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  • 1.
    Gren, Per
    et al.
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Tatar, Kourosh
    LTU.
    Granström, Jan
    Molin, Nils-Erik
    Jansson, E.V.
    Department of Speech, Music and Hearing, Royal Institute of Technology (KTH).
    Laser vibrometry measurements of vibration and sound fields of a bowed violin2006In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 4, p. 635-644Article in journal (Refereed)
    Abstract [en]

    Laser vibrometry measurements on a bowed violin are performed. A rotating disc apparatus, acting as a violin bow, is developed. It produces a continuous, long, repeatable, multi-frequency sound from the instrument that imitates the real bow-string interaction for a 'very long bow'. What mainly differs is that the back and forward motion of the real bow is replaced by the rotating motion with constant velocity of the disc and constant bowing force (bowing pressure). This procedure is repeatable. It is long lasting and allows laser vibrometry techniques to be used, which measure forced vibrations by bowing at all excited frequencies simultaneously. A chain of interacting parts of the played violin is studied: the string, the bridge and the plates as well as the emitted sound field. A description of the mechanics and the sound production of the bowed violin is given, i.e. the production chain from the bowed string to the produced tone

  • 2.
    Jahedi, Mohammad
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Experimental and Numerical Investigation of the Quenching Process on Rotary Hollow Cylinder by Multiple Impinging Jets2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The worldwide competitive market on metal products with higher quality in industry has increased the need to implement more advanced and controllable quenching techniques in the hardening stage of the heat treatment process. Moreover, sustainability and energy efficiency are key factors to consider in the development of advanced quenching techniques. Among various cooling methods that are used in industry, a water impinging jet quenching system is one of the few that offers wide flexibility to adjust cooling rate based on the chemical composition and proper phase transformation in the continuous cooling transformation diagram (CCT) to achieve desired material properties. On an industrial scale, a large number of water impinging jets are placed in the cooling configuration introducing multiple array of jets in the quenching system. In the literature study by the author, there has been interest to study the quenching heat transfer by single water jet in various applications. Even so, little scientific attention has been paid to the multiple array of water impinging jets and the importance of various quenching parameters on the quenching heat transfer with multiple array of jets. 

    This thesis deals with a study of quenching rotary hot hollow cylinder with multiple configurations of water impinging jets. The aim of this investigation is to obtain better understanding of boiling heat transfer phenomena in application of multiple array of water impinging jets and quenching parameters. An experimental test rig was designed to control most influential parameters in quenching experiments. The results of experimental study contained recorded temperature data beneath the quenching surface of a hollow cylinder. A heat conduction inverse solution based on the GMRES method was developed for application of quenching hollow cylinder. This model used the recorded temperature data of quenching experiments to predict surface temperature and heat flux. A thorough parametric study investigated the effect of various quenching parameters and multiple configuration of jets in terms of local and area-averaged heat transfer over surface as well as in the solid material.

    The local surface boiling curve captured clear effect of multiple array and cyclic variation of heat transfer caused by rotation of hollow cylinder. The delay in onset of wetting front flow growth over the surface, collision of adjacent wetting front flows and creation of upwash flow were captured on the surface heat flux contour plot. Higher heat flux was obtained around stagnation and upwash flow zones over the quenching surface. The relation between jet flow rate and multiple array configuration revealed a trade-off between these two parameters in terms of optimizing the water resource usage and desired cooling rate with this cooling technique.

    Comprehensive parametric study revealed effect of various quenching parameters in the local heat transfer in the boiling regimes. The results show improvement of heat flux in the film and nucleate boiling is more difficult than transition boiling regime. In the study of area-averaged heat transfer in 1-row array, higher subcooling and jet flow rate enhance the surface heat flux. In contrast, smaller rotation speed, jet-to-jet spacing and initial wall-superheat temperature increase the area-averaged surface heat flux of hollow cylinder. An extra row of nozzles in the array (2-row) also enhanced the area-averaged surface heat flux significantly. The results from comprehensive parametric study of 4-row in-line and staggered configurations have been used to propose correlation for surface area-averaged Nusselt number. In the local heat transfer, two correlations of average and maximum local heat flux at stagnation point of water impinging jet were proposed.

