Tuning of the Acoustical Analysis Model for Hypercompressors Through Strain Gage Pulsation Measurements

2019 ◽  
Author(s):  
Andrea Fusi ◽  
Leonardo Cappelli ◽  
Cosimo Carcasci ◽  
Marco Sacco
Keyword(s):  
Speed Of Sound ◽  
Pressure Range ◽  
High Pressures ◽  
Pressure Sensors ◽  
Compressibility Factor ◽  
Design Stage ◽  
Strain Gages ◽  
Pressure Pulsations ◽  
The Impact ◽  
Very High

Abstract Reciprocating compressor plants are typically exposed to vibrations, resulting from the discontinuity of the flow (pressure pulsations) and from external mechanical loads (compressor motion). To minimize the impact of pressure pulsations on vibration issues, a robust acoustical study is needed in the early design stage. Reliable standards and guidelines concerning vibration and pulsation are available for common applications (up to 350 bar) [1][2]. Within this pressure range it is possible to meet the standards by introducing pulsation suppression devices such as volume bottles or orifices. The Low-Density Polyethylene (LDPE) process requires very high pressures obtained with dedicated machines (Hypercompressors). There are no specific pulsation guidelines for these extreme pressures; in addiction reactive pulsation suppression devices like volume bottles are ineffective due to the high speed of sound in real gas (and related long wavelengths) at such pressures. This paper describes the case history of a plant which exhibited high piping vibration from the first machine start-up. A survey was made to measure vibrations and pressure pulsations by means of strain gages: internal pressure was derived from external deformation through pressure vessel theory. Strain gages were chosen because they can be easily installed without positioning restrictions, while dynamic pressure sensors require pressure taps and must be limited to specific points. Pulsation measurements were compared with an acoustic analysis, showing some discrepancy, especially at relatively high harmonics, mainly due to incorrect evaluation of the thermodynamic properties of high-pressure ethylene. In fact, in the LDPE process pressure range, isentropic exponent kv and compressibility factor Z can reach very high values, consequently affecting the calculation of the speed of sound. A new acoustic modelling was developed to achieve better consistency with the measurements. Pressure-dependent kv and Z were taken into account and a sensitivity analysis of the most relevant valve parameters was performed. Comparing the vibrations and pulsations spectra, once the MNF, compressor manifold arrangement and external loads are known, is fundamental to detect the origin of vibrations and how they are affected by pulsations.

Responses of cerebral arteries and arterioles to acute hypotension and hypertension

1978 ◽  
Vol 234 (4) ◽  
pp. H371-H383 ◽  
Author(s):  
H. A. Kontos ◽  
E. P. Wei ◽  
R. M. Navari ◽  
J. E. Levasseur ◽  
W. I. Rosenblum ◽  
...  
Keyword(s):  
Pressure Range ◽  
High Pressures ◽  
Cerebral Arteries ◽  
Pial Arteries ◽  
Small Vessels ◽  
Size Dependent ◽  
Arterial Blood ◽  
Vascular Bed ◽  
Acute Hypotension ◽  
Very High

The responses of cerebral precapillary vessels to changes in arterial blood pressure were studied in anesthetized cats equipped with cranial windows for the direct observation of the pial microcirculation of the parietal cortex. Vessel responses were found to be size dependent. Between mean arterial pressures of 110 and 160 mmHg autoregulatory adjustments in caliber, e.g., constriction when the pressure rose and dilation when the pressure decreased, occurred only in vessels larger than 200 micron in diameter. Small arterioles, less than 100 micron in diameter, dilated only at pressures equal to or less than 90 mmHg; below 70 mmHg their dilation exceeded that of the larger vessels. When pressure rose to 170- 200 mmHg, small vessels dilated while the larger vessels remained constricted. At very high pressures (greater than 200 mmHg) forced dilation was frequently irreversible and was accompanied by loss of responsiveness to hypocapnia. Measurement of the pressure differences across various segments of the cerebral vascular bed showed that the larger surface cerebral vessels, extending from the circle of Willis to pial arteries 200 micron in diameter, were primarily responsible for the adjustments in flow over most of the pressure range.

