Optimization of Wind Sail using Computational Fluid Dynamics Simulation

The marine industry is highly dependent on oil as the fuel and the increased consumption of this fast-depleting oil recourse creates a shortage of fuel for the future as well as pollutes the environment. The pollution of water bodies also seriously affects marine life. Thus, the need for an alternate sustainable fuel source is of great importance. One such feasible alternative energy source is wind energy. The abundance, free availability and ease of conversion make it an ideal alternative to oil. Wind energy can be extracted by wind turbines or by sails. The sails convert the wind energy directly into energy for propulsion. The challenge in the conversion is the relative angle of attack of wind on the sail. The wind cannot be expected to be always in the direction of the course of the ship. When the wind is at an angle to the direction of the course, the thrust in the course director will be reduced and a component of thrust is developed on the sail which shifts the course of the ship. Bringing the ship back to the original course will create an additional expenditure of fuel. In such circumstances modification of the sail section shape from its conventional form to an optimal form helps to reduce these deficiencies. Therefore, the effort here is to numerically analyze the aerodynamic characteristics of wing-sails and to optimize their shape. The aerofoil NACA 0018 used here was chosen through a high fidelity two-dimensional computational analysis which was done earlier. The tip of the NACA 0018 was further modified by tilting it through different angles and at different chord positions forming a flap. The main objective of the study is to optimize the angle and the position of the flap relative to the chord of the aerofoil. The flapped airfoils were formed by modifying them from 10% chord length to 60% chord length. That flap angle was also varied from 0 degrees to 50 degrees in steps of 10- deg. The angle of attack on the sail was varied from 0 to 10 degrees in steps of 2 degrees. The thrust in the direction of course and the lateral thrust of each of these sail sections were estimated, tabulated and graphs were plotted. Analyzing these, an optimum shape for the sail section is derived.

Staged correction of varus knee and lateral thrust in an achondroplastic (ACH) juvenile patient who underwent limb lengthening with IM nails: tips for proper timing and prioritisation of procedures

We present the case of a fifteen-year-old achondroplastic (ACH) woman who requested to have her femurs lengthened by intramedullary nails. She had undergone bilateral tibial lengthening at the age of eleven and presented with a varus deformity of the right lower limb, lateral thrust of the right knee and valgus deformity of the left lower limb. We performed deformity analyses based on mechanical axis measurements, and we came with a staged surgical plan. In ACH adolescences, correction of bony deformity needs to encounter continuous fibula growth dynamics. Lateral knee thrust was corrected by gradual distal translation of the fibula head via an Ilizarov frame and the amount of translation we decided clinically. Tibial lengthening and valgus osteotomy of the distal femur accentuate lateral collateral ligament (LCL) complex laxity. In patients with ACH, tibial lengthening and valgus osteotomy of the distal femur—if needed—should precede LCL complex tightening, and femoral lengthening should follow.

Single-stage medial plateau elevation and metaphyseal osteotomies in advanced-stage Blount’s disease: a new technique

Purpose Surgical treatment in advanced-stage infantile Blount’s disease with medial plateau (MP) depression is challenging. Several osteotomies and fixation methods have been described with no established benchmark. We conducted this study to evaluate the efficacy and safety of a new single-stage technique for acute medial condyle elevation and metaphyseal osteotomies with internal fixation. Methods A prospective case series of 19 consecutive patients (21 knees) with severe infantile Blount’s disease underwent a single-stage MP elevation and metaphyseal osteotomies, with internal fixation. The mean age was 10.3 years (8.2 to 13.6) and the mean follow-up was 5.1 years (3.2 to 8.3). The outcome measures included clinical and radiological parameters and patient-reported pediatric outcomes data collection instrument (PODCI) score. Results The mean PODCI score improved significantly from 50% to 88%. The mean internal tibial torsion improved from -27° to 11°. All cases maintained full knee extension, no limitation in flexion range of movement and no signs of instability or lateral thrust gait. All the radiographic parameters improved significantly; the mean tibiofemoral angle improved from -29° to 7°, the metaphyseal-diaphyseal angle improved from 33.4° to 4.7° and the angle of depressed MP improved from 38.3° to 2.4° (p < 0.001). At the latest follow-up, no cases of deformity recurrence were identified, the final limb-length discrepancy was < 1 cm in all patients. Conclusion Single-stage MP elevation and metaphyseal osteotomies with internal fixation significantly improved the clinical and radiographic parameters and PODCI score in advanced infantile Blount’s disease and precluded the use of external immobilization, with no evidence of deformity recurrence. Level of evidence IV

