Static Packing Research Articles

Vertically Integrated CMOS Ternary Logic Device with Low Static Power Consumption and High Packing Density.

A ternary logic system to realize the simplest multivalued logic architecture can enhance energy efficiency compared to a binary logic system by reducing the number of transistors and interconnections. For the ternary logic system, a ternary logic device to harness three stable states is needed. In this study, a vertically integrated complementary metal-oxide-semiconductor ternary logic device is demonstrated by monolithically integrating a thin-film transistor (TFT) over a transistor-based threshold switch (TTS). Because the TFT and the TTS have their own source (S), drain (D), and gate (G), there are physically six electrodes. But the hybrid ternary logic device of the TFT over the TTS has only four electrodes: S, D, GTFT, and GTTS like a single MOSFET. It is because the D of the underlying TTS is electrically tied with the S of the superjacent TFT. By combining an on- and off-state of the TFT and the TTS, ternary logic values of low current ("0"-state), middle current ("1"-state), and high current ("2"-state) are realized. Particularly, static power consumption at the "1"-state is decreased by employing the TTS with low off-state leakage current compared to previously reported other ternary logic devices. In addition, a footprint of the ternary logic device with the vertically overlaying structure that has a framework of "one over the other" can be lowered by roughly twice compared to that with the laterally deployed structure that has an organization of "one alongside the other".

Memory of fabric anisotropy in the static packing of granular materials

Memory of fabric anisotropy in the static packing of granular materials

Dynamic cloud manufacturing service composition with re-entrant services: an online policy perspective

Cloud manufacturing (CMfg) emerges as a promising manufacturing paradigm, where service composition (SC) is a critical process concentrating on matching tasks and services. Existing studies usually ignore the dynamic nature of the CMfg environment, where task information is not always known before. Moreover, CMfg services are re-entrant, i.e. after being occupied for a period of service time, these services re-enter the CMfg platform (i.e. be available again). Re-entrant services significantly complicate CMfg platform revenue management. In this regard, we study the dynamic SC problem of CMfg (CMfg-DSC) incorporating re-entrant services within an online setting for the first time. CMfg-DSC is reformulated as an online packing problem. If a task is accepted, each requested service will be occupied until service time terminates. We propose online policies with performance guarantees, namely, static online packing policy (Static), opportunity-cost-based policy (Oppo), and dual-based policy with/without known distribution (Dual-k & Dual-u). Experiment results show that (1) Static is applicable for most cases; (2) Oppo has the potential for decent performance but at the cost of time; (3) Dual-u is reliable when only past observations are available; (4) Dual-k performs well given abundant service provision, but its performance would deteriorate if we lower the reward-cost threshold.

OC-059 TEMPORARY ABDOMINAL CLOSURE NEGATIVE THERAPY IMPROVES DEFINITIVE FASCIAL CLOSURE RATES IN PATIENTS WITH OPEN ABDOMEN MANAGEMENT

Abstract Aims Encapsulating peritoneal sclerosis (EPS) is a rare phenomenon characterised by encasement of the bowel by a thickened peritoneum due to prolonged peritoneal dialysis exposure. We are an international referral centre, typically managing cases with a planned open abdomen (OAM) and scheduled relook after 24–48 hours. We compare outcomes for those patients whose OAM was with simple packing (betadine-soaked-gauze) with negative pressure therapy providing temporary abdominal closure (TAC). Methods A retrospective review of a contemporaneous database of patients who underwent surgery for EPS between 2010–2020 was performed. Primary endpoints were time to definitive closure and closure method (primary fascial closure vs. bridged biologic mesh closure vs. failure to close fascia). Secondary endpoints included comparison of stoma formation, bowel resection, fistulation rate, enterotomy formation, re-operation post closure, and wound infection. Results 99 patients had OAM (56 static packing; 43 TAC.) Patients with TAC were significantly more likely to undergo primary closure of fascia when compared to those patients managed with static packing, (63% vs 13%, p<0.0001, Chi Sq). The TAC group required fewer theatre episodes (n=2.27 vs. 4.78, p<0.0001, t-test) and time in days to achieve closure (n=2.78 vs n=4.68, p<0.005, Chi Sq), with less failure to close episodes and returns to theatre 30 days post closure. Conclusion This study provides definitive evidence of TAC efficacy for fascial closure following OAM. This provides definitive benefit over traditional open abdominal methods. It may provide benefit in definitive open abdominal management in other areas (sepsis and trauma) and requires further study.

