Different hull movements in the ocean—heel, trim, and pitch—represent different sea state levels, and a ship's seaworthiness rating is a crucial indicator. Therefore, ship design, especially for ocean-going and marine vessels, requires scientific calculation of the hull's wave resistance rating. However, these calculations are only theoretical values ​​and must be corrected through numerous sea and wave tests. Such testing is not only time-consuming and labor-intensive but also wastes significant financial resources. To make ocean-going and marine vessel design more scientific, time-saving, labor-saving, and cost-effective, we utilized Lingdian Automation's large-scale practical PLC AnSH and economical compact FX2NPLC, FR-E540 frequency converters, and employed the CC-Link fieldbus to develop a 50m long, 30m wide, and 6m deep water tank wave generation system. This system can simulate real-time sea conditions and provides a semi-physical simulation platform for ship design. It can not only provide ship design and certification units with semi-physical real-time simulation tests and near-real-world sea state test data for ship design but also facilitate the development and research of wave power generation devices for marine development units. Such a semi-physical distributed simulation platform system was already established abroad in the 1990s, and is currently undergoing trial production in Chinese ship design units. I. System Composition and Design (I) System Composition To simulate sea conditions such as wind, waves, currents, wave path, and wave height in real time, this wave-generating system consists of the following subsystems: 1. Wave-generating subsystem: The pool is equipped with three sets of high-power and low-power wave generators with double push plates. Different combinations of large and small wave generators can generate longitudinally propagating long-peaked waves with a maximum wave height of 0.3m. Computer-controlled, it can generate regular or irregular waves required for model testing. 2. Flow generation system: The pool is equipped with a high-pressure water jet flow generation system. Water jet pipes are evenly distributed on both sides of the pool wall. Water pumps draw water from the thick pipes, pressurize it, and then spray it out from the densely distributed water jet pipes, creating a uniform water flow in the pool. This system can generate longitudinal and transverse flows, with a maximum flow velocity of 0.1m/s. In addition, a local flow generation system is configured to adapt to the needs of high-speed water flow and tests with different flow directions. 3. Aeration system: A mobile blower aeration system is configured. The maximum wind speed can reach 5m/s, and the wind spectrum can be simulated through a computer control system. 4. Trailer system: During towing tests, towing tests can be carried out in the face of waves, with waves, and across waves. Towing tests can also be carried out in the oblique waves by adjusting the x and y directions. 5. Water tank filtration system: The water tank is equipped with a mechanical filtration system. 6. Wave damping system: A grid-type wave damping beach with a certain inclination is set on the opposite bank of the wave generator to absorb wave energy and prevent the generation of reflected waves. (II) System Design To achieve the above functions, the system adopts the concept of layering and unitization to realize true distributed control. The wave generation, current generation, and wind generation subsystems are each controlled by two PLCs. The sea conditions include large waves, small waves, and rippled waves. To realistically simulate the characteristics of sea conditions, the larger waves are controlled by an AnSH PLC, while the smaller waves and rippled waves are controlled by an FX2NPLC. The current generation subsystem is similar. Only in this way can we simulate the presence of many smaller, higher waves within two large waves. The wave generation process is as follows: the PLC's analog output module outputs a 0-10V control signal to control the output frequency of the FR-E540 frequency converter. The frequency converter controls the speed of the three-phase asynchronous motor in real time. The motor drives the wave generator's propeller blades to strike the water surface. Different motor speeds result in different wave lengths and crests between the two wave heads. Thus, different speeds of the three-phase asynchronous motor correspond to different wave heads, wave lengths, and crests. Therefore, different combinations of the speeds of the two three-phase asynchronous motors can reproduce and simulate different sea conditions in real time. The flow generation system is also controlled by a combination of AnSH PLC and FX2N PLC, each controlling its own power pump to generate different water flow energies. The air generation system is controlled by an AnSH PLC to operate a high-power fan. To improve reliability, a manual backup speed control system is also designed in this control system to ensure that wave generation is not affected in the event of a computer failure. When the computer fails, the switching device automatically switches to the manual backup speed control system without manual intervention, and the operator can adjust the inverter speed using a potentiometer to maintain the normal wave generation process. The system configuration of three local control units consisting of an AnSH PLC, an FX2N PLC, an FR-E540 inverter, and a three-phase asynchronous