Industrial Applicability of Modal Analysis on Operating Data, 2001

<div class="htmlview paragraph">The production unit number of small diesel engine cars tends to decline except recreational vehicles in Japanese market in recent years, while the production unit number in Europe market keeps on increasing owing to the merits of the durability and the fuel consumption. The small diesel engines will have to be improved in the near future by solving major problems such as noise and vibration pollution, environmental pollution, improvement in performance of diesel engines, in order to expand the production of the engines.</div> <div class="htmlview paragraph">This paper refers to a basic study on the experimental and analytical methods for the reduction of resonant vibration in each vibration mode on some cylinder blocks of small high-speed diesel engines in rated engine speed range. Hammering test method, which is easy and useful for measuring frequency response functions, is carried out in the experiments. In this test, the cylinder blocks are directly excited with the impulse hammer, and more the main journals are excited via the newly-made force transmission parts in the next experiment. Two kinds of the engines which have been recently recognized as low noise and vibration engines are chosen in this study. The cylinder blocks of the engines are called of long skirt type and ladder frame type, respectively. The vibration characteristics of these cylinder blocks are obtained in the frequency range from 500 <i>Hz</i> to 2 <i>kHz</i> using the experimental modal analysis. This frequency range is chosen in consideration of the reliability of the vibration experiments. And the force transmission routes from the piston heads to the crank journals of each cylinder block are considered as mentioned in the latter experimental method. The experimental results are used to calculate the natural frequencies by the modal analysis and the calculated results are compared with the ones obtained from FEM analysis. Furthermore, the cylinder blocks are remodeled in order to reduce the vibrations of all modes using FEM analysis.</div> <div class="htmlview paragraph">Consequently, it has been shown that the vibration stress of the cylinder block can be reduced by higher rigidities and more lightening weights of the crankcase and the crank journals in the measured frequency range.</div> <div class="htmlview paragraph">The conclusions are described as follows;</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1</span> <div class="htmlview paragraph">The hammering test method using the force transmission parts is useful to measure the natural frequencies of a cylinder block. This method can be easy to get the equal results with the measured ones on running conditions without engine operation.</div> </li> <li class="list-item"> <span class="li-label">2</span> <div class="htmlview paragraph">The hammering test method using the force transmission parts can easily analyze the natural frequencies at all the vibration modes on equal conditions with running ones. Then the method is a useful tool for improving the vibration characteristics.</div> </li> <li class="list-item"> <span class="li-label">3</span> <div class="htmlview paragraph">It has been proved from the analytical viewpoints that the cylinder block of the ladder frame type can be adopted as low-noise, small diesel engines with little increase of the engine weight while maintaining higher rigidity.</div> </li> </ol> </div>

<div class="section abstract"><div class="htmlview paragraph">The tests related to the exhaust emissions from non-road vehicles are currently performed on a chassis dynamometer under the name of NRSC (ISO 8178) and NRTC. In light of the growing requirements related to the environment protection in transport the authors recommend determining the exhaust emissions through real vehicle operating conditions. The tests carried out under real operating conditions could be used for the process of optimization of future power trains of regular road vehicles and non-road vehicles. What is more, these tests should be taken into account in the works on the changes of the legislation related to the emission limits from combustion engines. The paper presents the results of the tests on the exhaust emissions from an agricultural harvester engine and a tractor engine in real operating conditions. The harvester operation during the test consisted in crops collection from the field and the tractor operation during the test consisted in plowing. The authors used SEMTECH DS, a portable exhaust emissions analyzer by SENSORS. Based on the obtained results an analysis of the exhaust emissions was performed in the aspect of selected engine operating parameters. The paper also presents an analysis determining the most frequently used range of engine loads and engine speeds. The obtained time density characteristics (distribution of engine speeds and loads in time) of the engines were juxtaposed to the engine measuring points of the exhaust emissions homologation test. The final part of the paper discusses the prospects and trends in further works on the exhaust emissions measurement under real operating conditions from vehicle and machinery used in agriculture as well as other vehicles of non-road application.</div></div>

