# Design of a Full-Ocean-Depth Macroorganism Pressure-Retaining Sampler and Fluid Simulation of the Sampling Process

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Structure and Working Principle of the HSMPS

#### 2.1. Structure of the HSMPS

^{3}/h. The hydraulic source of the suction pump is provided by the submersible. The diversion area consists of a suction tube and a handle, and the capture of deep-sea organisms in any direction can be achieved using a robot grasping the handle on the suction tube. Suction pipe selection is PVC steel wire hose, with built-in spiral steel wire resistance to negative pressure and bending, expansion and contraction, good performance of heat and cold resistance, anti-aging, and other advantages. The inner diameter of the suction tube is 60 mm, which can achieve most macroorganism sampling in hadal environments. The HSMPS is mounted on a support frame, with the length, width, and height of the support frame being 700 × 300 × 160 mm. HSMPS has the following features: (1) HSMPS can control the suction rate during the capture of seafloor organisms; (2) it can maintain the in situ pressure of the sample; (3) all key components can withstand a pressure of 110 MPa; (4) it can be sealed in one trigger without external power and is easy to operate; and (5) it can achieve pressure drop-free transfer in the laboratory.

#### 2.2. Working Principle of HSMPS

- (a)
- Lowering: The HSMPS components are installed on the submersible after integration. Before lowering the submersible, open the outlet and inlet sealing valves, and limit them through the trigger lever. Then, a certain amount of nitrogen is pre-charged into the pressure compensator through the filling valve so that the piston is at the top of the pressure compensator. Put the bait package into the top of the bait barrel piston; the top rod at the bottom of the check valve on the bait barrel is in contact with the level of the trigger rod, so that the check valve on the bait barrel is in the open state, the fixed rod is limiting the piston rod, and the spring is in the compressed state. The suction pump is connected to the hydraulic source on the submersible through a hydraulic line (Figure 3a).
- (b)
- Sampling: During the dive of the submersible, the piston in the pressure compensator moves downward under the pressure of seawater until the pressure in the lower and upper chambers of the piston reach equilibrium. When the sampling point is reached, the deep-sea organisms are captured by the robot grabbing the handle on the suction pipe, triggering the hydraulic source button on the submersible to make the suction pump work, and the suction pump generates negative pressure to make the fish–water mixture enter the pressure-retaining cylinder through the suction pipe, and the seawater flows out from the suction pump outlet through the non-return device, and the macroorganisms are trapped in the pressure-retaining cylinder by the non-return device. The bait cartridge retaining lever is triggered by the robot to remove the restriction on the piston rod, causing the spring to drive the piston to compress the bait packet (Figure 3b).
- (c)
- Recycling: HSMPS sampling is completed, and the inlet and outlet trigger lever is pulled by a robot to cancel the restriction on the outlet and inlet sealing valves to achieve the pressure-retaining cylinder seal. During the recovery of HSMPS to the deck, the pressure-retaining cylinder expands and deforms due to the reduction in external seawater pressure, at which time the pressure compensator will compensate for the pressure loss caused by the expansion and deformation of the pressure-retaining cylinder, and the piston moves upward. The piston in the bait cylinder is driven by a spring to compress the bait packet, and the bait flows from the check valve into the pressure-retaining cylinder to provide nutrients to the macroorganisms (Figure 3c).

## 3. Description of the Simulation of Method

#### 3.1. Modeling Details

^{3}and 0.00161 kg/m·s [18]. The standard k-ε model, standard k-ω model, and realizable k-ε model are used to simulate the flow field of the HSMPS sampling process. The experimental results show that the calculation results of the three models are similar, within 10%. The k-ε model is the most widely used model in engineering, and the realizable k-ε model takes into account the rotation and curvature, so the realizable k-ε model was finally selected as the turbulent simulation model in this study.

^{3}/h, and the convergence rate R

_{g}can be used to verify the mesh convergence [19]. R

_{g}is given by the following formula:

_{1}, ε

_{2}, and ε

_{3}are the results of fine, medium, and coarse grids.

_{g}are in the range of 0–1, which indicates that the convergence is monotonic as the number of grids increases. To balance the simulation accuracy and time, an intermediate grid is adopted; that is, the number of grids is 5.12 million. As shown in Figure 5, the flow field around the hadal snailfish was finely drawn using a tetrahedral unstructured grid to divide the computational domain. The first grid thickness of the inner wall of the suction pipe in the diversion area is 1 mm, and the grid growth rate is 1.2. Using Fluent to improve the grid quality, 5% of the grids with quality less than 0.5 are increased to more than 0.7, and the final number of grids is 5.52 million.

