Deep-sea Operations Research Articles

A Highly Sensitive 3D-Printed Flexible Sensor for Sensing Small Pressures in Deep-Sea High-Pressure Environment.

The origin of life on Earth is believed to be from the ocean, which offers abundant resources in its depths. However, deep-sea operations are limited due to the lack of underwater robots and rigid grippers with sensitive force sensors. Therefore, it is crucial for deep-sea pressure sensors to be integrated with mechanical hands for manipulation. Here, a flexible stress sensor is presented that can function effectively under high water pressure in the deep ocean. Inspired by biological structures found in the abyssal zone, our sensor is designed with an internal and external pressure balance structure (hollow interlocking spherical structure). The digital light processing (DLP) three-dimensional (3D) printing technology is utilized to construct this complex structure after obtaining optimized structural parameters using finite element simulation. The sensor exhibits linear sensitivity of 0.114 kPa-1 within the range of 0-15 kPa and has an extremely short response time of 32 ms, good dynamic-static load response capability, and excellent resistance cycling stability. It shows high sensitivity of 1.74 kPa-1 even under 30 MPa static water pressures and the theoretical working pressure can exceed 110 MPa, which provides a new solution for deep-sea robots.

Research and application on in-situ monitoring of strata movement in submarine cold seeps area based on three-dimensional MEMS sensor network

Accurate monitoring of strata movement is crucial for understanding the geomorphological evolution of the cold seeps. However, the complex environments and inherent challenges of deep-sea operations present significant obstacles for existing observation methods. In this paper, we present a strata movement monitoring system based on a three-dimensional micro-electromechanical system (MEMS) sensor network that includes multiple short and long sensor arrays. The movement vector is reconstructed using triaxial-acceleration and cubic Hermite interpolation. In laboratory simulations with vertical and horizontal displacement of 250 mm and 100 mm, respectively, the root mean square error of the reconstruction model is 3.74 mm. Two sensor arrays were deployed and operated for 4 days in cold seeps in South China Sea, and the observed displacement showed micro-tremors, and the displacement ranges in the x- and y- directions were (−0.4 mm, 0.18 mm) and (−0.43 mm, 0.19 mm), respectively. These results affirm the feasibility of the proposed system.

Ultrawide sensing-range, super durable and high-strength epoxy/carbon fiber composites sensor based on stress-induced structure

Nowadays, high-pressure sensors are broadly utilized in manufacturing and applications for ensuring safe production and preventing failures. However, present high-pressure sensors are mainly fabricated by high-strength metal and cement, which are too heavy or easy-corrosive to satisfy long-term usage. Polymer piezoresistive materials have great potential due to their stability and light weight, but achieving high strength and durability at the same time remains a serious challenge. In this work, a high-strength pressure sensor is fabricated by epoxy resin/carbon fiber (EP/CF) composite, where CF builds a conductive network as a reinforcing phase and EP provides a durable and light-weight base phase. The conductive mechanism based on stress-induced structure has been elucidated, and the performance of related sensors in various conditions is revealed. The lightweight (∼1.28 g/cm3) pressure sensor manifests a wide sensing response range from 22 kPa to 80 MPa. Moreover, the durability of this novel pressure sensor is verified by repeating loading and unloading at a high pressure of 10 MPa for more than 3500 cycles. Meanwhile, the high temperature and water resistance are furtherly confirmed, where EP/CF composites exhibits excellent cycling stability (10 MPa, >1000 cycles) after heating (100 °C) or soaking in water. Attributed to the comprehensive performance of high-strength, ultrawide detection range, durability and light weight, EP/CF composites are applied for road safety monitoring and deep-sea operation, showing wide application prospects in high-pressure monitoring field.

Sound Velocity Profiles Time Series Prediction Method Based on EMD-NARX Model

To solve the problem of SVP (Sound velocity profiles) representative error caused by the difficulty of obtaining continuous time series SVP in deep-sea operations, an SVP timing prediction method combining EMD (Empirical mode decomposition) and NARX (Nonlinear autoregressive neural network with external input) is proposed. To begin with, the time-series SVP are stratified according to different depths, and the time-series variation curves of sound velocity at different depths are obtained; Furthermore, the EMD is used to decompose the time series variation curve of sound velocity into multiple IMF (Intrinsic mode function) components, each component contains local characteristic signals of different time scales of the original signal. The NARX is used to establish a prediction model for each IMF components, and the prediction values of the sound velocity at different depths are obtained. The EMD-NARX, NARX and polynomial fitting model are analyzed and verified by Argo buoys data in the South China Sea, and the results of the experiment show that EMD-NARX improves the time series prediction accuracy of sound velocity by 32.24% and 65.15% compared with NARX and polynomial fitting, respectively, so EMD-NARX has a good prediction effect on the time series SVP of the deep sea.

