Determination of Hydrodynamic Parameters for Remotely Operated Vehicles

2016 ◽  
Author(s):  
Ole A. Eidsvik ◽  
Ingrid Schjølberg
Keyword(s):  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Analytical Data ◽  
Relative Difference ◽  
Accurate Estimate ◽  
Six Degrees Of Freedom ◽  
Hydrodynamic Parameters ◽  
Planar Motion Mechanism ◽  
Rotational Degrees Of Freedom

In this paper the hydrodynamic parameters that characterize the behavior of a typical unmanned underwater vehicle are evaluated. A complete method for identifying these parameters is described. The method is developed to give a brief and accurate estimate of these parameters in all six degrees of freedom using basic properties of the vehicle such as dimensions, mass and shape. The method is based on both empirical and analytical results for typical reference geometries (ellipsoids, cubes, etc.). The method is developed to be applicable for a wide variety of UUV designs as these typically varies substantially. The method is then applied to a small observation class ROV. The results are first verified using an experimental method in which the full scale ROV is towed using a planar motion mechanism. An additional verification is performed with numerical simulations using Computational Fluid Dynamics and a radiation/diffraction program. The method shows promising results for both damping and added mass for the tested case. The translational degrees of freedom are more accurate than the rotational degrees of freedom which are expected as most empirical and analytical data are for translational degrees of freedom. The case study also reveals that the relative difference between the numerical simulations and the experimental results are similar to the relative difference between the proposed method and the experiment.

Development of a 6-DOF Testing Platform for Multirotor Flying Vehicles with Suspended Loads

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 355
Author(s):  
Saad M. S. Mukras ◽  
Hanafy M. Omar
Keyword(s):  
Degrees Of Freedom ◽  
Center Of Mass ◽  
Performance Testing ◽  
Flight Performance ◽  
Testing Platform ◽  
Six Degrees Of Freedom ◽  
Mass Properties ◽  
Test Platform ◽  
Suspended Loads

The development of multirotor vehicles can often be a dangerous and costly undertaking due to the possibility of crashes resulting from faulty controllers. The matter of safety in such activities has primarily been addressed through the use of testbeds. However, testbeds for testing multirotor vehicles with suspended loads have previously not been reported. In this study, a simple yet novel testing platform was designed and built to aid in testing and evaluating the performances of multirotor flying vehicles, including vehicles with suspended loads. The platform allows the flying vehicle to move with all six degrees of freedom (DOF). Single or three-DOF motions can also be performed. Moreover, the platform was designed to enable the determination of the mass properties (center of mass and moments of inertia) of small multirotor vehicles (which are usually required in the development of new control systems). The applicability of the test platform for the in-flight performance testing of a multirotor vehicle was successfully demonstrated using a Holybro X500 quadcopter with a suspended load. The test platform was also successfully used to determine the mass properties of the vehicle.

A Family of 3-DOF Translational Parallel Manipulators1

2003 ◽  
Vol 125 (2) ◽  
pp. 302-307 ◽  
Author(s):  
Marco Carricato ◽  
Vincenzo Parenti-Castelli
Keyword(s):  
Degrees Of Freedom ◽  
Translational Motion ◽  
Parallel Manipulators ◽  
Geometric Interpretation ◽  
The Other ◽  
Six Degrees Of Freedom ◽  
Revolute Joints ◽  
Rotational Degrees Of Freedom

This article addresses parallel manipulators with fewer than six degrees of freedom, whose use may prove valuable in those applications in which a higher mobility is uncalled for. In particular, a family of 3-dof manipulators containing only revolute joints or at the most revolute and prismatic ones is studied. Design and assembly conditions sufficient to provide the travelling platform with a pure translational motion are determined and two sub-families that fulfill the imposed constraint are found: one is already known in the literature, while the other is original. The new architecture does not exhibit rotation singularities, i.e., configurations in which the platform gains rotational degrees of freedom. A geometric interpretation of the translation singularities is provided.

scholarly journals In-situ measurement technologies for flow behaviour and contact status of fibre-reinforced thermoplastics during forming with a six degree of freedom press

2018 ◽  
Vol 190 ◽  
pp. 07004
Author(s):  
Birk Wonnenberg ◽  
Franz Dietrich ◽  
Klaus Dröder
Keyword(s):  
Degrees Of Freedom ◽  
Optical Measurements ◽  
Image Processing Algorithm ◽  
Forming Process ◽  
Contact State ◽  
Six Degrees Of Freedom ◽  
Reinforced Plastics ◽  
Reinforced Thermoplastics ◽  
Six Degree Of Freedom

