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This article presents a new simulator able to generate raw data for ocean wave radar spectrometer (OWRS). Data simulation involves three key procedures: generating 2-D sea wave height, velocity, and acceleration fields by use of a prescribed ocean wave height spectrum; calculating the 2-D sea surface normalized radar cross section (NRCS) field using a quasi-specular backscatter model; and incorporating the generated sea wave height, velocity, and acceleration fields into the radar instantaneous range equation (IRE). Our simulator’s reliability in replicating real-world ocean wave spectra has been confirmed by comparing retrieved wave spectra from simulated OWRS raw data with input reference wave spectra and real-measured radar data. The proposed simulator has several advantages over conventional simulators. Notably, OWRS data generated by the proposed simulator are complex in-phase/quadrature-phase (I/Q) raw data, instead of backscattered power modulation data as simulated by conventional simulators. Our simulator’s other advantages include its ability to reflect the effect of Doppler modulation induced by the motions of the radar platform and the sea waves in the speckle noise spectrum after processing OWRS raw data simulated by the proposed simulator, as well as its ability to embody the effect of range modulation caused by the sea surface topography, including both linear and higher order range modulation effects, in retrieved wave slope spectra. Our simulator offers a powerful tool for understanding complicated interactions between ocean wave dynamics and radar signals. Furthermore, it also provides radar engineers with a cost-effective way to evaluate potential designs for future spaceborne OWRS.

Heat storage is key to reducing the mismatch between energy supply and demand. The performance of thermal energy storage heat exchangers is determined by the exchanger structure and the heat transfer fluid (HTF) parameters. In this paper, the heat exchanger structure and HTF parameters of a plate-type latent heat thermal energy storage (LHTES) heat exchanger were investigated through experiments and simulations. From the experimental tests, it was observed that thermocouples accelerated the melting process of paraffin by 6 % on average for a single LHTES plate. The LHTES plate with aspect ratio of 3:1 was the optimal structure with the shortest melting time. To figure out the optimal thermal performance of the LHTES heat exchanger, a mathematical model was developed by FLUENT and verified against the experimental data. The influence of LHTES plate thickness as well as the HTF temperature and velocity was numerically studied. A performance factor was proposed to evaluate the thermal performance for the melting process of plate-type LHTES heat exchangers. Simulation analysis shows that the highest performance factor is realized when the LHTES plate thickness is 15 mm, independent to the HTF temperature and velocity. When the HTF velocity is small, it is critical to focus on the design of plate thickness of the heat exchangers rather than increasing the HTF temperature.

The rotor of the mud pulser will suffer severe erosive wear due to long-term scouring by solid particles in drilling mud. An important way to solve this problem is to improve the erosion resistance of the rotor. Polycrystalline diamond compact (PDC) has excellent mechanical properties. To explore the erosive wear characteristics of the PDC for enhancing mud pulser rotor, the influence of the impact angle (30°, 45°, 60°, 75°, and 90°) and diamond grain size (4 μm, 10 μm, 20 μm, and 30 μm) on the erosion rate of the PDC was investigated. The results show that the PDC erosion rate is positively correlated with the impact angle and diamond grain size. When the impact angle is 90° and the diamond grain size is 4 μm, the PDC erosion rate is the smallest, 0.81%, and when the diamond grain size is 30 μm, the PDC erosion rate is the largest, 2.12%. The erosive wear characteristics of the PDC are cobalt removal and diamond grain cutting at a low impact angle. At high-impact angles, there is a micro-fracture of the edge of the diamond grains and an intersection of transverse and radial cracks. The fine diamond in PDC is removed, and the coarse diamond in PDC seems to have a trans-granular fracture. An innovative cutting-crack damage model considering the diamond grain sizes and impact angles is proposed based on the erosion damage mechanism, which can better predict the evolving law of the PDC erosion rate. The results provide data support and theoretical guidance for the application of PDCs to enhance erosion resistance rotors.

The weak interfacial strength between Fe-based matrix and diamonds causes diamond particles to fall off prematurely, significantly affecting the cutting efficiency of diamond composites. This work aimed to optimize the interfacial microstructure and mechanical properties of the diamond/Fe-Ni-WC composites by coating a Mo2C layer on the diamond particles. The Mo2C-coated diamonds were prepared via the molten salt method. Diamond/Fe-Ni-WC composites were sintered by the hot-pressing process under a vacuum. The bending strength of composites with Mo2C-coated diamonds was improved from 804 to 996 MPa with the increased coating time. The energy dispersive spectroscopy scanning indicated that the Mo2C coating layer changed the interfacial composition between the matrix and the diamonds from Fe-C alloy to Mo2C, improving the interface strength. Moreover, the diamond protrusion heights of composites were raised by adding a Mo2C interface, resulting in an improvement in the cutting efficiency of impregnated diamond tools.

Depressurization combined with thermal stimulation is a promising method for gas hydrate production. Owing to its advantages of rapid uniform heating, microwave radiation is an efficient source of heat. However, the mechanisms of hydrate decomposition under depressurization combined microwave stimulation are currently unclear. In this study, methane hydrate was synthesized under 6 MPa and 2 °C, with hydrate saturation of approximately 42% in natural quartz sand. We then compared hydrate decomposition via rapid depressurization and piecewise depressurization, with or without microwave stimulation at 2.45 GHz and 400 W. When using the depressurization method alone, the hydrate decomposition rate increased with the depressurization amplitude. However, in the last stage of hydrate decomposition, the external flow of gas was hindered by the Jamin effect, especially under larger depressurization amplitudes; therefore, extremely low production pressure is not justified. When combined with microwave stimulation, both depressurization methods resulted in increased reservoir temperature within a few seconds, and microwave heating provided an extra driving force for hydrate decomposition. Furthermore, microwave heating was more effective when larger amounts of undecomposed hydrate remained after depressurization. When depressurization was combined with microwave stimulation, the average gas production rate at 100% gas production was 0.269–0.601 L/min, which was significantly higher than that for depressurization alone. However, the energy efficiency ratio was approximately 1, which has no practical value. Conversely, the average gas production rate at 90% gas production was 0.452–2.945 L/min and the energy efficiency ratio was 2.9–17.6. Under the combined method, gas hydrate decomposition at a production pressure of 1.9 MPa achieved the subtle balance between the average gas generation rate and energy efficiency. Thus, optimizing the gas production pressure and microwave stimulation time can improve the average gas production rate and energy efficiency ratio according to the reservoir hydrate conditions.

Polycrystalline diamond compact (PDC) cutters, the most widely used cutting tool in oil and gas drilling, often fail very quickly because of excessive wear and poor impact toughness in hard and complex formations. In this study, dense PDC samples doped with SiC whiskers (SiCw) were successfully synthesized under high pressure and high temperature (HPHT) conditions. The microstructures, elemental distributions, and phase compositions of the PDC samples were systematically investigated. The mechanical properties including the Vickers hardness, wear resistance, impact toughness and thermal stability, were tested. The introduction of SiCwreduced the Co content in the polycrystalline diamond layer. The testing results showed that the hardness of PDC doped with 0.5 wt% SiCwwas 75.25 GPa, wear ratio was 145.6 × 104and impact toughness reached 4020 J, which were 12.2%, 30.9%, and 142.2% higher than those of the control group (CG), respectively. The PDC-0.5 wt% SiCwhad the lowest thermal expansion value, with a 57.5% reduction compared with the CG. In addition, the strengthening mechanism of SiCwwas explored. SiCwpartially replaced the weakening cobalt phase in the binder phase, thus improving the hardness, wear resistance, and thermal stability of the PDC. The introduction of SiCwinhibited the abnormal growth of WC at the interface of the cemented carbide substrate and changed the fracture mode from intergranular to transgranular, which were the main mechanisms responsible for the significant increase in the impact toughness of PDC.

