HIERARCHY OF VEHICLE DYNAMIC MODELS
Gyeong Joong Lee (KRISO, Korea)
Abstract: Recently, the simulator systems are widely used for many fields and for many purposes. Therefore the dynamic model was developed for many types of vehicles, from small boat to very big tanker in the field of marine vehicles, and in the other field it was developed for helicopter, airplane, truck, racing car, motorcycle, train, crane, etc.. And the degree of detail is wide from simple predefined motion to real time motion under waves. Unfortunately the above various dynamic models seem not to be classified systematically. In many simulation tasks, the various vehicles play in the same environment and in the same time, so the various dynamic models are to be calculated in the same time at one computer. Therefore, there exist the needs to analysis of dynamic properties and make the hierarchy of vehicle in the viewpoint of dynamics, and to derive common properties from various dynamic models and finally to make the class structures for vehicle dynamic models. In this paper, the dynamic properties are surveyed and classified for various vehicles whose types were marine air-based, and land-based. The dynamic hierarchy and class structure of general vehicles are presented, which are being used in KRISO in the case of special simulation task.
By the help of rapid developments of computer hardware and software, the modeling and simulation technology is growing more and more. So the simulation objects become almost all things and cases. Within the limit of dynamic systems, the target of simulation continues to grow from single system such as ship, aircraft, car to complex system and complex situation such that the number of various types of vehicles are in the same situation and the interaction between vehicles are to be considered. Therefore the dynamic model was developed for many types of vehicles, from small boat to very big tanker in the field of marine vehicles, and in the other field it was developed for helicopter, airplane, truck, racing car, motorcycle, train, crane, etc.. And the degree of detail is wide from simple predefined motion to real time motion under waves.
However, it seems that the simulation carried out by case by case, and various dynamic models seem not to be classified systematically. So the effort and time to construct simulation model seems to be inefficient and possibility of error such as omission of required dynamic terms exits.
Therefore, there exist the needs to analysis of dynamic properties and make the hierarchy of vehicle in the viewpoint of dynamics, and to derive common properties from various dynamic models and finally to make the class structures for vehicle dynamic models. In this paper, the dynamic properties are surveyed and classified for various vehicles whose types were marine, air-based, and land-based. The dynamic hierarchy and class structure of general vehicles are presented, which are being used in KRISO in the case of special simulation task.
2. DYNAMIC CLASSIFICATION OF VEHICLES
The dynamic model of vehicles may have very many variables and forces and properties. It is required to classify those into common properties and peculiar properties. In this paper, it was done by the viewpoint of dynamic properties and equipments.
2.1 Dynamic Properties
The dynamic properties of every vehicle are characterized 4 main factors as follows,
Fig. 1 Dynamic properties tree grouped by 4 main factors.
A. Operation Region;
1. Under Water - Submarine
2. Water Surface - Surface Ships
3. Ground - Automobile
4. Air - Airplane
5. Space - Space Ship, Rocket
B. Method of support the gravitation;
1. Buoyancy - the force equal to the weight of the volume that is displaced by vehicle, submarine, surface ships and air ship
2. Lift - resulting forces of lifting devices caused by relative fluid velocity, airplane, hydrofoil ship, WIG
3. Ground Support - supporting forces of ground and road, automobile, airplane, train
4. Compressed Air - pressure force of compressed air, air cushion vehicle
5. Upward Propulsion - upward thrust forces of thruster, VSTOL airplane, rocket, helicopter
6. Electromagnetic Forces - electro magnetic forces between magnet and rail, magnetic levitation vehicle
7. Non-gravitation - lack of gravity in space, space vehicle
Above supporting method can be grouped by 2 methods: static and dynamic support.
1. Propeller - to get propulsive forces by accelerating surrounding fluid backward by propeller or impeller, submarine, surface ships, airplane
2. Jet - to get propulsive forces by jetting the fluid backward, airplane, rocket
3. Wheel - to get propulsive forces by rotating wheel in touch with ground or rail, automobile, train
4. Electromagnetic Thrust - to get propulsive forces using linear motor or Lorenz force, MHD ship, MAGLEV.
5. Pitch Control of Rotating Plane - to get propulsive force by adjusting pitch angle of rotating blade, helicopter, tag-boat (VSP)
6. External - towed vehicle, glider
Above propulsion methods can be grouped into 4 types: momentum change, friction, force field, and external.
1. Rudder & Elevator - using yaw and pitching moments by rudder and elevator, submarine, surface ship, airplane
2. Steering Wheel - using the angles of steering wheel and friction forces, automobile
3. Thruster - using thrust force directed in lateral or up-down direction, surface ship, space ship
4. Thruster angle - using the direction control of thruster, rocket, POD type propeller
5. Difference of Propulsion - using the difference of forces of propulsion devices pair, twin propeller ship, caterpillar vehicle
6. Moment device - using gyroscopic effect, gyroscopic stabilized vehicle, space station
7. Rail - following the rail road, train, sub way train
Fig.2 Dynamic Property Tree and Specifications
The vehicles have many types of equipment for the purpose of mission, operation, control, and for the convenience. In this paper, the equipments related vehicle dynamics are considered.
