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Abstract In recent years, large language models (LLMs) and vision language models (VLMs) have excelled at tasks requiring human-like reasoning, inspiring researchers in engineering design to use language models (LMs) as surrogate evaluators of design concepts. But do these models actually evaluate designs like humans? While recent work has shown that LM evaluations sometimes fall within human variance on Likert-scale grading tasks, those tasks often obscure the reasoning and biases behind the scores. To address this limitation, we compare LM word embeddings (trained to capture semantic similarity) with human-rated similarity embeddings derived from triplet comparisons (“is A closer to B than C?”) on a dataset of design sketches and descriptions. We assess alignment via local tripletwise similarity and embedding distances, allowing for deeper insights than raw Likert-scale scores provide. We also explore whether describing the designs to LMs through text or images improves alignment with human judgments. Our findings suggest that text alone may not fully capture the nuances humans key into, yet text-based embeddings outperform their multimodal counterparts on satisfying local triplets. On the basis of these insights, we offer recommendations for effectively integrating LMs into design evaluation tasks. 

Many data analysis and design problems involve reasoning about points in high-dimensional space. A common strategy is to embed points from this high-dimensional space into a low-dimensional one. As we will show in this paper, a critical property of good embeddings is that they preserve isometry — i.e., preserving the geodesic distance between points on the original data manifold within their embedded locations in the latent space. However, enforcing isometry is non-trivial for common Neural embedding models, such as autoencoders and generative models. Moreover, while theoretically appealing, it is not clear to what extent enforcing isometry is really necessary for a given design or analysis task. This paper answers these questions by constructing an isometric embedding via an isometric autoencoder, which we employ to analyze an inverse airfoil design problem. Specifically, the paper describes how to train an isometric autoencoder and demonstrates its usefulness compared to non-isometric autoencoders on both simple pedagogical examples and for airfoil embeddings using the UIUC airfoil dataset. Our ablation study illustrates that enforcing isometry is necessary to accurately discover latent space clusters — a common analysis method researchers typically perform on low-dimensional embeddings. We also show how isometric autoencoders can uncover pathologies in typical gradient-based Shape Optimization solvers through an analysis on the SU2-optimized airfoil dataset, wherein we find an over-reliance of the gradient solver on angle of attack. Overall, this paper motivates the use of isometry constraints in Neural embedding models, particularly in cases where researchers or designer intend to use distance-based analysis measures (such as clustering, k-Nearest Neighbors methods, etc.) to analyze designs within the latent space. While this work focuses on airfoil design as an illustrative example, it applies to any domain where analyzing isometric design or data embeddings would be useful.