofs were investigated. In particular, the flow mechanism generating large wind forces on the roof was discussed. An empirical formula was provided for the distribution of mean wind force coefficients along the center arc (Line C) at θ = 0° and 30° and along the edge arc (Line E) at θ = 40° for each f/B ratio. Note that these wind directions provided the maximum and minimum mean wind force coefficients within all wind directions for Lines C and E. Furthermore, the maximum and minimum peak wind force coefficients on the two arcs were presented. The effect of turbulence intensity of approach flow on the maximum and minimum peak wind force coefficients was investigated. The experimental results were compared with those estimated using a peak factor approach, which showed a relatively good agreement between them. The data presented here can be used to guide the design of the main wind force-resisting systems and the cladding/components of vaulted-free roofs. Full article

To improve the radial suspension force of heteropolar hybrid magnetic bearing (HMB), a novel AC six-pole heteropolar HMB is proposed. Firstly, the structure, magnetic circuit, and suspension force generation principle are introduced and analyzed. Secondly, the equivalent magnetic circuits are established. The mathematical models of magnetic resistances, air gap magnetic fluxes, and levitation force are derived by node magnetomotive force (MMF) method. The main parameters of prototype heteropolar HMB, such as outer and inner air-gap length, winding turns, and permanent magnets, are designed. Then, the analysis model is established by MagNet 3D. The magnetic circuit, air-gap flux density, suspension mechanism, force-current relationships, force-displacement relationships, and force coupling characteristics are analyzed and calculated. Finally, the experimental system was built to test the levitation force and levitation displacement waveforms. The research results have shown that the proposed novel six-pole heteropolar HMB has a reasonable structure and magnetic circuit. The design method is also proven to be correct. Furthermore, it is compared with the traditional heteropolar six-pole HMB, the maximum suspension forces in the X and Y directions are increased by 1.96 and 2.02 times, respectively. Full article

A monopile is the most conventional structure foundation for offshore wind turbines (OWTs) in the world. However, the Korean offshore wind industry has mostly been using the jacket type of foundation. The main reason for the current situation in Korea is that most of the marine soil consists of weak layers of sand and clay. Thus, the monopile foundation depth has to be deep enough to satisfy the intended serviceability design requirement of the monopile and the rotation limit at the seabed; a conventional monopile design concept alone might be insufficient in Korean offshore conditions, or otherwise could be very expensive, e.g., resulting in a rock socket installation at the tip of the monopile. The main objective of this paper is to introduce a novel hybrid monopile that is composed of a monopile and a supplemental support with three buckets, followed by assessing the lateral resistance of the hybrid system through physical experiments and finite element (FE) simulations. Namely, 1/64.5 small-scaled monopile and hybrid physical models with a monopile diameter of 7 m for a 5.5 MW OWT were loaded monotonically. The results show that the hybrid monopile improves the lateral bearing capacity regarding the initial lateral stiffness and ultimate load. The FE analyses of the corresponding physical models were also implemented to support the results from the physical model test. The numerical results, such as the structural member forces and soil deformation, were analyzed in detail. Additionally, a case study using FE analysis was conducted for the 5.5 MW OWT hybrid monopile support installed in a representative Korean weak soil area. The results show that the hybrid monopile foundation has a larger lateral resistance and stiffness than the monopile. Full article

This paper discusses the wind loads for designing vaulted free roofs based on a wind tunnel experiment, in which the wind force coefficients for the main wind force resisting system and the peak wind force coefficients for cladding are considered. The focus is on the dynamic load effects of fluctuating wind pressures on the wind force coefficients. Wind pressure distributions on the top and bottom surfaces were measured in a turbulent boundary layer. The results indicated that the distributions of wind force coefficients changed significantly with wind direction. Then, the wind direction providing the maximum load effect on the structural frame was detected from a dynamic response analysis using the time histories of wind pressure coefficients. In the analysis, the focus was on the bending moment at the windward column base and the axial force in the leeward column as the most important load effects. The LRC method proposed by Kasperski was employed for evaluating the equivalent static wind force coefficients providing the maximum load effects. Based on the results, a model of design wind force coefficient was proposed in the framework of the conventional gust effect factor approach. Finally, positive and negative peak wind force coefficients for designing the cladding were proposed based on the most critical maximum and minimum peak wind force coefficients among all wind directions. Full article