    The result of this study and the proposed correlations may provide a road map for engineers to design hollow cylinder quenching system with multiple array of water impinging jets based on cooling rate for proper phase transformation and optimized water resource and energy usage in the quenching process.

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  • 3.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Berntsson, Fredrik
    Department of Mathematics, Linköping University, Linköping, Sweden.
    Wren, Joakim
    Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Transient inverse heat conduction problem of quenching a hollow cylinder by one row of water jets2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 117, p. 748-756Article in journal (Refereed)
    Abstract [en]

    In this study, a two-dimensional linear transition inverse heat conduction problem (IHCP) was solved using the Generalized Minimal Residual Method (GMRES) in quenching process by water jets. The inverse solution method was validated by set of artificial data and solution sensitivity analysis was done on data noise level, regularization parameter, cell size, etc. An experimental study has been carried out on quenching a rotary hollow cylinder by one row of subcooled water jets. The inverse solution approach enabled prediction of surface temperature and heat flux distribution of test specimen in the quenching experiments by using measured internal specimen temperature. Three different boiling curves were defined in the quenching process of a rotary cylinder. Result obtained by the inverse solution showed clear footprint of rotation in surface temperature and heat flux on each revolution of cylinder and temperature variation damping from quenching surface toward interior of specimen.

  • 4.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Boiling heat transfer characteristics of rotary hollow cylinders with in-line and staggered multiple arrays of water jets2021In: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 143, no 11, article id 111601Article in journal (Refereed)
    Abstract [en]

    Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (∆Tsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af ) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area- averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

  • 5.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology. Linköpings universitet.
    Effect of Multiple Water Impinging Jet Array on Quenching Hot Rotary Hollow Cylinders2020Conference paper (Refereed)
    Abstract [en]

    Experimental study has been carried out to investigate transient quenching of a rotary hollow cylinder by water impinging jets in multiple jet arrays. Subcooled water jets (Δ𝑇𝑠𝑢𝑏= 55-85K) were placed into two types of nozzle arrays: 1-row and 2-row in-line array. The flow rate of water jets varied from 2.7 to 10.9 L/min, impinging on hot rotary cylinder (𝑇𝑖 =600℃) with rotation speed 10-50 rpm and different curvature ratio (𝐷𝑜/d = 12, 19 and 24). The local average and maximum boiling heat transfer at water jet’s stagnation point revealed effect of studied quenching parameters and multiple jet arrays in the boiling heat transfer. The result showed among the studied parameters, jet’s flow rate and curvature ratio influenced heat transfer in all the boiling regimes. Rotation speed was effective in film and transition boiling regime and strong effect of subcooling was captured in the transition boiling regime. The characteristics of maximum heat flux point in the boiling curve were found to be dependent on the studied quenching parameters as well as array of nozzles. Multiple jet arrays had effect on the spatial variation and rate of boiling heat transfer on quenching surface. Higher area-averaged and maximum surface heat flux was obtained by 2-row array while array’s total flow rate was kept constant. It was found that by impinging constant water flow rate into the jets, 2-row array with twice the number of impinging jets enhanced heat transfer significantly in film and transition boiling regime in combination with other quenching parameters.

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  • 6.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Experimental study of quenching process on a rotating hollow cylinder by one row of impinging jets2017In: 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 12-15 June, 2017, Iguazu Falls, Brazil, 2017Conference paper (Refereed)
    Abstract [en]

    Quenching cooling rate of rotary hollow cylinder by one row of water impinging jets has been experimentallystudied. Water jets (d = 8 mm) with sub-cooling 55 to 85°C and Reynolds number 8,006 to 36,738 impinged over rotaryhot hollow cylinder (rotation speed 10 to 70 rpm) with initial temperature 250 to 600°C. Impingement impact angle of row of jets varied between 0 to 135° and jet-to-jet spacing in row patten was 2 to 8d. The results revealed more uniformityon cooling rate of quenching in smaller jet-to-jet spacing (2 and 4d) where wetting front regions are located closer toneighbor jet’s region. By increasing spacing, footprint of annular transition region was highlighted in quenching coolingrate contour. A distinct quenching characteristic was obtained for impingement impact angle of 0° compare to otherangles. With initial temperature above the Leidenfrost temperature, low cooling rate was achieved in film and transitionboiling compare to a steep increase of cooling rate at start of quenching with higher maximum heat transfer for experimentswith initial temperatures less than Leidenfrost temperature. The effect of other parameters on quenching coolingrate was highlighted in film and transition boiling while no significant differences were observed in nucleate boiling.

