Dalius Mažeika

Cloud Software Performance Metrics Collection and Aggregation for Auto-Scaling Module

Cloud computing made a big impact on software architecture evolution. The demand to serve multiple tenants, to include continuous delivery practice into the development process as well as increased system load influenced the style of cloud based software architecture. Microservice architecture is preferred architecture despite its complexity when scalability is an essential attribute of quality of service. Microservices should be managed, i.e., hardware resources should be adjusted based on application load, as well as resiliency should be ensured. Popular IaaS and PaaS providers such as Amazon, Azure or OpenStack ensure auto-scaling and elasticity at the infrastructure level. This approach has the following limitations: (1) Scaling and resiliency is a part of the infrastructure and not emerging from application nature; (2) The software is locked in with a specific vendor; (3) It might be difficult to run and ensure smooth scalability by running software on different vendors at the same time. We are creating auto-scaling module for microservice-based applications. Collecting metrics both at infrastructure and application levels is one important task for auto-scaling. We’ve chosen to investigate ELK stack and build appropriate architecture around it.

Multifrequency Piezoelectric Energy Harvester Based on Polygon-Shaped Cantilever Array

This paper focuses on numerical and experimental investigations of a novel design piezoelectric energy harvester. Investigated harvester is based on polygon-shaped cantilever array and employs multifrequency operating principle. It consists of eight cantilevers with irregular design of cross-sectional area. Cantilevers are connected to each other by specific angle to form polygon-shaped structure. Moreover, seven seismic masses with additional lever arms are added in order to create additional rotation moment. Numerical investigation showed that piezoelectric polygon-shaped energy harvester has five natural frequencies in the frequency range from 10u2009Hz to 240u2009Hz, where the first and the second bending modes of the cantilevers are dominating. Maximum output voltage density and energy density equal to 50.03u2009mV/mm3 and 604u2009μJ/mm3, respectively, were obtained during numerical simulation. Prototype of piezoelectric harvester was made and experimental investigation was performed. Experimental measurements of the electrical characteristics showed that maximum output voltage density, energy density, and output power are 37.5u2009mV/mm3, 815.16u2009μJ/mm3, and 65.24u2009μW, respectively.

Investigation of Multifrequency Piezoelectric Energy Harvester

This paper presents results of numerical and experimental investigations related to the piezoelectric energy harvester that operates at multifrequency mode. Employment of such operation principle provides an opportunity for obtaining frequency response characteristics of the harvester with several resonant frequencies and in this way increasing efficiency of the harvester at a wide spectrum of excitation frequencies. The proposed design of the energy harvester consists of five cantilevers which forms square type system. Cross sections of the cantilevers are modified by periodical cylindrical gaps in order to increase strain value and to obtain more uniform strain distribution along the cantilevers. Cantilevers are rigidly connected to each other and compose an indissoluble system. Square type harvester has seismic masses at every corner. These masses are placed under specific angle in order to reduce natural frequencies of the system and to create additional rotation moments in the body of harvester. Results of the numerical investigation revealed that harvester has five resonance frequencies in the range from 15u2009Hz to 300u2009Hz. Numerical analysis of the harvester revealed that the highest open circuit voltage density is 19.85u2009mV/mm3. Moreover, density of the total electrical energy reached 27.5u2009μJ/mm3. Experimental investigation confirmed that frequency response characteristics are obtained during numerical investigation and showed that energy density of the whole system reached 30.8u2009μJ/mm3.

Investigation of the Traveling-Wave Oscillations of Piezoelectric Cylinder

Piezoelectric actuators are widely used for the nano/micro positioning and adjustment systems. In the paper, the investigation on the oscillations of contacting surfaces of the piezoelectric thick-walled cylinder is presented. Piezoelectric cylinder is the main component of piezomechanical system named as piezo-screw and is used to turn the screw. This investigated piezomechanical system can be used for the precise positioning with a high resolution (less than 50 nanometers). Piezoelectric cylinder has radial polarization. Traveling-wave oscillations of the second circumferential modal shape (n = 2, m = 1) are excited. Three different electrode topologies are used to drive the screw. Electrodes are grouped into upper and low groups in both topology cases. Each group consists of six electrodes where positions of corresponding electrodes in upper and lower group are shifted by π/6. Numerical investigation of the traveling wave oscillation is performed and dependencies oscillation trajectories of contact surfaces on excitation schemes are determined when three different electrode topologies are used. Dependency of oscillations of contacting points upon length of the actuator is analyzed as well. Advantages and disadvantages of each excitation case are discussed.

Investigation of Oscillations of the Piezoelectric Actuator with Two-Directional Polarization

The recent trends in robotics and mechatronics necessitate for developing small-size multi-DOF motion systems. Piezoelectric actuators are one of the feasible solutions of this problem. An investigation of the contact point multicomponent oscillations of the beam type piezoelectric actuator with two-directional polarizations under different excitation regimes is presented in the paper. Polarization of the actuator has perpendicular directions on the first and second half of the actuator. Two-directional polarization of the actuator is used to achieve flexural oscillations of the actuator in two perpendicular planes. Superposition of longitudinal and flexural modes allows achieving oscillations of contact point in different planes. Electrodes of the actuator are divided into sections, and several excitation schemes are used to control a trajectory of the contact point movement. Numerical simulation and experimental study of piezoelectric actuator oscillations were performed. Elliptical motions of the contact point were obtained in different planes. Dependencies of contact point oscillation trajectories from excitation voltage phase and amplitude are determined at different excitation regimes.

Piezoelectric Actuator Generating 3D-Rotations of a Sphere

Investigation of a new design piezoelectric actuator based on research of compound ultrasonic systems called shaking beam is presented in the paper. It was developed to rotate the sphere about three different axes and can be used in sophisticated positioning devices. The actuator consists of a vibrating frame, four piezostacks and four overlays. Elliptical motions of the four driving tips, which rotate the sphere, are achieved by using multimode oscillations of the vibrating frame. Control of the spheres motion is performed by managing the amplitude and phase of harmonic input signal on different piezostacks. Numerical modeling based on a finite element method is performed in order to obtain resonance frequencies and modal shapes of the actuator and to calculate the trajectories of contact points movements under different input regimes. A prototype actuator was made and the experimental outcomes of the actuators working surfaces oscillations are given. Results of the numerical and experimental research are analyzed and discussed.