Finite Conjugate Research Articles

An inverse estimation of frozen sand mold-melt heat transfer coefficient in the solidification of A356 alloy

Casting aluminum alloys is widely used in aerospace, rail transportation, automotive, ships, and other fields. The frozen sand mold casting (FSMC) technology provides a greener and low-cost solution for the sand mold casting industry, which has a better operating environment than the resin sand mold casting and a higher degree of subcooling for solidification process. The interfacial heat transfer coefficient (IHTC) is a significant parameter that affects the structure and properties of the frozen casting. It is also an important boundary condition in numerical simulation. In this paper, a frozen sand mold casting (FSMC) process thermal conductivity problem (IHCP) inversion model is proposed based on the 1-D heat transfer assumption using a combination of finite difference method (FDM) and conjugate gradient method (CGM). The inversion model is validated for its rationality and accuracy in terms of experiments and numerical calculations, respectively. The IHTC is determined under various frozen sand mold casting conditions, including different initial frozen temperatures, water contents, and molding sand. The accuracy of results is verified by comparing the experimental and numerical data. A new method is provided for determining IHTC in frozen casting.

Linear-space-variant model for Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) needs to realize well-accepted reconstruction by image segmentation and discarding problematic data due to artifacts caused by vignetting. However, the imaging results have long suffered from uneven color blocks and the consequent digital stitching artifacts, failing to bring satisfying experiences to researchers and users over the past decade since the invention of FPM. In fact, the fundamental reason for vignetting artifacts lies in that the acquired data does not match the adopted linear-space-invariant (LSI) forward model, i.e., the actual object function is modulated by a quadratic phase factor during data acquisition, which has been neglected in the advancement of FPM. In this Letter, we rederive a linear-space-variant (LSV) model for FPM and design the corresponding loss function for FPM, termed LSV-FPM. Utilizing LSV-FPM for optimization enables the efficient removal of wrinkle artifacts caused by vignetting in the reconstruction results, without the need of segmenting or discarding images. The effectiveness of LSV-FPM is validated through data acquired in both 4f and finite conjugate single-lens systems.

Numerical research on the focusing characteristics of steady state sound field in finite space by combining finite element and phase conjugation methods

The research on sound source identification in an infinite free sound field has been relatively in-depth, but there is relatively little research on sound source identification and localization in limited spaces, especially those with sound absorption and insulation materials. The identification and reconstruction of the acoustical steady propagation field radiated from a single frequency finite space are studied numerically using discrete elements based on the phase conjugation method by FEM. Two different kinds of array forms of phase conjugation arrays are studied for sound source localization such as the planar array and the linear array. In addition, the influences of the existence of sound-absorbing material on the wall on the focusing properties are also discussed. The numerical results show that: The phase conjugation method can completely achieve the identification and location of the acoustical source finite space no matter using the planar array form or the linear array according to FEM. The linear array form can obtain the subwavelength focusing with fewer elements. The optimal distance between the array and the sound source is 0.5 [Formula: see text] and 2 [Formula: see text] to get the best reconstruction results. The smaller the absorption coefficient, the more to meet the multi-path phase compensation principle, the better reconstruction of the sound source.

Numerical modeling of conjugate heat and mass transfer with water vaporization in solid materials inside a convective hot air tunnel

A two-dimensional conjugate model describes heat and mass transfer with liquid to vapor phase change of water in solid materials inside a hot air tunnel. Computational modeling allows to assess the evolution of convective fluid mechanics and heat convection in laminar airflow and coupled heat-mass transfer diffusion inside a rectangular solid. A transient finite volume method conjugate model characterizes the fluid mechanics and heat transfer in airflow, and the local convective heat (h(L)) and mass(hm(L)) transfer coefficients. The results indicate that h(L) was found to vary spatially on each surface of the solid between 5.71 and 101.62 W/m2K, while hm(L) varied from 5.05×10−6 to 1.38×10−6 m/s. Heat and mass transfer by unsteady diffusion inside the solid were accounted for by a second transient diffusion model. Experimental findings of apple slice dehydration kinetic reported in the literature allowed to validate the coupled heat and mass transfer model, with deviation lower than 2% for the water mass losses. Finally, the proposed model applied on a thin-layer of murta berry puree inside a hot air tunnel predicted transient non-uniform heat and mass transfer processes, with a difference of 13.5 K between the coldest and front areas.

