Pulsed Load Conditions Research Articles

Optimal transient power sharing method for shipboard MVDC System based on segmented variable step dynamic programming

Supplying power for large pulsed power load with shipboard medium voltage direct current integrated power system has continued to be a challenge. The energy storage device configured in the system can effectively mitigate the power impact on grid and gas turbine gensets, but it also complicates the system operation, requiring advanced power sharing and control strategies for support. In this paper, the control framework of system configured with hybrid energy storage is presented, the objective function to quantify transient power disturbance on gas turbine genset is established, and the segmented variable step dynamic programming method for system transient power sharing is innovatively proposed and employed to derive the optimal transient power-sharing scheme for the rectangular and triangular large pulsed power load conditions. Compared with the conventional approach through MATLAB/Simulink simulation, the scheme derived from segmented variable step dynamic programming demonstrates enhanced utilization of the transient power compensation capability of hybrid energy storage, and leads to a reduction in the power regulation pressure on gas turbine gensets. In the assumption of two typical operating processes, as the results of the power impacts，the transient regulation rate of the genset rotor is reduced from 10.4 % to 9.9 % and from 13.7 % to 8.6 %, respectively, the fatigue damage of shaft system is decreased by 53 % and 94.4 %, respectively, and the maximum inlet relative temperature of gas generator turbine is reduced by 0.015 and 0.139, respectively.

Hybrid energy storage power allocation strategy based on parameter-optimized VMD algorithm for marine micro gas turbine power system

The power system onboard ships is typically a low-inertia, small-capacity isolated grid that is highly susceptible to system disturbances and instability, especially when connected to high power pulse loads. To mitigate power fluctuations and ensure stable operation, a hybrid energy storage system (HESS), which comprises the battery system and flywheel energy storage devices, has emerged as a promising solution. This paper explores the control strategy and coordinated operation of marine gas turbine power generation systems operating under pulse load conditions and presents a novel hybrid energy storage power allocation strategy based on variational mode decomposition (VMD). Specifically, we propose to implement parameter optimization of VMD using an artificial hummingbird algorithm (AHA), which enables effective primary allocation of hybrid energy storage power. To achieve secondary power allocation, we design two fuzzy controllers to optimize the state of charge (SOC) of battery system and speed of flywheel device. To evaluate the feasibility and effectiveness of the proposed control strategy, we establish a theoretical model of a shipboard micro gas turbine (MGT) direct current (DC) power system, which includes an MGT, generator, HESS, and pulse power load. Our simulation results demonstrate that the artificial hummingbird algorithm outperforms the particle swarm algorithm concerning search speed and calculation accuracy for parameter optimization of variational mode decomposition. Moreover, the proposed parameter-optimized VMD method can adaptively decompose pulse load power fluctuations and achieve optimal allocation of the flywheel and battery power in the HESS. Finally, the parallel fuzzy controller design effectively optimizes the operation ranges of the flywheel device and battery system, prevents over-charging and over-discharging of energy storage equipment, ensures that the SOC of energy storage equipment remains within a fixed interval, and reduces frequent and high-power charging and discharging of batteries.

Hierarchical control of hybrid energy storage system in shipboard gas turbine power system with multiple pulsed power loads

Transient power fluctuations may occur in shipboard DC microgrids when switching a pulsed power load (PPL). However, shipboard power systems (SPSs) are isolated power grids with relatively low inertia and capacity, making them unable to respond immediately to sudden changes in pulsed loads, thereby resulting in considerable disturbances and even instability of the system. To mitigate such disturbances effectively, it is recommended to introduce energy storage devices to SPSs. In order to better leverage the buffering characteristics of energy storage devices, this paper establishes a simulation model of the SPS, which includes a micro gas turbine generator, a hybrid energy storage system (HESS), multiple PPLs and an energy management system (EMS). The HESS comprises a battery and a flywheel. Furthermore, a hierarchical coordinated control strategy for HESS in shipboard DC microgrids under multiple pulsed load conditions is proposed, which includes both an upper-layer control and a lower-layer control. The upper layer makes logical judgments through voltage difference and selects the appropriate energy storage mode for power supply. The lower layer adopts a series fuzzy logic control. To validate the effectiveness of the proposed control strategy, two scenarios of transient power mutation and total power demand exceeding the rated power of the generator were simulated by connecting different PPLs to the DC bus at different times. The results indicate that the control strategy effectively realizes the coordinated operation of HESS and gas turbine, as well as power allocation between flywheel and battery within HESS. Moreover, it reduces the frequency of charging and discharging of battery, improves battery life, and prevents the generator from running beyond the rated power.

