Today's flight simulation system is the most complex software systems now - Flight simulation system has a strong distribution, there are strict time requirements, but also must be able to be updated frequently in order to maintain verisimilitude and simulated aircraft and ever-changing environment. At the time of the design of the following aspects of these large-scale software systems to create and maintain presented a huge challenge to software development:
• strict real-time performance.
• Modifiability to adapt to changes in demand and the simulated aircraft and its environment.
• function expandability, this is - kind of modifiability. Scalability is an extension of these systems to enable them to simulate more real environment, and to further enhance simulation fidelity.
But, as the title of this chapter, as expressed, our primary concern is integration based sauce - Chapter 4 of this system did not elaborate quality attributes, but in large systems (especially those from the sub-group and defeat single organization developed system), integration can usually as - a driver appears. Integration may refer to the individual application development elements work together to achieve the requirements of the software. Li and other quality properties - like, can be achieved by employing a framework of integrated tactical (- integration of these objects can also be modified property). These tactics include the smaller interfaces, simple, stable: abide by the agreement have been defined: the loose coupling or minimal dependencies between elements: using the Component framework: using the existing version of the interface (which may allow existing elements in the original work at the same time constraints to be extended).
This chapter discusses some of the challenging questions about flight simulation, and introduces a new model framework to address these issues. This mode is called the structural model, it is highlighted as these aspects:
• The simplicity of the substructure and similarity system
• Communicating strategy and operations data and control information separated
• minimum number of module types
• Less system-level coordination strategy
• Design of transparency
As we shall see, under the guidance of these principles, the resulting architecture model can not only have a higher integration, but also to meet other quality attributes flight simulation software must have. The model is composed of a plurality of simple patterns.
8.1 relations with the business cycle framework
To study this chapter is part of the framework of the desired quality in the most severe phase associated framework of the business cycle. Figure 8.1 shows the architecture of the business cycle based flight simulation system of structural models. The customer is the US Air Force flight simulation systems, end-users is simulated airplane pilots and other crew members. Flight simulation systems for <the pilot fly the aircraft, the crew manipulate a variety of airborne weapons systems, the training for a task control of the airplane and so on. Some flight simulation systems are more inclined to use a separate, but more and more of these systems need to accomplish collaborative tasks while training more crew.
Flight simulation system is responsible for signing by the successful business development. Large-scale flight simulation systems (- • some system of up to 150 million lines of source code), long life (the life of the aircraft being simulated usually 40 years or more) but also in real time, fidelity, etc. have. demanding (the simulated aircraft simulation system must be identical to the aircraft under various real situation, such as normal flight i, and mission-critical equipment failure).
Structural model design began in 1987. At that time US Air Force is investigating the application of object-oriented design techniques. Electronic flight simulation system as early as the 1960s it had appeared. Investigation of new design technologies by
Related problems caused by the existing design. Both structural problems at the time of the flight simulation system (along with the size and complexity of the system increases, the complexity of the development phase of integration increases exponentially), there are fatal problems (some modification of the cost of access than the total development of the original system cost).
As we shall see, the structure of the model pattern can overcome these problems. In the wide variety of systems with concurrency B-2 weapons training systems, C-17 training systems and cross-ground special forces training system in the series we have used the structural model.
8.2 Demand and Quality
Flight training simulation system has three effect. The first role is to train pilots and crew. Trained personnel in the cabin of a movable, surrounded by a variety of instruments and switches to ensure the same with the real aircraft cockpit environment settings, trainees can see the external view and in real time the flight is completely similar . We do not do too much introduction to the display generator movement and external views of the simulation chamber. They are implemented by a dedicated processor, software architecture are not talking about our play areas. The purpose of the flight simulation system is to teach the pilot and crew Ge learn how to manipulate some kind of aircraft, how to complete tasks such as aerial refueling and the like as well as what to do when a reaction under attack and so on. I really simulated retreat is an important factor in the success of such training. For example, by the analog system must be able to experience the feeling of control of the embodiment do a specific operation. Otherwise, the pilot and crew can not receive the right training, and the effects of training may be counterproductive.