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  • 7.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology. Department of Management and Engineering, Linköping University.
    Quenching a rotary hollow cylinder by multiple configurations of water-impinging jets2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 137, p. 124-137Article in journal (Refereed)
    Abstract [en]

    Experiments have been conducted to analyze quenching of a hot rotary hollow cylinder by one and two rows of water-impinging jets. Sub-cooled water jets (ΔTsub = 45–85 K) with flow rate 8006 to 36,738 impinged on hollow cylinder with rotation speed 10 to 70 rpm at various initial wall superheat temperatures from 250 to 600ºC. Jet-to-jet and jet-to-surface spacing varied between 4 to 10d and 1.5 to 7d respectively and angular position of impinging jets were tested from 0 to 135º. Effectiveness of the defined parameters on stagnation point’s local average heat flux was found lower in the film and nucleate boiling compare to transition boiling regime where rotation speed had the highest impact. Characteristic of maximum heat flux (MHF) at stagnation point and upwash flow point were analyzed based on surface heat flux, time and temperature corresponding to MHF. Same maximum heat flux levels were captured in the both points which reveals importance of the flow behavior at the upwash flow point. The effectiveness of the parameters to improve average heat transfer was studied based on cooling area of each water impingingjet in the multiple configurations. Higher average heat transfer was obtained by increasing flow rate and subcooling temperature and lower initial wall superheat temperature corresponding to onset of transition boiling regime.

  • 8.
    Jahedi, Mohammad
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology. Linköping Universitetet.
    Quenching Hot Rotary Hollow Cylinder by 1-row and 2-row Water Impinging Jet Array2021In: Journal of Fluid Flow, Heat and Mass Transfer, ISSN 2368-6111, Vol. 8, p. 178-188Article in journal (Refereed)
    Abstract [en]

    Experimental study has been carried out to investigate transient quenching of rotary hollow cylinder by subcooled water impinging jets (∆Tsub= 55-85K) in 1-row and 2-row inline array. The flow rate of water jets varied from 2.7 to 10.9 L/min, impinging on hot rotary cylinder (Ti =600℃) with rotation speed 10-50 rpm and different curvature ratio (Do/d = 12, 19 and 24). The local average and maximum boiling heat transfer at water jet’s stagnation point revealed effect of studied quenching parameters and multiple jet arrays in the boiling heat transfer. The result showed among the studied parameters, jet’s flow rate and curvature ratio influenced heat transfer in all the boiling regimes. Rotation speed was effective in film and transition boiling regime and strong effect of subcooling was captured in the transition boiling regime. The characteristics of maximum heat flux point in the boiling curve were found to be dependent on the studied quenching parameters as well as array of nozzles. Multiple jet arrays had effect on the spatial variation and rate of boiling heat transfer on quenching surface. The heat transfer enhancement by larger number of rows, i.e. 2-row array, was studied based on two approaches of constant single jet’s flow rate and array’s total flow rate. The result shown better heat transfer performance is achieved by increasing number of row in the array while the total flow rate is constant. It was found that by impinging constant water flow rate into the jets, 2-row array with twice the number of impinging jets enhanced heat transfer significantly in film and transition boiling regime in combination with other quenching parameters.

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  • 9.
    Kocaarik, Toygarhan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Management, Industrial Design and Mechanical Engineering.
    Norberg, Jonas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Management, Industrial Design and Mechanical Engineering.
    Utveckling av hjälpmedel till palleteringsprocess2020Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis is aimed at improving a palletizing process. At present, the packaged cartons are loaded on pallets by hand and with a forklift as lifting aid. The process include several dangers for the operators, such as bad ergonomics and safety hazards. The dangers come from the fact that the packages weigh 70 kilograms, while also being stacked two meters above the floor. The goal is to develop a tool so that the palletizing process can be carried out with greater efficiency while at the same time improving ergonomics and safety for the operators. Risk assessments of the existing process were carried out, then a product development process where concept ideas were generated with a morphological matrix. To early focus the product development process towards ergonomics and to a large extent base the concept choice on the operator's ergonomics the REBA method was implemented. This resulted in a lifting device mounted in an overhead crane provided with motor-controlled claws for holding the carton, motor-controlled tipping device for tipping the carton and a hinged handle so that the operator can operate the lifting device ergonomically. By incorporating REBA into the product development work, a credible examination of the ergonomics could be carried out, where the difficulty was to investigate the angles between different body parts. The hinged handle provides a grip so that the operator can handle the lifting device at ergonomic height while the safety also is improved since the lifting device can be controlled from a distance. The efficiency of the palletizing process has been improved since the forklift is eliminated from the process. Previously, it was required additional personnel was called in to operate the forklift truck while the new solution only requires one operator throughout the whole process. 

