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Vortex Induced Motion (VIM) of multi-column floating platforms, such as Tension Leg Platform (TLP) and semi-submersible (SEMI), in current is well-acknowledged. Substantial VIM response of the multi-column floating platform may cause fatigue failure of mooring and riser systems, which can affect the normal operation of the platform. The present paper focuses on the numerical investigation on VIM of a TLP with circular columns using Computational Fluid Dynamics (CFD). Sensitivity analyses (e.g., mesh size, the number of prism layers and time-step size) for the VIM responses of the TLP are conducted. The effects of the current heading and mooring stiffness on the VIM are investigated. The three degrees of freedom VIM responses (in-line, transverse and yaw responses) and corresponding amplitude spectra are computed and analyzed. Motion trajectories are plotted to understand the VIM behaviors. Regarding the effect of the current heading, the largest transverse response is examined at 15° current heading and the corresponding maximum nominal amplitude is around 0.43. The difference of the maximum nominal amplitudes between the cases at 0° and 15° current headings is less than 5%. For 15°, 30° and 45° current headings, the nominal transverse amplitudes decrease as the current heading increases in the lock-in range. For the four studied current headings, the maximum width of the lock-in range is found at 0° current heading and narrows as the current incidence increases. The largest yaw response is observed at 0° current heading and the maximum nominal amplitude is around 9.1°. Regarding the effect of the mooring stiffness, the lock-in ranges and the maximum nominal amplitudes of the transverse motions have little difference for the four mooring stiffnesses. The maximum nominal transverse and yaw responses are around 0.25 and 5.1°, respectively, which occur when the mooring stiffness reaches the maximum. The flow pattern analyses indicate that the flow interference between the upstream and downstream columns may have significant effects on the VIM responses and a stronger interference at the present spacing ratio may lead to a larger VIM response. The contours of the vertical vorticity in the horizontal plane show that the mean positions of the flow separation points are always on highest or lowest (in the transverse direction perpendicular to the current heading) points of the columns, which is the reason that the VIM trajectories for the TLP with circular columns are always along the direction perpendicular to the current heading.

An Innovative Semi-submersible platform Optimization Program (ISOP) has been developed to solve the multi-objective optimization problem for semi-submersible platforms (SEMI). Three types of SEMIs, including semi-submersible floating production unit (SEMI FPU), heave and vortex induced motion (VIM) suppressed semi-submersible (HVS) and semi-submersible floating drilling unit (SEMI FDU) are selected for case studies. The hydrodynamic performances of three types of semi-submersible platforms are analyzed by using panel method and Morison's equation. In order to improve the computing efficiency, the hydrodynamic performances for different hull forms during optimization process are estimated by the surrogate models, which are built by artificial neural network prediction method and Inverse Multi-Quadric (IMQ) radial basis function (RBF). The accuracy of surrogate models is ensured by performing leave-one-out cross validation (LOOCV). The most probable maximum (MPM) heave motion and total weight, representing the safety and economy, respectively, are chosen as the two objectives for optimization. The transverse metacentric height, the MPM surge motion, and the most probable minimum (MPMin) airgap are selected as constraints. Based on surrogate models, multi-objective particle swarm optimization (MOPSO) is employed to search for the Pareto-optimal solutions. A Computational Fluid Dynamics (CFD) tool is adopted to validate the proposed model for the prediction of the motion responses. By comparing the obtained Pareto-optimal solutions with the initial design using simple panel method plus Morison's equation, it is confirmed that the MPM heave motions for SEMI FPU, HVS and SEMI FDU can be suppressed by up to 12.68%, 11.92%, and 14.96%, respectively, and the total weights can be reduced by up to 12.16%, 13.00%, and 24.91%, respectively. Through the detailed analyses of optimization results, the most efficient design strategies for semi-submersible platforms are discussed and proposed.

