This paper presents a fully coupled aero-hydro-servo-elastic method to simulate floating offshore wind turbines (FOWT) based on Modelica language and AeroDyn co-simulations. The main features of this ...method are as follows. (1) The features of Modelica language (equation-based, object-oriented, and hierarchy structure) afford extreme flexibility and efficiency in the modeling process, and wind turbine structures or theoretical methods can be easily upgraded or replaced. (2) AeroDyn, a relatively precise aerodynamic load calculation module, is integrated into the system; thus, the model is more accurate than the previous Modelica library in calculating the responses of FOWTs. First, this paper introduces the theory of the proposed model in Modelica and AeroDyn module to calculate offshore FOWT response. Second, the implementation method for Modelica with AeroDyn is introduced. A dynamic link library (DLL) is programmed as the channel for exchanging data, and a controller to coordinate the stepping relationship between Modelica and AeroDyn is established. Third, code-to-code comparisons are performed based on International Energy Agency (IEA) Wind Task 23 Subtask 2. The results show excellent agreements between the proposed method and FAST in predicting dynamic responses of the rotor, tower, platform, and mooring system under both steady and turbulent winds combined with wave conditions. Finally, a case about high altitude work is carried out to demonstrate the flexibility of modeling processes. A single pendulum model constrained at the bottom is used to model the motion of the worker at a high altitude, coupled to the motion of a FOWT. The results show that the motion along the Y-axis is effectively suppressed as the damping force at the bottom increases, while the suppression is less pronounced on the X-axis. This method comprising the structure properties of blade and time domain potential flow hydrodynamic loads is more complete than the previous method using Modelica language to construct the fully coupled FOWT simulation model. Besides, it provides a more flexible modeling and simulation tool for some engineering practices, such as FOWT combined with fish cages, and FOWT operation and maintenance.
•A fully coupled dynamics model is established by Modelica language and AeroDyn module.•A code to code comparison with the IEC benchmark model verifies the feasibility of the proposed method.•The shared memory is programmed to account for the aero-hydro-mooring coupling effects.•The method can construct the model of the new FOWT concept with complex geometry or multi-rotor turbines.•The method shows good flexibility and scalability for unconventional load cases modeling of FOWT.
Hydropower generation is an important part of global renewable energy development. The vertical axis hydrokinetic turbine (VAHT) is a typical device to capture the kinetic energy of water. The ...optimization of its hydrodynamic performance can improve power coefficient. In this study, the Taguchi method was used to optimize the typical parameters of the vertical axis turbine, i.e., airfoil (NACA), pitch angle (β), enwinding ratio (ϖ), solidity ratio (σ), and small shaft position (O). An orthogonal array with five parameters and four levels was established; then, sixteen runs were simulated using computational fluid dynamics (CFD) software. A signal-to-noise (S/N) ratio analysis of the CFD simulation results was carried out, and the hydrodynamic performance of the optimized VAHT was studied. The results show that the influence strength order of each parameter on the power coefficient of the VAHT is featured by the relation NACA >σ > O > ϖ > β. According to the S/N ratio, the optimal combination of the five factors is as follows: NACA = 0020, β = 0°, ϖ = 1.25, σ = 0.382, and O = 0.5. In comparison with the initial design, the optimized minimum self-starting torque coefficient of the turbine is increased by 15.9%, which means that the self-starting performance is optimized. The power coefficient (CP) of optimized turbine is 0.1951, which is 17.59% higher than in the initial design, and the power coefficient fluctuation is 87.56% lower. Finally, the research findings could provide a reference for the optimal design of vertical axis turbines.
Wave energy is considered to be a kind of promising renewable energy due to its high energy density and enormous reserves. This study aims at examining the hydrodynamic performance of the ...multi-degree of freedom oscillating-buoy Wave Energy Converter (WEC). A three-dimensional numerical wave tank was developed using Star-CCM + software to investigate the interaction of waves with WEC. A mathematical model is built based on the structure of the multi-degree of freedom oscillating-buoy WEC. This paper investigated the variation in the device's energy conversion efficiency for different wave periods and spectral analyses of the motion of the floater. The effect of different elastic and damping coefficients on the device's performance was compared. The results demonstrate that the surge motion is the leading cause of the periodic variation in amplitude of floater motion. Heave motion is the main contributor to energy capture. Wave height has an influence on the contribution of the elastic and damping coefficients to the energy conversion efficiency.
•Hydrodynamic performance of the multi-degree of freedom oscillating-buoy wave energy converter (WEC) is investigated.•A mathematical model is built based on the structure of the multi-degree of freedom oscillating-buoy WEC.•The effect of floater motion on the performance of WEC is analyzed.•The influence of PTO Parameters and wave height on Energy Conversion Efficiency is investigated.
