Behavior of Short Lateral Dead Ends on Pipeline Transients: A Lumped Parameter Model and an Analytical Solution

2005 ◽  
Vol 127 (3) ◽  
pp. 529-535 ◽  
Author(s):  
Xiao-Jian Wang ◽  
Martin F. Lambert ◽  
Angus R. Simpson
Keyword(s):  
Analytical Solution ◽  
Side Branch ◽  
Relative Volume ◽  
Lumped Parameter Model ◽  
Efficient Manner ◽  
Lumped Parameter ◽  
Dead End ◽  
Fluid Transients ◽  
Harmonic Components ◽  
The Impact

By integrating the continuity equation over a short lateral dead end, the effects of a short lateral dead end side branch on pipeline fluid transients can be lumped into a node. The analytical solution to a linearized equation shows that a pipeline transient can be expressed as a Fourier series and presence of a lateral dead end reduces the frequencies of the harmonic components. The impact of the lateral dead end on the observed transients depends on a parameter Sd, which is related to the location of the lateral dead end, the relative volume, and the wave speed of the lateral dead end with respect to the pipeline. A lumped parameter approach that can be incorporated into the method of characteristics has also been developed in this paper. It has been found that it is possible to take account of the effects of a short lateral dead end in an accurate and computational efficient manner.

A Simple Dynamic Modeling of Head Slap in Hard Disk Drive

2001 ◽  
Author(s):  
Seong-Hun Lee ◽  
Jeong-Hak Lee ◽  
Kwang-Joon Kim
Keyword(s):  
Hard Disk Drive ◽  
Dynamic Modeling ◽  
Structural Design ◽  
Continuous System ◽  
Disk Drive ◽  
Lumped Parameter Model ◽  
Test Results ◽  
Lumped Parameter ◽  
Shock Resistance ◽  
The Impact

Abstract In order to understand mechanism of the impact between head and disk of a HDD subject to a shock and to improve the shock resistance effectively, it is essential to develop a dynamic model which can represent well the head slap. Although motion of the head and disk subject to a shock requires modeling by a continuous system to be rigorous, in this study, a simplified lumped parameter model is developed to understand basic dynamics of the head slap and to determine crucial parameters for the improvement of the structural design. In addition, drop test results of the HDD are presented to back to up the derived model.

Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control

1994 ◽  
Author(s):  
Wiktor M. Jungowski ◽  
Marvin H. Weiss ◽  
Glenn R. Price
Keyword(s):  
Active Control ◽  
Centrifugal Compressor ◽  
Passive Control ◽  
Side Branch ◽  
Lumped Parameter Model ◽  
Stability Criteria ◽  
Pressure Oscillations ◽  
Short Side ◽  
Lumped Parameter ◽  
Surge Control

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side-branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30%. In general, the experiments qualitatively confirmed the derived stability criteria.

Gravitational effects on ocular pressure and perfusion pressure

2021 ◽  
Author(s):  
Lonnie G. Petersen ◽  
Richard Stuart Whittle ◽  
Justin Hyunwoo Lee ◽  
Jeremy Sieker ◽  
Joseph Carlson ◽  
...  
Keyword(s):  
Supine Position ◽  
Perfusion Pressure ◽  
Lumped Parameter Model ◽  
Lumped Parameter ◽  
Postural Changes ◽  
Gravitational Stress ◽  
Gravitational Vector ◽  
Head Up Tilt ◽  
The Impact ◽  
Ocular Hemodynamics

