Effects Of Geometry Parameters Research Articles

Numerical study on flow-induced vibration of LBE-cooled wire-wrapped rod bundle

Flow-induced vibration (FIV) characteristics of LBE-cooled wire-wrapped rod bundle are crucial to the wire-to-cladding fretting. In the present study, numerical simulation on FIV of wire-wrapped rod bundle in LBE flow was performed using a fluid–structure interaction methodology based on the coupling between fluid and solid domains. The effects of geometry parameters on the FIV of wire-wrapped single rod and rod bundle were obtained. The results show that the circumferential force of coolant on the single fuel rod was uneven, which made the fuel rod undergo elliptical and off-axis periodic vibration. The variations of structure parameters of wire spacers had weak effects on the vibration of the single rod, while significant effects on the vibration trajectory of rod bundle. The vibration characteristics of border rods were more sensitive to the variations of transverse flow, while the center fuel rods were more sensitive to the difference in support constraint.

Acoustic transmission characteristics based on coiled-up space metamaterials

Coiled-up metamaterials with solid plate (SC) and with micro-perforated plate (MPC) are proposed for broadband low-frequency acoustic insulation and absorption. Firstly, the sound transmission theory of the double-layer plate and the impendence of the micro-perforated plate coupled with the coiled-up channel are introduced to obtain the dependence of structural parameters on the acoustic characteristics. Then, the acoustic performances of SC and MPC are investigated numerically and verified by experiments, and the effects of geometry parameters are analysed to predict the acoustic performance of SC and MPC. The minimum sound transmission loss (STL) of SC with a thickness of less than 2 cm is higher than 20 dB and the average STL reaches 45 dB at [0, 1600] Hz. The multi-order resonances of coiled-up space induce STL valleys but provide 10 dB improvement at valleys compared with double-layer plates. The MPC achieves narrow absorption at 422 Hz and 1232 Hz, which are induced by the resonances of coiled-up channels and 99.99 % of total energy dissipation is viscous dissipation mainly occurring in MPP. Coiled-up space with embedded porous materials (PTM) achieves above 0.9 absorption coefficient at [700, 1600] Hz. The optimized MPTMs, which consists of three parallel MPCs guided by the genetic algorithm (GA) and a single PTM unit, can reach a normal incident average absorption coefficient of 0.80 at [342–2000] Hz and a random incident absorption coefficient above 0.5 at [352–1862] Hz.

Design and Thermal Analysis of a 3-D Printed Impingement Pin Fin Cold Plate for Heterogeneous Integration Application

Miniaturization high heat flux of power electronic devices have posed a colossal challenge for adequate thermal management. Conventional air-cooling solutions are inadequate for high-performance electronics. Liquid cooling is an alternative solution due to the higher specific heat and latent heat associated with the coolants. Liquid-cooled cold plates are typically manufactured by different approaches, such as skived, forged, extrusion, and electrical discharge machining. When researchers are facing challenges in creating complex geometries in small spaces, 3-D-printing can be a solution. In this article, a 3-D-printed cold plate was designed and characterized with water coolant. The printed metal fin structures were strong enough to undergo pressure from the fluid flow even at high flow rates and small fin structures. A copper block with the top surface area of 1 in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,1$ </tex-math></inline-formula> in was used to mimic a computer chip. Experimental data have good match with a simulation model, which was built using commercial software 6SigmaET. Effects of geometry parameters and operating parameters were investigated. The fin diameter was varied from 0.3 to 0.5 mm and the fin height was maintained at 2 mm. A special manifold was designed to maximize the surface contact area between coolant and metal surface and therefore minimize thermal resistance. The flow rate was varied from 0.75 to 2 L/min and the coolant inlet temperature was varied from 25 °C to 48 °C. It was observed that for the coolant inlet temperature 25 °C and aluminum cold plate, the junction temperature was kept below 63.2 °C at an input power of 350 W and the pressure drop did not exceed 23 Kpa. Effects of metal materials used in 3-D-printing on the thermal performance of the cold plate were also studied in detail.

