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For floppy molecules showing internal rotations and/or large amplitude motions, curvilinear internal coordinates are known to be superior to rectilinear normal coordinates within vibrational structure calculations. Due to the myriad definitions of internal coordinates, automated and efficient potential energy surface generators necessitate a high degree of flexibility, supporting the properties arising from these coordinates. Within this work, an approach to deal with these challenges is presented, including key elements, such as the selection of appropriate fit functions, the exploitation of symmetry, the positioning of grid points, or elongation limits for different coordinates. These elements are tested for five definitions of curvilinear coordinates, with three of them being generated in an automated manner. Calculations for semi-rigid molecules, namely H2O, H2CO, CH2F2, and H2CNH, demonstrate the general functionality of the implemented algorithms. Additional calculations for the HOPO molecule highlight the benefits of these curvilinear coordinates for systems with large amplitude motions. This new implementation allowed us to compare the performance of these different coordinate systems with respect to the convergence of the underlying expansion of the potential energy surface and subsequent vibrational configuration interaction calculations. [ABSTRACT FROM AUTHOR]

While the vibrational spectra of semi-rigid molecules can be computed on approaches relying on the Watson Hamiltonian, floppy molecules or molecular clusters are better described by Hamiltonians, which are capable of dealing with any curvilinear coordinates. It is the kinetic energy operator (KEO) of these Hamiltonians, which render the correlated calculations relying on them rather costly. Novel implementation of vibrational self-consistent field theory and vibrational configuration interaction theory on the basis of the Podolsky Hamiltonian are reported, in which the inverse of the metric tensor, i.e., the G matrix, is represented by an n-mode expansion expressed in terms of polynomials. An analysis of the importance of the individual terms of the KEO with respect to the truncation orders of the n-mode expansion is provided. Benchmark calculations have been performed for the cis-HOPO and methanimine, H2CNH, molecules and are compared to experimental data and to calculations based on the Watson Hamiltonian and the internal coordinate path Hamiltonian. [ABSTRACT FROM AUTHOR]

The efficiency of quantum chemical simulations of nuclear motion can in many cases greatly benefit from the application of curvilinear coordinate systems. This is rooted in the fact that a set of smartly selected curvilinear coordinates may represent the motion naturally well, thus decreasing the couplings between motions in these coordinates. In this study, we assess the validity of different Taylor expansion-based approximations of kinetic energy operators in a (curvilinear) polyspherical parametrization. To this end, we investigate the accuracy as well as the numerical performance of the approximations in time-independent vibrational coupled cluster and full vibrational interaction calculations for several test cases ranging from tri- to penta-atomic molecules. We find that several of the proposed schemes reproduce the vibrational ground state and excitation energies to a decent accuracy, justifying their application in future investigations. Furthermore, due to the restricted mode coupling and their inherent sum-of-products form, the new approximations open up the possibility of treating large molecular systems with efficient vibrational coupled cluster schemes in general coordinates. [ABSTRACT FROM AUTHOR]

The analysis and modeling of high-resolution spectra of nonrigid molecules require a specific Hamiltonian and group-theoretical formulation that differs significantly from that of more familiar rigid systems. Within the framework of Hougen–Bunker–Johns (HBJ) theory, this paper is devoted to the construction of a nonrigid Hamiltonian based on a suitable combination of numerical calculations for the nonrigid part in conjunction with the irreducible tensor operator method for the rigid part. For the first time, a variational calculation from ab initio potential energy surfaces is performed using the HBJ kinetic energy operator built from vibrational, large-amplitude motion, and rotational tensor operators expressed in terms of curvilinear and normal coordinates. Group theory for nonrigid molecules plays a central role in the characterization of the overall tunneling splittings and is discussed in the present approach. The construction of the dipole moment operator is also examined. Validation tests consisting of a careful convergence study of the energy levels as well as a comparison of results obtained from independent computer codes are given for the nonrigid molecules CH2, CH3, NH3, and H2O2. This work paves the way for the modeling of high-resolution spectra of larger nonrigid systems. [ABSTRACT FROM AUTHOR]

The present study aims to develop an original solid-like shell element for large deformation analysis of hyperelastic shell structures in the context of isogeometric analysis (IGA). The presented model includes a new variable to describe the thickness change of the shell and allows for the application of unmodified three-dimensional constitutive laws defined in curvilinear coordinate systems and the analysis of variable thickness shells. In this way, the thickness locking affecting standard solid-shell-like models is cured by enhancing the thickness strain by exploiting a hierarchical approach, allowing linear transversal strains. Furthermore, a patch-wise reduced integration scheme is adopted for computational efficiency reasons and to annihilate shear and membrane locking. In addition, the Mixed-Integration Point (MIP) format is extended to hyperelastic materials to improve the convergence behaviour, hence the efficiency, in Newton iterations. Using benchmark problems, it is shown that the proposed model is reliable and resolves locking issues that were present in the previously published isogeometric solid-shell formulations. [ABSTRACT FROM AUTHOR]

We develop low-order triangular virtual elements for linear Kirchhoff–Love shells from an engineering point of view. Flat element geometry is considered, which enables a direct shell discretization with no need for a curvilinear coordinate system or predefined initial mapping. Along with the assumed linearity of the problem, the superposition of the uncoupled membrane and plate energies is performed by unifying aspects of the virtual element method when applied to linear two-dimensional elasticity and plate bending problems. We explore low-order cases, namely linear to quadratic membrane displacements and quadratic to cubic deflection polynomial approximations such that no internal degrees of freedom are needed. For all elements, a single stabilization available in the literature is employed to stabilize the element formulations. Numerical examples of static problems show that the presented formulation is capable of solving complex shell problems. Possible extensions are discussed in future works. [ABSTRACT FROM AUTHOR]