Nonparaxial diffraction of the Cartesian oval

We study the nonparaxial diffraction of the well-known Cartesian oval in finite and infinite conjugate configurations. We started by expressing the refraction of the Cartesian oval by analytical closed-form equations. These equations are convenient to obtain the pupil apodization function of the Cartesian oval, which is needed to compute the diffraction pattern using Richard–Wolf theory. A comparison of the diffraction patterns of the Cartesian oval with finite/infinite objects, the aplanatic lens, and the parabolic mirror for radially polarized illumination is presented. From this comparison, we conclude that a Cartesian oval for a far object is not a good candidate for tight focusing and super-resolution applications and the performance of a Cartesian oval in a finite conjugate configuration is similar to the performance of an aplanatic lens and in some scenarios, it can perform better than the aplanatic lens.

A Monochromatic Optical Analytical Study of a Stepped Refractive Index Shell Spherical Polymeric Lens

The GRIN (gradient refractive index) Luneburg lens cannot be used in visible region applications including imaging systems and in the integrated photonic lens as static concentric symmetry lenses. Furthermore, in order to obtain free monochromatic aberration, the ray must be focused on the lens's rear surface. As a result, the detector must be movable on the rear surface. Technically, this procedure is difficult. This work presented a straightforward and practical method based on the usage of a double shell gradient stepped index of symmetry concentric polymeric lens (SCPL). The obtained results revealed that the proposed lens can be used in the visible region, as well as the shifting of the focus point from the lens's rear surface. The (SCPL) lens was optically evaluated using the trigonometric ray tracing method. The evaluation was performed using a mathematical iterative method applied in MATLAB program. The iterative method was used to determine the best shell thicknesses of shelled ball lens (double shell) for constructing the (SCPL) parameters. The constructive parameters were examined using the ZEMAX optical design program for infinite conjugate conditions and monochromatic wavelength. According to the analysis results, the Sterhl ratio is greater than (0.97), and the total transverse aberration coefficients are approaching zero.

Flameless combustion of low calorific value gases, experiments, and simulations with advanced radiative heat transfer modeling

Thermal radiation is the dominant mode of heat transfer in many combustion systems, and in typical flameless furnaces, it can represent up to 80% of the total heat transfer. Accurate modeling of radiative heat transfer is, thus, crucial in the design of these large-scale combustion systems. Thermal radiation impacts the thermochemistry, thereby the energy efficiency and the temperature sensitive species prediction, such as NOx and soot. The requirement to accurately describe the spectral dependence of gaseous radiative properties of combustion products interacts with the modeling of finite rate chemistry effects and conjugates heat transfer and turbulence. Additionally, because of the multiple injection of fuels and/or oxidizers of various compositions, case-specific radiative properties' expressions are required. Along these lines, a comprehensive modeling to couple radiation and combustion in reacting flows is attempted and applied to the simulation of flameless combustion. Radiation is modeled using the spectral line-based weighted-sum-of-gray-gases approach to calculate gaseous radiative properties of combustion products using the correlation of the line-by-line spectra of H2O and CO2. The emissivity weights and absorption coefficients were optimized for a range of optical thicknesses and temperatures encountered in the considered furnace. Efforts were also made on the development of a reliable and detailed experimental dataset for validation. Measurements are performed in a low calorific value syngas furnace operating under flameless combustion. This test rig features a thermal charge which can extract about 60% of combustion heat release via 80% of radiative heat transfer, making it of special interest for modeling validation. The comparison between the simulation and the experiment demonstrated a fair prediction of heat transfer, energy balance, temperature, and chemical species fields.

