Systems and methods for restricting movement in flexible ducts

A method of increasing a resonant frequency of a flow mixer that includes a plurality of lobes that each includes a trough and a pair of sidewalls, said method comprising:

• integrally forming a first end portion of a stiffening mechanism with a bottom surface of an apex of a first lobe of the plurality of lobes during a lay-up process;
• integrally forming a second end portion of the stiffening mechanism with a top surface of an apex of a second lobe of the plurality of lobes during the lay-up process;
• and
• integrally forming a body portion of the stiffening mechanism with the first end portion and the second end portion during the lay-up process such that the body portion restricts movement of the first and second lobes, wherein the body portion extends linearly between the apexes of the first lobe and the second lobe.

An aircraft exhaust system comprising:

• a flow mixer comprising:
• a plurality of first lobes, wherein at least one first lobe comprises a pair of opposing first sidewalls and a first trough extending between said pair of opposing first sidewalls;
• and
• a plurality of second lobes, wherein at least one second lobe comprises a pair of opposing second sidewalls and a second trough extending between said pair of opposing second sidewalls, wherein each second trough is aligned with and spaced a distance from a corresponding first trough;
• and
• a stiffener mechanism integrally molded with said flow mixer from a metallic or metal alloy material and extending linearly between an apex of a first lobe, of the plurality of first lobes, and an apex of a second lobe, of the plurality of second lobes, in at least one pair of corresponding first lobe and second lobe such that said stiffener mechanism is configured to restrict movement of said first lobe and said second lobe, said stiffener mechanism comprising:
• a first end portion integrally molded with a bottom surface of the apex of said first lobe;
• a second end portion integrally molded with a top surface of the apex of said second lobe;
• a body portion integrally molded with said first end portion and said second end portion;
• and
• a pair of spacers coupled between said body portion and each of the at least one first lobe and the at least one second lobe.