Mechanical Components

Using Describing Functions for Aeroservoelastic Models with Free-Play

The effect of free-play in a system can be accurately estimated without the need for simulation. Neil A. Armstrong Flight Research Center, Edwards, California Aerodynamic control surfaces, with excessive free-play, can cause limit cycle oscillations (LCO), a sustained vibration of constant amplitude. The LCO is caused by a combination of aeroservoelastic effects and free-play. If the amplitude is sufficiently large, it can impact handling qualities, ride quality, and can cause structural fatigue, ultimately leading to structural failure. Free-play is typically distributed throughout the actuator and control surface, with contributions from actuator mounting bearings as well as the surface hinge.

Posted in: Mechanical Components, Software, Briefs

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Design Environment for Multi-Fidelity and Multi-Disciplinary Components

John H. Glenn Research Center, Cleveland, Ohio Many of the most challenging aspects of propulsion system development are related to the prediction of interacting effects among fluid loads, thermal loads, and structural deflection. A typical design practice might ignore the interaction between the physical phenomena where the outcome of each analysis can be heavily dependent on the inputs. Such a rigid design process also lacks the flexibility to employ multiple levels of fidelity in the analysis of each of the components.

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Shipping Foam Designer Software

Lyndon B. Johnson Space Center, Houston, Texas An easy-to-use design tool was developed in response to a large number of documented cases of critical (flight and ground) hardware failing after experiencing drops during commercial shipment. By entering the mass of the hardware to be protected, and the drop height, the software helps the user select the type and dimensions of the shock attenuating foam needed. Hundreds of drop tests were conducted with metal plates instrumented with accelerometers that were protected by common shipping foams of different thicknesses, along with foam compression tests conducted at various speeds to develop mathematical material models for these foams. The foam drops were video recorded at a very high rate of speed to capture foam deformation due to drop.

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Evolutionary Mission Trajectory Generator

Goddard Space Flight Center, Greenbelt, Maryland The Evolutionary Mission Trajectory Generator (EMTG) is a global trajectory optimization tool for designing interplanetary missions that perform multiple flybys and either low-thrust or high-thrust propulsive maneuvers on the way to destinations in the solar system. Some targets, such as Mars and Venus, are reachable using direct flights with chemical propulsion technology. Others, such as Mercury, main-belt asteroids, and comets are not easily accessible. One way to mitigate this problem is by using more efficient propulsion systems, such as low-thrust solar electric propulsion. Another is to find more efficient paths to the destination, possibly including gravity assist maneuvers, or planetary flybys.

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Visual International Space Station Configuration Viewing Tool

Lyndon B. Johnson Space Center, Houston, Texas Communicating the current International Space Station (ISS) configuration and also potential ISS configurations is a necessity during ISS trade studies and Ops Con development. Often, multiple configuration options will need to be communicated. Doing so without a means of displaying an image of the description can be very confusing. Historically, visual information needed for presentations and meetings was conveyed using still images or pre-generated videos. This form of information provides only a single view, and it is not always at the optimum location.

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Two-Equation Turbulence Models for Application to Internal Flow Through Pneumatic Valves

Applications include design, analysis, and optimization of valves and pumps. John F. Kennedy Space Center, Florida Predicting turbulent flowfield and pressure drop in complex internal flows, such as valves, pumps, and turbines, is of great interest in many areas of technology. Accurate prediction of three-dimensional (3D) flowfield in complex devices is critically dependent on the accuracy of the turbulence model used to describe the turbulence energy production and dissipation processes within the flowfield region of interest.

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Swan Seal

The seal can be sized to any application while maintaining its important features. John H. Glenn Research Center, Cleveland, Ohio This seal features dual sealing capabilities: a face seal and an axial seal. The name swan seal is derived from its cross section, which resembles a swan. Most injector designs require fuel to be delivered from an inlet fitting, through a feed arm, to the injector tip. Temperature variation from the inlet to the tip, from the cool fuel to hot combustion air, and from startup to full power, often poses a challenge due to thermal growth. One of the most challenging areas is accommodating the growth differential between a hot feed arm and a cool fuel delivery tube, which is exacerbated by the relatively long distance. Several methods have been used to allow for this including coiling the fuel tube, utilizing an O-ring sliding seal, metal C-seals, or incorporating stretchable bellows. Some of the drawbacks of these methods include limited space, poor durability at high temperatures, serviceability, long lead times, and cost. The swan seal presents a compact, high-temperature, replaceable, low-cost option for this and other applications where a sliding axial seal is required.

Posted in: Mechanical Components, Briefs, TSP

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