Fast extended depth of focus meta-optics for varifocal functionality

Extended depth of focus (EDOF) optics can enable lower complexity optical imaging systems when compared to active focusing solutions. With existing EDOF optics, however, it is difficult to achieve high resolution and high collection efficiency simultaneously. The subwavelength spacing of scatterers in a meta-optic enables the engineering of very steep phase gradients; thus, meta-optics can achieve both a large physical aperture and a high numerical aperture. Here, we demonstrate a fast ( f / 1.75 ) EDOF meta-optic operating at visible wavelengths, with an aperture of 2 mm and focal range from 3.5 mm to 14.5 mm (286 diopters to 69 diopters), which is a 250 × elongation of the depth of focus relative to a standard lens. Depth-independent performance is shown by imaging at a range of finite conjugates, with a minimum spatial resolution of ∼ 9.84 μm (50.8 cycles/mm). We also demonstrate operation of a directly integrated EDOF meta-optic camera module to evaluate imaging at multiple object distances, a functionality which would otherwise require a varifocal lens.

Design and thermomechanical analysis of a cell-integrated, tapered channel heat sink concept for prismatic battery cells

Temporal and spatial temperature variations can negatively affect the performance, lifetime, and safety of Lithium-ion batteries used in electric vehicles. Air-cooled thermal management systems offer advantages in durability and simplicity. Here, we demonstrate a novel air-cooled system in which cooling features are integrated directly into the prismatic battery cells. When cells are stacked in a battery module, the topographic features integrated into the battery case contact each other and provide mechanical resistance against deformation due to internal battery pressure as well as form a plurality of cooling channels. A series of finite element analyses and conjugate heat transfer analyses are performed to identify the optimal geometric parameters for the design concept under consideration of both battery cell internal pressure and thermal loading. For a wide spacing between fins, the cooling efficiency is high when battery internal pressure is absent but low in the presence of cell deformation due to battery internal pressure. As the number of additional fins is increased, the effect of deformation on cooling performance decreases. Consequently, there exists an optimal number of cooling fins. The utilization of tapered channels and the addition of secondary fins provides additional and significant improvements in temperature uniformity, however at cost of increased pressure drop and maximum temperature compared with the design of parallel channels. This study seeks to make two contributions. One contribution is a fundamental one in heat transfer. It addresses the performance of heat sinks under consideration of mechanical deformation of the heat sink. The other contribution is related to battery thermal management. It describes a novel approach to establish an effective cooling system for battery cells in battery packs with forced air cooling.

Novel defocus hologram aberration compensation method in digital holography integrated pathology microscope for label free 3-D imaging

In this paper we report successful integration of digital holography in off- axis transmission configuration into a commercially available pathology microscope (PathologyDHM), where Mach-Zehnder interferometric configuration was achieved in pathology microscope using 1 × 2 single mode fiber coupler and custom built optical modules. A smartphone/webcam positioned at the image plane of the finite conjugate microscope captures the interference pattern generated by the system. Using PathologyDHM, we have demonstrated a novel and simple method for compensation of aberration due to microscope objective (MO). The proposed method is called defocus hologram method and it is particularly useful in cases, where samples do not have specimen free or background flat region. Proper validation of the method was done by imaging a transmissive grating (commercial compact disc, CD-R), which doesn't have a flat background region and comparing phase profile of CD-R computed by our proposed method with self-reference conjugated hologram method. For reiterating its biological applications, phase profile of a biological sample, red blood cell smear (RBC smear), was computed with our defocus hologram method and compared with already established reference conjugated hologram method. Phase profiles of CD-R and RBC smear computed with defocus hologram method agree with self-reference and reference conjugated hologram methods respectively, within the phase error limits of the system. Integration of digital holography in to commercial pathology microscope enables 3D imaging, which coupled with artificial intelligence may prove useful in disease diagnostics and monitoring response of cells to treatment.

Violet-Blue Emitters Featuring Aggregation-Enhanced Emission Characteristics for Nondoped OLEDs with CIEy Smaller than 0.046.

High emission efficiency and finite molecular conjugation in the aggregate state are two desirable features in violet-blue emitters. Aggregation-induced emission luminogens (AIEgens) have emerged as promising luminescent materials that offer these features. Herein, we report the design and synthesis of a group of violet-blue tetraphenylbenzene-based AIEgens with photoluminescence quantum yields over 98% in their film states. When utilizing these AIEgens as nondoped emitting layers, the fabricated organic light-emitting diode exhibits a maximum external quantum efficiency of 4.34% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.159, 0.035), which is amenable to the next-generation ultrahigh-definition television (UHDTV) display standard.