Discrete element simulation of powder flow in revolution powder analyser: Effects of shape factor, friction and adhesion

Through discrete element method (DEM) simulations in Revolution Powder Analyser (RPA), we found a strong correlation between the static powder bed packing density and the avalanche flow. A wider powder size distribution and a higher fraction of non-spherical powders caused larger misfits in the static packing of powders, and thereby enhanced the powder mobility during revolution, leading to an earlier avalanche. It performs a gradual avalanche under low friction, and an abrupt avalanche under high friction. The rolling motion of non-spherical powders was found to cause an instantaneous disturbance to the flow of neighbouring powders. It was also found that other factors, such as the filling degree, drum rotation speed and inter-powder adhesion, can also influence the measurement results and hence they must be controlled or standardized in order to achieve reliable and consistent measurements. Furthermore, based on the experimental measurements of avalanche angle and packing fraction, we extracted the intrinsic powder friction coefficient and adhesion energy. • DEM powder flow models with realistic powder size and shape distributions. • Performed DEM simulations to study powder flow profiles and avalanche phenomena. • Examined and identified the effects of system factors for reliable RPA measurements. • Extracted the rolling COF and adhesion energy by including powder non-sphericity.

A link between mechanical heterogeneity and nontrivial local structural power-law response in a model metallic glass

The structural heterogeneity and mechanical inhomogeneity of metallic glasses at the nanoscale have been demonstrated by extensive experimental investigations, while their inherent correlation remains ambiguous. Based on elasticity theory, a model is developed to describe the local structural response of metallic glasses under hydrostatic deformation. We establish a linear relationship between the local bulk modulus and the nontrivial power-law exponent of the structural response and further verify this relationship by molecular dynamics simulations. The intrinsic link between the local structural response and elastic modulus reveals that the mechanical heterogeneity reflects not only the static atomic packing but also the dynamic evolution of the amorphous structure. Our findings provide direct evidence that mechanical heterogeneity is a feasible indicator for describing the structural heterogeneity of metallic glasses and shed some light on the non-cubic structural power law of disordered materials.

Determining a representative element volume for DEM simulations of samples with non-circular particles

Numerical studies on the number of particles or system size required to attain a representative element volume (REV) for discrete element method (DEM) simulations of granular materials have almost always considered samples with spherical or circular particles. This study considers how many particles are needed to attain a REV for 2D samples of 2-disc cluster particles where the particle aspect ratio (AR) was systematically varied. Dense and loose assemblies of particles were simulated. The minimum REV was assessed both by considering the repeatability of static packing characteristics and the shearing behaviour in biaxial compression tests, and by investigating the effect of sample size on the measured characteristics and observed shearing behaviour. The repeatability of the data considered generally improved with increasing sample size. The packing characteristics of the dense samples were more repeatable suggesting that the minimum REV reduces with increasing packing density. The minimum REV was observed to be sensitive to the characteristic measured. Although the overall responses of the samples during shear deformation were similar irrespective of the sample sizes, the smaller the sample size, the higher the fluctuations observed in the responses. Analysis of the coefficient of variation of the fluctuations around the critical state stress ratio can provide insight as to whether a REV is attained. The particle AR influences the effect of sample size on shearing characteristics and thus the minimum number of particles required to attain a REV; this can be explained by the influence of AR on the number of contacts within the samples.

