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Floating breakwaters (FBs) play an important role in protecting coastlines, marine structures, and ports due to their simple construction, convenient movement, cost-effectiveness, and environmental friendliness. However, the traditional box-type FBs are flawed due to their requiring large sizes for wave attenuation and their overly high level of wave reflection. In this paper, a novel partial T special-type FB with wave attenuation on the surface and flow blocking below the water has been presented. First, the User-Defined Function (UDF) feature in ANSYS Fluent was employed to compile the six degrees of freedom (6-DOF) motion model. A two-dimensional viscous numerical wave flume was developed using the velocity boundary wave-generation method and damping dissipation wave-absorption method, with fully coupled models of the FBs developed. A VOF multiphase flow model and a RANS turbulence model were employed to capture the free flow of gas–liquid two-phase flow. Then, the performance of wave attenuation of the new FB was compared with that of the traditional box-type FB of the same specifications. The simulation results showed that the transmission coefficient of the new FB is significantly lower than that of the box-type FB, and the dissipation coefficient is notably higher, demonstrating excellent performance of wave attenuation, particularly for long-period waves. As wave height increases, the novel FB benefits from its wave attenuation mechanism, with a lower reflection coefficient compared to the box-type FB. Finally, through parametric analysis, some design recommendations of the novel FB suitable for practical engineering applications in deep-sea aquaculture are presented. [ABSTRACT FROM AUTHOR]

Floating breakwaters (FBs) play an important role in protecting coastlines, marine structures, and ports due to their simple construction, convenient movement, cost-effectiveness, and environmental friendliness. However, the traditional box-type FBs are flawed due to their requiring large sizes for wave attenuation and their overly high level of wave reflection. In this paper, a novel partial T special-type FB with wave attenuation on the surface and flow blocking below the water has been presented. First, the User-Defined Function (UDF) feature in ANSYS Fluent was employed to compile the six degrees of freedom (6-DOF) motion model. A two-dimensional viscous numerical wave flume was developed using the velocity boundary wave-generation method and damping dissipation wave-absorption method, with fully coupled models of the FBs developed. A VOF multiphase flow model and a RANS turbulence model were employed to capture the free flow of gas–liquid two-phase flow. Then, the performance of wave attenuation of the new FB was compared with that of the traditional box-type FB of the same specifications. The simulation results showed that the transmission coefficient of the new FB is significantly lower than that of the box-type FB, and the dissipation coefficient is notably higher, demonstrating excellent performance of wave attenuation, particularly for long-period waves. As wave height increases, the novel FB benefits from its wave attenuation mechanism, with a lower reflection coefficient compared to the box-type FB. Finally, through parametric analysis, some design recommendations of the novel FB suitable for practical engineering applications in deep-sea aquaculture are presented.

The bird ingestion test is an important means of verifying the safety and reliability of aviation engines. In order to investigate the variation of flight trajectory after the ejection of bird body in engine bird ingestion tests and optimize bird ejection strategies, dynamic mesh technique was employed to calculate and analyze the trajectory of bird body using a six-degree-of-freedom model. The results indicate that after the ejection of bird body, a high-pressure region is formed at the shoulder area while a lowpressure region is formed at the tail. This generates aerodynamic drag, with the maximum drag occurring in the direction of motion. The drag force stabilizes at a certain value during the flight process. The aerodynamic forces acting on the bird body in the vertical and lateral directions are small, but exhibit large fluctuations with no regular pattern. The bird body experiences minimal speed decay during flight and follows a straight trajectory, making it feasible to launch the bird body to the desired location using direct aiming. [ABSTRACT FROM AUTHOR]

The 6-DOF Stewart parallel elevation platform serves as the platform for mounting the tea-picking robotic arm, significantly impacting the operational scope, velocity, and harvesting precision of the robotic arm. Utilizing the Stewart setup, a parallel elevation platform with automated lifting and leveling capabilities was devised, ensuring precise halts at designated elevations for seamless harvesting operations. The effectiveness of the platform parameter configuration and the reasonableness of the posture changes were verified. Firstly, the planting mode and growth characteristics of Yunnan large-leaf tea trees were analyzed to determine the preset path, posture changes, and mechanism stroke of the Stewart parallel lifting platform, thereby determining the basic design specifications of the platform. Secondly, a 3D model was established using SolidWorks, a robust adaptive PD control model was built using MATLAB for simulation, and dynamic calculations were carried out through data interaction in Simulink and ADAMS. Finally, the rationality of the lifting platform design requirements was determined based on simulation data, a 6-DOF Stewart parallel lifting platform was manufactured, and a motion control system was built for experimental verification according to the design specifications and simulation data. The results showed that the maximum deviation angle around the X, Y, and Z axes was 10°, the maximum lifting distance was 15 cm, the maximum load capacity was 60 kg, the platform response error was within ±0.1 mm, and the stable motion characteristics reached below the millimeter level, which can meet the requirements of automated operation of the auxiliary picking robotic arm. [ABSTRACT FROM AUTHOR]