Novel hybrid robust method for uncertain reliability analysis using finite conjugate map

Due to the limitation of measured data, the random and epistemic uncertainties must be simultaneously handled for the reliability analysis of curvilinear aircraft stiffened panels with multiple cutouts. A hybrid iterative conjugate first-order reliability method (CFORM) and adaptive dynamical harmony search (ADHS) optimization are developed for fuzzy reliability analysis (FRA) of stiffened panels. The proposed global level performs fuzzy analysis using ADHS, while the local level is utilized for reliability evaluation using efficient FORM. In ADHS, two adjusting procedures are implemented to update the new positions of reliability index bounds with dynamical parameters Due to the computational burden of fuzzy reliability analysis with robust iterative formula, a conjugate FORM is applied using finite-step size, which is formulated by applying the Armijo rule. A limited conjugate scalar factor is utilized to determine the conjugate nonlinear describe map. The proposed conjugate formula is examined by various FORM formulas. The fuzzy reliability index is obtained using alpha level set-based ADHS in terms of extracted results by conjugate FORM for stiffened panels. Furthermore, by the sensitivity measure of the fuzzy reliability index, boundaries of uncertainty interval for stiffener heights and thicknesses of the panel were proposed. Moreover, the influences of different stiffener height, design load, stiffener thickness, and skin thickness on buckling mode were discussed. Survey results demonstrated that the proposed FRA is more accurate to handle epistemic uncertainties of curvilinear aircraft stiffened panels than the classic reliability method-based FORM. The conjugate reliability method provides robust and efficient results compared to the modified iterative reliability methods.

Thermal Management of Electronic Devices Using Gold and Carbon Nanofluids in a Lid-Driven Square Cavity Under the Effect of Variety of Magnetic Fields

Heat is an inevitable by-product of every electronic device and thermal management is very much essential for them to improve reliability and to prevent premature failure. Liquid coolants are one of the best switching options to achieve higher cooling rates. However, by adopting them in cooling systems such as microchannel heat sinks in which flow enters in to and out of the system may cause leakage of the coolant, which results in the complete firing of the electronic device. Hence, in the present study, this problem is avoided by adopting lid-driven square cavity as a cooling system. A 2-D numerical study has been carried out to obtain the convective heat transfer efficiency (CHTE) of gold and carbon nanofluid (NF) in a lid-driven square cavity over silicon solid block under the influence of a variety of magnetic fields. The geometrical domain consists of a square cavity containing NF that is driven by means of lid moving in one direction. This circulating NF will extract an enormous amount of heat from the solid block underneath the cavity resulting in conjugate heat transfer. A finite volume method-based conjugate homogeneous heat transfer model has been developed, validated, and used in the present study. The heat efficient Gold (Au) and single-walled carbon nanotube (SWCNT) NF pairs obtained by Nimmagadda and Venkatasubbaiah are used in the present study. Moreover, efficiently varied magnetic fields identified by Nimmagadda et al. are also implemented and compared with the uniform magnetic field. Furthermore, the magnetic field is applied over the geometrical domain along the two axial directions separately and the effective CHTE is obtained. The significant impact of broad parameters, such as magnetic field type, location and strength, nanoparticle concentration and type, and Reynolds number on the CHTE, is systematically analyzed and presented.

Thermal and Fluid Dynamic Performance Comparison of Three Nanofluids in Microchannels Using Analytical and Computational Models