The paper presents investigations on a forming process, which is implemented in a forming press based on a Stewart platform. In contrast to common forming techniques, this buildup offers not only one but six degrees of freedom. This is of particular interest when it comes to the forming of materials that show significant anisotropic behaviour such as fibre-reinforced plastics. Therefore, an experimental setup is presented to record characteristic variables during the forming process of fibre-reinforced thermoplastics. The contact state is of particular interest for this kind of forming process because it changes continuously in shape and position as the forming process progresses. For this purpose, temperatures at different places in the tool are recorded to provide information about the flow velocity of the material and the contact state between tool and workpiece. This allows the determination of the exact time and position of the contact between material and forming tool as well as the duration of this contact. The results are compared with optical measurements analysed by image processing algorithm and process forces measured by load cells.

A Six-Degree-of-Freedom Test System for the Study of Joint Mechanics and Ligament Forces

1995 ◽  
Vol 117 (4) ◽  
pp. 383-389 ◽  
Author(s):  
J. M. Hollis
Keyword(s):  
Degrees Of Freedom ◽  
Test System ◽  
Testing System ◽  
Joint Mechanics ◽  
Six Degrees Of Freedom ◽  
Position Feedback ◽  
Six Degree Of Freedom ◽  
Good Agreement

A joint testing system was designed to transmit a specified motion or force to a joint in all six degrees of freedom (d.o.f.) using a spatial linkage system for position feedback. The precise reproducibility of position provided by this method of position feedback allows determination of in situ ligament forces for external joint loadings. Load on the structure of interest is calculated from six d.o.f. load cell output after the loaded position is reproduced with all other structures removed. In a test of this system, measured loads showed good agreement with applied loads.

scholarly journals A Gyro-Free System for Measuring the Parameters of Moving Objects

2014 ◽  
Vol 14 (5) ◽  
pp. 263-269 ◽  
Author(s):  
Dimitar Dichev ◽  
Hristofor Koev ◽  
Totka Bakalova ◽  
Petr Louda
Keyword(s):  
Degrees Of Freedom ◽  
Moving Objects ◽  
Measuring System ◽  
Measurement Channel ◽  
Measuring Instruments ◽  
Additional Measurement ◽  
Free System ◽  
Six Degrees Of Freedom ◽  
Measurement Concept

Abstract The present paper considers a new measurement concept of modeling measuring instruments for gyro-free determination of the parameters of moving objects. The proposed approach eliminates the disadvantages of the existing measuring instruments since it is based, on one hand, on a considerably simplified mechanical module, and on the other hand, on the advanced achievements in the area of nanotechnologies, microprocessor and computer equipment. A specific measuring system intended for measuring the trim, heel, roll, and pitch of a ship has been developed in compliance with the basic principles of this concept. The high dynamic accuracy of this measuring system is ensured by an additional measurement channel operating in parallel with the main channel. The operating principle of the additional measurement channel is based on an appropriate correction algorithm using signals from linear MEMS accelerometers. The presented results from the tests carried out by means of stand equipment in the form of a hexapod of six degrees of freedom prove the effectiveness of the proposed measurement concept

scholarly journals A 6-parameter triangular flat shell element for nonlinear analysis

2019 ◽  
pp. 237-268 ◽  
Author(s):  
Professor Mohammad Rezaiee-Pajand ◽  
Amir R. Masoodi ◽  
E. Arabi
Keyword(s):  
Degrees Of Freedom ◽  
Shell Element ◽  
Geometrically Nonlinear ◽  
Nonlinear Analyses ◽  
Six Degrees Of Freedom ◽  
Triangular Shell Element ◽  
Rotation Method ◽  
Flat Shell Element ◽  
Rotational Degrees Of Freedom ◽  
Convergence Study

In this paper, an improved flat triangular shell element is proposed. This element has three nodes, and in each node, six degrees of freedom are considered. Since there are three rotational degrees of freedom at each node, the drilling effect can be incorporated in authors' formulation. A new procedure is also suggested for updating the director vectors about which the rotational degrees of freedom are defined. In order to study large displacements and rotations, Total Lagrangian principles are employed. In addition, updating the rotational degrees of freedom is implemented using enriched updated director vectors, which are formulated based on the finite rotation method. On the other hand, small strains are considered in this formulation. By utilizing MITC method, shear and membrane locking is mitigated from new element. To examine the performance, the element passes three basic tests, including isotropy, and patch test. Moreover, a convergence study is also implemented to show the elemental behavior. Several popular benchmarks are considered to illustrate the accuracy and capability of the suggested element in geometrically nonlinear analyses.    