Collapse Behavior of Tensegrity Barrel-Vault Structures Based on Di-Pyramid (DP) Units

In this study, the collapse behavior of a family of tensegrity structures, i.e. di-pyramid (DP) barrel-vaults that can offer promising solutions for civil engineering applications is analyzed. Depending on whether struts’ snap or cables’ rupture dictate the occurrence of overall collapse, two different designs are considered. The effects of geometric parameters, self-stress properties, loading type, boundary conditions and strengthening schemes on the structural behavior are discussed. It is found that the structures with symmetric and ridge loading types undergo bifurcation type instability instead of limit point which is encountered in the cases with asymmetric loading type. Constraint against lateral thrust is beneficial in improving strength and initial stiffness of the studied cases, by as much as 60% and 90%, respectively. In most cases, the rate of strength variation associated with increasing self-stress levels is quite slow, while the slackness load increases by at least 400% being the primary achievements. By using non-uniform self-stress distribution, the initial stiffness of these structures can be increased up to 240%. Increasing the rise-to-span ratio improves the initial stiffness and collapse strength of the structure significantly at the expense of expedition of cables slackness. Significant gains in collapse resistance of these structures under symmetric loading are obtained with strengthened critical struts or cables, depending on which collapse case dominates, but the initial stiffness is generally not influenced by these schemes.

Vault

Vaults are curved masonry surfaces for roofs and ceilings, able to give shelter and protection. Fireproof and very durable, they were the only massive constructions available for such purposes before modern reinforced concrete was invented. Vaulted ceilings have often been a major issue in the creation of architectural space—as dominating elements with sculptural quality, and as fascinating constructions, often elegant, sometimes astonishing or even daring, always artful, and requiring and demonstrating great expertise and skill in their design and building. In early stone architecture, vaults built with horizontal circular courses can already be characterized as spatial structures. Since the early Great Civilizations, vaults were constructed with blocks arranged in radial bed joints—they could be built with great economy, with complex shape and adapting to irregular plans, as they are still in modern vernacular architecture, such as in Central Asia or in northern Africa. In Late Antiquity, vaults made with dressed stone show great ability in the geometric design—this art was later resumed both in the Middle East and in European Renaissance architecture. In Imperial Rome, vaults made of concrete reached enormous spans, were robust enough to last many centuries, and could be built virtually in any shape. Vaults of brick or stone masonry or of dressed stonework are among the greatest masterpieces of architecture, including the marvelous vaults in Persian architecture, the high vaults of Gothic cathedrals perfectly balanced upon slender pillars, the magnificent spatial inventions of Baroque vaulting, the great domes, and finally the creation of modern shell structures. By principle, vaults are stable by their shape. Their equilibrium demands curvature, regularly resulting in shapes with complex geometry. Therefore, they are very demanding in design, planning, and construction. Systems of anchoring or abutment have to be devised to contain the lateral thrust, and a shape must be created that enables the stability by counterbalancing the heavy components within the vault. Moreover, the building of the curved shape requires form control during bricklaying, geometric design of the temporary support structure, and, in case of stone structures, the formulation of precise specification for producing the single building elements. Therefore, beyond symbolic values, ideas of space in architecture, and the expertise and virtuosity of planners and builders, vaulted ceilings also reflect the historical development of applied geometry and mechanics. Their study gives an insight to the knowledge society that created the buildings.

A physical model for the interaction between unsaturated soils and retaining structures

Temporary and permanent retaining structures interact with soils that are usually in unsaturated conditions. In this work, a 1g-scale physical model is presented to investigate the interactions between retaining walls and unsaturated soils. The physical model is equipped with a water-filled hydraulic cylinder connected to a pressure-volume controller to measure the horizontal component of the later earth thrust and high capacity tensiometers to measure soil matric suction. A system of low-friction linear guideways has been installed at the base of the wall-model. The failure surface is observed through a 3 cm thick glass wall on one side of the container. A series of images are acquired during the tests, and Particle Image Velocimetry (PIV) technique has been used to identify the displacement field. Selected test results on a fine sandy soil are presented, emphasizing the differences in the lateral thrust between dry and partially saturated conditions. The presented results show the impact of the partially saturated condition on both the magnitude of the horizontal component of the lateral earth thrust and the failure mechanism at active state.