Geometric Porosity Research Articles

High-Fidelity Simulations of Flight Dynamics and Trajectory of a Parachute–Payload System Leaving the C-17 Aircraft

This article examines the flight dynamics and trajectory analysis of a parachute–payload system deployed from a C-17 aircraft. The aircraft is modeled with an open cargo door, extended flaps, and four turbo-fan engines operating at an altitude of 2000 feet Above Ground Level (AGL) and an airspeed of 150 knots. The payloads consist of simplified CONEX containers measuring either 192 inches or 240 inches in length, 9 feet in width, and 5.3 feet in height, with their mass and moments of inertia specified. At positive deck angles, gravitational forces cause these payloads to begin a gradual descent from the rear of the aircraft. For aircraft at zero deck angle, a ring-slot parachute with approximately 20% geometric porosity is utilized to extract the payload from the aircraft. This study specifically employs the CREATE-AV Kestrel simulation software to model the chute-payload system. The extraction and suspension lines are represented using Kestrel’s Catenary capability, with the extraction line connected to the floating confluence points of the CONEX container and the chute. The chute and payload will experience coupled motion, allowing for an in-depth analysis of the flight dynamics and trajectory of both elements. The trajectory data obtained will be compared to that of a payload (without chute and cables) exiting the aircraft at positive deck angles. An adaptive mesh refinement technique is applied to accurately capture the engine exhaust flow and the wake generated by the C-17, chute, and payloads. Friction and ejector forces are estimated to align the exit velocity and timing with those recorded during flight testing. The results indicate that the simulation of extracted payloads aligns with expected trends observed in flight tests. Notably, higher deck angles result in longer distances from the ramp, leading to increased exit velocities and reduced payload rotation rates. All payloads exhibit clockwise rotation upon leaving the ramp. The parachute extraction method yields significantly higher exit velocities and shorter exit times, while the payload-chute acceleration correlates with the predicted drag of the chute as demonstrated in prior studies.

Effect of Different Geometric Porosities on Aerodynamic Characteristics of Supersonic Parachutes

The supersonic parachute plays an important role in the descent and landing of Mars missions. Next-generation supersonic parachutes, such as disksail parachutes, are alternatives to disk-gap-band (DGB) parachutes. Disksail parachutes have larger porous gaps and smaller porous seams on the canopy surface than DGB parachutes. To date, the influence mechanism of porous seams or gaps and their locations on the performance of supersonic parachute systems in Martian atmospheric conditions remains unclear. In this study, different canopy models with seams and gaps based on NASA’s supersonic disksail parachutes were designed, and the aerodynamic characteristics of such geometric porosity models were studied numerically. For seam-only models, the drag coefficient of the parachute decreases when the position of the seam is close to the middle of the canopy. When the seam is close to the mouth of the canopy, the pressure difference between the inner and outer surface of the canopy becomes small, reducing the risk of tearing the canopy. For gap-only models, the drag coefficient of the middle gap model is higher, while the lateral force stability of the top gap model is better. The results show that the addition of a seam can improve the drag performance of the top gap model and improve the lateral stability of the canopy with the middle gap. This study provides some theoretical references for designing the porosity of parachutes under different requirements for Mars exploration missions in the future.

Ampero-Coulometry: A New Technique for Understanding Lithium-Sulfur Electrochemistry