Considering the massive simulations required by the full long-term analysis, the environmental contour method is commonly used to predict the long-term extreme responses of an offshore renewable system during life time. Nevertheless, the standard environmental contour method is not applicable to the wind energy device due to the non-monotonic aerodynamic behaviour of the wind turbine. This study presents the development of a modified environmental counter method and its application to the extreme responses of a hybrid offshore renewable system. The modified method considers the variability of the responses by checking multiple contour surfaces so that the non-monotonic aerodynamic behaviour of the wind turbine is considered. The hybrid system integrates a floating wind turbine, a wave energy converter and two tidal turbines. Simulation results prove that the modified method has a better accuracy.

A lightweight convolutional neural network (CNN) is presented in this study to automatically indentify atrial fibrillation (AF) from single-lead ECG recording. In contrast to existing methods employing a deeper architecture or complex feature-engineered inputs, this work presents an attempt to employ a lightweight CNN to confront current drawbacks such as higher computational requirement and inadequate training dataset, by using representative rhythms features of AF rather than raw ECG signal or hand-crafted features without any electrophysiological considerations. The experimental results suggested that this method presents the following significant advantages: (1) higher performances for indentifying AF in terms of accuracy, sensitivity, and specificity that are 97.5%, 97.8%, and 97.2%, respectively; (2) It is capable of automatically extracting the shared features of AF episodes of different patients and would be much robust and reliable; (3) with the cardiac rhythm features as input dataset, rather than complex transforming and classifying the raw data, thus requiring a lower computational resource. In conclusion, this automated method could analyze large amounts of data in a short time while assuring a relative high accuracy, and thus would potentially serve to provide a comfortable single-lead monitoring for patients and a clinical useful tool for doctors.

Early risk identification of an unexpected sudden cardiac death (SCD) in a person who is suffering malignant ventricular arrhythmias is highly significant for timely intervention and increasing the survival rate. For this purpose, we have presented an automated strategy for prediction of SCD with a high-level accuracy by using measurable arrhythmic markers in this paper. The set of arrhythmic parameters includes three repolarization interval ratios, such as TpTe/QT, JTp/JTe, and TpTe/JTp and two conduction-repolarization markers, such as TpTe/QRS and TpTe/(QT×QRS). Each of them is calculated directly from the detected QRS complex waves and T-wave of electrocradiogram (ECG) signals. Then, all calculated markers are used for the automatical classification of normal and SCD risk groups by employing machine learning classifiers, such as k-nearest neighbor (KNN), decision tree (DT), Naive Bayes (NB), support vector machine (SVM), and random forest (RF). The effectiveness and usefulness of the proposed method is evaluated using a database of measured ECG data acquired from 28 SCD and 18 normal patients. For the automated strategy, the set of five arrhythmic risk markers can predict SCD in less than one second with an average accuracy of 98.91% (KNN), 98.70% (SVM), 98.99% (DT), 97.46% (NB), and 99.49% (RF) for 30 minutes before the occurrence of SCD. Moreover, a practical and straightforward SCD index (SCDI) through a judicious integration of these markers is also proposed by using the Student's t-test. The obtained SCDIs are 1.2058 ± 0.0795 and 1.7619 ± 0.1902 for normal and SCD patients, respectively, which provide a sufficient discrimination degree with a p-value of 6.5061e-35. The present results show that both the automated classifier and the integrated SCDI can predict the SCD up to 30 minutes earlier, and that these predictions could be more practical and efficient if applied in portable smart devices with real-time requirements in hospital settings or at home.