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  • 10.
    Levin, Sebastian
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Implementering av centraldifferential i pansarbandvagn BvS10s fördelningsväxeln samt teoretisk utredning av ljudnivån i kuggväxlar2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract

    This thesis was made on behalf of BAE Systems Hägglunds AB a company that is designing and manufacturing military vehicles. The thesis was made on one of the products called BvS10 an armored personnel carrier. The purpose of this vehicle is to be able to transport soldiers in hard terrain and work as a shrapnel cover. This vehicle have a transfer gear box that is what this thesis is focusing on. This gear have the purpose to split the torque from the engine to back unit and to the front. The transfer gear box contains of three spur gears. In the gear box the noise level is high and BAE systems want to investigate what can be changed to reduce noise from the gearbox. They also want to integrate a differential gear. This is to reduce tensions in the gear and the shaft when the vehicle is traveling in harsh terrain. The purpose of this thesis is to theoretically examine what different parameters have an impact on the noise level of the gearbox and also to develop a concept model to integrate the differential gear. The method that’s been used to determine the different parameters for the noise in gears is to conduct a literature revue about noise in sprue gears and the results from a noise level test done by BAE systems ben included to get an idea of the noise level. The design work is based on specifications and framework that can’t be changed and has agreed upon with Bea Systems. After that different sketches was made on possible solutions the best of these solutions was chosen and modeled in Autodesk Inventor Professional. After that calculations was conducted on the spur gears regarding teeth strength. The calculations is based of Swedish standards recommendations. In the literature revue it was found that a big part of noise reduction in spur gears could be to use tighter tolerances witch also increases the manufacturing costs. Another factor to the noise is the helix angle in the spur gear that is also a good thing because it increases the teeth strength with regards for bending stresses. Another method that could be used is to use threaded wheel grinding as finishing method witch have been proven to decrees the noise level.  The result of the sound measurement resulted in that you could see an increase of the noise level with an increase of the RPM but it is hard to draw any more conclusions regarding this because it is hard to judge if this is caused by the hydraulic engine who are running the gearbox.  The result of the engineering work was to use fore different sprue gears. That solution was created because of the axle distance and the gear ratio that needs to stay the same and that the differential gear have a set dimension. The gears was calculated with regards on bending stress and edge stressThe conclusion is that it is possible to implement a differential in the transfer gearbox. The gear housings outer dimensions was kept intact but on one spot a part of the cooling flanges was used to fit the middle shaft. The bearings that was used was the same as in the old gearbox except for two spherical bearings that was used to set the differential in place.  The conclusion is that it is possible to implement a differential in the gearbox but if possible in the future a bigger gearbox should be developed or to change the ratio on the final drive the solution is safe because there is no rotating parts in the open and there is no environmental impact. For the noise reducing effects in the engineering part is hard to prove and to implement in this solution because of the lack of space the helix angel that was used was put to 20 degrees because this is a standard.  To reduce the noise level in a gearbox you can look at the problem in many ways reduction of transmission error is one big thing. It is a matter of building a stable gearbox and increase the tolerances in the gear. Another aria to look in to is to optimise the gear housing chap how is the cheapest solution. This things is possible to do.  Further studies may be to implement a differential lock as well as further studies can be conducted on the old transfer gear to find out where the noise is coming from with a detailed sound and vibration analysis.

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  • 11.
    Märs, Robert
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Management, Industrial Design and Mechanical Engineering, Mechanical Engineering.
    Kranse, Andreas
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Management, Industrial Design and Mechanical Engineering, Mechanical Engineering.
    Utveckling av hjälpmedel för bränsledränering till helikoptermodell Airbus H145 D22020Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The helicopter model Airbus H145 D2 requires a daily inspection of the fuel. The inspection means that a small amount of fuel is drained and inspected from the drainage points located under the helicopter. This is currently done by crawling in under the helicopter, which isn’t ergonomic and may involve some risks.

