Abstract
Development of industrial activities in the offshore areas has led to the importance of safety of helicopters. Understanding the behavior of the wind around Helideck, especially on take-off, approach and landing are essential to enhance the safe operation of helicopters. In this regard, legislators have imposed restrictions on the operation of helicopters under varying conditions of disturbance through the standards and rules. In this paper based on the Reynolds-averaged Navier-Stokes theory, the wind current on the SPD19-A offshore platform from the 19th phase of south pars gas field complex in the CFD environment is modeled, taking into account all the effective equipment. Considering variables such as wind direction, the horizontal and vertical direction of the crane boom, 42 scenarios considered to an appropriate insight of turbulence conditions been provided. The Norsok standard has been used to select the assessment criteria and the two criteria Horizontal velocity deviation and Turbulence energy has been evaluated, also the stream lines from numerical and experimental modeling have been compared. The results indicate that in the East-West wind direction, the increase in the vertical angle of the boom improves the turbulence conditions in the center of the Helideck. In the direction of the northeast-southwest, the increase in the vertical angle of the boom causes the turbulence conditions in the helideck center to become more complicated. Also, based on the turbulence kinetic energy index, the increase of the vertical angle of the boom for both wind directions makes turbulence conditions more complicated.

1. INTRODUCTION
Helicopters play a vital role in offshore operations for the rapid transportation of personnel and equipment to marine installations. The safety of helicopter operations near offshore platforms has become increasingly critical with the expansion of industrial activities in offshore areas. Understanding wind behavior around helidecks, particularly during take-off, approach, and landing maneuvers, is essential for enhancing operational safety. Regulatory bodies have established standards and guidelines to restrict helicopter operations under various turbulence conditions. Historical incidents highlight the significance of aerodynamic considerations in offshore platform design. The 1995 Claymore platform incident, while resulting in no fatalities, challenged existing knowledge about airflow hazards and demonstrated the need to consider environmental factors near platforms. According to marine accident databases, approximately 260 helicopter incidents occurred during offshore operations between 1970 and 2010, resulting in 646 fatalities, representing about 30% of all offshore accident-related deaths. Previous research has established that wind flow near platforms becomes non-uniform, creating turbulent zones, vortex flows, and regions with variable acceleration. Von Blohn et al. (1979) conducted early wind tunnel experiments on a 1:150 scale jacket platform model, demonstrating that increasing helideck elevation improves turbulence behavior. Chen et al. (1995) investigated flow around cube arrays, validating both Large Eddy Simulation (LES) and RANS approaches for turbulence prediction. de Carvalho e Silva et al. (2010) combined numerical modeling and wind tunnel testing for a ship with a helideck, confirming that numerical methods can provide adequate turbulence insight even for complex geometries. The NORSOK C-004 standard (2013) and CAP 437 (Authority, 2005) provide assessment criteria for helicopter operations, defining acceptable limits for horizontal velocity deviation (1.75 m/s) and turbulence kinetic energy. While considerable research exists on offshore helideck aerodynamics, most studies remain industrial with limited academic publication. The specific influence of crane configuration, as one of the most significant movable pieces of equipment on the upper deck, on wind turbulence around helidecks requires systematic investigation. This study aims to evaluate the effect of crane boom orientation on wind flow characteristics around an offshore platform helideck through comprehensive numerical simulation, considering various wind directions and crane positions.

2. MATERIALS AND METHODS
The research methodology combines numerical simulation using Computational Fluid Dynamics (CFD) with experimental validation through wind tunnel testing. The study framework addresses the research question: How do crane boom horizontal and vertical angles affect wind turbulence patterns on an offshore helideck? The numerical modeling employed the Reynolds-averaged Navier-Stokes (RANS) approach with the standard k-epsilon turbulence model, implemented in ANSYS CFD software. This approach was selected based on its proven accuracy for simulating turbulent flows around bluff bodies at moderate Reynolds numbers, as validated by previous researchers including Maleki et al. (2017), Abdi and Bitsuamlak (2014), and Mentzoni and Ertesvag (2015). The platform model was based on the SPD19-A jacket from the South Pars gas field complex Phase 19. The topside measures 40 m in length and 32 m in width, comprising five levels with a total height of 14 m. The helideck is cantilevered on the western face at 25.7 m above sea level, with the crane positioned on the eastern face. The computational domain consisted of a cylindrical control volume with a 100 m radius and 75 m height above sea level, with the platform centered within this volume. Forty-two scenarios were simulated, considering two primary wind directions (East-West and Northeast-Southwest) based on preliminary analyses indicating maximum crane influence on helideck turbulence. Wind velocity was set at 30 m/s, representing storm conditions in the region. Crane horizontal orientation varied across seven angles (0°, 30°, 60°, 90°, 120°, 150°, and 180°), with 0° aligned with the southern direction. Crane boom vertical angle varied across three positions (0°, 20°, and 40°). Mesh independence studies determined optimal element sizes: 1 m for the sea surface, 0.2 m for the upper deck, and 0.1 m for the helideck vicinity, resulting in approximately 2 million nodes and 10 million elements. The first-order upwind scheme was employed for equation convergence. Validation comprised two approaches. First, the Silsoe cube experiment (6 m cube in open terrain) was numerically reproduced and compared with field measurements by Richards and Hoxey (2002, 2006), demonstrating acceptable agreement. Second, a 1:200 scale 3D-printed model of the complete topside was tested in the educational-research wind tunnel at Khorramshahr University of Marine Science and Technology. The tunnel has a 35×35 cm cross-section, capable of generating 15 m/s wind velocity. Using Froude number similarity, an equivalent wind velocity of 1 m/s was employed for flow visualization using smoke generation. Turbulence assessment followed NORSOK C-004 (2013) and CAP 437 (Authority, 2005) criteria, evaluating horizontal velocity deviation and turbulence kinetic energy. According to these standards, significant turbulence corresponds to horizontal velocity deviation exceeding 1.75 m/s, with flight restriction zones identified where deviation exceeds 2.4 m/s or turbulence kinetic energy ranges between 6.8 and 12.8 m²/s².

