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The research and development of novel protective structures with excellent mechanical load-bearing and energy-absorbing characteristics are one of the current interests in aerospace, marine, and au...

In this paper, a hierarchical control framework with relevant algorithms is proposed to achieve autonomous navigation for an underactuated unmanned surface vehicle (USV) swarm. In order to implement automatic target tracking, obstacle avoidance and avoid collisions between group members, the control framework is divided into three layers based on task assignments: flocking strategy design, motion planning and control input design. The flocking strategy design transmits some basic orders to swarm members. Motion planning applies the potential function method and then improves it; thus, the issue of autonomous control is transformed into one of designing the velocity vector. In the last layer, the control inputs (surge force and yaw moment) are designed using the sliding mode method, and the problem of underactuation is handled synchronously. The proposed closed-loop controller is shown to be semi-asymptotically stable by applying Lyapunov stability theory, and the effectiveness of the proposed methodology is demonstrated via numeric simulations of a homogeneous USV swarm.

ispartof: ACS SUSTAINABLE CHEMISTRY & ENGINEERING vol:8 issue:23 pages:8469-8470 status: published

This article discusses the scale effects on a planing boat, utilizing the computational fluid dynamics method. The simulation is compared with a tank test for verification and validation. The planing boat sails use both aerodynamics and hydrodynamics. Studying the performances and wave patterns of different dimensions of the models is the best way to investigate the scale effect without using experimental data. The resistance is discussed in two parts, namely residuary resistance and friction resistance, and is compared to the calculated data using the international towing tank conference (ITTC) formula. The computational fluid dynamics (CFD) calculations of the model are increased by 4.77% on average, and the boat computations are also increased by 3.57%. The computation shows the scale effect in detail. The residuary resistance coefficients at different scales are approximately equal, and the friction resistance coefficients show the scale effect. The scale effect for longitudinal steadiness is also captured for the period of the porpoising behavior. The rational for the full-scaled boat oscillation period and the model is the root of the scales.

A detailed description of the flooding process is crucial to analyze the complex hydrodynamic behaviors and enhance the survivability of the damaged ship. In this paper, through establishing three typical damage scenarios with various locations, the commercial software CD Adapco STAR-CCM+ based on the Reynolds-Averaged Navier-Stokes (RANS) solver is applied to simulate the flooding process involving multiple compartments. The basic computational fluid dynamics (CFD) models and specific simulation settings are elaborated. The volume of fluid (VOF) method combined with the user defined field function is developed to distribute the initial free surface. The captured flooding process indicates that the air compression due to the restricted ventilation decreases the flooding amount. The obtained flooding time can provide necessary data to support for appropriate rescue management and evacuation options.

An accurate analysis of the entire flooding process is critical to assess the damaged stability when a ship encounters distressed accidents such as collision, stranding, or grounding. Among many factors affecting the flooding process and damaged stability, the complex effect of air compression is significant and worthy of further research. In this paper, through establishing scenarios of the damage flooding for a cruise ship, the commercial software CD Adapco STARCCM+ is applied to perform time domain simulation of flooding processes under different ventilation levels. The basic mathematical models about air compression and specific simulation settings of computational fluid dynamics (CFD) are presented in detail. The simulation results show that water ingression results in an increase of air pressure and density inside the flooded compartment. The corresponding air compression can significantly delay the flooding process if the ventilation level is limited to a certain ratio. Finally, the stability of the damaged ship is affected.

A nonlinear robust control strategy is proposed to force an underactuated surface ship to follow a predefined path with uncertain environmental disturbance and parameters. In the controller design, a high-gain observer is used to estimate velocities, thus only position and yaw angle measurements are required. The control problem of underactuated system is transformed into a control of fully actuated system through adopting an improved line-of-sight (LOS) guidance law. A sliding-mode controller is designed to eliminate the yaw angle error, and provide the control system robustness. The control law is proved semi-globally exponentially stable (SGES) by applying Lyapunov stability theory, and numerical simulation using real data of a monohull ship illustrates the effectiveness and robustness of the proposed methodology.

Composite to metal joints are gradually found in the marine industry for the attachment of lightweight components to metallic structures. The puropose of this study is to invistigate the composite sandwich to steel joint for naval ships. The main emphasis of the study was placed on the mechanical properties of a hybrid joint between a sandwich glass fibre reinforced plastic superstructure and a steel hull. Based on the experiments of a base joint, a new numerical simulation method was used to analyze the performance of the base joint and the optimized joint. The optimized joint was presented due to reducing weight and avoiding eccentric load. The numerical predictions of the base hybrid joint showed a very good correlation with the experiment results, which validated the reliability of the new numerical simulation method. The strength of the optimized hybrid joint was evaluated through static simulation. This phenomenon is similar to the base joint. But there is no additional stress concentration induced by load eccentricity and internal bending. The optimized joint has 11% lower weight than the base joint, and the stress of the optimized joint is only about 4% ~ 67% of the base one. The results of the present work imply that the change of geometry and material is an effective method to improve the performance of the composite sandwich to steel joint.