Modal analysis techniques are widely used to characterize vibrations in structures, vehicles, machinery, etc. Modal parameters obtained through modal analysis are useful for structural health monitoring and condition monitoring. The common goal is to ensure the integrity of a mechanical system through monitoring of different operational conditions. Operational conditions described by spatial measurements can for instance be used to observe the vibration characteristics of the system and its parts. Therefore, the main originality of this work is to experimentally investigate if the presence of a turbulent gas flow in seal geometries can facilitate operational modal analysis for a coupled rotor–foundation system. A consistent and automatic way of obtaining the vibration characteristics is necessary to be included in the monitoring schemes. Therefore, this work also proposes a method to automatically obtain modal parameters for a bed plate of a rotor–foundation system when the rotor is affected by active magnetic bearings and gas seals. The automatic modal parameter algorithm is built on the stabilization diagram of modal parameters obtained from the stochastic subspace identification. Intermediate results from the automatic modal parameter algorithm show that some of the distance measures i.e., dωn,d, dζ, dMACX, dλ, dMACXωn,d, dMACXζ, and dMACXλ, for modal parameters in a stabilization diagram are better suited than others when distinguishing between possible physical modes and certainly spurious poles. The frequency band of interest for the system is found to influence the number of possible physical modes identified by the automatic algorithm. Measurements from 13 roving accelerometers are combined with the automatic modal parameter algorithm to obtain the vibration characteristics of the rotor and bed plate. For different operational conditions in the seal geometry, seven modes are consistently identified as physical modes by the automatic modal parameter algorithm. The algorithm uses (i) a combination of a white noise disturbance pattern intentionally introduced into the system through the active magnetic bearings and (ii) the operational disturbance coming from the seals, non-intentionally introduced by the turbulent gas flow. The seven physical modes are also identified when (iii) the rotor–foundation system is only disturbed from the turbulent gas flow in the seals. The seven physical modes identified by the algorithm under conditions (i), (ii), and (iii) compare well to the vibration characteristics found in experiments via experimental modal analysis and impact hammer testing as well as via a mathematical model of the rotor–foundation system.

<div class="section abstract"><div class="htmlview paragraph">Vibration testing is an essential component of automotive product development, ensuring that components such as engines, transmissions, and electronic systems perform reliably under various operating conditions. The adoption of electronics in the automotive industry, particularly during the 1950s and 1960s, marked a shift in vibration testing approaches, moving from primarily low-frequency tests to methods that could address high-frequency vibrations as well. This evolution highlights the need for effective vibration fixture designs that can simulate real-world conditions, enabling manufacturers to detect potential weaknesses before products are integrated into vehicles. A key aspect of vibration testing is the identification of resonant frequencies within components. The coupled mass-spring-damper system, for example, can exhibit multiple resonances characterized by a Bode Diagram, where the Q factor technique is utilized to assess damping levels. Accurate vibration analysis can be achieved through various methodologies, including modal analysis and frequency response calculations, which help engineers understand how components will behave under different stimulus.</div><div class="htmlview paragraph">Furthermore, the use of advanced analytical tools, such as Finite Element Analysis (FEA) has become increasingly important in the automotive industry. These modern approaches allow for more precise and efficient vibration analysis, providing deeper insights into potential issues and enhancing overall product reliability.</div><div class="htmlview paragraph">By adhering to industry standards such as International Organization for Standardization standard i.e. (ISO) 16750-3, Society of Automotive Engineers standard i.e. (SAE) J1455, and Military standard (MIL-STD)-810G, manufacturers can ensure their products meet rigorous safety and durability requirements, ultimately leading to reduced warranty claims and increased customer satisfaction.</div><div class="htmlview paragraph">Utilizing FEA allows for virtual prototyping, which reduces the reliance on physical prototypes traditionally used to test and refine designs. This approach not only shortens the design-to-production cycle but also allows for comprehensive testing and optimization, ultimately resulting in a more efficient development process and lower costs associated with prototype creation.</div><div class="htmlview paragraph">The design process for vibration fixtures involves a cyclical approach where simulations guide modifications. By continuously analysing and adjusting designs based on performance data, engineers can refine fixtures to meet specific criteria such as cost efficiency, structural performance, and overall functionality. This iterative nature of design helps in exploring multiple configurations and ensuring that the final product achieves all desired performance targets within the constraints of the given package space.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Electrodynamic shakers or exciters are commonly used in experimental modal analysis. The practical aspects regarding the setup of the shakers, stingers and transducers are often the source of test difficulties and avoidable measurement errors. This paper reviews the basics of shakers as beneficial to modal testing, and common problems associated with setup issues and resulting measurement errors. These include shaker alignment, sensor's considerations, stinger selection, amplifiers, reciprocity assumptions and other test related circumstances.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Growing concerns about the emissions of internal combustion engines have forced the adoption of aftertreatment devices to reduce the adverse impact of diesel engines on health and environment.</div><div class="htmlview paragraph">Diesel particulate filters are considered as an effective means to reduce the particle emissions and comply with the regulations. Research activity in this field focuses on filter configuration, materials and aging, on understanding the variation of soot layer properties during time, on defining of the optimal strategy of DPF management for on-board control applications.</div><div class="htmlview paragraph">A model was implemented in order to simulate the filtration and regeneration processes of a wall-flow particulate filter, taking into account the emission characteristic of the engine, whose architecture and operating conditions deeply affect the size distribution of soot particles. The model is based on a lumped parameter approach able to be used for on-board monitoring and control, in order to provide knowledge of DPF status versus time.</div><div class="htmlview paragraph">The filtration model is based on the ‘unit collector’ and fluid dynamic approaches to predict trapped mass and filter backpressure evolution during time. The model accounts for the size distribution of soot particles in the engine exhaust and for its impact on the DPF properties during loading process. Regeneration model is based on a O<sub>2</sub> non-catalytic oxidation approach of the trapped soot.</div><div class="htmlview paragraph">The model was applied to simulate the loading/regeneration processes of a wall-flow DPF under real engine operation condition. Experimental tests were carried out and measurements were used to validate the proposed model.</div></div>