Despite limited commercial success, lithium sulfur technology (LST) is still far from replacing existing Li-ion technology. One of the main reasons hindering the success of LST is the limited understanding of lithium-sulfur chemistry during electrochemical charging and discharging. Dissolution of sulfur species in electrolyte solution further enhances the complexity of this system. Therefore, a comprehensive understanding of sulfur species and their kinetics during charge/discharge process is paramount for a high-performance lithium-sulfur battery. In this work, we used a chronoamperometric method to rapidly measure the rate capability of sulfur electrodes. The method allows us to interrogate rate performance of sulfur electrode from 0.1C up to 1000C in 26 mins of chronoamperometric measurement. Electrodes prepared with Super-P, carbon fiber and graphene platelets were compared to understand the relationship between electrode kinetics and geometrical porosity. Moreover, the electrical conductivity of sulfur electrodes with different thickness and material composition were compared to understand their dependence on C-rates. Finally, we developed a new technique 'Ampero-Coulometry' which utilizes the experimental results obtained from chronoamperometry and mathematically transform to reveal rate capability of carbon-sulfur electrodes at different state of charge/capacity (Figure 1a, b). This technique allowed us to track the overall rate of reactions inside Li-S cell over a complete state of discharge. For the first time, we were able to correlate Li+ diffusion coefficient with the chronopotentiometric discharge profile of a Li-S battery. As dissolution of sulfur species and their interplay inside a porous sulfur electrode has a significant role in limiting Li-S battery capacity, and we can now relate the known mechanism of polysulfide dissolution with the kinetics of a sulfur electrode and its performance.Figure 1: (a) Comparison of discharge curve and Ampero-Coulometry curve of lithium-sulfur battery (b) Comparison of discharge curve and differential rate curve of lithium-sulfur battery. Figure 1

Additive manufacturing of biodegradable Zn-xMg alloys: Effect of Mg content on manufacturability, microstructure and mechanical properties

Additive Manufacturing (AM) exhibits tremendous advantages in producing customized medical implants and has achieved successful clinical applications for non-degradable metals such as titanium, stainless steel and cobalt alloys, particularly in the form of porous scaffolds for bone implants. Biodegradable materials allow the metal to degrade while natural tissue grows thereby reducing implant lifetime within the body to a minimum. The design freedom of AM and especially Laser Powder Bed Fusion (LPBF) overcomes technical difficulties of conventional technologies to manufacture complex structures. Within this work test geometries and porous scaffolds were manufactured via LPBF with pre-alloyed Zinc-Magnesium (Zn-xMg) powder, where x = 0, 1, 2 and 5 wt% to investigate the effect of Mg on manufacturability, microstructure and mechanical properties. Relative material densities of cubic specimens above 99.5% were achieved with all pre-alloyed powders. The addition of Mg reduces the processing window compared to pure Zn. A decreased grain size and an increase in intermetallic precipitates is observed with the addition of Mg. Zn-1Mg samples exhibited 3.2x the maximum ultimate tensile strength (UTS) of pure Zn (i.e., 119 MPa). However, the tensile elongation is only a fifth compared to pure Zn. With increasing Mg content, the amount of Zn+Mg2Zn11 rises and MgZn2 forms. These brittle phases characteristically increase hardness but reduce ductility. Under the chosen processing conditions, all Zn-xMg scaffolds demonstrated good processability. The geometric porosity was designed to be 80.5% with the achieved value of 70.8 % for compression testing. Zn-1Mg scaffold showed the highest compressive strength and Young’s modulus (19.1 MPa and 0.65 GPa respectively). This paper summarizes the technical challenges of manufacturing Zn-xMg alloys via LPBF for tissue engineering applications.

Scalable wear resistant 3D printed slippery liquid infused porous surfaces (SLIPS)

Surface wettability is a measure of adhesion and repulsion of liquids on a material’s surface, where surface wettability may be altered by creating a new interfacial surface between the base material and the target liquid on top. Where the interface comprises of a liquid that is locked in the pores or ridges of the base material, it is then termed as liquid infused surface (LIS). LIS alters the wettability due to the distinctive properties of the interfacial liquid which now forms the new surface. If the interfacial liquid is repellent towards polar (hydrophobic) and non-polar (oleophobic) liquids, the overall surface becomes slippery (amphiphobic) and prevents any new target liquids from adhering. This phenomenon leads to the definition of slippery liquid infused porous surfaces (SLIPS), where this term not only describes its role but also its fabrication route. Here a two-step facile method is presented to quickly transform any 3D printable polymeric material into robust SLIPS, irrespective of the wettability properties of the original polymer. The complex geometrical porosity required for locking the interfacial liquid is achieved using Fused Deposition Modelling (FDM) setup. Surface wettability characteristics of the 3D printed porous structure are then enhanced by increasing the liquid-adsorption sites where the locking of the infused interfacial (repellent) liquid takes place. The SLIPS demonstrate low rolling-off (sliding) angles with both polar and non-polar solvents of up to 2 degrees with high resistance to mechanical abrasion undergoing sliding frictional wear. The robust SLIPS as produced can be quickly scaled up using existing processes used in the laboratory.