The performance of an Archimedes spiral turbine (AST) for hydrokinetic applications was examined using a three-dimensional unsteady numerical model utilizing the six degrees of freedom (6-DOF) solver that is available in ANSYs Fluent software. From the computational fluid dynamics (CFD) simulations, the power coefficient (Cp) curve was estimated. This curve was compared with the curve of an Archimedes screw hydrokinetic turbine (ASHT) reported in the literature. The ASHT was found to be more efficient than the AST for electricity generation. The highest value of Cp for the AST was 0.337, which is a relatively high value in comparison with that of other types of hydrokinetic turbines. The results calculated from the CFD for the AST were compared with an experimental study reported for wind applications. [ABSTRACT FROM AUTHOR]

Strong demand for autonomous vehicles and the wide availability of 3D sensors are continuously fueling the proposal of novel methods for 3D object detection. In this paper, we provide a comprehensive survey of recent developments from 2012–2021 in 3D object detection covering the full pipeline from input data, over data representation and feature extraction to the actual detection modules. We introduce fundamental concepts, focus on a broad range of different approaches that have emerged over the past decade, and propose a systematization that provides a practical framework for comparing these approaches with the goal of guiding future development, evaluation, and application activities. Specifically, our survey and systematization of 3D object detection models and methods can help researchers and practitioners to get a quick overview of the field by decomposing 3DOD solutions into more manageable pieces. [ABSTRACT FROM AUTHOR]

The mathematical model of 6-DoF dynamics is used in different applications. In general, software-based solutions are utilized to implement the 6-DoF dynamic model. This paper introduces the FPGA-based implementation of the 6-DoF dynamics accelerator. The proposed hardware-based approach ensures the accuracy of the nonlinear model without compromising computational speed. The model-based approach and high-level synthesis have been employed in the design and implementation stages. Regarding design strategy, standard processor architecture, and resource-sharing methods have been applied to achieve FPGA resource efficiency. Seven datapath and finite state machines have been designed for seven different subsystems. The design resulted in hardware blocks that can execute all non-linear model equations 396 times in 1 ms using fixed/floating-point hybrid case and 434 times using pure fixed-point case. The model equations, which took an average of $\mathbf {0.4986}$ s to simulate in the Simulink environment, have been run on an FPGA in $\mathbf {7.1924}~\mu \text{s}$ . For seven design cases, numerical errors, resource utilization, and timing metrics are tabulated and presented to the reader.

In this work, the efficiency of two horizontal-axis hydrokinetic turbines, whose blades were designed with and without multi-element hydrofoil cross-sections, has been numerical and experimentally investigated for tip speed ratio (λ) values ranging between 2.5 and 9.0 to compare the experimental rotor performance with numerical results. The Eppler 420 hydrofoil was used for the design of the blades applying the blade element momentum (BEM) theory. The variation of the power coefficient curve of the turbines was analyzed by using computational fluid dynamics (CFD) and experimental tests through ANSYs Fluent software with six-degrees of freedom (6-DoF) user-defined function (UDF) method and an open hydraulic channel, respectively. Numerically, for the turbine with a multi-element hydrofoil and without a multi-element (traditional) hydrofoil, maximum power coefficients (CPmax) of 0.5050 and 0.419 (at a λ value equal to 7.129 and 6.739, respectively) were obtained. It is worth noting that a reasonable agreement between the numerical and the experimental results was achieved. In this regard, the blade with a multi-element hydrofoil has a positive influence on the hydrokinetic turbine performance; therefore, it can be used for power generation in river or marine systems.