<div class="htmlview paragraph">Certification of heavy-duty diesel requires engines to be tested on an engine dynamometer and meet certification in accordance with specific procedures and cycles. However, real-world emissions have been observed to be significantly different from in-laboratory testing. The brake-specific emissions from vehicles are influenced by various operating parameters such as engine speed, load, traffic flow and ambient conditions, hence, vary from the values obtained from the certification tests. In the future, US EPA and other state regulating bodies will require the engine manufacturers to measure in-use emissions from vehicles operating under “real-world” operating conditions.</div> <div class="htmlview paragraph">A test vehicle instrumented with West Virginia University's (WVU) Mobile Emissions Measurement System (MEMS), a portable onboard tailpipe emissions measurement system, was used to obtain engine operating conditions, vehicle speed and in-use emission rates of CO<sub>2</sub> and NO<sub>x</sub>. The vehicle was driven on a specific route, which included a mix of highway and city driving patterns.</div> <div class="htmlview paragraph">Analysis was performed to determine the amount of time the engine spent in the NTE (Not-to-Exceed) zone of operation, and also over continuous 30s windows of NTE zone operation for the different driving routes. An attempt was made to establish a relationship between the time spent in the NTE region, and excursions in brake-specific emissions.</div> <div class="htmlview paragraph">Modal analysis was performed to determine the episodic nature of events and emissions during engine operation within the Not-to-Exceed (NTE) zone of operation, for each of the selected routes. The contribution of each mode of operation to variations in emissions rates has been documented.</div> <div class="htmlview paragraph">Analysis was performed to determine the effect of employing 30s, and the continuous windows on work done, and the consequent effect on brake-specific emissions in the NTE zone of operation. Results indicate a difference in the number of NTE windows of operation, and also in values of brake-specific emissions calculated by the two methods.</div>

A recent development in operational modal analysis (OMA) is the possibility of using measured, artificial loads in addition to the unmeasured, ambient excitation, while the ratio between forced and ambient excitation can be low compared to classical experimental modal analysis (EMA). Most of these so-called OMAX algorithms lack the intuitiveness of their EMA and OMA counterparts, since they fit a system model that takes both the measured and the operational excitation into account directly to the measured signals. A more physically intuitive subspace algorithm for OMAX, that starts with an accurate decomposition of the measured joint response in a forced and an ambient part, was recently introduced. In this paper, the performance of this algorithm, which is called CSI-ic/ref, is assessed by means of a case study, where a two-span steel arch footbridge is tested in operational conditions, with and without using additional actuators. From a comparison of the modal parameters with results from a finite elementmodel, an OMA algorithm, and an alternative OMAX algorithm, it can be concluded that CSI-ic/ref yields accurate modal parameter estimates.KeywordsMode ShapeModal ParameterBridge DeckModal Assurance CriterionExperimental Modal AnalysisThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