Path planning of unmanned aerial vehicles (UAVs) is one of the vital components that supports their autonomy and deployment ability in real-world applications. Few path-planning techniques have been thoroughly considered for multirotor UAVs for pursuing ground moving targets (GMTs) with variable speed and direction. Furthermore, most path-planning techniques are generally devised without taking into consideration wind disturbances; as a result, they are less suitable for real-world applications as the wind effect usually causes the UAV to drift and tilt from its original course, impacting the mission’s main objective of having an adequate non-deviant camera aim point and steady coverage over the GMT. This paper presents a novel UAV path-planning technique, based on the artificial potential field (APF) for following GMTs in windy environments, to provide steady and continuous coverage over the GMT, by proposing a new modified attractive force to enhance the UAV’s sensitivity to wind speed and direction. The modified wind resistance attractive force function accommodates for any small variation of relative displacement caused by wind leading the UAV to drift in a certain direction. This enables the UAV to maintain its position by tilting (i.e., changing its roll and pitch angles) against the wind to retain the camera aim point on the GMT. The proposed path-planning technique is hardware-independent, does not require an anemometer for measuring wind speed and direction, and can be adopted for all types of multirotor UAVs equipped with basic sensors and an autopilot flight controller. The proposed path-planning technique was evaluated in a Gazebo-supported PX4-SITL and a robot operating system (ROS) for various simulation scenarios. Its performance demonstrated superiority in handling wind disturbances and showed high suitability for deployment in real-world applications. Full article

The adequacy of the directional and envelope procedures for the design of the main wind force resisting system is not well understood. The purpose of this study is to evaluate the directional and envelope procedures based on wind tunnel test data for a set of low-rise enclosed buildings with gable-shaped roofs in open terrain (Exposure C). The base shear force and the conditional reliability index are used to determine the adequacy of the procedures. The base shear was compared to the design base shear in each direction based on the horizontal component of the wind load on the wall and roof. The reliability index, β conditional on the occurrence of the design wind speed was computed for a range of system capacities. The main findings are (1) the directional procedure produced a larger design base shear compared to the envelope procedure, primarily due to the difference in external pressure coefficients, (2) the directional procedure provided a higher β, and (3) the envelope procedure provided a β that did not meet the standard target β equal to 3.0 for the main wind force resisting systems with low variability in capacity, but neither procedure met the standard target β for the main wind force resisting systems with high variability in capacity. Full article

The barrier layer (BL) is a layer of water separating the thermocline from the density mixed layer in the upper ocean, which has the capability of reducing the negative feedback effect caused by tropical cyclone (TC) acting on the upper ocean and back on the TC itself. This study analyzed in-situ Argo floats measurements, data-assimilated HYCOM/NCODA reanalysis, and the longer-term (1961–2010) variations of Ocean Reanalysis System 4 (ORAS4) based BL in the TC main development region (MDR) to characterize the BL in the western North Pacific (WNP) for different temporal scales and to understand its role in resisting TC induced sea surface cooling. First, the result indicates that the effect of BL on TC enhancement in the MDR of WNP might be overestimated. Further analysis based on partial correlation shows that the BL plays a key role in resisting the cooling response only while BL is strong (BL thickness ≥ 5 m) and TC wind forcing is weak. Meanwhile, the distribution of BL demonstrates markedly the mesoscale characteristic. BL with thickness 0–5 m occupies the highest proportion (~67.55%), while thicker BL (BL thickness (BLT) larger than 5 m) takes up about 25–30%. Besides, there are ~3% with BL thicker than 30 m. For life length, BLT with 0–5 m is limited to 5 days, while BL with thickness more than 30 m can persist for more than 30 days. The scenario is attributed to diverse processes that result in different characteristic temporal scales of BL. Additionally, the analysis of coverage region and average BLT in the recent decade shows a serious situation: both the spatial coverage and BLT increase sharply from 2001 to 2010, which implies that TC–BL interactions might occur more frequently and more vigorously in future if the changing trend of BL remains unchanged. Full article