Horizontal flight system proposed second function is a simulation of the environment. - camel, though the environment may include other trainees in a multi-machine training, but the environment is usually a computer model. This environment includes air, threats, weapons and other aircraft. For example, if the purpose of the training is to practice aerial refueling, (simulated) tanker turbulence on playing in this air environment.
The third role is to simulate flight simulation systems for coaches. Each training usually have a very clear purpose. And there will be a variety of situations in the training process. In training, the coach is responsible for the pilot and crew performance monitoring. And is responsible for starting a variety of training environments. Sometimes issued written material in advance about the training environment, sometimes it is set up in such an environment by the coach during training. The typical case of faulty equipment (such as when landing gear is not | correct open), attacks on enemy aircraft, til the storm caused by atmospheric turbulence like environment. Coaches have an independent | console can be used to monitor the operation of the trainees, set up and control aircraft fault training environment. Figure 8.2 shows the modern flight simulation device sets representative.
8.2.1 Use of models
Our children almost able to put the aircraft model and simulation environment used to Cao Yuzhen any degree. As one example of the range of realistic consideration - modeling the influence of air pressure in the aircraft. A simple model is that the air pressure affects only the height of the aircraft affected. A slightly more complex model is highly affected by the air pressure and the local atmospheric models. To model the need for more computing power on the local weather patterns, but allow for consideration of the updraft and downdraft strong. Consider a more complex model to other computing needs is air pressure by height, affecting local weather patterns and nearby aircraft activities. When a plane through the airspace of the simulated aircraft will generate turbulence.
The results of the simulation environment to the airplane or the ability of high fidelity, in the past training simulation system is subject to the overall limit juice computational power (likely always will be this way). Because the crew simulator training is an important part of the whole flight training, so for slightly higher fidelity whether to increase the effectiveness of training and thereby raise lettuce skills trainees, • straight controversial • So, for flight simulation system, the performance is a very important quality attribute requirements.
8.2.2 operating status
Operational flight simulation systems involving multiple states, including:
•Operating status. Operating state corresponding to an analog system as a training tool in normal operating state.
• configuration status. Configuration corresponds to the state must be carried out on the current training situation changes. For example, suppose the crew undergoing a stand-alone training, and coaches want to change air refueling training. So, it is necessary to enter the configuration state of the analog system.
• Stop state. It refers to stop the current simulation.
• playback mode. Playback mode is intended to play a particular flight change without crew intervention situation. Playback function combined with other functions, can be used to demonstrate the operation they have done to the crew participating in the training. During training, the machine may be busy sister who operate the aircraft, no more consider their approach is appropriate. Chapter 5 has been recording / playback is determined as the tactical framework for testing. Here we also found that the process used to train in.
Simulation system discussed in this chapter has four major features:
(1) real-time performance requirements. To ensure realism, for flight simulation system must maintain a very high frame rate. For a frame rate of people do not understand, we can use the movie - under analogy. Each frame is a snapshot captured. When the order within a certain time interval sufficient number of photographed frames, a user can see or feel the continuous operation. Different 30HZ or detection requires a frame rate of 1/30 second or 1/60 60HZ- with different frame rates, a common simulation program. Within each frame rate, all running calculations must be completed.
Flight simulation system speed portions of the base are an integer factor frequencies coincide. If the fundamental frequency is 60HZ, slower part can run at 30HZ, 20HZ, 15HZ, 12HZ frequency, etc., can not be (e.g., 25HZ) operates at a frequency of a frequency non-integer factor, which made - one of the reasons of limitation a flight simulation system sensing input provided by trainees must be strictly coordinated. If you use the simulator pilot can not see a different picture in turn do the operation when turning or there is no such feeling (even in a very short period of time, such as within 1/10 of a second), the system is not in line with required. Even for those who are short duration, imperceptible to the people of a small delay, if not consider coordination will also be some problems. This delay could lead to a so-called analog tired of disease - due to the psychological reaction of one sensory input resulting from poor coordination.