Seismic parameter φ: Computation at very high pressure from laboratory data

1966 ◽  
Vol 56 (3) ◽  
pp. 725-731
Author(s):  
Orson L. Anderson
Keyword(s):  
High Pressure ◽  
Bulk Modulus ◽  
Ultrasonic Velocity ◽  
Pressure Range ◽  
High Pressures ◽  
Equations Of State ◽  
Laboratory Data ◽  
Second Derivative ◽  
Velocity Measurements ◽  
Very High

abstract By using the accuracy inherent in ultrasonic velocity measurements taken at pressures less than 10 kb, the seismic parameter φ=vp2−(43)vS2 can be computed at very high pressures. The equation used requires the assumption that the second derivative with respect to pressure of the bulk modulus be negligible at all pressures considered. This assumption is checked by computing the compression (V/V0) in the pressure range by equations of state using the assumption, and comparing the resulting values with measured compression. Illustrations are given for MgO and Al2O3.

scholarly journals The effect of hydrogen on the physical properties of natural gas and the metrological characteristics of its metering systems

2020 ◽  
pp. 45-50
Author(s):  
A. A. Stetsenko ◽  
S. D. Nedzelsky ◽  
V. A. Naumenko
Keyword(s):  
Natural Gas ◽  
Physical Properties ◽  
High Pressures ◽  
Compressibility Factor ◽  
Metrological Characteristics ◽  
Physical Parameters ◽  
Gas Mixture ◽  
The Impact ◽  
Accuracy And Repeatability

Given the promise of the concept of using a mixture of hydrogen and natural gas as an energy source, studies were conducted in the following areas: determination of the effect of hydrogen impurities on the physical properties of natural gas; study of the effect of adding hydrogen to natural gas on the metrological characteristics of its consumption metering systems. To solve these problems, the following was carried out: determination of the dependence of the physical parameters of natural gas on the percentage of hydrogen in its composition: determination of the permissible fraction (permissible concentration) of hydrogen in natural gas in modern gas transmission and gas consuming systems. study of the effect of hydrogen additions on the metrological characteristics of measuring instruments and gas commercial metering systems. To conduct objective research and modeling, natural gas samples having different component composition were prepared. An analysis of the physical properties of these gases was carried out — their physical parameters were calculated: adiabatic index and sound velocity, density, compressibility factor, higher calorific value and Wobbe number. Based on these samples, modeling was performed — the physical parameters of the gases were calculated by adding hydrogen at different concentrations (from 2 to 23 %). Based on the research results, the following conclusions are made: When hydrogen is added to natural gas in an amount of from 2 to 10 %, the physical parameters of the resulting mixture change slightly (within acceptable limits), therefore, the addition of hydrogen to natural gas in an amount of up to 10 % allows the use of existing gas transmission and gas-consuming systems without any reconstructions, improvements, changes in algorithms for calculating the physical parameters of the gas mixture and calculating (volume) volumetric flow for commercial accounting. The impact on gas meters of consumers will be within the acceptable ranges of accuracy and repeatability and, therefore, will not require the cost of updating the meters. The addition of up to 25 % hydrogen by volume does not require a radical new technology of burners and gas transmission systems. Safety will not be compromised by adding 25 % hydrogen by volume to the natural gas network. Changes in the physical properties in the gas mixture have a number of disadvantages, but, in the aggregate, they do not pose any additional safety risk. The addition of hydrogen in a volume of more than 25 %, as well as the use of the mixture at high pressures, requires additional research and the development of new algorithms.

scholarly journals Investigation of Vertical Slamming on Point Absorbers

2008 ◽  
Author(s):  
Griet De Backer ◽  
Marc Vantorre ◽  
Sam Victor ◽  
Julien De Rouck ◽  
Charlotte Beels
Keyword(s):  
Laboratory Experiments ◽  
Pressure Sensors ◽  
Occurrence Probability ◽  
High Resonance Frequency ◽  
Point Absorber ◽  
Drop Tests ◽  
Point Absorbers ◽  
The Impact ◽  
Very High ◽  
Wagner Theory

This paper focuses on the impact of vertical slamming on floating point absorber systems and the associated pressures that might be expected when these phenomena occur. In a first part it will be shown how the occurrence probability of slamming can be reduced by implementing a slamming restriction, i.e. by controlling the motion of the point absorber. The impact of these slamming restrictions on power absorption will be discussed. Secondly an investigation is made of the pressures that occur when the buoys are subject to vertical bottom slamming. Analytical results are presented, which give a pressure prediction of an impacting body with conical and hemispherical shape, using Wagner theory. Laboratory experiments have been carried out at Ghent University. Impact pressures were measured during drop tests with both hemispherical and conical buoy shapes. These pressures were measured by ICP pressure sensors with a range up to 345 kPa with small membrane and very high resonance frequency (> 250 kHz). Analytical and physical results are compared and conclusions are drawn.