Sailing efficiency optimization and experimental validation of a Petrel long-range autonomous underwater vehicle

Long-range autonomous underwater vehicles (LRAUVs) generally carry limited energy during observation missions, making it critical to enhance sailing efficiency through optimization design. Therefore, it is essential to understand the relationship between the shape parameters, motion modes, and sailing efficiency. This study proposes a LRAUV energy consumption model considering the variation in seawater density and drive loss, to obtain higher accuracy. In the optimization design, a surrogate model based on the response surface method is applied to establish the functional relationship between shape parameters, sailing parameters, and sailing efficiency. According to the optimization results, the AUV mode shows better efficiency in shallow sea, while the glider mode is more suitable for deep-sea operation. For the AUV mode, the applicable working band increases with the working time at fixed depth and/but decreases with the increase of the angle of attack at fixed depth. For the glider mode, the applicable working band increases the buoyancy compensation coefficient. The hotel load has less impact on the applicable working band for both modes. Based on the proposed method, a Petrel LRAUV with an optimized shape and sailing efficiency is developed, which can also serve as a reference for the preliminary design of other LRAUVs.

A computation effective singularity avoidance method for the underwater manipulator with a non-spherical wrist

In order to perform increasingly complex underwater tasks, we have designed a hydraulic underwater non-spherical wrist manipulator with a binocular vision system and a six-dimensional force sensor mounted behind the end-effector, which can improve the path accuracy and automation capabilities of the system. The system lays a foundation for the high precision and autonomous deep-sea operation and can improve its intelligence level. In this paper, we focus on solving the singularity avoidance problem of the hydraulic underwater manipulator for accurate control, and propose a computationally efficient singularity avoidance method to improve the path accuracy of the manipulator with the non-spherical wrist. Firstly, the singular configurations of the manipulator are analyzed. Secondly, the Jacobian is decomposed into sub-block matrices to obtain the singular factors according to the singular configurations. Thirdly, the singularities are avoided by the approximate damped reciprocal method. Theoretical analysis shows that the computation costs of the proposed method are only one-third to one-half of that of the traditional methods. The simulation results prove that the proposed method can largely improve the path accuracy of the manipulator with less computation costs, which shows that our method would have a certain significance in improving the precision and real-time response of deep-sea operations.

Tunable composite lattice structure for low-frequency and ultra-broadband underwater sound absorption.

The underwater sound absorption technique in low-frequency and broadband has far-reaching prospects since it is essential for noise reduction of deep-sea operation requirements and evading advanced underwater target detection. Here, we propose an underwater sound-absorbing composite lattice with low-frequency and ultra-broadband characteristics. The composite lattice is constructed by regular spatially stacking cells with different sizes of metallic core spheres. All the core spheres are coated with silicon rubbers, and cells are embedded in the rubber matrix. In the composite lattice stereostructure, the lattice cells convert incident longitudinal waves into transverse waves through multiple local resonance coupling and multiple scattering. The energy is localized and dissipated in the composite lattice. We analyze the relationship among the corresponding absorption spectrums, the displacement clouds, and the resonance modes of lattice cells. Then, we construct a composite lattice and realize low-frequency broadband absorption from 693 to 1106 Hz with absorptance above 0.8. Further, our investigation demonstrates that the absorption bandwidth can be extended to ultra-broadband from 1077 to 10 000 Hz, where the thickness of the composite lattice is λ/17.05. The proposed composite lattice provides a practical approach to designing ultrathin low-frequency and ultra-broadband acoustic absorption coating for underwater noise suppression.

Study on axial force characteristics of coiled tubing rotating operation in marine riser under helical post-buckling

When using offshore rotating platforms for deep-sea operation, coiled tubing (CT) is affected by both the ocean load and torque. Moreover, the variation law of axial force complexity increases when the CT is in a helical post-buckling state. Therefore, in this paper, a “pipe-in-pipe” system test bench was built to simulate the effects of ocean loads and torques on the CT. A helical post-buckling state was reached and the axial force variation law was analyzed. The results have shown that both the ocean load amplitude and the initial torque increased the axial force fluctuation of CT. The torsion direction of helical post-buckling was determined by the direction of applied torque. Additionally, given the equal injection force, the greater the torque, the greater the helical post-buckling degree of CT and the lower the axial force transmission efficiency. Obtained results supplement the theoretical system of pipe mechanics and improve the operation efficiency of offshore rotating platforms.