3. RESULTS
Analysis of horizontal velocity deviation at the helideck center reveals distinct patterns based on wind direction and crane configuration. For East-West wind direction, increasing the boom vertical angle from 0° to 40° reduces velocity deviation by approximately 20%, particularly evident at 0° and 60° crane horizontal angles. This improvement is most pronounced in the lower altitude regions critical for helicopter operations: the skid zone (0-0.5 m above deck), cabin and blade zone (0.5-4 m), approach zone (4-10 m), and control zone (10-30 m). For the Northeast-Southwest wind direction, crane configurations at 120° and 150° horizontal angles show significant sensitivity to boom vertical angle. In contrast to the East-West direction, increasing the boom vertical angle from 0° to 40° increases velocity deviation by approximately 15%, creating more complex turbulence conditions at the helideck center. Turbulence kinetic energy analysis provides a comprehensive assessment of flow conditions around the helideck. For East-West wind with crane at 0° horizontal angle, increasing boom vertical angle from 0° to 40° generates an elongated elliptical turbulent region of approximately 2500 m³ volume above the helideck and helicopter approach path. This turbulent zone corresponds to approximately a fivefold increase in turbulence kinetic energy compared to the horizontal boom configuration. At 30° crane horizontal angle (East-West wind), the vertical boom creates a high-velocity region around the helideck, with turbulent volume reaching approximately 500 m³ in the approach path. Similar patterns emerge at 150° horizontal angle, where vertical boom orientation generates substantial flow disturbance affecting approach corridor stability. Wind tunnel flow visualization confirms numerical model predictions. For East-West wind with a crane at 0° horizontal and vertical angles, flow streamlines show a transition from laminar to turbulent regime as the wind encounters the crane structure. When the crane orientation changes to a 90° horizontal angle, reducing the obstruction cross-section, flow remains predominantly laminar with reduced turbulence intensity. The comparison between numerical and experimental streamlines demonstrates acceptable agreement, validating the numerical approach for simulating turbulent flow around complex offshore structures at low wind speeds. Both methods capture the primary flow features, including separation zones, recirculation regions, and wake formation behind the crane structure.
4. DISCUSSION AND CONCLUSION
This study demonstrates that crane configuration significantly influences wind turbulence characteristics on offshore platform helidecks, with implications for helicopter operational safety. The research provides a quantitative assessment of how crane boom orientation affects turbulence patterns, enabling evidence-based recommendations for crane positioning during helicopter operations. The most critical finding relates to the adverse effect of increasing the crane boom vertical angle. Elevating the boom from horizontal (0°) to 40° generates extensive high-velocity turbulent regions above the helideck, reaching approximately 2500 m³ volume. This turbulent zone corresponds to approximately a fivefold increase in turbulence kinetic energy, exceeding established safety thresholds and necessitating suspension of helicopter operations according to NORSOK and CAP 437 criteria. Based on these results, the study recommends positioning crane booms horizontally during helicopter operations to minimize turbulence hazards. Crane horizontal orientation also substantially influences flow conditions. Maximum turbulence occurs when the crane boom is perpendicular to the wind flow crossing the helideck. For East-West wind direction, optimal crane positions correspond to horizontal angles of 90°, 120°, 150°, and 180°. For the Northeast-Southwest wind direction, optimal configurations similarly include 90°, 120°, 150°, and 180° horizontal angles. These orientations minimize boom interference with wind flow across the helideck. The validation process confirms that the RANS approach with the standard k-epsilon turbulence model adequately captures flow characteristics around complex offshore structures at low wind speeds. Acceptable agreement between numerical predictions, Silsoe cube field measurements, and wind tunnel experiments supports the methodology's reliability for engineering applications. Several limitations warrant consideration. The study assumes steady-state conditions with constant temperature, incompressible flow, and neglects atmospheric stratification and Earth's rotation effects. Future research should investigate unsteady flow phenomena, consider thermal effects from exhaust plumes, and evaluate additional equipment configurations. Experimental studies with Particle Image Velocimetry (PIV) could provide detailed validation of turbulent structures.
Practical implications extend beyond the specific platform geometry studied. The findings inform operational procedures for crane positioning during helicopter flights and contribute to design guidelines for future offshore installations. The demonstrated relationship between crane configuration and turbulence patterns supports the development of site-specific operational envelopes considering prevailing wind directions and crane usage patterns. In conclusion, this research establishes that crane boom orientation significantly affects helideck turbulence, with horizontal positioning providing optimal conditions for helicopter operations. The study contributes to enhanced safety in offshore aviation by providing quantitative guidance for crane management during flight operations.
5. ACKNOWLEDGEMENT
This research was supported by the Faculty of Marine Engineering, Khorramshahr University of Marine Science and Technology. The authors acknowledge the technical staff of the wind tunnel laboratory for their assistance with experimental measurements
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