Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode(CCM) are studied in this paper. First of all, the two-dimensional discrete mapping model is established....Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode(CCM) are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i_L–v_C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that,with the increase of reference current I_(ref), the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Irefdecreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.展开更多
In the present study, the surface elevation of wind waves observed in laboratory and in the Bohai Sea are adopted for the estimation of the wind wave frequency spectrtm by use of the method of the arcsine law (MAL)....In the present study, the surface elevation of wind waves observed in laboratory and in the Bohai Sea are adopted for the estimation of the wind wave frequency spectrtm by use of the method of the arcsine law (MAL). The traditional method uses the surface elevation to calculate the correlation and then estimate the frequency spectrum while the MAL, presented by Yu and l.an (1979), uses the time sequence of zero-crossing points of surface elevation rather than directly the surface elevation to calculate the correlation. 66 sets of wind wave data obtained in laboratory and 420 sets of data observed in the Bohai Sea are adopted for the examination of the method introduced by Yu and Lan. Results show that the MAL can give reliable estimation of wind wave spectra. Correlation and form of spectra estimated by the MAL are similar to those estimated by the traditional method. The peak frequency and the spectral density in peak frequency by the MAL are close to those obtained by the traditional method.展开更多
A numerical method is designed to examine the response properties of real sea areas to open ocean forcing. The application of this method to modeling the China's adjacent seas shows that the Bohai Sea has a highest p...A numerical method is designed to examine the response properties of real sea areas to open ocean forcing. The application of this method to modeling the China's adjacent seas shows that the Bohai Sea has a highest peak response frequency (PRF) of 1.52 d^-1; the northern Yellow Sea has a PRF of 1.69 d^-1; the Gyeonggi Bay has a high amplitude gain plateau in the frequency band roughly from 1.7 to 2.7 d^-1; the Yellow Sea (includ- ing the Gyeonggi Bay), the East China Sea shelf and the Taiwan Strait have a common high amplitude gain band with frequencies around 1.76 to 1.78 d^-1 and are shown to be a system that responds to the open ocean forcing in favor of amplifying the waves with frequencies in this band; the Beibu Gulf, the Gulf of Thailand and the South China Sea deep basin have PRFs of 0.91, 1.01 and 0.98 d^-1 respectively. In addition, the East China Sea has a Poincare mode PRF of 3.91 d^-1. The PRFs of the Bohal Sea, the northern Yellow Sea, the Bei- bu Gulf and the South China Sea can be explained by a classical quarter (half for the Bohai Sea) wavelength resonance theory. The results show that further investigations are needed for the response dynamics of the Yellow Sea-East China Sea-Taiwan Strait system, the East China Sea Poincare mode, the Talwan Strait, and the Gulf of Thailand.展开更多
<strong>Background: </strong>The 1st peak frequency of the hammering sound in total hip arthroplasty may serve as an evaluation index to prevent intraoperative fracture. Fixation of the stem and femur cann...<strong>Background: </strong>The 1st peak frequency of the hammering sound in total hip arthroplasty may serve as an evaluation index to prevent intraoperative fracture. Fixation of the stem and femur cannot be acquired unless the 1st peak frequency of hammering the stem into the femur stabilizes, and fixation can be judged as acquired when the 1st peak frequency becomes constant. To investigate whether the environmental sound in the operating room can be differentiated from the hammering sound of total hip arthroplasty, the 1st peak frequency of the hammering sound when impacting the stem into the femur with a hammer was identified. <strong>Method:</strong> The hammering sound of impacting the stem into a biomechanical test material through an impactor was analyzed using a fast Fourier transform analyzer. Environmental sound in the operating room was simulated and the 1st peak frequency of the sound on collision between the operator’s voice and the surgical instrument was measured. The 1st peak frequency of hammering sound was compared between patients indicated for total hip arthroplasty and healthy individuals to investigate whether there is a difference due to bone quality. <strong>Results:</strong> The natural frequency of the impactor was 3.41 ± 0.05 kHz, and the 1st peak frequency of the femur, stem, and impactor was 2.43 ± 1.45 kHz. The 1st peak frequency of hammering sound on simulated femur in patients indicated for total hip arthroplasty was 2.98 ± 0.73 kHz and that in healthy individuals was 2.15 ± 0.32 kHz. This suggested that the hammering sound in total hip arthroplasty-indicated patients overlaps with the frequency of the collision sound of surgical instruments.<strong> Conclusion: </strong>To develop a system to prevent intraoperative fracture, countermeasures, such as noise canceling, are necessary to prevent false detection of hammering sounds.展开更多
