scholarly journals Modeling and Mitigation of Acoustic Induced Vibration (AIV) in Piping Systems

2018 ◽  
Author(s):  
Brandon L. Ridens ◽  
Timothy C. Allison ◽  
Sarah B. Simons ◽  
Klaus Brun
Keyword(s):  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Mitigation Strategies ◽  
Cfd Modeling ◽  
Screening Methods ◽  
Element Analysis ◽  
Modeling And Analysis ◽  
Pressure Transducers ◽  
Piping Systems ◽  
The Impact

This paper explores new analysis techniques and mitigation concepts developed to extend the current state of the art acoustic induced vibrations (AIV) analyses. These new methods are intended to provide more accurate evaluations of this phenomenon in an attempt to solve AIV problems found in blowdown and piping systems. Current screening methods for AIV are based on pass/fail data with minimal or undesired options for reducing the likelihood of failure for AIV events. Computational fluid dynamics simulations and finite element analysis in combination with lab testing of novel mitigation options using accelerometers, dynamic pressure transducers, and strain gages were performed to better understand the phenomenon and develop possible solutions to reduce the impact of AIV on piping systems. Results of the testing and analyses performed at the Southwest Research Institute (SwRI) indicate that there is a possible correlation with acoustic modes, structural modes, and elevated stresses during AIV events. Minor reductions in dynamic pressure fluctuations throughout piping during AIV events can be made by changes in valve geometry and piping configurations. Results of CFD modeling and analysis demonstrate that computational analysis can be used to evaluate mitigation strategies and suggest that the use of a dampener as a mitigation technique may be successful in reducing the amplitudes of dynamic pressure waves in piping systems caused by AIV events.

Novel Mitigation Technique to Reduce Stress at Pipe Welds Caused by Acoustic Induced Vibrations (AIV)

2019 ◽  
Author(s):  
Brandon L. Ridens ◽  
Sarah B. Simons
Keyword(s):  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Cost Effective ◽  
Full Scale ◽  
Excitation Source ◽  
Screening Methods ◽  
Significant Lowering ◽  
Piping Systems ◽  
Current Screening ◽  
Mitigation Technique

Abstract Within blowdown and pressure relieving systems, a phenomenon known as acoustic induced vibrations (AIV) increases the risk of costly failures at branch connections, pipe supports and other discontinuities downstream of pressure relieving devices. Broadband pressure fluctuations generated during these AIV events lead to elevated stresses at welded connections. Based on recent research, modeling and measuring the effects of AIV in piping systems, it is possible to reduce the dynamic pressure fluctuations that cause AIV closer to the excitation source. This can lead to more cost effective and efficient means of reducing the likelihood of failures caused by AIV. This paper will discuss the results of full-scale testing of a novel mitigation technique that reduces pressure fluctuations that cause AIV. The reduction in dynamic pressure leads to significant lowering of the overall stresses near the pipe welds at discontinuities. In addition, results indicate that a reduction in dynamic pressure can be obtained with the mitigation technique tested to a level acceptable by current screening methods.

Acoustically Induced Vibration Mitigations in Compressor Piping Systems

2016 ◽  
Author(s):  
Timothy C. Allison ◽  
Jeffrey Bennett
Keyword(s):  
Safety Valve ◽  
Dynamic Pressure ◽  
Peak Stress ◽  
Acoustic Mode ◽  
Mitigation Strategies ◽  
Blow Down ◽  
Dynamic Stresses ◽  
Pressure Transducers ◽  
Southwest Research Institute ◽  
Piping Systems

Acoustically induced vibration (AIV) is a high-frequency vibration phenomenon that can occur downstream of pressure-reducing devices such as control valves, restriction orifices, and pressure relief or safety valves in compressor piping systems. These vibrations can lead to high cycle fatigue failures of downstream piping at side branches or welded supports. Existing methods for screening and analyzing acoustically induced vibration are not well-grounded in the underlying physics and thus do not provide a methodology for evaluating a variety of mitigation strategies. Modeling of acoustically induced vibration is computationally challenging, as it requires the interaction between tens or hundreds of higher-order acoustic modes with a similar number of piping shell modes. In order to obtain better insight into the underlying physics of AIV and to characterize the effectiveness of several mitigation methods, full-scale blow-down testing was performed at Southwest Research Institute. Tests were performed using 20 MPa nitrogen gas vented at 28 kg/s through a 3×4” pressure safety valve and multiple header pipe sizes ranging from 12” to 36”. Test configurations included baseline piping geometry at each size and several AIV mitigations including stiffening rings, viscous damping wrap, and internal acoustic mode disruptors. Test results from strain gauges, accelerometers, and dynamic pressure transducers show a broadband multimodal response with dynamic stresses up to 3 kHz near the safety valve tailpipe connection to the test header, and various mitigations reduced dynamic stresses by 8–52% depending on the piping and type of mitigation. Acoustic and structural finite element models were analyzed in order to determine the coincident modes that match in both axial/circumferential shape and natural frequency and compare coincident frequencies with measure stresses. The results show that observed peak stress frequencies do not generally correlate well with predicted coincident modes, and that flow-induced turbulence excites frequencies below piping shell modes that can also result in significant stresses that combine with AIV.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high cycle fatigue. In addition to the well-established high frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes, the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing high cycle fatigue during the design phase. The unsteady fluid-structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries, therefore they are not critical and confirm a robust and reliable design.