MEMPELAJARI KARAKTERISTIK FISIK BIJI KAKAO (Theobrema cacao L.) PADA SUHU PENGERINGAN YANG BERBEDA

Drying is a common process step for agricultural grain products for ease of handling and to achieve the desired quality levels. One of the commodities that have high economic value produced by farmers in Lampung Province is cocoa beans. The drying process may change the physical properties of the cocoa beans and affect the processing of cocoa beans at a later stage. This study aims to determine the effect of drying temperature on changes in the physical properties of cocoa beans such as dimension, volume, weight, surface area, true density, bulk density, porosity, sphericity, and angle of repose. This research was applied to fresh non-fermented cocoa beans in testing. The cocoa beans were dried at temperatures of 40, 50 or 60oC. The research data were then statistically tested using paired sample T-Test at the 95% level to determine whether there is any effect of drying temperature on changes in its physical properties. The results showed a significant effect of drying temperature on weight, volume, geometric mean diameter (Dg), surface area, bulk density, porosity, and angle of repose of cocoa beans. Meanwhile, the sphericity and true density parameters did not significantly change. Keywords: cocoa beans, drying, physical properties

Analysis and outlook of mass transport in ultralow Pt loading proton exchange membrane fuel cells

<p indent=0mm>Proton exchange membrane fuel cells (PEMFCs) for automotive propulsions have been regarded as an ideal and the most promising alternative to replace fossil-fuel based internal combustion engines due to the high performance, high energy efficiency and zero-emission. However, the high cost has severely impeded the commercialization of PEMFCs, especially the high cost of Pt-based precious metal catalyst used for the cathode oxygen reduction reaction (ORR). It is critical to reducing the amount of Pt and thus decreasing the cost of fuel cell stacks, which would lead to numbers of new challenges. On the one hand, the reduction of Pt load could increase the oxygen transport resistance in cathode catalyst layers (CCLs). In fact, the oxygen transport resistance could be divided into several constituent parts, i.e., oxygen transport resistances in CCLs, gas diffusion layers (GDLs) and the flow channels, where the transport resistance in CCLs is much higher than other resistances. Further, CCLs are constructed as heterogeneous composites of ORR electrocatalysts, conductive polymer such as perfluorinated sulfonic acid (PFSA) ionomer as well as the pore space determined. Hence, the oxygen transport resistance in CCLs includes the bulk transport resistance caused by oxygen diffusion in the nanopore and the local transport resistance caused by oxygen permeation through the ultrathin ionomer film covering on the Pt surface. Local oxygen transport behavior could be divided into three processes: (1) Oxygen adsorption from gas phase into ionomer, (2) oxygen diffusion inside the ionomer, and (3) oxygen adsorption from the ionomer to Pt surfaces. As the Pt loading decreases, local oxygen transport resistance would increase significantly, thus leading to a dramatical performance degradation at high current density of fuel cells. In specific, the oxygen adsorption at gas/ionomer interface used to be considered as Henry’s adsorption. However, it is proved recently that this type of adsorption should be quasi-logarithmic, due to the finiteness of the adsorption site on ionomer surface. In addition, the bulk oxygen transport resistance depends on the porosity and pore size distribution inside the electrodes. We summarized plenty of experimental results of effective oxygen diffusivities reported by different research groups, and found that all the experimental values are obviously smaller than the calculated results based on the classical Bruggeman approximation. It is believed that the effective porosity plays a more important role relative to the geometrical porosity in the estimation of bulk oxygen transport resistance in PEMFCs. On the other hand, confining effect of the ultrathin ionomer film could weaken the separation of hydrophilic and hydrophobic phases and then cut down the pathway of proton migration. There are two proton conduction mechanisms in CCLs: Grotthuss hopping and vehicular mechanism. The proton conduction in CCLs could be affected by numerous factors, such as temperature, ionomer structure, thickness of ionomer film, as well as cation contaminants in the ionomer film. Both high oxygen transport resistance and low proton conduction in ultra-low Pt membrane electrode assemblies would damage the performance and the lifetime of PEMFCs. In this review, the bulk and local transport behavior, proton transport in CCLs, as well as the corresponding influence on fuel cell performance are systematically analyzed, and a series of coping strategies are presented.