The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber(fiber of low elastic modulus) and steel fiber(fib...The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber(fiber of low elastic modulus) and steel fiber(fiber of high elastic modulus) reinforced concrete under medium strain rate(10-6 s-1-10-4 s-1). In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission(AE) technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor(DIF) of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.展开更多
Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes...Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about 0.1-1 microns. Microtremor measurement is fast, applica- ble, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplifica- tion factor were calculated for all microtremor stations. According to the analysis, the peak frequency varies from 0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor obser- vations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.展开更多
This paper presents a study of the characteristics of a railway vibration at three key sections containing different track structures in a metro depot.The results show that the vertical and horizontal vibration accele...This paper presents a study of the characteristics of a railway vibration at three key sections containing different track structures in a metro depot.The results show that the vertical and horizontal vibration acceleration levels are proportional to train speed.The Z-weighted vertical acceleration levels obtained showed that the vibration source strengths at the ballast foot of the testing line and the throat area were very close.The vibration attenuation at the repair line was larger than that of the testing line.In the throat area,the peak frequency of vibration obtained at the ballast foot(2.5 m)could be shifted to a lower frequency band by using polyurethane sleepers instead of standard concrete sleepers.Polyurethane sleepers can help to reduce vertical vibration in a frequency band of 0-10 Hz.The vibration levels would satisfy the limits given in the ISO2631-2-2003(2013)for any location more than 5 m away from the source at the testing line and 2.5 m away from the source at the repair line and throat area.展开更多
In this paper,the rotating instability(RI)in an axial compressor has been investigated numerically in order to examine the capability of URANS method to simulate its typical characteristics of RI broadband humps with ...In this paper,the rotating instability(RI)in an axial compressor has been investigated numerically in order to examine the capability of URANS method to simulate its typical characteristics of RI broadband humps with multi-peak frequencies(MPFs)and further to uncover the underlying flow mechanism.A full-annulus modeling solution has been adopted to fully capture the wide range of different length-scale flow disturbances that circumferentially propagating around the compressor rotor.During the transient computing process,long-term monitoring up to 50 revolutions has been carried out to achieve a fine frequency resolution,and that would be essential for resolving the MPFs with small frequency interval.It is shown that the MPFs feature of RI has been successfully captured by the full-annulus URANS approach,and also its frequency range and spectral feature agree well with the experimental results.Further,with a circumferential mode decomposition on the MPFs characteristics of RI,it has been found that the MPFs result from the interaction between long-and short-scale flow disturbances which circumferentially propagate around the compressor rotor near the clearance region.zDetailed examination on the numerical three dimensional flow field indicates that the short-scale disturbance is induced by the unsteady oscillation of tip clearance vortexes with inter-passage phase delay.The long-scale disturbance is caused by the mistuning of the wave number of the short-scale disturbance and the blade number within the whole annulus.展开更多
Combined with irregular wave-maker, the growing process of Wave Energy Spectrum in shallow water can be studied in wind wave channel on different water depth conditions, and its transformation characteristics and rule...Combined with irregular wave-maker, the growing process of Wave Energy Spectrum in shallow water can be studied in wind wave channel on different water depth conditions, and its transformation characteristics and rules can be obtained.展开更多
Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices (BMPs), like detention ponds...Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices (BMPs), like detention ponds and infiltration trenches, have been widely used to control flood runoff events for the past decade. However, low impact development (LID) options have been proposed as an alternative approach to better mimic the natural flow regime by using decentralized designs to control stormwater runoff at the source, rather than at a centralized location in the watershed. For highly urbanized areas, LID stormwater management practices such as bioretention cells and porous pavements can be used to retrofit existing infrastructure and reduce runoff volumes and peak flows. This paper describes a modeling approach to incorporate these LID practices and the two BMPs of detention ponds and infiltration trenches in an existing hydrological model to estimate the impacts of BMPs and LID practices on the surface runoff. The modeling approach has been used in a parking lot located in Lenexa, Kansas, USA, to predict hydrological performance of BMPs and LID practices. A performance indicator system including the flow duration curve, peak flow frequency exceedance curve, and runoff coefficient have been developed in an attempt to represent impacts of BMPs and LID practices on the entire spectrum of the runoff regime. Results demonstrate that use of these BMPs and LID practices leads to significant stormwater control for small rainfall events and less control for flood events.展开更多
Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration, especially for thin-layer below tuning thickness. In this article, we analyzed the seismic response cha- racteristics of rhy...Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration, especially for thin-layer below tuning thickness. In this article, we analyzed the seismic response cha- racteristics of rhythm and gradual type of thin-layer wedge models and presented a new method for thin-layer thickness estimation which uses relative peak frequency increment. This method can de- scribe the peak frequency to thickness relationship of rhythm and gradual thin-layers in unified equa- tion while the traditional methods using amplitude information cannot. What's more, it won't be in- fluenced by the absolute value of thin-layer reflection coefficient and peak frequency of wavelet. The unified equations were presented which can be used for rhythm and gradual thin-layer thickness cal- culation. Model tests showed that the method we introduced has a high precision and it doesn't need to determine the value of top or bottom reflection coefficient, so it has a more wide application in practice. The application of real data demonstrated that the relative peak frequency increment attribute can character the plane distribution feature and thickness characteristic of channel sand bodies very well.展开更多
Acoustic emission ( AE ) features during the fracture process of notched wrought aluminum alloy 7N01 and weld were investigated under the three-point bending load. Wavelet transform is used to investigate the time-f...Acoustic emission ( AE ) features during the fracture process of notched wrought aluminum alloy 7N01 and weld were investigated under the three-point bending load. Wavelet transform is used to investigate the time-frequency features of AE signals during the test. The experimental results showed that AE energy was effective indicators to detect the crack initiation for 7N01 aluminum. The digital images from monitoring the notch tip region of 7 NO1 aluminum sample verify the prediction of AE signals. The weld emits low energy, weak signal strength, and low peak amplitude, while stronger AE energy, amplitude, and more AE event counts for the base metal. In short, the AE technique was more sensitive to the changes in the fracture mode and could be used to monitor the damage development in welded structures.展开更多
In total hip arthroplasty, intraoperative femoral fractures can be avoided by analyzing the hammering sounds from the stem inserted into the femur. This procedure is based on a hammering test that makes use of the fac...In total hip arthroplasty, intraoperative femoral fractures can be avoided by analyzing the hammering sounds from the stem inserted into the femur. This procedure is based on a hammering test that makes use of the fact that sound depends on the stability of the object. This technique is generally used in engineering. A system designed to avoid excessive stem hammering by predicting the intraoperative fracture risk based on this technique and software for real-time spectra analysis has been developed with repetitive improvements. The remaining technical challenge lies in selecting an appropriate sound collection device and building a compact and easy unit for use. This study reviewed the types of directional microphones suitable for the sound collection system to develop a practical THA support system. Four types of microphones based on selected methods were used to collect and compare the peak frequencies of the hammering sounds and make comparisons between them, and the built system was used to conduct clinical trials. For miniaturization and operational ease of the unit, plug-in unidirectional microphones are appropriate. However, no laboratory-level data has been collected, and thus, further data accumulation is necessary.展开更多
Pressure fluctuations signals of a lab-scale fiuidized bed (15 cm inner diameter and 2 m height) at different superficial gas velocities were measured. Recurrence plot (RP) and recurrence rate (RR), and the simp...Pressure fluctuations signals of a lab-scale fiuidized bed (15 cm inner diameter and 2 m height) at different superficial gas velocities were measured. Recurrence plot (RP) and recurrence rate (RR), and the simplest variable of recurrence quantification analysis (RQA) were used to analyze the pressure signals. Different patterns observed in RP reflect different dynamic behavior of the system under study. It was also found that the variance of RR (a2R) Could reveal the peak dominant frequencies (PDF) of different dynamic systems: completely periodic, completely stochastic, Lorenz system, and fluidized bed. The results were compared with power spectral density. Additionally, the diagram of σ^2RR provides a new technique for prediction of transition velocity from bubbling to turbulent fluidization regime.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61376029)the Fundamental Research Funds for the Central Universities,Chinathe College Graduate Research and Innovation Program of Jiangsu Province,China(Grant No.SJLX15 0092)
文摘Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode(CCM) are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i_L–v_C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that,with the increase of reference current I_(ref), the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Irefdecreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.
