Jessica Yellin

A self-sensing active constrained layer damping treatment for a Euler - Bernoulli beam

In a self-sensing active constrained layer (SACL) damping treatment, the piezoelectric constraining layer is used simultaneously as both a sensor and an actuator. A variational formulation of ACL damping treatments has shown that an ACL damping treatment using a self-sensing and actuating piezoelectric element as the constraining layer in combination with rate of strain feedback as the control law will ensure that the power dissipated by the active damping always remains positive. This eliminates a major mechanism for system instability. Implementing this self-sensing actuator (SSA) as the constraining layer is made possible through the use of a bridge circuit that subtracts the strain signal from the actuator control voltage in the piezoelectric constraining layer and also differentiates the strain voltage in order to obtain the desired control law. An analytical model for ACL has been developed that can be used to predict theoretically the performance of a SACL damping treatment for a Euler - Bernoulli beam. A series of experiments studying the frequency response of an SACL test beam was performed and the results compared with the theoretical model. This theoretical model predicted the frequency of the first- and second-mode responses of the experimental beam very accurately and predicted the damping of these responses well. Therefore, this comparison indicated that the analytical model is capable of accurately predicting the frequency responses of beams treated with SACL.

An Analytical and Experimental Analysis for a One-Dimensional Passive Stand-Off Layer Damping Treatment

Passive stand-off layer (PSOL) damping treatments are presently being implemented in many commercial and defense designs. In a passive stand-off layer damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer (PCL) damping treatment. An analytical model which quantifies the bending and shearing contributions of the stand-off layer has been developed for a passive stand-off layer damping treatment applied to a beam. The equations of motion were derived and solved in order to simulate the frequency responses of several beams treated with passive stand-off layer damping. A series of experiments was conducted in order to test this analytical model. These experiments measured the frequency responses of a variety of beams treated with passive stand-off layer damping treatments. The experimentally measured results were normalized and calibrated and then compared with the theoretical predictions using the new analytical model. This comparison showed that the analytical model was able to predict very accurately the frequency responses of the beams treated with passive stand-off layer damping.

Analytical model for a passive stand-off layer damping treatment applied to an Euler-Bernoulli beam

Passive constrained layer (PCL) damping treatments have been shown to be a very effective and reliable method for the damping of structures and have been implemented successfully in many commercial and defense designs for the aerospace and automotive industries. A conventional passive constrained layer damping treatment consists of a viscoelastic layer sandwiched between the vibrating structure and a cover layer. In a passive stand-off layer (PSOL) damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment between the vibrating structure and the viscoelastic layer. The addition of this stand-off layer increases the distance of the viscoelastic and constraining layers from the neutral axis of the vibrating structure. This is thought to enhance damping by increasing the shear angle of the viscoelastic layer. To investigate how the bending and shearing rigidities of the stand-off layer (SOL) affect the damping performance, an analytical model has been developed for a PSOL damping treatment applied to an Euler-Bernoulli beam. In this paper, the equations of motion are derived and solved. The resulting simulations of the frequency response are then discussed.

Thickness Deformation of Constrained Layer Damping: An Experimental and Theoretical Evaluation

This paper presents a study of thickness deformation of the viscoelastic material in constrained layer damping (CLD) treatments. The first goal of the study is to demonstrate the feasibility of using direct measurement to investigate thickness deformation in CLD treatments. The experimental setup consisted of a constrained layer beam cantilevered to a shaker, an accelerometer mounted at the cantilevered end, and two laser vibrometers that simultaneously measured the responses of the base beam and the constraining layer, respectively, at the free end. A spectrum analyzer calculated frequency response functions (FRFs) between the accelerometer inputs and the vibrometer outputs. Measured FRFs of the base beam and the constraining layer were compared to detect thickness deformation. Experimental results showed that direct measurements can detect thickness deformation as low as 0.5 percent. The second goal is to evaluate the accuracy of a mathematical model developed by Miles and Reinhall [7] that accounts for thickness deformation. FRFs were calculated by using the method of distributed transfer functions by Yang and Tan [13]. Comparison of the numerical results with the experimental measurements indicated that consideration of thickness deformation can improve the accuracy of existing constrained layer damping models when the viscoelastic layer is thick.

Experimental investigation of a passive stand-off layer damping treatment applied to an Euler-Bernoulli beam

Passive stand-off layer (PSOL) damping treatments are presently being implemented in many aerospace and defense designs. In a PSOL damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer (PCL) damping treatment. The addition of this stand-off layer increases the distance of the viscoelastic and constraining layers from the neutral axis of the vibrating structure. This is thought to enhance the damping by increasing the shear angle of the viscoelastic layer. In this experimental study, a PSOL damping treatment was applied to an Euler-Bernoulli beam. The frequency response of the treated PSOL beam was then compared with a conventionally treated PCL beam of similar dimensions and materials. Previous theoretical studies indicated that PSOL treatments provided greater damping than similarly sized conventional PCL treatments. This study verified experimentally that the beam treated with PSOL had greater damping of the first four modes than a similarly sized beam treated with PCL.

