Application Notes & White Papers

Sources of Total Harmonic Distortion in Servo Hydraulic Systems

This report addresses questions regarding the source of Total Harmonic Distortion (THD) in Team Corporation vibration test systems that use high flow capacity V-2000P hydraulic servo valves for sine vibration testing. The intent of the report is to clarify why these valves have high THD at low excitation levels. An overview of some servo-hydraulic terms are presented, followed by a discussion of THD, and parameters that affect THD. Although this report specifically references systems with the V-2000P servo valve, the concepts and discussion apply in general to all Team Corporation hydraulic shakers. It is assumed that the reader has a basic understanding of hydraulic servo valve operation.

A 6DoF Vibration Specification Development Methodology

Multiple degree of freedom (MDOF) excitation systems and MDOF vibration control systems continue to improve, and are now standard equipment in many dynamic test laboratories. This paper concentrates on the often overlooked process of determination of an input specification for such MDOF systems. A pair of generalized six-degree-of-freedom (6-DOF) vibration specification development (VSD) techniques are proposed, discussed, and illustrated through an example. 


A Large Slip Table to Vibrate Ariane 5 Payloads

This paper presents some of the main features of the new ESA Large Slip Table project designed for the future needs of ESTEC’s Testing Division. This new table will be able to vibrate ARIANE 5 single passenger-class spacecraft. The trend in this class of payload is towards six tons and above. ESTEC’s Testing Division has therefore decided to replace the existing mono-axial slip table to be able to handle this class of specimen. This paper presents some key points of the design used to develop such a large slip table.


A Three Dimensional Vibration System - Fred Edgington WSMR

The design and performance of a three directional vibration system to allow the simulation of ground and air transportation vibration environments is presented. The basic system was built at the white sands missile range, New Mexico and utilizes a multi-axis drive unit designed and constructed by Team Corporation. 

Advanced High-Freq 6-DOF Vibration Testing using the Tensor 18kN-SV March 2013

What is a Tensor? Wikipedia defines a Tensor as "a geometric object that describes the linear relations between vectors, scalars, and other tensors. In basic engineering you may think of a Tensor in terms of the 3-dimensional stress state of a solid object. Remember the cube element showing the normal and shear stresses on each face? Now, in vibration testing you can think of a Tensor as the solution to reproducing high-frequency, multi-axis vibration "stress states" in the lab. Team Corporation's new Tensor 18kN is the most advanced commercially available vibration test system capable of replicating field vibration environments out to 2,000 Hz. 

An Accurate Repeatable SSTS

The US Navy needs a modern, computer controlled shock test system for testing a large and growing number of commercial products for use in its newest vessels. Team has been delivering earthquake test systems to test labs around the country for many years. By increasing the velocity capability and linearizing the valve response, these systems are shown to be well suited to doing the Navy's shock tests. Shock pulse waveforms and pseudo velocity spectrums of four separate tests show the accuracy and versatility of the system. The systems are defined, test results presented and future work suggested.

Benefits and Challenges of Over Actuated Excitation Systems

This paper provides a comprehensive discussion on the benefits and technical challenges of controlling over-determined and over-actuated excitation systems ranging from 1DOF to 6DOF. The primary challenges of over actuated systems result from the physical constraints imposed when the number of exciters exceeds the number of mechanical degree-of-freedom. 

 

Benefits of Force Limiting Vibration Testing

Since its founding, NASA has been dedicated to the advancement of aeronautics and spacescience. The NASA Scientific and Technical Information (STI) Program Office plays a key partin helping NASA maintain this important role.The NASA STI Program Office is operated byLangley Research Center, the Lead Center for NASA’s scientific and technical information. The NASA STI Program Office provides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA’s institutional mechanism for disseminating the results of its research and development activities. 

Brief Overview of Vehicle Seat Test Standards

This document offers a brief overview of some of the vehicle seat vibration test specifications in use today. Specifications for automobile and off-highway vehicles are reviewed and guidelines for test equipment selection presented. 


Bringing Broadband 6-DOF Vibration into the Lab

Commercially available vibration test systems able to reproduce and accurately control multipleinput, multiple-output vibration tests are often constrained by a limited frequency band due excessive tare mass and low natural frequencies of the fixtures. Consequently, their use in Department of Defense test facilities is limited to a select number of test profiles found in MIL STD documents and/or platform specific tests where the frequency band of interest is below 500 Hz. This frequency limitation has now been addressed with the introduction of a new system based upon multiple electro-dynamic shakers hydrostatically coupled to the specimen mounting table.

