As a legacy monolithic software become too large to deal with, many enterprises are drawn to breaking them down into the microservices architectural style. Migrating a monolithic architecture to an ecosystem of microservices is an epic journey. Each legacy monolithic application is unique and migration to microservices creates different challenges. This article elaborates on challenges and technics of legacy software migration from monolithic architecture to microservice architecture. Different migration methods and techniques are reviewed, and their benefits and drawbacks are analyzed. Microservices is a relatively new architectural style and legacy monoliths are very different in many aspects. Existing migration techniques and methods do not cover every use case.

A novel design of a multiple degrees of freedom (multi-DOF) piezoelectric ultrasonic motor (USM) is presented in the paper. The main idea of the motor design is to combine the magnetic sphere type rotor and two oppositely placed ring-shaped piezoelectric actuators into one mechanism. Such a structure increases impact force and allows rotation of the sphere with higher torque. The main purpose of USM development was to design a motor for attitude control systems used in small satellites. A permanent magnetic sphere with a magnetic dipole is used for orientation and positioning when the sphere is rotated to the desired position and the magnetic field synchronizes with the Earth’s magnetic dipole. Also, the proposed motor can be installed and used for robotic systems, laser beam manipulation, etc. The system has a minimal number of components, small weight, and high reliability. Numerical simulation and experimental studies were used to verify the operating principles of the USM. Numerical simulation of a piezoelectric actuator was used to perform modal frequency and harmonic response analysis. Experimental studies were performed to measure both mechanical and electrical characteristics of the piezoelectric motor.

Migration from a monolithic architecture to a microservice architecture is a complex challenge, which consists of issues such as microservices identification, code decomposition, commination between microservices, independent deployment, etc. One of the key issues is data storage adaptation to a microservice architecture. A monolithic architecture interacts with a single database, while in microservice architecture, data storage is decentralized, each microservice works independently and has its own private data storage. A viable option to fulfil different microservice persistence requirements is polyglot persistence, which is data storage technology selected according to the characteristics of each microservice need. This research aims to propose and evaluate the approach of monolith database migration into multi-model polyglot persistence based on microservice architecture. The novelty and relevance of the proposed approach are double, that is, it provides a general approach of how to conduct database migration from monolith architecture into a microservice architecture and allows the data model to be transformed into multi-model polyglot persistence. Migration from a mainframe monolith database to a multi-model polyglot persistence was performed as a proof-of-concept for the proposed migration approach. Quality attributes defined in the ISO/IEC 25012:2008 standard were used to evaluate and compare the data quality of the microservice with the multi-model polyglot persistence and the existing monolith mainframe database. Results of the research showed that the proposed approach can be used to conduct data storage migration from a monolith to microservice architecture and improve the quality of the consistency, understandability, availability, and portability attributes. Moreover, we expect that our results could inspire researchers and practitioners toward further work aimed to improve and automate the proposed approach.

A novel design concept of multi‐degree‐of‐freedom (multi‐DOF) piezoelectric actuator is introduced in the paper. The main idea is to connect two identical piezoelectric transducers by hyperelastic material in order to increase the total number of degrees‐of‐freedom of the system. Such design principle also allows to separate vibrations of two piezoelectric transducers and to control them independently. The ring‐ and cylinder‐type piezoelectric transducers were used to design two multi‐DOF ultrasonic actuators for precise laser beam positioning. Reflecting mirror is mounted on the top of the actuator and is preloaded by magnetic force. Both disc‐ and cylinder‐type actuators can realize up to six degrees‐of‐freedom, i.e., to rotate the mirror about three axes employing one transducer and to position mirror in the plane by using another transducer. Bidirectional rotation and translation motion of the mirror are obtained by switching excitation signals between different electrodes of the transducers. Both the numerical simulation and physical prototype were used to verify operating principle of the actuators. Numerical investigation of the piezoelectric actuator was performed to investigate modal‐frequency and harmonic response analysis while experimental study was performed to measure electrical and mechanical output characteristics of the piezoelectric actuator. A mathematical model of contacting force control was proposed, and numerical verification was performed when the mirror need to be rotated according to the specific motion trajectory.

The results of numerical and experimental investigation of trapezoidal cantilevers with irregular cross-sections are presented in this paper. Modifications of the cross-section were made in order to increase strain and improve its distribution in the piezo ceramic layer of a cantilever. The proposed modifications allowed improving the energy conversion coefficient and increasing the power density. The numerical investigation revealed that modifications have a positive influence on strain and its distribution characteristics. Moreover, the electrical characteristics of piezoelectric cantilevers were investigated by employing a numerical model. The analysis of the results revealed that modifications of the cross-section have positively affected the electrical outputs of the cantilevers. The results of the numerical investigation were validated by experimental investigation. Experimental investigation showed that output voltage density was increased by 9.9%, output current density by 6.9% and power density by more than three-times compared with a conventional cantilever.

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 10 Hz to 240 Hz, where the first and the second bending modes of the cantilevers are dominating. Maximum output voltage density and energy density equal to 50.03 mV/mm³ and 604 μJ/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 37.5 mV/mm³, 815.16 μJ/mm³, and 65.24 μW, respectively.