The use of a glass-fiber reinforced composite in marine structures is becoming more common, particularly due to the potential weight savings. The mechanical response of the joint between a glass-fiber reinforced polymer (GRP) superstructure and a steel hull formed is examined and subsequently modified to improve performance through a combined program of modeling and testing. A finite-element model is developed to predict the response of the joint. The model takes into account the contact at the interface between different materials, progressive damage, large deformation theory, and a non-linear stress-strain relationship. To predict the progressive failure, the analysis combines Hashin failure criteria and maximum stress failure criteria. The results show stress response has a great influence on the strength and bearing of the joint. The Balsawood-steel interface is proved to be critical to the mechanical behavior of the joint. Good agreement between experimental results and numerical predictions is observed.

It is of great significance and value to predict the roll of two ships, especially when one is replenishing for the other or in some other conditions. Autoregressive time series analysis method (AR) with Recursive least squares (RLS) theory is the mainstream currently and the effectiveness for the prediction of the motion attitudes have been fully validated. However, there are some differences between the prediction for the motion of two vessels and for that of one. The hydrodynamic interactions between two ships should be taken into consideration and be reflected in the application of the method. In order to solve this issue, this work firstly proposed a double ships autoregressive (DAR) method, which can determine the orders and the parameters of model in real-time with consideration of the interference between two ships and the DAR method was applied to forecast the roll motion between two ships. The simulative results of DAR method show the validity and veracity compared to real value and the advancement compared to the autoregressive (AR) method for single ship motion prediction.

A static-stability calculation method for ships which use the second-development of Solid Edge is presented in this paper. The second-development of Solid Edge applied Visual Basic to divide the waterplane and measure the parameters concerned static-stability calculation such as the volume and center of the underwater model. Furturemore, it makes the statics-stability calculation be convenient that the paragraph of static-stability is calculated on the parameters and the dismiss angle is returned. According to the comparison of the experiments and the theory, including different forms of superstructure models, it can be proved that this method is reliable and effective in the static-stability calculation for ships.

Continuous head pose estimation is an important visual component for human-computer interaction. However, an accurate and computationally efficient method to estimate the head orientation and position remains a challenging task in computer vision. We propose a Highly efficient Head Orientation and Position estimation (HeHOP) approach based on depth data which uses a stage-by-stage regression framework. At each stage, binary features are obtained from local areas of depth information. A global linear mapping is used to predict the head orientation and position update using the binary features. We evaluate our method on the BIWI dataset containing depth images labeled with head orientation and position. The results show that our approach is robust against occlusions and achieves state-of-the-art performance in terms of accuracy, has a low miss rate, and is several times faster than previous methods.

Vienna rectifier is one of the most popular topologies for three-phase PFC converter. DC voltage, grid current double loop controller and three-level SVPWM are normally used to control the Vienna rectifier. Accurately detecting the current zero-crossing point is required to achieve the correct SVPWM signals since the output level of Vienna rectifier is also decided by the direction of the phase current. The error of the duty ratio is decided by the error time of the current zero-crossing point detecting and the duty ratio before and after the current zero-crossing point. It can be concluded that the impact of current zero-crossing will be eliminated if the switches near current zero-crossing point are kept “on”. To achieve this goal, a novel SVPWM scheme is proposed by using the certain state combinations of short vectors in each sector. In this method, the calculation of duty ratio will not be affected by the direction of phase current near the zero-crossing point, and therefore the distortion of current caused by current zero-crossing detection error will be eliminated. Simulations and experiments are conducted to verify the presented method.

LCL filter presents a significant attenuation of switching harmonics, however its resonance peak influences the system stability. Passive damping reduces the switching current harmonics attenuation and increases the extra losses. Nevertheless, traditional active damping method often needs additional sensors or increases the complexity of algorithm. According the Nyquist stability criterion, a novel active damping method is proposed in this paper based on the grid current feedback compensation which adds no more sensors and easy to control. Two kinds of current compensation transfer function are presented. Moreover, the design principles and the range of stable system with active damping are derived step by step. Finally, it compares the damping effect of the different compensation methods through experiment and verifies the theoretical analysis at the same time.

In this paper, we utilize both Fault Tree Analysis (FTA) and Bayesian networks (BN) to analyze the safety of the vessel's oil plants' static electricity systematically. We use FTA to show the failure model of the system, namely the causal and generalization relations between events and BN to model the polymorphism and uncertainty of these events showed in the Fault Tree. By utilizing the BN methodology, the limitations and deficiencies of FTA can be made up of — the BN method can eliminate the restrictive assumptions in FTA. In the electrostatic safety analysis of vessel's oil system, we combine FTA and BN in order to enhance the analytic accuracy and according to the analytic result, we propose some measures about Electrostatic Protection. The analytic technique we propose is certified that it can fit with the Actual Engineering better.

