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Advances in the Application of Hybrid Simulation

Researchers in seismic engineering and other industries are deploying hybrid simulation as a tool for advanced design.

By combining computer modeling with physical testing, hybrid simulation technology overcomes many shortcomings common to conventional testing. Hybrid simulation simultaneously combines the mechanical testing of substructures with computer models of the remainder of the structure. This provides a practical and cost-effective means of understanding how seismic events will affect a civil structure, without having to physically test the entire structure.

For seismic engineers, hybrid simulation is a valuable method for understanding the dynamic behavior of civil structures in response to real-world earthquake conditions.

CIVIL SEISMIC SIMULATION
Objective: Determine the performance of a full-scale civil structure under real world earthquake conditions.

Conventional solutions:
Full-structure tests on large shake tables are cost-prohibitive due to the significant time and expense required for setup. Structures that can be tested are also limited by the size and payload capacities of the test equipment.

Substructure tests using multiple actuators apply forces and motions at a slower rate than would be experienced in actual earthquake event. This is appropriate for evaluating structural strength and stiffness, but not dynamic properties.

Scale-model tests using a small shake table cannot provide insight into true dynamics and failure mechanisms of full-scale structures.

Hybrid simulation solutions:
Quasi-static hybrid simulation is used to evaluate substructures that predominantly contribute stiffness and strength to a complete structure. Forces and motions are applied at an artificially slow rate, allowing the structure to be studied in detail.

Real-time hybrid simulation evaluates substructures or components that contribute damping or inertia effects to a structure. As the name implies, computer simulation is performed in real time.

Other hybrid simulation applications
Researchers outside seismic engineering are also exploring uses for hybrid simulation technology.

BIOMECHANICAL DEVICE SIMULATON
Objective:
Determine the expected life (wear) characteristics of an implantable knee replacement in the absence of the soft tissue constraints that are present in the body.

Conventional solution: Duplicate soft tissue constraints with the addition of physical motion or force controlled actuation. This is cost-prohibitive due to the extreme complexity of forces and motions involved, along with its questionable data integrity.

Hybrid simulation solution: A virtual signal is generated that acts upon existing control channels, combining the actual measured signal from a transducer with a supplemental or simulated signal based upon a modeled response. This results in a control mode that can replicate elements of constraints that are not physically present.

GROUND VEHICLE SUSPENSION SIMULATION
Objective: Validate component and subsystem interaction and impact on vehicle-level performance earlier in development and at less expense.

Conventional solutions: Computer-aided engineering (CAE) tools lack hard-to-model characteristics such as friction, and errors can be propagated through development. Track testing and prototypes lack repeatability, and late-stage measurements result in errors that are expensive to remedy.

Hybrid simulation solution: MTS Mechanical Hardware-in-the-Loop™ (mHIL) technology places mechanical systems or components in the loop of a real-time vehicle model, allong vehicle performance evaluations to be conducted well before the full-vehicle prototype is available.

DRIVING SIMULATION
Objective: Create realistic driving experiences for studying accident or near-accident scenarios, in order to aid in the development of active safety systems for future vehicles.

Conventional solution: Track testing requires professional drivers in staged collision events, which does not realistically recreate the average driver’s reactions. It also lacks repeatability and exposes drivers to dangerous situations.

Hybrid simulation solution: Vehicle manufacturers leverage hybrid simulation to reproduce the driving experience in the test lab. This provides new insight into how people react to various driving conditions and phenomena, much of which is too dangerous or non-repeatable to be performed on the proving ground.

In this scenario, the human being behind the wheel is the physical specimen and the surrounding driving experience represents the virtual portion of the test. Visual, auditory and force feedback makes drivers feel like they are actually operating a moving vehicle, allowing a statistically significant sampling to be generated without endangering drivers.

WIND TURBINE BLADE FATIGUE SIMULATION
Objective: Evaluate the fatigue life of very large wind turbine blades.

Conventional solution: Full blade assemblies are tested at the blade-resonant frequency. Generating a specific strain state along the length of a complete, full-scale wind turbine blade is expensive and time-consuming. Since tests are performed in only one direction at a time, the strain states that can be achieved do not match those seen in real-world environments.

Hybrid simulation solution: Sections of wind turbine blades can be tested instead of full structures, allowing complex multi-axial loading conditions to be applied that more closely replicate in-situ strain states. Test speeds can also be accelerated to enable faster data collection on critical sections of the blade. Additionally, specific blade design details can be validated more quickly in the laboratory, enabling faster development of optimized blade designs.

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