Sudden Load Increase Research Articles

Dynamic Behavior Modeling and Verification of Advanced Electrical-Generator Set Concept

Current development trends regarding mobile electrical-generator sets (EGSs) indicate that enhancement of efficiency is to be sought in means to operate the driving engine (either diesel or gasoline) continuously at its optimum speed. The engine-generator dynamics at a sudden load change (from low load to high load) remains a challenge in this regard. The dynamic behavior analysis presented here proves that the introduction of an energy storage element into the EGS with variable-engine-speed concept eliminates this drawback. This paper addresses the identification of the dynamic behavior of such variable-speed EGS systems and the problems encountered during a sudden increase of load (power and voltage drops).

Understanding the HIV coreceptor switch from a dynamical perspective.

BackgroundThe entry of HIV into its target cells is facilitated by the prior binding to the cell surface molecule CD4 and a secondary coreceptor, mostly the chemokine receptors CCR5 or CXCR4. In early infection CCR5-using viruses (R5 viruses) are mostly dominant while a receptor switch towards CXCR4 occurs in about 50% of the infected individuals (X4 viruses) which is associated with a progression of the disease. There are many hypotheses regarding the underlying dynamics without yet a conclusive understanding.ResultsWhile it is difficult to isolate key factors in vivo we have developed a minimal in silico model based on the approaches of Nowak and May to investigate the conditions under which the receptor switch occurs. The model allows to investigate the evolution of viral strains within a probabilistic framework along the three stages of disease from primary and latent infection to the onset of AIDS with a a sudden increase in viral load which goes along with the impairment of the immune response. The model is specifically applied to investigate the evolution of the viral quasispecies in terms of R5 and X4 viruses which directly translates into the composition of viral load and consequently the question of the coreceptor switch.ConclusionThe model can explain the coreceptor switch as a result of a dynamical change in the underlying environmental conditions in the host. The emergence of X4 strains does not necessarily result in the dominance of X4 viruses in viral load which is more likely to occur in the model after some time of chronic infection. A better understanding of the conditions leading to the coreceptor switch is especially of interest as CCR5 blockers have recently been licensed as drugs which suppress R5 viruses but do not seem to necessarily induce a coreceptor switch.

Rocky coast: geological constraints for hazard assessment

Abstract Geological hazard along rocky coasts is basically associated with processes of rapid sediment transfers. Massive transport of rock, regolith, sedimentary cover and soil occur episodically, accounting for cliff recession, sudden increase in solid load in short coastal rivers, and flank collapse of volcanic structures and rocky slopes. In geohazard terms, rocky coasts operate as transfer zones that deliver sediment directly from slopes to the coast and open sea at intermittent time intervals. Erosion and transport of material causes major physical changes and exposes coastal communities and human activity to hazard with potential damage to property and infrastructure, and loss of life. This paper focuses on geological processes that regulate rapid sediment transfers in rocky coastal areas, with examples drawn mostly from the Italian coasts. It is stressed that proper comprehension of coastal mass wasting hazard has to include marine and historical investigations. As a main delivery area, the submerged part of rocky coasts preserves reliable sedimentary records of past geological events occurring on land, which are often only partly detectable along subaerial rocky slopes and commonly reported in historical sources.

Super capacitors as electrical power buffers in military use

Abstract:The paper describes the possible sources of electrical energy for military purposes, dealswith the necessity of electrical energy accumulation and gives brief analysis of differenttypes of energy buffers, namely electrolytic capacitors, accumulators (batteries) andsupercapacitors. Dynamical properties of developed electrical energy generation setwith the variable speed-constant frequency technology have been analysed with respectto the effect of sudden extreme load increase. At low speeds the driving engine isoverloaded and generator is not able to deliver sufficient peak energy. Supercapacitor asthe controlled energy buffer in cooperation with respective DC/DC bi-directionalconverter and AC/DC/AC combined converter solves the problem. Results ofmeasurements and verification of reliable system operation proving the credibility ofperformed analyses and calculations are discussed in the paper conclusions.

Indentation fatigue behaviour of polycrystalline copper

Conventional indentation experiments have been widely used to extract the mechanical properties of materials from a load–depth curve. However, most of them are focused on static loading conditions. In the present study, the detailed indentation fatigue behaviour of polycrystalline copper under cyclic loading was studied experimentally. The experimental work emphasized indentation depth propagation behaviour such as the influence of overloading and underloading. It was shown that an increase in the maximum load can accelerate indentation depth propagation, while a decrease in the maximum load can retard indentation depth propagation. Further experiments showed that a sudden increase in maximum load after achieving a steady state followed by cycling at normal loading conditions can also delay indentation depth propagation, while a sudden drop in maximum load had a contrary effect. Those experimental phenomena implied that there were some similarities in the behaviour of indentation fatigue depth propagation and conventional fatigue crack propagation. In the following analysis, optical microscopy (OM) and scanning electron microscopy (SEM) were used to investigate the microstructures of the indentation cross-sections. The results revealed that the nucleation and accumulation of cavities to develop cracks was promised to be the main damage mechanism during the indentation fatigue.

