Modeling and optimization of a wide-band piezoelectric energy harvester for smart building structures

Piezoelectric energy harvesting refers to conversion of mechanical energy into usable electrical energy.In the modern connected world,wireless sensor nodes are scattered around the environment.These nodes are powered by batteries.Batteries require regular replacement,hence energy harvesters providing continuous autonomous power are used to power these sensor nodes.This work provides two different fixation modes for the resonant frequency for the two modes.Variation in geometric parameter and their effect on resonant frequency and output power have been analyzed.These harvesters capture a wide-band of ambient vibrations and convert them into usable electrical energy.To capture random ambient vibrations,the harvester used is a wide-band energy harvester based on conventional seesaw mechanism.The proposed structure operates on first two resonant frequencies in comparison to the conventional cantilever system working on first resonant frequency.Resonance frequency,as well as response to a varying input vibration frequency,is carried out,showing better performance of seesaw cantilever design.In this work,modeling of wide-band energy harvester with proof mass is being performed.Position of proof mass plays a key role in determining the resonant frequency of the harvester.Placing the proof mass near or away from fixed end results in increase and decrease in stress on the piezoelectric layer.Hence,to avoid the breaking of cantilever,the position of proof mass has been analyzed.

Modeling of High-frequency Electromagnetic Oscillation for DC Fault in MMC-HVDC Systems

DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system,strong electromagnetic oscillations with multiple frequencies occur during clearance transients.These oscillations will disturb the HVDC system’s protection and control systems.Therefore,this paper focuses on the modeling of these oscillations.First,an equivalent circuit for the MMC-based HVDC system is proposed,taking into account the parasitic capacitances of the system’s major components,such as DC reactors,connecting cables,and DC circuit breakers(DCCBs).Second,four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs,and the associated analytical equations for the oscillation frequencies are derived.Third,a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole(PTP)short-circuit test.Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz.The measured waveforms correspond well with simulated results,including the parasitic characteristics.Additionally,the relative errors between the simulated and measured frequencies are less than 5%.

Calculation of Wall Temperature for Aircraft Exhaust System with Considering Gas Radiation Heat Transfer

The coupled numerical simulation of flow field, solid temperature field, species concentration field and gas radiation transfer/ energy field based on statistical narrow-band correlated-k （SNBCK） model, is employed to accurately predict aerothermodynamic characteristic of aircraft exhaust system. A series of methods to increase computational efficiency and descend computational resources make it possible to finish the calculation in PC. The parameters of narrow-band model are evaluated by HITEMP line-by-line database. Three examples have proved the accuracy of using these methods to solve flow heat transfer coupled problem and radiation transfer/energy equation, which are the calculation of temperature distribution of water-cooling nozzle in rocket engine, the calculation of carbon dioxide absorptivity at 4.3 micron band, and the gas radiation heat transfer evaluation of the cylindrical furnace. Finally, the inner flaps temperature distribution of ejecting nozzle with floating outer flaps is computed, under high-altitude, high-speed and afterburning conditions. Two completely different air-inlet schemes of ejecting channel almost achieve the same effect in cooling inner flaps.