Percussion Hammer Research Articles

Dr Graham Steell and monaural stethoscopes: Cardiology before the ECG.

Dr Graham Steell, MB CM MD FRCP (1851-1942), an Edinburgh graduate, was a physician at the Manchester Royal Infirmary (1878-1911) and professor of medicine at the Victoria Manchester University (1907-1911). He is mainly remembered for describing the 'Graham Steel murmur', however his name is also associated with the 'Graham Steell monaural stethoscope', which he designed. His clinical examination of the cardiovascular system at the bedside was meticulous, using only his stethoscope, percussion hammer, and a sphygmograph to record the radial pulse. His work is described in his monograph, Diseases of the Heart (1906) and other numerous papers. The University of Manchester Museum of Medicine and Health has a collection of monaural stethoscopes, percussors and sphygmographs. This article explores Dr Steell's clinical techniques and contribution to cardiology in an era before chest X-rays and electrocardiography, and also discusses the use of monaural stethoscopes and percussion hammers by the wider medical profession during the Victorian and Edwardian period.

Realization of shorter substitutes for a percussive rock drill hammer by periodic redistribution of its mass and compliance

In percussive drilling of rock, use is made of high-amplitude short-duration force pulses generated through impacts of a hammer on a drill bit or a drill rod assembly. The mass of the hammer is crucial for the impact velocity and the impact frequency, while its length and variation of characteristic impedance control the duration and shape of the force pulses. High efficiency of conversion of kinetic impact energy to work results if the force pulses have suitable shapes and durations. Commonly, hammers of hydraulic rock drills are nearly uniform and generate nearly rectangular force pulses admitting high efficiencies. When space is constrained, short hammers are advantageous as they allow short rock drills. Here, therefore, shorter substitutes for uniform original hammers are sought. They should have the same mass as the original hammer, be shorter than the original hammer, and generate approximately the same impact force history as the original hammer. A method based on 1D theory is developed for realization of substitute hammers with axially periodic characteristic impedance. Impact force histories generated by such hammers agree well with that generated by a uniform original hammer in a 1D context, and also in a 3D context if 3D effects are small enough. Also, for bit-rock interaction conditions from soft to hard, the efficiencies obtained by use of substitute hammers agree well with that obtained by use of the original hammer.

History and national survey on reflex hammers: which is the chosen one of Brazilian neurologists?

Percussion is an important part of the neurological examination and reflex hammers are necessary to obtain it properly. We aimed to review the historical aspects of the main reflex hammers and to define the favorite one of Brazilian neurologists. We searched original and review articles about historical aspects of the reflex hammers in Scielo and Pubmed and conducted an online survey to investigate the favorite reflex hammer of Brazilian neurologists. In the first part, we describe the major milestones in the creation of the reflex hammers. Following, we exhibit the results of the online survey: Babinski-Rabiner was the most voted. The origins of the reflex hammers goes back long before their creation, from a basic clinical examination method: percussion. Since the description of deep tendon reflexes and the creation of percussion hammers, much has been improved in this technique. Among all the hammers surveyed, the Babinski-Rabiner was the chosen one by a significant portion of Brazilian neurologists.

The neurologist's bag

The first page of The Lancet Neurology portrayed the neurologist as “one of the few specialists who can diagnose a patient with just a hammer and a pin”.1 Well, not quite. In 1947, Merritt, Mettler, and Putnam2 listed the useful “tools of the trade” found in a neurologist's “basket or bag”: ophthalmoscope and otoscope, rubber percussion hammer, 128 cps tuning fork, steel pin through a tongue depressor, camel hair brush trimmed to 10–20 hairs, test odours (menthol, coffee, vanilla, peppermint), test taste vials (sugar, saccharin, salt, vinegar, quinine), Jaeger test types (or similar card), dynamometer, metal tubes for water temperature discrimination, and test objects for confrontation perimetry.