Large-amplitude vibrational motion influences the rovibrational structure of molecules that tunnel between multiple wells. Reaction path (RP) Hamiltonians, and curvilinear coordinates more generally, are useful for modelling pure vibrational motion in these systems and provide a practical framework for calculating accurate ab initio anharmonic vibrational energies and tunnelling splittings with perturbation theory. These computational tools also offer the means to address rotation-vibration coupling associated with large-amplitude motion in rotating molecules. In this paper, we incorporate the reduced axis system (RAS) frame embedding with RP Hamiltonians and second-order vibrational Møller-Plesset perturbation theory (VMP2). Because the RP-RAS Hamiltonian eliminates rotation-vibration momentum coupling everywhere along a one-dimensional reaction path, it is well suited for rovibrational VMP2 methods, the convergence of which relies critically on approximate vibration-vibration and vibration-rotation separability. The accuracy of this combined RP-RAS-VMP2 scheme is demonstrated by comparisons with numerically exact variational calculations and VMP2 parameters based on traditional Eckart embeddings for reduced-dimension models of torsional tunnelling in hydrogen peroxide and inversion tunnelling in cyclopropyl radical. The favourable computational scaling of VMP2 makes it a promising strategy for calculating accurate tunnelling-rotation parameters for medium-sized and larger molecules in full dimensionality. [ABSTRACT FROM AUTHOR]

We present a molecular geometry optimization algorithm based on the gradient-enhanced universal kriging (GEUK) formalism with ab initio prior mean functions, which incorporates prior physical knowledge to surrogate-based optimization. In this formalism, we have demonstrated the advantage of allowing the prior mean functions to be adaptive during geometry optimization over a pre-fixed choice of prior functions. Our implementation is general and flexible in two senses. First, the optimizations on the surrogate surface can be in both Cartesian coordinates and curvilinear coordinates. We explore four representative curvilinear coordinates in this work, including the redundant Coulombic coordinates, the redundant internal coordinates, the non-redundant delocalized internal coordinates, and the non-redundant hybrid delocalized internal Z-matrix coordinates. We show that our GEUK optimizer accelerates geometry optimization as compared to conventional non-surrogate-based optimizers in internal coordinates. We further showcase the power of the GEUK with on-the-fly adaptive priors for efficient optimizations of challenging molecules (Criegee intermediates) with a high-accuracy electronic structure method (the coupled-cluster method). Second, we present the usage of internal coordinates under the complete curvilinear scheme. A complete curvilinear scheme performs both surrogate potential-energy surface (PES) fitting and structure optimization entirely in the curvilinear coordinates. Our benchmark indicates that the complete curvilinear scheme significantly reduces the cost of structure minimization on the surrogate compared to the incomplete curvilinear scheme, which fits the surrogate PES in curvilinear coordinates partially and optimizes a structure in Cartesian coordinates through curvilinear coordinates via the chain rule. [ABSTRACT FROM AUTHOR]

Following the solution formula method given in Dong et al. (High order discontinuities decomposition entropy condition schemes for Euler equations. CFD J. 2002;10(4): 448–457), this article studies a type of one‐step fully‐discrete scheme, and constructs a third‐order scheme which is written into a compact form via a new limiter. The highlights of this study and advantages of new third‐order scheme are as follows: ① We proposed a very simple new methodology of constructing one‐step, consistent high‐order and non‐oscillation schemes that do not rely on Runge–Kutta method; ② We systematically studied new scheme's theoretical problems about entropy conditions, error analysis, and non‐oscillation conditions; ③ The new scheme achieves exact solution in linear cases and performing better in nonlinear cases when CFL → 1; ④ The new scheme is third order but high resolution with excellent shock‐capturing capacity which is comparable to fifth order WENO scheme; ⑤ CPU time of new scheme is only a quarter of WENO5 + RK3 under same computing condition; ⑥ For engineering applications, the new scheme is extended to multi‐dimensional Euler equations under curvilinear coordinates. Numerical experiments contain 1D scalar equation, 1D,2D,3D Euler equations. Accuracy tests are carried out using 1D linear scalar equation, 1D Burgers equation and 2D Euler equations and two sonic point tests are carried out to show the effect of entropy condition linearization. All tests are compared with results of WENO5 and finally indicate EC3 is cheaper in computational expense. [ABSTRACT FROM AUTHOR]

In this study, the bending-bending coupled static behavior of functionally graded and porous pretwisted cantilever Timoshenko beams is reported. Symmetric power-law distribution is employed as the material profile and it is assumed that porosity can disperse over the cross-section in two forms namely, even and uneven distributions. Two different yet equivalent forms of governing equations are obtained by formulating the problem in the fixed and curvilinear coordinate systems, respectively. The initial values method is adopted as the solution methodology. While the fundamental matrix is computed numerically by using the multiplicative integral of Volterra to obtain the solution in the fixed coordinate formulation, the matrix exponential which allows for obtaining exact expressions is utilized in the curvilinear coordinate formulation. Exact analytical deflection expressions are presented for space-fixed vertical tip force and body-fixed uniform distributed force cases. It is shown that both formulation approaches yield consistent results with each other and those obtained from the finite element analyses. In addition, several parametric studies that investigate the effects of the volume fraction index, porosity coefficient, and porosity distribution on the tip deflections are presented. [ABSTRACT FROM AUTHOR]

Ellipsoidal orthogonal curvilinear coordinates referred to a triaxial reference ellipsoid are not used in geodesy perhaps because of their theoretical complexity. However, many surveying and geodetic problems could be resolved by simply transforming variables between local frames. Herein it is shown that the computations of local displacements and variance-covariance matrices referred to currently used local curvilinear geodetic coordinate frames gives approximately the same answers than when referred to local ellipsoidal (triaxial) curvilinear frames. The theoretical procedures to obtain the required transformations between local geodetic and local ellipsoidal (triaxial) frames are introduced and examples explained. [ABSTRACT FROM AUTHOR]