Comparison of Electronic Component Durability Under Uniaxial and Multiaxial Random Vibrations

Multiaxial and uniaxial vibration experiments were conducted in order to study the differences in failure modes and fatigue life for the two types of excitation. An electrodynamic (ED) shaker capable of controlled vibration in six degrees of freedom (DOF) was employed for the experiments.

Comparison of Response of Simple Structure to Single and Multiple Axis Random Vibration Inputs

Random vibration experiments were performed on a simple structure to compare the response to single axis inputs and multiple axis inputs. The experiments were performed on a six degree of freedom (6-DOF) electrodynamic shaker described in a companion paper. The simple structure consisted of a lumped mass mounted on the end of a short rectangular beam. A finite element analysis of the structure was also performed. The experimental and model results are discussed in the paper. 


Comparisons of Simultaneous and Sequential Durabilty Testing

Component durability testing using shaker tables is a common part of product development programs in many different industries—a major one being the automotive industry. The goal is to predict the effects of long-term service on a component or even an entire piece of equipment without having to simply run it through a service life in expensive field testing.

Control of an Over-Actuated Single DoF Excitation System

This paper provides results of a laboratory experiment designed to illustrate the theoretical control considerations for an over-actuated excitation system. The experiment is based on control of a beam pinned at one end providing a single rotational degree of freedom and excited by two electrodynamic actuators. 

Defining the Global Error of a MIMO Vibration Test

A presentation by Team Corporation engineer Joel Hoksbergen on the multi axis vibration test. ESTECH Conference 2014

Development of 6DoF Motion Replication Based Production Acceptance Test

Performing quality, Six-Degree-of-Freedom (6-DOF) motion replication testing in the laboratory is rapidly becoming a feasible and attractive alternative to classical 1-DOF methods. This paper considers several of the open issues associated with performing laboratory based 6-DOF vibration testing. A recent 6-DOF laboratory test developed and performed at Redstone Technical Test Center (RTTC) will be used to illustrate the methods employed to aid the test engineer in proper transducer placement, test conduct, and development of the analysis tools used for test documentation purposes. 


Electrohydraulic Shakers

Mechanical shakers are inexpensive, reliable and simple to operate, but unfortunately limited in the types of testing they are able to perform.  At the opposite extreme, electromagnetic (EM) shakers are more versatile and expensive, and therefore generally limited to aerospace testing.  This article discusses the less well known, but highly versatile electrohydraulic shaker and its application for vibration and shock test needs.

Engine Simulator Reduces Development Time and Expense

Traditionally development of engine-driven products has required testing with an operating engine. Because an operating engine is required, many tests are delayed until operational engines are available for testing purposes. Engines are frequently not available until very late in the development process. Getting a late start on testing naturally limits the amount of testing that can be performed and the number of design alternatives that can be evaluated. 


Estimating CUBE Performance

This application note presents a simplified technique for estimating the single axis performance of a Team CUBE in each of the three linear directions of motion. The key to applying this technique is knowledge of the location of the payload center of gravity. Without this knowledge, it is not possible to estimate the performance capability of the CUBE.

Evaluation of 6DoF ED Shaker System

The paper describes the preliminary evaluation of a 6 degree of freedom electrodynamic shaker system. The 8 by 8 inch (20.3 cm) table is driven by 12 electrodynamic shakers producing motion in all 6 rigid body modes. 


Experimentation using Single and Multi Axis Vibration

The hypothesis for this test was that shaking on X, Y, and Z at the same time would have a different failure rate – presumably shorter – than anything calculated by the results of using the times to failures of the single axes. To make the results more traceable only one failure mechanism was looked at; the reaction of the LED. That does not by any means presume that an LED failure would be the only failure found. Other types would be expected. However, if the test was stopped as soon as any failure (or weakness) at all was found then all it would really show would be the likely first failure on each single axis. The idea was traceability on one particular failure mechanism. 

Gunfire Loads are Simulated in A-10 Fatigue Testing

A brief article in The Leading Edge newsletter; Team Corproation provides equipment for use in a simulated Gunfire fatigue testing with Northrop Grumman. 