Development and Fabrication of an Innovative Smart Tool to Monitor the Impact Carving Process on Brittle Stones and Marble

The art of sculpting is related to the processing of brittle materials, such as granite, marble, and stone, and is implemented using percussive hand tools or rotational roughing tools. The outcome of percussion carving is still directly related to the technique, experience, and capacity of the sculptor. Any attempt to automate the art of sculpturing is exhausted in the subtraction method of brittle materials using a rotating tool. In the process of percussion carving, there is no equivalent expertise. In this work, we present the design, manufacturing (3D printing and CNC machining), and use of a smart, percussion carving tool, either manually by the hand of a sculptor, adjusted in a percussive pneumatic hammer, or guided by a digitally driven machine. The scope is to measure and record the technological variables and sizes that describe and document the carving process through the sensors and electronic devices that the smart tool incorporates, the development and programming of which was implemented for the purposes of this work. The smart carving tool was meticulously tested in various carving stones and stressing scenarios to test the functionality and efficacy of the tool. All the tests were successfully implemented according to the specifications set.

A Modular Mechanism for Downhole Weight-on-Bit and Torque Reaction in Small Diameter Boreholes

Abstract Drilling systems that use downhole rotation must react torque either through the drill-string or near the motor to achieve effective drilling performance. Problems with drill-string loading such as buckling, friction, and twist become more severe as hole diameter decreases. Therefore, for small holes, reacting torque downhole without interfering with the application of weight-on-bit, is preferred. In this paper, we present a novel mechanism that enables effective and controllable downhole weight on bit transmission and torque reaction. This scalable design achieves its unique performance through four key features: (1) mechanical advantage based on geometry, (2) direction dependent behavior using rolling and sliding contact, (3) modular scalability by combining modules in series, and (4) torque reaction and weight on bit that are proportional to applied axial force. As a result, simple mechanical devices can be used to react large torques while allowing controlled force to be transmitted to the drill bit. We outline our design, provide theoretical predictions of performance, and validate the results using full-scale testing. The experimental results include laboratory studies as well as limited field testing using a percussive hammer. These results demonstrate effective torque reaction, axial force transmission, favorable scaling with multiple modules, and predictable performance that is proportional to applied force.

A new percussion hammer mechanism for a borehole deployable subglacial sediment corer

AbstractSubglacial sediments have the potential to reveal information about the controls on glacier flow, changes in ice-sheet history and characterise life in those environments. Retrieving sediments from beneath the ice, through hot water drilled access holes at remote field locations, present many challenges. Motivated by the need to minimise weight, corer diameter and simplify assembly and operation, British Antarctic Survey, in collaboration with UWITEC, developed a simple mechanical percussion corer. At depths over 1000 m however, manual operation of the percussion hammer is compromised by the lack of clear operator feedback at the surface. To address this, we present a new auto-release-recovery percussion hammer mechanism that makes coring operations depth independent and improves hammer efficiency. Using a single rope tether for both the corer and hammer operation, this modified percussion corer is relatively simple to operate, easy to maintain, and has successfully operated at a depth of >2130 m.

An Axial and Torsional Percussion Hammer with Considerable Potential to Increase the Drilling Speed of High-Temperature Geothermal Wells

Geothermal energy is a kind of green and sustainable energy and an essential alternative energy in the future. Improving the drilling speed of geothermal wells is helpful for the efficient exploitation of geothermal resources. Axial & Torsional Percussion Hammer (ATPH) was proposed in this paper for drilling enhancement. ATPH can convert the kinetic energy of the drilling fluid to percussion load, and improve the rock-breaking efficiency of the bit. Because of its mechanical seal design, it can operate efficiently at temperatures over 200 °C, which proves that it can be used in geothermal wells. The large eddy simulation (LES) method is chosen to calculate the percussion load characteristics of the ATPH oscillator, including its main frequency and amplitude. In the field drilling experiments of two high-temperature wells, ATPH showed better ROP enhancement ability and longer working life than PDM. In the well interval drilled by ATPH, the maximum temperature at the well bottom reached 202.54 °C.