Surface-set Diamond Bit Design for Deep-Sea Operating Environment of Seafloor Drill and Hole-Bottom Flow Field Analysis

Drilling sampling technology is an important means for obtaining underground physical data and evaluating mineral reserves. The coring diamond bit is located in the front of the drilling equipment, which can reflect the drilling efficiency and core recovery of the bit when drilling into the coring. In order to improve the drilling efficiency and core recovery, a design scheme of diamond bit for seafloor drills is proposed, which combines the formation characteristics of the seafloor within 300 meters. Based on the fluid dynamics theory and considering the effect of bit rotation on the flow field at the hole-bottom, the effects of bit water passage structure and drilling parameters on the flow field are analyzed. The results show that the designed bit can avoid the core erosion by 80% of the drilling fluid. The rotary speed should be controlled at 250 - 330 rpm, and the pump displacement should be 50 - 60 L/min. When the drilling fluid is up-return along the hole wall, the velocity first rises and then drops, then stabilizes between 0.8 - 1.3 ㎧, which meets the range requirements for the standard cuttings up-return and the stability of the hole wall. Finally, the rationality of the bit design scheme is verified by field drilling experiments. The average core recovery percent reaches 85 %, which is about 25% higher than the conventional bit of water passage system.

Influence of ambient pressure on sealing performance of O-ring in deep-sea hydraulic system

The power source of deep-sea operation equipment is usually a hydraulic system. The normal operation of the deep-sea hydraulic system relies heavily on the sealing performance of the widely used O-ring. The high ambient pressure in deep sea conditions can cause the O-ring to shrink in volume and change in compression, which seriously affect the sealing performance of the O-ring. In this paper, the structural deformation and the change of O-ring compression, both affected by the ambient pressure, are analyzed based on the elastic theory. With the finite element method, the non-linear model of the O-ring seal is established and its sealing performance in the deep-sea condition is simulated. The influence of dimensions and material properties on sealing performance is also analyzed. The research results in this paper can provide reference and theoretical support for the design and optimization of the O-ring seal in the deep-sea hydraulic system.

Assessment of the condition of conditioned reflex activity in the process of liquid respiration

Introduction. Liquid respiration is the ability of mammalian lungs to receive oxygen dissolved in a liquid for respiration and release carbon dioxide into it. A promising field of application is the provision of marine operations. For the use of liquid respiration during deep-sea operations, the technology must ensure the normal functioning of all organs and systems of the body, prevent decompression sickness, and allow conscious activity. The study aims to assess the safety of conditioned reflex activity during independent liquid respiration in laboratory animals in normobaric conditions. Materials and methods. We performed the study on male Syrian hamsters aged four months, weighing 120-140 g. Researchers have developed a stand with an eight-level maze with a lock. We immersed the labyrinth in an aquarium. The scientists carried out the study in two stages. At the first stage, we have developed in animals a conditioned reflex of actively avoiding drowning in conditions of breathing air. The researchers placed the animal on the lower level, then immersed the maze in an aquarium filled with water at a speed that only the animal's head was above the water level. The threat of drowning prompted the animal to search for a passage to a higher level. The training was three times a day for ten days. At the second stage, scientists studied the influence of various conditions of liquid respiration on the state of the conditioned reflex activity of animals. We used two respiratory fluids - perfluorohexane (PFH) and perfluorodecalin (PFD) in three temperature regimes: 22.0, 27.0, and 32.0°C. The researchers filled the aquarium with two oxygenated respiratory fluids of the required temperature instead of water. We have entirely immersed the maze with the animal fixed at the lower level in the aquarium. After switching to liquid respiration, scientists removed the animal from fixation. From the moment of removal from fixation, the countdown of the passage of the maze began. First, we assessed the condition of conditioned reflex activity by the number of animals in the group that successfully passed the maze and the average time of its passage. Results. Animals on liquid respiration in perfluorohexane successfully passed the labyrinth in all temperature conditions. The average transit time at 22.0°C was 323±94 s; 27.0°C - 45±12 s; 32.0°C - 147±101 s. Animals on liquid respiration in perfluorodecalin successfully passed the labyrinth at a temperature of 27.0°C; the average passage time is 131±79 s; at a temperature of 32.0°C, 20% of animals successfully passed the labyrinth, the average time is 32.5 s; at a temperature of 22.0°C, none of the animals passed the maze. Conclusions. Conditioned reflex activity during independent liquid respiration in small laboratory animals in normobaric conditions persists and depends on the physico-chemical properties and temperature of the respiratory fluid.

