This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on ...This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.展开更多
Based on the scalar wave equation, making use of the ray approximation of the reflected seismic data (CMP or CSP gathers), the authors derive respectively the projection function of the primary waves and multiple wave...Based on the scalar wave equation, making use of the ray approximation of the reflected seismic data (CMP or CSP gathers), the authors derive respectively the projection function of the primary waves and multiple waves at the near offset (CMP or CSP gathers) in the parabolic Radon transform(PRT)domain. From the geometric point, the authors prove that the energy of the reflection still distributes along hyperbola which has higher curvature in the PRT domain and becomes some energy masses. So the primary waves and the multiple waves which interweave each other in ( x, t ) domain can be completely separated, which helps the multiple waves eliminated by filtering or muting. It is important for the analysis of velocity and the separator and elimination of multiple waves.展开更多
COVID-19 is a disease caused by the novel coronavirus SARS-CoV-2 that emerged at the end of December 2019 and has since spread globally.In Kenya,the virus was first detected on 13^(th) March 2020.Soon after,the Kenyan...COVID-19 is a disease caused by the novel coronavirus SARS-CoV-2 that emerged at the end of December 2019 and has since spread globally.In Kenya,the virus was first detected on 13^(th) March 2020.Soon after,the Kenyan government implemented non-pharmaceutical interventions(NPIs)to slow the spread of the disease.The pandemic continued to spread and it evolved into several waves over the years despite the discovery of vaccines and treatment.Mathematical models have been developed to help analyse,predict and simulate the dynamics of the pandemic.These models have largely been confined to single waves,without ready extension to multiple waves.In this paper,we develop a mathematical and computational model that can be extended to multiple waves using various concepts.Among these is the application of computational techniques that convert infection curves with negative gradients to those with positive gradients,in the neighbourhood of the change point,namely,where transition occurs from one wave to the next.This effectively generates a new wave.We then introduce a jump mechanism for the susceptible fraction,allowing further computation to align itself with the observed infection curve.To commence the process,we solved the system of governing ordinary differential equations for the period the epidemic spread without intervention and obtained values for the transmission,recovery and death rates that yielded the basic reproduction number,R_(0)=2.76,which is consistent with other related research.We then applied our model to COVID-19 in Kenya and the computation successfully replicated all the waves and also identified the change points located within the months when COVID-19 variants became dominant.The findings strengthen the proposition that the dominant COVID-19 variants were the major drivers of the waves.The techniques can be extended to new strains of COVID-19,influenza and other respiratory viruses.展开更多
We applied the multiple exp-function scheme to the（2＋1）-dimensional Sawada-Kotera（SK） equation and（3＋1）-dimensional nonlinear evolution equation and analytic particular solutions have been deduced. The analyti...We applied the multiple exp-function scheme to the（2＋1）-dimensional Sawada-Kotera（SK） equation and（3＋1）-dimensional nonlinear evolution equation and analytic particular solutions have been deduced. The analytic particular solutions contain one-soliton, two-soliton, and three-soliton type solutions. With the assistance of Maple, we demonstrated the efficiency and advantages of the procedure that generalizes Hirota＇s perturbation scheme. The obtained solutions can be used as a benchmark for numerical solutions and describe the physical phenomena behind the model.展开更多
The multiple lump solutions method is employed for the purpose of obtaining multiple soliton solutions for the generalized Bogoyavlensky-Konopelchenko(BK)equation.The solutions obtained contain first-order,second-orde...The multiple lump solutions method is employed for the purpose of obtaining multiple soliton solutions for the generalized Bogoyavlensky-Konopelchenko(BK)equation.The solutions obtained contain first-order,second-order,and third-order wave solutions.At the critical point,the second-order derivative and Hessian matrix for only one point is investigated,and the lump solution has one maximum value.He’s semi-inverse variational principle(SIVP)is also used for the generalized BK equation.Three major cases are studied,based on two different ansatzes using the SIVP.The physical phenomena of the multiple soliton solutions thus obtained are then analyzed and demonstrated in the figures below,using a selection of suitable parameter values.This method should prove extremely useful for further studies of attractive physical phenomena in the fields of heat transfer,fluid dynamics,etc.展开更多
In this paper,we image the subsurface reflectors by interferometric imaging using primary and downgoing first-order free-surface related multiple reflections in walkaway VSP data.By analyzing the stack fold distributi...In this paper,we image the subsurface reflectors by interferometric imaging using primary and downgoing first-order free-surface related multiple reflections in walkaway VSP data.By analyzing the stack fold distribution,we find that primary-direct interferometric imaging has a smaller image range,but its stack fold is higher near the well while ghostdirect interferometric imaging is the opposite.We try to solve this problem by the joint interferometric imaging of walkaway VSP data,combining primary-direct interferometric imaging with ghost-direct interferometric imaging.In this way,we can effectively widen the imaging range,simultaneously increase the fold（especially near the well）,suppress spurious interference,and improve the image SNR,so that we can get a more credible image.Test results on synthetic walkaway VSP data and field data show that joint interferometric imaging is very effective.展开更多