Numerical simulation of the energy transfer efficiency and rock damage in axial-torsional coupled percussive drilling

Axial-torsional coupled percussive drilling helps improve the breaking efficiency of hard rock. This paper adopted the simulation method to study the energy transfer efficiency (ETE), and rock damage in axial-torsional coupled percussive drilling with a multiple-button bit. The axial-torsional coupled percussive system model was first built in the finite element calculation platform. And then the temperature-dependent model parameter values for rock were selected. Finally, we simulated axial-torsional coupled percussive process, and analyzed the effects of various parameters. The main simulation results are as follows. In axial-torsional coupled percussive process, axial percussion has a significant influence on the ETE of torsional percussion, while torsional percussion has little influence on the ETE of axial percussion. As the impact velocity of axial percussive hammer increases, the ETE of axial percussion, the ETE of torsional percussion, and the total ETE all augment. When the impact velocity is increased from 4 m/s to 16 m/s, the total ETE is increased by 62.8%. Both the ETE of torsional percussion and the total ETE decline with the pulse torque amplitude increasing. When the pulse torque amplitude is increased from 4000 N m to 28000 N m, the total ETE is reduced by 18.3%. For convenience, we abbreviate the ratio of the torsional input energy to the total input energy as RTT. An increase in RTT, or an increase in rock temperature will reduce the ETE of axial percussion, the ETE of torsional percussion, and the total ETE. When the RTT is increased from 2.3% to 84.4%, the total ETE is reduced by 34.5%. As the axial impact velocity increases, the rock damaged areas gradually expand. With the increase of the pulse torque amplitude, the rock damaged areas sharply expand. As the RTT increases, the number of narrow tensile damaged zones extending outwardly decrease, while the connectivity between the tensile damaged areas caused by buttons augments. As the rock temperature rises, the total damaged area of rock gradually shrinks. This study provides a theoretical basis for the efficient rock breaking in axial-torsional coupled percussive drilling.

Squeezing force detection and signal processing for robot assisted pneumatic percussive riveting system

Abstract Researches in the literature treated the pneumatic percussive riveting as an open-loop process. Vibration signals of the percussive hammer and driven-head based dimensions cannot be used to real-time control each impacting of the pneumatic percussive riveting. The paper installs a force sensor on the bucking bar to collect the squeezing force signal in pneumatic percussive riveting. And a squeezing force based closed-loop process control method for robot-assisted pneumatic percussive riveting is proposed. After introducing the robot assisted pneumatic percussive riveting system, the squeezing force and the impacting frequency under different pneumatic pressure are investigated extensively with the constructed pneumatic percussive riveting platform. A squeezing force signal processing method based on time-frequency analysis is used to extract the characteristics of the percussive riveting such as the peak squeezing force, the impacting frequency and the number of impacts etc. Based on the peak squeezing force and the impacting frequency, the pneumatic percussive riveting process is divided into four stages in order to control the squeezing force of the robot riveting efficiently. A squeezing force based real-time feedback algorithm is proposed to control the squeezing force of each impacting by adjusting the pneumatic pressure and the feed force. The squeezing force based real time control method outlined in the paper is found to be effective and accurate. It can be used for robot-assisted pneumatic percussive riveting system, and closed-loop control of percussive riveting in sheet metal assembly.

The neurologist’s hammer

From the obscurity of 18th century wineries to the hands of the greatest neurologists in history, the percussion hammer has a fascinating history. The first famous percussion hammer was created in 1841 by the German physician Max Wintrich and was initially used for thoracic percussion. In 1875, Erb and Westphal both published simultaneous articles with the results from research that they had conducted separately, from which they confirmed that percussive objects were useful for stimulating deep tendon reflexes, especially patellar reflexes. The percussion hammer, however, was not yet ideal. It was designed to strike the thorax rather than the tendons, so it did not have the right weight or ideal length, and even its shape was not practical. New modified versions of the instrument subsequently emerged, and the hammer became the characteristic symbol of the neurologist.

