Experimental Study on the Variation of Optical Imaging Characteristics with Zenith Angle due to Internal Solitary Waves in Sunglint

Internal solitary waves(ISWs)change the roughness of the sea surface,thus producing dark and bright bands in optical images.However,reasons for changes in imaging characteristics with the solar zenith angle remain unclear.In this paper,the optical imaging pattern of ISWs in sunglint under different zenith angles of the light source is investigated by collecting optical images of ISWs through physical simulation.The experiment involves setting 10 zenith angles of the light source,which are divided into area a the optical images of ISWs in the three areas show dark-bright mode,single bright band,and bright-dark mode,which are consistent with those observed by optical remote sensing.In addition,this study analyzed the percentage of the dark and bright areas of the bands and the change in the relative gray difference and found changes in both areas under different zenith angles of the light source.The MODIS and ASAR images display a similar brightness-darkness distance of the same ISWs.Therefore,the relationship between the brightness-darkness distance and the characteristic half-width of ISWs is determined in accordance with the eKdV theory and the imaging mechanism of ISWs of the SAR image.Overall,the relationship between them in the experiment is almost consistent with the theoretical result.

Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units.The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model.UDF(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology.The results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually decreases.And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner.The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude.The mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values.Compared with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and leakage.During actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

Experimental study on the variation of optical remote sensing imaging characteristics of internal solitary waves with wind speed

Optical remote sensing has been widely used to study internal solitary waves(ISWs).Wind speed has an important effect on ISW imaging of optical remote sensing.The light and dark bands of ISWs cannot be observed by optical remote sensing when the wind is too strong.The relationship between the characteristics of ISWs bands in optical remote sensing images and the wind speed is still unclear.The influence of wind speeds on the characteristics of the ISWs bands is investigated based on the physical simulation experiments with the wind speeds of 1.6,3.1,3.5,3.8,and 3.9 m/s.The experimental results show that when the wind speed is 3.9 m/s,the ISWs bands cannot be observed in optical remote sensing images with the stratification of h_(1)∶h_(2)=7∶58,ρ_(1)∶ρ_(2)=1∶1.04.When the wind speeds are 3.1,3.5,and 3.8 m/s,which is lower than 3.9 m/s,the ISWs bands can be obtained in the simulated optical remote sensing image.The location of the band’s dark and light extremum and the band’s peak-to-peak spacing are almost not affected by wind speed.More-significant wind speeds can cause a greater gray difference of the light-dark bands.This provided a scientific basis for further understanding of ISW optical remote sensing imaging.

Wave Characteristics at the South Part of the Radial Sand Ridges of the Southern Yellow Sea

Based on one-year wave field data measured at the south part of the radial sand ridges of the Southern Yellow Sea, the wave statistical characteristics, wave spectrum and wave group properties are analyzed. The results show that the significant wave height （H1/3） varies from 0.15 to 2.22 m with the average of 0.59 m and the mean wave period （Tmean） varies from 2.06 to 6.82 s with the average of 3.71 s. The percentage of single peak in the wave spectra is 88.6 during the measurement period, in which 36.3% of the waves are pure wind waves and the rest are young swells. The percentage with the significant wave height larger than 1 m is 12.4. The dominant wave directions in the study area are WNW, W, ESE, E and NW. The relationships among the characteristic wave heights, the characteristic wave periods, and the wave spectral parameters are identified. It is found that the tentative spectral model is suitable for the quantitative description of the wave spectrum in the study area, while the run lengths of the wave group estimated from the measured data are generally larger than those in other sea areas.

Analysis on the Temporal and Spatial Characteristics and Causes of Cold Wave in Qinhuangdao

[Objective] The aim was to study the temporal and spatial characteristics and causes of cold wave in Qinhuangdao.[Method] Based on temperature data from five surface meteorological stations in Qinhuangdao from 1970 to 2009 and the latest standards issuing cold wave early warning signal,statistical analysis on the temporal and spatial distribution of cold wave was carried out,and the causes were discussed preliminarily.[Result] From 1970 to 2009,the frequencies of blue and yellow cold wave in Qinhuangdao region were 2 334 and 105 times respectively,and cold wave occurred most frequently in Qinglong County and least frequently in Lulong County,which was related to the effects of underlying surface,latitude and altitude.Cold wave might happen from September to next May,and the earliest occurrence date was September 9,while the latest end date was May 26.In addition,the frequency of cold wave was the highest in January and lowest in May.From 1970 to 2009,blue cold wave occurred most frequently in 1972 and 1979 and least frequently in 1984,while the frequency of yellow cold wave was the highest in 1979 and lowest in 9 years.From decadal variation,cold wave appeared most frequently in the 1970s and least frequently in the 1990s.With the increase of temperature,the frequency of cold wave showed decrease trend,and the beginning date tended to postpone,while its end date advanced,and it showed that the changes of cold wave was mainly caused by climate warming.[Conclusion] The study could provide theoretical guidance for the meteorological disaster prevention and reduction and local agricultural service.