This article investigates an adaptive tracking control problem for a six degrees of freedom (6-DOF) nonlinear quadrotor unmanned aerial vehicle (UAV) with a variable payload mass. The changing payload introduces time-varying parametric uncertainties into the dynamical model, rendering a static control strategy no longer effective. To handle this issue, two adaptive schemes are developed to maintain the uncertainties in the translational and rotational dynamics. Initially, a virtual proportional derivative (PD) is designed to stabilize the horizontal position; however, due to an unknown and time-varying mass, an adaptive controller is proposed to generate the total thrust of the UAV. Furthermore, an adaptive controller is designed for the rotational dynamics, to handle parametric uncertainties, such as inertia and external disturbance parameters. In both schemes, a standard adaptive scheme using the certainty equivalence principle is extended and designed. A stability analysis was conducted with rigorous analytical proofs to show the performance of our proposed controllers, and simulations were implemented to assess the performance against other existing methods. Tracking fitness and total control efforts were calculated and compared with closed-loop adaptive tracking control (CLATC) and adaptive sliding mode control (ASMC). The results indicated that the proposed design better maintained UAV stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrofoil-flap arrangement has a positive effect on the blade performance. • Experimental tests were carried out for two different hydrokinetic turbine rotors. • CFD analyses were conducted through 6-DoF user-defined functions. • The CP value increases about 20.53% when a hydrofoil-flap arrangement is used. • The rotor optimization is crucial for reducing the energy transformation costs. In this work, the efficiency of two horizontal-axis hydrokinetic turbines, whose blades were designed with and without multi-element hydrofoil cross-sections, has been numerical and experimentally investigated for tip speed ratio (λ) values ranging between 2.5 and 9.0 to compare the experimental rotor performance with numerical results. The Eppler 420 hydrofoil was used for the design of the blades applying the blade element momentum (BEM) theory. The variation of the power coefficient curve of the turbines was analyzed by using computational fluid dynamics (CFD) and experimental tests through ANSYs Fluent software with six-degrees of freedom (6-DoF) user-defined function (UDF) method and an open hydraulic channel, respectively. Numerically, for the turbine with a multi-element hydrofoil and without a multi-element (traditional) hydrofoil, maximum power coefficients ( C Pmax ) of 0.5050 and 0.419 (at a λ value equal to 7.129 and 6.739, respectively) were obtained. It is worth noting that a reasonable agreement between the numerical and the experimental results was achieved. In this regard, the blade with a multi-element hydrofoil has a positive influence on the hydrokinetic turbine performance; therefore, it can be used for power generation in river or marine systems. [ABSTRACT FROM AUTHOR]

Purpose: The objectives of the present study were to investigate the length change in different bundles of the superficial medial collateral ligament (sMCL) and lateral collateral ligament (LCL) during lunge, and to evaluate their association with Knee Society Score (KSS) following medial-pivot total knee arthroplasty (MP-TKA). Methods: Patients with unilateral MP-TKA knees performed a bilateral single-leg lunge under dual fluoroscopy surveillance to determine the in-vivo six degrees-of-freedom knee kinematics. The contralateral non-operated knees were used as the control group. The attachment sites of the sMCL and LCL were marked to calculate the 3D wrapping length. The sMCL and LCL were divided into anterior, intermediate, and posterior portions (aMCL, iMCL, pMCL, aLCL, iLCL, pLCL). Correlations between lengths/elongation rate of ligament bundles from full extension to 100° flexion and the KSS were examined. Results: The sMCL and LCL demonstrated relative stability in length at low flexion, but sMCL length decreased whereas LCL increased with further flexion on operated knees. The sMCL length increased at low flexion and remained stable with further flexion, while the LCL length decreased with flexion on the contralateral non-operated knees. The lengths of aMCL, iMCL, and pMCL showed moderate (0.5 < r < 0.7, p < 0.05) negative correlations with the KSS, and the lengths of aLCL, iLCL, and pLCL were positively correlated with the KSS at mid flexion on operated knees (p < 0.05). The elongation rates of aLCL, iLCL, and pLCL were negatively correlated with the KSS at high flexion on operated knees (p < 0.05). However, no significant correlations between the length of different bundles of sMCL or LCL with KSS were found on contralateral non-operated knees. Conclusions: The elongation pattern of sMCL/LCL on MP-TKA knees showed differences with contralateral non-operated knees. The sMCL is tense at low to middle flexion and relaxed at high flexion, while LCL is relaxed at low to middle flexion and tense at high flexion following MP-TKA. Medial stability and proper lateral flexibility during mid flexion were associated with favorable postoperative outcomes in MP-TKA patients. In contrast, lateral relaxation at deep flexion should be avoided when applying soft-tissue balancing in MP-TKA. Level of evidence: Level III. [ABSTRACT FROM AUTHOR]