motor, along with a PC-based server and a human-machine interface server architecture, is shown in Figure 1. The configuration diagrams of the AnSH PLC and FX2N PLC are shown in Figures 2 and 3. Figure 1 Figure 2 Figure 3 1. AnSH PLC Characteristics and Configuration The A1SJHCPU is the most economical CPU component in the AnSH series. The unique feature of the A1SJHCPU is that its CPU, power supply, and circuit board are integrated into one unit, which significantly reduces manufacturing costs. AnSH utilizes the Mitsubishi Sequential Control Processor Chip (MSP), specifically developed by Mitsubishi for sequential control and mathematical operations. AnSH is not only faster than AnS, but also adds dedicated CC-Link instructions while retaining existing instructions (including PID calculations, floating-point operations, and trigonometric functions). Its built-in features, such as a lithium battery, backup RAM, user memory, real-time clock, and a flexible communication port, allow the AnS series to adapt to a wide range of applications. The completeness of its specialized components makes AnSH perfectly suited for process control, positioning control, and various other types of control. Compared to similar products, it offers high cost-effectiveness. Specifically: A1SH42 Digital Input/Output Module: Primarily controls the opening and closing states of control relays and contactors, and works with relays to control the power supply status of motors and frequency converters. A1SJ61BT11 CC-Link Fieldbus Communication Adapter: Primarily used for communication with the CC-Link master control module in the system server, transmitting the status and parameters of various quantities monitored by the AnSH PLC in real time, and simultaneously receiving control commands from the server. A1S66ADA Analog Input/Output Module: Monitors the water pressure change trend of the pool in real time (reflecting the sea state level), providing analog control signals to the FR-E540 frequency converter, causing the converter's output frequency to change, thereby controlling the speed of the three-phase asynchronous motor, and thus controlling and simulating the wind, waves, wave height, and wave length of the sea state. A1SD62D High-Speed ​​Counter Module: Monitors the speed of the three-phase asynchronous motor in real time, allowing the A1S66ADA module to perform PID regulation of the motor speed. 2. FX2N PLC Features and Configuration The FX2N series is the most advanced series in the FX PLC family. It encompasses the widest range of standard features, faster program execution, comprehensive communication functions, suitability for different power supplies worldwide, and a large number of special function modules to meet individual needs, providing maximum flexibility and control capabilities for factory automation applications. It also boasts unparalleled speed, advanced functions, logic options, and positioning control. The FX2N offers a variety of application options from 16 to 256 inputs/outputs. Its flexible configuration, high-speed operation, outstanding register capacity, and abundant component resources make it particularly suitable for process control with a small number of points. Specifically: FX2N-64MT-D Main Control Module: Its digital input/output module controls the opening and closing states of some control relays and contactors, and works with relays to control the power supply status of motors and frequency converters. FX2N-32CCL CC-Link Fieldbus Communication Adapter: Primarily used for communication with the CC-Link main control module in the system server, transmitting the status and parameters of various quantities monitored by the FX2N-64MT in real time, and receiving control commands from the server. FX2N-4AD Analog Input Module: Monitors the water pressure change trend of the pool in real time (reflecting the sea state level); FX2N-2DA Analog Output Module: Provides analog control signals to the FR-E540 frequency converter, causing changes in the converter's output frequency to control the speed of the three-phase asynchronous motor, thereby controlling and simulating sea conditions such as wind, waves, wave height, and wave path. FX2N-1HC high-speed counting module: Real-time monitoring of the speed of the three-phase asynchronous motor, enabling the FX2N-2DA module to perform PID regulation of the motor speed. 3. The server is configured with CC-Link in master-slave mode; therefore, a master-mode CC-Link communication adapter card (A80BD-J61BT11) must be inserted into the master server in the central control room. To improve real-time control performance, a communication rate of 2.5Mb/s was selected, and the operating system is Windows NT4.0+SP4. The system's programming development environment is Visual C++ Ver6.0. SQL Server V7.0 is also installed for tasks such as human-machine interaction, CC-Link network configuration, real-time database access, historical data playback, transmission and distribution of control commands, and display of simulated 3D graphics. (III) CC-Link Fieldbus CC-Link is short for Control & Communication Link, an open fieldbus network primarily based on the device layer. It boasts large data capacity, multi-level selectable communication speeds, and is a composite, open, and highly adaptable network system capable of accommodating networks ranging from higher management layers to lower sensor layers. It enables connections from CC-Link to the AS-i bus. CC-Link offers high-speed data transmission, up to 10Mb/s. The