(2) continuous development and modification. The use of flight simulation systems for training in actual aircraft costly or dangerous, the training environment provides the equivalent of a flight simulator. In order for trainees to have real-life experience of similar experience. Analog systems must be provided by the environment and the actual aircraft environment exactly Jiong - but whether civilian aircraft or military aircraft, they are modified, updated. So, for flight simulation system software also playing constantly revised and updated to ensure the fidelity of the simulation system. Moreover, the use of simulation systems for the training is also expanding. To be able to include new issues (failure) associated with the simulated aircraft and new environmental conditions, such as the use of military helicopters in the city.
(3) large-scale, high complexity of flight simulation software like to use tens of thousands of lines of code to achieve the simulation of the easiest training environment, to achieve complex, more than training environment at the same time, you have to spend millions of lines code. Moreover, the complexity of its 30-year history of flight in contrast, flight simulation system has demonstrated exponential growth trend.
(4) development in geographically dispersed locations. Military flight simulation system shares are distributed the way of development. There are two main reasons, one is technical, one is political. Technically ceremony, this simulation system
Different development needs of different portions of expertise, so some parts of the contracted providers to turn-by-case system developed by other professional organizations are more common. From a political point of view, the development of high-tech systems such as flight simulation of various political forces over the object, each faction wants to charge • parts. No matter from which side, since the integration lengthened, flight simulation system of communication links - because the code is already long and complex and not easy to achieve - the realization of the difficulty is greater.
In addition, two issues that exist in flight simulation systems led to the US Air Force began to study a new simulation system design.
(1) high debug, test, and modify the price. The complexity of flight simulation system is extremely high, strict real-time requirements and the need for frequent modifications to make the system test, integration and modification costs exceed the costs with concurrency. Therefore, the complexity (and associated costs) of the US Air Force starts its increasing emphasis on architecture and can be integrated modifiability.
(2) the correspondence between software architecture and aircraft structure is not clear. The development of the traditional flight simulation systems are efficient enough to run as the primary quality objective "Given the performance requirements of such systems, as well as seeking verisimilitude playing the first flight simulation system is (by today's standards) and memory complete with concurrency of various factors on the processing capacity is extremely limited platform, this situation is not surprising that the traditional design approach is based flight simulation systems control loop mentioned later based. these in turn activate the control loop this cycle of tasks triggered. For example, suppose a left turn to do the pilot operation. If it is on the actual aircraft, pilot rudder and aileron, which will change the control surface and the control surface affects the aerodynamic characteristics achieved turning the aircraft in flight simulation systems, a model reflecting a control means for controlling the relationship between the surface, and aerodynamic characteristics of aircraft flight direction. in the framework of the original flight simulation system used, this model is known as a "turn" module. for level flight, takeoff and landing, also can have Like module. This basic strategy is to establish decomposition made to inspect the operation of the pilot and crew. The component model of the actual implementation of these tasks, so that all operations are completed as far as possible the idea on the basis of local of.
With this strategy can be implemented in the task model of one (or a few) assembly, thereby minimizing the data communications to implement these operations required, it is possible to provide the maximum performance supplier. This architecture represents a problem playing the same physical members in a plurality of models. That the same physical component is present in the plurality of modules analog systems. And extensive interaction between these modules in turn cause problems and can be modified in terms of integration. If the control steering module module and control horizontal flight integrated together, but found to provide to the steering module of the data in question. The same data may also be used by the horizontal flight module. Therefore, integration and maintenance of the embroidery playing consider many coupling factor.
The remainder of this chapter discusses the frame mode (referred to as structural modeling) to re-analyze the problem Flight simulation system of Che obtained. Briefly, the model including an object oriented design. The controller sub-module to the aircraft subsystems and modeling. It real-time scheduling and the object-oriented design closely together. As a means of controlling the analog subsystem execution order, so that it is possible to ensure fidelity.