Compressive vacuum resistance to percussion hammer in downhole vibration source

The paper focuses on downhole vibration source used for wave generation in an oil stratum in order to increase oil recovery and stimulate hydrocarbon flow in a well. Simulation results of pre-shock compressive vacuum resistance to a hammer in an electromagnetic shock unit in a downhole vibration source are presented. The effect of axial hole in a hammer on induced compression is analyzed. Experimental data on changes in coil electromagnetic traction are presented depending on axial hole diameter in the hammer. Based on the effect of hammer hole diameter on compressive vacuum resistance and coil electromagnetic traction the present research findings can be of great use in designing an electromagnetic shock unit.

Caractérisation de l’industrie lithique de la fin du Néolithique, dans le bassin de la Seine (de la deuxième moitié du IVe millénaire à la fin du IIIe millénaire av. J.-C.)

Cet article présente une synthèse sur l’industrie lithique du Néolithique récent et final dans le bassin de la Seine (entre 3500 et 2100 avant notre ère). Son objectif est de distinguer l’industrie lithique du Néolithique récent de celle du Néolithique final et, plus largement, de préciser la définition des groupes culturels, leur localisation et leur chronologie par l’étude du mobilier lithique en contexte domestique et sépulcral. La première étape de la caractérisation porte sur les modalités de l’approvisionnement, généralement réalisé à proximité des occupations durant le Néolithique récent et final. L'importation de matières premières suit une même tendance, sur deux aspects, le sens de circulation des pièces en silex secondaire et tertiaire mais aussi la forme sous laquelle ces produits circulent. Le Néolithique final se distingue par une diffusion d’artefacts en roche verte et en silex du Turonien supérieur de la région du Grand-Pressigny. Au Néolithique récent, la production laminaire présente certaines caractéristiques au niveau du type de percussion utilisé (indirecte et directe tendre) mais aussi de la répartition géographique de ces techniques et sur le statut des produits laminaires en contexte sépulcral. Plusieurs indices suggèrent que le ralentissement de la production laminaire domestique débute à partir du Néolithique final. Cette période se distingue aussi par une diversification de l'outillage et par l’existence d’une production d’éclats par débitage centripète sur la façade maritime. L’étude comparative de plusieurs zones du bassin de la Seine met en évidence les variabilités temporelles et spatiales et interroge la validité des faciès régionaux (Augereau et al., 2007). L''existence d'un « faciès Marne » , proposé à l’issue de synthèses sur les pratiques funéraires, le mobilier en matière dure animale et la parure, est à nouveau validée par l''industrie lithique.

Acheulean breccias of Prince cave (Liguria, Italy): New insights and regional issues