Study of supply cut‐off and bearing geometric parameters on design of hybrid journal bearing

PurposeHybrid bearings have found increasing applications in various machines owing to their large number of favorable characteristics like high load carrying capacity, increased minimum fluid film thickness, long life and increased damping making them attractive for various applications such as turbo machinery, machine tool spindles, precision grinder spindles, etc. A careful design of such bearing for optimum performance has always been among the key issues of the researchers. The present work has been carried out to study the effect of bearing geometric parameters on performance of hybrid journal bearing and supply cut‐off behavior has also been studied for the improved performance.Design/methodology/approachThe generalized Reynold's equation governing the fluid flow in the clearance space between bearing and journal has been solved using finite element method to determine the pressure distribution, subsequently performance of hole‐entry hybrid journal bearing are computed. The journal centre equilibrium position for the given load is computed and the formulation is explained. The geometric parameters include aspect ratio, land width ratio, number of rows and number of holes per row. Further, performance of the bearing is computed with increasing the load, which induces negative pressure or the backpressure at the supply holes subsequently those are plugged to support the higher load.FindingsThe obtained results are presented in graphical form and logical conclusions are drawn and the modified configurations with reduced number of holes are suggested for higher load. It is observed that the bearing configuration with aspect ratio = 1.0 and land width ratio = 0.2 is best for high load support for low power requirement as less lubricant is required to be pumped in the bearing yet it provides sufficient fluid film thickness and lower values of maximum pressure. The load carrying capacity of the bearing can be further increased by plugging the holes on which backpressure is obtained for same bearing configuration. A feedback control with hybrid bearing system will sustain the sudden increase of load by shutting off the supply of the lubricant through supply hole where negative pressure is encountered.Originality/valueThe paper addresses the performance of non recessed hybrid journal bearings with wide range of geometric parameter. The results are quite useful for the bearing designer. The supply cut‐off is another aspect of originality of the paper as it provides the better load support.

Generators for independent power plants: performance and trends

Modern trends in designing generators for independent power plants require mass and volume reduction by means of increasing electromagnetic load. Conflicts arise with operational requirements regarding voltage drop limitation under sudden load increase. Practical methods to solve the problem at the present stage of generator design and manufacture are suggested. Several methods are outlined to limit generator reactances Open image in new window by selecting electromagnetic load levels, as well as choosing the geometry of stator teeth zone, of rotor poles, of damper winding. Besides, the problem of asynchronous motor starting from generators of independent power plants, working at no-load prior to the starting of the motor has been investigated in the article. Some additions to the standards for independent generators are proposed.

Achillodynie

Achilles tendinitis and posterior heel pain are caused by a wide variety of disorders. Understanding of the functional anatomy and pathomechanics of the Achilles tendon is essential for diagnosis and adequate therapy. Possible causes for heel pain include paratenonitis, tendinitis, tendinitis with partial rupture, insertional tendinitis, subachilles and retroachilles bursitis, Haglunds deformity and calcaneal spur. These chronic overuse symptoms may be triggered by pes plano valgus, lateral ankle instability, hyperlaxity, malalignement of the lower extremity, forefoot or hip disorders. In obese patients the deforming forces on the rear foot position and thereby overuse of the achillis tendon due to the overweight are increased. Lack of training with loss of muscular compensation or forefoot disorders also favor overuse problems. A sudden increase of load in an attempt of loosing weight by unaccustomed exercise, without giving the tissue adequate time for adaptation may lead to the start of the symptoms. Therapy of Achilles tendinitis is preferably conservative, in chronic cases operative therapy depends on the structures involved.

