A study of the kinematic characteristic of a coupling device between the buffer system and the flexible pipe of a deep-seabed mining system

International Journal of Naval Architecture and Ocean Engineering.
2014.
Sep,
6(3):
652-669

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

- Published : September 30, 2014

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Coupling device
;
Buffer
;
Deep-seabed mining system
;
Multi-body dynamic
;
Fluid Structure Interaction (FSI)
;
Kinematic characteristic
;
Flexible pipe.

INTRODUCTION

Many concepts for the commercial production of deep-seabed manganese nodules have been studied from the 1970s (
Brink and Chung, 1982
;
Chung, 1996
;
Herrouin et al., 1989
;
Amann et al., 1991
;
Liu and Yang, 1999
;
Hong and Kim, 1999
;
Deepak et al., 2001
;
Handschuh et al., 2001
). The accumulate ground of the deep-seabed has a problem, in that the bearing capacity of the ground is not strong, because the accumulate ground is formed by fine particles with high moisture content. So it is impossible to carry manganese nodules in the collection system. Therefore, the validity of continuous mining by lifting pipe from ground to vessel is highly appreciated.
A continuous mining system is composed of mining vessel, lifting pipe, buffer system, transfer tube (flexible pipe), and self-propelled mining robot. The shape of the transfer tube between the buffer system and mining robot has a big impact on the driving efficiency of the mining robot. Also, the relative position between the buffer system and mining robot influences the efficiency of the mining robot. So, dynamic analysis of the integration of the mining system (mining vessel-lifting pipe-buffer system-flexible pipe-mining robot) is a very important technique in building a deep-sea mining system.
Currently, the lifting pipe and the flexible pipe are actively studied, according to the growth of offshore plant and the ocean floor industry. But studies on the buffer system are at an early stage. Just several functions to temporarily store nodules were mentioned by researchers (
Chung, 2003
;
Kotlinski et al., 2008
).
The coupling device of the buffer system is the main subject of this study. The buffer system is currently developing. This coupling device makes a big impact on the dynamic movement of a mining robot. And it is a very important mechanic device in a deep-seabed mining system. The specs of the coupling device are determined by various efficiency tests and changes of design. But the production and experiment of a buffer system is costly and time-consuming. So the design specs of this device must be found by simulation. In general, this design method is called the simulation-based design.
Dynamic analysis of mechanical systems using computers is rapidly performed through the growth of computing power. The method of simulation-based design is a useful technique in otherwise impossible cases, which is verified by using an experiment with a model as an integrated deep-seabed mining system. The simulation technique is an excellent means of understanding qualitative (or quantitative) optimization design, and can skip the process of test model production, which is costly and time-consuming.
The mining robot and vehicle model used in this study is an MBD model. This MBD model was developed by Kim (
Kim et al., 2010
). The integrated simulation model is developed by
DAFUL (2012)
.
In this study, the used equations are the joint constraints, a beam elastic equation and a multi-body dynamic solution. The verifications of the joint constraints and the beam elastic equation are written in
DAFUL verification manual (2012)
.
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GOVERNING EQUATION

- Joint constraint

In this study, joint constraints (
Haug, 1989
) were applied to find optimum kinematic characteristics of the coupling device. The joint constraints are as follows.
- Fixed constraint

A fixed constraint can remove motion for all degrees of freedom of rigid bodies or flexible bodies. Eqs. (1) and (2) show the fixed constraint equations (
Haug, 1989
).
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- Revolute constraint

A revolute constraint is able to allow rotation between two bodies about one rotation axis. Eqs. (1) and (3) show the revolute constraint equations (
Haug, 1989
).
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- Beam elastic

Beam elastic theory is used to build flexible pipe and transfer tube. Euler and Timoshenko had verified the beam method using beam stiffness. The equation of beam stiffness is as in Eq. (4).
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- Multi-body dynamic

All mechanical systems are composed as an assembly of many objects. This assembly has been called a multi-body. Multibody solutions are different from basic dynamic solutions. Multi-body solutions must find dynamic responses of each object, and exact solutions must be obtained by applying components, which are in correlation. Each body is defined to calculate the dynamic responses of a multi-body. The method to define an object is in two ways. First, an orthogonal coordinate system is attached to each body, and a motion of the body coordinate system is expressed by a generalized coordinate system. Second, connected bodies in series are numbered in couplers of the multi-body.
The body’s equation of motion is defined as a differential equation. The multi-body system’s equation of motion has nonlinearity of relative coordinate, velocity and acceleration.
An eidetic method to change from nonlinearity to linearity is that the equation is expressed by only the relative coordinate, velocity and acceleration. And relative coordinates must be expressed as equations of independent coordinates, velocities and accelerations. An interaction formula between an independent coordinate and dependent coordinate is able to lead from a constraint equation of position, velocity and acceleration.
The equation of motion is defined as follows (
Haug, 1989
). A multi-body system can be modeled as a generalized coordinate of ‘ngc’ dimensions. These generalized coordinates are expressed as Eq. (13). Also, the velocity and acceleration coordinate are defined as Eqs. (14) and (15) respectively.
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DYNAMIC MODEL OF DEEP-SEABED MINING SYSTEM