    The purpose of this paper is to improve the working environment for the inspector with the goal of developing a functional prototype of a tool. To achieve this, previous research is used on risk assessment of work postures and the use and development of prototypes in a development process. Prototypes was manufactured, tested and evaluated to ease the design process. Risk analyzes using the risk assessment method Ovako Working Posture Analysis System, OWAS, was performed both with and without the tool.

    The developed prototype tool consists of a frame that can be pushed under the helicopter. On the frame is a pillar lift with a platform that can be raised and lowered using a combination of a lever and a clamping handle. The existing drainage tool is placed on the platform and thus the drainage valves can be opened and the fuel drained out. With the tool, the inspector no longer needs to crawl in under the helicopter. Work positions with an increased risk have been reduced from about 90 to 20 percent.

    The prototypes shows the advantages of using rapid prototyping methods early in the development and to risk analyze ideas already in the development process.

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  • 12.
    Nordkvist, Erika
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Konstruktion av hydraulben till mobilt siktverk tillhörande Aktiebolaget Arbrå Sikt & Matare2015Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
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  • 13.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Tatar, Kourosh
    LTU.
    Sound field determination and projection effects using laser vibrometry2006In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 10, p. 2843-2851Article in journal (Refereed)
    Abstract [en]

    Sound measurements using laser vibrometry have the advantage that field measurement can be obtained through scanning. It is a non-contact method that provides both qualitative and quantitative information. However, it must be noted that the measurement is an integral along the path of the probing beam. Some effects of this projection are investigated both through measurements and calculations. The sound field calculations are made from measured surface vibrations and they are in good agreement with the measured sound field. The calculations show that the projections very much depend on parameters such as integral depth, or probing depth, and the orientation of the sources. In addition to this, the calculated, or measured, amplitude experiences an enhancement which depends on the wavelength and the distance from the sound source. This enhancement can even result in increasing amplitude with distance. Even though this makes the quantitative data obtained not trustworthy, it is a benefit for the qualitative results which become clearer.

  • 14.
    Pappadà, Silvio
    et al.
    Departments of Materials and Structures Engineering, Technologies and Processes Area, Consorzio CETMA.
    Gren, Per
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Tatar, Kourosh
    LTU.
    Gustafson, Tord
    APC Composite, Karlsvik, Luleå.
    Rametta, Rocco
    Departments of Materials and Structures Engineering, Technologies and Processes Area, Consorzio CETMA.
    Rossini, Ettore
    Extreme Materials S.r.l., Costa Masnaga.
    Maffezzoli, Alfonso
    Department of Engineering for Innovation, University of Salento.
    Mechanical and vibration characteristics of laminated composite plates embedding shape memory alloy superelastic wires2009In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 18, no 5-6, p. 531-537Article in journal (Refereed)
    Abstract [en]

    Currently, there is a great interest in the study of shape memory alloy (SMA) composites, since SMA wires with a small diameter have become commercially available. Many potential uses have been found for SMA composites in shape control, vibration control, and for the realization of structures with improved damage tolerance. In this work, two types of SMA-hybridized composites are presented for investigating the mechanical and vibration characteristics. The first one contains unidirectional superelastic SMA wires, while the other has been realized with embedded knitted SMA layers. The samples from these laminates have been tested according to "Charpy method" (ASTM D256) and static flexural test method (ASTM D790) to evaluate the influence of the integration of thin superelastic SMA wires on the impact behavior and the mechanical properties of the hybrid composites. Moreover, since the SMA wires are expected to give damping capacity, by measuring the vibration mode of a clamped cantilever using laser vibrometry, the influence of both SMA arrangements on the vibration characteristics has been investigated. Finally, further tests have been carried out on composite panels realized by embedding unidirectional steel wires to distinguish the influence of the martensitic transformation from the pure introduction of a metallic wire into the polymeric matrix.