The fluid dynamic and thermal performance of three nanofluids containing aluminum oxide, copper oxide, and silicon dioxide nanoparticles dispersed in 60:40 ethylene glycol and water base fluid as a coolant in a microchannel heatsink are compared here by two methods. The first is a simple analytical analysis, which is acceptable for very low nanoparticle volumetric concentration (1–2%). The second method is a rigorous three-dimensional finite volume conjugate heat transfer and fluid dynamic model based upon a constant heat flux boundary condition, which is applicable for cooling electronic chips. The fluids’ thermophysical properties employed in the modeling are based on empirically derived, temperature dependent correlations from the literature. The analytical and computational results for pressure drop and Nusselt number were in good agreement with the nanofluids showing a maximum difference of 4.1% and 2.9%, respectively. Computations cover the practical range of Reynolds number from 20 to 200 in the laminar regime. Based on equal Reynolds number, all of the nanofluids examined generate a higher convective heat transfer coefficient in the microchannel than the base fluid, while copper oxide provided the most significant increase by 21%. Based on the analyses performed for this study, nanofluids can enhance the cooling performance of the heatsink by requiring a lower pumping power to maintain the same maximum wall temperature. Aluminum oxide and copper oxide nanofluids of 2% concentration reduce the pumping power by 23% and 22%, respectively, while maintaining the same maximum wall temperature as the base fluid.

Extendable, large-field multi-modal optical imaging system for measuring tissue hemodynamics.

Simultaneous imaging of multiple hemodynamic parameters helps to evaluate the physiological and pathological status of biological tissue. To achieve multimodal hemodynamics imaging with a large field of view, an infinite conjugate relay lens system compatible with the standard C-Mount camera lens is designed to adapt one camera lens with multiple CCD/CMOS cameras for simultaneously multi-wavelength imaging. Using this relay lens system, dual wavelength reflectance imaging and laser speckle contrast imaging were combined to simultaneously detect the changes in blood flow, oxygenation, and hemoglobin concentrations. To improve the accuracy of hemoglobin concentration measurement with an LED illumination source, an integral algorithm is proposed that accounts for the dependence of differential pathlength factors (DPF) on hemoglobin concentrations and the integral effect of both the emission spectrum of the light source and the spectrum response of the detector. The imaging system is validated by both phantom and in vivo experiments, including the arterial occlusion, and the detection of blood volume pulse (BVP) and blood flow pulse (BFP) signal in human subjects. The system helps in the exploration of macroscopic tissue hemodynamics.

Modelling shear loading of a cantilever with a crack-like defect explicitly including linear parameters

This article considers the influence of shear on a specimen with a crack-like defect (CRLD) as part of the general variational statement of the problem with a distinguished interactive layer. The delta-element fracture criterion is formulated as a generalized energy product (GEP), accounting for the influence of hydrostatic stress and the existence of an external boundary. The GEP convergence with a reduction of the layer thickness in the layers element is shown both in the simplified analytical solution and in the numerical solution by the finite elements method (FEM). The linear size determining the GEP convergence in the layers element is taken for the characteristic size of the finite element conjugate to the physical excision and its continuation. It is shown that, unlike the simplified analytical solution, the solution by FEM allows finding the maximum GEP outside the layer.

Design method for an aspheric Schwarzschild objective with a low obscuration and an infinite conjugate distance

This paper proposes a design method for an aspheric Schwarzschild objective with a low obscuration and infinite conjugate distance. The method takes the obscuration ratio as a priority condition, establishes the relationship between magnification and image distance of the infinite reflector objective, and solves the expressions of aspheric curvature radius and aspheric coefficient. It overcomes the constraint of concentric sphere in the conventional design method and effectively reduces the obscuration ratio. For different structural parameters of the Schwarzschild objective, the model can be used to obtain an initial structure whose imaging quality is close to the diffraction limit.

Identification of an unknown shear force in a cantilever Euler–Bernoulli beam from measured boundary bending moment