- Buffer system

A buffer system is a mechanical structure to save collected mineral lumps. A mass of the buffer system is 8
Components of buffer system.

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Characteristics of PVC pipe.

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- Integration simulation model of mining system

An integration model is built with the buffer system model, mining robot and transfer tube. They are shown in
Table 3
. The mining robot model is developed as in the Kim’s last study (
Kim et al., 2010
). The transfer tube is built by beam elastic theory, to advance solving time. In common, dynamic responses by the beam model are equal to the results by the finite element method. But the solving time is very fast. The characteristics of the transfer tube are shown in
Table 4
.
Components of the integration simulation model.

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Characteristics of the transfer tube.

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Characteristics of the buoyancy module.

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SIMULATION CONDITION

- Forced motion

Forced motion is the basic test condition to estimate loads. The test conditions for movements of the coupling device are as follows.
Forced motion condition.

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- Driving motion

When the vessel and mining robot are driven, motions of the coupling device may be different from the results of the forced motion condition. Load estimation about the combined model must be performed. But the driving effect of the vessel is applied to the buffer system. Its effect is irrelevant to the movement of the coupling device. And the solving time is advanced, due to it being a simple model.
In this study, the driving conditions of the vessel and mining robot are determined by the results of Brink (1981), and
Hong and Kim (2008)
. Detailed driving conditions for the load estimation are shown in
Table 7
.
Driving conditions for load estimation.

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NUMERICAL RESULT AND LOAD ESTIMATION

- Load estimation by forced motion

- Condition 1

Loads are estimated at the position of maximum stress and load in the flexible pipe. In figures, the color means size of stress. The red color is maximum stress of the pipe and the blue color is minimum stress. The position is shown in
Fig. 8
.
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Maximum load of flexible pipe in condition 1.

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- Condition 2

Loads are estimated at the position of maximum stress and load in the flexible pipe. The position is shown in
Fig. 10
.
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Maximum load of flexible pipe in condition 2.

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- Condition 3

In this case, measurement positions for the load estimation are not the same, because the maximum load and stress are applied by constraints at different points. The positions are shown in
Fig. 13
.
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Maximum load of flexible pipe in condition 3.

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- Condition 4

Loads are estimated at the position of maximum stress and load in the flexible pipe. The position is shown in
Fig. 15
.
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Maximum load of flexible pipe in condition 4.

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- Condition 5

Loads are estimated at the position of maximum stress and load in the flexible pipe. The position is shown in
Fig. 17
.
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Maximum load of flexible pipe in condition 5.

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- Load estimation by driving motion

The load results for each driving condition are as follows.
Load estimation by driving condition.

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Load estimation in DTP1 of driving condition.

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Load estimation in DTP2 of driving condition.

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CONCLUSION

Through this study, a concept of the simulation-based design by using multi-body dynamics is introduced through the kinematic design of the buffer system. The results of this study are as follows.
1) Kinematic design of the coupling device of the buffer system
The loads of the flexible pipe depend on the kinematic characteristics of the coupling device. The size of the loads as follows.
Acknowledgements

This study was initiated by an R&D Project, “Technology Development of Deep-Seabed Mining System for Manganese Nodules”, sponsored by the Ministry of Oceans and Fisheries of Korea. The authors are grateful for the full support shown for this research work.

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Citing 'A study of the kinematic characteristic of a coupling device between the buffer system and the flexible pipe of a deep-seabed mining system
'

@article{ E1JSE6_2014_v6n3_652}
,title={A study of the kinematic characteristic of a coupling device between the buffer system and the flexible pipe of a deep-seabed mining system}
,volume={3}
, number= {3}
, journal={International Journal of Naval Architecture and Ocean Engineering}
, publisher={The Society of Naval Architects of Korea}
, author={Oh, Jae-Won
and
Lee, Chang-Ho
and
Hong, Sup
and
Bae, Dae-Sung
and
Cho, Hui-Je
and
Kim, Hyung-Woo}
, year={2014}
, month={Sep}