  • 15.
    Sandberg, Mats
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Kabanshi, Alan
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Wigö, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Is building ventilation a process of diluting contaminants or delivering clean air?2020In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 29, no 6, p. 768-774Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to discuss the performance of air distribution systems intended for dilution of contaminants (e.g. mixing ventilation) and those intended for delivery of clean air to local regions within rooms (e.g. personalized ventilation). We first start by distinguishing the systems by their visiting frequency behaviour. Then, the performance of the systems with respect to their possibility to influence contaminant concentration in the room or regions within the room is dealt with. Dilution capacity concept for mixing systems is discussed, and delivery capacity concept for systems intended to deliver clean air locally is introduced. Various ways for supply of clean air to regions within the room are presented and their pros and cons are discussed. In delivery capacity systems, the most important single parameter is the entrainment of ambient air into the primary supply flow. Therefore, methods of determining entrainment in these systems need to be defined and the results should be included when describing the performance of the air terminal devices.

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  • 16.
    Sjödahl, Mikael
    et al.
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Gren, Per
    Tatar, Kourosh
    LTU.
    Olsson, Erik
    Laser metrology in experimental mechanics2005In: 10th NOLAMP Conference: the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden / [ed] Alexander Kaplan, Luleå: Luleå tekniska universitet , 2005, p. 41-52Conference paper (Refereed)
  • 17.
    Tatar, Kourosh
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Machine tool vibrations and violin sound fields studied using laser vibrometry2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The knowledge of the dynamic behaviour of a milling process is very important for finding an optimum process window. In today's manufacturing industry the machining parameters are often predicted using experimental data from non-rotating spindles. Many times the predicted machining parameters prove to be ineffective and inaccurate which lead to reduced quality of the machined surface, tool wear, noise or at worst spindle failure. The best way to study the dynamics of the milling spindle is of course to measure the spindle response under actual operating conditions. Laser vibrometry is a non-contact, non-disturbing method commonly used for measurements of vibrations on static objects. The technique offers the possibility to measure vibrations on thin-walled (light), and rotating objects as well as sound fields. However, two major problems occur when measuring on rotating spindles: (1) speckle noise and (2) crosstalk between the vibration components. These two drawbacks make vibration measurements on rotating spindles difficult to interpret. In this Licentiate thesis the principles of laser vibrometry is introduced and the speckle noise and the crosstalk between the velocity components of a rotating spindle is studied experimentally. The rotating spindle is excited by an adaptive magnetic bearing and the response is measured by laser vibrometry and non-contact inductive displacement sensors simultaneously. The work shows that by polishing the measurement surface optically smooth we are able to avoid the speckle noise and the crosstalk problem. By using this approach, the vibrations as well as the roundness of the measured target can be resolved. Hence, the laser vibrometry technique can be used for measuring the spindle dynamics under operating conditions. Measurements on a bowed violin are performed. The chain of interacting parts of the played violin is studied: the string, the bridge and the plates as well as the generated sound field. The string is excited using a rotating bow apparatus and the vibrations from the string transmits to the violin body via the bridge and produces the sound. The measurements on the string shows stick-slip behaviour and the bridge measurements show that the string vibrations transmit to the bridge both in the horizontal and the vertical direction. Measurements on the plates show complex deflection shapes which are a combination of different eigenmodes. The sound fields emitted from the violin were measured and visualized for different harmonic partials of the played tone. However, the visualized sound field obtained by the laser vibrometer is a projection of the sound field along the laser light and the image obtained is a 2D map of the real 3D sound field. This effect is illustrated by measurements of a sound field emitted from three ultrasound transducers.

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  • 18.
    Tatar, Kourosh
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Vibrationsmätning på roterande fräsverktyg med laservibrometri2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet , 2007, p. 75-Conference paper (Other academic)
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  • 19.
    Tatar, Kourosh
    et al.
    LTU.
    Gren, Per
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Measurement of milling tool vibrations during cutting using laser vibrometry2008In: International journal of machine tools & manufacture, ISSN 0890-6955, E-ISSN 1879-2170, Vol. 48, no 3-4, p. 380-387Article in journal (Refereed)
    Abstract [en]