Analysis of heat transfer characteristics and entransy evaluation of high viscosity fluid in a novel twisted tube

• A novel twisted tube is to improve the secondary flow distribution inside the tube. • Heat transfer performance and entransy evaluation are investigated numerically. • The novel twisted tube reduces the entransy dissipation compared with the plain tube. • Effects of geometry parameters and Reynolds number are analyzed comprehensively. The non-uniformity of the secondary flow distribution in the twisted oval tube has impeded its further improvement of the heat transfer performance. A novel twisted tube (NTT) improves the distribution of the secondary flow and enlarges the effect of the secondary flow on the main flow, intensifying the radial mixing and equalizing the temperature distribution of the fluid, which strengthens the convective heat delivery in the near wall region and the core zone comprehensively. Heat transfer characteristics and entransy evaluation of water and engine oil in the NTT are investigated in the low Reynolds number ( Re ) region. The heat delivery performance of the NTT improves with the reduction of the distance ratio ( DR ) and the twist pitch ratio ( PR ), and also raises with the increase of Re . The friction factor of the NTT increases with the reduction of DR and PR , and decreases with the rise of Re . Compared with the twisted oval tube, the NTT could elevate the Nusselt number and enlarge the friction factor by 1.49–1.56 times and 1.32–1.41 times, respectively. Compared with the plain tube, the NTT could improve the Nusselt number and increase the friction factor by 2.42–2.76 times and 1.48–1.56 times, respectively. The equivalent thermal resistance of the NTT decreases with the reduction of DR and PR and reduces with the increase of Re . The Case 4 with the minimum DR and the smallest PR shows the supreme heat transfer performance and the lowest equivalent thermal resistance. The NTT could reduce the entransy dissipation remarkably, compared with the plain tube, the NTT could decrease the equivalent thermal resistance by up to 58% for water under the condition of constant wall temperature and could reduce the equivalent thermal resistance by as much as 53% for engine oil under the condition of given heat flux on the tube wall.

Experimental and numerical investigation of melting/solidification of nano-enhanced phase change materials in shell & tube thermal energy storage systems

In this work, the melting/solidification process of the nano-enhanced phase change materials (NePCM) was investigated experimentally and numerically using a horizontal shell & tube heat exchanger equipped with longitudinal fins. The NePCM was prepared by dispersing titanium dioxide nanoparticles (TiO2NPs) in stearic acid (SA). The effect of geometry parameters and nano particle content on melting/solidification rate of PCM were investigated. The results showed that using longitudinal fins could reduce the required time for melting and solidification by around 54% and 76%, compared to the system without fins, respectively. while the greatest effect of adding the TiO2-NPs was related to unfinned tube heat exchanger, which reduced the required time by 6% and 8% for melting and solidification, respectively. Furthermore, it was concluded that adding nanoparticles could offer its positive effect for enhancing the melting rate only while using unfinned tube heat exchanger.

Free vibration of functionally graded porous non-uniform thickness annular-nanoplates resting on elastic foundation using ES-MITC3 element

In this paper, the free vibration of the functionally graded porous (FGP) non-uniform annular-nanoplates lying on Winkler foundation (WF) is studied by using the smoothed finite element method based on the first-order shear deformation theory (FSDT). The combination of the mixed interpolation of the tensorial components for the three-node triangular element (MITC3 element) and the edge-based smoothed finite element method (ES-FEM) creates the ES-MITC3 element. This element is employed to avoid the shear locking problem as well as to improve the accuracy of the original MITC3 element. The small-scale effect is considered based on the nonlocal theory. Applying Hamilton's principle, the governing equation of the FGP non-uniform thickness annular-nanoplate is derived. Material properties of the nanoplate are characterized by two parameters: power-law index (k) and maximum porosity distributions (Ω) in the forms of cosine functions. The results of the present work are compared with other published work to verify accuracy and reliability. Moreover, the effects of geometry parameters and material properties on the free vibration of FGP non-uniform annular-nanoplates are comprehensively investigated.

Study on hydrodynamic performance of structured packings for gas-liquid flow: Effects of geometry parameters

Structured packings are widely used in oil & gas industries, as they can provide substantial surface area and high void fraction, thus enabling high mass transfer efficiency at a low pressure drop. This study investigates the hydrodynamic performance of two structured packings, namely, Mellapak 250Y and Montzpak B1−500. The pressure drop and liquid distribution are reported for a column of 200 mm diameter and 400 mm packing height. Wire-mesh sensor (WMS) is used to monitor the liquid distribution at the location of packing transitions. Packing replicas manufactured using a Fused Deposition Modelling (FDM) 3D printer is compared with commercial packings in terms of pressure drop and liquid distribution. A Computational Fluid Dynamics (CFD) model is initially validated using experimental data and then is used to investigate the effects of packing features, such as plate thickness, packing corrugation angles, holes, and packing transitions. The 3D-printed replicas show consistent performance compared to the commercial packings but can provide more information when measuring liquid distribution. The methodology and results discussed in this study can provide in-depth insights into the performance of structured packings, which is of critical importance when optimising packing parameters and testing new designs.