Analysis of the dynamic response improvement of a turbocharged diesel engine driven alternating current generating set

Abstract Reliability of electric supply systems is among the most required necessities of modern society. Turbocharged diesel engine driven alternating current generating sets are often used to prevent electric black outs and/or as prime electric energy suppliers. It is well known that turbocharged diesel engines suffer from an inadequate response to a sudden load increase, this being a consequence of the nature of the energy exchange between the engine and the turbocharger. The dynamic response of turbocharged diesel engines could be improved by electric assisting systems, either by direct energy supply with an integrated starter–generator–booster (ISG) mounted on the engine flywheel, or by an indirect energy supply with an electrically assisted turbocharger. An experimentally verified zero dimensional computer simulation method was used for the analysis of both types of electrical assistance. The paper offers an analysis of the interaction between a turbocharged diesel engine and different electric assisting systems, as well as the requirements for the supporting electric motors that could improve the dynamic response of a diesel engine while driving an AC generating set. When performance class compliance is a concern, it is evident that an integrated starter–generator–booster outperforms an electrically assisted turbocharger for the investigated generating set. However, the electric energy consumption and frequency recovery times are smaller when an electrically assisted turbocharger is applied.

An Analysis of Turbocharged Diesel Engine Dynamic Response Improvement by Electric Assisting Systems

It is well known that turbocharged diesel engines suffer from an inadequate response to sudden load increase, this being a consequence of the nature of the energy exchange between the engine and the turbocharger. The dynamic response of turbocharged diesel engines could be improved by electric assisting systems, either by direct energy supply with an integrated starter-generator-booster (ISG) mounted on the engine flywheel, or indirect energy supply with an electrically assisted turbocharger. A previously verified zero dimensional computer simulation method was used for the analysis of both types of electrical assistance. The credibility of the data presented is further assured by the experimentally determined characteristics of the electric motors used as input parameters of the simulation. The paper offers an analysis of the interaction between a turbocharged diesel engine operating under various load conditions and electric assisting systems, as well as the requirements for supporting electric motors suitable for the improvement of an engine’s dynamic response. It is evident that an electrically assisted turbocharger outperforms an integrated starter-generator-booster for vehicle application, however ISG is the preferred solution when instant power increase is demanded.

Transient elastohydrodynamic analysis of elliptical contacts. Part 1: Isothermal and Newtonian lubricant solution

Transient elastohydrodynamic lubrication of general elliptical point contacts was analysed in the present study based on multi-level techniques. Both entrainment directions along the major and minor axes of the contact ellipse were considered, together with transient load and speed impulses. In this study, only a Newtonian lubricant and isothermal conditions were assumed. The computing time required for a typical case took only approximately 2 h on a personal computer with a 2.8 GHz central processing unit. The predicted film thickness and the pressure were found to be mainly governed by the squeeze-film or separation actions. A sudden load increase resulted in an increase in the contact conjunction and a significant development of the squeeze-film action. Consequently the lubricant film thickness was increased initially around the inlet region and then moved along in the entraining direction towards the exit. A significant increase in the predicted central film thickness was observed, long after the load impulse had ceased. Such a process was found to be mainly governed by the time period of the impulse, and the time taken for the lubricant to move through the contact conjunction in the entraining direction. The speed impulse had similar effects. However, a sudden speed decrease was found to have negligible effect on the predicted film thickness, due to the powerful squeeze-film action.

Elastohydrodynamic lubrication analysis of hip implants with ultra high molecular weight polyethylene cups under transient conditions

The transient variation of both the load and speed experienced during walking in an elastohydrodynamic lubrication (EHL) analysis for artificial hip joints employing an ultra high molecular weight polyethylene (UHMWPE) acetabular cup against either a metallic or ceramic femoral head was considered in this study. A general numerical procedure to solve the transient EHL problem in spherical ball-in-socket coordinates, developed in a previous study by Jalali-Vahid and Jin in 2002, was applied under three specific conditions experienced during typical gait cycles, including speed reversal, a sudden load increase and a sudden load decrease. The predicted minimum film thickness was found to stay remarkably constant and similar to that prior to the change in either the load or the angular velocity, despite a large change in these operating conditions. This was attributed to the remarkably effective squeeze-film action of preserving and maintaining the lubricating film developed before the transient variations in either the load or speed. It is therefore possible to neglect the effect of these specific transient variations of load and speed under physiological walking conditions considered in the present study on the predicted film thickness in hip implants with UHMWPE cups.