^{3}/h (1.0 m/s) of the suction pump.

_{i}and x

_{j}are the flow components; μ is the molecular viscosity C

_{1ε}= 1.44, C

_{2ε}= 1.92, and C

_{3ε}= 0.99; the Planck numbers σ

_{k}and σ

_{ε}are 1.0 and 1.3, respectively; u

_{i}, u

_{j}

_{,}and u

_{k}are the velocity components of the three coordinates; G

_{k}and G

_{b}are the mean velocity gradient and the buoyancy-induced turbulence energy generation terms, respectively; and S

_{k}and S

_{ε}are the user-defined source terms [21].

#### 3.2. Flow Field Distribution

^{3}/h is shown in Figure 6. The flow velocity at the inlet of the suction pipe in the diversion area increased from 0 to 1.3 m/s, which is greater than the limiting flow velocity of the hadal snailfish. The high-speed area of the flow field is mainly concentrated in the bending position of the inner wall of the suction pipe in the diversion area and the exit position of the deep-sea macroorganism sampler, with a maximum flow velocity of 1.7 m/s. The low-speed area is mainly concentrated in the outlet and inlet flap seal valve on both sides near the wall at the location, with a speed in the range of 0.3~0.6 m/s. The flow velocity in the pressure-retaining area is more stable, and the velocity gradient in the flow direction is small, with the flow velocity in the range of 1.0~1.3 m/s. The velocity vector diagram of the flow field of the deep-sea macroorganism sampler is shown in Figure 7. The backflow phenomenon occurs near the wall on both sides of the outlet and inlet sealing valves, which is the sudden increase in diameter when the fluid enters the outlet sealing valves from the diversion area, resulting in a small velocity near the wall. The pressure distribution of the flow field at the HSMPS pumping flow rate of 13.07 m

^{3}/h is shown in Figure 8. The HSMPS internal flow field formed a certain negative pressure environment, which created favorable conditions for the hadal snailfish to enter the pressure-retaining area through the diversion area. The inevitable bending of the diversion area suction tube in the process of capturing hadal snailfish causes a large local negative pressure, which increases the possibility of a collision between the HSMPS and the bending position of the inner wall of the diversion area suction tube in the process of capturing hadal snailfish. At the inlet sealing valve, due to the sudden change in the circulation area causing local pressure loss, the negative pressure near the inlet sealing valve is small, with a minimum of 599 Pa. At the pressure-retaining area, the pressure values at each position remain stable, with pressure values in the range of 1498 to 1798 Pa. At the outlet sealing valve, the negative pressure value is generated with a maximum of 3596 Pa.

^{3}/h).

## 4. Results and Analysis

#### 4.1. Distribution of Radial Velocity

^{3}/h, the maximum radial speed at the end of the pumping suction area is 2.25 m/s, and when the pumping flow rate is 12 m

^{3}/h, the maximum radial speed at the end of the pumping suction area is 1.52 m/s. The gradient of the radial velocity change in the pressure-retaining area is small because the inner diameter at each position of the pressure-retaining area is the same, and the radial velocity at each position is constant. In addition, the radial velocity of the upper wall surface is greater than the radial velocity of the lower wall surface, and the hadal snailfish are likely to collide with the upper wall surface of the pressure-retaining area during the HSMPS pumping process. For deep-sea soft gelatinous organisms, excessive collision speed is likely to cause the surface contusion of deep-sea organisms. Therefore, when designing a HSMPS, installing a layer of buffer material on the inner wall of the pressure-retaining area to reduce the possibility of deep-sea organism damage should be considered [24].

^{3}/h, the maximum radial velocity in the pressure-retaining area is 1.52 m/s. When the pumping flow rate is 12 m

^{3}/h, the maximum radial velocity at the end of the pressure-retaining area is 1.05 m/s, which is less than the limit flow rate of the fish, so the fish may swim against the current when they enter the pressure-retaining area [25]. The radial velocity variation at the lower wall of the diversion area is large, and the radial velocity variation trend at each position of the diversion area is the same. In addition, the radial velocity in the diversion area first decreases and then increases due to the eccentric design of our designed inlet seal valve, where the inner diameter of the inlet seal valve is first small and then large, and the position at the maximum inner diameter has the smallest radial velocity. At the inlet sealing valve, the radial velocity changes greatly, and shear flow easily occurs. Neitzel [26] found that at a high shear rate, it is easy to cause internal bleeding damage to the bodies of fish caused by the rupture of their swim bladders or internal organ damage. For most fish, when the shear rate is lower than 500 s

^{−1}, the shear rate has little effect on the fish.

