Resonance of Trapped Acoustic Modes of a Ducted Rectangular Cavity

2015 ◽  
Author(s):  
Michael Bolduc ◽  
Samir Ziada ◽  
Philippe Lafon
Keyword(s):  
Shear Layer ◽  
Particle Velocity ◽  
Acoustic Mode ◽  
Velocity Fields ◽  
Mode Shapes ◽  
Test Results ◽  
Trapped Modes ◽  
Cross Sectional ◽  
Acoustic Modes ◽  
Axisymmetric Cavities

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly & Ziada [1–3] investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross-section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.

Flow-Excited Acoustic Resonance of Trapped Modes of a Ducted Rectangular Cavity

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Michael Bolduc ◽  
Samir Ziada ◽  
Philippe Lafon
Keyword(s):  
Shear Layer ◽  
Particle Velocity ◽  
Acoustic Mode ◽  
Velocity Fields ◽  
Mode Shapes ◽  
Trapped Modes ◽  
Mean Flow ◽  
Cross Sectional ◽  
Shallow Cavities ◽  
Axisymmetric Cavities

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly and Ziada (2010, “Flow-Excited Resonance of Trapped Modes of Ducted Shallow Cavities,” J. Fluids Struct., 26(1), pp. 92–120; 2011, “Azimuthal Behaviour of Flow-Excited Diametral Modes of Internal Shallow Cavities,” J. Sound Vib., 330(15), pp. 3666–3683; and 2012, “Effect of Mean Flow on the Trapped Modes of Internal Cavities,” J. Fluids Struct., 33, pp. 70–84) investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.

Flow-Acoustic Coupling in T-Junctions: Effect of T-Junction Geometry

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
S. Ziada ◽  
K. W. McLaren ◽  
Y. Li
Keyword(s):  
Shear Layer ◽  
Flow Velocity ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Coupling Mechanism ◽  
Cross Sectional ◽  
Acoustic Coupling ◽  
Pipe Expansion ◽  
Junction Geometry ◽  
Acoustic Resonances

The flow-acoustic coupling mechanism in a T-junction, which combines flows from two branches, forming the “cross-bar” of the T-junction, into one pipe, forming the “stem” of the T-junction, is investigated experimentally. The T-junction has a step pipe expansion at its inlets. The shear layer separating from this step expansion is found to excite intense acoustic resonances over multiple ranges of flow velocity. The excited acoustic mode is confined to the branch pipes and has an acoustic pressure node at the centerline of the T-junction. The length of the expansion section of the T-junction is found to control the frequency of the shear layer oscillation and therefore determines the ranges of flow velocity over which acoustic resonances are excited. Introducing asymmetry in the T-junction expansion length has shown little influence on the excitation of acoustic resonance. An additional T-junction arrangement made of rectangular cross-sectional ducts is also investigated to facilitate a flow visualization study of unsteady flow structures in the T-junction during acoustic resonance, and thereby improve understanding of the acoustic resonance mechanism and the nature of the aero-acoustic sources in the T-junction.

Flow Induced Acoustic Resonances of an Annular Duct With Co-Axial Side Branches

2006 ◽  
Author(s):  
David Arthurs ◽  
Samir Ziada ◽  
Rafael Bravo
Keyword(s):  
Annular Flow ◽  
Branch Length ◽  
Acoustic Mode ◽  
Mode Shapes ◽  
Design Parameters ◽  
Fighter Aircraft ◽  
Acoustic Coupling ◽  
Acoustic Modes ◽  
Annular Duct ◽  
Quarter Wavelength

This paper investigates the aeroacoustic response of an annular duct with co-axial side branches, and examines the effect of several passive countermeasures. The investigated geometry is inspired by the design of the Roll Posts in the Rolls-Royce LiftSystem® engine, which is currently being developed for the Lockheed Martin Joint Strike Fighter aircraft. The effects of design parameters, such as diameter ratio, branch length ratio and thickness of the annular flow on the frequency and resonance intensity of the first acoustic mode are studied experimentally. Numerical simulations of the acoustic mode shapes and frequencies are also performed. The annular flow has been found to excite several acoustic modes, the strongest in all cases being the first acoustic mode, which consists of an antisymmetric quarter wavelength along the length of each branch. The ratios of the branch length and diameter, with respect to the main duct diameter, have been found to have strong effects on the frequency of the acoustic modes. The effects of passive measures to weaken the acoustic coupling between the co-axial branches have been also investigated. These include detuning the co-axial branches, by decreasing the length of one branch, and installing a pair of splitter plates in the annular flow duct.