基金This project was financially supported by the National Natural Science Foundation of China(Grant No.40406008) the Foundation for Open Projects of the Key Laboratory of Physical Oceanography,Ministry of Education,China(Grant No.200309)
文摘In the present study, the surface elevation of wind waves observed in laboratory and in the Bohai Sea are adopted for the estimation of the wind wave frequency spectrtm by use of the method of the arcsine law (MAL). The traditional method uses the surface elevation to calculate the correlation and then estimate the frequency spectrum while the MAL, presented by Yu and l.an (1979), uses the time sequence of zero-crossing points of surface elevation rather than directly the surface elevation to calculate the correlation. 66 sets of wind wave data obtained in laboratory and 420 sets of data observed in the Bohai Sea are adopted for the examination of the method introduced by Yu and Lan. Results show that the MAL can give reliable estimation of wind wave spectra. Correlation and form of spectra estimated by the MAL are similar to those estimated by the traditional method. The peak frequency and the spectral density in peak frequency by the MAL are close to those obtained by the traditional method.
基金The National Natural Science Foundation of China under contract Nos 40676009 and 40606006the Basic Research Project of Qingdao Science and Technology Program of China under contract No.11-1-4-98-jch
文摘A numerical method is designed to examine the response properties of real sea areas to open ocean forcing. The application of this method to modeling the China's adjacent seas shows that the Bohai Sea has a highest peak response frequency (PRF) of 1.52 d^-1; the northern Yellow Sea has a PRF of 1.69 d^-1; the Gyeonggi Bay has a high amplitude gain plateau in the frequency band roughly from 1.7 to 2.7 d^-1; the Yellow Sea (includ- ing the Gyeonggi Bay), the East China Sea shelf and the Taiwan Strait have a common high amplitude gain band with frequencies around 1.76 to 1.78 d^-1 and are shown to be a system that responds to the open ocean forcing in favor of amplifying the waves with frequencies in this band; the Beibu Gulf, the Gulf of Thailand and the South China Sea deep basin have PRFs of 0.91, 1.01 and 0.98 d^-1 respectively. In addition, the East China Sea has a Poincare mode PRF of 3.91 d^-1. The PRFs of the Bohal Sea, the northern Yellow Sea, the Bei- bu Gulf and the South China Sea can be explained by a classical quarter (half for the Bohai Sea) wavelength resonance theory. The results show that further investigations are needed for the response dynamics of the Yellow Sea-East China Sea-Taiwan Strait system, the East China Sea Poincare mode, the Talwan Strait, and the Gulf of Thailand.
文摘<strong>Background: </strong>The 1st peak frequency of the hammering sound in total hip arthroplasty may serve as an evaluation index to prevent intraoperative fracture. Fixation of the stem and femur cannot be acquired unless the 1st peak frequency of hammering the stem into the femur stabilizes, and fixation can be judged as acquired when the 1st peak frequency becomes constant. To investigate whether the environmental sound in the operating room can be differentiated from the hammering sound of total hip arthroplasty, the 1st peak frequency of the hammering sound when impacting the stem into the femur with a hammer was identified. <strong>Method:</strong> The hammering sound of impacting the stem into a biomechanical test material through an impactor was analyzed using a fast Fourier transform analyzer. Environmental sound in the operating room was simulated and the 1st peak frequency of the sound on collision between the operator’s voice and the surgical instrument was measured. The 1st peak frequency of hammering sound was compared between patients indicated for total hip arthroplasty and healthy individuals to investigate whether there is a difference due to bone quality. <strong>Results:</strong> The natural frequency of the impactor was 3.41 ± 0.05 kHz, and the 1st peak frequency of the femur, stem, and impactor was 2.43 ± 1.45 kHz. The 1st peak frequency of hammering sound on simulated femur in patients indicated for total hip arthroplasty was 2.98 ± 0.73 kHz and that in healthy individuals was 2.15 ± 0.32 kHz. This suggested that the hammering sound in total hip arthroplasty-indicated patients overlaps with the frequency of the collision sound of surgical instruments.<strong> Conclusion: </strong>To develop a system to prevent intraoperative fracture, countermeasures, such as noise canceling, are necessary to prevent false detection of hammering sounds.