Assuming that the streamlines are given by keeping constant one of the two orthogonal curvilinear coordinates in the Euclidean two-dimensional space, while considering a steady, two-dimensional, isentropic flow of an ideal gas through a convergent-divergent nozzle, and thus parallel to the curvilinear upper and lower walls of the nozzle, the theory of differential geometry together with the balance equations of physics was used to study the existence (or non-existence !) of real-valued, differentiable and integrable mass-density solutions to the problem, by means of analytical solutions, and corresponding to an expansion or compression of the gas along the streamlines. Thus, by initially assuming that the partial mass-density derivatives with respect to both curvilinear coordinates satisfy the integrability condition of Schwarz, the resulting system of four scalar partial differential equations led to an analytically derived quadratic equation for the determination of the ideal-gas mass density, based on generalised orthogonal curvilinear coordinates: Finally, the four orthogonal curvilinear coordinate systems, defined by the Killing two-tensors for the Euclidean two-dimensional space, were used, in order to examine whether these coordinate systems could satisfy the already mentioned generalised curvilinear-geometry equation as a quadratic equation, and the related requirements with regard to the partial mass-density derivatives, or not. Only real and nonzero, positive values for the mass density were considered, based on curvilinear streamlines of nonzero curvature. [ABSTRACT FROM AUTHOR]

Analogue space-times (and in particular metamaterial analogue space-times) have a long varied and rather complex history. Much of the previous related work to this field has focused on spherically symmetric models; however, axial symmetry is much more relevant for mimicking astrophysically interesting systems that are typically subject to rotation. Now it is well known that physically reasonable stationary axisymmetric space-times can, under very mild technical conditions, be put into Boyer–Lindquist form. Unfortunately, a metric presented in Boyer–Lindquist form is not well adapted to the "quasi-Cartesian" metamaterial analysis that we developed in our previous articles on "bespoke analogue space-times". In the current article, we shall first focus specifically on various space-time metrics presented in Boyer–Lindquist form, and subsequently determine a suitable set of equivalent metamaterial susceptibility tensors in a laboratory setting. We shall then turn to analyzing generic space-times, not even necessarily stationary, again determining a suitable set of equivalent metamaterial susceptibility tensors. Perhaps surprisingly, we find that the well-known ADM formalism proves to be not particularly useful, and that it is instead the dual "threaded" (Kaluza–Klein–inspired) formalism that provides much more tractable results. While the background laboratory metric is (for mathematical simplicity and physical plausibility) always taken to be Riemann flat, we will allow for arbitrary curvilinear coordinate systems on the flat background space-time. Finally, for completeness, we shall reconsider spherically symmetric space-times, but now in general spherical polar coordinates rather than quasi-Cartesian coordinates. In summary, this article provides a set of general-purpose calculational tools that can readily be adapted for mimicking various interesting (curved) space-times by using nontrivial susceptibility tensors in general (background-flat) laboratory settings. [ABSTRACT FROM AUTHOR]

Hydrodynamic flows induced by translational oscillations of cylindrical bodies of various cross-sectional shapes are studied. The motion of fluid around oscillating bodies is described using the system of Navier–Stokes equations written in a generalized curvilinear coordinate system. Transition to a given body shape is implemented using a conformal mapping. The problem is solved using the method of successive asymptotic expansions under the assumption that the oscillation amplitudes are small. In each asymptotic approximation, the subproblems are solved numerically using the finite-difference method. Based on the results of the work, estimates of the hydrodynamic effect are obtained, the applicability of the high-frequency asymptotic approximation is estimated, and secondary stationary flows near cylinders are studied, in particular, the occurrence of directed stationary flows near an oscillating asymmetric body is considered with reference to the Joukowski airfoil. [ABSTRACT FROM AUTHOR]

Abstract The hyperconcentrated fluid flow occurs as a result of heavy rainfall, during which a large amount of sediments from the upstream basin is washed away and suddenly increases the flow concentration of the alluvial channels. The stresses exerted by this type of fluid on the bed and body of the stream/river and related structures such as dam lead to the failure them and cause many human and financial losses. One of the important topics in the simulation of dam break caused by non-Newtonian fluid flow is the modeling of frictional stresses. In this research, after collecting several relationships to model the coefficient of friction loss of non-Newtonian fluid, a two-dimensional model was developed based on the numerical solution of shallow water equations in curvilinear coordinates to simulate hyperconcentrated flow. The results of the validation of the model were presented by comparing the measurement data of the suddenly complete dam break caused by the non-Newtonian fluid flow in the form of graphs, which all emphasize the accuracy of the developed model. It was also shown that for a suddenly complete dam break, with an increase in fluid volume concentration from 13.8 to 36.4%, the flow depth at the failure site increases by 18.8%. Next, asymmetric two-dimensional partial dam break of non-Newtonian fluid was simulated and compared with the results of Newtonian fluid. The results showed that the maximum flow velocity in the center of the fracture wall for the non-Newtonian fluid with a concentration of 32.2% is less than half of the maximum velocity of the Newtonian fluid.

