İlker Murat Koç

Hovering stability of a model helicopter

Purpose The purpose of this paper is to investigate the stability of a small scale six-degree-of-freedom nonlinear helicopter model at translator velocities and angular displacements while it is transiting to hover with different initial conditions. Design/methodology/approach In this study, model predictive controller and linear quadratic regulator are designed and compared within each other for the stabilization of the open loop unstable nonlinear helicopter model. Findings This study shows that the helicopter is able to reach to the desired target with good robustness, low control effort and small steady-state error under disturbances such as parameter uncertainties, mistuned controller. Originality/value The purpose of using model predictive control for three axes of the autopilot is to decrease the control effort and to make the close-loop system insensitive against modeling uncertainties.

Investigation of adhesion and friction of an isotropic composite pillar

In this work, studies are carried out on the adhesion and friction of composite pillars contact with a smooth flat surface. The composite pillar is obtained by allocating additive metal particles to a polymer matrix. The aluminum micron-sized particles are added to a polymer matrix in different mass ratios, which is aimed at an alteration of structural properties such as the stiffness and damping that is likely to permit adhesion and friction properties to be tuned accordingly. The results demonstrate that incorporating aluminum particles to a polymer matrix yields a loss of adhesion, and metal particles have a minor influence on the change of friction force for different sliding velocities.

Assessment of Friction Force between a PDMS Pillar and a Flat Glass Substrate

The friction force between a polydimethylsiloxane (PDMS) pillar in contact with a flat glass substrate is examined. The friction between the pillar and the glass is achieved with lateral loading of the glass under constant velocity. The friction force during the lateral motion is estimated by modelling the motion of the pillar as a lumped parameter system. The parameters of the lumped system are presented as equivalent mass, stiffness and damping components with addition of the contact interaction. Validation of the model is accumulated with experiments and the relative error between the analytical and experimental results is around %10.

Analytical and Experimental Analysis on Kinetics of a Laparoscopic Surgery Tool

Each laparoscopic surgery tool has specific design and task, which includes grasping, cutting, clamping, retraction etc. for surgery. This study deals with kinetic analysis of a conventional laparoscopic grasper in order to obtain a simple and valid analytical model that allows optimization of tool dimension, and verification of the model with experimental results. Additionally, simplified analytical model is compared with previously developed analytical model. The simplified model has the same results in calculation of actuator and grasper force compared to its predecessor. With the simplified analytical model, maximum error between the analytical and the experimental results is up to 2.8% in specific parameters.

Steady‐state vibration absorption using undamped linear substructures

This study extends the previous applications of linear energy sinks to steady‐state vibration absorption. First developed for the absorption of transient vibrations, linear energy sinks also act as effective vibration absorbers under steady‐state excitation. However, their effectiveness depends on the value of excitation frequency with respect to the natural frequency of the primary structure around which the frequencies of the attached oscillators of energy sink are distributed. Vibratory energy is absorbed efficiently for excitation frequencies above the natural frequency of the primary structure, while absorption is not as effective at lower excitation frequencies. [Research carried out while AA served at NSF.]

Vibration absorption by an undamped beam element

Through two complementary approaches, using modal response and wave propagation, this presentation will show the conditions under which a decaying impulse response, or a nearly irreversible energy trapping, takes place in a linear conservative continuous system. The results show that the basic foundation of near‐irreversibility or pseudo‐damping rests upon the presence of singularity points in the modal density of the systems. To illustrate the concept of pseudo‐damping in detail, a simple undamped beam is modified to introduce a singularity point in its modal density distribution. Simulations show that by a suitable application of a compressive axial force to an undamped beam on an elastic foundation, the impulse response of a beam shows the characteristics of a nearly irreversible energy trap and a decaying impulse response. Attaching such a modified beam to a single degree of freedom oscillator shows energy trapping by the beam producing pseudo damping. [Research carried out while AA served at NSF.]