Investigation into the outlying swirl instability in the hydro-turbine draft tube under part-load operation

2019 ◽  
pp. 095765091988979 ◽  
Author(s):  
Alexis Muhirwa ◽  
Wei-Hua Cai ◽  
Feng-Chen Li ◽  
Wen-Tao Su ◽  
Maxime Binama ◽  
...  
Keyword(s):  
Draft Tube ◽  
Pressure Sensors ◽  
Numerical Approach ◽  
Opposite Polarity ◽  
Pressure Amplitude ◽  
Frequency Range ◽  
Pressure Pulsations ◽  
Part Load ◽  
High Kinetic Energy ◽  
The Impact

The swirling trajectory of the draft tube flow improves the pressure recovery. Resultant flow instabilities are still problematic for an optimized hydropower generation. Engineering solutions are getting increasing importance. However; the depth of wall-mounted countermeasures is a challenging parameter. Performance assessment of countermeasures would rate dampened pressure pulsations in terms of their sources so as to place them at a proper location. A method for evaluating the instability in the outlying domain of the draft tube cone is herein suggested. Two part-load operating points with opposite polarity in pressure pulsations have been investigated. The numerical approach of Shear Stress Transport has been used, and experimental agreement of measurements for the pressure spectra is verified at the wall. Inlet flow conditions and the growth of the core instability are described. The outlying domain of the draft tube has been found to be composed of three distinct zones of influence: the shortest upper cone with upstream travelling influences, the longest middle cone with core excitation, and the lowermost cone dominated by the backward elbow influence. The wall response lies within a definite high-frequency range proper to the operating point. During admission, the frequency range becomes even wider due to high kinetic energy and the highest pressure amplitude of the draft tube is developed by the impact of blade passing frequency. The excitation from the vortex rope precession in the outlying domain strongly depends on the operating condition. Thus, further works should extend this study over a wider operation range, and mount pressure sensors on countermeasures in order to identify their own instability contribution.

Capacity Control Systems of LDPE Compressors and Influence on Cylinder Valves

2014 ◽  
Author(s):  
Enzo Giacomelli ◽  
Andrea Raggi ◽  
Antonio Giampà ◽  
Claudio Vaglini
Keyword(s):  
Control Systems ◽  
High Pressures ◽  
Variable Speed ◽  
Capacity Control ◽  
Start Up ◽  
Pros And Cons ◽  
New Generation ◽  
The Impact ◽  
Very High ◽  
Wide Operating

Booster, Primary and Hyper compressors are the pieces of machinery used to reach the extremely high pressures needed for the reaction in Low-Density Polyethylene plants. Wide operating ranges are necessary due to the different products and conditions required by the process to obtain both homo and co-polymers required by the market. A suitable capacity control system has to be studied during the design phase to optimize the operation particularly for Booster and Primary compressors, that are supplying the required flow to the Hyper, then compressed to the reactor. In the latter the traditional capacity control cannot be used because of the very high pressures involved and for start-up and various preparation activities the by-pass along the reactor is the only flow regulation possibility. On the contrary, in Booster and Primary there is a wider choice of CCS, from “clearance pockets” to “variable speed drive”, from step to step-less. This paper gives a brief overview of these systems, explains their pros and cons and examines the impact they have on valve behaviour explaining the CCS-valve interactions. In particular it focuses on the new generation of electro-mechanical step-less control systems.

scholarly journals Do Prospective Teachers Care About PISA Studies? A Pilot Study among University Students in Germany

2017 ◽  
Vol 10 (5) ◽  
pp. 26 ◽  
Author(s):  
Olga Ioannidou ◽  
Despoina Georgiou ◽  
Andreas Obersteiner ◽  
Nilufer Deniz Bas ◽  
Christine Mieslinger
Keyword(s):  
Teacher Education ◽  
University Students ◽  
Prospective Teachers ◽  
International Student ◽  
Teacher Education Program ◽  
Student Assessment ◽  
International Student Assessment ◽  
The Impact ◽  
Very High ◽  
Expected Outcomes