Prince cave is located along the Liguro-provençal corridor, in Italy (Liguria). Between mountains and sea, in the heart of a refuge zone, this site is part of the Paleolithic complex of sites called Balzi Rossi or Grimaldi. The excavations led from 1966 to 2002 managed to unearth Acheulean industries in two distinct brecciated deposits. Former interdisciplinary studies and analysis attributed Br2 to MIS 7 (220,000 ± 120/50 ka) and Br1 to MIS 6. With the aim to update the characterizations and the place of these assemblages within the regional Acheulean panorama, this work conducts for the first time an exhaustive study on the respective industries. It provides detailed data on their numerical distributions, territorial patterns, technical features, and technoeconomic strategies. The results leads undoubtedly to common behaviors but modulated by significant differences. Both groups were looking for available littoral pebbles as to shape heavy and large cutting tools, in particular in Br1 (n = 159) where they are better and wider represented (choppers, chopping-tools, handaxes, picks, unifacial, rostro-carinate, épannelé). Br2 (n = 290), richer in artefacts, delivers much fewer products among which larger choppers, chopping-tools and bifacial piece. In both cases, direct percussion with hard hammers is prevalent, but bipolar percussion and soft hammer (Br1) had also been employed in finalization phases. Furthermore, the corpuses always include large flakes coming from specific operating sequences of debitage. Local Ciotti flints and other semi-local hard siliceous materials (Perinaldo flints, microquartzite), collected on the ligurian littoral at 10–20 km to the east, were used for medium flakes productions and the confection of retouched tools. Western (15–20 km) and allochthonous (>30 km) procurements appear exclusive to Br2. However, Prince knappers shared the same techniques (direct percussion with hard hammers), methods (unifacial/bifacial Discoid, recurrent unipolar, bipolar, and centripetal Levallois, SSDA) and technoeconomic strategies (ramifications, recycling of isotropic materials, blanks, tools, in situ knapping and confections). Volumetric unipolar and orthogonal methods are only inventoried in Br2. Debitage schemes pursued the productions of unretouched elongated flakes and manufacturing of scrapers and denticulates. Br2 corpus revealed a better control and efficiency in this particular regard. Its operating sequences are longer, more complex and achieved. It offers also a more various toolkit (transversal scrapers, Clactonian and retouched notches, beaks, points, Tayac point, awls, end-scrapers). With a lower “pre-Mousterian” industry and a upper “final Acheulean”, Prince industries complete and inform the Acheulean neighboring complex.

A push corer developed for retrieving high-resolution sediment cores from shallow waters

Shallow water environments are often difficult ones from which to recover undisturbed sediment cores, lending themselves to neither deep water sampling, nor techniques employed for wetland areas. The most simple and obvious way to obtain a core in water depths of less than 2 m is to drive a core tube directly into the sediments using some form of push rod or a percussion (hammer) device. A core driven by percussive methods, however, may be difficult to recover and sealing the tube may be problematic for retention of the sample. Here we describe a simple coring device designed for shallow water operation. The design contains elements of both deeper water gravity and directly driven push rod coring equipment. The device can recover cores up to about 1 m in length in water depths up to about 3–4 m deep. The sampling device has been tested over a number of years from diverse limnological settings (high and mid-Arctic lakes, temperate lakes) with consistently satisfactory results.

Hydraulic Percussion Drilling System Boosts Rate of Penetration, Lowers Cost

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 172935, “Hydraulic Percussion Drilling System With PDC Bit Increases ROP and Lowers Drilling Costs,” by Scott W. Powell, NOV, and Ertai Hu, Greatwall Drilling Company, prepared for the 2015 SPE Middle East Unconventional Gas Conference and Exhibition, Muscat, Oman, 26–28 January. The paper has not been peer reviewed. Drilling the Severnaya Truba field in Aktobe, Kazakhstan, has been costly and time consuming. In combination with a drilling-fluid-powered percussion hammer (FPPH), a fit-for-application polycrystalline-diamond- compact (PDC) bit with depth-of-cut (DOC) -control features was used to minimize the exposure of the cutting structure and prevent breakage. The mechanical lifting and falling action creates a rapid variation in weight on bit (WOB), allowing the bit’s DOC to fluctuate while overcoming different stresses. These variations, along with the percussion pulse created with each stroke, led to increased rates of penetration (ROPs). Introduction Drilling with an air hammer is a technique whereby gases (typically compressed air or nitrogen) are used to operate a pneumatic hammer, to cool the drill bit, and to lift cuttings out of the wellbore. Air forced down the drillstring actuates the percussion tool, which, in turn, creates an axial percussion force directed down to a specially designed drill bit. The advantages of air drilling are that it is usually much faster than using drilling fluid and may eliminate lost-circulation problems. The disadvantages are the inability to control the influx of formation fluids into the wellbore and the destabilization of the borehole wall in the absence of wellbore pressure typically provided by the mud column. Air hammers are also limited to a lower WOB and will stop working if that weight is exceeded. An FPPH is the next step in performance drilling. Using the same flow rates and operating WOB of a conventional assembly, the tool offers the benefit of an axial percussion force to facilitate the cutting action of the bit. Like an air hammer, the axial percussion force is generated near the bit to give the cutting structure more energy and overcome the formation’s compressive strength.