Modelling the effect of grain anisotropy on inter-granular porosity

Porosity is the dominant factor that determines the exploitable capacity of sedimentary reservoir rocks. Generally, pore heterogeneity is poorly represented in subsurface geological models due to the complexity. Granular mixtures produce complex pore space controlled by grain size, grain shape, and grain sorting. Heterogeneities in pore space volume are present at micro- and nanoscales in granular mixtures due to packing conditions resulting from deposition and diagenesis. In the present study, three-dimensional packing models were generated to provide a realistic description of granular mixtures. Accordingly, this study presents static packing models for unit cells idealised for spherical and elongated grains using cubic, orthorhombic, and rhombohedral packing models. Subsequently, the grain shape effects in terms of elongation degree and grain size distribution in terms of the degree of sorting were evaluated. The mixing effect on the inter-granular porosity for each unit cell packing model was analysed. A range of porosity values was derived using grain parameters generated through in-house developed MATLAB codes from digital FESEM images of sandstone samples. Our study demonstrates that actual grain size does not influence porosity, but for real sandstone samples, the sorting and shape of grains affect porosity values. The range of porosity values estimated by this method can be realistic at the basin level as the grain shape effects replicate sediment maturity. The developed method can be adopted in the distributed spatial models on porosity, especially for basin-scale hydrocarbon resource estimation.

Comparative performance analysis of a static & dynamic evaporative cooling pads for varied climatic conditions

Evaporation significantly reduce the temperature of the space and it mainly depends on the external climatic conditions. Current work focuses on the development of an evaporative cooling unit to study the performance of the system for varying ambient conditions. A novel centrifugal evaporative cooling unit is constructed which consists of a cylindrical pad structure. Both static and dynamic conditions are analysed with the variation of water flow rate (WFR), air flow rate, and inlet relative humidity (RH). Rate of evaporation (ER), cooling effect, coefficient of performance (COP)and energy consumption (EC) for both stationary and dynamic packing for varying input conditions have been accessed. Experimental result indicated that, with the increase in the air flow rate, there is a drop in the ΔDBT, ΔRH, COP and humidification efficiency and a rise in the evaporation rate. Output parameters improve till a water flow rate of 0.6 LPM, there afterwards performance deteriorated. Maximum evaporation rate and Humidification efficiency (HE) obtained by the system are 2 g/s & 81.11% respectively. Transient analysis indicated that the dynamic packing achieved the thermal comfort faster than the static packing. Overall, Dynamic packing gave better performance compared to static packing and it is found that performances are highly dependent on the climatic conditions.

Experimental investigations of humidification parameters and transient analysis in a rotating centrifugal humidifier

Evaporative cooling is one of the easiest methods of achieving thermal comfort inside defined space, especially in arid regions. The current work adopts a novel approach in the design and fabrication of a humidifier unit that works on the centrifugal effect. The system consists of a cylindrical mesh that is filled with packing material driven by a motor. The rotating packing cylinder is soaked by the water dripping by gravity. The vortex effect caused by the centrifugal action on the packing allows dispersing the fine water particles in the air. Airblown inside the chamber gets humidified due to the evaporation of water. Output parameters such as evaporation rate (ER), cooling efficiency (HE), coefficient of performance (COP), cooling effect, and specific cooling effect (SCC) are determined for various combinations of air velocities and cylinder speed of rotation. Experiments are carried for both static and dynamic packing conditions. It is found that dynamic packing with 150 rpm and air velocity of 8 m/s gave a superior performance in terms of change in DBT, change in RH, humidification efficiency, and evaporation rate. The system gave a maximum COP of 5.85, an evaporation rate of 0.51 g/s, and a humidification efficiency of 79.23%. Transient analysis indicated that required thermal conditions could be attained in the dynamic case earlier than the static conditions saving both energy and valuable time. Overall, the performance of dynamic packing is superior compared to the stationary packing in terms of higher ΔRH, ΔDBT, humidification efficiency, and evaporation rate.

Effects of coefficient of friction and coefficient of restitution on static packing characteristics of polydisperse spherical pebble bed

The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method. Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed. The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor. Neither the coefficient of friction nor restitution affected the oscillation width of the wall, whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed. In both the contact force distribution and coordination number distribution, a left-shifted phenomenon appearing as the coefficient of friction occurred, and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9. In all simulation cases, the effects of the coefficients of friction and restitution are similar to that of cross-impact.