High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results fro...High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results from the interference of elastic microscopic multiple scattering waves. First, I propose a new theory on wave propagation in a two-phase medium which is based on the concept that the basic unit for wave propagation is a nano- mass point. As a result of the elasticity variations of pore fluid and rock framework, micro multiple scattering waves would emerge at the wavelength of the seismic waves passing through the two-phase medium and their interference and overlap would generate high- frequency seismic attenuation. Second, I present a study of the frequency response of seismic transmitted waves by modeling thin-layers with thicknesses no larger than pore diameters. Results indicate that high-frequency seismic waves attenuate slightly in a near-surface water zone but decay significantly in a near-surface gas zone. Third, I analyze the seismic attenuation characteristics in near-surface water and gas zones using dual-well shots in the Songliao Basin, and demonstrate that the high-frequency seismic waves attenuate slightly in water zones but in gas zones the 160-1600 Hz propagating waves decay significantly. The seismic attenuation characteristics from field observations coincide with the modeling results. Conclusions drawn from these studies theoretically support seismic attenuation recovery.展开更多
The relationship between the number of detonation waves and the evolution process of the flow field in a rotating detonation engine was investigated through a numerical analysis.The simulations were based on the Euler...The relationship between the number of detonation waves and the evolution process of the flow field in a rotating detonation engine was investigated through a numerical analysis.The simulations were based on the Euler equation and a detailed chemical reaction model.In the given engine model,the flow-field evolution became unstable when a single detonation wave was released.New detonation waves formed spontaneously,changing the operational mode from single-wave to four-wave.However,when two or three detonation waves were released,the flow field evolved in a quasi-steady manner.Further study revealed that the newly formed detonation wave resulted from an accelerated chemical reaction on the contact surface between the detonation products and the reactive mixture.To satisfy the stable propagation requirements of detonation waves,we proposed a parameter called NL,which can be compared with the number of detonation waves in the combustor to predict the evolution(quasi-stable or unstable)of the flow field.Finally,we verified the effectiveness of NL in a redesigned engine.This study may assist the operational mode control in rotating detonation engine experiments.展开更多
The overall development of the top of the gas reservoir of the Dengying Formation,Upper Sinian in the Anyue Gas Field of the Sichuan Basin,has been deployed,and the inner Dengying Formation is the next potential succe...The overall development of the top of the gas reservoir of the Dengying Formation,Upper Sinian in the Anyue Gas Field of the Sichuan Basin,has been deployed,and the inner Dengying Formation is the next potential succession layer.However,the high-quality reservoirs of inner Dengying Formation are undeveloped and cannot be identified on the seismic profiles,which restricts its deepened understanding,exploration and development.In this paper,the logging and seismic response characteristics of high-quality reservoirs were analyzed using the mud logging and well logging data of the Anyue Gas Field,and a seismic response model for high-quality reservoir was established by means of seismic forward modeling.Then,the target processing was carried out for the problem of weak effective signals.Finally,the plane distribution of high-quality reservoirs of inner Dengying Formation and the favorable exploration areas were predicted.And the following research results were obtained.First,there are two types of high-quality reservoirs inside the Dengying Formation,i.e.,concentrated vug type and independent cave type.Vertically,the independent cave reservoirs are mainly distributed within 100 m above the mudstone floor of the third Member of Dengying Formation.Horizontally,karst zones are developed along the bed.Laterally,they are scattered and beaded.And the scale is small.Second,seismic response of high-quality reservoirs inside the carbonate rocks is characterized by single-peak concealed“beaded”reflection,whose peak energy is relatively weak and can be easily covered by the noise of seismic data.Third,deep-seated weak signal recovery and processing technology can be used to deal with the weak seismic response of high-quality cave reservoirs,improve the amplitude preservation and S/N ratio of seismic data,and obtain the beaded reflections on seismic profiles so as to realize effective identification of high-quality cave reservoirs.In conclusion,the deep-seated weak signal recovery and processing technology is proved to be operable because the achieved results conform to the drilling data and the seismic forward modeling conclusions.In addition,high-quality cave reservoirs are developed at the bottom of the fourth Member of Dengying Formation,and they are locally distributed in a large scale.Therefore,it's one of the favorable succession layers for the following natural gas exploration and development of the Anyue Gas Field.展开更多