This manuscript presents an efficient algorithm for solving the inverse kinematics problem of a 6R robot manipulator to be deployed on embedded control hardware. The proposed method utilizes the geometric relationship between the end-effector and the base of the manipulator, resulting in a computationally efficient solution. The approach aims to minimize computational complexity and memory consumption while maintaining the accuracy and real-time performance demonstrated by simulations and verified by experimental results on an embedded system. Furthermore, the manipulator is analyzed in terms of singularities, limits, the workspace, and general solvability. Due to the simplicity of the algorithm, a platform-independent implementation is possible. As a result, the average calculation time is reduced by a factor of five to eight and the average error is decreased by a factor of fifty compared to a powerful analytical solver. [ABSTRACT FROM AUTHOR]

Pico hydro turbines are suitable for low head applications in power plants since their efficiency is more stable than other turbine types. In some situations, computational fluid dynamics (CFD) has also been utilized as well as experimental studies for the performance prediction of water turbines at a pico scale. Also, CFD methods are getting much closer to real conditions in terms of steady-state with moving references and transient domains with rotor movements. For this purpose, electricity production related to the flow in a PHT was investigated numerically. This study presents six degrees of freedom (6-DOF) and moving reference frame (MRF) methods to predict the maximum conditions of a pico scale two-dimensional turbine by comparing the torque and angular velocities on the runner based on the turbine output power of 1 W determined by an experimental study. Besides, the effect of the torque, angular velocity, tip speed ratio, and turbine body profile was investigated comprehensively. In this regard, MRF and 6-DOF methods were performed to validate and compare the numerical model with the experimental results. Also, the results obtained from 6-DOF and MRF methods were compared to experimental study. It is concluded that PHT is generating 0.3 W power under 6.47 rad/s angular velocity with 6-DOF method, however; this value corresponds to 31.4 rad/s angular velocity against 1 W with the MRF method. Also, the maximum velocity of the turbine was 6.1 m/s according to the simulation result. It is accepted that the turbine maximum velocity inlet was 0.53 m/s based on the experimental study. As a conclusion, numerical results for the pico hydro turbine were reasonable taking the experimental study into account. It is also concluded that there is a tip speed ratio of 2.36 with the MRF method and 0.48 with the 6-DOF method between water tangential velocity and runner velocity for the turbine model.

Drag-reduction and fuel conservation,one of the significant benefits of active center of gravity(CG)control function,plays an important role in iterative and optimal design of function scheme. Based on its principle and scheme,the active CG control function of a certain aircraft is modeled,coupling with flight control system model,automatic flight control system model,fuel system model,aerodynamic model,engine model and aircraft 6-DOF(degree of freedom)model,with the consideration of effect of CG variations induced by fuel consumption. At the given altitude and Mach number,the benefits of active CG control function are estimated,through setting different target CG positions. The results show that it can bring considerable benefits to aircraft with the application of active CG control technology,especially,the more backward the target CG is,the more obvious benefits will be generated. The Mach number has an impact on the benefits of the function. Under the same conditions,the larger the Mach number is,the greater the return will be.

In order to control the 6-DOF apple picking manipulator to complete the picking task accurately and safely, a new trajectory planning method of 6-DOF apple picking manipulator is studied. Based on the mathematical model of the 6-DOF apple picking manipulator, the pose information and arm shape information of the forward and reverse motion of the manipulator are analyzed. On the basis of the obstacle avoidance method for the apple picking manipulator based on the improved artificial potential field, the obstacle model is constructed to obtain the obstacle distribution information. Through the two-way planning algorithm of the manipulator obstacle avoidance based on the improved artificial potential field method, the pose information and arm shape of the forward and reverse motion of the manipulator are controlled. On this basis, the trajectory planning control method of 6-DOF apple picking manipulator based on sliding mode PID control is used to control the manipulator to pick apples accurately and safely. After testing, the 6-DOF apple picking manipulator can realize the safe picking of apples according to the set picking position and speed. [ABSTRACT FROM AUTHOR]

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With the wide application of robots in life and production, robotic grasping is also experiencing continuous development. However, in practical application, some external environmental factors and the factors of the object itself have an impact on the accuracy of grasping detection. There are many classification methods of grasping detection. In this paper, the parallel gripper is used as the end of grasping to carry out research. Aiming at the angle problem of robot grasping, this paper summarizes some research status of grasping detection from 2D image to 3D space. According to their respective application, advantages, and disadvantages, this paper analyzes the development trend of the two methods. At the same time, several commonly used grasping datasets are introduced and compared.

This manuscript presents an efficient algorithm for solving the inverse kinematics problem of a 6R robot manipulator to be deployed on embedded control hardware. The proposed method utilizes the geometric relationship between the end-effector and the base of the manipulator, resulting in a computationally efficient solution. The approach aims to minimize computational complexity and memory consumption while maintaining the accuracy and real-time performance demonstrated by simulations and verified by experimental results on an embedded system. Furthermore, the manipulator is analyzed in terms of singularities, limits, the workspace, and general solvability. Due to the simplicity of the algorithm, a platform-independent implementation is possible. As a result, the average calculation time is reduced by a factor of five to eight and the average error is decreased by a factor of fifty compared to a powerful analytical solver.