Most pumping action s entail l a physical volume change of the duct, which is frequently achieved by having a compliant wall or membrane. To the best of our knowledge, the current study is the first report on a mathematical model developed to analyze the peristaltic transport of a Newtonian fluid in a curved duct with rectangular face and compliant walls. Such geometries are most commonly used in clinical and biological equipment, where the walls of the duct need to be flexible. Flexible ducts are more useful than rigid ones because they do not require any extra modifications or accessories. Here, we have used the conditions of lubrication theory to construct an accurate model, and a common perturbation technique was incorporated to handle the Navier-Stokes equations with emphasis on various aspect ratios and curvatures. A system of curvilinear coordinates operating according to the principles of the cylindrical system was employed to represent the mathematical problem. No-slip boundary limitations were considered at the walls along with the extra constraint of compliant walls showing damping force and stiffness. Comprehensive graphical representations were made to illustrate the effects of all emerging factors of the study in both two- and three-dimensional formats. We found that large curvatures and flexure rigidity decreased the fluid velocity uniformly, but the aspect ratio and amplitude parameters could promote fluid velocity. Validation of the results was performed through the generation of a residual error curve. The current readings were taken again with a straight duct to make a comparison with the existing literature. [ABSTRACT FROM AUTHOR]

The numerical solution of the two–dimensional, time–dependent, incompressible Navier–Stokes equations (NSE) in curvilinear coordinates using the nodal integral method (NIM) is presented in this paper. The developed numerical scheme is applied to solve fluid flow problems in domains discretized using quadrilateral cells. Three test problems are numerically solved to assess the accuracy and efficiency of the method. The scheme is second-order accurate in space for all considered deformation levels and Re numbers. The results of the current scheme are compared with the other numerical results in the literature, and good agreement is obtained for all considered cases. The NIM demonstrates superior accuracy per cell compared to other second–order finite–volume schemes considered in this work. New benchmark results obtained from the solution on fine meshes are presented. • The time-dependent, 2D, incompressible Navier-Stokes equations are numerically solved in curvilinear coordinates using nodal integral method. • The accuracy and efficiency of the numerical scheme are assessed through three numerical test problems. • The scheme is found to be second-order accurate in space for all considered deformation levels and Reynolds numbers. • The developed scheme shows superior per-cell accuracy compared to other considered second-order finite-volume schemes. • The developed scheme is capable of simulating incompressible flows accurately using coarse meshes. [ABSTRACT FROM AUTHOR]

The computation of the finite difference method in curvilinear coordinates usually necessitates coordinate transformation. Eliminating geometric errors induced by coordinate transformation can be achieved with geometric conservation law. However, no research has been conducted to implement a difference scheme on two-dimensional three-neighboring-node unstructured meshes and achieve a second-order accuracy. In this paper, a new finite difference method is proposed for a numerical simulation on these meshes, and it can achieve a second-order accuracy with the use of the gradient interpolation and the discrete criterion, freezing the metrics and Jacobian at local nodes. The results of several numerical tests demonstrate that the method achieved reliable performance and robustness on unique and randomized unstructured grids for a complex flow with discontinuity, subsonic inflow, and diffraction. The method had comparable accuracy to the second-order difference scheme on structured grids. [ABSTRACT FROM AUTHOR]

The transport of complex rheological fluids in physiological ducts is often facilitated by the dynamic phenomenon of peristalsis. Additionally, peristaltic transport assisted by cilia plays a significant role in various natural processes such as respiration, circulation, locomotion, and reproduction. This study focuses on magnetically induced flow bounded by non-uniform curved walls, motivated by the importance of peristalsis and micro-organism motility. To characterize the complex rheology of the fluid liner, a viscoelastic model described by the constitutive equation of Jeffrey's fluid is employed. The flow problem is mathematically formulated using curvilinear coordinates. Subsequently, linear transformations and scaling factors are applied to convert the equations into dimensionless form, while considering biotic restrictions such as creeping transport and long wavelength to reduce dependent variables. By utilizing the stream function and cross-differentiation, a fourth-order equation is obtained and numerically approximated using the shooting method. The effects of various parameters on the flow are illustrated through graphs, and a physical interpretation of the graphical results is provided. It is observed that ciliated walls of the channel enhance the velocity and pumping, while trapping phenomena are more pronounced in a non-uniform channel compared to a uniform channel. [ABSTRACT FROM AUTHOR]

This investigation is an approach to setup an analytical solution of steady plane allied MHD fluid flow having infinite electrical conductivity in a rotating frame through porous media by Martin's method. The governing non-linear equations of the fluid flow are transformed into a new form called Martin's form by employing differential geometry where the curvilinear co-ordinates (Φ, Ψ) in the plane of flow shows that, the co-ordinate lines Ψ are the streamlines of flow and the co-ordinate lines Φ are arbitrary constants. Exact solution is obtained and velocity, vorticity, current density magnetic field and pressure distribution are found out. Also, the diagrams have been plotted to sketch the streamline patterns and to study variation of pressure function with angular velocity. [ABSTRACT FROM AUTHOR]

The coordinate-transformation-based differential method developed by Chandezon et al. is recognized as one of the simplest and most versatile approaches for modeling surface-relief gratings. In this study, we present a novel numerical solution using Legendre polynomial expansion, enabling us to deal efficiently with faceted gratings. Additionally, we introduce an oblique coordinate transformation to analyze overhanging faceted gratings. Notably, the C-method with polynomial expansion (CPE) demonstrates a dramatic improvement in convergence speed compared to the Fourier Modal Method (FMM). [ABSTRACT FROM AUTHOR]

In practice, slope instability failure often occurs in the form of an asymmetric three-dimensional (3D) slip surface. The movement trend of the asymmetric sliding body is in the form of simultaneous translation and rotation around the vertical axis; thus, the route of the main sliding (RMS) exhibits non-linear characteristics. Therefore, the purpose of this study was to propose a rigorous 3D limit equilibrium method for slope stability with the asymmetric 3D slip surface. The function of normal stress over the slip surface was assumed, and all the equilibrium conditions of the entire sliding body (i.e., three forces and three moments) were considered. The mapping function relationship between curvilinear coordinates and Cartesian coordinates was established, and the expressions of basic physical quantities in the equilibrium equations were derived. Through optimizing the RMS, a rigorous solution of the factor of safety was obtained for an asymmetric slip surface. The research results indicated that the present method well reflected the influence of the RMS, which was applicable to analyzing 3D slope stability with an asymmetric slip surface. We found that if the RMS is ignored, the factor of safety will be overestimated. The more significant the asymmetry of the 3D slip surface, the greater the proportion of rotation for the sliding body, and the more significant the bending degree of the RMS. The study results suggested that a rotation hardly existed, and the RMS tended to be a linear route in a symmetrical sliding body. The research results can provide a theoretical reference for 3D slope stability evaluation. [ABSTRACT FROM AUTHOR]