FAKTOR PERSONAL YANG BERHUBUNGAN DENGAN KOMITMEN ORGANISASI PERAWAT RSUD EMBUNG FATIMAH BATAM

2020 ◽  
Vol 5 (3) ◽  
pp. 875
Author(s):  
Asfri Sri Rahmadeni
Keyword(s):  
Organizational Commitment ◽  
Turnover Rate ◽  
Sampling Technique ◽  
Hospital Nurses ◽  
Test Results ◽  
Personal Factors ◽  
High Turnover ◽  
Chi Square ◽  
Cross Sectional ◽  
Chi Square Test

<p class="Normal1"><em>Commitment is the attitude or behavior of likes or dislikes shown by someone against the organization at work. Indonesia is recorded as a nurse who has a low organizational commitment (76%) so it harms services. This phenomenon in the hospital can be seen from the indicator of the high turnover rate of nurses which reaches 30.9% which exceeds the standard &lt;5%. Many factors affect organizational commitment. The purpose of this study was to analyze the Personal Factors Associated with Organizational Commitment of Hospital Nurses. This study is a cross-sectional analytic study and purposive sampling technique with a sample of 59 nurses. Chi-Square test results obtained personal factors that have a relationship with organizational commitment Nurse Hospital is age with p = 0,000 and education with p = 0,000, personal factors not related to organizational commitment are gender p = 1,053 and years of service with p = 1,147. Hospitals should conduct research/surveys on Organizational Commitment periodically as an evaluation material in the context of the organization's development and development in the future</em>.</p>

Faktor yang Berhubungan dengan Penggunaan Partograf dalam Persalinan oleh Bidan Praktik Mandiri

2020 ◽  
Vol 2 (2) ◽  
pp. 72-80
Author(s):  
Niluh Nita Silfia
Keyword(s):  
Total Population ◽  
Sampling Technique ◽  
Population Data ◽  
Statistical Test ◽  
Influential Factor ◽  
Test Results ◽  
Cross Sectional ◽  
Factors Associated ◽  
Survey Results ◽  
Research Criteria

Partographs are guidelines for childbirth observations that will facilitate labor assistants in first identifying emergency cases and complications for mothers and fetuses. Preliminary survey at the Sigi Community Health Sub-Center (Pustu) of the 8 Pustu midwives found two midwives (25%) to complete a complete partograph, six midwives (75%) incomplete. The purpose of this study was to determine the determinant factors associated with the use of partographs in labor. The design of this study used observational analytic methods with a cross-sectional approach. 24 BPM survey results were obtained with 30 samples of midwives who met the research criteria and data completeness. The sampling technique was by the total population. Data analysis used logistic regression. The multivariate analysis results showed that APN training was the most influential factor in the use of partographs in labor by midwives. Statistical test results obtained a POR value of 37.7 (95% CI 12.1 - 60.2). This study suggests that midwives must have APN certificates to be valid in providing services.

HUBUNGAN UMUR DAN PARITAS DENGAN PEMILIHAN ALAT KONTRASEPSI METODE OPERASI WANITA (MOW) DI POLIKLINIK KEBIDANAN RS BHAYANGKARA PALEMBANG TAHUN 2012

2019 ◽  
Vol 3 (2) ◽  
Author(s):  
Y. Widyastuti Y. Widyastuti
Keyword(s):  
Family Planning ◽  
Medical Records ◽  
Test Results ◽  
Family Planning Services ◽  
Chi Square ◽  
Cross Sectional ◽  
Planning Methods ◽  
Chi Square Test ◽  
Family Planning Methods ◽  
Selection Of

