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The Finish Line Vol. 28 • November 2022 [Q3 2022]

Understanding Mode Shapes and Advancing Frequency Analysis and Testing Capabilities at RMS

James Cardillo, Structural Analyst

Vibration analysis is an enabling technology shared across all of the RMS product families. Careful frequency analysis and product frequency tuning are used extensively at RMS and throughout the rotating machinery industry to ensure that an adequate separation margin exists between natural frequencies and excitation sources. Resonance coincidence in rotating machinery can have disastrous consequences, which designers and engineers take extensive measures to avoid.

On the surface, designing around resonance boils down to a simple game of avoidance: modes or natural frequencies must be altered such that they don’t coincide with known excitation frequencies. Alternatively, excitation sources can be changed to achieve a separation margin. To minimize risk, account for uncertainty, and recognize the fact that resonances can be excited over a “band” or range of frequencies (not just a single value), designers aim to create an adequate separation margin between natural frequencies and excitation frequencies. A Campbell diagram like the one shown below is typically used as a tool to aid in the design process which is often iterative in nature.

• Continued below •

Considering an axial compressor blade as an example, the task usually becomes one of altering the structure of the blade to alter its stiffness and mass. The combined effect results in natural frequencies shifting to higher or lower values. The goal is to shift these frequencies such that they remain sufficiently far away from any identified excitation sources. However, this simple game of avoidance becomes more complicated when one has to consider the actual response shapes of the blade’s natural frequencies in comparison to the nature and shapes of the excitation sources. Moreover, the ability to simply move these natural frequencies around by altering the design becomes further complicated by design constraints such as aerodynamic performance, weight, clearance, geometry, structural integrity, etc.

Not all natural frequencies are created equal and each natural frequency identified has its corresponding response shape or mode shape. For example, the first four mode shapes for a typical axial compressor blade are shown below.

It’s quite commonplace throughout the industry to calculate these mode shapes using finite element analysis software. The finite element method lends itself quite well to predicting both the frequencies and corresponding mode shapes for a given structure (as long as the user can provide the correct inputs). However, situations arise when the correct inputs are difficult to provide for a finite element model. In certain situations, it becomes necessary to correlate not only the predicted natural frequencies from a finite element model to the experimentally measured frequencies but also to correlate the predicted mode shapes with experimentally measured mode shapes. The ability to experimentally measure a structure’s mode shape is less commonplace and a more involved task that requires an in-depth testing process, additional tools, and more expertise. For these reasons, RMS has limited the majority of its frequency testing to experimentally measuring natural frequencies and correlating those frequencies to frequencies predicted using finite element modeling. As demand grows for a deeper understanding of vibrations, mode shapes, and how structures actually respond to real-world excitations, RMS has taken steps to meet this demand by expanding its frequency testing capabilities. Using improved technology and testing methods, RMS can now measure frequency response functions and mode shapes through physical testing.

RMS employs several methods and tools to experimentally measure mode shapes. The first step in the process involves performing a “roving accelerometer” or “roving impact” test to measure the frequency response at several locations on a physical part. In the axial compressor blade example, this involves measuring the response to a controlled excitation on a compressor blade at a specific location using an accelerometer. One then “roves” or moves the accelerometer to another location on the blade, repeats the excitation, and measures the response at the new location.

The procedure requires precise application as the tester needs to place the accelerometer at key locations on the structure to properly measure the response. Alternatively, one can employ the principle of “Maxwell’s reciprocity”, and rove the excitation (impact hammer) location while leaving the accelerometer stationary. However, extreme caution must be taken when using Maxwell’s reciprocity with rotating machinery as the assumptions behind it are violated once the machine is set in motion.

In most cases, sensor locations can be determined using a Modal Assurance Criteria tool. However, for the current compressor blade demonstration, a simple grid of sensor locations was adequate for resolving the easy-wise bending modes. The real blade with associated sensor locations marked is shown below on the left. A “skeleton” or flat wire-frame model of the blade is shown with the same measurement locations on the right.

Accessibility can be a challenge with sensor and impact sites. Interpolation is often used between measurement locations and locations where the tester could not gain access. From each measurement location, valuable frequency information is obtained in the form of a Frequency Response Function or FRF. The Frequency Response Function has certain characteristics that allow the calculation of the structure’s natural frequencies, and when combined with the FRFs at other measurement locations on the blade, this information can be used to calculate the actual mode shapes. A side benefit of measuring the FRFs and curve fitting specialized polynomials to these functions is the ability to calculate the structural “damping” associated with each natural frequency. Damping can be difficult to calculate for certain modes and largely depends on how close the polynomial can approximate or “fit” to the measured FRF. Shown below is a typical FRF measured at one location on the blade shown above. Not all FRFs are identical and across different blades, not all modes necessarily occur in the exact same order (The stiff-wise and 2nd order bending modes often switch places depending on the structural characteristics of the blade).