Plate-type debris is a typical type of windborne debris, often originating from roof tiles and shingles. Numerical simulation using aerodynamic models provides a practical method to predict trajectories of windborne debris. In this paper, we first propose a revised model for the 3-degree-of-freedom (3-DOF) flight motion of square plates in winds by integrating experimental data from previous studies. Thereby, we divide the aerodynamic force and moment into a translational part and a rotational part. In addition, we propose conditions of autorotation in the revised model. The calculation of the rotational force and moment depends on whether these conditions are fulfilled. The revised model is validated by comparing the numerical results with experimental results of plate trajectories. Next, based on the revised model for the 3-DOF motion, we propose an aerodynamic model for the 6-DOF motion by incorporating the findings about the rotational force and moment, which were obtained from the authors' previous study on the 6-DOF motion of square plates. Based on these findings, the model is developed in the way that the direction of the rotational force depends on the relative wind velocity and the angular velocity of plate, and the direction of the rotational moment depends on the translational moment. By doing so the proposed model in this paper avoids directly using a database of aerodynamics, which is large and difficult to obtain. Validation using the experimental results of plate trajectories shows that the proposed model, which has a relatively simple form, performs generally well. [ABSTRACT FROM AUTHOR]

Submarine-launched vehicle (SLV) is a research hotspot due to its strong strike capability, among which underwater launching technology is a key issue hindering its development. In this paper, a numerical model is proposed to simulate the launching problem of SLV. The high nonlinearity induced by the coupling of multi-degree-of-freedom motions and the interaction between fluid and structure is solved. Specifically, the 6-DOF motion model of structure considering its strong added-mass effect, cavitation model and collision model are adopted. This numerical model is firstly validated by simulating the launching of SLV in still water. And then, the applicability of this model is discussed, as well as the effect of cross flow and initial launching velocity on the launching process. The results indicate that proposed numerical model could be used under both low-speed and high-speed cross flow situations. Cross flow changes the attitude and locomotion state of SLV. When flow velocity exceeds 1.25 m/s, the collision occurs between SLV (with the initial launching velocity of 40 m/s) and its barrel. This obtained locomotion of SLV after leaving its barrel causes the launching failure. Besides, a method of increasing launching velocity is introduced to promote the success rate of launching in high-speed cross flow situation. • A numerical model is proposed for underwater launching problem under high cross flow. • 6-DOF motion of SLV during its barrel-exit stage is simulated. • Influences of locomotion of SLV after leaving its barrel on underwater-motion stage are discussed. • Mechanism of increasing launching velocity to improve underwater launching is revealed. [ABSTRACT FROM AUTHOR]

Pico hydro turbines are suitable for low head applications in power plants since their efficiency is more stable than other turbine types. In some situations, computational fluid dynamics (CFD) has also been utilized as well as experimental studies for the performance prediction of water turbines at a pico scale. Also, CFD methods are getting much closer to real conditions in terms of steady-state with moving references and transient domains with rotor movements. For this purpose, electricity production related to the flow in a PHT was investigated numerically. This study presents six degrees of freedom (6-DOF) and moving reference frame (MRF) methods to predict the maximum conditions of a pico scale two-dimensional turbine by comparing the torque and angular velocities on the runner based on the turbine output power of 1 W determined by an experimental study. Besides, the effect of the torque, angular velocity, tip speed ratio, and turbine body profile was investigated comprehensively. In this regard, MRF and 6-DOF methods were performed to validate and compare the numerical model with the experimental results. Also, the results obtained from 6-DOF and MRF methods were compared to experimental study. It is concluded that PHT is generating 0.3 W power under 6.47 rad/s angular velocity with 6-DOF method, however; this value corresponds to 31.4 rad/s angular velocity against 1 W with the MRF method. Also, the maximum velocity of the turbine was 6.1 m/s according to the simulation result. It is accepted that the turbine maximum velocity inlet was 0.53 m/s based on the experimental study. As a conclusion, numerical results for the pico hydro turbine were reasonable taking the experimental study into account. It is also concluded that there is a tip speed ratio of 2.36 with the MRF method and 0.48 with the 6-DOF method between water tangential velocity and runner velocity for the turbine model. [ABSTRACT FROM AUTHOR]