High Force Testing of Saturn IV-B

Vibration of major structural assemblies, referred to as high force testing, for dynamic environmental simulation was initiated by the Marshall Space Flight Center in testing off the Saturn I Instrument Unit. Large strains induced by low frequency vibration would not impair the structural integrity of the Saturn V Launch vehicle, NASA prime contractors were requested to preform high force dynamic tests on structural subassemblies of their respective stages. This paper describes the testing accomplished by the Douglas Missile and Space Systems Division on two large subassemblies of the S-IV/B stage.

High Intensity Noise Generation for Extremely Large Reverberant Room Test Applications

A recent operational need for the development of a large (101,000 ft3) reverberant acoustic chamber at the Space Power Facility of NASA Glenn Research Center’s Plum Brook Station with the requirement of generating sound pressure levels (SPL) as high as 163 dB has resulted in the need to re-examine the generation of noise in reverberant rooms. Early in the design stage, it was realized that the acoustic power level capability (10-30 kW) of conventional electrodynamic air modulators, such as those supplied by the Wyle Corporation, would be required in unprecedented numbers to meet the test spectra requirements.

Historical Development of High Performance Multi Axis Vibration Test Systems

The use of vibration testing to identify structural weaknesses is a widely accepted method to improve product quality. Vibration testing using a sinusoidal input, a random input or a replication of a deterministic waveform has proven to be a critical step in successful product improvement. Though long recognized that multi-axis testing provides a more realistic representation of actual field conditions, historically, single axis testing was the method of choice

Hydrostatic Pad Bearing Application Notes

The pad bearing is used to contrain test articles being subject to vibration and earthquake simulation. The pad bearing proves the test  engineer with a versatile, inexpensive support bearing. This paper will explain its principle of operation and give some applications.

 

Improved Reliability Test Using Multiaxial Electrodynamics Vibration

The functionality of next-generation DoD platforms, such as the Small Unmanned Ground Vehicles (SUGV), is strongly electronics rich. These electronics experience extremely harsh environments such as vibration and thermal fatigue. Therefor it is imperative to identify the failure mechanisms of these components through experimental and simulated failure assessment. 

Input Observer Convergence and Robustness: Application to Compression

The focus of this paper is the analysis of a high-gain observer for estimating un-steady inputs, including guarantees for robustness to measure uncertainty, and transient upper bound on estimate error.

Installation and Testing CUBE

A CUBE™ High Frequency 6-DOF Shaker has recently been installed at the KULeuven Noise and Vibration Laboratory. This paper describes the (pre-) installation phase and reports on the first results of an extensive performance testing program. Site preparation issues, like the lab layout and the isolation mass, performance issues, like the shaker concepts and the hydraulic supply, and results, for shock and vibration testing and the use of Time Wave Replication (TWR), are discussed. The results from the testing program are used to benchmark the performance of the CUBE™ shaker table for a small set of applications within the field of NVH, Durability and Certification testing.

Introduction to Engine Simulation Systems

The Team 900 Series of Engine Simulation Systems (ESS)provide unique test capabilities to developers and manufacturers of engine driven components and systems. This document has been prepared to introduce the reader to the range of applications and theory of operation of the Team ESS.

Leuven Cube Dynamics Analysis

A CUBE™ high frequency 6-DOF shaker table has recently been installed at the KULeuven Vehicle Technologies Laboratory. This paper describes a dual hardware-software approach for increased accuracy of Multi-Degree-Of-Freedom (MDOF) road reproduction experiments. On the KULeuven 6-DOF highfrequency shaker table, the hardware is calibrated using a mobile Coordinate Measuring Machine (CMM)and both hardware and software settings are tuned for better accuracy. In addition, a modified Time Waveform Replication (TWR) algorithm is presented that yields more stable control and reduction of unwanted rotations.

MIRA Article

The use of vibration testing to identify structural weaknesses is a widely accepted method to improve product quality. Vibration testing using a sinusoidal input, a random input or a replication of a deterministic waveform has proven to be a critical step in successful product improvement. Though long recognised that multi-axis testing provides a more realistic representation of actual field conditions, historically, single axis testing was the method of choice. Primarily the lack of economical and effective multi-axis test hardware and control software was the cause. 