<div class="htmlview paragraph">NO formation during direct-injection (DI) diesel combustion has been investigated using planar laser-induced fluorescence (PLIF) imaging. Measurements were made at a typical medium-speed operating condition in a heavy-duty size-class engine modified for optical access. By combining a unique laser system with a particular spectroscopic scheme, single-shot NO images were obtained at realistic operating conditions with negligible O<sub>2</sub> interference. Temporal sequences of NO PLIF images are presented along with corresponding images of combined elastic scattering and natural luminosity. These images show the location and timing of the NO formation relative to the other components of the reacting fuel jet. In addition, total NO formation was examined by integrating the NO PLIF signal over a large fraction of the combustion-chamber volume. These total NO measurements are corrected for the effects of pressure, temperature, and mixing so that a quantitative measure of the NO-formation time history is obtained.</div> <div class="htmlview paragraph">The NO PLIF data strongly support and extend the conceptual model of DI diesel combustion recently presented by one of the authors. The images show that NO is not produced by the initial premixed combustion (which is fuel-rich), but begins around the jet periphery just after the diffusion flame forms. NO formation then increases progressively throughout the remainder of the combustion event, with the NO being confined to the jet periphery until the jet structure begins to disappear toward the end of the apparent heat release. The data also show that NO formation continues in the hot post-combustion gases after the end of the apparent heat release, for the operating condition studied.</div>

<div class="section abstract"><div class="htmlview paragraph">The study of vibrations in the structures of vehicles are very important to ensure its quality and integrity; thus, the study of the dynamic behavior of a motorcycle chassis is highly significant for their improvement. For that study, the modal analysis allows us to obtain the dynamic properties of the structure, such as its inertia and stiffness. Likewise, the damping is also an important parameter, which could be obtained by the frequency response function (FRF) of an impact load. In a motorcycle the engine, producing a broad frequency range, is the main source of excitation. A harmonic analysis with a shaker producing a frequency sweep allows one to better understand the vibratory transfer function between the engine and all the parts of the motorcycle. The experimental modal analysis (EMA) was used to characterize the dynamic behavior of the chassis. For that, a software was developed to use in a commercial board for the acquisition and processing of the accelerometer’s signals to obtain the FRFs and the eigenvectors. In parallel a numerical model was adjusted and used to compute the transfer function of vibration between engine and chassis and to test the modifications proposed for the reduction of the vibration’s transmissibility. The methodology adopted in this study managed to reduce the displacement in the motorcycle by 88% at 60 Hz, 13% at 100 Hz, and 47% at 117 Hz.</div></div>

As an alternative to operational modal analysis and classical experimental modal analysis (EMA), a novel method was introduced previously, namely impact-synchronous modal analysis (ISMA). The effectiveness ISMA on rotor and structural dynamic systems has been proven in previous literature. More recently, an automated impact device (AID) was introduced which utilized tachometer pulse as initiation signal and its effectiveness on ISMA was proven. An attempt to further enhance this device in term of equipment and cost is then proposed by replacing the tachometer with the in-use tri-axial accelerometer through utilizing the filtered response of cyclic load component as an initiation signal to control the impact device, which is also the primary aim for this study. Prior to modal testing, accuracy of this device is illustrated at desired phase angles of 0 deg, 90 deg, 180 deg, and 270 deg. Subsequently, frequency response function (FRF) estimations obtained for ISMA using enhanced AID has demonstrated the suppression capabilities of this device on disturbances, i.e., reduction of 93.58% at 30 Hz and 57.78% at 60 Hz, resulting in a high correlation for signature assurance criterion (SAC) and cross signature assurance criterion (CSAC). Modal parameters extracted from the EMA and ISMA using impact device are presented and compared, for the first three natural modes of the test rig. It is found that natural frequencies are deviating by less than 6%, whereas modal assurance criterion (MAC) values between the mode shapes of the two tests are found to be above 0.9.