Application of bromocresol purple dye for plaster drying time determination

This paper verified the efficiency in using the acid-base indicator of bromocresol purple (BCP) dye to determine the moment when gypsum plaster reaches the dry state. For this purpose, the materials used were characterized by X-ray diffraction and by scanning electron microscopy (SEM). We determined the following parameters: workability time, geometric porosity, compressive strength, hardness, and tensile adhesion strength. Two dosages of the indicator, 1.6% and 3.2%, were tested and compared with the reference, and we observed that the addition of the indicator did not change the workability time of the paste. In addition, the values of compressive strength, hardness, and tensile adhesion strength, at the 1.6% dosage, were 6.41 ± 0.59 MPa, 14.19 ± 1.08 N·mm2 and 0.48 ± 0.24 MPa, respectively. At the 3.2% dosage, the values obtained for those properties were 5.55 ± 0.67 MPa, 13.81 ± 0.88 N·mm2 and 0.46 ± 0.23 MPa. Moreover, we verified that the BCP indicator can be used to determine the drying of the gypsum plaster coating, either through the analysis of the color change in the sample surface or by using reflectance spectroscopy.

The influence of obliquely perforated dual-baffles on sway induced tank sloshing dynamics

This paper examines the influence of oblique perforated baffles on the sloshing dynamics of rectangular liquid storage tanks. The analysis presented accounts for sway induced hydrodynamic forces and entropy generation. Internal liquid free surface oscillation is modelled by the volume of fluid method. The effect of baffle geometric parameters, orientation and porosity on loads is examined and numerical results are compared against a set of experiments. Consequently, an engineering method suggesting the optimum size, angle of inclination and topology of baffles for the case of a rectangular tank is presented. It is shown that implementation of optimized oblique porous dual baffles may reduce sloshing loads by up to 15%.

Diffusion of hard sphere fluids in disordered porous media: Enskog theory description

We use the Enskog theory for the description of the self-diffusion coefficient of hard sphere fluids in disordered porous media. Using the scaled particle theory previously developed by us for the description of thermodynamic properties of hard sphere fluids, simple analytical expressions for the contact values of the fluid-fluid and fluid-matrix pair distribution functions are obtained and used as the input of Enskog theory. The expressions obtained for the contact values are described only by the geometric porosity and do not include the dependence on other types of porosity that are important for the description of thermodynamic properties. It is shown that the application of such contact values neglects the effects of trapping of fluid particles by a matrix and at least the probe particle porosity $\phi$ should be included in the Enskog theory for a correct description of the matrix influence. In this paper we extend the Enskog theory by changing the contact values of the fluid-matrix and the fluid-fluid pair distribution functions with new properties which include the dependence not only on geometric porosity but also on probe particle porosity $\phi$. It is shown that such semi-empirical improvement of the Enskog theory corresponds to SPT2b1 approximation for the description of thermodynamic properties and it predicts correct trends for the influence of porous media on the diffusion coefficient of a hard sphere fluid in disordered porous media. Good agreement with computer simulations is illustrated. The effects of fluid density, fluid to matrix sphere size ratio, matrix porosity and matrix morphology on the self-diffusion coefficient of hard sphere fluids are discussed.