8.3 Architecture Solutions
Court gives 8.3 reference model flight simulation systems. The figure shows a front three already determined characters (aircraft, environmental and coaches), shows the interaction with the crew and various presentation system. Under normal circumstances. Coaches are not sitting in the same cabin crew trained in. Environment model may be set in another apparatus, the apparatus might also be used in the trainer.
Xing coach station and logically divided in two parts of him is obvious. Support coaches coach station control and monitoring operations crew. Other simulation is performed in two parts. Divided between the aircraft and the environment are not so obvious. For example, consider the case of an aircraft bomb. Before the bomb was cast out, should be part of the aircraft, the bomb was cast on the part of the environment has become. But. On the aerodynamic characteristics of the bomb and the bomb is very similar to the characteristics of the aircraft at the time ,, so just cast, modeling aerodynamic characteristics at least in the recently cast, is closely linked with the aircraft model. If the bomb is always seen as a part of the environment, the modeling of the bomb on the aircraft are required to be closely coordinated with the environment. If the bomb before the bomb considered Machine see - part, a cast H is considered part of the environment, control of the bomb from the Scheduling involves mode to the other - the conversion of the Scheduling mode.
8.3.1 The time of flight simulation system
Chapter 5 once said resource management is a tactic to achieve performance goals. In the real-time simulation system, the most important resource is the need to manage time. Flight simulation system should reflect the true status of anger, it is done by creating a time-based simulation of real-world behavior of the real situation. So, when sitting in the cabin of the pilot simulation meow press the button fly, flight simulation system must be made as to the appropriate anti-in real time like a real aircraft. The term "real time" means that this time neither too long nor too short. Reaction too fast or too slow to simulate the effect will be taken not to bring influence.
In the flight simulation system, there are two fundamentally different time management methods, which are based on the period and type of event. Both of these methods have been adopted. Periodic time management used in some (aircraft) must maintain real-time performance, time-based event management with real-time performance is not very critical areas (such as the coach station).
1. periodic time management
Time management has a periodic time-based quantum fixed frame rate (simulated), which is the basic system process scheduling. It is generally used - non-preemptive scheduling policy cycle. The scheduler performing a cycle of steps is repeated:
• When asked to set the initial simulation.
• Repeat the following two steps, until the end of the session
• fixed (real) time calling various quantum processes. Each process calls are calculated based on the current simulation time its own internal state and the next state report their internal simulation time soon. Each process calls are guaranteed to end their operations in real-time quantum.
• the current simulation time added to the time quantum.
So long as each sub-process can in the time allotted within the quasi-state of their own good grid and submitted to the next cycle. Based on the simulation cycle time management will be able to keep up simulation time and real time.
Usually this task by foot-tune the process of grain to achieve. To ensure each process task Qu small enough to be completed within the allocated time grant child. Designers need to play to provide the number of processors required. To ensure a high enough computing power to ensure that all processes can be counted grate competencies required "
2. The event-based time management
Based scheduling strategy similar to interrupt many operating systems Che using time-based events management strategies. In this manner, the loop of steps implemented by repeatedly performing the following schedule:
• Add simulated events to the event queue.
• If there are events in the event queue:
• sampling event simulation event queue minimum time (ie execution fastest).
• The current simulation time is set to the time of the selected event.
• Call a process for the selected event. The process can add events to the event queue
Here, the simulation time will be called with the process of the event into the event queue and promote, select the Scheduler - an event to be processed. In purely event-based simulation, the simulated time may progress faster than real time (in the war game simulation) or slower (in engineering simulation).
3. Mixing time system
Now we talk about scheduling three parts of the flight simulation system, usually the coach station to schedule time on the basis of - those events from the interaction of coaches - model aircraft scheduling enough to be on a periodic basis. of. Environment model can be scheduled using either way. Thus, the coupling between the aircraft and the environment may involve matching between different time management.
The proposed system must take flight cross cycle time simulation (such as in an aircraft model) and based on analog (as in certain environmental model) as well as other events - some event-based activities (such as interaction with the coach station or unpredictable The pilot set a switch) together. In this combination in. It can take many scheduling policy.
