Estimating Sound Exposure Levels Due to a Broadband Source over Large Areas of Shallow Sea

3D sound propagation modeling in the context of acoustic noise monitoring problems is considered. A technique of effective source spectrum reconstruction from a reference single-hydrophone measurement is discussed, and the procedure of simulation of sound exposure level (SEL) distribution over a large sea area is described. The proposed technique is also used for the modeling of pulse signal waveforms at other receiver locations, and results of a direct comparison with the pulses observed in the experimental data is presented.

Control of flow separation over a circular cylinder using synthetic jet

The development of methods of active separation flow control is of great applied importance for many technical and engineering applications. Understanding the conditions for the flow separation from the surface of a bluff body is essential for the design of aircrafts, cars, hydro and gas turbines, bridges and buildings. Drag, acoustic noise, vibrations and active flow mixing depend drastically on the parameters of the vortex separation process. We investigated the possibility of reducing the longitudinal length of a reverse-flow region using the method of «synthetic jet» active separation flow control. The experiment was carried out on a compact straight-through wind channel with a 1-m long test section of a cross-section of 125x125 mm. The jet was placed at the rear stagnation point of a circular cylinder. The Reynolds number, based on the cylinder diameter and the free-stream velocity, was 5000 and the von Kármán street shedding frequency without the synthetic jet was equal to 64.8 Hz. For the first time, for such a set of parameters, we applied high speed PIV to demonstrate that the injection of the synthetic jet into the cylinder wake region leads to a significant reduction in the longitudinal length of the reverse-flow region.

Geodynamic risks of developing rockburst-hazardous deposits in the Far Eastern region

Geodynamic activity of the Earth’s crust depends on the parameters of the movement of lithospheric plates and stress fields, both inherited in aseismic areas and modified in seismic active ones. Geomechanical processes occur in rock mass under the influence of various natural (endogenous and exogenous) and man-made (anthropogenic) factors. The degree of influence of these factors on the change in the energy saturation of blocks of various ranks will depend on various factors. In the geological environment of natural and man-made systems, there are dynamic phenomena of various energy levels from acoustic noise (microseismic) to rockburst and mining-induced earthquakes, that is, there is always a geodynamic risk in the geological environment of natural and man-made systems, especially in mining ones. The conditions of the geodynamic risks occurrence at specific deposits are considered on the example of rockburst hazardous deposits in the Far Eastern region of the Russian Federation. The influence of natural seismic activity on the realization of mining-induced seismicity is shown.

Numerical Investigation on Vibration Performance of an Improved Switched Reluctance Machine with Double Auxiliary Slots

Considerable vibration and acoustic noise limit the further application of Switched Reluctance Machine (SRM) due to its structural characteristics and working principle. An improved SRM model with double auxiliary slots (DAS) was proposed, in which the direction of the magnetic line of force was adjusted, and the radial magnetic density in the air gap was reduced by changing the local tooth profiles of the stator and the rotor. The effects of initial rotor position and turn-on angle and turn-off angle on radial Electromagnetic Force (EMF) and maximum torque were investigated. The results indicate the radial EMF and torque increase significantly with the advancement of the turn-on angle or the delay of the turn-off angle. In the orthogonal experimental design, initial rotor position, turn-on angle, and turn-off angle were taken as the factors, and the optimal set of parameters that minimized radial EMF was determined according to a greater output torque. In contrast to conventional SRM, the radial EMF of the SRM with DAS significantly reduces when the optimal set is applied.

Analysis of electromagnetic torque for induction motors with a novel non-skewed rotor structure

Purpose Pulsating torques cause a number of problems in electrical machines, including mechanical vibrations, acoustic noise and the depreciation of mechanical equipment. In induction motors, the slot skewing method is an effective way to solve these issues; however, it has some drawbacks such as output torque drop, stray loss intensification due to inter-bar currents and iron loss increment. Besides, slot skewing may not be practical in higher-rated induction motors. In this regard, this paper introduces a modified non-skewed rotor (MNSR) structure as a possible alternative to the skewed designs. Design/methodology/approach The proposed structure includes a two-segmented rotor with an intermediate ring between the rotor parts that are mounted on the shaft with a relative shift angle. Detailed information about the idea and structure of the MNSR as well as its manufacturing aspects will be presented in the second section of the paper. First, the working principle of the proposed design is described via analytical equations to provide an insight into the concept. The shifting angle will then be calculated by analyzing the harmonic contents of the electromagnetic torque. Finally, the validity of the analytical method will be verified by developing three-dimensional finite element models. Findings It is demonstrated that by using the proposed rotor structure, the torque ripple has been reduced to a satisfactory level without significantly affecting the mean torque, unlike the skewing method. Furthermore, the new method could avoid the disadvantages of the skewing method while enhancing other motor characteristics such as iron loss. Also, the total volume of the MNSR is equal to the initial design, and the mass and material differences are also negligible. Originality/value In this paper, a MNSR is introduced as a possible alternative to the skewed patterns. The study mainly focused on electromagnetic torque profile characteristics, i.e. the mean torque enhancement and the ripple reduction. The MNSR structure can be used for general purposes and high-performance applications, especially where excellent torque characteristics are required.

Comparative Study of Electric Machines for Stirling Generator Application

The choice of a machine for an application and a given specification remains a complex problem. This will involve, for example, bringing together criteria such as: performance, space saving, economical, reliable, little acoustic noise and others. The best machine selection to fulfill all constraints is an important step for the project to be realized. This work focus on Stirling Engine based Generator and study all types of rotating machines that can be employed for maximum electric power production. Analytical electromagnetic models where developed for all types of rotating machines that satisfied minimum requirement for the project by solving Maxwell equations. The purpose is to develop the design model and combine electromagnetic and thermal study of the machines. Finite Element Method is used to compare the performances of the generators for the best choice. Results show that for applications not requiring bigger output power, the major criteria for the selection is the optimal magnetic induction created by the inducer in the stationary part of the machine. For application such as Stirling generators, permanent magnet (PM) machine satisfy many comparison criteria such as maximum power at low speed, torque density, high efficiency. Beyond exposing a selection method for a project, this work lay down a step-by-step method for engineers and scientists for the crucial stage of design and conception work

Prediction of Room Noise Caused by Vibration of High Power Elevator Traction Machine

Total simulation from vibration of elevator motor to noise at sitting room with anti-vibration measures is confirmed in design stage. This procedure also presents decrease of acoustic noise in sitting room. In this simulation, FEM calculates wave motion, such as wave phase, interference, diffraction and natural frequency mode of sitting room wall. These procedures yield the ration between vibration of elevator motor and acoustic noise in sitting-room.

Design and Experiment of a Deformable Bird-inspired UAV Perching Mechanism

Energy consumption and acoustic noise can be significantly reduced through perching in the sustained flights of small Unmanned Aerial Vehicles (UAVs). However, the existing flying perching robots lack good adaptability or loading capacity in unstructured environments. Aiming at solving these problems, a deformable UAV perching mechanism with strong adaptability and high loading capacity, which is inspired by the structure and movements of birds' feet, is presented in this paper. Three elastic toes, an inverted crank slider mechanism used to realize the opening and closing movements, and a gear mechanism used to deform between two configurations are included in this mechanism. With experiments on its performance towards different objects, Results show that it can perch on various objects reliably, and its payload is more than 15 times its weight. By integrating it with a quadcopter, it can perch on different types of targets in outdoor environments, such as tree branches, cables, eaves, and spherical lamps. In addition, the energy consumption of the UAV perching system when perching on objects can be reduced to 0.015 times that of hovering.