Nassir Dhamin Mokhlif

The interactions between subsea pipelines and the seabed generate complex vibratory responses that can compromise structural integrity, yet these interactions remain difficult to characterize with sufficient fidelity for design purposes. This study examines a numerical workflow for incorporating hydrodynamic forces and displacement-dependent pipe-soil interaction into the finite element analysis of a nominally 400 m subsea pipeline. The hydrodynamic formulation includes irregular wave kinematics, directional spreading, current effects, and force corrections related to pipeline movement, while the geotechnical representation uses prescribed pipe-soil contact and lateral resistance relationships. The workflow links local resistance characterization with the global structural response and investigates the sensitivity of calculated lateral displacement to applied stabilization weight and seabed strength assumptions. This approach enables computationally efficient structural analysis without sacrificing the fidelity needed to assess whole-system performance, directly addressing the central modeling challenge posed by the pipe-soil interface. Over a 100-year simulated service life, the maximum lateral displacement recorded across the 400 m pipeline reached 5.43 m, while displacement peaked at approximately 3.98 m under a chain weight of 18.37 kg. These results demonstrate the model’s sensitivity to key design parameters governing pipeline stability. The analysis provides an implementation-based case study for assessing the consequences of alternative seabed-resistance assumptions rather than establishing a new soil constitutive model or an independently validated through-life design procedure, and it provides a robust foundation for future subsea pipeline engineering practices.

Solar energy storage is essential in renewable energy systems, considering that solar energy is a periodic energy source that depends on time, so the intensity of solar radiation changes from time to time. Therefore, solar energy systems require storing energy to save it during the night periods or on cloudy days. The current solar heater designs are not feasible and ineffective unless energy storage is utilized (energy retention). The present research addresses improving the home solar water heater (SWH) performance under the atmosphere of Iraq. This study improves the thermal performance of a solar water heater integrated with a thermal storage tank using materials storing heat to achieve the most extended possible period of receding solar radiation. The SWH system performance was experimentally tested in Tikrit-Iraq. Several experiments were performed from 8:30 am to 16:30 hours in February 2022 with a water mass flow rate (\dot{m_w}) of (0.016 kg/s) for the circulation system and with a thermal load on the hot water tank (\dot{m_{th.L}}) of (0.0066 kg/s) for the two porous medium design cases (with and without solar reflectors). The results manifested that the maximum daily thermal efficiency (ηo) of the SWH system was 36.40% for design case 2 (with porous media and reflectors) at a (0.006 kg/s) thermal load compared to the case 1 (with porous medium and without reflectors) of 32.21%. At the same load, the outcomes elucidated that the overall thermal efficacy of the SWH regime in the convection presence provided the uppermost value utilizing porous media and reflectors. Also, the outcomes of the present investigation were compared with the preceding study, and the comparison outcomes were better than the present design circumstances.

When it comes to renewable energy, solar water heaters are among the fastest-growing technologies. Comparatively speaking, integrated collector-storage solar water heater systems cost less than other solar water heater designs. Therefore, both the construction and the operation of a combined collector-storage solar water heater are quite straightforward. The integrated storage solar collector coupled with reflectors has been experimentally investigated. The reflectors were insulated from the back side when working during the day hours and as insulated cover during the night hours. While comparing the combined collector-storage solar water heater with and without insulated reflectors, the results showed that the insulated reflectors increased the thermal efficiency by 23%. Furthermore, on the coldest day, the stored water reached a high of 82 degrees Celsius, though it was only 46 degrees Celsius that same morning.

The deposition and gelation of paraffin wax are among the significant risks in flow assurance during crude oil transportation. These risks are highly influenced by the structure of hydrocarbons in the produced composition from the well. In the present paper, four crude oil samples acquired from different Malaysian fields were experimentally analysed through gas chromatography/mass spectrometry, differential scanning calorimetry, and thermal gravimetric analyses. The crudes were investigated, with focus on the carbon number distribution, wax appearance temperature, and wax content. The results demonstrate that the crude oil samples with high molecular percentage of carbon distribution within a range of C20 to C40 comprehend high wax content. Measurement results of the four investigated crude samples revealed that the wax content is relatively high compared to other crudes produced in East Asian fields. Also, the four samples possess low wax appearance temperature characteristics, and all four crudes might behave as non-Newtonian at temperature around 38°C. The results provide useful information to manage the risk of wax formation in the transportation pipeline and the flow assurance of the crude. [Received: August 30, 2015; Accepted: July, 24, 2016].

Measurements of wax-in-feedstock parameters are vital tools for successful simulation of the wax crystallization phenomena in the solvent dewaxing process. In this paper, comparisons are implemented between different methods to investigate the wax characteristics of SN500 feedstock before and after dewaxing. The measurements involved were the wax content, wax appearance temperature, wax disappearence temperature, solid mass yield of the wax removal. The measurement methods adopted in the analysis are the modified Universal Oil Production method 46-64, Differential Scanning Calorimetry thermal analyzer, Cross Polar Microscopy technique, and Gas Chromatography analysis. Results have demonstrated that the modified Universal Oil Production method is slightly under estimating the wax content in the feedstock compared to the DSC results. This under estimation becomes larger for the wax content in the base stock.

A mathematical model of a steady heat transfer and crystallization was established in double pipe scraped surface heat exchangers and chillers for solvent dewaxing process. The model equations were numerically solved to obtain, the temperatures distribution, wax volume fraction, crystals number and their size in the wax-oil-solvent solution. The prediction of the physical properties and the nucleation and crystal growth constants based on the adjustable selection of the higher carbon number as a solute and light ones as liquid. The procedure depends on experimental measurements of the carbon number distribution in the feedstock, dissolved temperature, onset crystallization temperature, and the wax content. The measurement results were linked to a solubility model, which attaches the wax content and the dissolving temperature of the feed stock to choose the wax compound. The numerical model results showed that the proposed solubility model give a good estimation of the wax crystals characteristics of such complex process.

This paper presents a numerical model describe the kinetic of wax crystallization in scraped surface exchangers that mostly used in solvent dewaxing as a separation technique. The model consists of a combination between the heat transfer and the kinetic of wax crystallization. Solvent dewaxing process is selectivity reduced the higher normal paraffin components. This fact provides easier handling of the characteristic of the kinetics of wax crystallization, physical properties, and flow behavior. Chemical analyses of the feedstock are important to specify the carbon number distribution, dissolved temperature, and wax content. Wax crystallization in scraped surface heat exchanger is dependent of a large number of variables and is still subject of unclassified researches within few companies. Such process as affected by multi-parameters, need a mathematical description of wax crystallization to predict e.g. the mass fraction, the crystals number, their size, and temperature distribution incrementally. Controlling of the solvent injection ratio is very important parameter e.g. to adjust the viscosity and supersaturation of the oil-solvent-wax mixture. The simulation results will satisfy the wax crystals characteristics and oil recovery.