The hydrodynamic performance and the flow field of two horizontal-axis hydrokinetic turbines with and without a high-lift hydrofoil with a flap were investigated using computational fluid dynamics (CFD) simulation. For improving the accuracy of the numerical simulation, the user-defined function (UDF) of 6-degrees of freedom (6-DoF) was used in the Ansys Fluent software. Unsteady Reynolds-averaged Navier–Stokes (URANS) equations coupled to the SST 𝑘 − 𝜔 turbulence model were employed during the simulation. A three-dimensional model of both of the turbines with three blades was conducted for obtaining the performance curve of the power coefficient (𝐶𝑃) versus the tip speed ratio (TSR). The maximum power coefficients (𝐶𝑃𝑀𝑎𝑥) of the hydrokinetic turbines with and without a high-lift hydrofoil arrangement were 0.5050 and 0.419, respectively. Experimental data from the literature were used for the validation of the numerical results, specifically for the case when a rotor with traditional blades is utilized. In general, the simulation results were in good agreement with the experimental data.
Buenaventura Bay is facing severe pollution due to the direct discharge of untreated wastewater from 695 outlets along the coast, which serves 500,000 people. To address this issue, a study was conducted using the RMA11 water quality model, which was previously calibrated and validated, coupled with the RMA10 3D hydrodynamic model to assess sanitation scenarios in the bay. Five effluent reduction scenarios were proposed and compared based on fecal coliform concentration as an indicator, with evaluation also based on areas where fecal coliform concentrations exceeded the standard for primary contact. The model results revealed poor water quality in the bay, indicating that immediate action was necessary to prevent further deterioration. The proposed staged reduction in discharges would initially have more severe effects than the current situation, but this would improve when the treatment plant became operational. However, even with the plant in operation, the complete sanitation of the bay cannot be achieved, and further measures are required. This study emphasizes the urgent need for effective and sustainable measures to improve water quality in Buenaventura Bay and demonstrates the usefulness of the modeling approach in identifying effective sanitation scenarios to achieve this goal. The results highlight the need for a comprehensive management strategy to tackle pollution in the bay and provide insights for other regions facing similar challenges.
Obi Island is a small, remote Indonesian island located in the Molucca Sea that is endowed with a variety of mineral resources. Since 2019, artisanal miners have produced colourful specimens containing various copper minerals in chalcedony from altered andesite breccia near the village of Sesepe in the north-eastern part of the island. The specimens are sawn open to reveal the copper mineralisation, and sold into the lapidary and collector market. Locals call this material batu kawat, meaning `wire rock'. Silica-rich areas of the deposit provide semi-transparent masses of chalcedony that are speckled with blue chrysocolla and shiny blebs of native copper (e.g. `confetti chrysocolla'). The combination of interesting textures and attractive colouration make these ornamental materials popular with collectors and lapidaries.
Ülkelerin savunma güçlerinde özellikle donanma kuvvetleri önemli bir yere sahiptir. Donanma kuvvetlerinin mihenk taşı olan denizaltılar II. Dünya Savaşı’nda ne kadar önemli bir güç olduğunu etkili bir biçimde göstermiştir. O günden günümüze denizaltılarda yapılan teknolojik gelişmeler bir hayli hız kazanmıştır. Bahsi geçen gelişmelerin en başında ise kuşkusuz tahrik sistemlerinde yapılan gelişmeler gelmektedir. Özellikle AIP (Havadan Bağımsız Tahrik) sistemlerinin kullanımı ile hızlı bir gelişim gözlenmiştir. Klasik dizel-elektrik denizaltılardan kapalı çevrimlere yakıt hücresi teknolojisine sahip denizaltılardan Stirling temelli denizaltılara kadar birçok varyant uygulanmaktadır. İsveç ve Japonya gibi gelişmiş ülkelerin donanmalarında da Stirling motor kullanımının denizaltı uygulamaları göze çarpmaktadır. Stirling motorlarının Yakıt hücrelerine kıyasla daha düşük yakıt ikmal maliyetleri ve MESMA sistemine göre daha sessiz olması başlıca avantajları olmaktadır. Ayrıca içten yanmalı motorlara kıyasla egzoz gaz atımının daha kontrollü olması tercih edilmesinin başlıca sebepleri arasında yer almaktadır. Stirling motorlarının yakın geçmişte geliştirilmesi ve NASA’ya ait radyoizitop aracında temel güç kaynağı olarak tercih edilmesi, motorun oksijene gerek duymaksızın ne kadar verimli ve bakım gereksiniminin minimum seviyede olduğunun göstergesidir. Bu makalede Stirling motorunun günümüze kadar gelen süreçte nasıl geliştirildiği ve denizaltı uygulamalarında neden tercih edildiği, avantajları ve geleceği hakkında irdelemelerde bulunulacaktır.