Analysis of Clinical Percussion Signals Using Matching Pursuit

Clinical percussion is a method of eliciting sounds from the body by tapping with either a percussion hammer or fingers to determine the area under the perused is air filled, fluid filled, or solid, and is used in clinical examinations to assess the condition of the thorax or abdomen. Successful diagnosis today is still highly subjective and dependent's on physician skill, experience and require quite surrounding areas. An automated system capable of delivering standardized percussion analysis would remove these limitations on the technique and allow for its usage by those without such specialized training and years of necessary experience. For this to be possible, efficient and informative signal processing algorithms must be employed. In this investigation, clinical percussions from healthy volunteers taken by trained medical professionals were analysed via the matching pursuit (MP) algorithm. Various types of possible dictionaries are discussed comparing their efficiency and convergence behaviour. Noise filtering methods are discussed and a noise reduction method based on MP analysis results is presented.MP is also compared to other methods for representing clinical percussions with regards to informativeness and efficiency. MP is ��(��log��) which is more efficient than current methods which have a complexity of at least ��(�� 3 ).

The outcome of lateral incision skin flap hypalgesia and knee functions for OA patients 5 years after total knee arthroplasty

Purpose: Nowadays, Total knee arthroplasty (TKA) has become an important treatment for late stage Osteoarthritis (OA) patients and almost all of the patients will report numbness on the lateral incision skin flap after surgery. Although many studies has revealed the reason and change of this numbness, no such conclusion has been made for the 5 years outcome and its effects on patients’ knee function based on both questionnaire and physical examinations. Methods: 40 OA patients (59 knees) after TKA were continuously recruited, and the areas of numbness (analgesia areas and hypalgesia areas) were marked and measured around the midline incisions one week after TKA. A technician used the pin of percussion hammer for crude test around the incisions, then tested with a needle outside-in and downward. Marks were made when patients began to feel loss of pain or decrease of pain. Tests were repeated every 1cm. Analgesia areas and hypalgesia areas were formed by linking the marked dots together, while the positions of the patella and tibial tuberosity were also marked (Shown as Fig.1). At the same time, the patients’ medical and surgical information were detailedly recorded, including gender, age, body mass index (BMI), one or both knees for TKA, left or right knee for TKA, got patellar replaced or not, as well as the intraoperative bleeding volumes, postoperative drainage volumes, prosthesis types, lengths of incisions, the lengths from the tibial tuberosities to the distal and proximal points of incisions, and preoperative KSS (Knee society score) clinical and function scores. The areas of numbness were measured again by the same technician with the same method at a mean follow-up of 5 years (60-63 months) (Shown as Fig.2). In addition, SF-36 questionnaire, KSS clinical and function scores, and the University of Western Ontario McMaster osteoarthritis Index visual scores (WOMAC) were also required to complete. All the areas were measured by the "AutoCAD" Software), and SAS statistical software was used for statistical analysis. We defined the objective numbness as tested hypalgesia area and subjective numbness as self-reported hypalgesia. Results: All of the 40 patients had analgesia areas(39.4±14.4) cm2 (14.4cm2_85.5cm2) and hypalgesia areas (71.6±23.9) cm2 (27.0cm2_127.3cm2) one week after TKA. 5 years after TKA, all of the patients had no more analgesia areas and the average of hypalgesia areas was (10.8±11.6) cm2 (0.0cm2_42.6cm2), with 16 knees of 10 patients reported a complete restoration of objective numbness. There was a decrease of 84.9% on hypalgesia areas from 1 week after TKA to 5 years after TKA (t = 17.6, P < 0.01). At the 1 week examination, there was positive correlations between the lateral incision skin flap hypalgesia areas with the lengths of incisions (t = 3.07, P = 0.002); and with the lengths from tibial tuberosities to the distal point of incisions (t = 3.78, P <0.001). At the 5 years examination, the lateral incision skin flap hypalgesia areas had no correlations with all of the variables we concerned. And the existence of the patients’ subjective or objective numbness (hypalgesia areas) at both 1 week and 5 years after TKA had no affection on their 5 years’ KSS clinical and function scores, WOMAC scores, or SF36 PCS and MCS scores, even adjusted for age, sex, BMI and the preoperative KSS clinical and function scores. Conclusions: All patients get lateral incision skin flap hypalgesia areas after TKA and its improvement occurs over the next few years. The lateral skin incision hypalgesia areas have no significant effect on the patients’ 5-year functional rehabilitation. Therefore, patients after TKA have no necessities to worry about the affecting of hypalgesia areas on their rehabilitation. However, the consent of this complication is necessary before TKA.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