We present a theoretical multi-frequency multi-sampling frequency-domain fluorescence lifetime imaging (FLI) technique, which determines fluorescence lifetime by measuring the phase delay and decrease of the modulation of the emission relative to the excitation. Such a system could be realized with high-speed line-scan cameras using more than 100000 frames per second. It is useful for the measurement of lifetimes in the microsecond range and can be, e.g., used to measure oxygen concentrations with Ruthenium complexes. Typically 100 samples are used, resulting in a temporal resolution of microsecond fluorescence lifetime measurement. By including frequency components with frequencies much higher than the Nyquist criterion, the measurement of fluorescence lifetimes much shorter than the sampling interval is possible. In order to optimize the SNR of the predict lifetimes, we investigate the photon economy of our technique. Various ranges of the exposure time relative to the range of modulation period and compositions of multiple frequencies have been studied. The presented approach is validated by numerical simulations by Monte Carlo method.

According to the characteristics of traffic accidents of long highway tunnel, this paper proposes a method to identify black spots based on improvable accident of tunnel environment. On the basis of the relationship of traffic accident and long highway tunnel system components, including the driver, the vehicle and the tunnel environment, accidents are classified into seven categories, and this paper only considers four categories relating to tunnel environment. The degree of membership of each accident in the tunnel environment component is used to represent the ability of accidents by tunnel environment improvement. Each accident is weighted by its ability. Then, the method of the equivalent of accident frequency and accident rate is used to identify black spots. Finally, the Kaoyishan tunnel in Beijing-zhuhai freeway in China was applied to analyze black spots using this method. The results show that

The first step towards the three-dimensional (3D) reconstruction of histological structures from serial sectioned tissue blocks is the proper alignment of microscope image sequences. We have accomplished an automatic rigid registration program, named Image-Reg, to align serial sections from mouse lymph node and Peyer's patch. Our approach is based on the calculation of the pixel-correlation of objects in adjacent images. The registration process is mainly divided into two steps. Once the foreground images have been segmented from the original images, the first step (primary alignment) is performed on the binary images of segmented objects; this process includes rotation by using the moments and translation through the X, Y axes by using the centroid. In the second step, the matching error of two binary images is calculated and the registration results are refined through multi-scale iterations. In order to test the registration performance, Image-Reg has been applied to an image and its transformed (rotated) version and subsequently to an image sequence of three serial sections of mouse lymph node. In addition, to compare our algorithm with other registration methods, three other approaches, viz. manual registration with Reconstruct, semi-automatic landmark registration with Image-Pro Plus and the automatic phase-correlation method with Image-Pro Plus, have also been applied to these three sections. The performance of our program has been also tested on other two-image data sets. These include: (a) two light microscopic images acquired by the automatic microscope (stitched with other software); (b) two images fluorescent images acquired by confocal microscopy (tiled with other software). Our proposed approach provides a fast and accurate linear alignment of serial image sequences for the 3D reconstruction of tissues and organs.

In this paper, an adaptive iterative learning control based on the accurate magnetization characteristics of the SRM is proposed to minimize the torque ripple and electromagnetic energy conversion losses by tuning the energization parameters of commutation angles and duty ratio. The electromagnetic energy conversion and torque in SRM are functions of the flux-linkage, current, and rotor angle. The optimal excitation current profile will result in optimal speed response, co- energy generation, and minimum torque ripple. An automatic characterizing system is developed to identify the SRMs' static magnetization curves accurately and take the nonlinearity of the magnetic circuit into account. The dSPACE DS1104 controller is utilized to setup the drive system for simulation and implementation. Experimental tests of a 4-phase 8/6 pole SRM at different operation conditions are given to demonstrate the effectiveness and performance of the proposed method.

This paper presents a new stable sliding-mode control method for a two-link planar robot arms, with a passive rotational joint. Our idea is first to divide the underactuated system into two subsystems, and define two first-level sliding surfaces. Then we get a two-level sliding surface for the whole system and use the Lyapunov law to define the control law for the arms. The control law can drive the subsystems toward their sliding surfaces and achieve their desired values. The asymptotic stability of the sliding surfaces is established and proved theoretically in Lyapunov sense. Therefore, we get that the whole system can be drive to its sliding surface and stable. Finally the simulation results show the controller's validity and its adaptive abilities to the system parameter variations.

A method for camera calibration in robotic binocular stereo vision is introduced in this paper. Camera calibration is a necessary step in 3D computer vision in order to extract metric information from 2D images. Being different from with single camera calibration, binocular stereo vision system not only need to ascertain intrinsic parameters, but also the relative position relation of two cameras. We compute it in two steps: first, we compute the intrinsic and initial extrinsic parameters of camera by Zhang Plane-based Calibration Method; Second, we suppose the intrinsic parameter is invariable, camera's moving parameters can be computed by self-calibration method, through finding the stereo matching point and calculating the fundamental matrix and essential matrix.