Investigation of Gas Transport Properties of PEMFC Catalyst Layers by Using a Microfluidic Device

Gas transport properties of catalyst layers (CLs) used in proton exchange membrane fuel cells (PEMFCs) are one of the important factors which affects cell performance. The gas transport properties are strongly affected by the porous structure of the CLs. In this study, a measurement system of gas diffusion flux through the CLs by using a microfluidic device was developed. Parallel channels were made on a Si chip by microfabrication techniques. Air and nitrogen were supplied to the two parallel channels in the device, respectively. Oxygen was transferred to a nitrogen flow channel through the CL under a rib between the two channels. Oxygen partial pressure in the nitrogen flow channel was measured at the outlet of the channel by using an optical oxygen sensor. The porous structure of the measured CLs was characterized. Effective gas diffusivity and tortuosity factor of the CLs can be calculated based on the measured gas transfer and porous structure properties. Several types of CLs were fabricated and characterized. The thickness and overall porosity of the CLs were evaluated from scanning electron microscopy and weight measurement. Pore size distribution and effective porosity were evaluated by using nitrogen physisorption measurement. Then effective diffusivity of CLs can be calculated by measuring oxygen partial pressure at the inlet and outlet of the flow channel. The CL, which has 1.0 of ionomer to carbon ratio, was evaluated. Oxygen partial pressure at the outlet of the nitrogen flow channel decreases with flow rate as shown in Figure 1. Effective gas diffusivities obtained from each flow rate showed almost constant value. Tortuosity factor was calculated from the effective diffusivity and measured structural properties and indicated around 3. This evaluation method was applied to the CLs containing a different type of carbon materials, which show different porous structure. Adding multi-walled carbon nanotube in the CL(1) instead of carbon black resulted in an increase of effective gas diffusivity, while geometrical porosity was decreased. Acknowledgments A part of this work was financially supported by JSPS KAKENHI Grant Number 16K18028. This study was supported by Osaka University Nanofabrication Platform [F-18-OS-0006] in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. References T. Suzuki, R. Hashizume and M. Hayase, J. Power Sources, 286, 109 (2015). Figure 1

Compressible-flow geometric-porosity modeling and spacecraft parachute computation with isogeometric discretization

One of the challenges in computational fluid–structure interaction (FSI) analysis of spacecraft parachutes is the “geometric porosity,” a design feature created by the hundreds of gaps and slits that the flow goes through. Because FSI analysis with resolved geometric porosity would be exceedingly time-consuming, accurate geometric-porosity modeling becomes essential. The geometric-porosity model introduced earlier in conjunction with the space–time FSI method enabled successful computational analysis and design studies of the Orion spacecraft parachutes in the incompressible-flow regime. Recently, porosity models and ST computational methods were introduced, in the context of finite element discretization, for compressible-flow aerodynamics of parachutes with geometric porosity. The key new component of the ST computational framework was the compressible-flow ST slip interface method, introduced in conjunction with the compressible-flow ST SUPG method. Here, we integrate these porosity models and ST computational methods with isogeometric discretization. We use quadratic NURBS basis functions in the computations reported. This gives us a parachute shape that is smoother than what we get from a typical finite element discretization. In the flow analysis, the combination of the ST framework, NURBS basis functions, and the SUPG stabilization assures superior computational accuracy. The computations we present for a drogue parachute show the effectiveness of the porosity models, ST computational methods, and the integration with isogeometric discretization.

