Raccolta casi Working Model, visualNastran & SimWise - Simulatore di volo e puntamento Carco


Contatto Editoriale:
Paolo Lista, Lista Studio srl®
Borgo Belvigo 33, 36016 Thiene Vi ITALY
tel/fax 0445,382056 o


New trends in engineering design practice are often driven by the changing needs of customers and the industry servicing that customer base.
In the aerospace and defense industries, the push for test equipment with higher performance and greater accuracy is motivating significant improvements in design methods.

The engineers at Carco Electronics, a Menlo Park, California company specializing in design and manufacture of flight motion simulators, have found that motion simulation software helps them bridge the gap created by the shortcomings of traditional 3D CAD tools. Moreover, they are able to optimize the design at reduced cost and reduce errors in manufactured parts.

Carco Electronics is a company that has been designing and manufacturing motion simulators used in the aerospace and defense markets for over 40 years. Carco Electronics is the world's major producer of missile flight motion simulators and inertial guidance test systems. They also produce target motion simulators, microwave boresight and boresight-error measuring systems. Four decades ago their design process was aided by producing plywood models. Today they employ visualNastran Desktop (formerly Working Model), a sophisticated motion simulation package made by MSC.Working Knowledge. visualNastran Desktop fully integrates with Carco's native CAD system, and lets designers view in motion almost touchable, life-like models that simulate product characteristics in a digital environment.

One of their more demanding current jobs is the design and manufacture of a 5-axis flight motion simulator that has been ordered by the Munitions Directorate of the Air Force Research Laboratory at Eglin Air Force Base (picture above in reality and under here in visualNastran simulation). This simulator will be used for the development and evaluation of smart weapon concepts within the Kinetic Kill Vehicle Hardware-In-The-Loop Simulation (KHILS) facility.

The primary limitation of 3D CAD software is the difficulty in determining if moving parts of the flight motion simulator will collide throughout their range of motion. Several parts move independently in close proximity under external computer control. Moving the model parts in a traditional CAD program does not guarantee that these parts stay clear of one another, as in the 3-axis machine in the following pictures.

Bringing the CAD model into visualNastran enables much more detailed motion analysis. Moving parts (slightly oversized to provide for safety envelope) of the simulator are set into sinusoidal motion. Random motion is required; therefore, each moving part is given a different period of motion. If a collision occurs, a sharp spike is observed on one of the force meters. By observing the parts position at collision, the engineers modify their design to avoid future collisions.

Carco fully integrated visualNastran Desktop software made by MSC.Working Knowledge with their native CAD software to analyze kinematics and rigid body dynamics of the 5-axis simulator. visualNastran Desktop offers integration with virtually all major CAD systems. This unique application merges the technologies from the Motion and FEA products into a single Functional Modeling system. Users can perform integrated motion and FEA simulations on their assemblies in one environment.

Designers can take into account the dynamic nature of the problem and simulate the entire assembly, rather than a part or a small subassembly, resulting in more accurate FEA results. FEA linear stress and strain simulations can be performed automatically at every step or individually, using the proven MSC.Nastran FEA solver technology. VisualNastran forms an integral part of the design process by successfully deploying simulation throughout the organization.

visualNastran also vastly improved the evaluation of gyroscopic torque coupling between the orthogonal axes on Carco Electronic's simulator. The missile under test can rotate around horizontal and vertical axes as the missile spins around its longitudinal axis.

"When a rigid body rotating along its longitudinal axis is rotated in the horizontal plane, the gyroscopic moment is developed in the vertical plane (up or down)," clarifies Dr. Mark Avory, Vice President of Engineering at Carco Electronics. "This could result in an undesirable anomaly in the test system if the actuators and controller are not designed to resist the gyroscopic moment. A properly designed system makes the deflections caused by the gyroscopic moments negligible."

Design engineers of the past were used to a higher design safety margin, because the tools that would pinpoint exactly when a failure would occur were not available. Reducing the safety design margin is the function of the designers' certainty about the analysis. The less they know about the design, the more they need to protect themselves against errors. Therefore, the designs of yesterday were in essence "overengineered" to decrease the likelihood of failure, and this cost money. visualNastran Desktop allows engineers to apply the best design methods possible based not on guesswork but on empowerment through knowledge.

"Nowadays design is done using engineering software tools," expands Dr. Avory. "The engineers want to know to what to expect, and the customers want the models to be fairly accurate. The answer, 'Oh, don't worry, we've done this in the past. We know what we're doing. A similar design works fine' doesn't suffice anymore. Customers want to know that the design will work before it is accepted for manufacturing. And they want to know what the expected performance is, whether interference is going to occur. For example, they want to know if they're going to lose expensive test article or scene generator as a result of our mistake."

Dr. Avory leads to an important point: What's the cost of making a mistake? What is the cost of modifying a finished product? In the worst-case scenario, this can lead to scrapping the whole project. This is the obvious cost, but the hidden cost is customer satisfaction. According to Dr. Avory, by preventing the occurrence of mistakes that would otherwise happen, Carco Electronics saves 5-10 percent on the cost, even when the cost of performing the analysis is subtracted.

These savings can translate into tens of thousands of dollars saved over a relatively brief period of time. "The cost of not performing the analysis can be looked at by imagining what would happen if a system were built that was not properly analyzed, and it ends up costing you enormous amounts of money in warranty costs. A scenario like this one can be avoided by having a proper design tool at your disposal. The moral is: if you don't do your homework, you may pay dearly."




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