Estimating the 6-DoF (Degree of Freedom) object pose from a single RGB image is one of the challenging tasks in the field of computer vision. Before the pose which is defined as the translation and rotation parameters can be derived by the traditional PnP algorithm, 2D image projections of a set of 3D object keypoints must be accurately detected. In this paper, we present techniques for defining 3D object surface keypoints and predicting their corresponding 2D counterparts via deep-learning network architectures. The main technique to designate 3D object keypoints is to employ quadratic fitting scheme for calculating the principal surface curvatures as the weights and then select from all surface points the ones mostly distributive with larger curvatures to describe the object shape as possible. However, the 2D projected keypoints are not directly regressed from the network, but encoded as the unit vector fields pointing to them, so that the voting scheme to recover back those 2D keypoints can be performed. Moreover, an effective loss function with the regularization term is adopted in training ResNet for predicting image projections of object keypoints by focusing on small-scale errors. Experimental results show that our proposed technique outperforms state-of-the-art approaches in both “2D projection” and “3D transformation” metrics.

Aiming at the application of parallel mechanism in flexible assembly and polishing， a new 6-DOF coupling parallel mechanism is designed. The mechanism branch chain is designed based on the spiral theory， and the branch chain mechanism is optimized for the purpose of improving the rigidity of the mechanism and reducing the motion inertia. The coupled parallel mechanism is decoupled and analyzed according to the fixed principle， and the kinematics and equivalent motion of the mechanism are obtained. The number of degrees of freedom of the mechanism is verified by the modified G-K formula. Finally， a prototype of the coupled parallel mechanism is fabricated， and a motion control experiment is carried out. The experimental results show that the mechanism configuration is reasonable and practical.

As multiple degree-of-freedom excitation systems continue to evolve and become standard hardware in many dynamic test facilities, there continues to be a lag in the development of associated spectral density based vibration specifications. The following discussion is centered on the development of a sixdegree- of-freedom spectral density matrix based vibration specification and various comparisons to traditional single-degree-of-freedom, combined three-degree-of-freedom, and synthesized six-degree-offreedom specification results, all computed from a common set of field data and assumptions of a common mission scenario. Laboratory test results and general observations are presented. [ABSTRACT FROM AUTHOR]

In this paper, the water-exit phenomenon has been studied experimentally and numerically. Based on the volume-of-fluid model and the Schnerr–Sauer cavitation model, the water-exit supercavitation around different shapes of cavitator projectiles is investigated using a dynamic mesh technology and three-dimensional six-degree-of-freedom method. The numerical results are compared with the experimental results obtained in our laboratory. Next, the effects of the cavitator shape on the characteristics of the projectile motion, breaking of the free surface, supercavitation size, and hydrodynamics of the water-exit supercavitation are analyzed. It was found that the hemispherical-nose projectile holds the best storage capacity and the longest displacement. The blunt disk-shaped nose projectile generates the maximum diameter of supercavity. The cavitation diameters of the conical-nose projectile and the hemispherical-nose projectile are relatively small. [ABSTRACT FROM AUTHOR]

The aerodynamic, structure and propulsion interactions in a six-degree-of-freedom (6-DOF) flexible hypersonic vehicle bring great challenges to vehicle modeling and control design. This paper focus on the modeling of a 6-DOF flexible hypersonic flight vehicle. The flexible dynamic and three-dimensional aerodynamic loads are calculated by using or combining an assumed modes method, variation theory and shock/expansion theory. A control-oriented nonlinear model (COM) is obtained using curve-fitted approximation of the forces and moments on the vehicle. The COM is then linearized about a steady flight condition, and the rigid/flexible dynamics and coupling of the 6-DOF vehicle model with aerodynamic, structure and propulsion interactions are analyzed comprehensively. [ABSTRACT FROM AUTHOR]

This paper first analyses and summarizes the research status of parallel robots and keeps track of the current development status and research prospects of parallel robots. Kinematics problems of 6-DOF parallel robots are analysed, and a relatively simple inverse kinematics expression has been established for some of the coordinate systems. Because the robot is a highly complex, strongly coupled, and highly nonlinear dynamic system, it is necessary to use a very systematic method to analyse and study the dynamic characteristics of the robot. This paper mainly uses mathematical modelling and PLC modelling methods. Through careful analysis of the structural characteristics of parallel robots, the dynamic equations are established. This article innovatively proposes an idea of using PLC for motion control based on WINCC OA. For most current robot controllers, the position and velocity of the robot are required to measure, and the relevant mathematical model is established. The simulation results showed that the desired control effect has been achieved and will continue in the future. It has laid a certain theoretical foundation for the in-depth study of parallel robots. [ABSTRACT FROM AUTHOR]