基金Funded by the National Natural Science Foundation of China(No.51009058)Postdoctoral Science Foundation of China(No.2011M501160)+1 种基金the University Natural Science Research Project of Jiangsu Province(No.13KJD560002)the Doctoral Research Start-up Fund of Jinling Institute of Technology(No.Jit-b-201321)
文摘The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber(fiber of low elastic modulus) and steel fiber(fiber of high elastic modulus) reinforced concrete under medium strain rate(10-6 s-1-10-4 s-1). In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission(AE) technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor(DIF) of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.
文摘Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about 0.1-1 microns. Microtremor measurement is fast, applica- ble, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplifica- tion factor were calculated for all microtremor stations. According to the analysis, the peak frequency varies from 0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor obser- vations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.
基金National Natural Science Foundation of China under Grant Nos.52068029,51878277 and 52178423the Major Discipline Academic and Technical Leaders Training Program of Jiangxi Province Youth under Grant No.20194BCJ22008the Key Research and Development Program of Jiangxi Province under Grant No.20192BBE50008。
文摘This paper presents a study of the characteristics of a railway vibration at three key sections containing different track structures in a metro depot.The results show that the vertical and horizontal vibration acceleration levels are proportional to train speed.The Z-weighted vertical acceleration levels obtained showed that the vibration source strengths at the ballast foot of the testing line and the throat area were very close.The vibration attenuation at the repair line was larger than that of the testing line.In the throat area,the peak frequency of vibration obtained at the ballast foot(2.5 m)could be shifted to a lower frequency band by using polyurethane sleepers instead of standard concrete sleepers.Polyurethane sleepers can help to reduce vertical vibration in a frequency band of 0-10 Hz.The vibration levels would satisfy the limits given in the ISO2631-2-2003(2013)for any location more than 5 m away from the source at the testing line and 2.5 m away from the source at the repair line and throat area.
基金The authors would like to acknowledge the supports of National Natural Science Foundation of China(Grant No.51906205)National Science and Technology Major Project(2017-Ⅱ-0009-0023).
文摘In this paper,the rotating instability(RI)in an axial compressor has been investigated numerically in order to examine the capability of URANS method to simulate its typical characteristics of RI broadband humps with multi-peak frequencies(MPFs)and further to uncover the underlying flow mechanism.A full-annulus modeling solution has been adopted to fully capture the wide range of different length-scale flow disturbances that circumferentially propagating around the compressor rotor.During the transient computing process,long-term monitoring up to 50 revolutions has been carried out to achieve a fine frequency resolution,and that would be essential for resolving the MPFs with small frequency interval.It is shown that the MPFs feature of RI has been successfully captured by the full-annulus URANS approach,and also its frequency range and spectral feature agree well with the experimental results.Further,with a circumferential mode decomposition on the MPFs characteristics of RI,it has been found that the MPFs result from the interaction between long-and short-scale flow disturbances which circumferentially propagate around the compressor rotor near the clearance region.zDetailed examination on the numerical three dimensional flow field indicates that the short-scale disturbance is induced by the unsteady oscillation of tip clearance vortexes with inter-passage phase delay.The long-scale disturbance is caused by the mistuning of the wave number of the short-scale disturbance and the blade number within the whole annulus.
文摘Combined with irregular wave-maker, the growing process of Wave Energy Spectrum in shallow water can be studied in wind wave channel on different water depth conditions, and its transformation characteristics and rules can be obtained.