  ABSTRACT [In advanced countries the number of permanent contraception option ( kontap ) approximately 10 % of all national family planning methods , while in Indonesia reached approximately 5.7 % . Based on data obtained from medical records Bhayangkara Hospital Palembang in 2010 the number of achievement when seen from the percentage of contraceptive use is only 9.10 % The purpose of this study is known age and parity relationship with the selection of contraceptive methods Surgery Women ( MOW ) in Palembang RS.Bhayangkara obstetrics clinic in 2012 . This study uses the analytic survey with cross sectional approach . The population in this study were women who become new acceptors were recorded in medical records at the hospital . Palembang Bhayangkara Hospitals January 1, 2012 to December 31 in 2012 . The sample in this study is part of a whole number of new acceptors ( either using contraception methods MOW and other family planning methods ) were registered in the hospital . Palembang Police Hospitals of January 1, 2012 to December 31 years of data 2012.Analisa univariate and bivariate statistical Chi - Square test with significance level α = 0.05 . The results showed there were 80 respondents ( 46.3 % ) who became MOW contraceptive acceptors , acceptors who have old age by 45 respondents ( 56.3 % ) and who has a young age by 35 respondents ( 43.8 % ) . acceptors which have high parity were 44 respondents ( 55 % ) who had low parity and a total of 36 respondents ( 45 % ) . From the results of Chi-square test value obtained ρ = 0.00 is smaller than α = 0.05 . There is a significant correlation between age and the selection of MOW Chi square test results obtained ρ value = 0.00 and there was a significant association between parity with the election MOW Chi square test results obtained ρ value = 0 , . From these results , it is expected to power health, especially family planning services at the hospital . Palembang Police Hospitals in order to improve the quality of family planning services in an effective, efficient , and safe are considered particularly suitable for users of contraception OperatingMethodWomen(MOW).                                      ABSTRAK Di negara sudah maju jumlah pilihan kontrasepsi mantap (kontap) sekitar 10% dari semua metode KB nasional, sedangkan di Indonesia baru mencapai sekitar 5,7 %. Berdasarkan data yang diperoleh dari Rekam medik  Rumah Sakit Bhayangkara Palembang tahun 2010 Jumlah pencapain tersebut jika dilihat dari persentasi penggunaan kontrasepsi MOW hanya  9,10% Tujuan penelitian ini adalah diketahuinya hubungan umur dan paritas dengan pemilihan alat kontrasepsi Metode Operasi Wanita (MOW) di poliklinik kebidanan RS.Bhayangkara Palembang Tahun 2012. Penelitian ini menggunakan metode survey analitik dengan pendekatan cross sectional. Populasi dalam penelitian ini adalah wanita yang menjadi akseptor KB Baru yang tercatat di rekam medik  di RS. Bhayangkara Palembang tanggal 1 januari 2012 sampai dengan 31 Desember  tahun 2012. Sampel dalam penelitian ini adalah sebagian dari seluruh jumlah akseptor KB Baru (baik yang menggunakan alat kontrasepsi Metode MOW maupun Metode KB lain) yang teregister di RS. Bhayangkara Palembang dari tanggal 1 januari 2012 sampai dengan 31 Desember  tahun 2012.Analisa data dilakukan secara univariat dan bivariat dengan uji statistik Chi-Square dengan tingkat kemaknaan α = 0,05. Hasil penelitian menunjukkan dari 80 responden terdapat (46,3%) yang menjadi akseptor kontrasepsi MOW, akseptor yang memiliki umur tua sebanyak 45 responden (56,3%) dan yang memiliki  umur muda sebanyak 35 responden (43,8%). akseptor yang memiliki paritas tinggi sebanyak 44 responden  (55%) dan yang memiliki  paritas rendah sebanyak 36 responden (45%). Dari hasil uji Chi square didapatkan ρ value = 0,00 lebih kecil dari α = 0,05. Ada hubungan yang bermakna antara umur dengan pemilihan MOW dari hasil uji Chi square didapatkan ρ value = 0,00 dan ada hubungan yang bermakna antara paritas dengan pemilihan MOW hasil uji Chi square didapatkan ρ value = 0,.Dari hasil penelitian ini, diharapkan kepada tenaga kesehatan khususnya pelayanan KB  di RS. Bhayangkara Palembang  agar dapat meningkatkan kualitas pelayanan KB secara efektif, efisien, dan aman yang dianggap cocok bagi penggunanya khususnya mengenai kontrasepsi Metode Operasi Wanita (MOW).    

