The influence of and the identification of nonlinearity in flexible structures

Several models were built at NASA Langley and used to demonstrate the following nonlinear behavior: internal resonance in a free response, principal parametric resonance and subcritical instability in a cantilever beam-lumped mass structure, combination resonance in a parametrically excited flexible beam, autoparametric interaction in a two-degree-of-freedom system, instability of the linear solution, saturation of the excited mode, subharmonic bifurcation, and chaotic responses. A video tape documenting these phenomena was made. An attempt to identify a simple structure consisting of two light-weight beams and two lumped masses using the Eigensystem Realization Algorithm showed the inherent difficulty of using a linear based theory to identify a particular nonlinearity. Preliminary results show the technique requires novel interpretation, and hence may not be useful for structural modes that are coupled by a guadratic nonlinearity. A literature survey was also completed on recent work in parametrically excited nonlinear system. In summary, nonlinear systems may possess unique behaviors that require nonlinear identification techniques based on an understanding of how nonlinearity affects the dynamic response of structures. In this was, the unique behaviors of nonlinear systems may be properly identified. Moreover, more accutate quantifiable estimates can be made once the qualitative model has been determined

On Providing Engineering Students with Culturally-Appropriate Design Experiences in Developing Countries

Academic institutions are encouraged to instill the impact of engineering solutions in a global and societal context. This paper summarizes the structural, planning, and logistical aspects of offering senior-level capstone and underclass extra-curricular design projects targeted for developing countries. These projects engage the students in year-long design and fabrication, and culminate in taking students to foreign soil for delivery and installation. The necessary infrastructure and culture at the academic institution, relationships with appropriate intermediaries, and the role of a receptive national host that needs engineering services are identified. The goal is to continue an on-going collaborative relationship that takes students and faculty abroad annually, who in turn help to identify new projects for future teams. The criteria by which projects are selected and staffed (i.e., academic merit, field need, and student interest) are discussed. A case study is presented that evaluates our pilot program. The projects that were selected focused on an organization\u27s infrastructure that provides mechanical services (e.g., electric power generation, water, and sanitation) to support a radio station, a hospital, a school and a host of Non Governmental Organizations. Additional projects were focused on needs of rural people. The results of our first team, which traveled to Liberia, West Africa in May 2007 are documented. They successfully installed a student-designed cooling system for diesel-powered generators, built a medical waste incinerator for the hospital, and distributed solar-powered reading lamps to rural dwellers. They also began a new senior capstone project - to improve the water distribution network - by collecting appropriate data and preparing CAD drawings of the facilities. Overnight trips to remote villages provided engineering students and faculty an opportunity to see how the rural dweller lives. These experiences provided rich insight for the students to see basic needs of people on a new level, and how they might develop engineering solutions which blend into the culture

On Providing Engineering Students with Ministry and Culturally-Appropriate Design Experiences in Developing Countries

Academic institutions are encouraged to instill the impact of engineering solutions in a global and societal context. This paper summarizes the structural, planning, and logistical aspects of offering senior-level capstone and underclass extra-curricular design projects targeted for developing countries. These projects engage the students in year-long design and fabrication, and culminate in taking students to foreign soil for delivery and installation. The necessary infrastructure and culture at the academic institution, relationships with appropriate intermediaries, and the role of a receptive national host that needs engineering services are identified. The goal is to continue an on-going collaborative relationship that takes students and faculty abroad annually, who in turn help to identify new projects for future teams. The criteria by which projects are selected and staffed (i.e., academic merit, field need, and student interest) are discussed. A case study is presented that evaluates our pilot program. The projects that were selected focused on an organization\u27s infrastructure that provides mechanical services (e.g., electric power generation, water, and sanitation) to support a radio station, a hospital, a school and a host of Non Governmental Organizations. Additional projects were focused on needs of rural people. The results of our first team, which traveled to Liberia, West Africa in May 2007 are documented. They successfully installed a student-designed cooling system for diesel-powered generators, built a medical waste incinerator for the hospital, and distributed solar-powered reading lamps to rural dwellers. They also began a new senior capstone project - to improve the water distribution network - by collecting appropriate data and preparing CAD drawings of the facilities. Overnight trips to remote villages provided engineering students and faculty an opportunity to see how the rural dweller lives. These experiences provided rich insight for the students to see basic needs of people on a new level, and how they might develop engineering solutions which blend into the culture. The Bible gives mandates to subdue the earth and to make disciples in all the nations. This paper describes our pilot program for engaging undergraduate engineering students to enable and encourage African believers in their ministry of meeting humanitarian needs and propagating the gospel in Liberia. This program helps undergraduate students discern God’s call on their lives as they complete engineering projects targeted for a developing country. Important components for the program\u27s success were: 1) infrastructure and culture at the academic institution, 2) relationships with appropriate intermediaries, and 3) a receptive national host that needs engineering services. These components were similar to those identified by others in recent literature. A case study is presented that evaluates our pilot program which took a team of students and faculty to Liberia, West Africa in May 2007. ELWA Ministries comprises a Christian radio station, a Christian hospital, and a Christian school; the 134-acre campus is also home to many families and provides housing for Non-governmental organizations. Four projects were selected focusing on ELWA’s physical plant that provides mechanical services. The team successfully installed a student-designed cooling system for diesel-powered generators and built a medical waste incinerator for the hospital. Students also prepared CAD drawings of the campus and documented the water system by taking many measurements. An additional project helped rural pastors; the students designed and distributed solar-rechargeable reading lights. Overnight trips to remote villages provided engineering students and faculty an opportunity to see how the rural dweller lives. These experiences provided the students intercultural worship opportunities and insight how to develop engineering solutions which blend into the culture. The ELWA services personnel and Liberian pastoral leadership expressed profound gratitude for the team’s ministry; student assessment also confirmed the value of the experience

Multiple solutions and corresponding power output of a nonlinear bistable piezoelectric energy harvester

We examine multiple responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine the appearance of various solutions and their basins of attraction. Identification of particular solutions of the energy harvester is important as each solution may provide a different level of power output

Regular and chaotic vibration in a piezoelectric energy harvester

We examine regular and chaotic responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine bifurcations from single well oscillations, to regular and chaotic vibrations between the potential wells. The appearance of chaotic responses in the energy harvesting system is illustrated by the bifurcation diagram, the corresponding Fourier spectra, the phase portraits, and is confirmed by the 0–1 test. The appearance of chaotic vibrations reduces the level of harvested energy