In this paper, we apply a CFD computer code to study the hydrodynamic behavior of a stand-alone cylinder and a dual coaxial-cylinder system (DCCS) via free-decay motion tests. The geometric proportions of a stand-alone cylinder and the inner and outer cylinder of the DCCS are chosen to be the same as those in [1] and [2], respectively, as ocean wave-energy converter (WEC) devices. Overset mesh based on the commercial code ‘Star-CCM+ 11’ is used to simulate the free-decay motion of the two systems. Five parameters chosen for the CFD implementation are: turbulence model, initial displacement, time step, number of prism layers and mesh size. Results obtained from using different values of these parameters are compared so as to confirm the validity of choices made. The hydrodynamic performance of the stand-alone cylinder and outer cylinder in the DCCS are compared with the experimental results to assess and validate the CFD models. In addition, the heave hydrodynamic coefficients, namely, the added mass and total damping, and ‘resonance’ frequency of the stand-alone cylinder and those of the inner cylinder of the DCCS, with the outer cylinder being fixed, are obtained by using the CFD procedure. The hydrodynamic coefficients of another stand-alone cylinder with the same dimensions as the inner cylinder of the dual-coaxial cylinder are also obtained by simulations. The vorticity-contour plots for the stand-alone cylinder and the outer cylinder in the DCCS in free-decay motion are presented and analyzed. Finally, the results of the three cases are compared to examine the effect of the outer cylinder on the heave hydrodynamic coefficients of the inner cylinder.

Malignant ventricular arrhythmia (especially ventricular fibrillation (VF)) is the main reason which causes sudden cardiac death (SCD). This paper presents an automatic SCD-patient classifier we developed to identify patients with unexpected VF using 60-minutes continuous single-lead electrocardiograms (ECG) signals before that. Patients are classified as having SCD if the majority of their recorded ventricular repolarization (VR) is recognized as characteristic of unexpected VF. Thus, the classifier's underlying task is to recognize individual VR delineated from single-lead ECG signals as SCD VR, where VR from non-SCD patients are used as controls. With the reported clinical practices of SCD, we extracted five morphological and temporal features (both commonly used and newly developed ones) from ECG signals for VR classification. To evaluate classification performance, we trained and tested k nearest neighbor classifier, a decision tree classifier, and a Naïve Bayes classifier using five-fold cross validation on 36 one-hour ECG signals (18 from patients at risk of SCD and 18 from control people). We compared the performance of these three classifiers, and the patient-classification sensitivity is approximately 98.02-99.51%. Moreover, the k nearest neighbor with a higher accuracy (98.89%) and specificity (98.27%) performed better than the other two. Importantly, the results show obvious superiorities of performance over that in the same duration and of usefulness over several minutes given by related works.Clinical Relevance- This could be integrated into a real-time, long-term out-of-hospital SCD predictor to improve the warning veracity and bring forward the warning time, especially for patients with implantable cardiac defibrillators or pacemakers, etc..

This study was to assess the feasibility of using non-standardized single-lead electrocardiogram (ECG) monitoring to automatically detect atrial fibrillation (AF) with special emphasis on the combination of deep learning based algorithm and modified patch-based ECG lead. Fifty-five consecutive patients were monitored for AF in around 24 hours by patch-based ECG devices along with a standard 12-lead Holter. Catering to potential positional variability of patch lead, four typical positions on the upper-left chest were proposed. For each patch lead, the performance of automated algorithms with four different convolutional neural networks (CNN) was evaluated for AF detection against blinded annotations of two clinicians. A total of 349,388 10-second segments of AF and 161,084 segments of sinus rhythm were detected successfully. Good agreement between patch-based single-lead and standard 12-lead recordings was obtained at the position MP1 that corresponds to modified lead II, and a promising performance of the automated algorithm with an R-R intervals based CNN model was achieved on this lead in terms of accuracy (93.1%), sensitivity (93.1%), and specificity (93.4%). The present results suggest that the optimized patch-based ECG lead along by deep learning based algorithms may offer the possibility of providing an accurate, easy, and inexpensive clinical tool for mass screening of AF.

OBJECTIVES This study evaluated the stiffness of tissue surrounding thyroid nodules using shear wave elastography (SWE). METHODS A total of 128 thyroid nodules in 108 patients were examined with conventional ultrasound imaging and SWE. The maximum Young modulus value was measured to evaluate the stiffness of the thyroid nodules (E) and the 2-mm perinodular region (Eshell ). The number of thyroid fibrocytes was evaluated by Masson trichrome staining and image-processing software. The arrangement of the fibrous structure was also classified. RESULTS The mean age ± SD of the 108 patients was 33.12 ± 13.34 years (range, 18-80 years). Thirty-nine thyroid nodules were classified as benign and 89 as malignant. Eshell was significantly higher for malignant nodules (95.0 ± 21.9 kPa) compared with benign nodules (48.1 ± 17.0 kPa; P