Multishaker Upgrade at ESTEC-ESA

The European Space Agency started upgrading its Multishaker system at ESTEC in 2002-2003 with the procurement of a large slip table for vibration testing along the lateral axis. To obtain coherent system performances along the three axes, a new interface is now needed to complete the upgrade for the vibration tests along the vertical axis. It is therefore planned to install a separate vertical system alongside the present system.

Multi Axis Testing of Underwing

High frequency multi-axis testing - controlled vibrations in all six degrees of freedom at the same time - is the latest tool used by the U.S. military for problem solving. This type of testing provides the test engineer with the most realistic duplication of the vibration environment, resulting in the ability to reproduce field observations in the laboratory, quickly solving the specific problem.

Multi-Axis Vibration Reduces Test Time

Widely accepted as a method to improve product quality, vibration testing is used to qualify products for production. Either alone or combined with an environmental chamber, vibration testing is a critical step in the successful development of new products. 


Nonlinear Model-Based Control of Combustion Timing in Premixed Charge Compression Ignition

One of the major challenges in the control of advanced combustion modes, such as premixed charge compression ignition, is controlling the timing of the combustion event. A nonlinear model-based controller is outlined and experimentally shown to be capable of controlling the engine combustion timing during diesel premixed charge compression ignition operation on a modern diesel engine with variable valve actuation by targeting the desired values of the incylinder oxygen mass fraction and the start of injection.

 

 

 

 

 

 

 

 

Novel Approach to Improve Electronics Reliability

Abstract The functionality of next generation the US Army’s platforms, such as the Small Unmanned Ground Vehicles and Small Unmanned Arial Vehicles, is strongly dependent on the reliability of electronics-rich devices. Thus, the performance and accuracy of these systems will be dependent on the life-cycle of electronics. These electronic systems and the critical components in them experience extremely harsh environments such as shock and vibration.

Novel Guided Head Expander

When vertical vibration testing of large test articles is required, it is common to install a head expander on the armature of a shaker. Larger test articles often have a center of gravity relatively far above the mounting surface. When combined with the armature and head expander, these test articles may exhibit multiple structural resonances within the desired test band that do not exist in the intended application. These test configuration-driven characteristics are likely to create unwanted cross-axis excitation during a vibration test

Reliability Test Multiaxial Electrodynamics Vibration

The increasing complexity of electronic equipment, especially in low volume and highly sophisticated and dense electronic systems, such as military, aerospace, and automotive applications, has resulted in an increased need to understand the failure mechanisms due to dynamic loads. Typically, electronic systems are subjected to various complex loadings, including vibration, during their life-cycle. Comprehending failure mechanisms due to dynamic loads can be achieved via accelerated vibration testing of electronic products.

Simulate and Stimulate

Vibration testing, whether employing a sinusoidal input, random input or replication of a deterministic waveform has proven to be a critical step in the successful development of new equipment. Traditionally, vibration tests have been conducted by sequentially applying uniaxial excitation to test articles along three orthogonal axes, using a linear shaker and rotating the test load after each test.

Space Power Facility: Capabilities for Space Environmental Testing in a Single Facility

This paper by Richard N. Sorge describes the current and near-term environmental test capabilities of the NASA Glenn Research Center's Space Power Facility (SPF) located in Sandusky, Ohio. 

Spatial Requirements for Transducer Mapping

Preforming quality 6DoF motion replication testing in the laboratory begins with carefully planned selection of measurement locations and orientation. This paper considers the typical scenario involving linear accelerometer reference measurements. 


Structural Developments Improve High-Frequency Vibration Testing on Cube System

The frequency response of a multiple-input, multiple-output (MIMO) vibration test system is typically limited by the dynamic response of the table structure between the vibration exciters and the test payload. The primary design goal in developing this structure is to minimize the moving mass and maximize the stiffness to give the highest possible first vibration mode, while realizing all other structural requirements. Many Department of Defense random vibration test profiles have a 500 Hz bandwidth, and depending on the system and test article, often the first mode of the loaded table structure must be outside of the test bandwidth to adequately control the test.

Subsidiary (Component) Shock Test System (SSTS)

The US Navy needs a modern, computer controlled shock test system for testing a large and growing number of commercial products for use in its newest vessels. Team has been delivering earthquake test systems to test labs around the country for many years. By increasing the velocity capability and linearizing the valve response, these systems are shown to be well suited to doing the Navy's shock tests. Shock pulse waveforms and pseudo velocity spectrums of four separate tests show the accuracy and versatility of the system. The systems are defined, test results presented and future work suggested.