Abstract An inverse problem of identifying an unknown shear force g ⁢ ( t ) {g(t)} on the inaccessible boundary x = l {x=l} in a system governed by the general form Euler–Bernoulli beam equation ρ ⁢ ( x ) ⁢ u t ⁢ t + μ ⁢ ( x ) ⁢ u t + ( r ⁢ ( x ) ⁢ u x ⁢ x ) x ⁢ x = 0 , ( x , t ) ∈ ( 0 , l ) × ( 0 , T ) \rho(x)u_{tt}+\mu(x)u_{t}+(r(x)u_{xx})_{xx}=0,\quad(x,t)\in(0,l)\times(0,T) subject to the boundary conditions u ⁢ ( 0 , t ) = u x ⁢ ( 0 , t ) = 0 , u x ⁢ x ⁢ ( l , t ) | x = l = 0 , - ( r ⁢ ( x ) ⁢ u x ⁢ x ⁢ ( x , t ) ) x | x = l = g ⁢ ( t ) , u(0,t)=u_{x}(0,t)=0,\quad u_{xx}(l,t)|_{x=l}=0,\quad-(r(x)u_{xx}(x,t))_{x}|_{x% =l}=g(t), is studied. The bending moment 𝙼 ⁢ ( t ) :- - r ⁢ ( 0 ) ⁢ u x ⁢ x ⁢ ( 0 , t ) {\mathtt{M}(t)\coloneq-r(0)u_{xx}(0,t)} given at the accessible boundary x = 0 {x=0} is assumed to be a measured output. The Neumann-to-Neumann operator Φ [ ⋅ ] : 𝒢 ⊂ H p ( 0 , l ) ↦ L 2 ( 0 , T ) , ( Φ g ) ( t ) :- - r ( 0 ) u x ⁢ x ( 0 , t g ) \Phi[\,{\cdot}\,]\colon\mathcal{G}\subset H^{p}(0,l)\mapsto L^{2}(0,T),\quad(% \Phi g)(t)\coloneq-r(0)u_{xx}(0,t_{g}) corresponding to this inverse problem is shown to be compact ( p = 3 {p=3} ) and Lipschitz continuous ( p = 2 {p=2} ). These properties allow us to prove the existence of a solution of the minimization problem for the Tikhonov functional J ⁢ ( g ) :- ∥ Φ ⁢ g - 𝙼 ∥ L 2 ⁢ ( 0 , T ) 2 {J(g)\coloneq\lVert\Phi g-\mathtt{M}\rVert^{2}_{L^{2}(0,T)}} . It is proved that this functional is Fréchet differentiable. Furthermore, an explicit formula for the Fréchet gradient of this functional is derived by making use of the unique solution to corresponding adjoint problem. A numerical method based on Hermitian finite elements and conjugate gradient algorithm is developed for the solution of the inverse boundary value problem. Numerical examples with random noisy measured outputs are presented to illustrate the validity and effectiveness of the proposed approach.

An adaptable two-lens high-resolution objective for single-site resolved imaging of atoms in optical lattices.

In this paper, we present a high-resolution, simple, and versatile imaging system for single-site resolved imaging of atoms in optical lattices. The system, which relies on an adaptable infinite conjugate two-lens design, has a numerical aperture of 0.52, which can in the ideal case be further extended to 0.57. It is optimized for imaging on the sodium D2-line but allows us to tune the objective's diffraction limited performance between 400 nm and 1000 nm by changing the distance between the two lenses. Furthermore, the objective is designed to be integrated into a typical atomic physics vacuum apparatus where the operating distance can be large (>20 mm) and diffraction limited performance still needs to be achieved when imaging through thick vacuum windows (6 mm to 10 mm). Imaging gold nanoparticles, using a wavelength of 589 nm which corresponds to the D2-line of sodium atoms, we measure diffraction limited performance and a resolution corresponding to an Airy radius of less than 0.7 µm, enabling potential single-site resolution in the commonly used 532 nm optical lattice spacing.

Design of two spherical mirror unobscured relay telescopes using nodal aberration theory.

Nodal aberration theory is used to calculate the third-order aberrations that result in image blur for an unobscured modified 4f relay (2f1 + 2f2) formed by two tilted spherical mirrors for objects at infinity (infinite conjugate) and near the front focal plane of the first mirror (finite conjugate). The field-averaged wavefront variance containing only non-rotationally symmetric aberration coefficients is then proposed as an optimization metric. Analytical and ray tracing optimization are demonstrated through sample designs. The particular cases of in-plane and orthogonal folding of the optical axis ray are discussed, followed by an analysis of a modified 2f1 + 2f2 relay in which the distance of the first mirror to the object or pupil is allowed to vary for aberration correction. The sensitivity of the infinite conjugate 2f1 + 2f2 relay to the input marginal ray angle is also examined. Finally, the optimization of multiple conjugate systems through a weighted combination of wavefront variances is proposed.