Development and validation of SuperDEM for non-spherical particulate systems using a superquadric particle method

This article presents the development and validation of the Superquadric Discrete Element Method (SuperDEM) for non-spherical particle simulation using a superquadric particle method in open-source CFD suite MFiX. A superquadric particle–particle contact algorithm with accelerating and stabilizing strategy was developed. A superquadric particle–arbitrary wall contact algorithm was developed, which enables the simulation in complex geometry. The solver was validated by comparing with experimental data generated in this study or available in the literature. Tests include cylinder contacting with a wall, static packing of M&M chocolate candies in a cylindrical container, static packing of cylinders in a cylindrical container, dynamic angle of repose of cylinders in a rotating drum, and discharging of chocolate candies from a hopper. Besides, MPI parallelization of the solver was implemented and the parallel performance of the solver using MPI was assessed through large-scale simulations of 1 million, 10 million, and 100 million particles on up to 6800 cores, which demonstrates that the SuperDEM solver has great potential for industrial-scale systems simulation.

Interior-Point-Based Online Stochastic Bin Packing

A New Algorithm for Static Bin Packing

Janssen effect in dynamic particulate systems.

The Janssen model of stress redistribution within laterally bounded particulate assemblies is a longstanding and valuable theoretical framework, widely used in the design of industrial systems. However, the model relies on the assumption of a static packing of particles and has never been tested in a truly dynamic regime nor for a constraining system whose geometry is dynamically altered. In this paper, we explore the pressure distributions of granular beds housed within a container possessing a laterally mobile sidewall, allowing the depth, height, and cross-sectional areas of the systems studied to be dynamically altered, thus, inducing particle rearrangements and flow in the particulate system constrained thereby. We demonstrate that the systems studied can be successfully described by the Janssen model across a wide range of system expansion rates, including those for which liquidlike flow is clearly observed and propose an extension to the model allowing for an improved characterization of constrained dynamic systems.

Packing and flow profiles of soft grains in 3D silos reconstructed with X-ray computed tomography

The outflow of hard grains from storage containers with narrow outlets has been extensively studied in the past. Most experiments focused on discharge rates and avalanche statistics. Flow fields inside such containers have been detected optically in two-dimensional (2D) or quasi-2D geometries. Soft grains behave qualitatively different in many respects, both in their static packing properties and during silo discharge. We employ X-ray computed tomography to map the particles in a 3D container and we compare the static packing characteristics and the flow profiles of soft hydrogel spheres with those of hard spheres. The local fill fraction of the soft grains depends upon the depth below the granular surface. The outflow of the soft, low frictional hydrogel spheres involves the complete container volume, stagnant zones are absent.

Influence of non-spherical shape approximation on DEM simulation accuracy by multi-sphere method

Hoppers are widely used in many engineering and industrial processes. The discharge of hoppers is one of the most important issues in the industry, and our main focus in this project is the discharge behavior in the hoppers. Many factors affect the flow rate and discharge time in the hoppers including particle shape, material properties and hopper type. In this study, discharge of non-spherical particles from the flat bottom hoppers has been simulated using a discrete element method (DEM), which is a technique for granular systems. In order to model the elliptical particles in the experiment, multi-sphere method was used, which is a suitable method for approximation of curved and smooth surface particles. Model was validated using experimental results in the literature and good agreement between them in particle static packing, the flow behavior and hopper discharging rates was found. An important factor that influences the accuracy of the simulation of non-spherical granular systems is the accuracy in modeling of the particles. For this purpose, non-spherical granular particles were modeled with several arrangements of spheres, and the effect of three parameters including the number of spheres forming particles, shape factor, and angularity factor (which indicates the accuracy of the particle shape approximation), on the simulation accuracy was studied. The results briefly showed that the angularity factor, which is a factor affecting the particle surface properties, is an effective parameter controlling the simulation accuracy, such that the linear relationship (R2 of 0.96 and 0.91) exists between the angularity factor and simulation accuracy.