Periodic scheduling processor Cao, a management event simplest approach is in sync immediately after the periodic process. And completed before any non-periodic process begins. Aperiodic limited period of time to complete the process as much as possible to retrieve and process messages that period. Message is not processed in a given time must be deferred to a later period, and requires the same - the source of all messages are processed in the order received.
As described above, based on the events of each intermediate portion of each communication system performance management system and a portion of non-scheduling management cycle period.
After understanding the mechanisms of management time flight simulation system, let's talk about the complexity of dealing with this architecture model that is used aircraft. Therefore, the discussion of time management is carried out from the perspective of the aircraft.
8J.2 structural model framework model
As the structural model as defined in section 2.3 is the frame mode. It enough that structured collaborative model includes a set of configuration elements and the elements at run time. This section will be given of the structure of the model pattern, and discuss the reason for this pattern. It should be noted that the structure of the model aircraft itself might play run with multiple processors. Therefore, various portions of the structure model aircraft must Hydrocotyle coordinated, but also (may be run on small devices with buried at) the simulated environment model and coach stations communicating portion.
■ structural model framework can be divided into two parts in the style coarse-grained level, that is part of the management and application part.
• Management Coordinator part of the problem: real-time scheduling subsystem, synchronization, management of the event from the stage coach, data sharing, data integrity between processors.
• Apply arithmetic processing portion of the flight simulation system: the aircraft model. Application of a functional part of the various subsystems and components is accomplished.
On the part of our management of First detailed flight simulator, and then discuss its application modules section.
Model management section 8.1.3 flight simulator module
8.4 Ge shows the structure of a fine foreign model aircraft management portion of the assembly constituted. The module management section synchronizer time, cycle timing, a member Shi processor, an analog system agent, and other parts.
4. Agent
On behalf of the buried negative capital to complete the system-level communication between the aircraft model and the environment model or coach station model, it is the kind of application, "Using arbiter" tactics. Acting understand the physical details of the system communicate, problems of communication protocols like your address issues such as negative, said.
E.g. coach station monitors the state data from the aircraft model. And display data related to the Coach. Agent collect the required data in obtaining control of the processor. Coaches and sends the data to the station. Another aspect • Coaches may want to Qiu crew set 1: specific training status. Agency responsible for receiving such an event, and send it to stab cattle processors to distribute to the relevant subsystem.
I make way Agent r mean cycle scheduler and event handlers "] • specific details are not to test Cong coach station platform or operating environment of the silver chess all related to the specific details of the system are embedded in the proxy. modifications to these platforms just play the notification system in aircraft mode rejection agent on it, no further dissemination of such information.
8J.4 flight simulator model application modules
8.5 Ge shows the structure of the application portion of the mold Han row t only two module types • • Most i.e. subsystem controller
And components. Data can be transferred between the various mutually r a system controller, but only pass data to the Ran subassembly. Assembly can only pass number noted cyanosis its parent member, the data can not be transferred to any other components. The reception component can be controlled to the parent element, only the feedback control information to the parent component. These limitations make "the transfer of data and control information to avoid or control components noted in the number of siblings of a case where information delivery times. The basic idea is to these limitations by eliminating the components between the parent-child relationship instances other than All coupling situation, to simplify integration and maintenance. maintenance or influence brought about by a higher integrated subsystem controllers to mediate. this is. an example of a "restriction of communication" tactical use "
8.4 Summary
In this chapter, we describe the architecture of flight simulation systems, in the design of the system to achieve the performance, integration and modification of the project to achieve the most severe of these quality at cost-quiet conditions. For example, the number of on-site installation team previously only required half, because they can more easily find and correct errors. Achieved by the design of these quality attributes: limit the number of configuration module type structured model framework mode, limiting the type of communication between the modules, changing the split functionality of the aircraft expected.
These improvements are mainly due to the analog system to better understand and thus keep after careful analysis, well-documented software architecture. Chastek and Brownsword the results of using this architecture model • obtained were introduced [Chas Shu ek 96, 28]:
Before the data driving simulation system of the same type of aircraft (B-52), a factory acceptance test is determined in the test described 2000-3000 (i.e., test question). With the development of structural modeling method, only 600 - 700 test described developers found that this method is easier to correct the problem, many of these problems ...... developers due to the incorrect understanding of the document can be caused by general reported the problem kept offline without having to visit the website ......