Analogy between crack initiation due to dynamic pulse load and mass-spring system failure: fracture delay effect

In this short communication application of the incubation time fracture criterion (ITFC) for analysis of crack initiation under short pulse loading conditions is discussed. It is shown that the ITFC can be used to predict and investigate one of the key effects of the dynamic fracture – the fracture delay. The fracture delay phenomenon manifests itself when fracture occurs at a drop stage of local stress fields. In addition to this an analogy between crack instability under pulse loads and linear oscillator failure is drawn in the work. It is shown that the fracture process exhibits inertia when intensive loads are applied and a virtual oscillator with a particular eigen frequency can be formally attributed to a cracked sample. The applied theoretical models are calibrated against experimental data on crack onset under pulse loading conditions.

Experimental investigation of high frequency pulse loading on fatigue crack growth in 5052-H32 series aluminum

In the marine industry, designers utilize 5052-H32 marine grade series aluminum for its strength to weight ratio, and the ability of this series to resist marine corrosive environments. During the operating lifetime of a marine vessel, it experiences constant and variable amplitude loading conditions from the sea environment, plus overloads/underloads in the form of high frequency pulses. These high frequency pulses can influence the fatigue crack growth behavior of the aluminum structure. Foundational models like Wheeler and Willenborg have previously been used to predict effects of underloads/overloads on fatigue crack growth, but have proven to be inadequate for all high frequency pulse loading conditions. In this paper, we coupled observations of the crack growth path obtained using an optical microscope with detailed measurements of surface strain fields using Digital Image Correlation (DIC) to elucidate the effects resulting from these high frequency pulses. An experimental test matrix was developed for applying pulses of varying amplitude and frequency to gain fundamental understanding of the characteristics of the high frequency pulses on crack growth behavior. Experimental results indicated there is a novel crack kinking behavior which results in retardation of the fatigue crack growth. Using DIC, we identified changes in the plastic zone ahead of the crack tip that mimic a hard inclusion, affecting not only the crack path, but also the crack opening displacements and subsequent crack growth rates. This work provides a foundation for understanding effects of high frequency pulses on crack growth to enable future development of a model incorporating the effects of the plastic zone on the growth mechanisms.

Novel inverted fin configurations for enhancing the thermal performance of PCM based thermal control unit: A numerical study

• Novel fin configuration inside PCM is investigated to reduce the peak temperature. • Heat load: 11 W; Operating Time: 10, 12 min out of 100 min cycle. • Heating time, % mass, number, shape & cross-section of fins are studied numerically. • Temperature drop of 29 K is achieved through novel star inverted frustum fin. In the present study, the phase change material (PCM) based thermal control unit (TCU) has been analyzed to control the peak temperature (T pk ) of an electronic device. The pulsed heat load conditions are considered as an input to TCU. The PCM's low thermal conductivity is overcome by introducing the novel metallic fins, which are less complicated and easy to manufacture. Various parameters associated with the fin geometry are analyzed to identify fins' efficacy, namely, number of fins, % mass of fins, shape of fins, and cross-section of fins. Eight distinct fin configurations are studied viz. Prism – triangle and star; Frustum – triangle and star; Novel inverted frustum – circular, square, triangular, and star. The novel inverted fins have attained the highest area augmentation ratio with the lowest T pk of 331.41 K at 25% mass of fins than other configurations. An overall reduction in T pk is achieved around 9%, with novel inverted fins showing their significance inside PCM. The heating and cooling cycle ratio is 0.141, highest for the star inverted frustum at 25% mass of fin, suggesting that it can attain an initial temperature of 313 K way faster than other configurations.

Research of ANSYS Autodyn capabilities in evaluating the landmine blast resistance of specialized armored vehicles