The hyperconcentrated fluid flow occurs as a result of heavy rainfall, during which a large amount of sediments from the upstream basin is washed away and suddenly increases the flow concentration of the alluvial channels. The stresses exerted by this type of fluid on the bed and body of the stream/river and related structures such as dam lead to the failure them and cause many human and financial losses. One of the important topics in the simulation of dam break caused by non-Newtonian fluid flow is the modeling of frictional stresses. In this research, after collecting several relationships to model the coefficient of friction loss of non-Newtonian fluid, a two-dimensional model was developed based on the numerical solution of shallow water equations in curvilinear coordinates to simulate hyperconcentrated flow. The results of the validation of the model were presented by comparing the measurement data of the suddenly complete dam break caused by the non-Newtonian fluid flow in the form of graphs, which all emphasize the accuracy of the developed model. It was also shown that for a suddenly complete dam break, with an increase in fluid volume concentration from 13.8 to 36.4%, the flow depth at the failure site increases by 18.8%. Next, asymmetric two-dimensional partial dam break of non-Newtonian fluid was simulated and compared with the results of Newtonian fluid. The results showed that the maximum flow velocity in the center of the fracture wall for the non-Newtonian fluid with a concentration of 32.2% is less than half of the maximum velocity of the Newtonian fluid. [ABSTRACT FROM AUTHOR]

Salt mixing enables the transport of water between the inflow and outflow layers of estuarine circulation and therefore closes the circulation by driving a diahaline exchange flow. A recently derived universal law links the salt mixing inside an estuarine volume bounded by an isohaline surface to freshwater discharge: it states that on long-term average, the area-integrated mixing across the bounding isohaline is directly proportional to the freshwater discharge entering the estuary. However, even though numerous studies predict that periods of extreme discharge will become more frequent with climate change, the direct impact of such periods on estuarine mixing and circulation has yet to be investigated. Therefore, this numerical modeling study focuses on salinity mixing and diahaline exchange flows during a low-discharge and an extreme high-discharge period. To this end, we apply a realistic numerical setup of the Elbe estuary in northern Germany, using curvilinear coordinates that follow the navigational channel. This is the first time the direct relationship between diahaline exchange flow and salt mixing as well as the spatial distribution of the diahaline exchange flow is shown in a realistic tidal setup. The spatial distribution is highly correlated with the local mixing gradient for salinity, such that inflow occurs near the bottom at the upstream end of the isohaline. Meanwhile, outflow occurs near the surface at its downstream end. Last, increased vertical stratification occurs within the estuary during the high-discharge period, while estuarine-wide mixing strongly converges to the universal law for averaging periods of the discharge event time scale. Significance Statement: Inside estuaries, such as river mouths, terrestrial freshwater is mixed with salty ocean water. This is accompanied by an estuarine circulation with inflow of saltwater into the estuary and outflow of brackish water toward the ocean. Here, we aim to better understand how salt mixing and estuarine circulation in a tidal estuary react to periods of extreme freshwater discharge. We find that even during extremely high or low discharge, salt mixing follows the freshwater discharge on time scales as short as days, and that estuarine circulation patterns are largely explained by the local distribution of mixing. As extreme runoff events are likely to occur more often with climate change, these findings may help to understand the dynamics inside future estuaries. [ABSTRACT FROM AUTHOR]

Different standard VPT2 codes employ Cartesian coordinates for the computation of rotational and vibrational spectroscopic parameters. However, curvilinear internal coordinates offer a number of advantages provided that a general non-redundant set of coordinates can be built and employed in an unsupervised workflow. In the present paper I summarize the main results and perspectives of a general engine employing curvilinear internal coordinates and perturbation theory for the computation of rotational and vibrational spectroscopic parameters of large molecules beyond the conventional rigid rotor/harmonic oscillator model. Some examples concerning biomolecule building blocks are discussed in some detail in order to better analyze the performance of the proposed strategy. [ABSTRACT FROM AUTHOR]

The present study focuses on numerical simulations of magnetohydrodynamic mixed convection and entropy formation in a lid-driven wavy enclosure filled with non-Newtonian power-law ferrofluid. The physical model is a two-dimensional wavy square chamber with thermally adiabatic horizontal boundaries, while the right and left vertical walls maintain a constant temperature of the T C and T H , respectively. For mapping the wavy domain to a simple square domain the Cartesian curvilinear coordinates are used. The governing equations are solved using the finite volume method to explore the mixed convection characteristics in terms of heat transport, velocity, streamlines, isotherms, and entropy formation. Pertinent non-dimensional parameters, such as the Reynolds number (Re), Hartmann number (Ha), power-law index (n), ferroparticle volume fraction (ϕ ), and a fixed Prandtl number ( Pr = 6.8377 ), are used for the numerical simulation. According to the findings, the mean Nusselt numbers ( Nu ¯ ) grow when Ha is reduced and Re, n and ϕ are augmented, and the highest magnitude of Nu ¯ is found, while 4 % ferroparticles are added to the base fluid. The influence of key variables on total entropy production (E s) t reduced by raising Ha. [ABSTRACT FROM AUTHOR]

