Research- Publications

This study investigates how five selected upper-body parameters, including Neck Angle (NA), Head Angle (HA), Shoulder Alignment Angle (SAA), Thoracic Kyphosis Angle (TKA), and Sitting Acromial Height (SAH), are related to the measures of human-seat interaction in headrest region, which involve the perceived comfort, contact loading, and muscle activity. Experiments with 25 participants were carried out on a conventional aircraft seat at different conditions to identify and understand the significant upper body parameters that affect the human-seat interaction through cross-correlation analyses. The results show the occupant’s initial HA, SAH, and SAA are correlated with multiple human-seat interaction measures for general seating. Among the body parameters

investigated, HA appears to be the most influential factor in the seating experience in the upper body region under various sitting conditions. The head movement (ΔHA) with different backrest inclinations is found to be closely associated with the headrest contact loading. This study  highlights the dependence of the sitting experience on the characteristics of an individual’s natural upper-body position and movement when seated, considering both subjective and objective measures. The findings from this study can be used as anthropometric reference guidelines in seat design and optimization to satisfy more customized demands from the perspective of the individual’s body characteristics.

Aircraft seats play a key role in the competition between aircraft companies seeking to differentiate themselves in terms of passengers’ inflight experience. The seat design process relies on computational and experimental methods based on subjective measures, such as comfort rating questionnaires, and objective comfort indicators of seat-occupant interaction, such as contact pressure distribution and muscle activation. Previous studies around muscle activity for seating comfort assessment have primarily focused on more active scenarios or active systems. As such, there are limited studies about the role of muscle force in normal and relaxed sitting conditions, common in aircraft settings. This paper explores the relationship between activities of the neck muscles, sternocleidomastoid, and upper trapezius, measured from human participants seated sedentarily on conventional business aircraft seats and their perceived comfort with different backrest inclinations. The results show, for normal seating without neck pillow, no significant association is found between the backrest inclination and the neck’s comfort or muscle activation. For general seating across different backrest inclinations, a positive medium correlation between muscle activation and comfort is found in upper trapezius (R = 0.5332, p = 0.0187). This work serves as a pilot study of this new approach of comfort evaluation using muscle feedback in seat designing processes and highlights the posterior’s effect to seating experience in the neck region.Aircraft seats play a key role in the competition between aircraft companies seeking to differentiate themselves in terms of passengers’ inflight experience. The seat design process relies on computational and experimental methods based on subjective measures, such as comfort rating questionnaires, and objective comfort indicators of seat-occupant interaction, such as contact pressure distribution and muscle activation. Previous studies around muscle activity for seating comfort assessment have primarily focused on more active scenarios or active systems. As such, there are limited studies about the role of muscle force in normal and relaxed sitting conditions, common in aircraft settings. This paper explores the relationship between activities of the neck muscles, sternocleidomastoid, and upper trapezius, measured from human participants seated sedentarily on conventional business aircraft seats and their perceived comfort with different backrest inclinations. The results show, for normal seating without neck pillow, no significant association is found between the backrest inclination and the neck’s comfort or muscle activation. For general seating across different backrest inclinations, a positive medium correlation between muscle activation and comfort is found in upper trapezius (R = 0.5332, p = 0.0187). This work serves as a pilot study of this new approach of comfort evaluation using muscle feedback in seat designing processes and highlights the posterior’s effect to seating experience in the neck region.

The objective of this systematic review is to investigate the various approaches that have been undertaken in finite element analysis (FEA) of human–seat interactions and synthesize the existing knowledge. With advances in numerical simulation and digital human modeling, FEA has emerged as a powerful tool to study seating comfort and discomfort. FEA employs various biomechanical factors to predict the contact stress and pressure distribution in a particular seat design. Given the complexity of human–seat interaction, several modeling and processing steps are required to conduct realistic FEA. The steps of how to perform an FEA simulation on human–seat interactions, the different models used, the model mesh compositions, and the material properties are discussed and reviewed in this paper. This can be used as a guideline for future studies in the context of FEA of human–seat interactions. 

Limited studies present the comprehensive biomechanical analysis of sitting consisting of the external load and muscle force evaluation. This study uses a 3D multibody model representing the upper body to simulate the sitting postures and backrest support through the Newton-Euler equations. Then, the back-backrest contact pressure distribution is simulated using the contact mechanics method. Additionally, the forces of neck muscles are calculated based on inverse dynamic and static optimization. The muscle force result is compared to the simulation by OpenSim 4.2. A case study is presented, with the scaled human model and two simple backrest configurations with different headrest widths (type A and type B) based on a parameterized backrest model. The contact force, pressure distribution, and neck muscle forces are simulated while sitting with a backrest recline angle of 30∘, 40∘, and 50∘ (from the vertical direction). It is found that the analyzed different backrest designs generate different contact loadings and neck muscle forces. The type A backrest with a narrower headrest width generates 13.7 ±1.9% higher load in the upper thoracic region but lower support on the head compared to type B. Additionally, 17.1% higher peak contact pressure at maximum was found on Type A. Regarding the muscle forces, Type A reduces the overall tension of neck muscles by 54.2% compared to Type B; the muscle activations on both backrests remain low (<11.2% of maximum muscle force). The deviation and sources of error of the neck muscle force results from the proposed model and OpenSim 4.2 were discussed. The proposed model can be applied to predict static loadings required for back support and evaluate the backrest design from the user perspective. 

The contact loading and pressure distribution on the back are important measures to assess the comfort of a seat's backrest. On the other hand, the backrest design also influences the pressure on the back. Limited studies show how the variation on the backrest affects the loadings to the back surface, especially for the upper trunk region of the human body. In this study, a parameterized backrest model with the back support and headrest combined is created to describe design variations with different headrests. This study uses a 3D multibody model to evaluate the loadings and predict the pressure to analyze the headrest design's influences on the loading and pressure within the head-cervical-thoracic region. As a result, the headrest variation based on the parameterized model impacts the supportive load on the head. Within the thoracic region, the upper part is more sensitive to the change of design and sitting condition than the lower part. Different designs also affect the location of higher-pressure areas. The pros and cons of the analyzed designs are discussed. This study provides an example of assessing the design using the proposed load and pressure prediction method for the backrest.