In order to extract more electricity from triboelectric nanogenerator (TENG), improving charge density are key issues. Herein, a rotating tower-like triboelectric nanogenerator (RT-TENG) with an ...innovative circuit which combine discharge tube (DT) with voltage boost circuit (D-VBC) is proposed for ultrahigh charge density breakthrough. This work designs a TENG that stacks multiple tower-like units to achieve charge compensation and systematically analysed the electromechanical coupling performance of blades. Moreover, D-VBC is established to highly improve the power and charge density. Combining the injection and storage of charge with the discharge effect, the surface charge density increases from 457 µC m−2 to 22 mC m−2(48-fold), and the average power density improves from 41 mW m−2 Hz−1 to 7300 mW m−2 Hz−1, which rapidly charge a 3.3 mF capacitor to 4.2 V within 50 s under the speed of 200 rpm. Furthermore, the power of RT-TENG with 4 tower-like units remains stable after 4 days continuous operation. Thus, this work provides a paradigm for improving the charge density and power of TENGs.
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•A rotating tower-like triboelectric nanogenerator with an innovative circuit which combine discharge tube with voltage boost circuit is proposed.•The electromechanical coupling performance of blades is systematically analysed.•This work designs a TENG that stacks multiple tower-like units to achieve charge compensation.•Combining the injection and storage of charge with the discharge effect, the surface charge density increases from 457 µC m-2 to 22 mC m-2(48-fold).
Semi-submersible offshore platforms play a vital role in deep-sea energy exploitation. However, the vast waves threaten the platform’s operation, usually leading to severe consequences. It is ...essential to study the wave-slamming mechanism of offshore platforms under extreme wave conditions. Existing research usually simplifies the offshore platform slamming problem. This paper establishes a model of a semi-submersible platform and a flexible mooring system in a numerical pool by means of the computational fluid dynamics (CFD) method. The distribution and the sensitivity of the slamming load on columns and deck in waves were investigated, and the model was verified through the basin test. Firstly, based on the Reynolds-averaged Navier–Stokes model, this study considers the volume-of-fluid method to track the free liquid level. After the column and floating body grid are locally refined, the slamming load under extreme regular wave impact is measured by measuring points on the column and deck. Then, the slamming experiment of the semi-submersible was carried out in the basin. The experiment model with a scale ratio of 1:100 was established to investigate the platform’s motion and slamming loads under extreme regular and irregular waves. The findings indicate that the slamming load at the junction of the column and deck significantly increased, exhibiting a ‘double-peak’ phenomenon at the middle of the column. The maximum pressure of slamming at the top of the column demonstrated an inverted U-shaped distribution, with negative pressure occurring after the peak value, indicating a pronounced oscillation effect.
The psychological well-being of students in higher education has become an increasingly important concern in the context of the COVID-19 pandemic. The majority of prior studies were cross-sectional ...and thereby failed to capture the individual changes in mental health over time. Moreover, few studies have explored whether and how socioeconomic and education backgrounds could be related to college students' mental health changes. This study aimed to fill these gaps.
Data were from a nationwide, two-wave panel survey of college students in China. Baseline information was collected in November 2019, i.e., before the outbreak of the COVID-19 epidemic in China. A follow-up survey was conducted in November and December 2020, when the epidemic was effectively contained in mainland China. In both waves, mental health was assessed with the 10-item Kessler Psychological Distress Scale (K10). The between-wave changes in psychological distress were measured and categorized.
Overall, 13.5% of students experienced at least a one-standard-deviation increase in psychological distress over the one-year follow-up. Results from both bivariate and multivariable analysis showed that this marked distress increase was more pronounced among vocational college students (vs. academic undergraduate and postgraduate students) and those with lower levels of academic performance. In contrast, family socioeconomic status (as measured by parental education, family economic condition, and current residence) was not associated with distress changes over time.
These findings highlight the importance of the educational disparities within the higher education system in understanding the mental health dynamics of college students in the context of the COVID-19 pandemic.
•Lip reading is a novel and intelligent way of human-computer interaction.•Quad-tree Markov random field based unsupervised lip segmentation is proposed.•Multi-scale characteristics of wavelet ...transform is applied to MRF segmentation.•Better lip segmentation accuracy is achieved compared to other MRF-based methods.
In this paper, we propose a new extended method to implement lip segmentation. Based on a quad-tree structure (QTS) Markov random field (MRF) model under unsupervised situation, the proposed method achieves the lip segmentation in wavelet domain. Firstly, we set up a multi-layer hierarchical model, in which each pixel of every layer corresponds to the four nodes in quad-tree structure. Then the probability of a branch node can be calculated by using the probability of the previous branch node through the tree structure easily. Subsequently, a Markov random field derived from the model is obtained so that the segmentation problem is formulated as a labeling optimization problem in the framework of the maximum a posteriori Markov random field (MAP-MRF). Assuming that the pre-assigned cluster of data segments may overestimate the underlying fact, and leads to over-segmentation, we propose a variable-weight segmentation approach to improve the robustness of the segmentation. The experimental results show that this method has better segmentation accuracy than traditional methods.