    Spindle and tool vibration measurements are of great importance in both the development and monitoring of high-speed milling. Measurements of cutting forces and vibrations on the stationary spindle head is the most used technique today. But since the milling results depends on the relative movement between the workpiece and the tool, it is desirable to measure on the rotating tool as close to the cutters as possible. In this paper the use of laser vibrometry (LDV) for milling tool vibration measurements during cutting is demonstrated. However, laser vibrometry measurements on rotating surfaces are not in general straight forward. Crosstalk between vibration velocity components and harmonic speckle noise generated from the repeating revolution of the surface topography are problems that must be considered. In order to overcome the mentioned issues a cylindrical casing with a highly optically smooth surface was manufactured and mounted on the tool to be measured. The spindle vibrations, radial tool misalignment, and out-of-roundness of the measured surface were filtered out from the signal; hence the vibrations of the cutting tool were resolved. Simultaneous measurements of cutting forces and spindle head vibrations were performed and comparisons between the signals were conducted. The results showed that vibration velocities or displacements of the tool can be obtained with high temporal resolution during cutting load and therefore the approach is proven to be feasible for analyzing high-frequency milling tool vibrations.

  • 20.
    Tatar, Kourosh
    et al.
    LTU.
    Gren, Per
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Digital holographic interferometry for simultaneous orthogonal radial vibration measurements along rotating shafts2008In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, no 18, p. 3269-3274Article in journal (Refereed)
    Abstract [en]

    A digital holographic interferometry setup used to measure radial vibrations along a rotating shaft is presented. A continuous Nd:YAG laser and a high-speed digital camera are used for recording the holograms. The shaft was polished optically smooth to avoid speckle noise from the rotating surface. The light reflected from the shaft was directed onto a diffuser which in turn was imaged by the holographic system. Simultaneous measurements with a laser vibrometer were performed at one point and comparisons between the signals showed good agreement. It is shown that different vibration components of a rotating shaft can be simultaneously measured with this technique.

  • 21.
    Tatar, Kourosh
    et al.
    LTU.
    Olsson, Erik
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Tomographic reconstruction of 3D ultrasound fields measured using laser vibrometry2007In: Experimental analysis of nano and engineering materials and structures: proceedings of the 13th International Conference on Experimental Mechanics, Alexandroupolis, Greece, July 1-6, 2007 / [ed] Emmanuel Gdoutos, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag , 2007Conference paper (Refereed)
    Abstract [en]

    A method for obtaining the amplitude and phase distribution of an ultrasound field in air, using laser vibrometry and computed tomography, is described. Radiating ultrasound transducers causes pressure variations in the air, which lead to refractive index changes, which in turn can be recorded by the use of interferometric instruments like the laser vibrometer. This point measuring method for the measurement and visualization of sound fields was proposed by Zipser et al. [1, 2]. In order to measure the whole sound field, the laser beam is scanned over the area of interest. With this technique, the absolute phase of the field is obtained directly from the measurements while the amplitude needs some calculations using the Gladstone Dale equation [3]. Moreover, the obtained result using laser vibrometry for sound measurements is an integral of the sound field along the laser light path. The projection effects due to this integral were studied by Olsson and Tatar [4]. In this paper however, the projection property of the measurement method is taken into advantage. Tomographic 3D reconstruction of the sound field is obtained using several projections taken at different angles. The phase and the amplitude distributions of an ultrasound field due to several transducers, emitting at a frequency of 40 kHz, positioned both symmetrically and non-symmetrically are reconstructed.

  • 22.
    Tatar, Kourosh
    et al.
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Rantatalo, Matti
    Luleå tekniska universitet, Drift, underhåll och akustik.
    Gren, Per
    Luleå tekniska universitet, Strömningslära och experimentell mekanik.
    Laser vibrometry measurements of an optically smooth rotating spindle2007In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 21, no 4, p. 1739-1745Article in journal (Refereed)
    Abstract [en]

    Laser doppler vibrometry (LDV) is a well-established non-contact method, commonly used for vibration measurements on static objects. However, the method has limitations when applied to rotating objects. The LDV signal will contain periodically repeated speckle noise and a mix of vibration velocity components. In this paper, the crosstalk between vibration velocity components in laser vibrometry measurements of a rotating dummy tool in a milling machine spindle is studied. The spindle is excited by an active magnetic bearing (AMB) and the response is measured by LDV in one direction and inductive displacement sensors in two orthogonal directions simultaneously. The work shows how the LDV crosstalk problem can be avoided if the measurement surface is optically smooth, hence the LDV technique can be used when measuring spindle dynamics.

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