The methods of finite-gap integration are used to construct orthogonal curvilinear coordinate systems in the Euclidean space corresponding to sheaves of rank one without torsion over reducible singular spectral curves. [ABSTRACT FROM AUTHOR]

Radiative heat transport involving complex geometries is an important area of investigation. The formulation of the transport phenomenon is more involved and consideration of the proper treatment of the irregular geometry becomes necessary for accurate estimation of heat transfer rates. Therefore, the present study focuses on the modeling and the solution of the radiative transfer equation (RTE) in an absorbing, emitting, and isotropically scattering, participating media for complex geometries using the body-fitted coordinates. The RTE in an orthogonal coordinate system is formulated and is then numerically solved in conjunction with a numerically generated, body-fitted, curvilinear coordinate system. The geometries are considered to be opaque and, in the analysis, both the radiative as well as the non-radiative equilibrium cases are considered. The formulation is validated through the previously published results. Notable agreement is observed between the results and those reported earlier for different complex geometries and various properties of the participating media. [ABSTRACT FROM AUTHOR]

It is shown that the new precise formulation of the Large Number Hypothesis (LNH), relating by means of the large number N0 = 5.73×1060 the modern cosmological parameters (age, size, mass, average density, and minimum temperature of the universe) with the corresponding Planck units, allows to determine the time course of these cosmological parameters during the expansion. It was found that the dimensions and mass of the universe increase linearly with time from Planck time t = tP to the present day, starting from Planck values and increasing N0 = 5.73×1060 times to now. The amazing result was found that for each discrete time step (beat) with a unit Planck time Δt = tP, the size of the universe increases by one Planck length lP and its mass increases by one Planck mass mP. It is shown that the average density of the universe decreases proportionally to the square of time, and starting from the Planck density ρP ~ 1096 kg m-3 decreases N0 2 = 3.28×10121 times to 9.46×10-27 kg m-3 in the current epoch. The minimum measurable temperature, which is equal to the Hawking temperature for the universe TH decreases linearly with time 5.73×1060 times, and starting from the Planck temperature TP = 1032 K, it falls to 1.75×10-29 K at the present time. It is shown that the found time course of cosmological parameters and the Planck values of the size, mass, average density, and temperature of the universe at the initial moment of the expansion t = tP follow from the requirement to preserve the Euclidean geometry of space throughout the time of the cosmological expansion. Therefore, the suggested cosmological model based on the new formulation of LNH is free of singularity because the size and density of the universe remain finite/Planckian in the initial moments of its emergence. Besides, this model conserves the flatness and homogeneity of the universe during cosmological expansion and does not need an inflationary epoch in the early universe. [ABSTRACT FROM AUTHOR]

Nearshore waves and currents induced by breaking of obliquely incident waves are important dynamic factors that significantly affect pollutants movement at offshore zones. A combined numerical model in orthogonal curvilinear coordinates is developed to simulate pollutants movement in surf zones, including a wave transformation model based on the parabolic mild slope equation, a wave-induced current model, and a pollutant transport model driven by waves and currents. This combined model has been applied to pollutants movement laboratory cases, and comparison of the simulations with experimental measurements shows good agreement. The model has also been applied to simulation of the Gourlay experiment and it shows consistent results with the distribution of waves and offshore currents. This coupled numerical model has preliminarily improved the situation of rare numerical research on the nearshore pollutant transport in coastal wave and wave-induced current based on wave radiation stress theory in orthogonal curvilinear coordinates. [ABSTRACT FROM AUTHOR]

Cilia play important roles in fluid transport and development by propagating metachronal waves along cell surfaces. This study numerically investigates the biomechanics of cilia-driven flow of Jeffrey nanofluid in a wavy curved channel. The orthogonal curvilinear coordinates are used for the mathematical formulation of the problem in a set of partial differential equations. The governing equations are simplified using the dimensionless numbers and stream functions and then reduced using the long wavelength and low Reynolds number assumptions. Shooting method is applied to determine velocity, temperature, and nanoparticle concentration profiles. The resultant velocity, temperature profiles, nanoparticle concentration profiles, and streamlines are interpreted and elucidated graphically. The parametric analyses systematically examine the impacts of channel curvature, thermal buoyancy forces, nanoparticle concentrations, Jeffrey fluid rheology, and cilia motion kinematics on transport phenomena. Key findings show temperature and concentration gradients strongly influenced by cilia beating. The study provides deeper insight into the influence of these parameters on the cilia-driven flow in a complex wavy curved channel, bearing potential applications in heat transfer systems, nanotechnology, and biotechnology, among other fields. [ABSTRACT FROM AUTHOR]

The Laplace equation in three-dimensional Euclidean space is R -separable in bi-cyclide coordinates leading to harmonic functions expressed in terms of Lamé–Wangerin functions called internal and external bi-cyclide harmonics. An expansion for a fundamental solution of Laplace's equation in products of internal and external bi-cyclide harmonics is derived. In limiting cases this expansion reduces to known expansions in bi-spherical and prolate spheroidal coordinates. [ABSTRACT FROM AUTHOR]

The methods of classical differential geometry are used to integrate the two-dimensional Heisenberg model. After the hodograph transformation, the model equations are written in terms of the metric tensor associated with a curvilinear coordinate system and its derivatives. It is shown that their general solution describes all previously known exact solutions except a flat vortex. A new type of vortex structure, a "vortex strip," is predicted and analyzed in two-dimensional ferromagnets. Its typical properties are the finite dimensions of the domain of definition, the finiteness of the total energy, and the absence of a vortex core in the presence of a vortex structure. [ABSTRACT FROM AUTHOR]