Changes in the gravitational vector by postural changes or weightlessness induce fluid shifts impacting ocular hemodynamics and regional pressures. This investigation explores the impact of changes in direction of the gravitational vector on intraocular pressure (IOP), mean arterial pressure at eyelevel (MAPeye), and ocular perfusion pressure (OPP), which is critical for ocular health. Thirteen subjects underwent 360° of tilt (including both prone and supine positions) at 15º increments. At each angle, steady-state IOP and MAPeye were measured and OPP calculated as MAPeye-IOP. Experimental data were compared to a 6-compartment lumped parameter model of the eye. Mean IOP, MAPeye, and OPP significantly increased from 0º supine to 90º head down tilt (HDT) by 20.7±1.7 mmHg (ᵅD; < 0.001), 38.5±4.1 mmHg (ᵅD; < 0.001), and 17.4±3.2 mmHg (ᵅD; <0.001), respectively. Head up tilt (HUT) significantly decreased OPP by 16.5±2.5 mmHg (ᵅD; < 0.001). IOP was significantly higher in prone vs. supine position for much of the tilt range. Our study indicates that OPP is highly gravitationally dependent. Specifically, data show that MAPeye is more gravitationally dependent than IOP, thus causing OPP to increase during HDT and to decrease during HUT. Additionally, IOP was elevated in prone position compared to supine position due to the additional hydrostatic column between the base of the rostral globe to the mid-caudal plane, supporting the notion that hydrostatic forces play an important role in ocular hemodynamics. Changes in OPP as a function of changes in gravitational stress and/or weightlessness may play a role in the pathogenesis of spaceflight-associated neuro-ocular syndrome.

Can high rates of passive volcanic gas emissions induce reservoir depressurization at Ambrym volcano (Vanuatu)?

2021 ◽  
Author(s):  
Tara Shreve ◽  
Raphaël Grandin ◽  
Marie Boichu
Keyword(s):  
Ground Deformation ◽  
Lumped Parameter Model ◽  
Magma Ascent ◽  
Large Reservoir ◽  
Gas Emissions ◽  
Volcanic System ◽  
Lumped Parameter ◽  
Gas Geochemistry ◽  
The Impact

&lt;p&gt;Satellite-based UV spectrometers can constrain sulphur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;) fluxes at passively degassing volcanoes over decadal time scales. From 2005 to 2015, more than 15 volcanoes had mean passive SO&lt;sub&gt;2 &lt;/sub&gt;fluxes greater than 1 kiloton per day. Although the processes responsible for such high emission rates are not clearly established, this study aims to investigate the impact of strong degassing on the pressurization state of volcanic systems and the resulting ground deformation. One possible result of high degassing rates is the depressurization of the region where the melt releasing gas is stored, which may result in subsidence at the Earth&amp;#8217;s surface. Passive degassing may depressurize pathways between deep and shallow magma storage regions, resulting in magma ascent and possibly eruption.&lt;/p&gt;&lt;p&gt;A lumped-parameter model developed by Girona et al., 2014 couples the mass loss by passive degassing with reservoir depressurization in an open volcanic system. However, this model has yet to be tested using real measurements of gas emissions and ground deformation. In our study, we focus on Ambrym volcano, the past decade&amp;#8217;s top passive emitter of volcanic SO&lt;sub&gt;2&lt;/sub&gt;, which exhibits intriguing long-term subsidence patterns and no obvious pressurization preceding eruptive periods. We compare subsidence rates measured by InSAR to the system&amp;#8217;s average daily SO&lt;sub&gt;2&lt;/sub&gt; flux, focusing on a subsidence episode spanning 2015 to 2017 that is not clearly linked to magma removal from the system. Using realistic input parameters for Ambrym&amp;#8217;s system constrained by petrology and gas geochemistry, a range of reservoir volumes and conduit radii are explored. Large reservoir volumes (greater than 30 km&lt;sup&gt;3&lt;/sup&gt;) and large conduit radii (greater than 300 m) are consistent with depressurization rates obtained from geodetic modelling of InSAR measurements using the Boundary Element method. By comparing these values of reservoir volume and conduit radius with those estimated from geodesy, gas geochemistry, and seismology, we test the applicability and discuss uncertainties of the aforementioned lumped-parameter physical model to interpret the long-term subsidence at Ambrym volcano as a result of sustained passive degassing.&lt;/p&gt;

scholarly journals The total cavopulmonary connection resistance: a significant impact on single ventricle hemodynamics at rest and exercise

