Mechanical Engineering / Makina Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4129

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Subject: search.filters.subject.Design optimization

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  • Article
    Citation - WoS: 10
    Citation - Scopus: 12
    A Robot Arm Design Optimization Method by Using a Kinematic Redundancy Resolution Technique
    (MDPI, 2022) Maaroof, Omar W.; Dede, Mehmet İsmet Can; Aydın, Levent
    Redundancy resolution techniques have been widely used for the control of kinematically redundant robots. In this work, one of the redundancy resolution techniques is employed in the mechanical design optimization of a robot arm. Although the robot arm is non-redundant, the proposed method modifies robot arm kinematics by adding virtual joints to make the robot arm kinematically redundant. In the proposed method, a suitable objective function is selected to optimize the robot arm’s kinematic parameters by enhancing one or more performance indices. Then the robot arm’s end-effector is fixed at critical positions while the redundancy resolution algorithm moves its joints including the virtual joints because of the self-motion of a redundant robot. Hence, the optimum values of the virtual joints are determined, and the design of the robot arm is modified accordingly. An advantage of this method is the visualization of the changes in the manipulator’s structure during the optimization process. In this work, as a case study, a passive robotic arm that is used in a surgical robot system is considered and the task is defined as the determination of the optimum base location and the first link’s length. The results indicate the effectiveness of the proposed method.
  • Article
    Citation - WoS: 22
    Citation - Scopus: 22
    Emergence of Rectangular Shell Shape in Thermal Energy Storage Applications: Fitting Melted Phase Changing Material in a Fixed Space
    (Elsevier, 2021) Demirkıran, İsmail Gürkan; Çetkin, Erdal
    Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging.