Wave Calculations Research Articles

Parameterized Forward Operators for Simulation and Assimilation of Polarimetric Radar Data with Numerical Weather Predictions

Many weather radar networks in the world have now provided polarimetric radar data (PRD) that have the potential to improve our understanding of cloud and precipitation microphysics, and numerical weather prediction (NWP). To realize this potential, an accurate and efficient set of polarimetric observation operators are needed to simulate and assimilate the PRD with an NWP model for an accurate analysis of the model state variables. For this purpose, a set of parameterized observation operators are developed to simulate and assimilate polarimetric radar data from NWP model-predicted hydrometeor mixing ratios and number concentrations of rain, snow, hail, and graupel. The polarimetric radar variables are calculated based on the T-matrix calculation of wave scattering and integrations of the scattering weighted by the particle size distribution. The calculated polarimetric variables are then fitted to simple functions of water content and volume-weighted mean diameter of the hydrometeor particle size distribution. The parameterized PRD operators are applied to an ideal case and a real case predicted by the Weather Research and Forecasting (WRF) model to have simulated PRD, which are compared with existing operators and real observations to show their validity and applicability. The new PRD operators use less than one percent of the computing time of the old operators to complete the same simulations, making it efficient in PRD simulation and assimilation usage.

The influence of viscosity and turbulence on the supersonic flow compression and expansion corner

Super- and hypersonic flow around aircraft elements is accompanied by the formation of a complex flow structure, which is characterized by the presence of strong shock waves, rarefaction waves, contact discontinuities, separation and reattachment of the flow. For such problems, the interaction of shock waves with viscous boundary layers is characteristic. Such interaction is quite complex and largely determines the effectiveness of aircraft. When flowing around complex structures of aircraft and their power plants in the vicinity of convex corner points of the geometry, compression and expansion flows are locally realized. The calculation of oblique shock waves, formed when flowing around the compression angle, and simple expansion waves, formed around the flowing angle of expansion, is included as an element of solving many problems of constructing streamlines and finding the pressure distribution on the streamlined surface. Based on the technology of adaptive meshes, a numerical model is proposed for studying two-dimensional effects arising from supersonic flow around the angles of compression and expansion. Numerical simulation was performed using various models such as inviscid, laminar or turbulent. In the calculations, the Mach number of the incident shock wave varies from 2 to 15, and the flow angle varies from 5 to 15 degrees. The Reynolds number, calculated from the characteristics of the unperturbed flow, is equal to 105. The working gas is air (γ = 1.4). A qualitative picture of the flow during diffraction of a shock wave on steps of different geometry is considered. When the shock wave interacts with the compression angle, flow separation and the formation of a recirculation region are observed, and when the shock wave interacts with the expansion angle, the Prandtl–Mayer wave is misaligned. The results of calculations are compared with theoretical data on the parameters of the flow behind the shock front or fan of the rarefaction wave. Studies have shown the influence of the effects of viscosity and turbulence on the flow structure and distribution of flow characteristics when flowing around the angles of compression and expansion. The simulation results can find application in solving problems related to the design of air intakes of high-speed flying aircrafts, in particular, in parametric and optimization calculations of gas-dynamic flows that arise in the elements of propulsion systems of supersonic and hypersonic aircraft.

Modified Equation of Impulse for Solitons in an Open Water Channel

On the basis of the certain form of write of an impulse equation the modeling of the solitary waves in the water channel is examined at action of gravitation forces. It is shown that as against an existing method of modelling where the waves propagating from left to right turn out from the equation of an impulse, and from right to left from the continuity equation in the offered technique both waves turn out from the equation of impulse. It is marked that the given method is physically more correct. Calculation of a solitary wave, its velocity and geometrical characteristics is submitted.

An ab initio investigation of structural, electronic, magnetic and mechanical properties of La2NiGe3

Full-Potential linearized augmented plane wave calculations are performed in order to investigate structural, electronic, magnetic and elastic properties of La2NiGe3 in the low symmetry phase SG (P6−2c). The generalized gradient approximation (GGA) and GGA + U are used to describe the exchange and correlation potential. The obtained cell parameters are in very good agreement with those reported at 2.8 K in the literature. The authors calculations indicate that the material under focus has an antiferromagnetic behavior, which agrees well with experiment. Using the finite difference method, the elastic constants are calculated. All stability conditions are satisfied, indicating that the material of interest is mechanically stable. Based on the calculated elastic constants, the mechanical parameters such as bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio have been obtained. A close examination of elastic anisotropy has shown that the material in question exhibits a pronounced anisotropy.

Semi-Analytical Calculation of No-Load Radial and Tangential Electromagnetic Force Waves of a Non-Salient Pole Synchronous Generator

For a marine electrical machine, its high power density and large electromagnetic (EM) load tend to bring high saturation to the magnetic circuit. When the non-linearity of ferromagnetic material is not taken into consideration, large errors will appear in the calculation of air-gap flux density and EM force wave. Considering the radial and tangential EM force waves that cause the stator core to vibrate and deform are the primary sources of EM vibration of a non-salient pole synchronous generator (NSPSG), this paper introduces a semi-analytical method of calculating the radial and tangential EM force waves, with the non-linearity of ferromagnetic material taken into account. The method includes the distributed magnetic circuit method (DMCM), the separation variable method (SVM) and the complex variable conformal transformation method (CVCTM). First of all, the radial air-gap flux density is obtained by using the DMCM to calculate the no-load magnetic circuit of the NSPSG and dealing with the non-linearity of ferromagnetic material by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B-H</i> curve. Then, the tangential air-gap flux density is calculated by the SVM and the complex relative air-gap permeance is calculated by the CVCTM to determine the effect of slotting. Finally, the radial and tangential EM force waves are obtained by Maxwell stress tensor method. The proposed semi-analytical method is verified through measuring vibration acceleration of the NSPSG.

Prediction of Ship Motions in Irregular Waves Based on Response Amplitude Operators Evaluated Experimentally in Noise Waves

Abstract The most common methods for predicting ship roll motions in a specified sea state are direct measurements of motions in a representative irregular wave realisation (time domain) or calculations of motions from response amplitude operators (RAOs) in the frequency domain. The result of the first method is valid only for the tested sea state, whilst the second method is more flexible but less accurate. RAO-based predictions are calculated assuming a linear model of ship motions in waves. RAO functions are usually evaluated by means of tests in regular waves for a limited number of frequencies and a constant wave amplitude. This approach is time-consuming and the discrete form of the RAO functions obtained for a limited number of frequencies may lead to discrepancies in the prediction of seakeeping and often does not allow the actual amplitude of the response in resonant frequency to be determined. Another challenge is the appropriate selection of wave amplitude for tests due to the considerable influence of viscous damping on roll response in irregular sea waves. There are alternative methods for the experimental determination of RAO functions and one of them is presented in this study. The presented approach allows RAO functions to be evaluated in one run by the generation of irregular waves characterised by a white or coloured noise spectrum. This method reduces the experiment duration, with almost continuous RAO characteristics obtained. The flat (white noise) and linear (coloured noise) wave spectral energy characteristics are considered in the experiment and the obtained predictions are compared with the results of accurate measurements in irregular waves.

Influence of the sag-to-span ratio on the dynamic response of a long-span bridge suspended from floating towers under wave and wind loads

ABSTRACT Long-span bridges suspended from floating towers are a promising design concept to cross the strait with deep water depth. This paper presents an alternative dynamic simulation framework for floating suspension bridge by integrating the calculations of wave, radiation and wind loads with common software and computing scripts, and verifies the numerical models, including structure, wave load, radiation and wind load. Bridge schemes with different sag-to-span ratios inspired by a prototype long-span floating bridge were proposed. Static, modal and dynamic analyses are conducted through the developed simulation framework to obtain the bridge response. The influence of the sag-to-span ratio on the dynamic response of a long-span bridge suspended from floating towers under wave and wind conditions was investigated. The results indicate that the natural period of the floating bridge decreases with the reduction in the sag-to-span ratio, and the sag-to-span ratio significantly affects the dynamic response of the example floating bridge.

Comparative DFT study of the oxy(hydr)oxides of iron and aluminum – structural, electronic and surface properties.

The Goethite (α-FeOOH, Goe), hematite (α-Fe2O3, Hem) and their Al-isomorphs diaspore (α-AlOOH, Dia) and corundum (α-Al2O3, Cor) are an important class of materials. Hem and Cor have been intensely investigated. However, the Goe and Dia have not received much attention commensurate with their importance for many geochemical and technological processes. We have reviewed the literature and revisited by DFT/Plane Waves calculations the structural and electronic properties of their bulk and their predominant surfaces. The calculated values have been compared and discussed in the light of the available experimental and previously published theoretical data. Insights of relevant and important properties of the less investigated Goe and Dia are provided, fulfilling the lack of information about these systems. Furthermore, the topological analysis of the electron density has been performed for all investigated minerals. The differences in the structural, electronic, and adsorptive properties of their surfaces have been discussed in detail. The smaller structural and energetic relaxation of the Fe-isomorph surfaces compared to their Al-isomorphs is explained in terms of larger covalent character cushioning the changes of the metal electronic structure. The water adsorption on the predominant surfaces has been investigated and the dissociative mechanism is at least 10 kJ mol−1 more favored than the molecular mechanism. The estimated adsorption energies for the Goe and Dia oxyhydroxides are 70 and 39 kJ mol−1, respectively. For the Hem and Cor oxides, the water adsorption energies are estimated to be 105 and 148 kJ mol−1, respectively. These values reinforce the observations that the Goe and Dia present different surface reactivities which must be observed in geochemical processes.

New Pharmaceutical Salts of Trazodone.

New pharmaceutically acceptable salts of trazodone (trazodone hydrogen bromide and trazodone 1-hydroxy-2-naphthonic acid) for the treatment of central nervous system disorders are synthesized and described. Although trazodone salts are poorly crystalline, single-crystal X-ray diffraction data for trazodone 1-hydroxy-2-naphthonic acid were collected and analyzed as well as compared to the previously described crystal structure of commercially available trazodone hydrochloride. The powder samples of all new salts were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and 13C solid-state nuclear magnetic resonance spectroscopy. Spectroscopic studies were supported by gauge including projector augmented wave (GIPAW) calculations of carbon chemical shielding constants. The main goal of our research was to find salts with better physicochemical properties and to make an attempt to associate them with both the anion structure and the most prominent interactions exhibited by the protonated trazodone cation. The dissolution profiles of trazodone from tablets prepared from various salts with lactose monohydrate were investigated. The studies revealed that salts with simple anions show a fast release of the drug while the presence of more complex anion, more strongly interacting with the cation, effects a slow-release profile of the active substance and can be used for the preparation of the tables with a delay or prolonged mode of action.

Osobennosti vetrovogo volneniya v Balaklavskoy bukhte v ekstremal'nykh vetrovykh usloviyakh

Wind waves in bays and harbors have a significant impact on the safety of navigation and operation of the coastal infrastructure. The purpose of this work is to study the characteristics of wind waves in the Balaklava Bay (Crimean Peninsula) under different wind conditions. The study was carried out on the basis of a numerical spectral SWAN wave model using a sequence of nested grids. Specific calculations of waves in the Balaklava Bay are carried out for constant winds of different directions and for an extreme storm emerged in the Black Sea in November 2007. It was found that in the southern part of the bay the most intense waves are formed with southerly winds. At the bay entrance, at wind speeds, which can occur once a year and once every 25 years, the maximum values of the significant wave height hs amount to 3 and 5.4 m, respectively. In the northern part of the bay, the maximum values hs with winds, which can occur once a year and once every 25 years, respectively, are equal to 0.25 and 0.46 m. It was defined that the storm waves penetrating into the southern part of the bay quickly attenuate as they spread through the narrowness to the northern part of the bay. Thus, the local wind field is the determining factor affecting the intensity of waves in the northern part of the Balaklava Bay.

Future Changes in Wave Conditions at the German Baltic Sea Coast Based on a Hybrid Approach Using an Ensemble of Regional Climate Change Projections

In this study, the projected future long-term changes of the local wave conditions at the German Baltic Sea coast over the course of the 21st century are analyzed and assessed with special focus on model agreement, statistical significance and ranges/spread of the results. An ensemble of new regional climate model (RCM) simulations with the RCM REMO for three RCP forcing scenarios was used as input data. The outstanding feature of the simulations is that the data are available with a high horizontal resolution and at hourly timesteps which is a high temporal resolution and beneficial for the wind–wave modelling. A new data interface between RCM output data and wind–wave modelling has been developed. Suitable spatial aggregation methods of the RCM wind data have been tested and used to generate input for the calculation of waves at quasi deep-water conditions and at a mean water level with a hybrid approach that enables the fast compilation of future long-term time series of significant wave height, mean wave period and direction for an ensemble of RCM data. Changes of the average wind and wave conditions have been found, with a majority of the changes occurring for the RCP8.5 forcing scenario and at the end of the 21st century. At westerly wind-exposed locations mainly increasing values of the wind speed, significant wave height and mean wave period have been noted. In contrast, at easterly wind-exposed locations, decreasing values are predominant. Regarding the changes of the mean wind and wave directions, westerly directions becoming more frequent. Additional research is needed regarding the long-term changes of extreme wave events, e.g., the choice of a best-fit extreme value distribution function and the spatial aggregation method of the wind data.

Reflection and transmission of plane waves at an interface separating two poro-viscoelastic materials with continuity and elastic consistence

SUMMARYThe seismic reflection/transmission (R/T) problems have been investigated for various complicated porous materials described by various poro-viscoelastic theories. However, it was also reported that even for a simple plane wave at a plane interface between two dissimilar isotropic viscoelastic solids, they were proved to be more complicated than expected and still required further study. The main difficulty is to correctly select the signs of the vertical components of the slowness vectors (or vertical slowness q) of the viscoelastic R/T waves to calculate R/T coefficients (including the relevant displacement amplitudes and phase delays) without unphysical discontinuity but with elastic consistence. Logically, if this problem had not been solved in the relatively simple case of waves in isotropic viscoelastic materials, it would not be expected to be solved in the complicate porous media. The existing criterion to select the sign of vertical slowness for poro-viscoelastic waves is the radiation condition that has been reported to cause unphysical discontinuity for the R/T coefficients of viscoelastic waves. In this paper, the radiation condition is illustrated to cause the unphysical discontinuities. Meanwhile, the continuity criterion is for the first time applied in the R/T coefficients calculation for poro-viscoelastic waves. The continuity criterion is simply suggested to be conducted in the complex vertical slowness square (q2) plane by swapping the sign of the q for the relevant wave whose q2 locus crosses the branch cut. Furthermore, the elastic consistence is also for the first time considered for poro-viscoelastic waves. We stress the importance of consistence between the R/T coefficient equations of poro-viscoelastic waves and those of pure elastic waves, which includes three consistent assumptions: time dependence of harmonic waves, the z-direction of the coordinate system and particle motion (polarization) vectors. With the numerical examples of poro-viscoelastic interfaces, the R/T coefficients of three types of incident waves, that is, homogeneous S waves, inhomogeneous S waves and homogeneous P waves, are investigated for frequencies 1000 and 0.001 Hz, representing highly and weakly dissipative poro-elastic waves, respectively. The calculated R/T coefficients are shown to be continuous without unphysical discontinuity under the continuity criterion. For the cases of homogeneous S- or P-wave incidence, the R/T coefficients of poro-viscoelastic waves with 0.001 Hz well match the corresponding coefficients of elastic waves in terms of amplitudes and phases, and thus the elastic consistence is well confirmed. For the highly dissipative poro-elastic waves (1000 Hz), the R/T coefficients significantly depend on the degrees of inhomogeneity of the incident waves. In a similar manner to the viscoelastic wave, a higher degree of inhomogeneity of an incident wave better tends to smooth the R/T coefficients of poro-viscoelastic waves. The methods suggested in this paper to solve the problems of R/T coefficient continuity and elastic consistence for the poro-viscoelastic waves can also be applied for viscoelastic waves as the special case.

Mathematical modelling of bottom deformations in the kinematic wave approximation

Two possible approaches for generalizing the kinematic wave model for deformable channels are being discussed in this paper, including the approximation in which the law of conservation of fluid mass includes erosion and sedimentation; and approximation that the fluid flow is determined by the kinematic wave equation without taking into account bottom deformations.Systematic comparison of the results of calculations of self-similar waves for different values of the change in water flow was carried out as well.

A Chebyshev collocation method for band structure calculations of the longitudinal elastic waves in phononic crystals

AbstractIn this study, a Chebyshev collocation method (CCM) is developed and applied to calculate the band structures of longitudinal elastic waves in periodically multi‐layered phononic crystals. The general form of the CCM for a unit‐cell is derived, in which the periodic boundary conditions and continuity conditions on the interface between different component materials are imposed directly to the CCM scheme. The band structures or dispersion relations can be obtained by solving the corresponding linear eigenvalue problem, where the unknown frequencies are the eigenvalues and the components of the Bloch wave vector are given. The proposed CCM is verified by using the corresponding results obtained by the transfer matrix method. Due to the advantages of the CCM, the CCM presented in this paper can be easily generalized and applied to the high‐dimensional such as two‐dimensional (2D) problems.

Temperature Distribution of Radiofrequency Hyperthermia in a Capacitance System in Breast Equivalent Tumor Ablation: A Simulation Study

Introduction: For decades, hyperthermia had been used for tumor ablation by increasing the temperature of cancerous tissues. For clinical treatment, a capacitance system was developed over the world, widely. In this study, a capacitance system of the radiofrequency hyperthermia is simulated to achieving the temperature distribution map of the entire breast equivalent phantom. Therefore, the efficiency of this method in treating the breast cancer was investigated. Materials and Methods: In this paper, a radiofrequency system with a frequency of 13.56MHz was simulated by Comsol multiphysics software. The geometry of the breast cancerous tissue by considering three different tissues including the fat, the gland and the tumor was modeled. The two electrodes of the system were modeled as two disks with a radius of 15cm with the water bolus for cooling the healthy tissues. The calculations of the radiofrequency wave and the bioheat equation were accomplished by numerical simulation and finite element method (FEM). Results: The temperature plots were obtained in 5 minutes. The results were compared with experimental results to checking the accuracy of the radiofrequency device and the precision of the thermometry device. The Temperature distribution map was achieved in 3D to investigate the increasing temperature amount of the cancerous and the healthy tissues, entirely. Conclusion: The results was shown that the temperature of the whole tumor region increased equal, approximately (3-4 ˚C). Moreover, the temperature of the whole healthy tissues (the gland and the fat) did not increase, highly (1.9- 2.1 ˚C). Hence, in the capacitive hyperthermia system, the tumor reaches extreme heat while the healthy tissues are protected from damages, completely. On the other hand, the difference between the simulation and the experimental results were about 9-15%, approximately. Therefore, the accurate operation of the radiofrequency device and the precise of the thermometry device were confirmed, either.

A localized meshless collocation method based on semi‐analytical basis functions for bandgap calculation of elastic waves in phononic crystals

AbstractThis paper makes the first attempt to develop an efficient localized meshless collocation method (LMCM) based on the semi‐analytical T‐complete functions to calculate the bandgaps of elastic waves in solid phononic crystals. In comparison with the FEM (COMSOL software), the proposed LMCM can provide the similar accurate results with less computational resources for band structure calculation.

Математическое моделирование волнового режима бухты Ай-Тодор

Investigation of wave regime of coastal water areas is practically important for safe shipping, constructing and using of coastal infrastructure objects. At the present paper statistical characteristics and space distribution of parameters of wind waves in the Ay-Todor Bay region placed on the Crimea South Coast of the Black Sea are obtained on the basis of mathematical simulation. Analysis of the wind wave parameters for the year diapason of 1979–2017 has shown that waves running from the east and having 0.5 m heights and 3.0–3.5 s mean periods are the most repeatable. The most durable storms are formed by waves coming from East–South-South-West sector in the period from December to January. The multiannual calm duration is equal to ~11 days. Estimation of extremal characteristics (height, period and length) of wind waves of different probability, which possible one time in a year, 5, 10, 25, 50 and 100 years are made. For the storm probable one time in 25 years the mean wave height near the boundary of the Ay-Todor Bay is equal to 4.5 m. For this storm the wave height of 1% probability reaches 9.6 m. For the directions of winds of 4 % regime probability which causes the most dangerous waves calculations of wave characteristics with high space resolution (~1.5 m) are carried out by using of SWAN model and nested grid technology. Fields of significant wave height, mean wave length, bottom wave orbital velocities and space distribution of wave breaking zones are analyzed. It is found that most intensive waves are generated by wind having south-east, east and south directions. Maximal bottom orbital velocities of wave current reaches of 2.5–3.5 m/s and occurs along the coast till 10 m depth. Model calculation of wave currents by using of SWASH model allowed obtained presence in the coastal zone near beach of local cyclonic eddy, which transport suspended sediments along its south edge from beach towards the sea.

Parameters of shock waves during detonation and deflagration of fuel-air clouds

Methods for calculation of shock wave (SW) parameters used in industrial safety to assess the effects of explosions are considered. It is shown that existing methods do not provide the necessary accuracy of calculations. For the correct calculation of wave parameters, it is proposed to use high-accuracy CFD methods. The dimensionless dependences of pressure on distance are obtained for estimation of SW parameters, which allow to improve prediction of the effects of accidental explosions.

A combined density functional theory and x-ray photoelectron spectroscopy study of the aromatic amino acids

Amino acids are essential to all life. However, our understanding of some aspects of their intrinsic structure, molecular chemistry, and electronic structure is still limited. In particular the nature of amino acids in their crystalline form, often essential to biological and medical processes, faces a lack of knowledge both from experimental and theoretical approaches. An important experimental technique that has provided a multitude of crucial insights into the chemistry and electronic structure of materials is x-ray photoelectron spectroscopy. While the interpretation of spectra of simple bulk inorganic materials is often routine, interpreting core level spectra of complex molecular systems is complicated to impossible without the help of theory. We have previously demonstrated the ability of density functional theory to calculate binding energies of simple amino acids, using ΔSCF implemented in a systematic basis set for both gas phase (multiwavelets) and solid state (plane waves) calculations. In this study, we use the same approach to successfully predict and rationalise the experimental core level spectra of phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), and histidine (His) and gain an in-depth understanding of their chemistry and electronic structure within the broader context of more than 20 related molecular systems. The insights gained from this study provide significant information on the nature of the aromatic amino acids and their conjugated side chains.

Quantum chaos in topologically massive gravity

We study quantum chaos of rotating BTZ black holes in Topologically Massive gravity (TMG). We discuss the relationship between chaos parameters including Lyapunov exponents and butterfly velocities from shock wave calculations of out-of-time-order correlators (OTOC) and from pole-skipping analysis. We find a partial match between pole-skipping and the OTOC results in the high temperature regime. We also find that the velocity bound puts a chaos constraint on the gravitational Chern-Simons coupling.