We calculate energies of shallow donors confined in a rolled-up quantum well in the presence of the electric field by solving numerically the Schrödinger equation in natural curvilinear coordinates. It is found that the curves of density of states (DOSs) are very sensitive to the variation of the donor position, the geometry of the spiral and the applied electric field value. Novel results for dependencies of donor's dipole moment and its polarizability on the electric field strength and its orientation, for different donor positions are presented. Additionally, we found that the anisotropic Stark effect of the first order provides in this structure a dependency of the polarizability on the external electric field in a spike-like shape, giving rise to a sharp variation of the dipole moment. [ABSTRACT FROM AUTHOR]

The coordinate-transformation-based differential method developed by Chandezon et al. is recognized as one of the simplest and most versatile approaches for modeling surface-relief gratings. In this study, we present a novel numerical solution using Legendre polynomial expansion, enabling us to deal efficiently with faceted gratings. Additionally, we introduce an oblique coordinate transformation to analyze overhanging faceted gratings. Notably, the C-method with polynomial expansion (CPE) demonstrates a dramatic improvement in convergence speed compared to the Fourier Modal Method (FMM).

The most relevant features of FLIPEC (Free fLow Iterative Plasma Equilibrium Code) are presented. This new code iteratively calculates free-boundary, axisymmetric ideal MHD equilibria with arbitrary poloidal and toroidal plasma flows. FLIPEC is a mature code that has emerged from a complete overhaul of a previous version (F-Torija Daza 2022 et al Nucl. Fusion 62 126044). It uses a (inverse) curvilinear coordinate representation for the Grad–Shafranov–Bernoulli equation system, which allows FLIPEC to extend its free-boundary capabilities to arbitrary plasma shapes and removes many limitations with regards to the distance between plasma and external coils. Run-time stabilization of vertical modes has also been implemented by means of artificial feedback coils. Finally, active targeting schemes have also been included. These capabilities are illustrated on two very different cases: the ITER tokamak baseline configuration and a NSTX spherical tokamak equilibrium.

In this paper, we report a series of transformations for the construction of a Hamiltonian model for nonrigid polyatomic molecules in the framework of the Hougen–Bunker–Johns formalism (HBJ). This model is expressed in normal mode coordinates for small vibrations and in a specific coordinate ρ to describe the large amplitude motion. For the first time, a general procedure linking the "true" curvilinear coordinates to ρ is proposed, allowing the expression of the potential energy part in the same coordinate representation as the kinetic energy operator, whatever the number of atoms. A Lie group-based method is also proposed for the derivation of the reference configuration in the internal axis system. This work opens new perspectives for future high-resolution spectroscopy studies of nonrigid, medium-sized molecules using HBJ-type Hamiltonians. Illustrative examples and computation of vibrational energy levels on semirigid and nonrigid molecules are given to validate this method. [ABSTRACT FROM AUTHOR]

A generalized Frenkel–Holstein Hamiltonian is constructed to describe exciton migration in oligo(para-phenylene vinylene) chains, based on excited state electronic structure data for an oligomer comprising 20 monomer units (OPV-20). Time-dependent density functional theory calculations using the ωB97XD hybrid functional are employed in conjunction with a transition density analysis to study the low-lying singlet excitations and demonstrate that these can be characterized to a good approximation as a Frenkel exciton manifold. Based on these findings, we employ the analytic mapping procedure of Binder et al. [J. Chem. Phys. 141, 014101 (2014)] to translate one-dimensional (1D) and two-dimensional (2D) potential energy surface (PES) scans to a fully anharmonic, generalized Frenkel–Holstein (FH) Hamiltonian. A 1D PES scan is carried out for intra-ring quinoid distortion modes, while 2D PES scans are performed for the anharmonically coupled inter-monomer torsional and vinylene bridge bond length alternation modes. The kinetic energy is constructed in curvilinear coordinates by an exact numerical procedure, using the TNUM Fortran code. As a result, a fully molecular-based, generalized FH Hamiltonian is obtained, which is subsequently employed for quantum exciton dynamics simulations, as shown in Paper II [R. Binder and I. Burghardt, J. Chem. Phys. 152, 204120 (2020)]. [ABSTRACT FROM AUTHOR]

In high dimension, the bifurcation theory of periodic orbits of nonlinear dynamics systems are difficult to establish in general. In this paper, by performing the curvilinear coordinate frame and constructing a Poincaré map, we obtain some sufficient conditions of the bifurcation of periodic solutions of some 2n-dimensional systems for the unperturbed system in two cases: one is a decoupled n-degree-of-freedom nonlinear Hamiltonian system and the other has an isolated invariant torus. We use a new method and study new types of systems compared with the existing results. As an application we study the bifurcation and number of periodic solutions of an ice covered suspension system. Under a certain parametrical condition, the number of periodic solutions of this system can be 2 or 1 with the variation of parameter p 2 . [ABSTRACT FROM AUTHOR]

This study introduces a novel computational approach for optimizing the design of cam knife-edge followers by utilizing potential energy analysis. In this methodology, cam parameters are succinctly represented using curvilinear coordinate systems, and the objective function is derived from the potential energy. To stabilize the position between two points, a stabilization function is incorporated. The cam curve is discretized through finite element analysis, and the resulting nonlinear equation is solved using the Newton-Raphson method. Additionally, the optimal design of the cam knife-edge follower considers cam size, which is associated with the base circle radius and pressure angle. Results demonstrate that the proposed method offers greater flexibility in evaluating and optimizing the design parameters of cam knife-edge followers compared to existing approaches. This study not only provides new insights into the optimization of cam knife-edge followers but also has potential applications in other related fields. [ABSTRACT FROM AUTHOR]