Experimental investigation of a self-sensing active constrained layer damping treatment

A variational formulation of active constrained layer (ACL) damping treatments has indicated that the power dissipated through the active damping is the product of the electric field and the axial velocity of the piezoelectric constraining layer at the boundaries. This feature, unique to this formulation, suggests that a self-sensing and actuating piezoelectric constraining layer using rate of strain feedback may be an appropriate method of dissipating vibration energy with less instability, since the sensor and actuator are truly collocated. A partial ACL damping treatment design for an Euler-Bernoulli beam using a self-sensing actuator (SSA) as the active layer has been developed. The open loop transfer functions of the treated beam given by the SSA rate of strain circuit show great similarity to transfer functions taken from a reference sensor laminated directly to the beam. It has been shown experimentally that this beam treatment significantly increased the damping coefficient of the first mode in closed loop.

The Real World: A Factor That Engineering Faculty Consider in Making Decisions About Teaching

This paper describes a critical decision method (CDM) study for investigating the phenomenon of teaching-related decision-making in engineering education. We interviewed 33 engineering faculty using this method and asked them to identify two memorable, recent teaching-related decisions: one pre-active (planning) decision and one interactive (in-class) decision. Faculty described the situation, the process of making the decision, the factors that they took into account, and their level of satisfaction with the outcomes of their teaching-related decision. In this paper, we focus on one specific factor that emerged across the majority of the interviews: the real world. We present ways in which faculty referred to the real world, and more specifically preparing students for professional practice, when making decisions about their teaching. Three themes provided insight regarding the participants’ beliefs about this concept; that the real world is hands-on, defineable in terms of professional standards, and that addressing it explicitly in teaching involves trade-offs.Copyright

Experimental and finite element analysis of stand-off layer damping treatments for beams

Passive stand-off layer (PSOL) and slotted stand-off layer (SSOL) damping treatments are presently being implemented in many commercial and defense designs. In a PSOL damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment. In an SSOL damping treatment, slots are included in the stand-off layer. A set of experiments using PSOL and SSOL beams in which the geometric properties of the stand-off layer were varied was conducted to analyze the contribution of the stand-off layer to the overall system damping. This set of experiments measured the frequency response functions for a series of beams in which the total slotted area of the stand-off layer was held constant while the number of slots in the stand-off layer was increased for a constant stand-off layer material. Finite element analysis models were developed in ANSYS to compare the predicted frequency response functions with the experimentally measured frequency response functions for the beams treated with PSOL and SSOL damping treatments. In these beams, the bonding layers used to fabricate these treatments were found to have a measurable and significant effect on the frequency response of the structure. The finite element model presented here thus included an epoxy layer between the base beam and the stand-off layer, a contact cement layer between the stand-off layer and the viscoelastic layer, and a method for modelling delamination.

Analytical model for a one-dimensional slotted stand-off layer damping treatment

Passive stand-off layer and slotted stand-off layer damping treatments are presently being implemented in many commercial and defense designs. In a passive stand-off layer damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment. Additionally, this stand-off layer can be slotted in order to reduce the bending rigidity and total mass of the damping treatment. A preliminary analytical model has being developed for a slotted stand-off layer damping treatment applied to a beam. This mathematical model is based on Euler-Bernoulli beam theory, and may be able to provide an analytical solution of the frequency response for a beam treated with slotted stand- off layer damping.

User-centered design of course-based portfolios for mechanical engineering student learning

One challenge for engineering educators is to design appropriate educational curricula that address both students’ needs and educators’ expectations. It is therefore important for the engineering education community to think about how to include students and faculty into the assignment design process. In this paper we discuss our use of user-centered design (UCD) principles, including early focus on users, empirical measurements, and iteration design, to design course-based portfolio (CBP) assignments for mechanical engineering students. To support the assignment design decisions, we collected early information about mechanical engineering students’ learning needs and educators’ expectations. Based on the design considerations that we identified for portfolio design, the CBP assignment is designed to ask students build a persuasive document and identify the connections between the course and mechanical engineering discipline. We measured our design by piloting the assignment with students and getting feedback from faculty in the Mechanical Engineering Department; this feedback reflects the effectiveness of the CBP and leads to design iterations and tradeoffs. We also identified several students’ learning opportunities and formed these opportunities into hypotheses to evaluate the impacts of course-based portfolios on students learning in the next formal study. This research demonstrates a successful practice of using user-centered design principles to design a course-based portfolio assignment for mechanical engineering students.Copyright