Finite Element Analysis of Heat Transfer Behaviors of Aluminum Honeycomb Sandwich Structures

Honeycomb sandwich structures show excellent heat-shielding performance. This paper studies heat transfer mechanisms of aluminum honeycomb sandwich structures by finite element analysis. The heat conduction/radiation coupling relationship is considered, where the transient first-order heat conduction governing equation is used to describe the relationship between the temperature change and the external heat source, and the heat radiation is formulated by the Stefan–Boltzmann governing equation that describes the relationship between the effective radiation and the temperature field. Thus, the coupling relationship is represented by the imposition of heat source due to radiation as the boundary condition on the heat conduction equation. The finite difference algorithm is used to solve the temperature distribution of structures. Effects of geometry parameters and boundary conditions on the temperature field of structures are explored. Numerical results by ABAQUS software demonstrate the advantage of honeycomb structures in area of heat shielding.

Geometrically nonlinear mechanical properties of auxetic double-V microstructures with negative Poisson's ratio

Double-V microstructure (DVM) is a type of auxetic cellular material with negative Poisson's ratio (NPR). Accurate predictions of the mechanical properties of these microstructures at large strains are critical for many engineering applications. In this paper, nonlinear theoretical models of two-dimensional (2D) and three-dimensional (3D) DVM based on a large beam deflection model are established to predict the normalized Young's modulus and Poisson's ratio in the principal directions. The theoretical solutions are compared to solutions obtained from numerical finite element analyses and quasi-static compression experiments of a 2D prototype manufactured using additive printing technique. It is found that there is good agreement between these results, validating the accuracy of the proposed theoretical model. Effects of geometry parameters on the mechanical properties of the DVM are also investigated to understand the mechanical behavior at large strains. This study provides validated models for predicting the behavior of these microstructures at large strains, useful for engineering designs.

Study of the flow distribution in parallel micro-channels with a triangular manifold

Flow distribution and pressure drop in parallel micro-channels are two effective parameters on the performance of different devices. These two parameters are affected by different factors, such as the manifold geometry, channels geometry, flow rate and fluid direction of inlet flow. In the present work, the structure of the inlet manifold (the triangular geometry, with straight and curved walls) has been studied as the main subject. However, the effect of the flow rate (as the Reynolds number) and fluid direction of inlet flow has been studied on the flow distribution and pressure drop with these manifold geometries. The results show that in the low-Reynolds number range, with increasing the Reynolds number, the flow distribution does not change, but the pressure drop increases. Also, the vertical direction of the inlet flow in comparison with the horizontal direction is preferable. Flow distribution with triangular manifolds with curved walls is more uniform than with straight walls, while, in straight walls, equilateral triangle is a better choice. At the end of this consideration, the effect of geometry parameters (such as the channel number, channel width and depth of curvature) on the non-uniformity parameter was studied with concave manifolds.

The effect of geometry parameters on light harvesting performance of GaN nanostructure arrays—a numerical investigation and simulation

In this paper, COMSOL Multiphysics Commercial Package software is used to simulate the models of two kinds of GaN nanostructure arrays, and to study how the geometric structure and periodicity of arrays affect the optical properties of GaN nanostructures. By analyzing the schematic diagram of electric field distribution and absorption curves of GaN nanostructure arrays, we concluded that the absorptivity is a decreasing function of periodicity in non-homogenous shaped nanostructures. In addition, a gentle change in geometric structure or having a lower effective refraction index on the incident side of the light are more conducive to enhancing the light absorption ability of GaN nanostructure arrays. Simulation experiments on GaN nanostructures will provide some references for the structural design of photocathodes, which will help UV detectors to achieve efficient light absorption.

