Oscillating water column (OWC) is one of the mechanisms for extracting wave energy from ocean waves. In this study, we experimentally investigated the hydrodynamic performance of a pile-supported OWC ...structure as a breakwater, for which the air-flow through a small opening in the top cover contributes to energy extraction from waves and reduction in transmission coefficients. The effects of relative breadth, draught and opening conditions on wave reflection, wave transmission, energy dissipation and the pressure fluctuation inside the OWC chamber were examined. Compared with other types of pile-supported breakwaters, the hydrodynamic performance of the pile-supported OWC structure is remarkable and the pile-supported OWC structure has the potential for wave energy utilization.
•Wave transmission through a pile-supported OWC structure is studied experimentally.•A small opening in the top cover of OWC chamber models the power-take-off mechanism.•Transmission coefficient can be minimized by optimizing the opening size.•The OWC-type breakwater is not inferior to other pile-supported breakwaters.
Development of smart city has been increasingly accepted as a new technology-based solution to mitigate urban diseases. The Chinese government has been devoting good efforts to the promotion of smart ...city through introducing a series of policies. However, policies may have limited effectiveness in application if they do not respond to the practice. There is little study examining what results have been achieved in practice by applying policy measures. This study presents a holistic evaluation of smart city performance in the context of China. The evaluation indicators in this study are selected by applying a hybrid research methodology including literature review and semi-structured interviews. Indicator data are collected from 44 sample smart cities. The evaluation was conducted by applying Entropy method and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) technique collectively. This study highlights that the overall smart city performance in China is at a relatively low level. There is also a significant unbalance in performance between five smart city dimensions including smart infrastructure, governance, people, economy and environment. The smart performance between cities varies significantly since cities implement smart city programs in different ways. These differences impede experience sharing between cities. Actions have been recommended in this study for promoting further development of smart city in the context of China, such as increasing the investment on smart infrastructure, providing training programs, and establishing evaluation mechanism.
► Integrating oscillating water column devices with floating breakwaters can reduce costs. ► The integrated system can widen the frequency range for energy extraction. ► The integration of OWC ...devices can improve the performance of a floating breakwater.
Integrating oscillating-water-column type converters (pneumatic chambers) with slack-moored floating breakwaters can be a viable option for cost-sharing between wave energy capturing devices and shore-protection structures, and thus enhance the cost-effectiveness of wave energy utilization. When designing such integrated systems, it is desirable to have a system that can capture wave energy over a wide range of wave frequency. In this study, a configuration of floating breakwater with asymmetric pneumatic chambers (a narrower chamber on the seaside and a wider chamber on the leeside) is proposed to increase the amplitude of the oscillating air-pressures inside both chambers over a wide range of wave frequency (thus to improve the performance in wave energy extraction). A series of experiments were carried out under regular wave conditions to study the effects of asymmetric pneumatic chambers on the hydrodynamic performance of the floating breakwater and on the oscillating air-pressures inside the two chambers. It was shown that (1) the breakwater with asymmetric chambers performed as good as that with symmetric chambers in terms of wave transmission and motion responses and (2) with asymmetric configuration, it is possible to increase the amplitude of the oscillating air-pressures inside both chambers. The new concept provides a promising way to extend the frequency range over which wave energy can be extracted.
Interpersonal relationship is one of the important factors affecting college students’ mental health. The relationship between interpersonal relationship and college students’ mental health has also ...become a large number of academic research topics. In order to explore whether there is a correlation between optimism and college students’ mental health, and if so, what kind of situation it presents. Based on literature review, mathematical statistics and questionnaire survey, this study optimized the iterative process of clustering algorithm. Extract valuable parts from a large amount of precipitation of students’ psychological data, establish data models, and provide decision-making guidance for managers. The results show that there are significant differences between optimists and pessimists in optimistic factors and pessimistic factors. Optimists score significantly higher on optimistic factors than pessimists, while pessimists score significantly lower than pessimists. Conclusion optimism can significantly alleviate life stress and intervene psychological crisis.
Feature representation is critical not only for pattern recognition tasks but also for reinforcement learning (RL) methods to solve learning control problems under uncertainties. In this paper, a ...manifold-based RL approach using the principle of locally linear reconstruction (LLR) is proposed for Markov decision processes with large or continuous state spaces. In the proposed approach, an LLR-based feature learning scheme is developed for value function approximation in RL, where a set of smooth feature vectors is generated by preserving the local approximation properties of neighboring points in the original state space. By using the proposed feature learning scheme, an LLR-based approximate policy iteration (API) algorithm is designed for learning control problems with large or continuous state spaces. The relationship between the value approximation error of a new data point and the estimated values of its nearest neighbors is analyzed. In order to compare different feature representation and learning approaches for RL, a comprehensive simulation and experimental study was conducted on three benchmark learning control problems. It is illustrated that under a wide range of parameter settings, the LLR-based API algorithm can obtain better learning control performance than the previous API methods with different feature representation schemes.