Experiments of the runup of two solitary waves on a plane beach are carded out in a wave flume. The two solitary waves with the same amplitude and the crest separating distances are generated by using an improved wave...Experiments of the runup of two solitary waves on a plane beach are carded out in a wave flume. The two solitary waves with the same amplitude and the crest separating distances are generated by using an improved wave generation method. It is found that, with regard to the two solitary waves with same wave amplitude, the runup amplification of the second wave is less than that of the first wave if the relative crest separating distance is reduced to a certain threshold value. The rundown of the first solitary wave depresses the maximtlm runup of the second wave, If the leading solitary wave is of relatively smaller amplitude for the two solitary waves, the runup amplification is affected by the overtaking process of two solitary waves. It turns out that the runup amplification of the second wave is larger than that of the first wave if the similarity factor is approximately larger than 15, which means the larger wave overtakes the smaller one before the waves runup on a beach.展开更多
The multiple-order line rogue wave solutions method is emp loyed for searching the multiple soliton solutions for the generalized(2+1)-dimensional Camassa-HolmKadomtsev-Petviashvili(CHKP)equation,which contains first-...The multiple-order line rogue wave solutions method is emp loyed for searching the multiple soliton solutions for the generalized(2+1)-dimensional Camassa-HolmKadomtsev-Petviashvili(CHKP)equation,which contains first-order,second-order,and third-order waves solutions.At the critical point,the second-order derivative and Hessian matrix for only one point will be investigated and the lump solution has one minimum value.For the case,the lump solution will be shown the bright-dark lump structure and for another case can be present the dark lump structure-two small peaks and one deep hole.Also,the interaction of lump with periodic waves and the interaction between lump and soliton can be obtained by introducing the Hirota forms.In the meanwhile,the cross-kink wave and periodic wave solutions can be gained by the Hirota operator.The physical phenomena of these gained multiple soliton solutions are analyzed and indicated in figures by selecting suitable values.We alternative offer that the determining method is general,impressive,outspoken,and powerful and can be exerted to create exact solutions of various kinds of nonlinear models originated in mathematical physics and engineering.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11174322 and 11074273)the Research Council of Norway (GrantNo. 186923/I30)
文摘This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.
文摘Based on the scalar wave equation, making use of the ray approximation of the reflected seismic data (CMP or CSP gathers), the authors derive respectively the projection function of the primary waves and multiple waves at the near offset (CMP or CSP gathers) in the parabolic Radon transform(PRT)domain. From the geometric point, the authors prove that the energy of the reflection still distributes along hyperbola which has higher curvature in the PRT domain and becomes some energy masses. So the primary waves and the multiple waves which interweave each other in ( x, t ) domain can be completely separated, which helps the multiple waves eliminated by filtering or muting. It is important for the analysis of velocity and the separator and elimination of multiple waves.
文摘COVID-19 is a disease caused by the novel coronavirus SARS-CoV-2 that emerged at the end of December 2019 and has since spread globally.In Kenya,the virus was first detected on 13^(th) March 2020.Soon after,the Kenyan government implemented non-pharmaceutical interventions(NPIs)to slow the spread of the disease.The pandemic continued to spread and it evolved into several waves over the years despite the discovery of vaccines and treatment.Mathematical models have been developed to help analyse,predict and simulate the dynamics of the pandemic.These models have largely been confined to single waves,without ready extension to multiple waves.In this paper,we develop a mathematical and computational model that can be extended to multiple waves using various concepts.Among these is the application of computational techniques that convert infection curves with negative gradients to those with positive gradients,in the neighbourhood of the change point,namely,where transition occurs from one wave to the next.This effectively generates a new wave.We then introduce a jump mechanism for the susceptible fraction,allowing further computation to align itself with the observed infection curve.To commence the process,we solved the system of governing ordinary differential equations for the period the epidemic spread without intervention and obtained values for the transmission,recovery and death rates that yielded the basic reproduction number,R_(0)=2.76,which is consistent with other related research.We then applied our model to COVID-19 in Kenya and the computation successfully replicated all the waves and also identified the change points located within the months when COVID-19 variants became dominant.The findings strengthen the proposition that the dominant COVID-19 variants were the major drivers of the waves.The techniques can be extended to new strains of COVID-19,influenza and other respiratory viruses.