^{3}/h, the minimum radial velocity in the diversion area is 0.48 m/s, and the maximum radial velocity in the diversion area is 1.75 m/s. When the pumping flow rate is 12 m

^{3}/h, the minimum radial velocity in the diversion area is 0.23 m/s, and the maximum radial velocity is 1.15 m/s. The maximum radial velocity is less than the limit flow velocity of the fish, and the fish may not be captured. When the pumping flow rate is 14 m

^{3}/h, the maximum radial velocity is 1.2 m/s. Therefore, we tried to pump a flow rate greater than 14 m

^{3}/h in the process of pumping the hadal snailfish on the bottom to ensure the success rate of capture.

#### 4.2. Distribution of Radial Pressure

^{3}/h, the minimum radial pressure in the diversion area is −2400 Pa, and the maximum radial pressure in the diversion area is −2900 Pa. When the suction flow rate is 12 m

^{3}/h, the minimum radial pressure in the diversion area is −1080 Pa, and the maximum radial pressure is −1280 Pa. The Electric Power Research Institute of the United States found, through experimental research, that the sharp pressure drop on the surface of fish generally may lead to internal organ damage caused by the internal bleeding of fish and expansion of the swim bladder [27]. When the minimum pressure in the flow channel is more than 60% of the fish’s adaptive environmental pressure, it is considered that the flow field pressure will not have a substantial impact on the fish [28]. Compared with the deep-sea ultra-high-pressure environment, the pressure change in the internal flow field of the HSMPS is very small, so it can be considered that the flow field of the hadal snailfish will not affect its tissues and organs before they are sucked in.

^{3}/h, the radial pressure in the pressure-retaining area is around −2800~2900 Pa. When the suction flow rate is 12 m

^{3}/h, the radial pressure in the pressure-retaining area is about −1250~1300 Pa, which creates favorable conditions for the hadal snailfish to enter the pressure-retaining cylinder in the pressure-retaining area through the suction pipe in the diversion area. When the width of the deep-sea creatures captured using the HSMPS is large, the deep-sea creatures form gap flow at the elbow position of the diversion, and the pressure-retaining barrel of the pressure-retaining area, which easily “blocks” the flow channel, reduces the cross-sectional area of the flow channel, increases the radial velocity and pressure of the fluid, and easily damages the deep-sea creatures. Therefore, the size of the capture target should be considered when designing a HSMPS.

^{3}/h, the maximum radial pressure in the pumping suction area is −4300 Pa, and when the pumping flow rate is 12 m

^{3}/h, the maximum radial pressure in the pumping suction area is −1945 Pa. As the HSMPS is equipped with a non-return device at the outlet end of the pressure-retaining area during the pumping of the hadal snailfish, the pressure change in the flow field within the pumping suction area does not affect the damage to the hadal snailfish.

#### 4.3. Suction Test

^{3}/h, the experimental fish feel the current and escape. When the suction flow is in the range of 14 m

^{3}/h~16 m

^{3}/h, the HSMPS can catch experimental fish, and one should check that the experimental fish can swim normally after catching. When the suction flow is in the range of 16 m

^{3}/h~18 m

^{3}/h, the HSMPS can catch experimental fish, but it is found that the surfaces of the experimental fish are bruised, which may be caused by the excessive suction speed and the experimental fish hitting the HSMPS. Therefore, the HSMPS should try its best to keep the pump flow between 14 and 16 m

^{3}/h in the process of sucking organisms from the seabed to balance the damage and the escape speed of the deep-sea organisms.