Pipeline Pressure Loss in Deep-Sea Hydraulic Systems Considering Pressure-Dependent Viscosity Change of Hydraulic Oil

The high ambient pressure in deep-sea conditions greatly increases the viscosity of hydraulic oil and then the pipeline pressure loss in deep-sea hydraulic systems. Large pipeline pressure loss can lead to a further change of viscosity on the basis of the viscosity increase caused by the ambient pressure when the hydraulic oil flows through the pipeline. Therefore, the classic Poiseuille’s law can no longer accurately calculate the pipeline pressure loss in deep-sea conditions since it treats the viscosity as a constant. In this paper, based on laminar flow theory and the viscosity-pressure characteristics of hydraulic oil, a novel equation for pipeline pressure loss is proposed, in which the viscosity change when flowing through the pipeline is taken into account. A CFD (Computational Fluid Dynamics) model of a pipeline in the deep-sea hydraulic system has been established, and CFD simulations have been conducted to verify the correctness of the proposed equation for pipeline pressure loss. Theoretical analysis shows that the proposed novel equation for pipeline pressure loss is equivalent to the classic Poiseuille’s law when the pipeline pressure loss or the viscosity change is low. The research results in this paper can provide theoretical support for work efficiency optimization, load capacity improvement, and precise control of deep-sea operation equipment or deep-sea hydraulic systems.

Analysis of longitudinal coupling dynamic characteristics of deep sea mining vessel and stepped lifting pipe

In deep-sea mining, the coupling dynamic response between the mining vessel and the lifting pipe is a significant problem, which directly affects the structural design of the lifting system and the safety of field operation. The characteristics of coupled motion model have not been fully considered in the existing research. Therefore, this paper uses time-domain coupled numerical model as the research object, considering ocean current, surface wave, pipe dynamics and vessel-pipe contact mechanics, to study the dynamic behavior of the lifting pipe and mining vessel during the process of deep-sea mining using AQWA and OrcaFlex softwares. The response amplitude operator (RAO) is used to compare the measured and simulations dynamic response of the mining vessel. There is a very good agreement in RAO between the experiments and simulations. The coupling simulation results show that the coupling effect has a significant effect on the time domain dynamic response of the lifting pipe, but has little effect on the average effective tension and longitudinal amplitude along the pipe length. The research results of this paper are of great significance to the safety design of deep-sea mining lifting system and the planning of deep-sea operation activities.

Hierarchical NMPC–ISMC of active heave motion compensation system for TMS–ROV recovery

This study reveals the operating risk of cable breaking when the TMS–ROV recovery is carried out beneath rough ocean waves. To release the negative impact of the support vessels vertical heave motion on the station-keeping and position tracking performance of TMS, a robust hierarchical control scheme for a hydraulic-driven winch-based active heave compensation (AHC) system is proposed based on the combination of a nonlinear model predictive control (NMPC) strategy, an integral sliding mode control (ISMC) scheme and a vessel heave motion prediction algorithm. The motivation of utilizing the ISMC-based internal level combined with the integral state transformation technique is given by the robust capability to eliminate the uncertainties, which provides the nominal model for NMPC-based external level to guarantee the optimal evolution satisfying the state and input constraints and resisting the dynamical hysteresis caused by the employed extremely long cable length for deep-sea operation. Comparative simulation studies contribute to the analysis of the surge in cable tension during the TMS–ROV recovery and demonstrate the superior tracking and heave compensation performance, strong robustness and constraint satisfaction of the proposal.

A Novel Simulation Platform for Underwater Data Muling Communications Using Autonomous Underwater Vehicles

Autonomous Underwater Vehicles (AUVs) are seen as a safe and cost-effective platforms for performing a myriad of underwater missions. These vehicles are equipped with multiple sensors which, combined with their long endurance, can produce large amounts of data, especially when used for video capturing. These data need to be transferred to the surface to be processed and analyzed. When considering deep sea operations, where surfacing before the end of the mission may be unpractical, the communication is limited to low bitrate acoustic communications, which make unfeasible the timely transmission of large amounts of data unfeasible. The usage of AUVs as data mules is an alternative communications solution. Data mules can be used to establish a broadband data link by combining short-range, high bitrate communications (e.g., RF and wireless optical) with a Delay Tolerant Network approach. This paper presents an enhanced version of UDMSim, a novel simulation platform for data muling communications. UDMSim is built upon a new realistic AUV Motion and Localization (AML) simulator and Network Simulator 3 (ns-3). It can simulate the position of the data mules, including localization errors, realistic position control adjustments, the received signal, the realistic throughput adjustments, and connection losses due to the fast SNR change observed underwater. The enhanced version includes a more realistic AML simulator and the antenna radiation patterns to help evaluating the design and relative placement of underwater antennas. The results obtained using UDMSim show a good match with the experimental results achieved using an underwater testbed. UDMSim is made available to the community to support easy and faster evaluation of underwater data muling oriented communications solutions and to enable offline replication of real world experiments.

RETRACTED ARTICLE: Underwater image segmentation based on computer vision and research on recognition algorithm

Due to the continuous growth of the world’s population, the development and utilization of marine resources have received great attention. At present, marine fishing relies heavily on divers for underwater operations, which have the disadvantages of high risk, low efficiency, and high cost. Therefore, the development of underwater capture robot which can automatically detect, locate, and capture targets is of great significance for the development of marine economy. Underwater robot is an indispensable equipment for deep-sea operation and plays an irreplaceable role in the development of the ocean. When autonomous underwater vehicles perform underwater operations, they can use computer vision system to obtain clear underwater images and accurate target category information, which can help the manipulator select different grasping parts for different shapes and categories and improve work efficiency. The current underwater vision technology includes “acoustic vision” and “light vision.” Due to the influence of multichannel effect and blind area, the acoustic vision research in detecting and tracking underwater targets is not deep enough. Compared with the acoustic image processing system, the underwater optical vision system has the advantages of image and video capture and has higher real-time performance, which can aim at the target faster and more conveniently. Underwater vision optical system plays an important leading role in the detailed research of underwater vehicle sensing system, which can further improve the autonomous performance of underwater vehicle. In addition, considering the nature of underwater image imaging, we are developing an underwater image segmentation and recognition system based on image processing.

ПОВЫШЕНИЕ ПОИСКОВЫХ ВОЗМОЖНОСТЕЙ АВТОНОМНЫХ НЕОБИТАЕМЫХ ПОДВОДНЫХ АППАРАТОВ ЗА СЧЕТ ПРИМЕНЕНИЯ МНОГОКАНАЛЬНЫХ МАГНИТОМЕТРИЧЕСКИХ СИСТЕМ

The article substantiates the relevance of solving the problems of searching for unexplodedordnance, as well as archaeological and geological surveys in the waters of inland waters andcoastal zones of the Russian Federation. Using examples of mine clearance operations in the BalticSea and a detailed magnetometric survey of the Phanagoria water area, the extensive capabilitiesof modern equipment for localization of objects covered by bottom sediments and visuallyinvisible on the bottom surface are shown. The advantages of using autonomous uninhabited underwatervehicles for the method of searching for ferromagnetic objects based on the registrationof spatially distributed magnetic anomalies are considered. The directions of development of multichannelmagnetometric search tools are shown. The potential capabilities of multichannelmagnetometric systems for identifying search objects are revealed. Using the example of the existingtechnology of diving search, it is shown that the rate of exploration provided in this way isextremely low even under the most favorable conditions: the best visibility, a gentle slope of thebottom with a solid base. At the same time, the time for exploration of a section of the water areaby diving along one shore will be about 5 hours in favorable conditions, and, therefore, this methodcannot be used when examining large water areas. Taking into account the level of technologyachieved at the present stage, it is proposed to use autonomous uninhabited underwater vehicleswith a multi-channel magnetometric system installed as a target load for automating underwateroperations. In addition to automating the process of performing tasks, the use of uninhabited underwatervehicles will either completely eliminate or significantly reduce the dangerous impact onhumans of measures to search for unexploded ordnance and harmful factors of deep-sea operations,as well as reduce material and time costs by reducing operations for servicing divingequipment. Processing the survey results and creating a map of magnetic anomalies will allow youto identify structures whose geomagnetic properties are markedly different from the natural magneticbackground. Such a technique can significantly increase the information content and reliabilityof the results of the survey of water areas, providing the identification of visually invisibleobjects that have their own magnetic field. Based on the theory of the electromagnetic field andmagnetostatics, a method for calculating the parameters and efficiency of the multichannelmagnetometric system for uninhabited underwater vehicles has been developed. The method isdesigned to evaluate the parameters and capabilities for detecting ferromagnetic objects and tomake a preliminary assessment of the search efficiency. As a criterion (achieving a positive resultof evaluating the parameters and efficiency of the multi-channel magnetometric system), in accordancewith the IMAS Mine Action Standards, the following condition is accepted: detection ofan object of a certain type at a given depth. The influence of the above data on the solution of theproblem was evaluated as a result of computer simulation in the software environment of the computer-aided design system MathCAD with further visualization of the results.