2008 ◽  
Vol 295 (6) ◽  
pp. H2427-H2435 ◽  
Author(s):  
Kartik S. Sundareswaran ◽  
Kerem Pekkan ◽  
Lakshmi P. Dasi ◽  
Kevin Whitehead ◽  
Shiva Sharma ◽  
...  
Keyword(s):  
Heart Rate ◽  
Single Ventricle ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Lumped Parameter Model ◽  
Total Cavopulmonary Connection ◽  
Dynamic Simulations ◽  
Lumped Parameter ◽  
The Impact ◽  
Cavopulmonary Connection

Little is known about the impact of the total cavopulmonary connection (TCPC) on resting and exercise hemodynamics in a single ventricle (SV) circulation. The aim of this study was to elucidate this mechanism using a lumped parameter model of the SV circulation. Pulmonary vascular resistance (1.96 ± 0.80 WU) and systemic vascular resistances (18.4 ± 7.2 WU) were obtained from catheterization data on 40 patients with a TCPC. TCPC resistances (0.39 ± 0.26 WU) were established using computational fluid dynamic simulations conducted on anatomically accurate three-dimensional models reconstructed from MRI ( n = 16). These parameters were used in a lumped parameter model of the SV circulation to investigate the impact of TCPC resistance on SV hemodynamics under resting and exercise conditions. A biventricular model was used for comparison. For a biventricular circulation, the cardiac output (CO) dependence on TCPC resistance was negligible (sensitivity = −0.064 l·min−1·WU−1) but not for the SV circulation (sensitivity = −0.88 l·min−1·WU−1). The capacity to increase CO with heart rate was also severely reduced for the SV. At a simulated heart rate of 150 beats/min, the SV patient with the highest resistance (1.08 WU) had a significantly lower increase in CO (20.5%) compared with the SV patient with the lowest resistance (50%) and normal circulation (119%). This was due to the increased afterload (+35%) and decreased preload (−12%) associated with the SV circulation. In conclusion, TCPC resistance has a significant impact on resting hemodynamics and the exercise capacity of patients with a SV physiology.

scholarly journals Optimal Occupant Kinematics and Crash Pulse for Automobile Frontal Impact

2009 ◽  
Vol 16 (1) ◽  
pp. 61-73 ◽  
Author(s):  
Zhiqing Cheng ◽  
Joseph A. Pellettiere ◽  
Jeff R. Crandall ◽  
Walter D. Pilkey
Keyword(s):  
Lumped Parameter Model ◽  
Frontal Impact ◽  
Vehicle Interior ◽  
Impact Speed ◽  
Vehicle System ◽  
Lumped Parameter ◽  
Passive Restraint ◽  
System Optimal ◽  
Occupant Kinematics ◽  
The Impact

Based on a lumped-parameter model of the occupant-vehicle system, optimal kinematics of the occupant in frontal impact are investigated. It is found that for the minimization of the peak occupant deceleration, the optimal kinematics move the occupant at a constant deceleration. Based on this the optimal vehicle crash pulse is investigated. The optimal crash pulse for passive restraint systems is found to be: a positive impulse at the onset, an immediate plunge followed by a gradual rebound, and finally a positive level period. The relation of the peak occupant deceleration to the impact speed, crash deformation, and vehicle interior rattlespace is established. The optimal crash pulse for active and pre-acting restraint systems is discussed.

Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control

1996 ◽  
Vol 118 (1) ◽  
pp. 29-40 ◽  
Author(s):  
W. M. Jungowski ◽  
M. H. Weiss ◽  
G. R. Price
Keyword(s):  
Active Control ◽  
Centrifugal Compressor ◽  
Passive Control ◽  
Side Branch ◽  
Lumped Parameter Model ◽  
Stability Criteria ◽  
Pressure Oscillations ◽  
Short Side ◽  
Lumped Parameter ◽  
Surge Control

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30 percent. In general, the experiments qualitatively confirmed the derived stability criteria.

scholarly journals Investigation of the Influence of Splitter Blades on the Resonance Conditions of Impellers

2019 ◽  
Vol 9 (10) ◽  
pp. 2051
Author(s):  
Kaicheng Liu ◽  
Cheng Yan
Keyword(s):  
Natural Frequency ◽  
Excitation Frequency ◽  
Specific Form ◽  
Lumped Parameter Model ◽  
Hazard Evaluation ◽  
Spatial Harmonic ◽  
Harmonic Response ◽  
Lumped Parameter ◽  
Engine Order ◽  
Harmonic Components