Finite Element Parametric Acoustic Modeling and Analysis of Ship Floating Cabins

2013 ◽  
Vol 333-335 ◽  
pp. 2146-2150 ◽  
Author(s):  
Bing Nan Liang ◽  
Hong Liang Yu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Parametric Design ◽  
Structural Parameters ◽  
Sound Field ◽  
Acoustic Modeling ◽  
Element Analysis ◽  
Modeling And Analysis ◽  
Solid Models ◽  
The Impact

The development of parametric calculation module program based on APDL, the completion of 3D acoustic modeling of a ship floating cabin, the selection of constraints according to the actual work situations, the finite element modal analysis of the overall cabin in the ANSYS environment and comparative analysis of a low-order vibration frequency of the cabin under different fire ratings. Acoustic calculation program of the fluid-structure interaction is used to analyze harmonic sound field and verify the impact of different thickness fireproof rockwools on the cabin acoustic performance. Parametric Design and Finite Element Analysis are combined to achieve the adjustment of the structural parameters of the complex models, automatically generate solid models and complete finite element analysis, which is important for the optimization of the acoustic design of the ship cabins.

Effect of Substrate Flexibility on the Pressure Distribution and Lifting Force Generated by a Bernoulli Gripper

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
X. Brun ◽  
S. N. Melkote
Keyword(s):  
Pressure Distribution ◽  
Radial Pressure ◽  
Silicon Wafers ◽  
Cfd Modeling ◽  
Element Analysis ◽  
Modeling And Analysis ◽  
Lifting Force ◽  
Computational Fluid Dynamics Cfd ◽  
Thin Silicon ◽  
Good Agreement

This paper presents the modeling and analysis of the pressure distribution and lifting force generated by a Bernoulli gripper when handling flexible substrates such as thin silicon wafers. A Bernoulli gripper is essentially a radial airflow nozzle used to handle large and small, rigid and nonrigid materials by creating a low pressure region or vacuum between the gripper and material. Previous studies on Bernoulli gripping have analyzed the pressure distribution and lifting force for handling thick substrates that undergo negligible deformation. Since the lifting force produced by the gripper is a function of the gap between the handled object and the gripper, any deformation of the substrate will influence the gap and consequently the pressure distribution and lifting force. In this paper, the effect of substrate (thin silicon wafer) flexibility on the equilibrium wafer deformation, radial pressure distribution and lifting force is modeled and analyzed using a combination of computational fluid dynamics (CFD) modeling and finite element analysis. The equilibrium wafer deformation for different air flow rates is compared with experimental data and is shown to be in good agreement. In addition, the effect of wafer deformation on the pressure and lifting force are shown to be significant at higher volumetric airflow rates. The modeling and analysis approach presented in this paper is particularly useful for evaluating the effect of gripper variables on the handling stresses generated in thin silicon wafers and for gripper design optimization.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high-cycle fatigue. In addition to the well-established high-frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes (IGVs), the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing the high-cycle fatigue during the design phase. The unsteady fluid–structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns, dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries, a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries; therefore, they are not critical and confirm a robust and reliable design.

scholarly journals Safe Surgery During the COVID-19 Pandemic

2021 ◽  
Author(s):  
Rishi Singhal ◽  
Luke Dickerson ◽  
Nasser Sakran ◽  
Sjaak Pouwels ◽  
Sonja Chiappetta ◽  
...  
Keyword(s):  
Elective Surgery ◽  
Risk Mitigation ◽  
Surgical Techniques ◽  
Research Priorities ◽  
Mitigation Strategies ◽  
Screening Methods ◽  
Safe Surgery ◽  
Increased Risk ◽  
Surgical Teams ◽  
The Impact

Abstract Purpose of Review Coronavirus Disease-2019 (COVID-19) has had an enormous impact on all aspects of healthcare, but its effect on patients needing surgery and surgeons has been disproportionate. In this review, we aim to understand the impact of the pandemic on surgical patients and teams. We compiled the emerging data on pre-operative screening methods, vaccinations, safe-surgery pathways and surgical techniques and make recommendations for evidence-based safe-surgical pathways. We also present surgical outcomes for emergency, oncological and benign surgery in the context of the pandemic. Finally, we attempt to address the impact of the pandemic on patients, staff and surgical training and provide perspectives for the future. Recent Findings Surgical teams have developed consensus guidelines and established research priorities and safety precautions for surgery during the COVID-19 pandemic. Evidence supports that surgery in patients with a peri-operative SARS-CoV-2 infection carries substantial risks, but risk mitigation strategies are effective at reducing harm to staff and patients. Summary Surgery has increased risk for patients and staff, but this can be mitigated effectively, especially for elective surgery. Elective surgery can be safely performed during the COVID-19 pandemic employing the strategies discussed in this review.

