## 1 Introduction  
In the field of high-efficiency vibration isolation of marine propulsion devices, there is a serious conflict between low-frequency vibration isolation and shaft alignment stability [1]. The air spring vibration isolation system (ASVIS) can realize an excellent vibration isolation effect for the main engine. However, at the same time, the safe operation is affected by shaft misalignment, caused by strong disturbances such as output torque [2]. Shaft misalignment is divided into parallel misalignment (offset), angular misalignment (skew), and combined misalignment (including parallel misalignment and angular misalignment). The influence of parallel misalignment is dominant at two times the characteristic frequency [3]. Parallel misalignment shows a stronger 1X axial and torsional response, and the angular misalignment shows a very strong 3X harmonic component in the axial and torsional vibration response at one-third of the critical speed [4]. The control of alignment will affect the isolation effect of the system. [PERSON] et al. [2] used a simplified impedance method to estimate the isolation effect of the system. In practice, larger shaft misalignments will increase the vibration of the mounting foundation. However, the shaft misalignment has a more significant influence on the safe operation of the device than on the vibration isolation effect. Through a series of studies [5; 6; 7; 8; 9], the alignment stability and controllability of the air spring vibration isolation system for the main engine under the conventional running state have been preliminarily solved. When the new-type high power density main engine is applied to marine [10], there will be a problem of failure control of shaft alignment due to high torques. Compared to a conventional DC motor, the output torque dramatically increases as the power density can rise by dozens of times while the mass of the device changes at a glacial pace [11]. Compared with low parameter conditions, failures occur more prominently in high parameter conditions, such as high pressure, high power, high flow rate, large thrust-weight ratio, and so on [12]. In comparison with the traditional main engine, the alignment control failures of the high power density main engine (HPDME) at high power are more prominent [11]. When the traditional alignment control methods are still used in the HPDME, it will lead to poor alignment stability. The methods of [5; 6; 7; 8; 9] did not investigate the case where the output torque reaction is extremely prominent at high power density. It will force the system into an uncontrollable state, which is also known as an alignment control fault state. Therefore, it is necessary to reconfigure this alignment control fault state in the high output torque running state of the ASVIS for the HPDME (HPDME-ASVIS). With the increased complexity of engineering systems, there are some dynamic characteristics during system failure, such as sequence dependency, functional dependency, and spares [13]. [PERSON] et al. [14] analyzed that the main reason for many serious spacecraft accidents is defects in fault diagnosis and treatment, which are due to the lack of reconfigurability. [PERSON] et al. [15] reviewed and studied the reconfigurability of spacecraft control systems. They define reconfigurability as \"the ability of a system to overcome failures and recover all/partial of its established functions by autonomously changing spatial configurations or control algorithms within a safe time under certain resource allocation and operating conditions\" [15]. The measure of control reconfigurability can be considered intrinsic reconfigurability [16; 17]. [PERSON] et al. [16] used the controllability gramian under partial failure to estimate system reconfigurability, but this method is only suitable for control systems with limited energy consumption. [PERSON] et al.