The object of research is the processes of pulse explosive loading in an explicit formulation for simulation of complex nonlinear dynamics of solids, gases, and their interactions. One of the most problematic areas of modern studies of nonlinear dynamic loads of materials using a numerical analysis is that such studies usually do not take into account the characteristic transition of the stationary deformation zone of the loaded material to the unsteady one and the front pressure and shockwave velocity variation by time. The work is aimed at developing a mathematical model of a pulsed load of materials by a shockwave, developing a mathematical apparatus for calculating the parameters of a shockwave, creating analytical dependences of the interaction of a shockwave with a loaded surface. A study of dynamic explosive loading using software based on an explicit method for solving the equations of continuum mechanics is proposed. In this work, the stress-state equation at a point of the material under pulsed load conditions was further developed, methods for determining the principal stresses and the invariant of the stress tensor, taking into account the pulsed nature of the load, were established. The character of the behavior of the shockwave formed as a result of the detonation of the explosive has been established. Analytical dependences of the interaction of a shockwave with a loaded surface are compiled. A mathematical apparatus has been developed for calculating such parameters of the shockwave as the detonation front pressure and its change in time and the velocity of the shockwave at the moment when it reaches the surface. Mathematical dependences have been developed and proposed, which, in contrast to the existing ones, make it possible to determine the current values of stresses and strains passing through the points of the actual stress curve, as well as the intensity of stresses and strains under pulse loading of metals. On the basis of theoretical and experimental studies of the parameters of body material deformation under the action of explosive loading, the mechanisms of destruction of the KrAZ «Shrek» and KrAZ «Fiona» (Ukraine) specialized armored vehicles body were clarified to establish the compliance of the declared landmine resistance of vehicles with the STANAG 4569 standardization agreement.

Analysis of Operation Characteristics of a Diesel Generator Set with Constant-Power Pulsed Load

To improve the power quality of a diesel generator set with a pulsed load in a microgrid, this paper studied the operation characteristics of the system and proposed pulsed load conditions for an actual project based on test data. For a low average pulse power and a high peak power, a new mathematical model of the pulsed load in different operation modes was proposed. Then, a simulation model of the microgrid was established in MATLAB/Simulink, and the operation of the system was studied considering changes in various pulsed load parameters (the peak power Pk, output duty cycle D and switching period Ts). It was verified by tests that the simulation model is effective and can reflect the operation of the system. Based on the simulation model, the operation characteristics of the system with a bivariate pulsed load were studied, and qualification conditions for the diesel generator set in an actual project were proposed.

Comparison of Biomechanical Properties and Hemodynamics of Three Different Vena Cava Filters

The interaction mechanism of three types of vena cava filters (VCFs) with blood vessels and their influence on the bloodstream during the process of implantation are investigated by finite element method and computational fluid dynamics. The VCF models are set up with Solidworks software. Using ABAQUS software, we simulate the working conditions of the VCFs in the vessel to analyze the stress distribution and radial support stiffness of the vessel wall and the filter surface. Using FLUENT software, we simulate and analyze the velocity, pressure and shear stress distributions of blood flow when the VCFs are at their working conditions. For the retrievable VCF (R-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest, and the support stiffness is the lowest. For the permanent VCF (P-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest, and the support stiffness is the highest. Because of the structure of scaffolding support units and the tendency to form intimal hyperplasia on their support units, both the convertible VCF (C-VCF) and the P-VCF can embed their support units in the hyperplasia skin. This effectively prevents them from harming blood veins through filter damage at the pulse load conditions. As the biomechanical property of the C-VCF is between those of the R-VCF and the P-VCF, it has smaller obstacle to blood flow after conversion and has some fragmentation effects on the thrombus. The results show that different types of VCFs differ in their biomechanical and hemodynamic properties after implantation. Therefore, the simulative analysis can provide a reference basis for filter design and clinical decision making.

Ceramic breeder pebble bed packing stability under cyclic loads

Considering the optimization of blanket performance, it is desired that the bed morphology and packing state during reactor operation are stable and predictable. Both experimental and numerical work are performed to explore the stability of pebble beds, in particular under pulsed loading conditions. Uniaxial compaction tests have been performed for both KIT’s Li4SiO4 and NFRI’s Li2TiO3 pebble beds at elevated temperatures (up to 750°C) under cyclic loads (up to 6MPa). The obtained data shows the stress-strain loop initially moves towards the larger strain and nearly saturates after a certain number of cyclic loading cycles. The characterized FEM CAP material models for a Li4SiO4 pebble bed with an edge-on configuration are used to simulate the thermomechanical behavior of pebble bed under ITER pulsed operations. Simulation results have shown the cyclic variation of temperature/stress/strain/gap and also the same saturation trend with experiments under cyclic loads. Therefore, it is feasible for pebble bed to maintain its packing stability during operation when disregarding pebbles’ breakage and irradiation.