Due to the existence of the side walls in a towing tank, the measured hydrodynamic forces would present some discrepancies compared to the open sea results. This phenomenon is referred to as the side wall effect. The objective of the present study is to investigate the side wall effects on ship model testing in a towing tank. The method used in the present study involves a 3D panel method based on the Rankine type Green function. Both the steady and unsteady problems were investigated numerically. The numerical results were validated against ship model test results. After the validations, a large scale computations were performed to investigate the parameters which could determine the side wall effects. Two diagrams of side wall effects (one in calm water and the other one in waves), were obtained which showed whether the side wall effect was less than the permissible error to be included in the measured values.

This paper presents numerical studies on vortex-induced motions (VIM) of a multi-column floating oil and gas exploration platform. Numerical computations are performed using an improved delayed detached eddy simulation (IDDES) together with a moving grid approach. The transverse (sway) and yaw motion responses, motion trajectories, motion frequencies and power spectral density of motions are computed and analyzed systematically. After extensive comparisons with experiments, it is confirmed that the present numerical solutions using IDDES agree well with the experimental results and are better than those via delayed detached eddy simulation (DDES). The differences of transverse motion responses between computational results and experiments are less than 10% in the lock-in region. The numerical simulations reveal that the transverse VIM responses occur in a range of reduced velocities from 7.0 to 14.0 at H / D = 1.44 ( H and D are the column height and width, respectively). The largest nominal transverse amplitude, around 35 % of the column width, occurs for 22 . 5 ∘ current incidence. It is found that the VIM responses mainly perform along the platform diagonals for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences. The transverse and yaw motion frequencies for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences are higher than those for 0 ∘ current incidence. The energy levels of the yaw motion responses for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences are about 10% of that for 0 ∘ current incidence. Moreover, parametric studies have been performed to examine the effect of submerged column height on VIM. It demonstrates that VIM in transverse direction grows significantly when submerged column height H / D is greater than 1.0. To be more specific, compared to the case with H / D = 1.44, VIM in transverse direction at H / D = 3.0 increase by around 120%.

Real-time control has been widely adopted to enlarge the energy extraction of a wave energy converter (WEC). In order to implement a real-time control, it is necessary to predict the wave excitation forces in the close future. In many previous studies, the wave forces over the prediction horizon were assumed to be already known, while the wave force prediction effect has been hardly examined. In this paper, we investigate the effect of wave force prediction on the energy absorption of a heaving point-absorber WEC with real-time latching control. The real-time control strategy is based on the combination of optimal command theory and first order-one variable grey model GM(1,1). It is shown that a long prediction horizon is beneficial to the energy absorption whereas the prediction deviation reduces extracting efficiency of the WEC. Further analysis indicates that deviation of wave force amplitude has little influence on the WEC performance. It is the phase deviation that leads to energy loss. Since the prediction deviation accumulates over the horizon, a moderate horizon is thus recommended.

In this paper, a boundary element programme MHydro, which is based on 3-D Rankine source method, was developed to investigate the ship-to-ship interaction problem. The method developed considers both stationary and forward speed cases. A new radiation condition, which takes Doppler shift into account, is imposed on the control surface. For the stationary case, the validations were carried out both in head sea and beam sea conditions. The experimental measurements, as well as the published numerical results, were used for the comparison. For the ship-to-ship with forward speed case, we validated our method through the experimental tests. Good agreement was achieved except the roll motion. The hydrodynamic coefficients and wave excitation forces were investigated and a very large sway force was predicted when the transverse distance between two ships equalled to the wave length. The wave elevations in the gap were also calculated. Discussions are highlighted on the shallow water effects.