Thermal analysis on a nanofluid-filled rectangular cavity with heated fins of different geometries under magnetic field effects

Rectangular cavity filled with a non-Newtonian shear-thinning nanofluid was investigated considering varied fin geometry under a vertical magnetic field. Irreversibility and entropy generation mechanisms were investigated by finite element method. The effect of geometry parameter (a), Hartmann number (Ha), nanoparticles volume fraction (φ) and nanoparticles type (Fe3O4, CuO and Al2O3) on the Nusselt numbers, entropy generations and Bejan numbers were investigated by the response surface methodology (RSM). Increasing a leads to an increase in both local and average Nusselt numbers and increment in different terms of entropy generation, while it reduces the Bejan number. Fe3O4 nanoparticle shows the highest Nusselt number compared to other nanoparticles. RSM analysis revealed that a = 0.29 and φ = 0.04 are the optimized values for the goal of maximum Nusselt number and minimum Bejan number.

Effect of geometry parameters on the hydrocarbon fuel flow rate distribution in pyrolysis zone of SCRamjet cooling channels

Hypersonic air-breathing propulsion (>Mach 5) based on SCRamjet promotes the revolutions of both military and civilian applications. However, the engine thermal protection is seriously challenged due to high Mach number. One of the key problems is mal-distribution of hydrocarbon fuel in regenerative cooling channels under the complex thermal boundaries and channel geometry, which may cause structural failure. To improve the cooling channel design and achieve better fuel flow distribution, the effect of channel geometry parameters on flow distribution in pyrolysis zone is numerically studied. Both geometry induced and heat flux induced flow mal-distribution are concerned. The study indicates that the flow and heat transfer features in pyrolysis zone of parallel channels differs with those in non-pyrolysis zone. The flow distribution deviations in pyrolysis zone are lower. When the channel aspect ratio varies, thermal stratification dominates flow distribution more than the variation of heat flux on heated surface in pyrolysis zone, which is opposite of that in non-pyrolysis zone. Besides, thinner rib and smaller total flow area achieve better cooling performance while consuming less fuel chemical heat sink. The results help to conclude possible references to the design of cooling channels with fuel pyrolysis considered.

The Effect of Geometry Parameters and Flow Characteristics on Erosion and Sedimentation in Channel’s Junction using Finite Volume Method

One of the most critical problems in the river engineering field is scouring, sedimentation and morphology of a river bed. In this paper, a finite volume method FORTRAN code is provided and used. The code is able to model the sedimentation. The flow and sediment were modeled at the interception of the two channels. It is applied an experimental model to evaluate the results. Regarding the numerical model, the effects of geometry parameters such as proportion of secondary channel to main channel width and intersection angle and also hydraulic conditionals like secondary to main channel discharge ratio and inlet flow Froude number were studied on bed topographical and flow pattern. The numerical results show that the maximum height of bed increased to 32 percent as the discharge ratio reaches to 51 percent, on average. It is observed that the maximum height of sedimentation decreases by declining in main channel to secondary channel Froude number ratio. On the assessment of the channel width, velocity and final bed height variations have changed by given trend, in all the ratios. Also, increasing in the intersection angle accompanied by decreasing in flow velocity variations along the channel. The pattern of velocity and topographical bed variations are also constant in any studied angles.

Crashworthiness optimisation of a step-like bi-tubular energy absorber for subway vehicles

This paper presents the crashworthiness optimisation of a step-like energy absorber which is composed of nested thin-walled rectangular tubes. The impact experiment and numerical simulation were carried out. The results had a good agreement and indicated that the collapse process is clearly divided into two phases. To investigate the effects of geometry parameters of the structure on essential crashworthiness characteristics, two groups of samples with different wall thickness and inner tube dimensions were simulated, respectively. The change in the outer tube and inner tube wall thickness has obvious influence on energy distribution and crashworthiness characteristics. The thickness of the diaphragms has little influence on these responses. The increase of inner tube dimensions leads to the interactive obstruction of outer tube and inner tube. The decrease of inner tube dimensions leads to the self-obstruction of inner tube. The above two results lead to the increase of EA1 and MCF2 values. Then, the design of experiments (DOE) based on simulations were established. Finally, based on the developed surrogate models, optimisation design for the absorber to maximize the specific energy absorption (SEA) under the constraint of two important indicators was carried out. It was clearly found that the optimal solution increased the value of SEA from 8.93 to 9.36 kJ/kg while satisfying the two constraints.

Dynamic Modeling of the Multiring Disk Resonator Gyroscope.