underlying communication protocol of CC-Link follows RS-485. Generally, CC-Link primarily uses a broadcast-polling method for communication. CC-Link also supports instantaneous communication between the master station and local stations, as well as between intelligent device stations. CC-Link offers outstanding advantages such as superior performance, wide application, ease of use, and cost savings. (IV) System Reliability Design The small relays within the PLC output module have very small contacts and poor arc-breaking capability, making them unsuitable for direct use in plant-level AC220V~380V circuits. External relays must be driven by the PLC, and the contacts of these external relays must drive AC380V loads. Meanwhile, many AC 220V-380V solenoid valves have normally closed limit switch contacts connected in series with their coils. When the solenoid valve coil is energized and the valve core actuates, the circuit is broken by the internal contacts of the valve. In this case, a small relay with smaller contacts should be selected to transfer the PLC output signal. This system uses high-power thyristor devices, so the PLC should be kept away from strong interference sources. The PLC should not be installed in the same switch cabinet as high-voltage electrical appliances. Inside the cabinet, the PLC should be kept away from power lines (the distance between them should be greater than 200mm). Inductive components such as relays and contactor coils installed in the same switch cabinet as the PLC should be connected in parallel with RC arc suppression circuits. The PLC's I/O lines and high-power lines should be routed separately. If they must be routed in the same cable tray, signal lines should use shielded cables. AC lines and DC lines should use different cables. Switching and analog I/O lines should be laid separately, and the latter should use shielded cables. Different types of lines should be installed in different cable conduits or cable trays, with as much space as possible between them. In addition, since CC-Link is required to complete all data communication in this system, the communication cable must be highly reliable. Therefore, the dedicated cable recommended and provided by the CC-Link Promotion Center should be selected. II. System Characteristics and Software Design (I) System Characteristics This system can conduct various ship hardware-in-the-loop simulation experiments and marine energy development experiments: development and research of new marine engineering structures, analysis of ship component stress and model testing technology; development and research of wave power generation devices; simulation and analysis processing technology of wave states under the interaction of waves, currents, and wave-currents; simulation verification of marine environmental numerical forecasting; design, calibration, and verification of marine buoys and marine hydrological instruments; design, structural strength, and hydrodynamic performance research of various types of ships. (II) System Software Design The system simulation control software is the key core of this system design, and also the most challenging aspect. It includes two main parts: upper-level human-computer interaction visualization software and PLC control software. The human-computer interaction visualization software mainly consists of a human-computer interface program module, a digital signal processing program module, and a database program module, all programmed using Visual C++. During the control process, the main program can read and write relevant data in the database at any time using SQL query statements through DAO. After the simulation experiment, data statistics can be performed to illustrate the process. The start and end times of the statistics can be arbitrarily selected, and the computer automatically classifies and statistically analyzes all measurement data within that time period. This data can be displayed intuitively in 3D animation. Related data can be backed up, deleted, exported, and reports printed for easy human-computer interaction. On the simulation server, due to the need for extensive data analysis, image processing, and human-computer interaction, Windows NT was chosen as the operating system to handle data analysis, simulation communication, sea state simulation fitting, and simulation evaluation. The overall structure of the system software is shown in Figure 4. Figure 4 III. Application Experience In this system, hardware selection is crucial. Choosing a cost-effective and reliable hardware platform is one of the key design considerations for this simulation platform, and system reliability design is also a focus. Compared to other products, Mitsubishi PLCs have simple instructions, greatly facilitating programming and maintenance for users, reducing production costs, and significantly shortening the development cycle. The CC-Link fieldbus has a high transmission rate and good data transmission reliability, ensuring the reliable transmission of a large amount of simulation data, thus guaranteeing the system's real-time performance and reliability. Meanwhile, the application of CC-Link significantly reduces on-site wiring, improving system maintainability. The system employs a truly distributed concept, reducing the correlation between simulation platforms and facilitating system design, analysis, and application. The system offers both on-site manual control and remote computer-controlled automatic control modes, increasing its flexibility.