The conventional resonance conditions are derived based on the conventionally designed impellers without splitter blades. This paper proposes the resonance conditions for impellers under the excitation from the impeller–diffuser interaction with attention paid on the influence of splitter blades. A lumped parameter model is established and the modal analysis is carried out. The blade-based representative modal vector (RMV) is defined. The influence of splitter blades on the impeller’s traits of modes is investigated by analyzing the spatial harmonic contents of the RMV. Then, given the specific form of the diffuser-induced engine order excitation acting on the main and splitter blades, the resonance conditions are derived. Tuned and mistuned cases are provided for a practical impeller. The resonance conditions are verified by harmonic response calculations. The applications of the proposed resonance conditions in resonance identification and hazard evaluation of different excitations are given. The differences between the proposed resonance conditions and the conventional ones are discussed. The research indicates that even the RMV of the tuned impeller contains two harmonic components due to the existence of splitter blades. When the excitation frequency equals the natural frequency of the impeller and the excitation order matches with either harmonic index of the two harmonics, the resonance occurs. The results of case studies show that the harmfulness of various engine orders of excitation can be exactly evaluated by the joint use of the spatial harmonic contents analysis result and the proposed resonance conditions; however, analyzing based on the conventional resonance conditions may lead to the misjudgment of the harmfulness of the excitations.

scholarly journals Multiphase CFD Simulation of Solid Propellant Combustion in a Small Gun Chamber

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Ahmed Bougamra ◽  
Huilin Lu
Keyword(s):  
Cfd Simulation ◽  
Numerical Study ◽  
Lumped Parameter Model ◽  
Charge Weight ◽  
Maximum Pressure ◽  
Multiphase Model ◽  
Velocity Increase ◽  
Muzzle Velocity ◽  
Lumped Parameter ◽  
The Impact

The interior ballistics simulations in 9 mm small gun chamber were conducted by implementing the process into the mixture multiphase model of Fluent V6.3 platform. The pressure of the combustion chamber, the velocity, and the travel of the projectile were investigated. The performance of the process, namely, the maximum pressure, the muzzle velocity, and the duration of the process was assessed. The calculation method is validated by the comparison of the numerical simulations results in the small gun with practical tests, and with lumped-parameter model results. In the current numerical study, both the characteristics and the performance of the interior ballistic process were reasonably predicted compared with the practical tests results. The impact of the weight charge on the interior ballistic performances was investigated. It has been found that the maximum pressure and the muzzle velocity increase with the increase of the charge weight.

EFFECT OF SURFACE LAYER ON ELECTROMECHANICAL STABILITY OF TWEEZERS AND CANTILEVERS FABRICATED FROM CONDUCTIVE CYLINDRICAL NANOWIRES

2016 ◽  
Vol 23 (02) ◽  
pp. 1550101 ◽  
Author(s):  
MARYAM KEIVANI ◽  
ALI KOOCHI ◽  
HAMID M. SEDIGHI ◽  
MOHAMADREZA ABADYAN ◽  
AMIN FARROKHABADI ◽  
...  
Keyword(s):  
Surface Layer ◽  
Homotopy Perturbation Method ◽  
Differential Quadrature Method ◽  
Surface Elasticity ◽  
Lumped Parameter Model ◽  
Governing Equations ◽  
Lumped Parameter ◽  
The Stability ◽  
The Impact ◽  
Effect Of Surface

Herein, the impact of surface layer on the stability of nanoscale tweezers and cantilevers fabricated from nanowires with cylindrical cross section is studied. A modified continuum based on the Gurtin–Murdoch surface elasticity is applied for incorporating the presence of surface layer. Considering the cylindrical geometry of the nanowire, the presence of the Coulomb attraction and dispersion forces are incorporated in the derived formulations. Three different approaches, i.e. numerical differential quadrature method (DQM), an approximated homotopy perturbation method (HPM) and developing lumped parameter model (LPM) have been employed to solve the governing equations. The impact of surface layer on the instability of the system is demonstrated.

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