#### 4.4. High-Pressure Chamber Test

## 5. Conclusions

- (1)
- A full-ocean-depth hydraulic suction macrobiotic pressure-retaining sampling method is proposed, and the sampler achieves accurate sampling of seafloor organisms using pumping. The HSMPS integrates a pressure compensation mechanism, bait replenishment mechanism, and sample transfer mechanism, which can realize the pressure-retaining sampling of microorganisms at full ocean depth and can complete the sample transfer in the laboratory. The HSMPS can realize a pressure-retaining seal with one trigger of a robot, a simple structure, and a reliable seal.
- (2)
- In the process of collecting seafloor organisms using the HSMPS, the high-speed area of the flow field is mainly concentrated in the bending position of the inner wall of the suction tube in the diversion area and the position of the outlet sealing valve in the pressure-retaining area, and the organisms easily collide with the bending position of the inner wall of the suction tube during the collection process of the HSMPS, so excessive speed should be avoided to avoid damage to the organisms as much as possible. The low-speed region is mainly concentrated in the pressure-retaining area out- and inlet sealing valves on both sides near the wall at the location, with an easy- to-produce backflow phenomenon.
- (3)
- The radial velocity variation in the inflow area is the largest, with a maximum radial velocity variation of 1.72 m/s. When the sampling flow rate of the sampler is greater than 14 m
^{3}/h, it is necessary to ensure that the organisms can be sucked into the HSMPS. The radial pressure and velocity change gradient in the pressure-retaining area is small, and the radial velocity of the upper wall surface is large, so with the HSMPS, it is very easy for the organisms to collide with the upper wall surface of the pressure-retaining area during the pumping process. The radial pressure variation in the pumping suction area is the largest, with a maximum radial pressure variation of 2355 Pa. - (4)
- The HSMPS was subjected to suction tests and simulated sampling tests under a 110 MPa high-pressure environment in the laboratory, and the test results show that the HSMPS was able to capture the test fish; in addition, the all-seas deep macro-biological pump suction sampler was able to complete the sampling action under a 110 MPa high-pressure environment. The test results verify the feasibility of the HSMPS design, which will provide strong support for the deep abyssal seafloor sampling operations of the full-ocean-depth manned submersible.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 9.**Radial velocity distribution of HSMPS. (

**a**)12 m

^{3}/h, (

**b**)14 m

^{3}/h, (

**c**) 16 m

^{3}/h, (

**d**) 18 m

^{3}/h.

**Figure 10.**Radial pressure distribution of HSMPS. (

**a**) 12 m

^{3}/h, (

**b**) 14 m

^{3}/h, (

**c**) 16 m

^{3}/h, (

**d**) 18 m

^{3}/h.

Structures | Values | Structures | Values |
---|---|---|---|

Inner diameter of inlet sealing valve/D_{1} | 60 mm | Length of pressure compensator/L_{2} | 300 mm |

Maximum internal diameter of sealing valve/D_{2} | 68 mm | Inner diameter of pressure compensator/D_{6} | 50 mm |

Inner diameter of outlet seal valve/D_{3} | 62 mm | Inner diameter of bait cartridge/D_{7} | 60 mm |

Length of pressure-retaining cylinder/L_{1} | 526 mm | Length of bait cartridge/L_{3} | 187 mm |

Inner diameter of suction pipe/D_{4} | 60 mm | Eccentric angle of sealed valve/θ | 10° |

Inner diameter of pressure-retaining cylinder/D_{5} | 68 mm | Maximum pumping flow rate/Q | 18 m^{3}/h |

Grid | Maximum Inlet Speed | Global Maximum Speed |
---|---|---|

4259452 | 2.35 | 2.32 |

5117974 | 2.19 | 2.38 |

6122362 | 2.14 | 2.42 |

R_{g} | 0.31 | 0.67 |

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## Share and Cite

**MDPI and ACS Style**

Liu, G.; Jin, Y.; Peng, Y.; Liu, D.; Wan, B.
Design of a Full-Ocean-Depth Macroorganism Pressure-Retaining Sampler and Fluid Simulation of the Sampling Process. *J. Mar. Sci. Eng.* **2022**, *10*, 2007.
https://doi.org/10.3390/jmse10122007

**AMA Style**

Liu G, Jin Y, Peng Y, Liu D, Wan B.
Design of a Full-Ocean-Depth Macroorganism Pressure-Retaining Sampler and Fluid Simulation of the Sampling Process. *Journal of Marine Science and Engineering*. 2022; 10(12):2007.
https://doi.org/10.3390/jmse10122007

**Chicago/Turabian Style**

Liu, Guangping, Yongping Jin, Youduo Peng, Deshun Liu, and Buyan Wan.
2022. "Design of a Full-Ocean-Depth Macroorganism Pressure-Retaining Sampler and Fluid Simulation of the Sampling Process" *Journal of Marine Science and Engineering* 10, no. 12: 2007.
https://doi.org/10.3390/jmse10122007