Typhoons are recurring meteorological phenomena in the southeastern coastal area of China, frequently triggering debris flows and other forms of slope failures that result in significant economic ...damage and loss of life in densely populated and economically active regions. Accurate prediction of typhoon-triggered debris flows and identification of high-risk zones are imperative for effective risk management. Surprisingly, little attention has been devoted to the construction of physical vulnerability curves in typhoon-affected areas, as a basis for risk assessment. To address this deficiency, this paper presents a quantitative method for developing physical vulnerability curves for buildings by modeling debris flow intensity and building damage characteristics. In this study, we selected the Wangzhuangwu watershed, in Zhejiang Province of China, which was impacted by a debris flow induced by Typhoon Lekima on August 10, 2019. We conducted detailed field surveys after interpreting remote sensing imagery to analyze the geological features and the mechanism of the debris flow and constructed a comprehensive database of building damage characteristics. To model the 2019 debris flow initiation, entrainment, and deposition processes, we applied the Soil Conservation Service-Curve Number (SCS-CN) approach and a two-dimensional debris flow model (FLO-2D). The reconstructed debris flow depth and extent were validated using observed debris flow data. We generated physical vulnerability curves for different types of building structures, taking into account both the degree of building damage and the modeled debris flow intensity, including flow depth and impact pressure. Based on calibrated rheological parameters, we modeled the potential intensity of future debris flows while considering various recurrence frequencies of triggering rainfall events. Subsequently, we calculated the vulnerability index and economic risk associated with buildings for different frequencies of debris flow events, employing diverse vulnerability functions that factored in uncertainty in both intensity indicators and building structures. We observed that the vulnerability function utilizing impact pressure as the intensity indicator tends to be more conservative than the one employing flow depth as a parameter. This comprehensive approach efficiently generated physical vulnerability curves and a debris flow risk map, providing valuable insights for effective disaster prevention in areas prone to debris flows.
In catheter based polarization sensitive optical coherence tomography (PS-OCT), a optical fiber with a rapid rotation in the catheter can cause low signal-to-noise ratio (SNR), polarization state ...instability, phase change of PS-OCT signals and then heavy noise-induced depolarization, which has a strong impact on the phase retardation measurement of the sample. In this paper, we analyze the noise-induced depolarization and find that the effect of depolarization can be reduced by polar decomposition after incoherent averaging in the Mueller matrix averaging (MMA) method. Namely, MMA can reduce impact of noise on phase retardation mapping. We present a Monte Carlo method based on PS-OCT to numerically describe noise-induced depolarization effect and contrast phase retardation imaging results by MMA and Jones matrix averaging (JMA) methods. The peak signal to noise ratio (PSNR) of simulated images processed by MMA is higher than about 8.9 dB than that processed by JMA. We also implement experiments of multiple biological tissues using the catheter based PS-OCT system. From the simulation and experimental results, we find the polarization contrasts processed by the MMA are better than those by JMA, especially at areas with high depolarization, because the MMA can reduce effect of noise-induced depolarization on the phase retardation measurement.
Radiation is the fourth most prevalent type of pollution following the water, air and noise pollution. It can adversely affect normal bodily functions. Radiation alters the protein and mRNA ...expression of drugmetabolizing enzymes and drug transporters and the pharmacokinetic characteristics of drugs, thereby affecting drug absorption, distribution, metabolism, and excretion. Therefore, it is important to study the pharmacokinetic changes in drugs under radiation.
To update data on the effects of ionizing radiation and non-ionizing radiation caused by environmental pollution or clinical treatments on the protein and mRNA expression of drug-metabolizing enzymes and drug transporters. Data and information on pharmacokinetic changes in drugs under radiation were analyzed and summarized.
The effect of radiation on cytochrome P450 is still a subject of debate. The widespread belief is that higherdose radiation increased the expression of CYP1A1 and CYP1B1 of rat, zebrafish or human, CYP1A2, CYP2B1, and CYP3A1 of rat, and CYP2E1 of mouse or rat, and decreased that of rat's CYP2C11 and CYP2D1. Radiation increased the expression of multidrug resistance protein, multidrug resistance-associated protein, and breast cancer resistance protein. The metabolism of some drugs, as well as the clearance, increased during concurrent chemoradiation therapy, whereas the half-life, mean residence time, and area under the curve decreased. Changes in the expression of cytochrome P450 and drug transporters were consistent with the changes in the pharmacokinetics of some drugs under radiation.
The findings of this review indicated that radiation caused by environmental pollution or clinical treatments can alter the pharmacokinetic characteristics of drugs. Thus, the pharmacokinetics of drugs should be rechecked and the optimal dose should be re-evaluated after radiation.