For each location or grid test point on the blade, a frequency response function like the one above is created. Polynomials are fit to the peaks in the frequency response function (the peaks are the resonances or natural frequencies of the structure at that location). With these polynomials, a quantity called a “residue” is calculated. These quantities are then “mapped” onto the skeleton model shown previously. Frequency response functions and curve fits are assigned to each of these measurement points or grid points on the skeleton model. In between these grid points, interpolations are performed and sometimes additional guidance is necessary for the interpolations depending on how many test points were created (in general, the more test points, the better the quality of the interpolation). Finally, with this information, the mode shape can be calculated based on the FRFs and calculated “residues”. Two of the measured mode shapes are shown below for the test blade shown previously:

The two modes measured from the test correlate to the fundamental “Easy-Wise Bending” and “2nd Order Bending” modes shown previously. New possibilities arise from being able to experimentally measure mode shapes.

For the first time, RMS can correlate predicted FE frequencies and mode shapes to improve the accuracy and fidelity of FE models. Additionally, damping can be experimentally calculated and used to calibrate and improve FE model accuracy. The experimentally measured mode shapes also provide an opportunity to determine mode shapes for complex assemblies where FE models are not available or possible due to configuration… Furthermore, RMS design engineers can pursue more targeted frequency tuning and optimizations based on experimentally measured mode shape data, and ensure that not only frequencies were altered as desired, but actual mode shapes were altered in a more favorable way. This paves the way for new and exciting innovations when it comes to frequency tuning and design at RMS.

RMS Engineering Capabilities

This edition of 'The Finish Line' includes:

  • Understanding Mode Shapes and Advancing Frequency Analysis and Testing Capabilities at RMS
  • RMS Metrology In Action
  • Digital Twins: Using Advanced Metrology Technology Leads To Improved Customer Outcomes
  • RMS Philanthropy: Supporting Pediatric Cancer Foundation of The Lehigh Valley
  • RMS at TPS Recap
  • New Hires
  • Turbo Toons
Read previous editions of 'The Finish Line'

RMS Metrology in Action

Marc Rubino, Director of Metrology Services | Garrett Lewis, Principal Technologist

RMS’s Metrology team was recently at a customer site to scan their centrifugal compressor as part of an upcoming rerate project. This on-site scanning required abbreviated machine downtime to gather the critical dimensional data needed to engineer a solution for the customer thanks to the use of 3D scanning and probing technology.

During RMS’s recent field scanning operation, the team used a combination of portable laser scanners and probes to completely map the impeller, stationary flowpath, and casing of the customer’s centrifugal compressor. This machine was left in place during this work and the customer experienced limited downtime. RMS will utilize the resulting digital models to work on the rerate design for this customer’s machine. These digital models will live on as a digital twin and assist with future 3D assembly work. On-site metrology data-gathering projects like this are only part of the solutions offered by RMS’s Metrology team.

RMS Metrology Solutions

RMS is committed to world-class engineered solutions to best serve the needs of our customers. Part of this commitment requires the investment and use of cutting-edge tools to gather critical data in an accurate and timely manner. Thanks to the latest scanning technology fielded by experienced operators, the RMS Metrology team can gather critical measurements in our shops and in the field.

Reduced Inspection Lead Times

With the use of laser scanning tools, RMS offers rapid inspections to gather accurate dimensional data. 3D scanned inspections allow for the creation of a complete model for every component of your machine and the ability to quickly identify tolerance deficiencies. This meticulous data-gathering capability leads to more detailed inspections and a digital twin of the subject machine to reference during future overhauls to compare wear.

Multi-OEM Parts Support

Gathering dimensional data is only part of creating spare parts for your machines. RMS is not just a parts replicator and will pair the dimensions gathered by the RMS Metrology team with engineering support. These engineered parts will not only fit but meet, or exceed, their performance and quality requirements

Streamlined Overhauls

The use of 3D scanning technology and probing allows RMS to reduce the time needed to complete an overhaul while delivering superior results. During the assembly process, 3D scanning is used to verify fits, clearances, and compare physical results against engineering models. Rapid scanning means that dimensional information is quickly verified to support quality results in a shorter time frame.

Field Scanning Support

The RMS Metrology team is a mobile unit capable of scanning machinery and parts around the world. RMS can arrive at your site to provide scanning support to execute a host of projects. The use of 3D scanning means that RMS can gather critical dimensional data with reduced machine downtime and unparalleled accuracy.