Experimental research on the instability propagation characteristics of liquid kerosene rotating detonation wave

In order to study the instability propagation characteristics of the liquid kerosene rotating detonation wave(RDW),a series of experimental tests were carried out on the rotating detonation combustor(RDC)with air-heater.The fuel and oxidizer are room-temperature liquid kerosene and preheated oxygenenriched air,respectively.The experimental tests keep the equivalence ratio of 0.81 and the oxygen mass fraction of 35%unchanged,and the total mass flow rate is maintained at about 1000 g/s,changing the total temperature of the oxygen-enriched air from 620 K to 860 K.Three different types of instability were observed in the experiments:temporal and spatial instability,mode transition and re-initiation.The interaction between RDW and supply plenum may be the main reason for the fluctuations of detonation wave velocity and pressure peaks with time.Moreover,the inconsistent mixing of fuel and oxidizer at different circumferential positions is related to RDW oscillate spatially.The phenomenon of single-double-single wave transition is analyzed.During the transition,the initial RDW weakens until disappears,and the compression wave strengthens until it becomes a new RDWand propagates steadily.The increased deflagration between the detonation products and the fresh gas layer caused by excessively high temperature is one of the reasons for the RDC quenching and re-initiation.

Analysis of Energy Characteristics in the Process of Freak Wave Generation

The energy characteristics in the evolution of the wave train are investigated to understand the inherent cause of the freak wave generation. The Morlet wavelet spectrum method is employed to analyze the numerical, laboratory and field evolution data of this generation process. Their energy distributions and variations are discussed with consideration of corresponding surface elevations. Through comparing the energy characteristics of three cases, it is shown that the freak wave generation depends not only on the continuous transfer of wave train energy to a certain region where finally the maximum energy occurs, but also on the distinct shift of the converged energy to high-frequency components in a very short time. And the typical energy characteristics of freak waves are also given.

Wave Characteristics and Extreme Parameters in the Bohai Sea

This paper is aimed at the whole Bohai Sea, as the complement and improvement of wave characteristics and extreme parameters. Wave fields were simulated in the Bohai Sea by using wave model SWAN from 1985 to 2004. The input data based on the hindcast of high-resolution wind fields from RAMS and water level fields from POM, which have been tested and verified well. Comparisons of significant wave heights between simulation and station observations show a good agreement in general. By statistical analysis, the wave characteristics such as significant wave heights, dominant wave directions and their seasonal variations are discussed. In addition, main wave extreme parameters and directional extreme values particularly for 100-year return period are investigated.

Temperature Characteristics of Surface Acoustic Waves Propagating on La_3Ga_5SiO_4 Substrates

Langasite (LGS) is a novel piezoelectric crystal. The authors numerically analyses the temperature stability of surface acoustic waves (SAW) and the relation of SAW propagation with temperature on certain optimal cuts on LGS in this paper. The results show that LGS has better temperature stability than traditional piezo crystals. The results also demonstrate that the velocity of SAW decrease with temperature, the electro-mechanical coupling constant (k2) and temperature coefficient of frequency increases parabolically and the power flow angle increases linearly on certain optimal cuts of LGS. The calculation result compared with the experimental and show good agreement.

Study on Propagation Characteristics of Plasma Surface Wave in Medium Tube

Axial propagation characteristics of the axisymmetric surface wave along the plasma in the medium tube were studied. The expressions of electromagnetic field inside and outside the medium tube were deduced. Also, the impacts of several factors, such as plasma density, signal frequency, inner radius of medium tube, collision frequency, etc., on plasma surface wave propa- gation were numerically simulated. The results show that, the properties of plasma with higher density and lower gas pressure are closer to those of metal conductor. Furthermore, larger radius of medium tube and lower signal frequency are better for surface wave propagation. However, the effect of collision frequency is not obvious. The optimized experimental parameters can be chosen as the plasma density of about 10^17 m^-3 and the medium radius between 11 mm and 19 mm.