The Pirro Nord site (Apricena, Fg, Southern Italy) in the context of the first European peopling: Convergences and divergences

Pirro Nord, located in Apricena, Southern Italy, represents one of the earliest records of hominin dispersal into Europe. The site is dated on a biochronological basis between 1.6 and 1.3 Ma and a significant vertebrate assemblage (Pirro Nord Faunal Unit) is associated with lithic artefacts which show many similarities with more or less contemporaneous lithic assemblages in Europe and with the African Mode 1.Since 2006, 340 artefacts have been found in the Pirro 13 fissure, and the lithic series is considered as a homogenous assemblage in terms of taphonomical, technological and raw material characteristics. Flint is the main raw material and the available and exploited flint cobbles and pebbles have different morphologies and sizes. The raw material has been collected in a secondary position near the actual location of the deposit.Two main reduction sequences have been performed by hominins in Pirro Nord: an “opportunistic” debitage, with multiple striking platforms in order to produce flakes of different morphologies including some “debordant” flakes and at least one cutting edge, and a “centripetal” or convergent debitage for the production of flakes with convergent cutting edges. The “opportunistic” approach has been adopted for the reduction of the largest flint cobbles and the polyhedral pebbles/cobbles. This method is considered as an adaptation to the raw material shape. The debitage is always made by direct percussion and hard hammer. Most of the cores are abandoned non-exhausted. In some rare cases, the use of flint pebbles of poor quality is also documented and seems to be the result of a very opportunistic and expeditious behaviour. Four flakes are retouched and are from an advanced phase of the debitage.The patterns from Pirro Nord fit well with the technological features provided by most of the European Mode 1 sites. Some peculiar features may be observed, possibly due to the main use of flint. The site with the highest similarities with Pirro Nord is Cà Belvedere di, possibly because the raw materials are ovoid flint pebbles. The lithic strategies at Pirro Nord are characterized, (1) by “opportunistic” and expedient behaviour adapted to the raw material constraints, suggested by the very short reduction sequences and by the non-exhaustion of the cores and, (2) by a series of products (pointed flakes) that appears to indicate a presumable intentionality.

Numerical modelling of percussion water jets driven by multiple collisions

A numerical model is proposed in this research to analyse the behaviour of the pulse jet driven by percussion hammer. The mass of the hammer is usually larger than that of the piston and the resistance of compressed water can low down the piston, thus multiple collisions occur each time when the hammer strikes the piston. The proposed model has the merit to consider various striking possibilities to simulate the process of pulse water jet generated by multiple hammer collisions. In addition, a hammer-driven percussion pulse jet is developed and the corresponding experiments are carried out for verifying the reliability of the numerical model. Comparison results show that the predicted pressure and velocity values match well with the experimental data. The simulation of the generation of pulsed jet reveals the collisions and motions of the hammer and the piston and provides understanding of the mechanism of the pulse jet generation. The design of the hammer-driven pulse water jet device can be optimised through modelling different combinations of the parameters of the chamber, hammer, piston and nozzle for a specific purpose of rock fragmentation.