1. Reciprocating Engine - for various types of land-based vehicle, air-based vehicles, and marine vehicles.
2. Gas/steam Turbine - for high speed marine vehicles, train.
3. Electric Motor - for automobile, submarine.
4. Electromagnetic Thruster - for MHD ship, train, magnetic levitation vehicle.
5. Jet Engine - for many air-based vehicles.
6. Rocket Engine - for rocket and space vehicle.
7. Manual Force - for bicycle, row boat.
1. Propeller - for many marine vehicles, air-based vehicles.
2. Water Jet - for high-speed marine vehicles.
3. Wheel - for almost all the types of land-based vehicles.
4. Jet - for many air-based vehicles.
5. Rocket - for rocket and space vehicles.
6. Helicopter Blade - for helicopter.
G. Maneuvering and Control
1. Rudder - for ships, airplane, and submarine.
2. Steering Wheel - for automobile.
3. Elevator - for airplane and submarine.
4. Aileron - for airplane.
5. Bow/Stern Thruster - for ships, helicopter.
6. Flap - for airplane.
7. Jet Control - for VTOL airplane.
8. Rocket Vector Control - rocket and space vehicle.
9. Blade Pitch/Cyclic Pitch - for Voith-Sneider propeller and helicopter.
10. Center of Mass Control(Trim Control) - for submarine, airplane, bicycle, and hang-glider.
11. Ballasting - for submarine.
12. Control Fin - for ships, missile.
H. Special Devices
1. Air Cushion - for air-cushion vehicle
2. Electromagnetic Levitation - for maglev.
In the above, the numbering A,B,... and 1,2,... is numbered for the convenience of classification in KRISO.
3. FORCE PROPERTIES
The dynamic vehicles undergo various types of forces; these forces can be grouped into 6 types of forces as follows.
3.1 Body Forces
・Gravitational force - the force due to the existence of gravitational field, all the vehicles are object of this force except space vehicles in non-gravitational field. This force is directed to the center of earth.
・Buoyancy force - the force equals to the weight of the volume that is displaced by vehicle, submarine, surface ships and air ship are object of this force. This force can be calculated by displaced volume or direct pressure integration on the surface.
・Field force - the force due to existence of force field such as electro static and magnetic field.
・Ground force - for the ground vehicles, the ground supports the vehicle as the reaction of the gravity. This force act at the touching part of the vehicle with the ground, such as tires of automobile.
3.2 Forces due to Own motion
・Inertial force - include acceleration, Coriolis, centrifugal forces. All the vehicles are object of this force.
・Added Inertial force - force due to the pressure field of surrounding fluid when the own vehicle accelerates the surrounding fluid.
・Drag force - in the case that the vehicle has relative speed with water or air, drag force come out, this force consists of pressure drag and friction drag.
・Lift force - the force of the foil or fin, directed right angle to the incoming fluid velocity. This is the supporting force of the airplane, and is proportional to the square of velocity.
・ Bank force - the force due to the existence of the rigid wall very near the vehicles. This force comes out when the vehicle has relative speed.
・Radiation force - for the case of existence of free surface, the vehicle's motion makes waves on the free surface, and the waves make pressure field in the fluid, this pressure field act on the surface of vehicles. Generally this force has frequency dependent properties and the memory effect properties.
3.3 Propulsion forces
・Propeller/impeller force - the propeller/ impeller accelerates the surrounding fluid backward, the forward thrust force comes out in the reaction of this action. This force will be considered in the case of propeller and water jet device.
・Jet force - the force due to the reaction of jetting the particles backward. This force will be considered in the case of jet engine and rocket engine.
・Wheel force - in the case of wheel drive vehicles, the propulsion force comes out when the wheels rotate forward. This force consists of static friction and kinetic friction between the wheels and supporting material. Almost all the ground vehicles use this force as propulsion force.
・Electromagnetic propulsion force - this force comes out from the electromagnetic phenomena, its mechanism is divided into two types, one is using Lorenz force effect, and the other is using the induced current like linear motor. MHD ship, magnetic levitation vehicle, special train, and launcher of aircraft in the aircraft carrier use this force for propulsion.
・Human force - in the special case, human being can push and pull the vehicle.
3.4 Control Forces
・Rudder/fin/elevator/aileron - force due to the lift of the fin, this force is used for the attitude control and heading control of ships, submarine, and airplane.
・Movement of center of gravity - moment due to change of gravity force center, this moment is used for the attitude control of submarine, airplane, and bicycle.
・Steering wheel - force due to static friction between wheel and supporting material, this force is used for the course control of automobile by changing the angle of wheel.
・Difference of angular velocity of wheels - heading moment due to the difference of forces of right and left wheels, this moment is used for heading control of caterpillar craft.
・Difference of rotational speed of propellers - heading moment due to the force difference of the left and right propeller, this moment is used for the heading control of ships.
・Bow/stern thruster - force due to the thruster directed sideward, this force is used for heading control of ships and helicopter (called as tail rotor).
・Control jet - force due to the change of jet direction and multi-point jet, this force is used for the attitude control of VTOL aircraft, missile, rocket, and space vehicle.
・Angle of axis of propeller - force due to the direction change of thrust line, this force is used for heading control of POD ship, and for lift control of VSTOL aircraft.
・Air cushion - force due to the compressed air in the pressure chamber, this force is used for lift and ride control of air-cushion vehicle.
3.5 External Forces
・Wind force - force due to the incoming wind, this force can be represented as drag force. All the vehicles except submarine and space vehicle are the objects of this force.
・Rain force - force due to rain, this force can be represented as momentum change of the raindrops falling on the vehicles.
・Wave force - force due to the incoming waves, this force can be represented as so-called Froude-Krylov force and diffraction force, and can be calculated by integration of incoming pressure field and diffracted pressure field on the vehicle surface.
・Current force - force due to incoming current, this force can be represented as drag force like wind force.
・Collision - force due to collision to other vehicles and ground. Normally the simulation will be stop when the collision takes place, but for the simulation of landing vehicles and for the purpose of analyzing the crash stage of the collision, this force will be considered.
・Interaction forces between other vehicles - forces due to the existence of other vehicles, this force can take place in the case when the other vehicles exit very near the own vehicle in the form of suction or repelling forces. Other case is takes place when the own vehicle is in the region of wake and wave, which is made by forgoing other vehicles.