Investigating the vibrational behaviour of a rotating two-blade propeller by using a self-tracking method

2018 ◽  
Vol 233 (3) ◽  
pp. 835-847 ◽  
Author(s):  
Mohammad-Reza Ashory ◽  
Farhad Talebi ◽  
Heydar R Ghadikolaei ◽  
Morad Karimpour
Keyword(s):  
Natural Frequency ◽  
Measurement Errors ◽  
Mode Shapes ◽  
Model Parameters ◽  
Test Results ◽  
Modal Assurance Criterion ◽  
Tracking Method ◽  
Strong Resemblance ◽  
Test Scenarios ◽  
Good Agreement

This study investigated the vibrational behaviour of a rotating two-blade propeller at different rotational speeds by using self-tracking laser Doppler vibrometry. Given that a self-tracking method necessitates the accurate adjustment of test setups to reduce measurement errors, a test table with sufficient rigidity was designed and built to enable the adjustment and repair of test components. The results of the self-tracking test on the rotating propeller indicated an increase in natural frequency and a decrease in the amplitude of normalized mode shapes as rotational speed increases. To assess the test results, a numerical model created in ABAQUS was used. The model parameters were tuned in such a way that the natural frequency and associated mode shapes were in good agreement with those derived using a hammer test on a stationary propeller. The mode shapes obtained from the hammer test and the numerical (ABAQUS) modelling were compared using the modal assurance criterion. The examination indicated a strong resemblance between the hammer test results and the numerical findings. Hence, the model can be employed to determine the other mechanical properties of two-blade propellers in test scenarios.

scholarly journals A frictional Cosserat model for the slow shearing of granular materials

2002 ◽  
Vol 457 ◽  
pp. 377-409 ◽  
Author(s):  
L. SRINIVASA MOHAN ◽  
K. KESAVA RAO ◽  
PRABHU R. NOTT
Keyword(s):  
Angular Velocity ◽  
Granular Material ◽  
Shear Layer ◽  
Granular Materials ◽  
Layer Thickness ◽  
Couette Flow ◽  
Velocity Fields ◽  
Cosserat Continuum ◽  
Cosserat Model ◽  
Cylindrical Couette Flow

A rigid-plastic Cosserat model for slow frictional flow of granular materials, proposed by us in an earlier paper, has been used to analyse plane and cylindrical Couette flow. In this model, the hydrodynamic fields of a classical continuum are supplemented by the couple stress and the intrinsic angular velocity fields. The balance of angular momentum, which is satisfied implicitly in a classical continuum, must be enforced in a Cosserat continuum. As a result, the stress tensor could be asymmetric, and the angular velocity of a material point may differ from half the local vorticity. An important consequence of treating the granular medium as a Cosserat continuum is that it incorporates a material length scale in the model, which is absent in frictional models based on a classical continuum. Further, the Cosserat model allows determination of the velocity fields uniquely in viscometric flows, in contrast to classical frictional models. Experiments on viscometric flows of dense, slowly deforming granular materials indicate that shear is confined to a narrow region, usually a few grain diameters thick, while the remaining material is largely undeformed. This feature is captured by the present model, and the velocity profile predicted for cylindrical Couette flow is in good agreement with reported data. When the walls of the Couette cell are smoother than the granular material, the model predicts that the shear layer thickness is independent of the Couette gap H when the latter is large compared to the grain diameter dp. When the walls are of the same roughness as the granular material, the model predicts that the shear layer thickness varies as (H/dp)1/3 (in the limit H/dp [Gt ] 1) for plane shear under gravity and cylindrical Couette flow.

scholarly journals Using Combined Diagnostic Test Results to Hindcast Trends of Infection from Cross-Sectional Data

2016 ◽  
Vol 12 (7) ◽  
pp. e1004901 ◽  
Author(s):  
Gustaf Rydevik ◽  
Giles T. Innocent ◽  
Glenn Marion ◽  
Ross S. Davidson ◽  
Piran C. L. White ◽  
...  
Keyword(s):  
Diagnostic Test ◽  
Test Results ◽  
Cross Sectional
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