Thanks to RMS’s combination of the latest in metrology tools and software, coupled with an experienced engineering staff, RMS offers the highest quality solutions for our customers. Reach out to your RMS sales rep today to learn more about how RMS’s metrology team can support your needs today.

RMS Engineering Services

Digital Twins

Using Advanced Metrology Technology Leads To Improved Customer Outcomes

Marc Rubino, Director of Metrology Services | Garrett Lewis, Principal Technologist

After the scanning is complete and the data is collected, the RMS Metrology team begins work on the creation of digital twins. Digital twins are files of scanned machines and components that RMS stores in a controlled environment. These 3D scan files assist with the assembly of machines, prepare for future inspections, and even plan upgrades and rerates before future overhauls.

At the start of a project, the RMS Metrology team scans a machine to catalog critical data regarding the fit, critical clearances, and condition of a machine. This work can be done in the field or the shop depending on the project, but the impactful results remain the same. With this data, the RMS Metrology team can support both the engineering and shop to assist with an expedited inspection and then reassembly of the machine to meet customer requirements.

The digital twin is stored in RMS’s controlled filing system for future reference. When this same machine returns for its next overhaul, the scan data of the current condition is compared to the previous model. This allows the RMS team to quickly identify machine wear patterns caused by its most recent service run for expedited inspections. This precision data also allows for a detailed report showing the exact locations and dimensional data of complex wear patterns.

Digital twin data also allows for upgrades and rerates while a machine operates. The digital twin of a machine contains all of the critical dimensional data allowing RMS’s engineering team to create bespoke upgrades without the need to shut down mid-run.

The critical historical database of digital twins allows for a complete record of a machine through every phase of its operating life. This detailed record allows for predictive overhaul plans based on past machine wear patterns and the ability to assemble quicker thanks to detailed clearance data.

To learn more about digital twins for your machinery, reach out to your RMS sales rep to see how digital twins can support your machinery.

Contact Your RMS Rep

RMS Philanthropy

Kathy Ehasz, Vice President of Human Resources | Jennifer Zeigler, Benefit Specialist

RMS recently held a company fund raiser to support the Pediatric Cancer Foundation of The Lehigh Valley. This incredible non-profit organization supports local families around the RMS Bethlehem, PA location who are managing the impact of pediatric cancer. PCFLV provides a host of services to help families overcome pediatric cancer and ensure both the parents and children are surrounded by a caring community. RMS’s sponsorship of this special charity will help PCFLV execute its live changing services.

PCFLV supports families from diagnosis on, providing support from a team of dedicated volunteers that use donations to provide:

  • CHEMO CIRCUS: PCFLV staff and volunteers visit the Pediatric Hematology and Infusion Clinic at the Lehigh Valley Reilly Children’s Hospital each month, taking gifts and crafts for children receiving treatment; often a clown, superhero or princess accompany them. PCFLV will also make a visit to the in-patient unit if requested by a family.
  • FAMILY ASSISTANCE FUND: PCFLV created a fund at Lehigh Valley Reilly Children’s Hospital, which provides funding for bills, mortgages, utilities, etc.
  • CAREGIVER COFFEE: An opportunity for parents to grab a cup of coffee, to talk and to receive gas and grocery cards.
  • GAS AND GROCERY GIFT CARDS: To help pay for gas to get to appointments and healthy food when at home.
  • HOSPITAL CAFETERIA CARDS: To defray the cost of living in the hospital with your child.
  • BIRTHDAY CARDS FOR KIDS AND SIBLINGS: PCFLV sends a birthday card and gift to cancer kids and their siblings until their 18th birthday; $25 for cancer kids and bereaved siblings; $5 for siblings.
  • KIDS KONNECT PROGRAM: PCFLV holds events for kids with cancer and their siblings, along with bereaved siblings; often an art project is involved, along with food and fun games. These events are broken up into various age groups and the program changes each month.
  • MOM'S, DAD'S AND PARENTS' NIGHT: PCFLV holds rotating events for moms, dads and parents. Attendees are able to chat with each other and provide support, all while doing an art project or an activity.
  • TEEN NIGHTS: PCFLV hosts events specifically for teenage cancer patients, survivors and their siblings, along with teenage bereaved siblings; the venue/activity changes each month.
  • COLLEGE SCHOLARSHIPS: PCFLV provides a one-time, $3,000 scholarship to a higher education institution for any cancer patient who wishes to further their education.
  • CAMP SMILE: Camp Smile is a week-long day camp offered to kids with cancer and their siblings, along with bereaved siblings (campers are aged 4-15); activities each day include art, theater, sports, swimming, games and typical camp fun.
  • ADOPT-A-FAMILY PROGRAM: PCFLV distributes gift cards to families who need assistance with Holiday shopping.
  • EVENT AND ENTERTAINMENT TICKETS: PCFLV provides tickets to local sports and entertainment events to allow families a bit of fun and time to bond.
  • DORNEY DAY: PCFLV, along with several sponsors, provide a day of fall fun at Dorney Park. Tickets and lunch are provided.
  • BACK TO SCHOOL SUPPLIES: PCFLV provides a backpack filled with school supplies to families who need assistance.