This paper reviews recent progress in the study of perforated/slotted breakwaters, with an emphasis on two main groups of such breakwaters: (1) perforated/slotted breakwaters with impermeable back ...walls, and (2) perforated/slotted breakwaters without a back-wall. The methods commonly used to simulate the interactions between such structures and various linear/nonlinear waves are summarized. The transmission and reflection characteristics of perforated/slotted breakwaters in these two groups are reviewed extensively. Several methods for calculating wave forces on perforated caissons are also reviewed. Some recent works published in Chinese journals, which are generally not well-known to non-Chinese researchers, are reviewed with a hope that these works can be beneficial to other researchers working in this area.
Maintaining network connectivity is an important challenge for vehicular ad hoc network (VANET) in an urban scene, which has more complex road conditions than highways and suburban areas. Most ...existing studies analyze end-to-end connectivity probability under a certain node distribution model, and reveal the relationship among network connectivity, node density, and a communication range. Because of various influencing factors and changing communication states, most of their results are not applicable to VANET in an urban scene. In this article, we propose a connectivity prediction-based dynamic clustering (DC) model for VANET in an urban scene. First, we introduce a connectivity prediction method (CP) according to the features of a vehicle node and relative features among vehicle nodes. Then, we formulate a DC model based on connectivity among vehicle nodes and vehicle node density. Finally, we present a DC model-based routing method to realize stable communications among vehicle nodes. The experimental results show that the proposed CP can achieve a lower error rate than the geographic routing based on predictive locations and multilayer perceptron. The proposed routing method can achieve lower end-to-end latency and higher delivery rate than the greedy perimeter stateless routing and modified distributed and mobility-adaptive clustering-based methods.
The wind energy industry has been growing rapidly during the past decades.Along with this growth,engineering problems have gradually emerged in the wind power industry,including those related to the ...structural reliability of turbine towers.This study proposes a rapid seismic analysis methodology for existing wind turbine tower structures.The method is demonstrated and validated using a case study on a 1.5 MW tubular steel wind turbine tower.Three finite element(FE)models are developed first.Field tests are conducted to obtain the turbine tower’s vibrational characteristics.The tests include(1) remotely measuring the tower vibration frequencies using a long range laser Doppler Vibrometer and(2) monitoring the tower structural vibration by mounting accelerometers along the height of the tubular structure.In-situ measurements are used to validate and update the FE models of the wind turbine tower.With the updated FE model that represents the practical structural conditions,seismic analyses are performed to study the structural failure,which is defined by the steel yielding of the tubular tower.This research is anticipated to benefit the management of the increasing number of wind energy converters by providing an understanding of the seismic assessment of existing tubular steel wind turbine towers.
Previous research has established a strong link between pulse pressure (PP) and diabetes, but there is limited investigation into the connection between PP and prediabetes. This study aims to explore ...the potential association between PP and prediabetes. A retrospective cohort study encompassed 202,320 Chinese adults who underwent health check-ups between 2010 and 2016. Prediabetes was defined in accordance with the World Health Organization criteria, indicating impaired fasting glucose, with fasting blood glucose levels ranging from 6.1 to 6.9 mmol/L. To assess the PP-prediabetes relationship, we employed Cox regression analysis, sensitivity analysis, and subgroup analysis. Cox proportional hazards regression, coupled with cubic spline functions and smooth curve fitting, helped elucidate the non-linear PP-prediabetes relationship. Upon adjusting for confounding factors, we observed a positive association between PP and prediabetes (HR 1.15, 95% CI 1.11-1.18, P < 0.0001). Participants in the fourth quartile (PP ≥ 51 mmHg) had a 73% higher likelihood of developing prediabetes compared to those in the first quartile (PP < 36 mmHg) (HR 1.73, 95% CI 1.52-1.97, P < 0.0001). Moreover, the relationship between PP and prediabetes was non-linear. A two-piece Cox proportional hazards regression model identified an inflection point at 40 mmHg for PP (P for log-likelihood ratio test = 0.047). Sensitivity and subgroup analyses corroborated the robustness of our findings. Our study reveals a non-linear correlation between PP and prediabetes, signifying an increased risk of prediabetes when PP levels exceed 40 mmHg. This discovery has significant clinical implications for early prediabetes prevention and intervention, ultimately contributing to improved patient outcomes and quality of life.
This study uses a multi-phase flow model to examine the impulsive waves generated by collapse of steep slopes at a water body. Possible effects of slope’s erodibility on the motion of the landslide ...and the resulting waves are investigated by comparing a sub-aerial landslide on a rigid slope to that on an erodible slope. Key parameters that are relevant to the generation of the impulsive waves are examined, including the time series of the elevation and location of first wave crest, the location and thickness of granular flow front, submerged granular volume, and potential and kinetic energy for water and granular landslide. Before it is free from the influence of the granular front, the generated wave is a forced wave traveling at the speed of the granular flow front. The first wave crest is about to leave the granular flow front when the speed of the granular front is close to the celerity at which a free long wave can propagate in the water above the granular front, and the maximum height of the first wave crest is reached at the time when the first wave has completed its transition from a forced wave to a free wave. It appears that the erodible slope can increase (1) the volume of the granular material plunged into water, (2) the thickness of granular flow front, and (3) the height of the first wave generated by the landslide. However, the total volume of the granular material plunged into water is not directly related to the height of the first wave.
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