Effect of pebble size and bed dimension on the distribution of voidages in pebble bed reactor

The HTR-10 built at Tsinghua University is an advanced pebble bed reactor because of its inherent safety and economic efficiency. It is fundamental to explore the voidage of the pebble bed. The existing experimental bed is limited in depth and contains mono-size pebbles. The effects of pebble size and bed dimension of voidage distribution are still not well known. In this work, the discrete element method is used to simulate the static packing of pebbles of three sizes in 2D and 3D pebble beds under the same load. The effects of bed dimension and pebble size on voidage distribution are analyzed. The results are useful for better understanding of the voidage distribution of pebble bed reactor and the effects of bed dimension and particle size as well as the wall effects.

Compatibility-based static VM placement minimizing interference

The static (or initial) packing of VMs into a cloud provided host is done based on their expected resource requirements as specified in Service Level Agreements (SLAs). SLAs in Infrastructure as a Service (IaaS) clouds, however, capture neither changes in requirements over a VM's lifetime nor their dynamic characteristics (e.g. cache behaviour). Placing VMs for packing efficiency alone can result in “incompatible” VMs being co-located that interfere with one another's executions. This can result in the need for costly early VM migrations. In this paper, we address this problem by introducing Compatibility-based Static VM Placement (CSVP). CSVP contributes by exploiting easy-to-obtain information about VMs’ expected load variation to co-locate compatible VMs within a scheduling batch together thereby improving their initial performance. We have implemented CSVP in CloudSim and done simulations using workloads derived from a subset of the Google traces. Our results show that even using only simple threshold information about VM behaviour CSVP provides better initial VM placements to avoid some VM interference. Using CSVP, VMs are thus more likely to execute effectively together from their start thereby decreasing the overhead of VM migration.

Model of the saltation transport by Discrete Element Method coupled with wind interaction

We study the Aeolian saltation transport problem by analysing the collision of incident energetic beads with granular packing. We investigate the collision process for the case where the incident bead and those from the packing have identical mechanical properties. We analyse the features of the consecutive collision process. We used a molecular dynamics method known as DEM (soft Discrete Element Method) with 20000 particles (2D). The grains were displayed randomly in a box (250X60). A few incident disks are launched with a constant velocity and angle with high random position to initiate the flow. A wind velocity profile is applied on the flowing zone of the saltation. The velocity profile is obtained by the calculi of the counter-flow due to the local packing fraction induced by the granular flow. We analyse the evolution of the upper surface of the disk packing. In the beginning, the saltation process can be seen as the classical “splash function” in which one bead hits a fully static dense packing. Then, the quasi-fluidized upper layer of the packing creates a completely different behaviour of the “animated splash function”. The dilation of the upper surface due to the previous collisions is responsible for a need of less input energy for launching new ejected disks. This phenomenon permits to maintain a constant granular flow with a “small” wind velocity on the surface of the disk bed.

Maximum disorder model for dense steady-state flow of granular materials

A flow model is developed for dense shear-driven granular flow. As described in the geomechanics literature, a critical state condition is reached after sufficient shearing beyond an initial static packing. During further shearing at the critical state, the stress, fabric, and density remain nearly constant, even as particles are being continually rearranged. The paper proposes a predictive framework for critical state flow, viewing it as a condition of maximum disorder at the micro-scale. The flow model is constructed in a two-dimensional setting from the probability density of the motions, forces, and orientations of inter-particle contacts. Constraints are applied to this probability density: constant mean stress, constant volume, consistency of the contact dissipation rate with the stress work, and the fraction of sliding contacts. The differential form of Shannon entropy, a measure of disorder, is applied to the density, and the Jaynes formalism is used to find the density of maximum disorder in the underlying phase space. The resulting distributions of contact force, movement, and orientation are compared with two-dimensional DEM simulations of biaxial compression. The model favorably predicts anisotropies of the contact orientations, contact forces, contact movements, and the orientations of those contacts undergoing slip. The model also predicts the relationships between contact force magnitude and contact motion. The model is an alternative to affine-field descriptions of granular flow.