•Establishing the digital twin approach aimed at monitoring the RUL of the components.•Computationally fast DT models of drivetrain components based on torsional measurements.•Confidence interval for ...components damage by stochastic models and statistical approaches.•A robust and computationally fast method to estimate drivetrain ROM parameters of different DOFs.•Using estimated parameters for automated fault diagnosis and prognosis.•Physics-based degradation model to estimate RUL of shafts by estimated ROM, real-time measurements and load observer.•Taking into account the uncertainties by statistical approaches and stochastic modeling of damage.
This paper presents a digital twin (DT) condition monitoring approach for drivetrains on floating offshore wind turbines. Digital twin in this context consists of torsional dynamic model, online measurements and fatigue damage estimation which is used for remaining useful life (RUL) estimation. At first, methods for system parameter estimation are presented. The digital twin model provides sufficient inputs for the load observers designed in specific points of the drivetrain to estimate the online load and subsequently stress in the different components. The estimated real-time stress values feed the degradation model of the components. The stochastic degradation model proposed for estimation of real-time fatigue damage in the components is based on a proven model-based approach which is tested under different drivetrain operations, namely normal, faulty and overload conditions. The uncertainties in model, measurements and material properties are addressed, and confidence interval for the estimations is provided by a detailed analysis on the signal behavior and using Monte Carlo simulations. A test case, using 10 MW drivetrain, has been demonstrated.
This research is organized to carry out the Natural Frequency Factors (NFFs) coupled with the most functional structure employed in the various fields of engineering and one of the essential ...structures in industries made by assembling Spherical (S), Cylindrical (Cy), and Conical (Co) shells named Assembled Spherical-Cylindrical-Conical Shell (ASCCS). In addition, four new sandwich nanocomposite models, including agglomerated Functionally Graded Carbon Nano-Tubes (FG-CNTs) for Top Face Sheet (TFS) and Bottom Face Sheet (BFS) and Core Layer (CL) with porosity feature, are employed to enhance applications of the ACCCS structure here. The Eshelby-Mori-Tanaka Hypothesis (EMTH) is applied to discover the TFS and BFS mechanical features for this object. The Equivalent Single Layer Technique (ESLT) is also implemented to obtain the mechanical characteristics of the new sandwich nanocomposite. In addition, to discover the effects of Elastic Boundary Conditions (EBCs), the Artificial Spring Scheme (ASS) is engaged in this work. Moreover, The First Share Deformation Theory (FSDT) and Donnell’s Simplifications (DSs) are applied to determine the fundamental relationships of the ASCCS (for each part). Also, Hamilton's method is used for each element to seek the Governing Motion Equations (GMEs) affiliated with the ASCCS. Next, the GMEs of the structure are discretized by employing the well-structured scheme titled the Generalized Differential Quadrature (GDQ) strategy. Afterward, the NFFs of the ASCCS are found by determining the eigenvalues. Then, the NFFs obtained from the presented method are compared with the NFFs determined by FE-based commercial software. Ultimately, various novel examples are planned and solved to illustrate the effects of the geometrical, material, and the EBCs changes on the NFFs of the ASCCS structure.
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Alkyl ketene dimer (AKD) is frequently used in paper industry as an inexpensive sizing agent. The formation of a porous structure after curing the solidified AKD for an extra-long ...time (4–6 days) results in superhydrophobicity. In this study, a facile and low-cost method was utilized to turn the surface of AKD superhydrophobic in a very short period of time.
We fabricated superhydrophobic coatings by dipping glass and paper substrates in molten AKD and then treating them with ethanol after solidification. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Confocal laser scanning microscopy, and dynamic contact angle goniometry.
The results show that briefly treating the coatings, obtained from isothermally heated AKD melt at 40 °C for 3 min, with ethanol leads to superhydrophobicity with advancing and receding contact angles of 158.7 ± 1.4° and 156.8 ± 0.9°, respectively. By increasing the melt temperature to 70 °C and its heating time to 6 h followed by ethanol treatment, the advancing and receding contact angles increased to 163.7 ± 1.3° and 162.6 ± 1.2°, respectively. This enhancement in superhydrophobicity is due to the formation of porous, entangled irregular micro/nano textures that create air cushions on the surface resulting in droplet state transition from Wenzel to Cassie.
•THUMOS challenge was introduced in 2013 to serve as a benchmark for action recognition.•In this paper we describe the THUMOS benchmark in detail.•Give an overview of data collection and annotation ...procedures.•Present results of submissions to the THUMOS 2015 challenge and review the participating approaches.•We conclude by proposing several directions and improvements for future THUMOS challenges.
