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1.INTRODUCTIONIn the totality of ship simulation, simulation of the main power system unit is a very important part. However, there are many inevitable difficulties using computer simulation technology in the study of ship’s main power system. With the knowledge of Marine power system equipment, we can use the method of computer simulation, through some software test simulation. In addition, most of the research and development of ship driving simulators at home and abroad are based on the secondary development of hardware systems1, which has high development cost. This topic will be developed based on the Unity3D software platform, which can reduce the development cost to a certain extent. The main research contents are as follows: 2.ESTABLISHMENT OF MATHEMATICAL MODEL OF SHIP POWER SYSTEM2.1.Quasi-steady state model of marine power plant system2.1.1.Building the compressor model.The temperature of the press can be calculated by the following equation2: Outlet temperature: Pressure at outlet: The rotation of the compressor needs to be driven by the shaft of the turbocharger, which requires the following torque: 2.1.2.Establishing the intercooler model.The outlet pressure of the compressor is represented by pc; The pressure at the outlet end of the intercooler is represented by pi; Tci is the outlet temperature of the intercooler; Kcp is the actual diesel data. Outlet temperature of intercooler: Pressure of intake pipe: 2.1.3.Building the Cylinder Process Model.Suction flow Gi1 plus scavenging flow Gi2 is the flow through the intake valve Gi, therefore: Suction flow: In the quasi-steady state model, the average value of the flow section is This paper adopts the set scavenging coefficient. The calculation method is shown in the equation below: The values of Φs can be derived by fitting with actual test data. 2.1.4.Diesel Engine Ontology Modeling.As for the effective output torque Qe of diesel engine, the calculation method of effective torque is as follows: Excess air coefficient: Gi1 represents the suction flow of the diesel engine: Gf represents the mass flow rate into the cylinder: 2.1.5.Exhaust temperature of the cylinder.In general, the value n of diesel engine speed and the total air-fuel ratio AFR are closely related to the exhaust temperature Te: 2.1.6.Establish injection pump model.There is also a certain relationship between the fuel supply per cycle and the oil pump camshaft speed (diesel engine speed). Thus, the linear relationship between the circulating oil supply and rack displacement is obtained as follows 2.2.Paddle model2.2.1.Mathematical model of propeller.When the propeller is rotating, the thrust and water resistance moment can be calculated as follows: In practice, propellers are usually mounted at the rear of the hull, which causes a thrust reduction effect: 2.2.2.Creating a hull model.In the process of sailing, the ship will be affected by resistance, which can be divided into vortex resistance and wave resistance. The following formula can be used to calculate ship resistance: The following formula can also be used to calculate ship resistance: Ship speed vs in dynamic simulation is calculated as follows: In this expression, kw means water retention coefficient; m means the overall mass of the ship. 3.POWER SYSTEM PROGRAMMINGIn this design, the clock variables, ship speed, sailing speed and other variables should be adjusted. By changing the clock, the speed of the ship changes. The results are shown in Figure 1. 4.THE CONSTRUCTION OF VIRTUAL SCENE4.1.Construction of solid modelBasic shape modeling, lofting modeling, modifier modeling, polygon modeling and graphics modeling were used to establish the basic model. Then import the FBX file exported from 3D MAX into Unity3D. Because too many models increase the CPU performance burden, it is necessary to minimize the number of models in the scenario and merge multiple models to form a new overall model to reduce the burden3, 4. 4.2.Construction of virtual ocean sceneIn this paper, radioactive LOD grids are used to achieve sea level grid modeling. A level 5 LOD are used and the outermost layer was loaded with a circular Mesh to fill the outermost scene. All Mesh are generated under the Object named Ocean5. The partially generated Mesh list is shown in Figure 2. The hull is always within a 5*5 mesh area. The LOD level is LOD_0. Draw the finest details and effects. The rest takes a lower level LOD. To achieve virtual ocean dynamic effects:
The generated virtual ocean scene and the previously constructed entity model are put into the same scene, and finally the completed virtual scene as shown in Figure 3 is obtained. 5.DESIGN OF SIMULATION SYSTEM5.1.Interactive interface designThe built-in GUI system of Unity3D is chosen for this topic. The built-in GUI system is used based on Unity3D to create an interactive interface in line with user operation habits6, 7, which is shown in Figure 4. 5.2.Ship monitoring and alarm systemIn terms of monitoring system, several instruments are set up to monitor the running state of the ship in real time to realize the basic monitoring of ship operation. In this project, five different instruments are set up to monitor the ship in real time, including SPEED, RPM, RATE OF TURN, RUDDER, DEPTH. The interface after running is shown in Figure 5. In terms of alarm system, this paper takes the simulation training system of ship engine room in Marine Engineering Laboratory of Jiangsu University of Science and Technology as the entity reference model. A set of alarm system is constructed to reflect the ship’s bad operation state through alarm lights. The interface after completion is shown in Figure 5. 6.CONCLUSIONThis topic is a more complete design of the Marine diesel engine power plant system mathematical model, in Visual Studio 2017 using C# language to write these mathematical models, integration, and finally complete a power system program. According to the change of rack position, calculate the ship sailing speed, diesel engine speed and other data. Compared with the data of the real ship of 7000 tons, the simulation results are valid within the allowable error range. The simulation system can fully realize the basic navigation and control of the ship. REFERENCESZhao, Q.,
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