Modeling Escherichia coli removal in constructed wetlands under pulse loading

Manure-borne pathogens are a threat to water quality and have resulted in disease outbreaks globally. Land application of livestock manure to croplands may result in pathogen transport through surface runoff and tile drains, eventually entering water bodies such as rivers and wetlands. The goal of this study was to develop a robust model for estimating the pathogen removal in surface flow wetlands under pulse loading conditions. A new modeling approach was used to describe Escherichia coli removal in pulse-loaded constructed wetlands using adaptive neuro-fuzzy inference systems (ANFIS). Several ANFIS models were developed and validated using experimental data under pulse loading over two seasons (winter and summer). In addition to ANFIS, a mechanistic fecal coliform removal model was validated using the same sets of experimental data. The results showed that the ANFIS model significantly improved the ability to describe the dynamics of E. coli removal under pulse loading. The mechanistic model performed poorly as demonstrated by lower coefficient of determination and higher root mean squared error compared to the ANFIS models. The E. coli concentrations corresponding to the inflection points on the tracer study were keys to improving the predictability of the E. coli removal model.

PLASTIC INSTABILITY ANALYSIS OF 5052 ALUMINUM SHEETS IN MAGNETIC DYNAMIC TENSION PROCESS

In order to reveal the hyperplasticity mechanism of electromagnetic forming (EMF), the plastic instability mechanisms and formation behaviors of 5052 aluminum alloy sheets in pulsed magnetic tension process were investigated by theoretical analysis and microanalysis. Results show that inertia force plays an important role in dynamic forming, which has the suppression effect on structural instability and thus improves the formability of sheet and spreads instability. The nature of dynamic formation is much similar with that of quasi-static formation and no special formation structures arise in dynamic process for 5052 aluminum alloy sheets. The formation mechanism of both processes is dislocation slip mechanism. For quasi-static formation, the dislocations show a uniform single-slip pattern, fracture combined with dislocation tangling and climbing. While for dynamic formation, dislocation system tends to more slips, large areas showing clear cross-slip structures. The dislocation bands are narrower and much denser than those shown in the quasi-static process, and a much more uniform dislocation configuration is also exhibited after pulsed magnetic loadings. The characteristics of multi-slips and uniform effect of dislocations under pulsed magnetic loading conditions will result in much higher plasticity and strength of materials.

Plane problem of the impact of several shock pulses on a viscoelastic plate floating on a fluid surface

The impact of a series of sequential and simultaneous pulse loads on the deflection and stress of ice covering a body of water is considered. The effects of the water-body depth, plate thickness, pulse loading conditions, and interpulse interval on the height of the flexural-gravity wave and plate bending stress are analyzed.

Integrated modelling of conventional pollutants and organic contaminant fate in rivers: a microcosm study

A new conceptual dynamic integrated model is presented which can be used to describe both conventional pollutants and organic contaminant fate in rivers. The model is designed to assess the short-term fate of organic contaminants in two compartments (bulk water and benthic sediment), taking into account the effect of nutrient dynamics. The biodegradation submodel was refined using a microcosm (artificial river) study and Linear Alkylbenzene Sulphonate (LAS) as an example. Based on data generated during the microcosm study, the model was calibrated and validated in both steady state (continuous constant load) and dynamic (pulse load) conditions. The results show that the simulated data set agrees well with the measured data set. Furthermore, thorough investigation of the model output sensitivity to the model inputs was made, and the results show that the fate of LAS is sensitive to the following model input variables: ammonia nitrogen, dissolved oxygen, microbial biomass and readily biodegradable soluble COD, and the model parameters mainly related to the biodegradation submodel. The model provides good understanding of the interaction between conventional pollutants and organic contaminants fate in rivers.

Energy balance in the crack growth initiation under pulsed-load conditions

1. ENERGY APPROACHTO THE FRACTURE PROBLEMThe classical approach to fracture mechanics goingback to Griffith is based on the statement that a crackpropagates if this process leads to a decrease in the totalenergy e of a system. For a plate of unit thickness, thecrack-growth conditions can be written as . (1) Griffith initially interpreted the quantity 2 γ as thesurface energy, because it represented the specific work(per unit area) expended to form a new surface. Irwinand Orowan showed that this quantity should be inter-preted as the total work (including the plastic one) inthe fracture zone. This work can be taken as the resis-tance to a certain dissipative process proceeding in asmall region near the crack tip. The study of this char-acteristic includes the determination of its physical ori-gin (different for different classes of materials) and itsmeasurement.For the fracture near the crack tip loaded by mode I,criterion (1) is equivalent to the criterion for the criticalstress-intensity factor K

