## 1 Introduction  
Voice production is the basic and most important communication tool for humans. The ability of a person to produce normal voice or, more specifically, voiced speech depends on different factors and may change during the lifetime. These factors include predisposition, gender, training, age and state of health [1, 2]. Voice disorders restrict or even inhibit the oral communication of patients. As a result, both personal and economic restrictions arise that can lead to isolation and depression in patients [3, 4, 5]. Furthermore, the productivity reduction of the work-related disabilities of these people can be a significant social constraint [6, 7]. In this context, [PERSON] [8] estimated the loss to the US Gross National Product to be up to $186 billion per year assuming that only 5 to 10% of the US population suffer from communication disorders. This trend was also predicted to increase due to the change to a communication-based economy in the present century. The associated annual healthcare cost of these patients totals hundreds of million dollars, which is comparable to that for other chronic diseases [9]. In general, the negative impact of voice disorders on quality of life targets not only the occupational group but also the general population of all societies [10; 11; 12; 13; 14]. Phonation is the process of voice production in the human larynx. Periodic oscillations of the vocal folds are induced by the airflow from the lungs and produce the basic sound of the voice. This flow-induced sound is filtered in the vocal tract, forming the typical spectral characteristics of voiced speech. The production of sound sources in the larynx is a complex process which results from the fluid-structure interaction between the airflow and the structural mechanics of the tissue of the vocal folds. A major problem in voice research and clinical diagnostics is the restricted access to the larynx during phonation, which allows only visual inspection of the vibration of the vocal folds with stroboscopy [15] or high-speed videoendoscopy [16; 17]. Other measuring techniques include acoustic voice measurement and electroglottography (EGG) [18], both of which provide indirect measurements of the process in the larynx. As a consequence, synthetic [19] and ex-vivo [20] larynx models have been established in experimental voice research that provide almost unconfined access to the laryngeal flow region. As an alternative and complementary method, computational models have been developed in recent decades. With the development of advanced numerical methods and improvement of computational power, more aspects of the phonation process, from glottal flow analysis [21; 22; 23; 24; 25] to mechanical analysis of oscillations of the vocal folds [26; 27; 28] and acoustic analysis of voice sources [29; 30; 31; 32], have been investigated numerically in detail. These computational models have the advantage of simulating the entire process with enormously high spatial and temporal resolution in the flow region and the structural domain of the vocal fold tissue. However, the ultimate goal of employing these computational tools in clinical work, for instance as a clinically standardized pre-surgery tool, has not yet been achieved. The main reason is the high computational costs for these highly accurate simulations. Computational fluid dynamics (CFD) and structural mechanics have been employed in recent decades to investigate biomedical processes, especially hemodynamics [33; 34; 35]. These computational tools have also been applied for potential pre- and post-surgical planning of cardiovascular [36; 37; 38] and upper airway systems [39; 40; 41; 42; 43]. [PERSON] et al. [42] used CFD tools to develop an effective surgical strategy for patients with obstructive airway disorders by comparing different virtual surgery techniques for treating coexisting glottic and subglottic stenosis by measuring the airway resistance and pressure distribution in airway lumen.