Automatically recognizing and localizing wide ranges of human actions are crucial for video understanding. Towards this goal, the THUMOS challenge was introduced in 2013 to serve as a benchmark for action recognition. Until then, video action recognition, including THUMOS challenge, had focused primarily on the classification of pre-segmented (i.e., trimmed) videos, which is an artificial task. In THUMOS 2014, we elevated action recognition to a more practical level by introducing temporally untrimmed videos. These also include ‘background videos’ which share similar scenes and backgrounds as action videos, but are devoid of the specific actions. The three editions of the challenge organized in 2013–2015 have made THUMOS a common benchmark for action classification and detection and the annual challenge is widely attended by teams from around the world.
In this paper we describe the THUMOS benchmark in detail and give an overview of data collection and annotation procedures. We present the evaluation protocols used to quantify results in the two THUMOS tasks of action classification and temporal action detection. We also present results of submissions to the THUMOS 2015 challenge and review the participating approaches. Additionally, we include a comprehensive empirical study evaluating the differences in action recognition between trimmed and untrimmed videos, and how well methods trained on trimmed videos generalize to untrimmed videos. We conclude by proposing several directions and improvements for future THUMOS challenges.
The COVID-19 pandemic has become a global health issue and has had a major impact on education. Consequently, half way through the second semester of the academic year 2019/2020, learning methods ...were delivered through distance learning (DL). We aimed to evaluate the student perspective of DL compared to classroom learning (CL) in the undergraduate dentistry study program at the Faculty of Dentistry Universitas Indonesia.
An online questionnaire was sent at the end of the semester. A total of 301 students participated in the study.
Duration of study influenced student preference. Higher number of first-year students preferred DL compared to their seniors (p < 0.001). Students preferred CL for group discussion, as DL resulted in more difficult communication and gave less learning satisfaction. Only 44.2% students preferred DL over CL, although they agreed that DL gave a more efficient learning method (52.6%), it provided more time to study (87.9%) and to review study materials (87.3%). Challenges during DL included external factors such as unstable internet connection, extra financial burden for the internet quota and internal factors such as time management and difficulty to focus while learning online for a longer period of time.
Despite some challenges, dental students could adapt to the new learning methods of full DL and the majorities agreed blended learning that combined classroom and distance learning can be implemented henceforth. This current COVID-19 pandemic, changes not only the utilization of technology in education but the pedagogy strategies in the future.
This paper presents a numerical multiscale formulation for analysis of the transient heat and fluid flow in deformable heterogeneous porous media. Due to the heterogeneity of the media, the direct ...numerical simulation of the micro-structures leads to high computational costs. Hence, the multi-scale method can provide an efficient computational procedure. To this end, the first-order computational homogenization is adopted for two-scale simulation of THM problems. The governing equations of the problem contain a stress equilibrium equation, a mass continuity equation and an advection–diffusion equation in a fully coupled manner. Accordingly, the proper virtual power relations are defined as a bridging stage between the scales. The boundary conditions of the microscopic domain are specified in terms of the macroscopic information to fulfill the averaging constraints. In order to consider the transient effects, the micro-inertial terms are included in the micro-scale simulation, and then the microscopic boundary conditions are enhanced to assess the efficiency and accuracy. The macroscopic properties including the homogenized tangent operators and equivalent quantities are determined from the microscopic solution through the appropriate mathematical procedures. Moreover, an upwind finite element squared method is employed for highly advective heat transfer to achieve the accurate spatial results. Finally, several comprehensive examples are simulated to study the effectiveness and validity of the proposed computational model, particularly the boundary conditions; moreover, different case studies are discussed such as the highly advective flow, pure conduction heat transfer and a combined conduction–convection heat transfer.
•A two-scale method is developed for transient heat and fluid flow in porous media.•Advection-diffusion equation is adopted to account for heat transfer phenomenon.•Micro-inertial terms are included in the micro-scale analysis.•The microscopic boundary conditions are enhanced to assess the accuracy.•An upwind FE2 is employed for highly advective heat transfer.