Effect of Bubbles on Flow Induced Vibration

2006 ◽  
Author(s):  
Angela R. Pelletier ◽  
Ian A. McKelvey ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Bubble Size ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Flow Induced Vibration ◽  
Pressure Transducers ◽  
Plate Vibrations ◽  
Wall Pressure Fluctuations ◽  
Bubble Sizes ◽  
The Impact

The effects of a turbulent, bubbly boundary layer on wall skin friction have been investigated in numerous previous studies. However, the impact of such a multiphase flow on fluid-structure interactions has not been studied. To this end, the present project examines experimentally the effect of a bubbly boundary layer on the vibration of a vertical plate. Using a combination of accelerometers and pressure transducers, we simultaneously measure the plate vibrations and wall pressure fluctuations for varying flow rates, gas void fractions, and characteristic bubble sizes. The results show that the presence of bubbles substantially increases both the plate vibrations and the wall pressure fluctuations. The vibrations increase by up to 20 dB compared to the same flow without bubbles. The spectra of vibrations become broad and vary significantly with the characteristic bubble size. The variations with bubble size are consistent with the resonant frequency of the bubbles, indicating that, in addition to changing the compressibility of the medium, individual bubbles act at sources.

Dynamic Pressure Data Acquisition Via Strain Gage Measurements

2005 ◽  
Author(s):  
Gyorgy Szasz ◽  
Karen K. Fujikawa ◽  
Raju Ananth
Keyword(s):  
Strain Gage ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Dynamic Pressure ◽  
Operating Conditions ◽  
Pressure Transducers ◽  
Piping Systems ◽  
Dynamic Pressure Measurements ◽  
Main Steam

Dynamic pressure measurements are often helpful in characterizing operating conditions within industrial piping. The most straight forward method to obtain this type of data is to mount pressure transducers on the piping [6]. The orifice necessary for these instruments, frequently presents an undesirable opening in the pressure boundary of the affected system. One type of pressure transducer employs a strain gage mounted internally on a membrane that is exposed to the pressure to be measured [4, 5]. The deformation of the membrane is proportional to the pressure to be measured and is reported as a pressure value. A union of these two concepts yields the idea of mounting the gages directly on the piping and thereby eliminating the need for compromising piping integrity. One of the challenges is performing this measurement in the presence of significant axial train that is not related to the internal pressure. In the recent past Structural Integrity Associates Inc. has successfully applied this innovative technique to several main steam piping systems in various nuclear power plants in the US. This paper will describe some of the considerations regarding compensation for interfering axial strains as well as provide sample results from existing installations.

Verification of CFD Prediction Accuracy of Flow Turbulence Induced Vibration Loadings Around a Pipe Bend

2019 ◽  
Author(s):  
Xidong Hu ◽  
Shaoxiang Qian ◽  
Kota Matsuura ◽  
Shunji Kataoka
Keyword(s):  
Prediction Accuracy ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Flow Induced Vibration ◽  
Engineering Applications ◽  
Element Analysis ◽  
Pipe Bend ◽  
Wall Pressure Fluctuations ◽  
Power Spectral ◽  
Piping Systems

Abstract Bends widely used in process piping systems can cause strong pressure fluctuations on pipe wall for a high-velocity flow, and hence, flow induced vibration (FIV) of piping occurs. Currently, the FIV assessment is made primarily based on the guideline published by Energy Institute. However, it is based on very conservative assumptions, and thus, results in excessive design of piping systems. The coupling analysis of CFD/FEA (Computational Fluid Dynamics/Finite Element Analysis) is expected to be a useful approach for more proper FIV assessment. The present study mainly aims at verifying CFD prediction accuracy of wall pressure fluctuations or FIV loadings around a pipe bend. In CFD benchmark study, large eddy simulations (LES) with dynamic Smagorinsky model (DSM) were performed for a 90° mitred bend used in the experiments in literature, under two different flow velocity conditions. The benchmark simulation results show that the power spectral density (PSD) of the LES-predicted wall pressure fluctuations at the sampling locations is near to the experimental results with moderate conservativeness desirable for engineering applications. Also, the LES-predicted peak frequencies are close to the experimental data. Therefore, it is suggested that the applied numerical approaches be applicable to predict the FIV loadings with moderately high accuracy for engineering applications.

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