Active structure
This article needs additional citations for verification. (April 2011) |
An active structure (also known as a smart or adaptive structure) is a
The term active structure also refers to
Function
The result of the activity is a structure more suited for the type and magnitude of the load it is carrying. For example, an orientation change of a
An active structure consists of three integral components besides the load carrying part. They are the sensors, the processor and the actuators. In the case of a human body, the sensory nerves are the sensors which gather information of the environment. The brain acts as the processor to evaluate the information and decide to act accordingly and therefore instructs the muscles, which act as actuators to respond. In heavy engineering, there is already an emerging trend to incorporate activation into bridges and domes to minimize vibrations under wind and earthquake loads.
Aviation engineering and aerospace engineering have been the main driving force in developing modern active structures. Aircraft (and spacecraft) require adaptation because they are exposed to many different environments, and therefore loadings, during their lifetime. Prior to launching they are subjected to gravity or dead loads, during takeoff they are subjected to extreme dynamic and inertial loads and in-flight they need to be in a configuration which minimizes drag but promotes lift. A lot of effort has been committed into adaptive aircraft
Design
Human-made actuators existing in the market, even the most sophisticated ones, are nearly all one-dimensional. This means they are only capable of extending and contracting along, or rotating about 1 axis. Actuators capable of movement in both forward and reverse directions are known as two-way actuators, as opposed to one-way actuators which can only move in one direction. The limiting capability of actuators has restricted active structures to two main types: active truss structures, based on linear actuators, and manipulator arms, based on rotary actuators.
A good active structure has a number of requirements. First, it needs to be easily actuated. The actuation should be energy-saving. A structure which is very stiff and strongly resists morphing is therefore not desirable. Second, the resulting structure must have structural integrity to carry the design loads. Therefore, the process of actuation should not jeopardize the structure's strength. More precisely, we can say: We seek an active structure where actuation of some members will lead to a geometry change without substantially altering its stress state. In other words, a structure that has both
Applications
Active-control technology is applied in civil engineering, mechanical engineering and aerospace engineering. Although most civil engineering structures are static, active control is utilized in some civil structures for deployment against seismic loading, wind loading and environmental vibration.[1] Also, active control is proposed to be used for damage tolerance purposes where human intervention is restricted.[2] Korkmaz et al. demonstrated configuration of active control system for a damage tolerance and deployment of a bridge.[3]
See also
- James E. Hubbard, Jr.
- Tuned mass damper
References
External links
- Swiss Federal Institute of Technology (EPFL), Applied Computing and Mechanics Laboratory (IMAC)
- Cambridge University Deployable Structures Lab
- Hoberman Associates - Transformable Design
- CRG Technology: Morphing Processes
- A free-standing space elevator structure: A practical alternative to the space tether