02/16/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation defense by Catherine Barry on "Studies into the Mechanical Behavior of a Braided Parachute Suspension Line and its In-Service FSI."

Candidate Name: Catherine Barry
Degree: Doctoral
Defense Date: Thursday, Feb. 29, 2024
Time: 10 to noon
Location: Southwick 240, North Campus

Committee:

  • Advisor James A. Sherwood, Ph.D., Dean of Francis College of Engineering, UMass Lowell
  • David J. Willis, Ph.D., Associate Chair for Undergraduate Studies, Mechanical Engineering
  • Scott E. Stapleton, Ph.D., Associate Professor, Mechanical Engineering
  • Keith Bergeron, Ph.D., (Lt Col, USAF-ret), DEVCOM SC - Aerial Delivery Division

Brief Abstract:

GPS-guided parachutes are used by the military to deliver supplies and equipment to personnel in the field. These delivery systems consist of a payload, a canopy and a set of braided polyester suspension lines. While in flight, the suspension lines vibrate creating noise that can be heard for several kilometers, and this noise can compromise the silent entry of the payload. The vibrations also degrade the flight performance of the parachute system and challenge its ability to land on target. These undesirable vibrations result from the airflow over the noncircular cross-sections of the lines, leading to changes in the orientation of the line with respect to the airflow and fluctuation of the aerodynamic forces that cause the vortex-induced vibration and line gallop. The aims of the current research are (1) to conduct an experimental program to characterize the mechanical behavior of a suspension line, (2) to replicate that mechanical behavior in a mesomechanical finite element model, and then (3) to investigate the in-service fluid structure interaction (FSI) of the suspension line using the line stiffnesses found from the characterization data. The overall goal of this work is to develop the framework for a virtual design-build-test methodology to study the relationship between suspension line design and line vibration. Experimental vibration analyses were conducted to characterize the transverse and torsional stiffnesses of the lines as a function of the state of tension. These stiffness properties were then used to assist in creating a calibrated mesomechanical finite element model of the braided suspension line. The transverse stiffness was then implemented in a two-dimensional FSI model to replicate tests of a suspension line under tension in a wind tunnel. The models were also used to investigate how the surface topology and angle of incidence relate to the flow-induced motion of the line. The characterization program found that the transverse and torsional stiffnesses increased with increasing tension in the suspension line. The transverse stiffness as determined from the characterization program correlated well with the vibrating string equation. The torsional stiffness was replicated in the mesomechanical finite element model of the braid and provided insight as to the significance of the tow-to-tow interaction in modeling the tensile and torsional behavior of the line. The FSI models showed that they were able to replicate the general motion of the suspension line in the wind tunnel and variations in the angle of incidence, cross-sectional geometry, and excitation frequency had an impact on the resulting motion. The proposed methodology has the potential to be a fully virtual approach for the design of parachute suspension lines and can be used to conduct parametric studies of changes in the design of the suspension line to mitigate undesirable vibrations.