## 1 Introduction  
Hydrostatic thrust bearings have excellent advantages of high film stiffness, large load capacity, low friction, good vibration damping behaviors, and precision relative motion even at low speeds, and are broadly employed in ultra-precision machine tools, aerospace industries, and so forth [1, 2, 3]. The design of hydrostatic thrust bearings requires accurate selection of a series of parameters such as bearing structure, pocket, restrictor, supply pressure, bearing clearance, and so on. Therein, the restrictor is an essential feature of the hydrostatic bearing which can significantly affect the performance characteristics of the hydrostatic bearing. In order to meet the prescribed requirements with respect to specific characteristics of load capacity, stiffness, precision, and so forth in a wide range of industrial products, the investigation on restrictors of hydrostatic bearings has been constantly updated over the last several decades. [PERSON] et al. comparatively studied the effects of various types of restrictors, such as orifice, capillary, membrane restrictors, and constant flow valve, on the performance of a multirecess flexible journal bearing [4]. [PERSON] et al. studied the static characteristics of a water-lubricated hydrostatic thrust bearing using a membrane restrictor to achieve higher stiffness and lower power consumption at high speeds [5]. [PERSON] et al. studied a hydrostatic bearing using a variable inherent restrictor with a thin metal plate and found that the bearing stiffness and response behaviors were improved and the oil flow was reduced by applying the inherent restrictor with a thin metal plate [6]. [PERSON] et al. studied the combined effects of the geometric shape of the recess (such as circular, rectangular, elliptical, and annular recesses) and the compensating device (such as capillary, orifice, and constant flow valve restrictors) on the performance of the hydrostatic thrust pad bearing [7]. Moreover, thermal effects of the hydrostatic bearing with orifice restrictors or porous domain were studied by the computational fluid dynamics (CFD) simulation method [8; 9; 10]. Orifice restrictors, which are very compact devices, are most commonly restrictors for hydrostatic bearings because of simple manufacturing [11; 12; 13; 14]. [PERSON] et al. analyzed the influence of wear on the performance of a four-pocket hybrid conical journal bearing compensated with an orifice restrictor of which the length-diameter ratio was more than 2.5 [15]. [PERSON] et al. investigated the performance of a four-pocket orifice-compensated hydrostatic journal bearing system with various recess shapes (square, circular, elliptical, and triangular) operating with micropolar lubricant [16]. [PERSON] et al. found that the orifice-compensated hybrid bearings were better from the point of stability than capillary-compensated hybrid bearings for a rigid rotor subject to a specific load [17]. [PERSON] et al. investigated the static performance behaviors of the orifice-compensated hydrostatic bearing with four lubrication-fluid cases by numerically solving the turbulent Reynolds equation [18]. [PERSON] et al. conducted a theoretical study on the static and dynamic performance characteristics of the hydrostatic multirecess journal bearings with orifice restrictors using non-Newtonian lubricants [19]. [PERSON] and [PERSON] investigated the effects of microdimples on the frictional power loss of the hybrid orifice-compensated circular thrust pad bearing system and found that partial texture thrust bearing could significantly decrease the frictional power loss [20; 21]. The orifice length-diameter ratio (OLDR) is one of the significant geometrical parameters of the orifice restrictor which directly affects the performance of the bearing. Although many papers had been published on the orifice-compensated hydrostatic bearing, the design of the OLDR is mainly dependent on engineering experience, and little literature was reported on the effects of the OLDR for the orifice-restricted hydrostatic thrust bearing.