Measurement of Gas Transport Properties in PEFC Catalyst Layers Consisted of Different Carbon Materials by Using a Microfluidic Device

Gas transport properties in polymer electrolyte fuel cell catalyst layers consisted of different carbon materials were evaluated by using a microfluidic device. The microfluidic device consists of catalyst coated membrane and Si chip having parallel microchannels. Air and nitrogen were supplied to the two parallel channels in the device, respectively. Gas transport properties were evaluated by measuring outlet partial pressure of oxygen which was diffused through the catalyst layer. Adding multi-walled carbon nanotube in the catalyst layer instead of carbon black resulted in an increase of effective gas diffusivity, while geometrical porosity was decreased.

Porosity models and computational methods for compressible-flow aerodynamics of parachutes with geometric porosity

Spacecraft-parachute designs quite often include “geometric porosity” created by the hundreds of gaps and slits that the flow goes through. Computational fluid–structure interaction (FSI) analysis of these parachutes with resolved geometric porosity would be exceedingly challenging, and therefore accurate modeling of the geometric porosity is essential for reliable FSI analysis. The space–time FSI (STFSI) method with the homogenized modeling of geometric porosity has proven to be reliable in computational analysis and design studies of Orion spacecraft parachutes in the incompressible-flow regime. Here we introduce porosity models and ST computational methods for compressible-flow aerodynamics of parachutes with geometric porosity. The main components of the ST computational framework we use are the compressible-flow ST SUPG method, which was introduced earlier, and the compressible-flow ST Slip Interface method, which we introduce here. The computations we present for a drogue parachute show the effectiveness of the porosity models and ST computational methods.

X-ray computed tomography of packed bed chromatography columns for three dimensional imaging and analysis

Physical characteristics critical to chromatography including geometric porosity and tortuosity within the packed column were analysed based upon three dimensional reconstructions of bed structure in-situ. Image acquisition was performed using two X-ray computed tomography systems, with optimisation of column imaging performed for each sample in order to produce three dimensional representations of packed beds at 3μm resolution.Two bead materials, cellulose and ceramic, were studied using the same optimisation strategy but resulted in differing parameters required for X-ray computed tomography image generation. After image reconstruction and processing into a digital three dimensional format, physical characteristics of each packed bed were analysed, including geometric porosity, tortuosity, surface area to volume ratio as well as inter-bead void diameters. Average porosities of 34.0% and 36.1% were found for ceramic and cellulose samples and average tortuosity readings at 1.40 and 1.79 respectively, with greater porosity and reduced tortuosity overall values at the centre compared to the column edges found in each case. X-ray computed tomography is demonstrated to be a viable method for three dimensional imaging of packed bed chromatography systems, enabling geometry based analysis of column axial and radial heterogeneity that is not feasible using traditional techniques for packing quality which provide an ensemble measure.

Statistical scaling of geometric characteristics in stochastically generated pore microstructures

We analyze the statistical scaling of structural attributes of virtual porous microstructures that are stochastically generated by thresholding Gaussian random fields. Characterization of the extent at which randomly generated pore spaces can be considered as representative of a particular rock sample depends on the metrics employed to compare the virtual sample against its physical counterpart. Typically, comparisons against features and/patterns of geometric observables, e.g., porosity and specific surface area, flow-related macroscopic parameters, e.g., permeability, or autocorrelation functions are used to assess the representativeness of a virtual sample, and thereby the quality of the generation method. Here, we rely on manifestations of statistical scaling of geometric observables which were recently observed in real millimeter scale rock samples [13] as additional relevant metrics by which to characterize a virtual sample. We explore the statistical scaling of two geometric observables, namely porosity (ϕ) and specific surface area (SSA), of porous microstructures generated using the method of Smolarkiewicz and Winter [42] and Hyman and Winter [22]. Our results suggest that the method can produce virtual pore space samples displaying the symptoms of statistical scaling observed in real rock samples. Order q sample structure functions (statistical moments of absolute increments) of ϕ and SSA scale as a power of the separation distance (lag) over a range of lags, and extended self-similarity (linear relationship between log structure functions of successive orders) appears to be an intrinsic property of the generated media. The width of the range of lags where power-law scaling is observed and the Hurst coefficient associated with the variables we consider can be controlled by the generation parameters of the method.