We study the global hydrodynamic performance of a semi-submersible floating platform unit in order to optimize the hull form in the future. The hydrodynamic problem is solved by employing potential flow theory and Morison equation for modelling of the viscous effects. The added mass and damping coefficients, as well as the first-order motion responses, second-order mean drift forces, diffracted and radiated wave field, and airgap are computed to examine the hydrodynamic behavior of the floating production unit. The computational results show that the motion responses in short-crested waves are mostly smaller than those in long-crested waves. The maximum wave elevation occurs at WP45 in 45 ° wave heading in long-crested waves. In addition, the minimum airgap occurs at AG45 in 45 ° wave heading in linear waves, while the worst airgap point in nonlinear waves is AG0 in 0 ° wave heading. Extensive parametric studies have been performed to examine the dependence of the motion responses and the other key design criteria on the principal dimensions including hull draft, column width, column spacing, column corner radius, pontoon height, pontoon width, and the size of cakepiece. By comprehensive and systematic hydrodynamic computations and analyses, it is revealed that the combined vertical motion at the worst airgap location is almost in phase with the wave elevation in extreme wave condition with a peak wave period around 14–15 s. Moreover, it is found that the most efficient way to reduce the motion is to increase the hull draft, though the airgap may also decrease. Besides, reducing the pontoon height can achieve better motion performance and larger airgap simultaneously. This paper aims to provide a benchmark for future studies on automatic hull form optimization.

The vortex-induced motions (VIM) of deep draft semi-submersible platforms have been challenging engineering issues because of its impact to the fatigue life of mooring and riser systems. This paper presents numerical studies on the vortex-induced motions (VIM) of a deep draft semi-submersible. Numerical simulations are performed by using an improved delayed detached eddy simulation (IDDES). VIM amplitudes for in-line (surge), transverse (sway) and yaw motions and hydrodynamic force coefficients are obtained for different current incidence angles. The sensitivity analyses on grids and time step sizes are carried out to ensure convergences of the computational results. Comparisons with experimental data demonstrate the capability of the present numerical model. It is observed that the transverse motions for 22.5° current incidence are larger than those for 0° and 45° current incidences. The mean drag force coefficients for these simulated current incidence angles tend to grow as the transverse motion amplitudes increase. In addition, parametric studies have also been performed to examine the effects of the column corner radius on VIM.Copyright © 2017 by ASME

Objectives To evaluate the therapeutic effect of early fluid resuscitation under the guidance of Pulse indicator Continuous Cardiac Output (PiCCO) on patients with severe acute pancreatitis (SAP). Methods Clinical data of 18 SAP patients (the study group), who had undergone fluid resuscitation under the guidance of PiCCO from October 2011 to October 2013, were analyzed prospectively. Clinical data of 25 cases (control group) who had undergone fluid resuscitation without the guidance of PiCCO from January 2009 to September 2011 were collected. Then, retrospective and prospective case–control study was carried out. Results During the first 6 h, 0–24 h, 24–48 h, and 0–72 h of admission, the study group received more volume of fluid than the control group. There were significantly faster decline of APACHE II score and the value of blood lactate in study group, as well as the length of ICU stay and the proportion of renal failure at 72 h of admission. According to the 2012 Atlanta classification, six cases in study group turned into moderate SAP (33.30%), significantly higher than the control group (8.00%) ( p = 0.0049). The volume of fluid infusion and clinical parameters were linearly relative. Conclusions The PiCCO device may be a useful adjunct for fluid resuscitation monitoring in patients with SAP in the early stage. Early fluid resuscitation under the guidance of PiCCO can improve tissue perfusion, reduce the SIRS persistence time and the length of ICU stay. This program did not increase the risk of respiratory failure and influence the mortality.

The open platform screen door systems including the platform full height door system and the platform half-high security door system are studied in the paper. The three-dimensional mathematical and physical models are established respectively. The entrance/exit boundary of the model is the subway piston wind calculated from the one-dimensional flow equation. Under the platform full height door system and half-high security door system, the influence of air quantity and amount of heat of subway platform and station hall is analysis in different running condition of subway train for the influence of metro train piston wind. The result can offer a reference for the design and engineering application of subway train environmental control system.