Abstract: In the synthetic aperture radar (SAR) system with low pulse repetition frequency (PRF) sampling, it is difficult for the motion parameters estimation of the moving targets, because of the Doppler spectrum ambiguity and Doppler centroid frequency ambiguity of the echo signals. Considering that moving targets are sparsely distributed in the observed scene, their positions and velocities can be reconstructed by using the compressed sensing (CS) technique. In this paper, the range-walk correction are implemented by the Keystone transform and the sparse range-walk correction (SRWC), then the CS technique is proposed to reconstruct motion parameters by processing the azimuth signals of the moving targets. Experiments using the simulated and real data are performed, and the results confirm the validity of the proposed method.

Photosensitizer fluorescence photobleaching and Singlet Oxygen (1O2) Luminescence Dosimetry (SOLD) are being studied as potential dosimetric tools for ALA-PDT of skin diseases. However, the correlation of both SOLD data and PpIX fluorescence to 1O2distribution is difficult to interpret because of the temporal and spatial variations of the PDT parameters (light fluence rate, photosensitizer concentration and oxygen concentration). This work used our dynamic model to investigate both dosimetry approaches for varied PpIX concentration and distribution, and three commonly used treatment wavelengths. The results show that SOLD is much less dependent upon the treatment parameters, which implies it has better potential as a "gold standard" dosimetric tool for clinical PDT.

Both photosensitizer fluorescence photobleaching and singlet oxygen luminescence (SOL) have been measured during ALA-PDT of skin in attempts to estimate PDT dose. However, the relationship of these detected signals to singlet oxygen (1O2) dose in a given volume and to its depth distribution are not well understood and difficult to verify experimentally because of the temporal and spatial variations of the essential parameters in PDT. A model for ALA-PDT of normal human skin was developed to simulate the dynamic progress of PDT. The model incorporates Monte Carlo simulations of excitation light fluence and both SOL and PpIX fluorescence signals, 1O2-mediated photobleaching mechanism, ground-state oxygen (3O2) diffusion and perfusion, a cumulative 1O2-dependent threshold vascular response and any initial distribution of PpIX. The simulated time-resolved evolution of the instantaneous PpIX fluorescence photobleaching and cumulative SOL signals are examined as functions of irradiance and related to both the time-resolved distribution of cumulative 1O2production at various depths and the average dose in the dermis. The simulations used a green light source at 523 nm. The correlation of SOL signals with the average dose was found to be less irradiance-dependent than that of fluorescence photobleaching, which indicates the great potential of SOL as a clinical dosimetric tool in PDT.

Polycrystalline diamond compact (PDC) is one of the most widely used cutting tools in the field of oil and gas drilling. In this paper, PDC was cryogenically treated at temperature of around −190 °C and then the mechanical properties such as microhardness, wear ratio, and impact toughness after cryogenic treatment were tested. The morphology, elemental composition and crystal structure of the PDC was investigated by scanning electron microscope (SEM), Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD). Meanwhile, the residual stress of the PCD layer was analyzed using Raman spectroscopy. Untreated and cryogenically treated PDC were respectively fabricated into drill bits and the drilling performance were tested. The results showed that the average microhardness of the PDC after cryogenic treatment was increased by 5.3GPa/10.4%, the maximum wear ratio was increased by 11.8%, and the impact toughness was greatly improved to reach 420 J and increased by 79.4% on average. The average rate of penetration (ROP) of the bit equipped with untreated PDC was 1.03 m/h, while the ROP of the bit equipped with cryogenically treated PDC was 1.56 m/h, increased by 51.4%. Microscopic characterization revealed that the change of fracture mode and the evolution of residual stress in PDC was the main mechanism for the improvement of mechanical properties.