The results of international comparison studies such as the Program for International Student Assessment (PISA) have initiated intense discussions about educational reforms in Germany. Although in-service and pre-service teachers are an essential part of such reforms, little is known about their attitudes towards PISA studies. The present study aims to fill this gap through the investigation of pre-service teachers’ awareness, interest, perception, and attitudes towards PISA. A questionnaire was used to survey a sample of 107 university students who were participating in a teacher education program. The results reveal that 100% of the participants are aware of PISA. Nearly 69% of the participants think that the impact of PISA is rather high or very high, while 41% of them believe that PISA results are reliable. Accordingly, half of the participants seem to be interested in PISA results for their country. The present study discusses these findings in the light of the expected outcomes as proposed in standards for teacher education.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

scholarly journals Review on Urban Heat Island in China: Methods, Its Impact on Buildings Energy Demand and Mitigation Strategies

2021 ◽  
Vol 13 (2) ◽  
pp. 762
Author(s):  
Liu Tian ◽  
Yongcai Li ◽  
Jun Lu ◽  
Jue Wang
Keyword(s):  
Energy Consumption ◽  
Urban Heat Island ◽  
Building Energy ◽  
Design Stage ◽  
Heat Island ◽  
Building Energy Consumption ◽  
Rapid Urbanization ◽  
Substantial Impact ◽  
Urban Heat ◽  
The Impact

High population density, dense high-rise buildings, and impervious pavements increase the vulnerability of cities, which aggravate the urban climate environment characterized by the urban heat island (UHI) effect. Cities in China provide unique information on the UHI phenomenon because they have experienced rapid urbanization and dramatic economic development, which have had a great influence on the climate in recent decades. This paper provides a review of recent research on the methods and impacts of UHI on building energy consumption, and the practical techniques that can be used to mitigate the adverse effects of UHI in China. The impact of UHI on building energy consumption depends largely on the local microclimate, the urban area features where the building is located, and the type and characteristics of the building. In the urban areas dominated by air conditioning, UHI could result in an approximately 10–16% increase in cooling energy consumption. Besides, the potential negative effects of UHI can be prevented from China in many ways, such as urban greening, cool material, water bodies, urban ventilation, etc. These strategies could have a substantial impact on the overall urban thermal environment if they can be used in the project design stage of urban planning and implemented on a large scale. Therefore, this study is useful to deepen the understanding of the physical mechanisms of UHI and provide practical approaches to fight the UHI for the urban planners, public health officials, and city decision-makers in China.

scholarly journals ‘I’m fine!’: Assertions of lack of support need among patients with chronic obstructive pulmonary disease: A mixed-methods study

2021 ◽  
pp. 174239532110003
Author(s):  
A Carole Gardener ◽  
Caroline Moore ◽  
Morag Farquhar ◽  
Gail Ewing ◽  
Efthalia Massou ◽  
...  
Keyword(s):  
Chronic Obstructive Pulmonary Disease ◽  
Pulmonary Disease ◽  
Mixed Method ◽  
Self Report ◽  
Design Stage ◽  
Chronic Obstructive ◽  
Support Needs ◽  
Obstructive Pulmonary Disease ◽  
Stage 1 ◽  
The Impact

Objectives To understand how people with Chronic Obstructive Pulmonary Disease (COPD) disavow their support needs and the impact on care. Methods Two stage mixed-method design. Stage 1 involved sub-analyses of data from a mixed-method population-based longitudinal study exploring the needs of patients with advanced COPD. Using adapted criteria from mental health research, we identified 21 patients who disavowed their needs from the 235 patient cohort. Qualitative interview transcripts and self-report measures were analysed to compare these patients with the remaining cohort. In stage 2 focus groups (n = 2) with primary healthcare practitioners (n = 9) explored the implications of Stage 1 findings. Results Patients who disavowed their support needs described non-compliance with symptom management and avoidance of future care planning (qualitative data). Analysis of self-report measures of mental and physical health found this group reported fewer needs than the remaining sample yet wanted more GP contact. The link between risk factors and healthcare professional involvement present in the rest of the sample was missing for these patients. Focus group data suggested practitioners found these patients challenging. Discussion This study identified patients with COPD who disavow their support needs, but who also desire more GP contact. GPs report finding these patients challenging to engage.

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