Spatiotemporal characteristics of water exchange between the Andaman Sea and the Bay of Bengal

A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Channel(TDC),and the Great Channel(GC),based on the daily averaged simulation results ranging from 2010 to 2019.Spectral analysis and Empirical Orthogonal Function(EOF)methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms.The results of model simulation indicate that the net average transports of the PC and GC,as well as their linear trend,are opposite to that of the TDC.This indicates that the PC and the GC are the main inflow channels of the AS,while the TDC is the main outflow channel of the AS.The transport variability is most pronounced at surface levels and between 100 m and 200 m depth,likely affected by monsoons and circulation.A 182.4-d semiannual variability is consistently seen in all three channels,which is also evident in their second principal components.Based on sea level anomalies and EOF analysis results,this is primarily due to equatorial winds during the monsoon transition period,causing eastward movement of Kelvin waves along the AS coast,thereby affecting the spatiotemporal characteristics of the flow in the AS.The first EOF of the PC flow field section shows a split at 100 m deep,likely due to topography.The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series.Meanwhile,the first EOF of the GC flow field section indicates a stable surface inflow,probably influenced by the equatorial Indian Ocean’s eastward current.

Gaussian beamed millimetre wave propagation characteristics due to reflecting behaviour in circle tunnel

Propagation characterization is one of the main building blocks for millimetre wave （MMW） communication. The Gaussian beam has attractive features to become a prospective wave form for millimetre radio communication, especially for the utility inside tunnels. A ray tracing method embedded with spectral features of Gaussian beam is employed to analyze mil- limetre wave propagation in a circle tunnel in this paper. In consideration of geometrical figure of the tunnel, the superposition behaviour of direct and reflective beams is analyzed via simplified approximation of Gaussian beam spectral feature. Then the propagation models are established to derive amplitude, phase, and delay spread of received wave. A typical straight tunnel model is used to simulate the propagation behaviour, where strong multi-path effect with deeply fading of signal intensity and dramatically enhancing of delay spread emerges. For investigation of the spectral feature of the multi-path effect, a reflection loss of 14 dB is taken into consideration at a designated point. To analyze the influences of frequency and transmission distance, the propagation characteristics at three different frequencies of 45 GHz, 65 GHz and 85 GHz are compared with the beam travelling down the tunnel. In addition, three different reflection losses of 14 dB, 20 dB, and 26 dB at the frequency of 65 GHz are also investigated to research the influence of the reflecting coefficient.

Study on Wave Field Characteristics and Imaging of Collapse Column in Three-Dimensional Detection with Love Channel Wave Reflected outside the Working Face

The safety accidents caused by collapse column water diversion occur frequently, which has great hidden danger to the safety production of coal mine. Limited by the space of underground, the detection of collapse column on the outside of working face has been a difficult problem. Based on this, numerical simulation and imaging research were carried out in this paper. The results indicate that when a seismic source near the roadway is excited, a part of seismic wave propagates along the roadway direction, namely direct P-wave, direct S-wave and direct Love channel wave. When the body waves and Love channel wave propagating to the outside of working face meet the interface of collapse column, the reflected Love channel wave and reflected body waves are generated. Reflection body waves and direct waves are mixed in time domain, which is difficult to identify in seismic records, while reflected Love channel wave whose amplitude is relatively strong. The reflected Love channel wave which has a large interval from other wave trains in the time domain is easily recognizable in seismic record, which makes it suitable for advanced detection of collapse column. The signal-to-noise ratio of X component is higher than that of Y component and Z component. According to the seismic records, polarization filtering was carried out to enhance the effective wave, which removed the interference waves, and the signal was migrated to get the position parameters of collapse column interface, which was basically consistent with the model position.

Wind Wave Characteristics and Engineering Environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea （SCS） using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast （NE） along the southwest （SW）-NE axis, east northeast in the northwest （NW） part of SCS, and north northeast in the southeast （SE） part of SCS. The joint distributions of wave heights and wave periods （directions） were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the south- ern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme Hs values is focus in E in the northem and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.

Numerical simulation for propagation characteristics of shock wave and gas flow induced by outburst intensity

In order to analyze the propagation characteristics of shock wave and gas flow induced by outburst intensity, the governing equations of shock wave and gas flow propagation were put forward, and the numerical simulation boundary condition was obtained based on outburst characteristics. The propagation characteristics of shock wave and gas flow were simulated by Fluent software, and the simulation results were verified by experiments. The results show that air shock wave is formed due to air medium compressed by the transient high pressure gas which rapidly expands in the roadway; the shock wave and gas flow with high velocity are formed behind the shock wave front, which significantly decays due to limiting effect of the roadway wall. The attenuation degree is greater in the early stage than that in the late stage, and the velocity of gas convection transport is lower than the speed of the shock wave.The greater the outburst intensity is, the greater the pressure of the shock wave front is, and the higher the speed of the shock wave and gas flow is.

