Equal-Area Planform Screening of Isolated Low-Rise Offshore-Intended Modules: Separating Wind Exposure from Projected-Area Drag

Planform can change the mean wind force on exposed offshore-intended modules, but isolating that effect requires a deliberately controlled screening model. This study compares nine equal-plan-area, equal-height idealized isolated modules from a rounded square to a circle and at canonical face/vertex endpoints, using steady Reynolds-averaged Navier–Stokes simulations (PHOENICS, Chen–Kim k–ε). The bodies are isolated, deck-free geometries under one +X inflow. Equal plan area is a geometric control and does not imply equal usable space, constructability or structural performance. A common-area coefficient compares integrated mean streamwise force under the shared footprint, whereas an actual-projected-area coefficient reports drag per exposed area. Pressure contributed 98.7–99.4% of the integrated streamwise force. On the common production grid, the circle and vertex-oriented dodecagon reduced the common-area coefficient by 25.3% and 21.9% relative to Square 0°, whereas Square 45° increased it by 57.8%. Targeted uniform fine-grid checks changed the corresponding coefficients by −2.83% for the circle, −5.04% for Dodecagon 15° and −13.17% for Square 45°, preserving the principal large-effect contrasts. At fine resolution, Square 45° remained 39.3% above Square 0°, close to its 39.8% increase in frontal exposure, while its projected-area drag factor relative to Square 0° was essentially neutral (η = 0.997). The Square 0° three-grid sequence converged monotonically, with a 1.65% medium-to-fine change and a 1.80% fine-grid GCI. The streamwise-force resultant height remained within zcp/H = 0.466–0.494 on the production grid, and targeted fine checks showed that moment sensitivity was driven mainly by Fx rather than large shifts in the resultant height. A matched Tokyo Polytechnic University benchmark reproduced mean-pressure ordering (r = 0.942) and integrated pressure drag within 0.75%, while underpredicting separated-flow suction. The evidence supports comparative, pressure-dominated integrated mean streamwise loading and the associated mean streamwise-force overturning metric within the stated geometry and inflow. It does not validate roof uplift, local cladding pressures, total base or torsional moments, connection reactions, peak or unsteady loads, a full directional envelope, or complete offshore-topside layouts. The dual normalization is a reporting diagnostic for selecting cases for higher-fidelity assessment, not a code-design rule.