A Reward-Directed Diffusion Framework for Generative Design Optimization

TL;DR

This paper introduces a reward-guided diffusion framework for engineering design optimization that efficiently generates high-performance designs, especially when performance metrics are costly or non-differentiable, achieving significant improvements in ship hull and airfoil designs.

Contribution

It develops a reward-directed sampling method within a diffusion model using soft-value guidance, enabling high-quality design generation beyond training data with reduced computational costs.

Findings

25% reduction in ship hull resistance

Over 10% improvement in airfoil lift-to-drag ratio

Effective generation of designs beyond training data

Abstract

This study presents a generative optimization framework that builds on a fine-tuned diffusion model and reward-directed sampling to generate high-performance engineering designs. The framework adopts a parametric representation of the design geometry and produces new parameter sets corresponding to designs with enhanced performance metrics. A key advantage of the reward-directed approach is its suitability for scenarios in which performance metrics rely on costly engineering simulations or surrogate models (e.g. graph-based, ensemble models, or tree-based) are non-differentiable or prohibitively expensive to differentiate. This work introduces the iterative use of a soft value function within a Markov decision process framework to achieve reward-guided decoding in the diffusion model. By incorporating soft-value guidance during both the training and inference phases, the proposed approach reduces computational and memory costs to achieve high-reward designs, even beyond the training data. Empirical results indicate that this iterative reward-directed method substantially improves the ability of the diffusion models to generate samples with reduced resistance in 3D ship hull design and enhanced hydrodynamic performance in 2D airfoil design tasks. The proposed framework generates samples that extend beyond the training data distribution, resulting in a greater 25 percent reduction in resistance for ship design and over 10 percent improvement in the lift-to-drag ratio for the 2D airfoil design. Successful integration of this model into the engineering design life cycle can enhance both designer productivity and overall design performance.