Compared with the previous data driving simulation system, the structured modeling, project development defect rate is reduced by half.
: At the beginning of this chapter, we identified three structural modeling photo quality objectives: performance, integration and modifiability.
: Here, we summarize in this mode • how to achieve these goals. Table 8.1 summarizes the information
8.4.1 Performance
Real-time performance is a key quality objectives modeling structure. The main objective through the implementation of management procedures and the use of periodic scheduling strategy to achieve. Each subsystem manages the calling program she has no running time limit. Further, also identified hardware scale simulation system, to ensure that the subsystem can tolerate time requirements. Sometimes this need with a single processor to achieve, and sometimes they play with multi-processors. Considering the scheduling strategy, real-time performance is achieved by requiring control cycle time allocated to the sub-system is less than a cycle of operation of the simulation system. So, combine real-time performance is guaranteed by giving architectural pattern (configuration management module) and a functional decomposition (how to call instance).
8.4.2 integratable
In the structural model, the data connection and control connections between the two subsystems are we intentionally minimized. First, in the subsystem, between siblings can neither directly transmitted control information can not be directly transferred data. Any data or control information transfer times are done by the subsystem controller. Therefore, playing the additional components into a subsystem must ensure that the data in the controller subsystem which is internally consistent, but also to ensure that the data transmitted between the controller and the subsystem components are correct. This process is much simpler new components communicate directly with other components, because the integration process to be involved in all of these components than others. In other words, the scale of integration problems are no longer exponentially with the number of components, but reduced to a linear relationship.
When two integrated subsystems, components, subsystems do not interact directly, so the problem and simplifies, playing only guarantee the data transfer between the two systems consistent with it. Add a new subsystem could affect several other subsystems, but much less than the number of components of subsystems, so the complexity of the issue will not be too high.
Therefore, in the configuration of the model, by intentionally limiting the number of possible connections. Integration problem may be simplified. The cost of this limitation is often a subsystem controller pure individual components common data channel, which will increase the complexity and performance Jian pin. But in practice, this approach benefits far beyond their cost. These benefits include the creation
To conduct an incremental development and more easily integrated framework system. In the project using a structured model of concurrency and work integration phase are relatively easy, no major difficulties.
8.4.3 Modifiability
When the design and maintenance personnel just a few basic components arranged appreciated, due to the function and localization of changed so that only involves a small number of children controller subsystems or components. Modifiability get simplified. FIG n2 is connected using a reduced number of the premise.
And for the subsystem based on the actual physical components, the physical structure of the component corresponding to the decomposition, also corresponds to modify the physical structure. Subsystems (e.g., the equation of motion) than the physical member is unlikely to modify. Used structural modeling of development organizations say rarely encountered any side effects in the modification.
8.5 may further refer to the literature
About this relates to the past, flight simulation system developed computational problems and engineering problems, see [Fogarty 67], the [Marsman 85] and [Perry 66
Structured Modeling from 1987 developed "• Some older literature on this mode see [Lee 88], [Rissman 90] and [Abowd93b]. The result of this view using the harmonic mode See [Chastek96].
Details of flight simulation systems used in functional decomposition of the interested reader may refer to [ASCYW94].
8.6 Discussion Questions
The close relationship between the structure and the structure of simulation software (1) to be simulated system is to make the structural model for the simulation model system modification, expansion or contraction showed a major reason for great flexibility. Applications no longer assume that is an analog system, a structured model model is still appropriate? Please explain why. Under what circumstances is feasible, not feasible under what conditions it Qian?
(2) to limit the flow of data and control subsystem controller and components are very demanding, as component designers and implementors. Do you prefer to limit such restrictions still think too dead?
Use (3) skeleton system designers to create what kind of restrictions? Please describe its harmful and benefits respectively.