Upon completion of treatment, PCFLV assist with transitioning back to a more normal life. All survivors and their families are part of PCFLV community forever with continued community support. PCFLV also continues to provide services and programs to families who have lost a child to cancer. These families have bonded with fellow pediatric cancer families and PCFLV staff, and they are invited to join in any of our activities and events.

RMS is proud to support this impactful local charity with philanthropic support to make our local community a better place. If you are interested in learning more about PCFLV or donating please see the below link.

Donate to Support PCFLV's Work

RMS at TPS

Chris Okula, Marketing Lead

RMS was recently part of the Turbomachinery and Pump Symposia that took place in Houston, TX this past September. During this trade show event RMS had a booth on the trade show floor, held a Monday evening dinner event, and a casino night hospitality suite on Tuesday evening. RMS is proud to share in this exciting event with all of our colleagues from the rotating equipment industry.

Thank you to all those who participated and if we missed, we hope to see you in 2023!

Turbo Toons

Marc Rubino, Quality Manager

New Hires

Christopher Suarez, CNC Lathe Machinist — Chris joins the RMS Breaux Machine Works team as a CNC Lathe Machinist. Chris is a Skilled machinist with 15 years experience as a CNC set up/operator for lathe; experience with slant bed, horizontal, live tooling, manual chuck, and hydraulic.

Jerry Hymel, CNC Lathe Machinist — Jerry joins the RMS Breaux Machine Works team as a CNC Lathe Machinist. Jerry has over 20 years of precision machining experience with a strong attention to detail. RMS looks forwarding to having Jerry as part of our expert machining team.

Rogelio Orduna, CNC HBM Machinist — Rogelio joins the RMS Breaux Machine Works team as a CNC HBM Machinist. Rogelio offers over 10 years of experience in HBM-Horizontal Boring Mill CNC machining. Rogelio is also an expert in ejector and gun drilling as well as Kuraki and Toyoda mills. RMS is excited to have Rogelio as part of the team.

Douglas Steen, CNC Mill-Programmer — Douglas joins the RMS Breaux Machine Works team as a CNC Mill-Programmer. Douglas has four years of experience as a Manufacturing Engineer, seventeen years of Mill Programming experience, twelve years of Lathe and Mill/Turn Programming, and twelve years of experience operating G-code CNC mills. Douglas is a great addition to the RMS team and we look forward to having him on board.

Stephen Zepeda, Mechanic's Helper — Stephen joins the RMS Mepco shop team as a Mechanic’s Helper. Stephen has experience working as a pipefitter helper, ironworker helper, and mechanics helper. Stephen’s interest to learn more and support the mechanic team as he grows in his career makes him a great fit for the RMS Mepco team.

Michael Dargay, Manufacturing/Production Scheduler — Michael joins the RMS Mepco team as a Manufacturing and Production Scheduler. Michael offers over 37 years of manufacturing experience in leadership roles. Michael’s experience includes managing the manufacture of critical machined parts used in coal mining, managing a 40,000ft2 metal shop, and most recently the manufacture of custom lighting solutions for skyscrapers. Michael’s diverse manufacturing experience makes him a great fit for the RMS Mepco shop team.

Eric Dubose, 2nd Shift Mechanic — Eric is a highly skilled Millwright with an exceptional ability to produce and repair mechanical equipment with precision and strong attention to detail. Eric has over 26 years of Millwright experience working on rotating machinery in both field and shop environments. RMS is excited to welcome Eric to the RMS Mepco shop team.

Michael Muehr, 2nd Shift Machinist — Michael joins the RMS Mepco shop team with over 15 years of machining experience. Michael received a Certificate in Machining from the College of Mainland. Michael’s experience repairing and supporting rotating machinery makes his a great fit for RMS.

Jon Burnett, Mechanic — Jon joins the RMS Mepco shop team as an experienced rotating equipment mechanic. Jon has over 10 years of rotating machinery experience in the repair and overhaul of rotating equipment. Jon also has experience managing rotor repair teams. RMS is excited to have Jon as part of the team.