文摘We applied the multiple exp-function scheme to the（2＋1）-dimensional Sawada-Kotera（SK） equation and（3＋1）-dimensional nonlinear evolution equation and analytic particular solutions have been deduced. The analytic particular solutions contain one-soliton, two-soliton, and three-soliton type solutions. With the assistance of Maple, we demonstrated the efficiency and advantages of the procedure that generalizes Hirota＇s perturbation scheme. The obtained solutions can be used as a benchmark for numerical solutions and describe the physical phenomena behind the model.
文摘The multiple lump solutions method is employed for the purpose of obtaining multiple soliton solutions for the generalized Bogoyavlensky-Konopelchenko(BK)equation.The solutions obtained contain first-order,second-order,and third-order wave solutions.At the critical point,the second-order derivative and Hessian matrix for only one point is investigated,and the lump solution has one maximum value.He’s semi-inverse variational principle(SIVP)is also used for the generalized BK equation.Three major cases are studied,based on two different ansatzes using the SIVP.The physical phenomena of the multiple soliton solutions thus obtained are then analyzed and demonstrated in the figures below,using a selection of suitable parameter values.This method should prove extremely useful for further studies of attractive physical phenomena in the fields of heat transfer,fluid dynamics,etc.
基金supported by the National 863 Program of China (Grant No.2006A09A102-11)National Natural Science Foundation of China (Grant No.40730424)Important National Science & Technology Specific Projects (Grant No.2008ZX05023-005)
文摘In this paper,we image the subsurface reflectors by interferometric imaging using primary and downgoing first-order free-surface related multiple reflections in walkaway VSP data.By analyzing the stack fold distribution,we find that primary-direct interferometric imaging has a smaller image range,but its stack fold is higher near the well while ghostdirect interferometric imaging is the opposite.We try to solve this problem by the joint interferometric imaging of walkaway VSP data,combining primary-direct interferometric imaging with ghost-direct interferometric imaging.In this way,we can effectively widen the imaging range,simultaneously increase the fold（especially near the well）,suppress spurious interference,and improve the image SNR,so that we can get a more credible image.Test results on synthetic walkaway VSP data and field data show that joint interferometric imaging is very effective.
文摘High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results from the interference of elastic microscopic multiple scattering waves. First, I propose a new theory on wave propagation in a two-phase medium which is based on the concept that the basic unit for wave propagation is a nano- mass point. As a result of the elasticity variations of pore fluid and rock framework, micro multiple scattering waves would emerge at the wavelength of the seismic waves passing through the two-phase medium and their interference and overlap would generate high- frequency seismic attenuation. Second, I present a study of the frequency response of seismic transmitted waves by modeling thin-layers with thicknesses no larger than pore diameters. Results indicate that high-frequency seismic waves attenuate slightly in a near-surface water zone but decay significantly in a near-surface gas zone. Third, I analyze the seismic attenuation characteristics in near-surface water and gas zones using dual-well shots in the Songliao Basin, and demonstrate that the high-frequency seismic waves attenuate slightly in water zones but in gas zones the 160-1600 Hz propagating waves decay significantly. The seismic attenuation characteristics from field observations coincide with the modeling results. Conclusions drawn from these studies theoretically support seismic attenuation recovery.
基金Project supported by the National Natural Science Foundation of China(No.11702329)the Open Project Program of the Key Laboratory of Aerodynamic Noise Control of China Aerodynamics Research and Development Center(CARDC)(No.ANCL20180103)+1 种基金the CARDC Fundamental and Frontier Technology Research Fund(No.PJD20180143)the Open Project Program of Rotor Aerodynamics Key Laboratory(No.RAL20180403),China。
文摘The relationship between the number of detonation waves and the evolution process of the flow field in a rotating detonation engine was investigated through a numerical analysis.The simulations were based on the Euler equation and a detailed chemical reaction model.In the given engine model,the flow-field evolution became unstable when a single detonation wave was released.New detonation waves formed spontaneously,changing the operational mode from single-wave to four-wave.However,when two or three detonation waves were released,the flow field evolved in a quasi-steady manner.Further study revealed that the newly formed detonation wave resulted from an accelerated chemical reaction on the contact surface between the detonation products and the reactive mixture.To satisfy the stable propagation requirements of detonation waves,we proposed a parameter called NL,which can be compared with the number of detonation waves in the combustor to predict the evolution(quasi-stable or unstable)of the flow field.Finally,we verified the effectiveness of NL in a redesigned engine.This study may assist the operational mode control in rotating detonation engine experiments.