The multiring disk resonator gyroscope (DRG) has been a candidate for high performance gyroscopes, however nowadays the finite element method (FEM) is the main method for its analysis due to its complex structure. In this paper we propose a new method to mathematically model the DRG for its vibrating modes and lumped parameters based on the component mode synthesis (CMS) method. Firstly, the natural frequencies and the associated mode shapes of the DRG are mathematically modeled and a comparison with the FEM results is conducted. It shows that the mode shapes of DRG obtained by FEM and mathematical modeling are identical and in the full ranges of geometrical parameters, natural frequency error of the simulation, and calculation results are limited in ±15%. It demonstrates the effectivity and feasibility of the mathematical modeling method. Then, based on the calculated natural frequencies and mode shapes, the lumped mass-spring model of the DRG and effects of geometry parameters on the lumped mass-spring parameters are investigated, which can be used on the design of the DRG. This mathematical modeling method can effectively improve the analyzing efficiency of the DRG and the method can also be used on the analysis of other complex multiring-type resonators.

The effect of geometry parameters on the heat transfer performance of supercritical CO2 in horizontal helically coiled tube under the cooling condition

Experimentally and numerically studied the heat transfer performance of supercritical CO2 (S-CO2) cooled in small (d ≤ 4 mm) horizontal helically coiled tube (HCT). Five HCTs with fixed coil pitch b = 34 mm, coil diameters D ranging from 36–140 mm and tube diameters d ranging from 2 to 4 mm were used. The results showed that the heat transfer coefficient (HTC) has tripled as the tube diameter decreases from 4 to 2 mm. HTC increases up to 30% with the coil diameter decreasing from 140 to 36 mm. Based on the modified theory derived from the straight tube (ST) with upward flow, the onset value of buoyancy effect in horizontal HCT was obtained, which confirmed that the buoyancy in the present experimental study can be neglected. Totally, 33 test runs and 426 points were performed, and from which a new correlation was proposed to evaluate the HTC of S-CO2 in the horizontal HCT under cooling condition.

Free Vibration of Rectangular Plates with Porosity Distributions under Complex Boundary Constraints

Free vibration of rectangular plates with three kinds of porosity distributions and different boundary constraints has been performed by means of a semianalytical method. The distribution of porous varies along the thickness of the plate, in which the mechanical properties are defined by open‐cell metal foam. Regardless of boundary conditions, displacement admissible functions are represented by combination of standard cosine Fourier series and auxiliary sine series. The kinetic energy and potential energy of plates are also expressed on the basis of first‐order shear deformation theory (FSDT) and displacement admissible functions. Finally, the coefficients in the Fourier series which determine natural frequencies and modal shape are derived by means of the Rayleigh–Ritz method. Convergence and dependability of the current method are verified by comparing with the results of FEM and related literatures. In addition, some new results considering geometry parameters under classical and elastic boundary constraints are listed. The effects of geometry parameters, material parameters, and boundary constraints have been discussed in detail.

Nonlinear Forced Vibration of Curved Microbeam Resting on Nonlinear Foundation Using the Modified Strain Gradient Theory

The nonlinear forced vibrations of a curved micro-beam resting on a nonlinear foundation are examined. The equations of motion are derived using Hamilton’s principle and the modified strain gradient theory which is capable to examine the size effects in microstructures. The nonlinear partial differential equations of motion are reduced to a time-dependent ordinary differential equation containing quadratic and cubic nonlinear terms. The frequency response of the curved microbeam at the primary resonance is determined using the multiple time scales perturbation method. From the application point of view, the frequency response curves may be useful to select the optimum values of design parameters. The effects of geometry parameters and foundation moduli on the vibration behavior of the curved microbeam are illustrated.

Reduction of steady flow torques in a single-stage rotary servo valve

In this paper, geometry optimization of spool is proposed to reduce the steady flow torques in a single-stage rotary servo valve. The steady flow torques under different spool structures are studied by computational fluid dynamics simulation and experimental test and the most effective spool structure is found out. Then, the effects of geometry parameters on the steady flow torques are studied and an optimized solution for reduction of the steady flow torques is suggested by considering the optimization qualities and production costs. The results show that modification of the geometry of spool can make the jet angle at the orifices much closer to 90°, with almost no effect on the flow rate. Processing annular groove in the spool land with increased number of grooves on one side of the spool land is an effective way to reduce the steady flow torques. The maximum value of steady flow torques reduces with a gradual decrease in reduction as the external diameter of annular groove and the number of grooves increase. With the optimized spool structure, the maximum value of steady flow torques can be reduced significantly.