The China France Oceanography Satellite (CFOSAT) and Haiyang‐2B (HY‐2B) satellites were successively launched in China on the 29th and 25th of October 2018, respectively. HY‐2 B carries the second Chinese radar altimeter along with three other microwave sensors, whereas CFOSAT contains the first Surface Waves Investigation and Monitoring (SWIM) instrument and a fan beam rotating scatterometer. As missions for measuring the dynamic marine environment, both satellites can measure the nadir significant wave height (SWH). For data obtained from a newly launched satellite to be utilized with confidence, the quality of SWH from the two satellites requires validation. In this study, the HY‐2B altimeter and CFOSAT nadir SWHs have been validated against the National Data Buoy Center (NDBC) buoys and the Jason‐3 altimeter SWH data, respectively, which resulted in CFOSAT nadir SWH having the best accuracy and HY‐2B having the best precision. The SWHs of the two missions are also calibrated by Jason‐3 and NDBC buoys. Following calibration, the root mean square error (RMSE) of CFOSAT and HY‐2B are 0.21 and 0.27 m, respectively, when compared to Jason‐3, and 0.23 and 0.30 m, respectively, compared to the buoys. Our results show that the two missions can provide good‐quality SWH and can be relied upon as a new data resource of global SWH. CFOSAT and HY‐2B are new satellites launched approximately one and a half years ago. Both have the capability to provide global ocean wave observations, the quality of which is critical, especially in climate change research. In this study, the SWH from both satellites are validated against the NDBC buoy and Jason‐3 altimeter SWH data. Lastly, a calibration method is used for the application of the new SWH data. Significant wave height from China France Oceanography Satellite (CFOSAT) and Haiyang‐2B (HY‐2B) satellites are validated against Jason‐3 and NDBC dataThe significant wave height from CFOSAT and HY‐2B have nearly the same performance, although there are small differences comparing to the two referencesLinear calibrations against Jason‐3 and NDBC buoy data are proposed Significant wave height from China France Oceanography Satellite (CFOSAT) and Haiyang‐2B (HY‐2B) satellites are validated against Jason‐3 and NDBC data The significant wave height from CFOSAT and HY‐2B have nearly the same performance, although there are small differences comparing to the two references Linear calibrations against Jason‐3 and NDBC buoy data are proposed

Wind waves contribute a significant component to the sea surface currents detected by synthetic aperture radar (SAR) systems via the orbital velocity; this component is typically referred to as the wind wave‐induced artifact surface velocity (WASV). Accordingly, it is essential to precisely describe the WASV effect, so that the real sea surface currents can be obtained from SAR measurements. In order to enhance our understanding about WASV, we carried out a numerical analysis of the sea state dependence of WASV under various radar configurations. The simulated WASV compares reasonably well with observations reported in the literature. It is found that WASV not only depends on the wind speed but also increases considerably with the development of the wind waves, as characterized by wave age. WASV may increase by two to three times, in fully developed wind wave conditions, as compared to young waves. The wave age dependence appears to largely account for the observed uncertainty in WASV at a given wind speed; moreover, swell is also found to significantly influence WASV through hydrodynamic modulation of wind wave properties. These effects are stronger at higher wind speeds and vary significantly with the different radar configurations that are possible, in terms of polarizations and incidence angles. The variations in WASV using different shortwave spectral functions and angular spreading functions are examined in this manuscript. The measurement of surface currents is of wide interest to a number of oceanographic communities. SAR serves as a powerful tool in detecting the surface velocity with a high spatial resolution. However, the detection can be greatly contaminated by surface waves because of their orbital velocity or the phase speed of the scatters, which has no effect on the mass transport and is typically referred to as the wind wave‐induced artifact surface velocity (WASV). Correcting for the WASV is a big challenge, despite the efforts that have been made to relate WASV to the wind speed. We use numerical simulations to suggest that WASV strongly depends on wave age at any given wind speed and that the effect of background modulation due to swell can also be significant. The wind wave effects can be reasonably verified by comparisons of the numerical simulations with available observations that are reported in the literature. We also examined the sensitivity of different spectral short wave models on the simulation results. Wind wave effects on the SAR‐detected surface velocity are shown reliable by comparisons with numerical simulations and other observationsWind wave influence on surface velocity increases considerably with wave age, and the effect is stronger for higher wind speedsSwell can significantly change the surface velocity measured by SAR by hydrodynamic modulation of the wind waves