The two families of principal stress trajectories can be regarded as an orthogonal curvilinear coordinate system under plane strain and axial symmetry. Under plane strain, the equilibrium equations in conjunction with a yield criterion comprise a statically determinate system. Under axial symmetry, a statically determinate system results from the above equations supplemented with the hypothesis of Haar von Karman. In both cases, the compatibility equations for mapping the principal line coordinate system to a given coordinate system show that the scale factors of the former satisfy a simple algebraic or transcendental equation for many yield criteria. Using this equation, one can develop a method for reducing boundary value problems in plasticity to purely geometric problems. The method is independent of any flow rule that can be chosen to calculate displacement or velocity fields, as well as independent whether elastic strains are included. The present paper summarizes available results related to using principal stress trajectories in plasticity and emphasizes the advantages of the method above. [ABSTRACT FROM AUTHOR]

A new adaptive clipping‐and‐redistribution method is presented which provides bounds‐preservation for multidimensional interpolation in the context of high‐order finite‐volume discretizations with adaptive mesh refinement (AMR). The underlying finite‐volume method (FVM) for the computational fluid dynamics applications is fourth‐order accurate for smooth solutions and utilizes AMR for computational efficiency in solving multiscale problems involving turbulence and combustion. High‐order interpolation between different AMR levels is required. However, this operation often leads to numerical issues because combustion species must have physical bounds preserved. The present study overcomes two major challenges in the development of the high‐order interpolation method. First, the method needs to be bound‐preserving near extrema or discontinuities to prevent the emergence of unphysical oscillations while maintaining fourth‐order accuracy in smooth flows. Second, the method needs to satisfy the conservation requirement in multiple dimensions, particularly in the context of curvilinear coordinate transformations. Additionally, the method is designed to be localized and computationally inexpensive. The new interpolation scheme is demonstrated by solving reacting flows, which are extremely sensitive to unphysical overshoots in conserved quantities. The test problems are shock‐induced H2$$ {\mathrm{H}}_2 $$‐O2$$ {\mathrm{O}}_2 $$ combustion and a C3H8$$ {\mathrm{C}}_3{\mathrm{H}}_8 $$‐air flame in a practical bluff‐body combustor. Results show the method prevents new extrema near discontinuities while maintaining high‐order accuracy in smooth regions. In particular, the method is extremely beneficial for combustion with stiff chemistry. With the proposed new method, even if flame fronts cross AMR interfaces or new grids are created in the vicinity of the flame, solution stability is retained. [ABSTRACT FROM AUTHOR]

In this work, a 3D fully coupled hygro-elastic model is proposed. The moisture content profile is a primary variable of the model's displacements. This generic fully coupled 3D exact shell model allows the investigations into the consequences arising from moisture content and elastic fields in terms of stresses and deformations on different plate and shell configurations embedded in composite and laminated layers. Cylinders, plates, cylindrical and spherical shells are analyzed in the orthogonal mixed curvilinear reference system. The 3D equilibrium equations and the 3D Fick diffusion equation for spherical shells are fully coupled in a dedicated system. The main advantage of the orthogonal mixed curvilinear coordinates is related to the degeneration of the equations for spherical shells to simpler geometries thanks to basic considerations of the radii of curvature. The exponential matrix method is used to solve this fully coupled model based on partial differential equations in the thickness direction. The closed-form solution is related to simply supported sides and harmonic forms for displacements and the moisture content. The moisture content amplitudes are directly applied at the top and bottom outer faces through steady-state hypotheses. The final system is based on a set of coupled homogeneous second-order differential equations. A first-order differential equation system is obtained by redoubling the number of variables. The moisture field implications are evaluated for the static analysis of the plates and shells in terms of displacement and stress components. After preliminary validations, new benchmarks are proposed for several thickness ratios, geometrical and material data, lamination sequences and moisture values imposed at the external surfaces. In the proposed results, there is clearly accordance between the uncoupled hygro-elastic model (where the 3D Fick diffusion law is separately solved) and this new fully coupled hygro-elastic model: the differences between the investigated variables (displacements, moisture contents, stresses and strains) are always less than 0.3%. The main advantages of the 3D coupled hygro-elastic model are a more compact mathematical formulation and lower computational costs. Both effects connected with the thickness layer and the embedded materials are included in the conducted hygro-elastic analyses. [ABSTRACT FROM AUTHOR]

In this work, a coupled 3D thermo-elastic shell model is presented. The primary variables are the scalar sovra-temperature and the displacement vector. This model allows for the thermal stress analysis of one-layered and sandwich plates and shells embedding Functionally Graded Material (FGM) layers. The 3D equilibrium equations and the 3D Fourier heat conduction equation for spherical shells are put together into a set of four coupled equations. They automatically degenerate in those for simpler geometries thanks to proper considerations about the radii of curvature and the use of orthogonal mixed curvilinear coordinates α , β , and z. The obtained partial differential governing the equations along the thickness direction are solved using the exponential matrix method. The closed form solution is possible assuming simply supported boundary conditions and proper harmonic forms for all the unknowns. The sovra-temperature amplitudes are directly imposed at the outer surfaces for each geometry in steady-state conditions. The effects of the thermal environment are related to the sovra-temperature profiles through the thickness. The static responses are evaluated in terms of displacements and stresses. After a proper and global preliminary validation, new cases are presented for different thickness ratios, geometries, and temperature values at the external surfaces. The considered FGM is metallic at the bottom and ceramic at the top. This FGM layer can be embedded in a sandwich configuration or in a one-layered configuration. This new fully coupled thermo-elastic model provides results that are coincident with the results proposed by the uncoupled thermo-elastic model that separately solves the 3D Fourier heat conduction equation. The differences are always less than 0.5% for each investigated displacement, temperature, and stress component. The differences between the present 3D full coupled model and the the advantages of this new model are clearly shown. Both the thickness layer and material layer effects are directly included in all the conducted coupled thermal stress analyses. [ABSTRACT FROM AUTHOR]