基金Project supported by the National Key R&D Program of China“Theory and Technology Integration of Deep Resource Exploration and Mining”(No.:2018YFC0603706)Scientific Research and Technology Development Project of CNPC“Field Test and Integration Matching of Major Geophysical Technology”(No.:2017D-3503)。
文摘The overall development of the top of the gas reservoir of the Dengying Formation,Upper Sinian in the Anyue Gas Field of the Sichuan Basin,has been deployed,and the inner Dengying Formation is the next potential succession layer.However,the high-quality reservoirs of inner Dengying Formation are undeveloped and cannot be identified on the seismic profiles,which restricts its deepened understanding,exploration and development.In this paper,the logging and seismic response characteristics of high-quality reservoirs were analyzed using the mud logging and well logging data of the Anyue Gas Field,and a seismic response model for high-quality reservoir was established by means of seismic forward modeling.Then,the target processing was carried out for the problem of weak effective signals.Finally,the plane distribution of high-quality reservoirs of inner Dengying Formation and the favorable exploration areas were predicted.And the following research results were obtained.First,there are two types of high-quality reservoirs inside the Dengying Formation,i.e.,concentrated vug type and independent cave type.Vertically,the independent cave reservoirs are mainly distributed within 100 m above the mudstone floor of the third Member of Dengying Formation.Horizontally,karst zones are developed along the bed.Laterally,they are scattered and beaded.And the scale is small.Second,seismic response of high-quality reservoirs inside the carbonate rocks is characterized by single-peak concealed“beaded”reflection,whose peak energy is relatively weak and can be easily covered by the noise of seismic data.Third,deep-seated weak signal recovery and processing technology can be used to deal with the weak seismic response of high-quality cave reservoirs,improve the amplitude preservation and S/N ratio of seismic data,and obtain the beaded reflections on seismic profiles so as to realize effective identification of high-quality cave reservoirs.In conclusion,the deep-seated weak signal recovery and processing technology is proved to be operable because the achieved results conform to the drilling data and the seismic forward modeling conclusions.In addition,high-quality cave reservoirs are developed at the bottom of the fourth Member of Dengying Formation,and they are locally distributed in a large scale.Therefore,it's one of the favorable succession layers for the following natural gas exploration and development of the Anyue Gas Field.
基金supported by the National Natural Science Foundation of China(Grant No.10972138)the Natural Science Foundation of Shanghai Municipality(Grant No.11ZR1418200)
文摘Experiments of the runup of two solitary waves on a plane beach are carded out in a wave flume. The two solitary waves with the same amplitude and the crest separating distances are generated by using an improved wave generation method. It is found that, with regard to the two solitary waves with same wave amplitude, the runup amplification of the second wave is less than that of the first wave if the relative crest separating distance is reduced to a certain threshold value. The rundown of the first solitary wave depresses the maximtlm runup of the second wave, If the leading solitary wave is of relatively smaller amplitude for the two solitary waves, the runup amplification is affected by the overtaking process of two solitary waves. It turns out that the runup amplification of the second wave is larger than that of the first wave if the similarity factor is approximately larger than 15, which means the larger wave overtakes the smaller one before the waves runup on a beach.
文摘The multiple-order line rogue wave solutions method is emp loyed for searching the multiple soliton solutions for the generalized(2+1)-dimensional Camassa-HolmKadomtsev-Petviashvili(CHKP)equation,which contains first-order,second-order,and third-order waves solutions.At the critical point,the second-order derivative and Hessian matrix for only one point will be investigated and the lump solution has one minimum value.For the case,the lump solution will be shown the bright-dark lump structure and for another case can be present the dark lump structure-two small peaks and one deep hole.Also,the interaction of lump with periodic waves and the interaction between lump and soliton can be obtained by introducing the Hirota forms.In the meanwhile,the cross-kink wave and periodic wave solutions can be gained by the Hirota operator.The physical phenomena of these gained multiple soliton solutions are analyzed and indicated in figures by selecting suitable values.We alternative offer that the determining method is general,impressive,outspoken,and powerful and can be exerted to create exact solutions of various kinds of nonlinear models originated in mathematical physics and engineering.