Precision grip deficits in cerebellar disorders in man

Objective: To investigate the effect of a variety of cerebellar pathologies on a functional motor task (lifting an object in a precision grip). Methods: The study involved 8 patients with unilateral damage in the region of the posterior inferior cerebellar artery (PICA), 6 with damage in the region of the superior cerebellar artery (SUPCA), 12 patients with familiar or idiopathic cortical cerebellar degeneration, and 45 age-matched normal subjects. Subjects lifted an object of unpredictable load (internally guided task) or responded to a sudden load increase while holding the object steadily (externally guided task). Results: Damage to the dentate nucleus (SUPCA) or its afferent input (cerebellar atrophy) resulted in disruption of the close coordination normally seen between proximal muscles (lifting the object) and the fingers (gripping the object) during a self-paced lift. Both the SUPCA group and, more markedly, the atrophy group, showed exaggerated levels of grip force. All patients showed a normal rate of grip force development. Damage in the PICA region had no significant effect on any of the measured lifting parameters. All patient groups retained the ability to scale grip force to different object loads. The automatic grip force response to unexpected load increase of a hand held object showed normal latency and time course in all patient groups. The response was modulated by the rate of the load change. Response magnitude was exaggerated in the atrophy patients at all 3 rates tested. Conclusions: Disturbances associated with cerebellar disorders differed from those seen following damage to the basal ganglia, with no evidence of slowed rates of grip force development. Disruption of temporal coordination between the proximal muscles (lifting) and the fingers (gripping) in a lift was apparent, supporting the role of the cerebellum in coordinating the timing of multi-joint movement sequences. Exaggeration of grip force levels was found in association with damage to the dentate nucleus or, in particular, to its afferent input. This could support a role or the cerebellum in sensorimotor processing, but might also represent a failure to time correctly the duration of grip force generation.

An interfacial mechanical model for the analysis of earthquake

In this paper, the shear beam model for analysis of interface failure under joint action of anti-plane shearing and lateral compression and its principal behavior were briefly introduced. The calculation of energy release that is related to the strength of earthquake was presented by using the shear beam model. The sudden increase of load resulted from the "stress locking" at the interface layer in the reloading process was investigated. At the end of the paper, discussions on the mechanism of earthquake were given out.

Loading during the stance phase of walking in humans increases the extensor EMG amplitude but does not change the duration of the step cycle.

Prior work from mammals suggests that load experienced by extensor muscles of the hindlimbs (i.e. Duysens and Pearson 1980; Pearson and Collins 1993; Fouad and Pearson 1997) or cutaneous afferents from the plantar surface of the foot (Duysens and Pearson 1976; Guertin et al. 1995) enhances activity in extensor muscles during the stance phase, and delays the onset of flexor activity associated with the swing phase. The presumed functional significance of this phenomenon is that extensor activity of the supporting limb during walking can: (a) reinforce the supporting function in proportion to the load experienced, and (b) prolong the stance phase until unloading of the limb has occurred. Whether a similar functional role exists for load-sensitive afferents during walking in the human is unknown. In this study, the effect of adding or removing a substantial load (30% of body weight) at the centre of mass was studied in healthy adult human subjects. Loads were applied near the centre of mass to avoid the need for postural adjustments which might confound the interpretation of the results. Subjects walked on a treadmill with either: (a) a sustained increase or decrease in load, or (b) a sudden unexpected increase or decrease in load. In general, subjects responded to the changes in load by changing the amplitude of the extensor electromyographic (EMG) bursts. For example, with sudden unexpected additions in load, the average increase in amplitude was 40% for the soleus across the stance phase, and 134% for the quadriceps during the early part of the stance phase. Extensor EMGs increased with both sustained and sudden increases in load. Extensor EMG durations also increased (average increase in duration of 4% for soleus with sudden loading, and 7% for sustained loading). Cycle duration hardly changed (average increase of 0.5% with both sudden and sustained loading). These results differ from those of infants subjected to a similar perturbation during supported walking. A large change in timing (i.e. an increase in the duration of the stance phase by 30% and the step cycle by 28%) was seen in the infants, with no change in the amplitude of the EMG burst (Yang et al. 1998). These results suggest that the central nervous system can control the timing and amplitude of extensor EMG activity in response to loading independently. Maturation of the two components most likely occurs independently. In the adult, independent control of the two components may provide greater flexibility of the response.

Optimal dynamic load shedding policy for generation load imbalances including characteristics of loads

Modern electrical power systems are highly interconnected and heavily loaded. An emergency may occur as a result of a sudden increase in system load or unexpected partial or total outage of a generator. This paper presents an optimal dynamic load shedding policy for generation load imbalances. The effects of voltage and frequency characteristics of system loads, transmission lines, transformers and reactive power compensator are reported. Equality and inequality system constraints are also considered in the formulation of this nonlinear programming problem. The further effects of system average time constant, speed drop factor, load reduction ratio (load frequency sensitivity factor), system inertia, load shedding and spinning reserve are included. Furthermore a simple load distribution factor is considered in this algorithm. Results of the unified power system of lower Egypt have been presented to validate the algorithm and show its effectiveness. Copyright © 1999 John Wiley & Sons, Ltd.

Perturbation of precision grip in Friedreich's ataxia and late-onset cerebellar ataxia.