基金supported by the National Natural Science Foundation of China(Grants No.51279064 and 51209090)
文摘Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices (BMPs), like detention ponds and infiltration trenches, have been widely used to control flood runoff events for the past decade. However, low impact development (LID) options have been proposed as an alternative approach to better mimic the natural flow regime by using decentralized designs to control stormwater runoff at the source, rather than at a centralized location in the watershed. For highly urbanized areas, LID stormwater management practices such as bioretention cells and porous pavements can be used to retrofit existing infrastructure and reduce runoff volumes and peak flows. This paper describes a modeling approach to incorporate these LID practices and the two BMPs of detention ponds and infiltration trenches in an existing hydrological model to estimate the impacts of BMPs and LID practices on the surface runoff. The modeling approach has been used in a parking lot located in Lenexa, Kansas, USA, to predict hydrological performance of BMPs and LID practices. A performance indicator system including the flow duration curve, peak flow frequency exceedance curve, and runoff coefficient have been developed in an attempt to represent impacts of BMPs and LID practices on the entire spectrum of the runoff regime. Results demonstrate that use of these BMPs and LID practices leads to significant stormwater control for small rainfall events and less control for flood events.
基金supported by the Fundamental Research Funds for the Central Universities,Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110022120004)China National Key S&T Project on Marine Carbonate Reservoir Characterization(No.2011ZX05004003)
文摘Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration, especially for thin-layer below tuning thickness. In this article, we analyzed the seismic response cha- racteristics of rhythm and gradual type of thin-layer wedge models and presented a new method for thin-layer thickness estimation which uses relative peak frequency increment. This method can de- scribe the peak frequency to thickness relationship of rhythm and gradual thin-layers in unified equa- tion while the traditional methods using amplitude information cannot. What's more, it won't be in- fluenced by the absolute value of thin-layer reflection coefficient and peak frequency of wavelet. The unified equations were presented which can be used for rhythm and gradual thin-layer thickness cal- culation. Model tests showed that the method we introduced has a high precision and it doesn't need to determine the value of top or bottom reflection coefficient, so it has a more wide application in practice. The application of real data demonstrated that the relative peak frequency increment attribute can character the plane distribution feature and thickness characteristic of channel sand bodies very well.
文摘Acoustic emission ( AE ) features during the fracture process of notched wrought aluminum alloy 7N01 and weld were investigated under the three-point bending load. Wavelet transform is used to investigate the time-frequency features of AE signals during the test. The experimental results showed that AE energy was effective indicators to detect the crack initiation for 7N01 aluminum. The digital images from monitoring the notch tip region of 7 NO1 aluminum sample verify the prediction of AE signals. The weld emits low energy, weak signal strength, and low peak amplitude, while stronger AE energy, amplitude, and more AE event counts for the base metal. In short, the AE technique was more sensitive to the changes in the fracture mode and could be used to monitor the damage development in welded structures.
文摘In total hip arthroplasty, intraoperative femoral fractures can be avoided by analyzing the hammering sounds from the stem inserted into the femur. This procedure is based on a hammering test that makes use of the fact that sound depends on the stability of the object. This technique is generally used in engineering. A system designed to avoid excessive stem hammering by predicting the intraoperative fracture risk based on this technique and software for real-time spectra analysis has been developed with repetitive improvements. The remaining technical challenge lies in selecting an appropriate sound collection device and building a compact and easy unit for use. This study reviewed the types of directional microphones suitable for the sound collection system to develop a practical THA support system. Four types of microphones based on selected methods were used to collect and compare the peak frequencies of the hammering sounds and make comparisons between them, and the built system was used to conduct clinical trials. For miniaturization and operational ease of the unit, plug-in unidirectional microphones are appropriate. However, no laboratory-level data has been collected, and thus, further data accumulation is necessary.
基金Supports from the Iran National Science Foundation(INSF) in lran(No.91001766)
文摘Pressure fluctuations signals of a lab-scale fiuidized bed (15 cm inner diameter and 2 m height) at different superficial gas velocities were measured. Recurrence plot (RP) and recurrence rate (RR), and the simplest variable of recurrence quantification analysis (RQA) were used to analyze the pressure signals. Different patterns observed in RP reflect different dynamic behavior of the system under study. It was also found that the variance of RR (a2R) Could reveal the peak dominant frequencies (PDF) of different dynamic systems: completely periodic, completely stochastic, Lorenz system, and fluidized bed. The results were compared with power spectral density. Additionally, the diagram of σ^2RR provides a new technique for prediction of transition velocity from bubbling to turbulent fluidization regime.