Dylan Brown, Engineering Intern — RMS is pleased to welcome Dylan to our engineering internship program. Dylan is an engineering student at Drexel University where he is pursuing his Bachelors of Science in Mechanical Engineering. Prior to RMS, Dylan worked as an intern at Philadelphia Gear where he supported the development of a new gear box. We look forward to having Dylan on board as he works through his engineering degree journey.

Jaime Hinke, Applications Engineer — The RMS Applications team is pleased to welcome Jaime on board. Jamie offers over 17 years of engineering experience and a Masters Degree in Mechanical Engineering from the University of Houston. Jaime started his career working at NASA where he worked as a Robotic Systems Engineer. From there, Jaime’s career took him into the world of rotating machinery where he worked as an Applications Engineer. RMS is excited to have Jaime on board as part of our growing team.

Evan DeBonis, Design Engineer I — RMS welcomes Evan DeBonis to the RMS Engineering Team where he is starting his career in rotating machinery. Even graduated from Penn State University with and Bachelor of Science in Mechanical Engineering. During his time at Penn State, Evan was part of the The Pennsylvania State University Formula Society of Automotive Engineers where he supported the design, test, and manufacture of power, transmission, and cooling parts. RMS looks forward to having Evan as part of the team as he embarks on his journey in turbo machinery.

Thomas Kernan, Talent Acquisition Manager — RMS is pleased to welcome Tom to the RMS Human Resources team to support the continued growth of RMS with quality candidates. Tom started his career, having been recruited by Ingersoll-Rand upon graduation from Johnson College, where he progressed from machinist to sales engineering intern. He was then promoted to machine shop manager, transitioned into aftermarket account manager for West Texas and the Gulf Coast and then became the Business Development Manager, Field Services, for the Domestic US at Dresser Rand. In 1998, he founded a staff augmentation company that focused on mid-stream, downstream oil and gas as well as power generation, light industrial and commercial. Starting in 2008, he went on to deep-dive into the human capital market, holding varying positions at nationwide staffing companies which included AVP, Branch Manager, General Manager and International Recruiting & Service Manager. We look forward to having Tom as part of the team to support the continued growth of RMS.

Brian Lagaras, Sales Representative — Brian is a skilled Sales Engineer with over 10 years of experience in the field of Rotating Equipment Service Sales. Brian has a thorough technical knowledge of Steam Turbines, Centrifugal compressors, pumps and other rotating equipment making him a great addition to the RMS Sales Team. Brian also has experience assisting customers & Field Services with pre-planning of all planned turnarounds, shutdowns and special engineering projects. Brian’s dedication to his customers and passion for rotating equipment make him a strong addition to RMS’s Canadian Sales Team.

Sean Chung, Designer — Sean is an experienced Mechanical Designer with a passion for rotating equipment. Sean graduated from Drexel University with a Bachelors in Mechanical Engineering. Sean started his career in the design of plastic tensile covers before transitioning to the world of rotating equipment. Prior to working at RMS Sean gained experience designing seals, gaskets, cast cases, impeller wheels, vanes, and components used in turbo machinery. RMS is excited to have Sean as part of the growing Drafting and Design team.

Bridgitte Reiss, Administrative Assistant — RMS is excited to welcome Bridgitte to the RMS Admin team. Bridgitte is a knowledgeable administrative support professional experienced working in fast paced environments demanding strong organization, technical and interpersonal skills. Prior to working at RMS Brigitte worked in the financial sector as a Legal & Estate Advisor.

Joshua Phillips, Lead Information Technology Network Administrator — The growing RMS IT team is excited to welcome Joshua Philips. Joshua has eight years of experience assembling, troubleshooting, repairing, and maintaining hardware/software configurations; network administration, system administration, as well as providing customer service and technical support for enterprise and small to medium size businesses. Joshua attended ECPI University, Virginia Beach, VA where he achieved his Bachelor of Science Degree in Computer Information Science with a concentration in Cyber and Network security. RMS is excited to have Joshua as part of the team to support RMS’s IT infrastructure.

Aaron Claypool, Staff Accountant — RMS is excited to welcome Aaron to the accounting team. Aaron has over 6 years of accounting experience and a Masters Degree in Accounting from Strayer University. Aaron is a CPA with experience working in the Oil/Gas, Non-Profit, Construction, Pharmaceuticals, Automotive, and Manufacturing sectors.

RMS Career Opportunities

Pictured: Evan DeBonis, Design Engineer I

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