An improved active disturbance rejection control (IADRC) is proposed to stabilize and reject exogenous disturbances and system uncertainties for a 6-degree of freedom (DOF) quadrotor system. We used the nonlinear model of the 6-DOF quadrotor system to design four IADRC units for the altitude and attitude stabilization. Stability analysis is demonstrated for both the extended state observers of each IADRC unit and the overall closed-loop system using Hurwitz stability criterion. The simulations are implemented under the MATLAB environment where the parameters of the IADRC units are tuned to minimize the multi-objective output performance index. The unmanned aerial vehicle is tested with different tracking scenarios while subjected to exogenous disturbances and system parameter uncertainties. The performance of the proposed IADRC is compared with that of the PID controller, and the simulations revealed that the proposed IADRC scheme stabilized and excellently counteracted the exogenous disturbances and system uncertainties and outperformed the PID used in this work. [ABSTRACT FROM AUTHOR]

Maneuverability, which is closely related to operational performance and safety, is one of the important hydrodynamic properties of an underwater vehicle (UV), and its accurate prediction is essential for preliminary design. The purpose of this study is to analyze the turning ability of a UV while rising or submerging; the computational fluid dynamics (CFD) method was used to numerically predict the six-DOF self-propelled maneuvers of submarine model BB2, including steady turning maneuvers and space spiral maneuvers. In this study, the overset mesh method was used to deal with multi-body motion, the body force method was used to describe the thrust distribution of the propeller at the model scale, and the numerical prediction also included the dynamic deflection of the control planes, where the command was issued by the autopilot. Then, this study used the published model test results of the tank to verify the effectiveness of the CFD prediction of steady turning maneuvers, and the prediction of space spiral maneuvers was carried out on this basis. The numerical results show that the turning motion has a great influence on the depth and pitch attitude of the submarine, and a “stern heavier” phenomenon occurs to a submarine after steering. The underwater turning of a submarine can not only reduce the speed to brake but also limit the dangerous depth. The conclusion is of certain reference significance for submarine emergency maneuvers.

Georeferencing a kinematic Multi-Sensor-System (MSS) within crowded areas, such as inner-cities, is a challenging task that should be conducted in the most reliable way possible. In such areas, the Global Navigation Satellite System (GNSS) data either contain inevitable errors or are not continuously available. Regardless of the environmental conditions, an Inertial Measurement Unit (IMU) is always subject to drifting, and therefore it cannot be fully trusted over time. Consequently, suitable filtering techniques are required that can compensate for such possible deficits and subsequently improve the georeferencing results. Sometimes it is also possible to improve the filter quality by engaging additional complementary information. This information could be taken from the surrounding environment of the MSS, which usually appears in the form of geometrical constraints. Since it is possible to have a high amount of such information in an environment of interest, their consideration could lead to an inefficient filtering procedure. Hence, suitable methodologies are necessary to be extended to the filtering framework to increase the efficiency while preserving the filter quality. In the current paper, we propose a Dual State Iterated Extended Kalman Filter (DSIEKF) that can efficiently georeference a MSS by taking into account additional geometrical information. The proposed methodology is based on implicit measurement equations and nonlinear geometrical constraints, which are applied to a real case scenario to further evaluate its performance.

Accurately sensing the global position and posture of vehicles in traffic surveillance videos is a challenging but valuable issue for future intelligent transportation systems. Although in recent years, deep learning has brought about major breakthroughs in the six degrees of freedom (6-DoF) pose estimation of objects from monocular images, accurate estimation of the geographic 6-DoF poses of vehicles using images from traffic surveillance cameras remains challenging. We present an architecture that computes continuous global 6-DoF poses throughout joint 2D landmark estimation and 3D pose reconstruction. The architecture infers the 6-DoF pose of a vehicle from the appearance of the image of the vehicle and 3D information. The architecture, which does not rely on intrinsic camera parameters, can be applied to all surveillance cameras by a pre-trained model. Also, with the help of 3D information from the point clouds and the 3D model itself, the architecture can predict landmarks with few and/or blurred textures. Moreover, because of the lack of public training datasets, we release a large-scale dataset, ADFSC, that contains 120 K groups of data with random viewing angles. Regarding both 2D and 3D metrics, our architecture outperforms existing state-of-the-art algorithms in vehicle 6-DoF estimation. [ABSTRACT FROM AUTHOR]

