- 1.0 A New Product Development Paradigm
- 1.1 Computational Engineering and Virtual Prototypes
- 1.2 Computational Science and Digital Surrogates
- 1.3 The Computational Engineering and Science Ecosystem
- 1.4 High-Performance Computers: The Enablers
- 1.5 Full-Featured Virtual Prototypes
- 1.6 The Advantages of Virtual Prototyping for Systems of Systems
- 1.7 Virtual Prototyping: A Successful Product Development and Scientific Research Paradigm
- 1.8 Historical Perspective
This chapter is from the book
This chapter is from the book
This chapter is from the book
1.6 The Advantages of Virtual Prototyping for Systems of Systems
The construction and analysis of virtual prototypes is a natural and powerful method for analyzing the behavior of systems of systems. A major advantage is that it forces the engineer or scientist to address all the important effects that determine the behavior of the system of systems, not just the ones that are the easiest to address. We illustrate that with the example of air vehicles.
1.6.1 Systems of Systems: Aircraft
Air vehicles are an example of systems of systems that provide natural tests of our depth of understanding of their operation. To accurately model and predict their behavior, it is necessary to successfully integrate all the crucial physics elements that determine the system performance. If the software cannot successfully do that, it is missing at least one key part of the required physics capability. In practical terms, this means that the software developer has to build and implement solution algorithms that can smoothly integrate all the important individual physics effects and operational controls (see Figure 1.8). One of the CREATE software applications, Kestrel, illustrates this (McDaniel 2016 and McDaniel 2020).
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Figure 1.8 Major aircraft systems and functions for a generic commercial airliner (VectorMine/Shutterstock)
The major physics effects include the following:
Time-dependent motion with six degrees of freedom (pitch, yaw, roll, surge, heave, and sway—6DoF)
Gravity and Newton’s laws of motion
The forces on the aircraft structure due to the flow of air across the outer surfaces
The reaction of aircraft structure to those forces
The forces due to propulsion systems (jet engines or propellers)
The forces from the air flow on the passive and active control systems
The forces on the landing gear
Kestrel was developed to smoothly integrate all these effects to be able to accurately calculate aircraft flight for subsonic and supersonic aircraft. The predicted flight path and other measures of performance compare well with measured flight data and wind tunnel tests. Kestrel is being used extensively by the U.S. Naval Aviation and Air Force communities (Shafer 2014), as well as U.S. industry (Stookesberry 2015). Kestrel includes:
A six degrees of freedom (6DoF) algorithm for computing the aircraft motion in response to the forces acting on it
A computational fluid dynamics solver for computing the air flow and resultant forces on the structure, including the passive and active control systems
A computational structural dynamics solver for computing the response of the structure to the airflow and other loads
A hierarchy of models for computing the effects of the propulsion systems, from one-dimensional empirical models to turbo-machinery models
The capability to dynamically move the active control surfaces and accurately calculate their effect on the flight path and the loads placed on them
Described in very simple terms, aircraft are solid objects moving rapidly through a fluid (air). Their forward motion is driven by a propulsion system (propeller or jet). As the aircraft moves, it pushes air out of the way. The air flowing around the aircraft (particularly the wings) produces forces (lift and drag) on its structure that enable it to overcome gravity and fly (lift). Displacing the air and friction with the airplane exterior skin takes energy that generates resistance to the forward motion of the aircraft (drag). An aircraft moves through time and space with six degrees of freedom, based on the forces from the airflow, the propulsion system, the passive and active control surfaces, and gravity. The airflow can exhibit turbulence, depending on local conditions. The software must be capable of computing this complex motion.
As evident from Figure 1.8, aircraft are highly complex systems. The major external components are the fuselage, wings, engines, control surfaces, and landing gear (not shown). Interior struts, ribs, and so on embedded in the fuselage, wings, static control surfaces (vertical and horizontal stabilizers), and the landing gear provide most of the aircraft’s structural strength.
Much of the complexity of an aircraft system is due to the need for flight control. This representation of commercial aircraft has 12 active control systems (6 on the right and 6 on the left) and 7 passive control systems. A real commercial airliner likely has more. Flight control is essential. The Wright brothers were among the first to appreciate this and the first humans to successfully achieve powered, controlled flight. This insight made it possible for humans to be able to fly.
Below their exterior surface, modern aircraft are highly complex as well. In addition to structural supports for the aircraft exterior, there are fuel tanks, propeller and jet engines, fuel lines, avionics, the flight cabin, the cockpit, cargo spaces, hydraulic systems, steel cables, power lines, electronic cables, sanitary systems and plumbing, exterior and interior sensors, communication systems, radar systems, weather systems, flight recorders, navigation systems, ventilation, emergency oxygen, cabin pressure systems, cabin doors and windows, life rafts, life preservers, and myriad other systems. The aircraft doesn’t need all these systems to fly, but they are all essential for the aircraft to meet all its operational goals for a pleasant safe flight. The only safer way to travel today is in elevators.