Power and life extension of battery-ultracapacitor hybrids

The performance of a battery-ultracapacitor hybrid power source under pulsed load conditions is analytically described using simplified models. We show that peak power can be greatly enhanced, internal losses can be considerably reduced, and that discharge life of the battery is extended. Greatest benefits are seen when the load pulse rate is higher than the system eigenfrequency and when the pulse duty is small. Actual benefits are substantial; adding a 23 F ultracapacitor bank (3 /spl times/ 7 PC10 ultracapacitors) in parallel with a typical Li-ion battery of 7.2 V and 1.35 A hr capacity can boost the peak power capacity by 5 times and reduce the power loss by 74%, while minimally impacting system volume and weight, for pulsed loads of 5 A, 1 Hz repetition rate, and 10% duty.

Investigation of time-dependent characteristics of materials and micromechanisms of plastic deformation on a submicron scale by a new pulse indentation technique

A new pulse technique is proposed to investigate dynamics and micromechanisms of plastic deformations of materials underneath the indenter during microindentation. It is established that the process of indenter penetration under pulse loading conditions can be described by several distinct stages (as many as four in some cases) differing in kinetics and activation parameters. In each investigated material, the first stage was characterized by a high strain rate (≥103 s−1) and the high contact stresses (dynamic hardness), which exceeded static hardness by factor of 5–10. Typical values of activation volumes during the first stage were of the order of 10−30 m3, i.e. close to the volume occupied by an atom (ion) in a lattice. During the second and the subsequent stages, the activation volume in ionic crystals increased up to about 10−28 m3,( i.e. 10b 3, where b is Burger's vector of glide dislocations). Dynamics of initial stages of the indenter penetration was, therefore, determined by elastic and subsequently by plastic deformation, which is carried out by non-equilibrium point defects (most likely by interstitials or crowdions). A relative role of point defects in the process of mass transfer underneath the indenter and its contribution to microhardness is estimated. In soft materials (NaCl, LiF, Pb) during long indentation times (≥1 s) contribution of point defects can be estimated as more than 10%, and in the case of hard materials (Si, amorphous alloys) became closer to 100%. Dynamics of the final stages of the indenter penetration in soft crystals were governed by the dislocation creep. In all investigated materials for short indentation times (≪1 s) plastic deformation underneath the indenter occurred predominantly via generation and motion of interstitials and their clusters containing a few atoms.

Fracture of Polymethylmethacrylate under Pulse Loading Conditions

Crack propagation in polymethylmethacrylate has been investigated experimentally under shock loading conditions generated by a pulse magnetic field. Using microstructural investigations, dynamic fracture surfaces of polymethylmethacrylate were analyzed and compared depending on the distance from the notch tip. A diagram of various fracture types depending on the pulse loading duration has been constructed.

A hybrid power source for pulse power applications

Abstract Portable 12 V power supplies are used extensively for communications and power tool applications. These devices demand fast response times of the power supply. Fuel cells are generally best suited to continuous power applications and require an initial warm-up period, although they offer the prospect of increased operational duration over a battery for a given weight of portable system. This paper investigates the combination of specific energy performance from the fuel cell system with the specific power and response time of the battery. Two separate hybrid systems have been developed and tested; a planar, 20-cell, polymer electrolyte membrane fuel cell (PEMFC) stack together with either a lead–acid or nickel/cadmium battery; and a conventional 20-cell, bipolar, PEMFC stack. Both systems have been tested under pulse-load conditions at temperatures between −20°C and +40°C, and for comparison, the individual components have undergone similar tests. The hybrid systems have successfully operated continuously for several weeks under load profiles that the fuel cell alone could not sustain.

Effect of carbon ion bombardment and surface oxidation on the twinning rate of single-crystal bismuth

A study is made of the change in the dependences of the normal velocity of twinning boundaries on the magnitude of shear stresses in the twinning plane vn=vn(τ) in bismuth crystals owing to ion-cluster doping and oxidation of the irradiated surface. Irradiation was by 25 keV carbonions at a dose of 1017 ion/cm2. Twinning of the crystals took place under pulsed loading conditions with pulse durations of 10−5−10−4 s and stress amplitudes of (0.2–2.0)×103 g/mm3. Carbon ion bombardment of single-crystal bismuth causes a shift in the vn=vn(τ) curve toward lower stresses. An oxide film slows down the motion of twinning dislocations.