T-Film Slip Table Analysis

The T-Film slip table has been designed to lower the cost and improve the quality of vibration testing. This paper shows that the critical slip table parameter for determining performance is the stiffness of the bearing. It is then shown that the T-Film bearing is more than 50 times stiffer than our standard journal bearing. This results in deflections and cross axis accelerations that are 1/50th those of our (or anyone else's) standard journal bearing slip table.

Team Spherical Couplings

The TEAM hydrostatic bearing spherical coupling is a replacement to Conventional rod end bearings in applications requiring high stiffness, Zero backlash and virtually infinite wear life. The spherical surfaces are separated by a small fluid film of oil under high pressure, (about .001 inches at 3000psi.) Because of the mechanical configuration of the bearing surfaces, the load path is quite stiff; that is there is a minimum amount of bending elements. This is contrasted by the bending in a pin through the center of a conventional rod end. 

Technical Analysis of Team T-Film Slip Table

When vertical vibration testing of large test articles is required, it is common to install a head expander on the armature of a shaker. Larger test articles often have a center of gravity relatively far above the mounting surface. When combined with the armature and head expander, these test articles may exhibit multiple structural resonances within the desired test band that do not exist in the intended application. These test configuration-driven characteristics are likely to create unwanted cross-axis excitation during a vibration test

TENSOR Multi Axis Vibration System

Vibration testing is evolving at a rapid pace. Driven by market pressures for greater reliability, improved realism in testing methodology is in demand. There is widespread consensus that simultaneously exciting a test object in multiple axes will reproduce real-world stress loading. Consequently Multiple Degree of Freedom (MDoF) testing is believed to be the path to enhanced product reliability with the added benefit of possible test time compression. Simultaneously exciting all axes and rotations, MDoF testing is in the process of being codified in testing standards, most notably being Method 527 in MIL STD 810(G). 

Testing behind the Test Facility Acoustic Design NASA Glenn

Vibration testing is evolving at a rapid pace. Driven by market pressures for greater reliability, improved realism in testing methodology is in demand. There is widespread consensus that simultaneously exciting a test object in multiple axes will reproduce real-world stress loading. Consequently Multiple Degree of Freedom (MDoF) testing is believed to be the path to enhanced product reliability with the added benefit of possible test time compression. Simultaneously exciting all axes and rotations, MDoF testing is in the process of being codified in testing standards, most notably being Method 527 in MIL STD 810(G).

Time Domain and Frequency Domain Techniques for Multi Shaker Time Waveform Replication

This paper describes two techniques for controlled Multi Degree of Freedom (MDOF) time waveform replication with examples of their application to a variety of test conditions. The paper outlines the basic concepts of time domain and frequency domain control and illustrates the techniques using MDOF applications where one or the other method is more suitable. 


Validation Techniques for 6DoF Vibration Data Acquisition

Multiple Degree of Freedom (MDOF) excitation systems and MDOF vibration control systems continue to improve, and are now standard equipment in many dynamic test laboratories. Determination of an input specification for such MDOF systems is critically dependent on properly acquired field data. Validation of field data will be discussed and demonstrated employing the same transformation tools used in both transformation-based 6-degree-of-freedom (6-DOF) vibration control and generalized MDOF vibration specification development (VSD). 


Vibration Test Evolution

Vibration testing is widely accepted as a method to improve product quality by identifying structural weaknesses. Historically, single axis, single shaker testing is the method of choice. This is largely due to the lack of economical and effective test hardware and control software. Significant advances have been made in both arenas, resulting in test equipment design that permits multiple shaker applications, with both single axis or multi-axis excitation capabilities. This paper documents the chronology of test equipment design and reviews the advantages afforded by current hardware and software technologies.

Waveform Replication for Accurate Replication

Hydraulic actuators are versatile vibration and shock test systems. However, their nonlinear response causes significant waveform distortion that precludes their use in many common testing situations. Waveform Replication controllers overcome the nonlinear response, turning the hydraulic actuator into the capable performer it should be. Two properties of a hydraulic actuator cause the non-linear response: the oil column resonance and the oil flow through the servo valve. For both single axis and multi axis hydraulic vibration systems a waveform replication controller compensates for these effects by learning of their existence in the error between the desired and achieved waveforms.