<div class="section abstract"><div class="htmlview paragraph">The increasing trend toward electric and hybrid-electric vehicles (HEVs) has created unique challenges for NVH development and refinement. Traditionally, characterization of in-vehicle powertrain noise and vibration has been assessed through standard operating conditions such as fixed gear engine speed sweeps at varied loads. Given the multiple modes of operation which typically exist for HEVs, characterization and source-path analysis of these vehicles can be more complicated than conventional vehicles.</div><div class="htmlview paragraph">In-vehicle NVH assessment of an HEV powertrain requires testing under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. Generally, it is necessary to assess issues related to IC engine operation and electric motor operation (running simultaneously with and independent of the IC engine), under both motoring and regeneration conditions. Additionally, mode transitions, including IC engine start/stop must be assessed.</div><div class="htmlview paragraph">An analysis is presented here, which explores the differences in NVH performance of multiple HEVs currently available in the US-market. Measurements were conducted on these vehicles to assess noise and vibration at the powertrain-level and vehicle interior. Two of the vehicles included in this investigation were then chosen for a more in-depth comparative analysis. The analysis of these two vehicles included assessment of source level excitations and vehicle NVH sensitivities, in the context of boundary conditions driven by their hybrid system architectures.</div><div class="htmlview paragraph">Based on the powertrain and vehicle NVH performance assessments, methods were explored for developing powertrain level NVH targets. For the initial phase of this target cascading process, the analysis was limited to full load (IC engine operational) and part load (EV-only) modes. Based on in-vehicle performance, and vehicle sensitivity information, test procedures and targets were defined for powertrain radiated noise and mount vibration content.</div></div>

<div class="htmlview paragraph">The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head.</div> <div class="htmlview paragraph">The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases. Guidelines on the effect of various parameters on the octane requirement of an engine can be summarized as follows:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">Spark Advance: 1 ON/1° SA</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Air Temperature: 1 ON/7 K</div></li> <li class="list-item"><div class="htmlview paragraph">Air/Fuel Ratio: peaks at 5% rich of stoichiometric, decreases by around 2 ON / air/fule ratio around peak</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Pressure: 3-4 ON/10 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Compression Ratio: 5 ON/CR</div></li> <li class="list-item"><div class="htmlview paragraph">Exhaust Back Pressure: 1 ON/30 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Coolant Temperature: 1 ON/10 K (Similar effect of head and block temperature., Larger effect at low speed.)</div></li> </ul> </div>

To enhance the design and research work on dynamic characteristics of high-rise laminated timber buildings, this paper carried out a modal analysis study on one of the largest laminated timber buildings in China. The finite element calculating modal analysis was carried out using SAP2000 software, and the experimental modal analysis of the building was carried out via environmental excitation. The calculating modal results and the experimental modal results showed good agreement. The calculating modal frequency values were generally lower than the experimental modal frequency values. The natural frequencies obtained by the two methods appeared in the Y-direction first-order bending mode and had values of 2.03 and 2.5 Hz, respectively. The corresponding frequencies of the first-order torsional mode were 2.82 and 3.25 Hz, respectively. The distribution of the CLT core tube along the length direction of the building has an impact on the vibration mode. The six-story part shows the second-order bending form, while the four-story section only shows the first-order bending form. The above work provides a case study and reference for the simulation and modal analysis of high-rise laminated timber buildings, demonstrating the critical role of the core tube structure in such wooden buildings. This insight contributes to a better understanding of structural performance and design considerations in similar projects.

<div class="section abstract"><div class="htmlview paragraph">The European Union has defined legally binding CO2-fleet targets for new cars until 2030. Therefore, improvement of fuel economy and carbon dioxide emission reduction is becoming one of the most important issues for the car manufacturers. Today’s conventional car powertrain systems are reaching their technical limits and will not be able to meet future CO2 targets without further improvement in combustion efficiency, using low carbon fuels (LCF), and at least mild electrification.</div><div class="htmlview paragraph">This paper demonstrates a highly efficient and performant combustion engine concept with a passive pre-chamber spark plug, operating at stoichiometric conditions and powered with liquefied petroleum gas (LPG). Even from fossil origin, LPG features many advantages such as low carbon/hydrogen ratio, low price and broad availability. In future, it can be produced from renewables and it is in liquid state under relatively low pressures, allowing the use of conventional injection and fuel supply components.</div><div class="htmlview paragraph">To take advantage of the specific capabilities of LPG a combustion system is designed to increase combustion efficiency and decrease fuel consumption and engine-out emissions. The applied combustion chamber geometry, including the passive pre-chamber, leads to lower exhaust gas temperatures and consequently higher peak power when operating under stoichiometric conditions.</div><div class="htmlview paragraph">The presented combustion system was developed by means of extensive 3D-CFD simulations and experimental single-cylinder engine results by applying advanced combustion diagnosis and analysis tools. The potential of the combustion system is demonstrated over the entire engine map focusing on certification and real operating conditions such as idle, low load and maximum power. The potential of the combustion process will be figured out, both for low and high-power densities, with respect to future emission limitations.</div></div>