Material microstructure topology optimization of piezoelectric composite beam under initial disturbance for vibration suppression

This study proposes a material microstructure topology optimization model for a piezoelectric composite beam subject to initial disturbance. The optimization model is built through the Solid Isotropic Material with Penalization interpolation subject to the material volume fraction on the microlevel. And the objective function is to minimize the time integral about local structural response. By introducing the Lyapunov second equation, this time integral is simplified and does not need any numerical integration technique. It can also be used to measure the global vibration response instead of short time gap. Besides, different objectives such as a regional structural response can also be obtained by only changing the weight matrix form. And the sensitivity of the objective function with respect to the design variables are also deduced by solving the Lyapunov equation. A bidirectional evolutionary structural optimization algorithm is used to acquire the optimal results. Four numerical examples including multiphase material microstructure topology optimization verify the developed method that can effectively suppress local structural vibration level and obtain lighter structure.

How the excitation system parameters and the generator protection settings affect the reliability of electricity delivery from distributed generation facilities

The paper analyzes the causes of disruptions in electricity delivery to critical users in power areas that operate distributed generation facilities (DG), hereinafter referred to as DG areas. Statistics is shown to be affected by the types of the excitation systems (ES) chosen for the DG generators, as well as by the relay protection (RP) settings as configured when designing the facilities. The paper dwells upon the specifications of the ES’s used in low-power generators, their effective applications, as well as the consequences of disturbances in the power area or in an external grid. It is proven herein that RP settings as configured by generator manufacturers are often suboptimal, which jeopardizes their further operation, prevents the operator from aligning these settings to those of the grid RPs, and results in unnecessary disconnections. The paper also details upon calculating the parameters of DG-enabled grids in the common software suits, as well as on how to make a list of effective contingencies. It further gives recommendations on grouping the calculation problems by initial disturbance to optimize the number of projected scenarios. The authors prove that ES selection and generator RP configurations must be appropriate if DG facilities are to deliver electricity reliably.

Study on Initial Disturbance of Airborne Missile’s Horizontal Backward Derailment under Continuous Gust

This paper studies the effect of continuous gusts on the initial disturbance of the airborne missile’s horizontal backward derailment on large transport aircraft. The longitudinal fluctuation of the airborne launching platform under continuous gust was obtained with different calculation methods, and the finite element model of the derailing process was established then verified by experiments. Finally, combined with the longitudinal fluctuation of the launching platform and the finite element model of the missile and launching platform, the influence of platform fluctuation on separation time, missile speed, pitch angle, and descending distance while derailing was studied and analyzed. It is found that the longitudinal fluctuation of the launching platform is similar to that of the gust but lags behind, and the missiles under the fluctuating platform have longer separation time, lower derailing speed, and greater derailing pitch angle and descending distance.

Evaluation of disturbance effect on geese caused by an approaching unmanned aerial vehicle

SummaryUnmanned aerial vehicles (UAVs) are useful tools in ornithological studies. Importantly, though, UAV-caused disturbance has been noted to vary among species. This study evaluated guidelines for UAVs as a tool for researching geese. Twenty-four flocks of foraging geese were approached at an altitude of 50–100 m with a quadcopter UAV and disturbance effects were analysed across different horizontal distances between the UAV and the flocks. Geese were increasingly disturbed when approached by a UAV, with birds showing increased vigilance behaviour within approximately 300 m. Increasing UAV flight altitude as well as increasing take-off distance from the flocks both decreased the risk of bird flocks flushing. In conclusion, when monitoring geese using UAVs, flight altitudes of 100 m and take-off distances of ideally ∼500 m are recommended, to minimise initial disturbance and reducing the risk of birds flushing.

Asymmetry of jet streams formed under nonlinear geostrophic adjustment in shallow water

The process of geostrophic adjustment in a rotating layer of shallow water is considered. For initial distributions of the fluid depth in the form of a step and a localized rectangle, this process results in the formation of an isolated jet stream and a system of two counter jet streams, respectively. In this paper, the features of these flows structure, related to the nonlinearity of the adjustment process, are studied. The main feature for an isolated jet stream is the horizontal asymmetry of its velocity profile. For a system of two opposing flows, a mirror asymmetry is characteristic, which is caused by the dependence on the sign of the amplitude of the initial disturbance of depth. The velocity of flows with a negative sign (depression) always exceeds the velocity with a positive sign (elevation).

Neural effects of elevated CO2 in fish may be amplified by a vicious cycle

Lay summaries: The altered behaviours of fish exposed to elevated CO2 have been linked to changes in ion gradients and neurotransmitter function. To explain how relatively small changes in ion concentrations could have such profound neural effects, we propose that a vicious cycle can be triggered that amplifies the initial disturbance.