Design and Performance Study for Electrothermally Deep-Sea Drive Microunits Using a Paraffin Phase Change Material.

Considering the further exploration of the ocean, the requirements for deep-sea operation equipment have increased. Many problems existing in the widely used deep-sea hydraulic system have become increasingly prominent. Compared with the traditional deep-sea hydraulic system, actuators using a paraffin phase change material (PCM) have incomparable advantages, including lightweight structure, low energy consumption, high adaptability to the deep sea, and good biocompatibility. Thus, a deep-sea drive microunit (DDM) based on paraffin PCM is proposed in this paper. The device adopts a flexible shell, adapting to the high-pressure environment of the deep-sea based on the principle of pressure compensation. The device realizes the output of displacement and force through the electrothermal drive, which can be used as actuator or power source of other underwater operation equipment. The microunit successfully completes the functional verification experiments in air, shallow water, and hydrostatic pressure of 110 MPa. In accordance with experimental results, a reasonable control curve is fitted, highlighting its potential application in deep-sea micro electro mechanical systems, especially in underwater soft robot.

Deformation and leakage mechanisms at hydraulic clearance fit in deep-sea extreme environment

Hydraulic system is widely used as a power source in deep-sea operation equipment. The sealing performance and the relative movement of the parts in hydraulic components are significantly affected by the structural deformation at the clearance fit and the viscosity increase of the hydraulic fluid medium, which are both caused by high seawater pressure. In this paper, the deformation formula at the clearance fit in the deep-sea environment is deduced, which indicates that the deformed height of the fit clearance decreases linearly in the axial direction. A minimum clearance design criterion is proposed, and it is found that the smaller the difference between the bulk modulus of the matching parts and the fit radius are, the smaller the variation of the height of the fit clearance is under various working conditions and the smaller the required minimum initial height is. The leakage flow rate formula at the clearance fit in the deep-sea environment is deduced as well, which introduces modified factors to consider the effects of structural deformation, viscosity increase, and eccentricity. The calculation result shows that under the condition of 11 000 m deep sea, the leakage flow rate calculated by the classic formula is about five times larger than that of the modified formula. Multi-parameter fluid–solid-interaction simulations are carried out to verify the correctness of the deduced deformation and leakage flow rate formulas. The leakage flow rate of the situation with inclination involved is also analyzed through numerical simulations.

Development and Mechanical Characterization of HGMS-EHS-Reinforced Hollow Glass Bead Composites.

Hollow glass microsphere-reinforced epoxy hollow spheres (HGMS–EHSs) were prepared by a “rolling ball method” using expanded polystyrene beads, HGMSs, and epoxy resin (EP). The three-phase epoxy syntactic foam (epoxy/HGMS–EHS–HGMS composite) was fabricated by combining HGMS–EHS as a lightweight filler with EP and HGMS by a “molding method”. The HGMS–EHS and epoxy curing agent systems were well mixed by scanning electron microscopy. Experiments show that higher HGMS–EHS stack volume fraction, lower HGMS–EHS layer number, higher HGMS–EHS diameter, lower HGMS–EHS density, higher HGMS volume fraction, and lower HGMS density result in a decrease in the density of the three-phase epoxy syntactic foam. However, the above factors have the opposite effect on the compressive strength of the three-phase epoxy syntactic foam. Therefore, in order to obtain the “high-strength and low-density” three-phase epoxy syntactic foam, the influence of various factors should be considered comprehensively to achieve the best balance of compressive strength and density of the three-phase epoxy syntactic foam. This can provide some advice for the preparation of buoyancy materials for deep sea operations.