The addition of surfactants to pure water for specific applications has made controlling the impact dynamics of surfactant-laden droplets a complex phenomenon. This work investigates the influence of ...the molecular weight (MW), concentration, and ionic nature of the surfactants as well as the substrate surface characteristics on the impact dynamics of surfactant-laden droplets using a high-speed camera at 10 000 frames per second. Sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and n-decanoyl-n-methylglucamine were used as anionic, cationic, and nonionic surfactants, respectively. We used hydrophilic glass slides, hydrophobic polytetrafluoroethylene, and superhydrophobic alkyl ketene dimer (AKD) as substrates. The results show that the efficiency of the surfactant addition in increasing the maximum spreading diameter is significantly influenced by the molecular weight and ionic nature of the solutions as well as the nonwettability of the substrate. Among all of the surfaces examined, the concentration and ionic nature of the solutions were found to be more dominant parameters in determining the energy dissipation in the retraction phase of the droplet impact on the superhydrophobic AKD surfaces. As the concentration decreases or positive charges are present in the solution, it is more likely to observe a similar retraction dynamic to pure water when the droplet hits the superhydrophobic AKD having negatively charged surface sites. Finally, in terms of the impact outcomes of the surfactant-laden droplets on the superhydrophobic AKD, it is shown that the influence of the surfactant addition is more noticeable at lower Weber numbers, where the droplet tries to rebound by overcoming the energy loss that occurred in the spreading.
Despite the usual belief that only curved micro-structures can behave bi-stably, recently, it has been substantiated that flat micro-structure can also experience this type of behavior. In this way, ...the present paper aims to investigate snapping behavior in pressurized 2-D flat micro-electro-mechanical plates with a rectangular shape. To this end, a size-dependent and geometric non-linear thin plate model based on the modified couple stress theory is employed. The governing equilibrium equations as well as their corresponding boundary conditions are obtained using the principle of the minimum total potential energy. Employing an efficient Galerkin's discretization procedure, the instability thresholds of the system are determined by vanishing the first and the second variations of the total potential energy expression of the system. The present findings for non-pressurized systems are verified by those published in previous studies. Furthermore, the results concerning the cases under the differential pressures are validated through direct comparison with those extracted from 3-D finite element simulations carried out in COMSOL Multiphysics commercial software. Results reveal that flat micro-plates may experience snap-through instability when they are subjected to some certain values of the differential pressure in the opposite direction of the electrical field. To find the conditions in which a flat micro-plate may face with the snapping behavior, a large number of systems with different material and geometric properties are analyzed. Employing this detailed parametric study, snapping criteria which provide the combination of the system properties and the level of the applied pressure required for prompting snap-through instability are then introduced.
The design of a medium‐speed drivetrain for the Technical University of Denmark (DTU) 10‐MW reference offshore wind turbine is presented. A four‐point support drivetrain layout that is equipped with ...a gearbox with two planetary stages and one parallel stage is proposed. Then, the drivetrain components are designed based on design loads and criteria that are recommended in relevant international standards. Finally, an optimized drivetrain model is obtained via an iterative design process that minimizes the weight and volume. A high‐fidelity numerical model is established via the multibody system approach. Then, the developed drivetrain model is compared with the simplified model that was proposed by DTU, and the two models agree well. In addition, a drivetrain resonance evaluation is conducted based on the Campbell diagrams and the modal energy distribution. Detailed parameters for the drivetrain design and dynamic modelling are provided to support the reproduction of the drivetrain model. A decoupled approach, which consists of global aero‐hydro‐servo‐elastic analysis and local drivetrain analysis, is used to determine the drivetrain dynamic response. The 20‐year fatigue damages of gears and bearings are calculated based on the stress or load duration distributions, the Palmgren‐Miner linear accumulative damage hypothesis, and long‐term environmental condition distributions. Then, an inspection priority map is established based on the failure ranking of the drivetrain components, which supports drivetrain inspection and maintenance assessment and further model optimization. The detailed modelling of the baseline drivetrain model provides a basis for benchmark studies and support for future research on multimegawatt offshore wind turbines.
Carbon nanotubes (CNT) have recently been studied as novel and versatile drug and gene delivery vehicles. When CNT are suitably functionalized, they can interact with various cell types and are taken ...up by endocytosis.
Anti-cancer drugs cisplatin and doxorubicin have been delivered by CNT, as well as methotrexate, taxol and gemcitabine. The delivery of the antifungal compound amphotericin B and the oral administration of erythropoietin have both been assisted using CNT. Frequently, targeting moieties such as folic acid, epidermal growth factor or various antibodies are attached to the CNT-drug nanovehicle. Different kinds of functionalization (e.g., polycations) have been used to allow CNT to act as gene delivery vectors. Plasmid DNA, small interfering RNA and micro-RNA have all been delivered by CNT vehicles. Significant concerns are raised about the nanotoxicology of the CNT and their potentially damaging effects on the environment.
CNT-mediated drug delivery has been studied for over a decade, and both in vitro and in vivo studies have been reported. The future success of CNTs as vectors in vivo and in clinical application will depend on achievement of efficacious therapy with minimal adverse effects and avoidance of possible toxic and environmentally damaging effects.
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