Perturbations of precision grip were tested in 7 patients with Friedreich's ataxia (FA) and 11 patients with late-onset cerebellar ataxia (CA). Subjects were instructed to hold a small compressible manipulandum between thumb and index finger and to resist any perturbation of maintained finger position. A sudden increase of load induced a displacement of fingers until this was stopped by subjects' active intervention. The amount of initial displacement emerged as a highly sensitive parameter to differentiate the clinical subgroups: Responses in FA patients were missing or massively delayed, whereas displacements in CA patients were normal or only moderately abnormal. This discrimination of impaired hand function in FA and CA patients has not been possible by using only tasks of isometric grip force control. We concluded that our task relies more on intact sensory afferents, which are known to be impaired in FA, than on cerebellar function. In a second task the stiffness of the maintained grip was determined. On the average, preresponse stiffness was lower in FA patients as compared with CA patients and normal controls. However, stiffness appeared to be an independent parameter that did not influence the amount of displacement in the perturbation task.

Cardiovascular Performance in Embolism

Summary The hemodynamic consequences of acute obstruction of the pulmonary arterial tree result from physiologic changes in the pulmonary circulation. Normal mean pulmonary arterial pressure, about 12 to 15 mm Hg, is one-sixth to one-eighth the systemic pressure. Acute reduction in pulmonary vascular cross-sectional area creates a sudden increase in output load on the right heart chambers resulting in right heart failure. In the absence of preexisting cardiovascular disease, right ventricular decompensation sets in at a mean pressure in the pulmonary artery of approximately 40 mm Hg. At this point, performance of the thin-walled right ventricle deteriorates dramatically. Support of the pulmonary circulation begins with volume resuscitation and inotropic support for the right ventricle. Right coronary perfusion should also be optimized through support of aortic root pressure. Afterload stress to the right ventricle may be reduced with oxygen therapy. There are no other reliable selective pulmonary vasodilators available at this time. The impact of pulmonary embolization and therapy supportive of right ventricular function have recently been studied through assessment of incremental resistance in pulmonary vascular pressure flow curves. The utility of agents such as norepinephrine was confirmed in this model that revealed improved right ventricular function without deterioration in pulmonary vascular bed response. More recent studies utilizing thrombolytic therapy also suggest improved response of the right ventricle and pulmonary vascular bed with immediate administration following pulmonary embolic events. Finally, there are few data describing the utility of different anesthetic regimens in the management of patients during acute cardiopulmonary compromise secondary to pulmonary thromboembolism. Based on the limited data available, a narcotic technique with supplementation using nitrous oxide in inspired concentrations that allows adequate oxygenation can be recommended.

Influences of object weight and instruction on grip force adjustments

This study investigated the influence of object weight and instructions on grip force responses in humans. Using a precision grip, subjects lifted a small instrumented test object to a predetermined height. Prior to each set of 40 trials, subjects were verbally instructed to either "hold" or "let go" of the object in response to any change in weight. Unpredictably on some trials (less than 20%), a sudden sustained increase (load) or decrease (unload) in vertical load was applied to the object. Grip responses to these induced weight changes were evaluated by measuring grip force, object position, and associated electromyographic (EMG) activity. Grip force changes for a load were over three times greater than those for an unload. Such asymmetry may reflect everyday grasp and manipulation in a gravity-influenced world. Grip force adjustments to loads following "hold" instructions were on the average somewhat larger than those following "let go" instructions, but there was no influence of instructions on responses to unloads. These findings contrast with more robust influences of verbal instruction on automatic postural and proximal upper limb responses and also may suggest that grip force adjustments are influenced to a greater extent by intrinsic task variables than by extrinsic volitional intent. Such organization appears tailored to functional task requirements in natural environmental contexts.

TRANSIENT PERFORMANCE OF A 5-PH BRUSHLESS DC GENERATOR

The paper studies the transient performance of a 28 V, 14 KW brushless 5-phase DC genertor, with its associated automatic voltage regulator (AVR). The study describes the performance of the generator when subjected to sudden increase and sudden decrQase in load as well as the case when the generator is connected to a dynamic load which may regenerate power into the generator. A mathematical model is developed for the system to enable these studies to becarried out. Modelling of the generator/rectifier and exciter/rectifier arrangements is achieved using tensor methods to define the changing conduction pattern of the diodes in the rectifier bridges owing to the local ocnditions and the changing magnitudes of the armature voltages. The AVR is modelled in terms of the actual configuration, rather than by the more familiar transfer function approach, and the resulting differential equations are integrated together with those for the generator and the exciter. Experimental results are presented in excellent agreement with those from the computer predictions, thereby validating the model and illustrating its use as a valuable tool for engineers involved in the design of control systems containing electrical machines.