Sediment transport is fundamentally a two-phase phenomenon involving fluid and sediments; however, many existing numerical models are one-phase approaches, which are unable to capture the complex fluid-particle and inter-particle interactions. In the last decade, two-phase models have gained traction; however, there are still many limitations in these models. For example, several existing two-phase models are confined to one-dimensional problems; in addition, the existing two-dimensional models simulate only the region outside the sand bed. This paper develops a new three-dimensional two-phase model for simulating sediment transport in the sheet flow condition, incorporating recently published rheological characteristics of sediments. The enduring-contact, inertial, and fluid viscosity effects are considered in determining sediment pressure and stresses, enabling the model to be applicable to a wide range of particle Reynolds number. A k − ε turbulence model is adopted to compute the Reynolds stresses. In addition, a novel numerical scheme is proposed, thus avoiding numerical instability caused by high sediment concentration and allowing the sediment dynamics to be computed both within and outside the sand bed. The present model is applied to two classical problems, namely, sheet flow and scour under a pipeline with favorable results. For sheet flow, the computed velocity is consistent with measured data reported in the literature. For pipeline scour, the computed scour rate beneath the pipeline agrees with previous experimental observations. However, the present model is unable to capture vortex shedding; consequently, the sediment deposition behind the pipeline is overestimated. Sensitivity analyses reveal that model parameters associated with turbulence have strong influence on the computed results.

Meckel's diverticulum (MD), a seemingly innocuous anomaly of the gastrointestinal tract, presents distinctive challenges to a clinician, as it is prone to varied complications that are frequently elusive to diagnosis with conventional diagnostic modalities. This case series illustrates the diverse presentations and advantages of laparoscopic-assisted management of Meckel's diverticular complications in children. Between October 2002 and April 2006, 36 patients (27 males and 9 females) aged 1.5 to 16 years (median 10 years) underwent laparoscopic-assisted trans-umbilical Meckel's diverticulectomy (LATUM). Sixteen (44.4%) patients presented with lower gastrointestinal bleeding (14 with painless bleed and 2 with perforated peptic ulcer in the ileum adjacent to the MD), six (16.7%) patients presented with intestinal obstruction (four due to a mesodiverticular band and one each due to intussusception and floppy giant cystic dilatation of MD causing intestinal compression) and four (11.1%) patients presented with features masquerading as appendicitis (one with Meckel's diverticulitis and perforation, one with perforated peptic ulcer adjacent to MD and two with a torted and gangrenous MD). In ten (27.8%) patients, incidental MD with a narrow base was noted at laparoscopic exploration for suspected appendicitis. All patients underwent successful LATUM along with appendicectomy in 15 (41.7%) patients. The operative duration ranged from 72 to 266 min (mean 125.9+/-48.4). There were no intra-operative complications and none required conversion to open surgery. The hospital stay was 3 to 9 days (mean 5.3+/-1.2). There were three (8.3%) cases of postoperative adhesive intestinal obstruction; two underwent successful laparoscopic adhesiolysis and one necessitated conversion to suprapubic laparotomy to release the pelvic adhesions. There were no other complications during the follow-up (median 16 months). LATUM is a safe, effective and an esthetic procedure offering timely diagnosis and cure for diverse Meckel's diverticular complications. The technique also allows palpation of the MD and avoids usage of expensive staplers.

No abstract

No abstract

No abstract