Motion deblurring is essential for reconstructing sharp images from given a blurry input caused by the camera motion. The complexity of this problem increases in a light field due to its depth-dependent blur constraint. A method of generating synthetic 3 degree-of-freedom (3-DOF) translation blur on a light field image without camera rotation has been introduced. In this study, we generate a camera translation and rotation (6-DOF) motion blur model that preserves the consistency of the light field image. Our experiment results show that the proposed blur model can maintain the parallax information (depth-dependent blur) in a light field image. Furthermore, we produce a synthetic blurry light field dataset based on the 6-DOF model. Finally, to validate the usability of the synthetic dataset, we conduct extensive benchmarking using state-of-the-art motion deblurring algorithms. [ABSTRACT FROM AUTHOR]

Bi‐cruciate retaining (BCR) total knee arthroplasty (TKA) design preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. Abnormal knee kinematics and "paradoxical" anterior femoral translation in conventional TKA designs have been suggested as potential causes of patient dissatisfaction. However, there is a paucity of data on the in vivo kinematics and articular contact behavior of BCR‐TKA. This study aimed to investigate in vivo kinematics, articular contact position, and pivot point location of the BCR‐TKA during gait. In vivo kinematics of 30 patients with unilateral BCR‐TKA during treadmill walking was determined using validated dual fluoroscopic imaging tracking technique. The BCR‐TKA exhibited less extension than the normal healthy knee between heel strike and 48% of gait cycle. Although the average external rotation trend observed for BCR TKA was similar to the normal healthy knee, the range of motion was not fully comparable. The lowest point of the medial condyle showed longer anteroposterior translation excursion than the lateral condyle, leading to a lateral‐pivoting pattern in 60% of BCR TKA patients during stance phase. BCR‐TKA demonstrated no statistical significant differences in anterior–posterior translation as well as varus rotation, when compared to normal healthy knees during the stance phase. However, sagittal plane motion and tibiofemoral articular contact characteristics including pivoting patterns were not fully restored in BCR TKA patients during gait, suggesting that BCR TKA does not restore native tibiofemoral articular contact kinematics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1929–1937, 2019 [ABSTRACT FROM AUTHOR]

This paper deals with three-dimensional (3D) numerical simulations involving 3D moving geometries with large displacements on unstructured meshes. Such simulations are of great value to industry, but remain very time-consuming. A robust moving mesh algorithm coupling an elasticity-like mesh deformation solution and mesh optimizations was proposed in previous works, which removes the need for global remeshing when performing large displacements. The optimizations, and in particular generalized edge/face swapping, preserve the initial quality of the mesh throughout the simulation. We propose to integrate an Arbitrary Lagrangian Eulerian compressible flow solver into this process to demonstrate its capabilities in a full CFD computation context. This solver relies on a local enforcement of the discrete geometric conservation law to preserve the order of accuracy of the time integration. The displacement of the geometries is either imposed, or driven by fluid–structure interaction (FSI). In the latter case, the six degrees of freedom approach for rigid bodies is considered. Finally, several 3D imposed-motion and FSI examples are given to validate the proposed approach, both in academic and industrial configurations. [ABSTRACT FROM AUTHOR]

Six-degree-of-freedom (6-DOF) motions of structures widely exist in aeronautics and ocean engineering. It is significant to study the 6-DOF motion for simulating the trajectory and impact load of structures. This paper uses the smoothed particle hydrodynamics (SPH) method combined with some modified numerical techniques to simulate the fluid-solid interactions (FSI), then a quaternion-based method is adopted to simulate the free motion of rigid bodies, where the calculation process of 6-DOF motions based on quaternion is elaborated in detail. The accuracy of this method is verified through two benchmark tests, including water entry of a cuboid and skipping stone, which can prove the pressure calculation and motion prediction of rigid bodies are consistent with the experimental results. At last, the 6-DOF ditching process of a seaplane is simulated by the quaternion method embedded in the SPH model, and the simulation results are consistent with those simulated by the finite volume method (FVM). The above three tests demonstrate that the SPH model combined with a 6-DOF quaternion-based solver can accurately solve FSI problems from basic to complex at different scales. Besides, the SPH model shows significant advantages in capturing large-deformed free surfaces and splashing droplets compared with Eulerian-grid-based methods. • A six-degree-of-freedom (6-DOF) quaternion-based solver is developed to simulate the 6-DOF motion of rigid bodies. • A multi-resolution 3D SPH model combined with improved numerical techniques is adopted to simulate the 6-DOF fluid-solid interactions (FSI). • Three numerical examples from basic to complex applications are selected to verify the accuracy of the numerical model. [ABSTRACT FROM AUTHOR]