FSI modeling of the reefed stages and disreefing of the Orion spacecraft parachutes

Orion spacecraft main and drogue parachutes are used in multiple stages, starting with a "reefed" stage where a cable along the parachute skirt constrains the diameter to be less than the diameter in the subsequent stage. After a period of time during the descent, the cable is cut and the parachute "disreefs" (i.e. expands) to the next stage. Fluid---structure interaction (FSI) modeling of the reefed stages and disreefing involve computational challenges beyond those in FSI modeling of fully-open spacecraft parachutes. These additional challenges are created by the increased geometric complexities and by the rapid changes in the parachute geometry during disreefing. The computational challenges are further increased because of the added geometric porosity of the latest design of the Orion spacecraft main parachutes. The "windows" created by the removal of panels compound the geometric and flow complexity. That is because the Homogenized Modeling of Geometric Porosity, introduced to deal with the flow through the hundreds of gaps and slits involved in the construction of spacecraft parachutes, cannot accurately model the flow through the windows, which needs to be actually resolved during the FSI computation. In parachute FSI computations, the resolved geometric porosity is significantly more challenging than the modeled geometric porosity, especially in computing the reefed stages and disreefing. Orion spacecraft main and drogue parachutes will both have three stages, with computation of the Stage 1 shape and disreefing from Stage 1 to Stage 2 for the main parachute being the most challenging because of the lowest "reefing ratio" (the ratio of the reefed skirt diameter to the nominal diameter). We present the special modeling techniques and strategies we devised to address the computational challenges encountered in FSI modeling of the reefed stages and disreefing of the main and drogue parachutes. We report, for a single parachute, FSI computation of both reefed stages and both disreefing events for both the main and drogue parachutes. In the case of the main parachute, we also report, for a 2-parachute cluster, FSI computation of the disreefing from Stage 2 to Stage 3. With results from these computations, we demonstrate that we have to a great extent overcome one of the most formidable challenges in FSI modeling of spacecraft parachutes.

Geometric Porosityを解像したリングセールパラシュートの数値流体解析

Geometric Porosityを解像したリングセールパラシュートの数値流体解析

Engineering Properties of Bitter Kola Nuts and Shell As Potentials for Development Processing Machines

The knowledge of engineering properties of any biomaterial is fundamental. It facilitates the design and development of equipment for harvesting, handling, conveying cleaning, delivering, separation, packing, storing, drying, mechanical oil extraction and processing of agricultural products. The study was conducted to investigate the physical, mechanical and frictional properties of bitter kola nut and shell, namely, axial dimensions, 1000 unit mass, arithmetic mean diameter, geometric mean diameter, surface area, sphericity, aspect ratio, bulk density, true density, porosity and angle of repose and coefficient of static friction were determined using standard methods. The engineering properties of bitter kola nut and shell were investigated at the moisture content of 20.8% and 23.1% dry basis respectively. The result obtained from the study revealed mean length, width, thickness, arithmetic and geometric diameter, sphericity, surface area and 1000unit mass ranged from 21.90-24.13 mm, 11.65-12.96 mm, 12.07-19.10 mm,15.21-22.03 mm, 14.55- 18.14 mm, 65- 75%, 447.9-1033.9 mm² and 3087.05- 3350.12 g respectively. The coefficient of static friction was determined for four frictional surfaces, namely, fibreglass, plywood, galvanized steel and rubber. The coefficient of static friction was the highest for bitter kola nut and shell on rubber surface and lowest for fiberglass.

Fluid–structure interaction modeling of clusters of spacecraft parachutes with modified geometric porosity

To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the "rings" and "sails" with hundreds of "ring gaps" and "sail slits." This creates extra computational challenges for fluid---structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such "modified geometric porosity," the flow through the "windows" created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space---Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models.