PSI - Issue 47

Andreal Muhammad Naufal et al. / Procedia Structural Integrity 47 (2023) 133–141 Naufal et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Energy needs have become a basic human need (Prabowo and Prabowoputra, 2020; Prabowoputra and Prabowo, 2022). Electricity production in the country is expected to reach 1200 TWh by 2050 or four times compared to electricity production in 2021 which is only around 280 TWh (Hilmawan et al., 2021). Currently, 90% of energy sources in Indonesia are still fossil energy which is converted to other storage, e.g., battery (Dabit et al., 2020; Nubli et al., 2022). This dependence is the main problem of the national energy supply. Seeing this condition, of course, new renewable energy (NRE) sources are currently needed to support increasing energy consumption. New renewable energy is energy derived from sustainable natural processes. Renewable energy is energy that is always available by nature so that it will not run out and will not be lost if used continuously. Examples of new renewable energy are solar power plants, wind power plants, hydroelectric power plants, and, geothermal power plants (PLTG) (Prabowoputra et al., 2020a-b). The plant that the author conveys is a type of NRE that is popularly used in Indonesia. However, several plants are very suitable for use in Indonesia because of their geographical location, namely ocean thermal energy conversion (OTEC). OTEC is a plant that utilizes the temperature difference between sea level and temperature in the depths of the sea. This temperature difference can range from 20 degrees to 26 degrees (Dalil et al., 2021). This temperature difference is used to evaporate fluid with a low boiling point, which is then used to rotate turbines and then produce energy (Adiputra and Utsunomiya, 2019; 2021). Cold Water Pipe (CWP) is a pipe that hangs on the OTEC platform which functions to deliver low-temperature deep seawater to the OTEC platform where there will be a heat exchanger process with water on the surface. In this paper, the author will discuss mass-produced materials to facilitate and minimize costs in making cold water pipes. Due to the use of standardized materials by the factory, it does not make special materials outside of mass production. The sandwich material was chosen as a solution for use in cold water pipes (CWP), due to the large ratio of strength and weight. The material chosen is Nomex honeycomb as the core of the sandwich and carbon fiber as the facing. This paper will discuss flexural strength and material strength by three-point bending testing and Finite Element (FE) analysis (Adiputra et al., 2022; Ansori et al., 2022; Do et al., 2022; Fajri et al., 2022). 2. Sandwich material The honeycomb sandwich structure consists of two thin-facing layers affixed on both sides of the core (Feng et al., 2020) (as displayed in Figure 1). The sandwich structure allows the outer layer to bear axial load, bending moment, and in-plane shear. Meanwhile, the core of the material bears normal flexural shear. Sandwich structures are prone to failure caused by local stress with large concentrations this is due to the heterogeneous composition of cores and face sheets (Rayjade et al., 2008). However, for OTEC applications, the advantage that can be relied on from sandwich material is its very lightweight. This weight is achieved by a combination of facing carbon which has a large strength to-weight ratio combined with carbon aramid which has a large compressive strength and is a lightweight material.

Figure 1. Configuration of a typical sandwich structure.