Descriptions of Recommended Analysis Codes

Bearings

ROMAC has become well-known for the excellent performance of our fluid film bearing analysis tools. These codes are capable of analyzing various types of fixed geometry bearings, tilting pad bearings, squeeze film dampers, modern bearing designs with unique fluid delivery methods, and bearings operating under unique fluid conditions. Descriptions of some of our most popular codes follow.

THBRG and THPAD, two bearing codes developed by a ROMAC student in the late-1980s and updated multiple times since, are one-dimensional, radial fixed geometry and tilting pad bearing solvers that have been widely validated and used by industry for design and performance analysis. Both codes include thermal effects, laminar and turbulent flows, and cavitation models. THBRG can be used to analyze plain journal, elliptical, offset, two axial groove, and multi-lobe bearings. THPAD is used to analyze conventional tilting pad bearings and also allows the user to include various thermal and mechanical deformations. Both of these analysis tools have been found by industry users to be accurate while having very short run times.

MAXBRG and HYDROBRG are two bearing analysis tools developed by a ROMAC student in the mid-2000s, with MAXBRG in the process of being further enhanced by a current ROMAC student. MAXBRG is a highly accurate two-dimensional radial bearing solver for fixed geometry, tilting pad, leading edge groove, spray bar, and pressure dam bearings. This code includes all of the features of codes like THBRG and THPAD but with options to analyze new bearing geometries, new fluid flow types (ex. high ambient pressure, axial flow, starvation, etc.), and a wide range of thermal and deformation options. Also widely validated, this code is known for its high degree of accuracy while still maintaining reasonable run times. HYDROBRG is a two-dimensional solver for hybrid hydrostatic/hydrodynamic radial bearings, providing a validated tool capable of analyzing these unique bearing designs with hydrostatic lift pockets and grooves machined into the bearing surface to provide support during high load, low speed operation.

SLEEVEBRG is a student-developed code released in 2015 that is used to analyze submerged cylindrical bearings lubricated from the axial ends with low viscosity lubricants including water. This two-dimensional Reynold’s equation solver accounts for the inertia inherent in these low viscosity environments, providing users with stiffness, damping, and added mass coefficients for rotordynamic analyses. The author of the code also created a soon-to-be-released squeeze film damper analysis tool MAXSFD, a two-dimensional solver for squeeze film dampers that includes the effects of end seals, supply holes, and circumferential grooves.

THRUST is ROMAC’s primary analysis tool for axial thrust bearings. Developed by a ROMAC student in the mid-1990s and updated as recently as 2015, this code is also popular and widely used by our membership due to its high degree of accuracy, extensive validation, and versatility. This code solves a two-dimensional Reynold’s equation along with a three-dimensional energy equation for over 15 different thrust pad geometries. Various thermal and deformation effects are also included along with a wide range of options for including turbulence, cavitation, centrifugal inertia, and independent material properties for the runner and various parts of the bearing pad.

MAGAUD is a magnetic bearing audit package developed in the late-1990s and updated recently by ROMAC faculty. This package includes codes for constructing system models, assessing actuator performance, determining system forced response and stability, and for converting measured frequency response functions into equivalent transfer functions.

Rotordynamics

ROMAC offers a wide range of rotordynamics programs for lateral, axial, and torsional systems, a few of which are highlighted below.

ROTORSOL, a new industry standard in rotordynamic analysis, is a finite element-based rotordynamics solver that was developed by a ROMAC student and released in 2013. This analysis tool solves for up to six degrees of freedom per node for coupled lateral, axial, and torsional analyses. This code solves for steady state critical speeds, force response, and damped mode shapes while including various turbomachinery components along with multiple rotor capabilities.

GEARROTOR is a finite element-based rotordynamics tool for multi-shaft systems connected by spur or helical gears. Released in 2014, this code solves for up to six degrees of freedom per node for coupled lateral, axial, and torsional analyses, including a 12 degree of freedom gear stiffness model. This code solves for steady state critical speeds, force response, and damped mode shapes while including various turbomachinery components.

GEARTRAN is a soon-to-be-released finite-element based rotordynamics code for geared, multi-shaft systems. This time-transient code solves for six degrees of freedom per node for coupled lateral, axial, and torsional analyses and accounts for complex time-varying gear behavior including backlash and parametric excitation from time-varying tooth stiffness. Outputs include 3D whirl plots, time-varying displacement and orbit plots for all nodes with FFTs, time-varying gear mesh stiffness and forces with FFTs, and time-varying dynamic transmission error with FFTs.

BALOPT provides multiplane and multispeed balance capabilities with the options of least squares or min-max balancing solutions. Influence coefficients can either be calculated or user-specified. Runout compensation and constraint capabilities are included. Practical constraints can be handled through weighting or directly specified such as response amplitude or maximum correction weight. Correction weight splitting is also available.

TWIST2 calculates the undamped torsional natural frequencies and mode shapes for single shafts, geared shafting with branching, or looped systems. The finite element method is used to obtain the set of equations governing the motion of the system. The program also determines the steady-state forced response characteristics of the system from harmonic torsional input using modal analysis. In the forced response calculations, damping may be added to the system through modal damping ratios or discrete dampers. The input torque magnitudes and phases may be specified as a function of excitation frequency. In addition, several modeling features such as disk models and the “degree rule” are included.

TORTRAN3 is a transient response program for torsional rotor systems. It can analyze rotor systems with non-linear couplings that are driven by synchronous machines, variable frequency drives, or any other torsional forcing function that can be expressed as a function of time or rotor speed. One important feature of TORTRAN3 is its cumulative fatigue analysis. Rotors that undergo large periodic loading, such as synchronous motor driven machines during startup, may fail after a finite number of starts.

Seals

ROMAC also offers a wide range of annular seal analysis tools for various seal geometries and fluid environments in turbomachinery. A few highlights of these capabilities follow.

DAMPERSEAL is a seal analysis tool released in 2016 as part of RotorLab+ 4.0. This code performs analyses of smooth and hole pattern seals using Hirs bulk flow theory for liquids, gases, or a combination of the two. Outputs include seal leakage, location-specific flow properties, and dynamic coefficients.

HybridSeal is a seal analysis tool released in 2016 as part of RotorLab+ 4.0 that utilizes a combination of CFD and bulk flow analysis to achieve the high accuracy of CFD with the shorter analysis times of bulk flow codes. This code is designed to analyze smooth and hole pattern seals. Outputs include seal leakage, location-specific flow properties, and dynamic coefficients.

Laby3 is a widely used bulk flow code for gas labyrinth seal analysis. This code calculates leakage and dynamic coefficients for straight-through and uniform interlocking labyrinth seals.

Seal3 is a bulk flow analysis for liquid annular seals. This code calculates leakage and dynamic coefficients for smooth and circumferentially grooved seals.

New codes for radial bearings, thrust bearings, helical seals, brush seals, and labyrinth seals are also currently in development by ROMAC students.