The grouping characteristics of sea waves in the Shijiu Port

A review concerning the methods of studying and describing wave groups is presented in this paper. After analysing 78 field records collected in the Shijiu Port, China, the measured parameters of wave groups and some factors describing wave groupness and their variations are given. Moreover, these results are compared with those of theory.

Analysis of the characteristics of gravity waves during a local rainstorm event in Foshan,China

A detailed analysis of the dynamic frequency spectrum characteristics of gravity waves(GWs)during a local heavy rainfall event on 20–21 November 2016 in Foshan,China,is presented.The results of this analysis,which was based on high-precision microbarograph data,indicate that GWs played a key role in generating the rainstorm.The GWs experienced two intermittent periods of amplitude enhancement and period widening.The largest amplitudes of the GWs were 80–160 Pa,with a corresponding period range of 140–270 min,which were approximately 4 h ahead of the rainstorm.The severe storms appeared to affect the GWs by augmenting the wave amplitudes with center amplitudes of approximately 80–100 Pa and periods ranging between 210 and 270 min;in particular,the amplitudes increased to approximately 10 Pa for GWs with shorter periods(less than 36 min).The pre-existing large-amplitude GWs may be precursors to severe storms;that is,these GWs occurred approximately 4 h earlier than the time radars and satellites identified convections.Thus,these results indicate that large-amplitude GWs constitute a possible mechanism for severe-storm warning.

Blast wave characteristics of multi-layer composite charge:Theoretical analysis,numerical simulation,and experimental validation

This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the charge,a peak overpressure prediction model for the composite charge under singlepoint detonation and simultaneous detonation was established.The effects of the charge structure and initiation method on the overpressure field characteristics were investigated in AUTODYN simulation.The accuracy of the prediction model and the reliability of the numerical simulation method were subsequently verified in a series of static explosion experiments.The results reveal that the mass of the inner charge was the key factor determining the peak overpressure of the composite charge under single-point detonation.The peak overpressure in the radial direction improved apparently with an increase in the aspect ratio of the charge.The overpressure curves in the axial direction exhibited a multi-peak phenomenon,and the secondary peak overpressure even exceeded the primary peak at distances of 30D and 40D(where D is the charge diameter).The difference in peak overpressure among azimuth angles of 0-90°gradually decreased with an increase in the propagation distance of the shock wave.The coupled effect of the detonation energy of the inner and outer charge under simultaneous detonation improved the overpressure in both radial and axial directions.The difference in peak overpressure obtained from model prediction and experimental measurements was less than 16.4%.

Theoretical solution for wave diffraction by wedge or corner with arbitrary reflection characteristics

An exact analytic solution for wave diffraction by wedge or corner with arbitrary angle (rπ) and reflection coefficients (R0 and Rr) is presented in this paper. It is expressed in two forms-series and integral representations, corresponding recurrence relation and asymptotic expressions are also derived. The solution is simplified for some special cases of rπ. For Rr= R0,r= 1/N and Rr≠R0,r = 1/2N, the solution can be reduced to linear superpositions of incident and partially reflected waves, hence a nonlinear solution of forth order for this problem can be obtained by using the author's theory of nonlinear interaction among gravity surface waves. The given solution is related to inhomogeneous Robin boundary conditions, which include the Neumann boundary conditions usually accepted in wave diffraction theory.

Influence of Axial Loads to Propagation Characteristics of the Elastic Wave in a Non-Uniform Shaft

The vibration propagates through the shaft in the form of elastic waves. The propagation characteristics of the elastic waves are a ected by the axial loads. The influence of the axial loads to the propagation characteristics of the elastic waves is studied in this paper. Firstly, the transfer matrix of the elastic waves for the non-uniform shaft with axial loads is deduced by combining the transfer matrix without axial load and the additional equation caused by the axial load. And then, a numerical method is used to study the influence of the axial load, non-uniformity and the rotating speed to the propagation characteristics of the elastic waves. It’s found that a new Stop Band will appear due to the axial force, and the central frequency of which will decrease as the increase of the force, while the band width of which remains the same. The central frequency of the new Stop Band will also increase as the increase of the cross-section area ratio;however, the rotating speed of the shaft doesn’t a ect the propagation characteristics of the elastic waves obviously. Finally, an experimental rig is built up for further study, even though there are some small local errors, the results of experiments match well with the numerical ones, which indicates the validation of the theoretical results. The result can help to study the influence of the axial load to the dynamics of a non-uniform shaft and help to reveal the vibration propagating mechanism in such a shaft.