Recent Contributions Under the Bureau of Ships Fundamental Hydromechanics Research Program

1959 ◽  
Vol 3 (02) ◽  
pp. 47-64
Author(s):  
M. St. Denis ◽  
J.P. Craven
Keyword(s):  
Research Program ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Elastic Response ◽  
Inertial System ◽  
Ship Motions ◽  
Six Degrees Of Freedom ◽  
The Third ◽  
Ship Performance

The third main nautical objective, Seakeeping, refers to that aspect of ship performance in which the seaway enters in a dominant manner and affects fundamentally the character of the problem. In the section on Control [3],1 a pattern was introduced according to which seakeeping was related to the uncontrolled as well as the controlled oscillations which take place with reference to a ship's inertial system. But, more broadly speaking, seakeeping includes all of the following subjects:Description of the seaway.Determination of the forces imposed by the seaway on the vessel—the excitation (hydrodynamic loadings, wave bending moment, slamming forces, and so on).Determination of the response of the ship in her six degrees of freedom (ship motions).Prediction of the perils to which a ship may be exposed (capsizing, foundering, safety at sea).Prediction of the loss in speed she will sustain in heavy weather.Evaluation of the amount of stabilization necessary to prevent unacceptable or undesirable displacements and accelerations. The elastic response and strength of a vessel's structure, though not included under seakeeping, depend, nevertheless, in an essential manner thereon.

scholarly journals Prediction of Ship Unsteady Maneuvering in Calm Water by a Fully Nonlinear Ship Motion Model

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
Ray-Qing Lin ◽  
Tim Smith ◽  
Michael Hughes
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Ship Motion ◽  
Ship Motions ◽  
Motion Model ◽  
Forward Speed ◽  
Fully Nonlinear ◽  
Six Degrees Of Freedom ◽  
Calm Water

This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL). In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water. During the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge, sway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage, respectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions and their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering, a universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces and moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an Experimental Hull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL and experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder, which is included using a flow acceleration factor.

scholarly journals Design and development of anchoring positioning control system for riprap leveling ship

2021 ◽  
Vol 233 ◽  
pp. 04007
Author(s):  
Xiaotao Hua ◽  
Yan Liu ◽  
Haiyang Sun ◽  
Jianru Chen
Keyword(s):  
Control System ◽  
Equilibrium State ◽  
Degrees Of Freedom ◽  
Wind Wave ◽  
Control Method ◽  
Positioning Control ◽  
Six Degrees Of Freedom ◽  
Hydrodynamic Parameters ◽  
Convergence Control ◽  
Heading Angle

It is very important to level foundation bed by riprap in water and soil engineering. In this paper, a real-time feedback convergence control method is proposed to control the position and heading angle of the riprap leveling ship. The wind, wave, current and hydrodynamic parameters are obtained by empirical formula; the tension of four cables is calculated according to the balance equation of six degrees of freedom, and then the cable deformation is obtained. According to the deformation of the cable, the length of the cable in a certain equilibrium state can be obtained. The length of four cables can be lengthened or shortened by comparing the length of cables at two balanced positions. The length of cables can be controlled by winch to complete the anchoring and positioning control of leveling ship.

A Family of 3-DOF Translational Parallel Manipulators

2001 ◽  
Author(s):  
Marco Carricato ◽  
Vincenzo Parenti-Castelli
Keyword(s):  
Degrees Of Freedom ◽  
Translational Motion ◽  
Parallel Manipulators ◽  
Geometric Interpretation ◽  
The Other ◽  
Six Degrees Of Freedom ◽  
Revolute Joints ◽  
Rotational Degrees Of Freedom

Abstract This article addresses parallel manipulators with fewer than six degrees of freedom, whose employ may prove valuable in those applications in which a higher mobility is uncalled-for. In particular, a family of 3-dof manipulators containing only revolute joints or at the most revolute and prismatic ones is studied. Design and assembly conditions sufficient to provide the travelling platform with a pure translational motion are determined and two sub-families that fulfill the imposed constraint are found: one is already known in the literature, whilst the other is original. The new architecture does not exhibit rotation singularities, i.e. configurations in which the platform gains rotational degrees of freedom. A geometric interpretation of the translation singularities is provided.

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